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MANAGING EDITOR EDITOR IN CHIEF LAYOUT AND DESIGN COVER PAGE ADVERTISING INQUIRIES ADDRESS CHANGES ACCOUNTS PRINT COPY SUBSCRIPTIONS

International Standard Serial Numbers PUBLISHED BY

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Lyra Naomi Fourie Axel Grabowski Lyra Naomi Fourie Artwork & Lay-out Lyra Naomi Fourie Lyra Naomi Fourie sadtj@dentasa.co.za Elize Morris dentasa@absamail.co.za Elize Morris dentasa@absamail.co.za Tel: 012 460 1155 Fax: 0862337122 Elize Morris dentasa@absamail.co.za Tel: 012 460 1155 PO Box 95340, Waterkloof, 0145 Electronic: ISSN 2077-2793 Print: ISSN 2077-0871 The Dental Technology Association of South Africa

The Dental Technology Association of South Africa ADDRESS

PHONE FAX OFFICE HOURS URL E MAIL STATEMENT OF INTENT

Association Incorporated under Section 21 Reg No: 2005/035340/08 P O Box 95340, Waterkloof, 0145 105 Club Ave, Waterkloof Heights, Pretoria 012-460 1155 0862337122 Mon-Fri 08:00-13:00 www.dentasa.org.za dentasa@absamail.co.za

The Southern African Dental Technology Journal is published 3 times a year. The main objective of the Journal is to provide the professional with the opportunity to earn CEU’s through completing the questionnaires, or writing articles. All papers in English, on any aspect of dental laboratory science or related disciplines, will be considered on merit and subject to the review of the editorial board and the CEU accreditation committee.

EDITORIAL, ADVERTISING AND COPYRIGHT POLICY

Copyright of individual articles appearing in this publication reside with the individual authors. No article appearing in this publication may be reproduced in any manner, or in any format without the express written permission of its author and a release from this publication. All rights are reserved. Opinions and statements, of whatever nature, are published under the authority of the submitting author and should not be taken as the official policy of the Dental Technology Association of South Africa.

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Content: Editorial

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Annual Report from DENTASA COO

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Move the world with your hands

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Peter Adair: Father of All -Ceramic Dentistry

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Looing your house and Lab in a fire

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Password: Technology

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Financial Titbits

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Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

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Who needs Models

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Comparative analysis of transmittance for different types of commercially available zirconia and lithium disilicate materials

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CPD Questionnaires

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At last,we are able to publish! The gremlins have been giving us a very difficult time. I would say that everything that could possibly go haywire did. But here we are, back on track and my team and I apologize for the delay. Firstly I must again congratulate the Western Cape on the magnificent DENTASA Summit and AGM 2015. Well organized, well attended and very good lectures. Looking forward the 2016 AGM at the Birchwood Hotel and conference centre in South Gauteng. As you will notice, the main feature is about the father of metal free dentistry. Not only did Peter Adair invent metal free dentistry, but he was also the father of dental technology at the UoT’s as we know it today. Being in the first group that started in 1972, I was in a very fortunate position to become good friends with Peter. (Yes, that does give my age away)Peter was not only highly intelligent, but also extremely artistic. Those students that were in our group will support me when I say that he was the only person I knew that would draw (with chalk on a blackboard) a full upper and lower, anatomically perfect, roots and all, three dimensional, in under an thirty minutes. That used to place a huge amount of pressure on us, to try and never succeed to do the same. His pen/pencil sketches of nature were superb, and am happy to be the owner on some. In later years, before his passing, he became a full time artist in the USA. Peter also experimented extensively with placing loops on spectacles for now commonly used magnification. He was years ahead. He was however not all work, he partied just as hard. His favourite stunt was to mix a very potent cocktail in a disused fresh water fish bowl. Dynamite to say the least, and always welcomed by poor students. I was fortunate to have spent seven weeks with him in the USA and Europe, and this was supposed to be all work and attending different courses mainly at Boston University, School of Dentistry. Happy to report, that the longer we were there, we attended more parties than courses. Peter was a real ‘’ Mensch” and this profession should be extremely proud of him. I have no doubt, that the class of 72’ will remember him with fondness, his achievements, his being a peoples person, and just being Peter. RIP. Editorially yours Axel

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Mr Axel Grabowski

It gives me great pleasure to welcome all Past Presidents of DENTASA, foreign dignitaries, traders, the DENTASA Executive, and most importantly you the members . I wish to start by thanking the outgoing Exco, for all their hard work during their term of office. It is often not recognised by the profession just how much time and effort you give for the betterment of this wonderful profession. I think it will be appropriate ladies and gentlemen to give them a huge and well-earned round of applause. It also gives me great pleasure to welcome the new Exco, mostly the same, but thank you for giving your private time and effort for the next term of office. Since our last AGM in August 2014, it has been an extremely

busy time. The planning of this AGM started almost immediately after the last one. We received two proposals, one from the Eastern Cape, and one from the Western Cape. After much deliberation, the W/C was awarded the opportunity to host the 2015 AGM. A big thank you for the proposal and hard work done by the Eastern Cape branch. Don’t give up. The decision to have alternate years in Gauteng stand, and therefore the 2016 AGM will be hosted by the combined Gauteng North and South branches. As we all know by now, SADA once again tried their very best to undermine the Technicians by advocating that if Laboratories do self- claiming, it can only be done after the Dentist has placed the case and signed it off. Having discussed this matter with a director

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of Best-Med, Prof. Jan Meiring, the Registrar of the SADTC and the Advocate of the SADTC, it was a unanimous decision that this is in fact not so. The minute someone in the practice has signed the delivery note or book, your part of the contract is completed and you can send in your claim. The never ending problem with medical aids, especially Discovery, not wanting to accept new codes was once again addressed by the Registrar, and hopefully now after more than two years put to rest. The meeting with the SADTC, DENTASA and the CEO Dr.Buyiswa Mjamba Matshoba of the HPCSA was interesting to say the least. I must thank the Registrar of the SADTC for arranging this meeting. One of the many points

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of discussion was the persistence of SADA’s admin fee. According to SADA, the HPCSA made a ruling that this was indeed allowed and legal. When I questioned Dr.Matshoba about this, she informed me that she has no idea who the SADTC, DENTASA or Dental Technicians were. The in-house Advocate of the HPCSA also had no idea that we even existed, and therefore the validity that such a ruling was made, is in all probability non-existent. I must also mention that the entire top structure of the HPCSA was suspended by the Minister of Health at the beginning of this year due to incompetence. We must therefore at all costs refrain from ever joining the HPCSA instead of the SADTC. We are an unknown factor. I was also told by Dr. Matshoba that I may not speak about this meeting. I ask myself, WHY NOT. I was invited to attend the Heads Meeting at CPUT, for the following reason, as I am not part of any University and most definitely not a Head of Department. I have been serving on the Education Committee of Council for many years, and so have some background. Mr. Bass of DUT went on pension at the end of April, and in all likelihood Mr. Boshoff from TUT will leave at the end of the year. This means that only Mr. Steyn from CPUT will remain, and for the sake of continuation, I was invited to participate and give my input. I will remain there until the new heads feel I no longer have a contribution to make, I think? One issue that was discussed

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in detail, was the re-introduction of a board exam. I, for one am 100% for this. I was asked what the professions view would be, and on my recent country wide walk-about, the response was very positive. The profession out there would like to see an even playing field. I am sure that Grant did the necessary explanation in his lecture. As I mentioned, I serve on the Education Committee, and can inform you that the new curriculum will be implemented by DUT in 2016. CPUT and TUT will in all likelihood commence implementation by 2017. I also serve on the Legislative Review Task Team of Council, and its main function is to re-write the very out-dated Dental Technicians Act. We progressed well, until we experienced a slight snag with the DoH. The SADTC was unable to get an audience with the Minister, so work came to a grinding halt. However, the good news is that the decision was taken to carry on with the work, and on Saturday the 6th June we did just that. The work is progressing well. The following Regulations were out for public comment: 1: REGULATIONS RELATING TO THE MANDATORY REGISTRATION OF INFORMALLY TRAINED DENTAL LABORATORY ASSISTANTS 2: REGULATIONS RELATING TO THE SCOPE OF PROFESSION OF DENTAL TECHNICIANS AND DENTAL TECHNOLOGISTS 3: REGULATIONS RELATING TO THE SUPERVISION OF REGISTERED DENTAL LABORATORIES

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I can inform you that all three Regulations have now gone the Minister to be signed into law. The LRTT made the final corrections on Saturday. Not surprising, SADA was the only body to comment. It is a shame, that not one person within our profession made the effort, after repeated requests by me, to forward any comments that you may have had. Regulations only come into effect once signed by the Minister. The interesting thing about all three Regulations that were out for public comment, are that they are signed, one will have to take a closer look at the meaning of this. As far as the Trust Fund goes, it remains a headache for all. Mr Andre Ferreira has been appointed as the chairman of the Fund, and he furnished Council with a comprehensive report with all the necessary documentation that this money does not belong to the SADTC, but to the Technicians. As the chairman is present, I would appreciate it if Andre will enlighten you more of what is transpiring. Denturism. Just in case you thought that this has come to a complete standstill, it hasn’t. A meeting is taking place in early July between the following individuals, being invited by CPUT. Dr.Padayachy-CEO of SADTN Mr.Ishmael Larney - Advocate for Denturism from Australia Mr.Louis Steyn - CPUT Mr.Axel Grabowski I am sure that there will be other Dr Padayachy has been in contact with Louis Steyn regarding


the broadening of the Dental Assistance Scope of Practice, and we therefor grabbed the opportunity for her assistance in the broadening of Dental Technology Scope of practice. She is very well connected, and will be a huge step in the right direction towards the implementation of Denturism. Louis you are welcome to expand more on this meeting, as you are in a better position to do so. It also gives me great pleasure to announce to you that at last year’s AGM we asked that you put your hands in your pocket and contribute to the Denturismn Fund A total of R 83127.99 Ishmael Larney gave R34000.00 I want to take this opportunity to thank the traders and individuals who so generously contributed. This enabled Duffy Malherbe to go to Ireland and represent SA on the world congress of Denturism. Thank you all. Cad/Cam. This is and will stay a serious bone of contention between us and the Dentists.

The SADTC called a meeting for all the roll players to participate, with one aim in view, to get a Term of Reference. NOT everybody was invited, due to time constraints. It makes no sense to give each roll player two minutes to present their case. This was unfortunately misinterpreted by many dentists and SADA in particular. A few uninvited individuals were asked to leave, and it did not go down well with them. There was a follow up meeting on Friday the 5th June between the some SADTC members and SADA. Unfortunately DENTASA did not receive an invite, and you are free to ask the Council members in the Q& A session what was discussed, if you so wish. SADA has had two Cad/Cam meetings since the first Council meeting, and I was invited to both for my input. Council was not invited, whether this was tit for tat, I am not sure. I would like to read the document that came from these two meetings. It is a great pity that since the Council meeting in October where

three of our colleagues and I were asked to leave the meeting after less than an hour due to the sensitivity of items to be discussed, the feedback of information on a number of issues has come down to a trickle. I realize that some issues are of a sensitive nature, especially the cases that involve possible closures of laboratories. I did voice my dissatisfaction to the Registrar, and am eagerly awaiting the promised meeting to discuss this current impasse. Hopefully this will be sooner rather than later. This matter was again discussed at the Council meeting on Saturday 6 June, and a date will be set shortly. I most certainly do not, and I repeat, do not want to sour our relationship with the SADTC as this profession deserves the best cooperation between Regulator and Association. Thank You.

r G l e Ax

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sk w o ab

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Message from the newly elected president of DENTASA

Michael Lazarevic “Move the world with your hands, embrace the passion within your soul and you will walk with the heroes!” With these inspirational words Mr Michael Lazarevic addressed the delegates at the AMG as the new president of DENTASA. The theme of this year’s DENTASA Summit and AGM were: The passion gap. Michael’s passion for dental technology, and for serving our industry was evident as he continued his speech in these words:

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“Move the world with your hands, embrace the passion within your soul and you will walk with the heroes!”

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“ The word ‘passion’ has constantly stuck with me since the day I commenced my studies and I truly believe that having passion for what you do will make you great. It may take a few years, it may even take a lifetime, but passion is not tangible. It is something within your soul. Everyone in this room today shares a common passion. A common thread is woven between us and a gathering of us all in this way is manifestation of this fact.” Everyone was welcomed and Michael shared his thoughts behind the theme for this year’s DENTASA Summit and AGM. “The theme for this year’s AGM is the passion gap within our industry. I believe that as life passes us by so quickly, the rat race we face on a daily basis, we sometimes lose focus of what we are trying to achieve. So I ask you. Take a breath, relax and really digest what it is we do every day of our lives. We move the world with our hands!!! It's a privilege to be able to fulfill the needs of the person on the other side of that plaster model. We are a select few that have this ability! Let's up our game. Let's be the best we can be! Following this belief, you will release the passion within you and you will thrive. Re ignite what we take for granted every day. Your ability to forge something with your hands and change the life of someone!” The DENTASA Executive Committee is made up of dental technicians who does voluntary work, to add value to the industry, and ensure a better tomorrow for us all. Michael thanked the EXCO for their tireless work and introduced them to the audience. Anso Steenkamp Past President Johan Havenga Treasurer Melanie Van Deemter Chair- Eastern Cape Lukie Steenkamp Chair - Free State Harry George Chair - KZN Wicus Kruger Chair - Gauteng North Gerhard Combrink Employee Matters Mariaan Roets Management Commit- tee and AGM Michael reminded the delegates that the executive committee of DENTASA does not constitute the organization, but that DENTASA is made up of all its members. He thanked everyone for their support

and called everyone to unite and thus strengthen the association. After thanking the organizers, traders and delegates for their participation and support, Michael shared this anonymous phrase: “I love working with my hands...you can actually feel the job being done...and at the end of the day you can look at what you have accomplished...I can walk over this plaza in 30 years’ time and know that I laid these stones” In closing he said: “Let this AGM inspire you, re-kindle the passion you have inside. After all...without a little Passion...there can't be a little Magic.”

“I love working with my hands... you can actually feel the job being done...and at the end of the day you can look at what you have accomplished...I can walk over this plaza in 30 years’ time and know that I laid these stones”

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by Lyra Naomi Fourie

Scratching in my mom’s kitchen cupboard the other day I came across a pie-dish that she got as a wedding present, a gazillion years ago. I smiled, as it immediately reminded me of a wonderful piece of South African dental history, I have been fortunate

enough to know about. So what has my mom’s virtually industrucable Corningware dish and All Ceramic Dentistry have in common? A similar question has been asked by journalists 31 years ago when the first all ceramic dental restorations made news headlines in the US. The answer of cause, a man call Peter Adair.

Left to right: P. Adair, A. Erasmus, A.Charlton

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The first time I heard this name, I had a blank stare. I could sense that the people in the conversation expected me to react but I had no reference: “Before my time” was the best excuse I could offer. Yet, mention the name to some of the first students in dental technology at Pretoria Technikon [now Tshwane University of Technology] and you see and instant smile on their faces and respect in their eyes.


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Originally from Rhodesia [now call Zimbabwe], Peter was one of the first lecuturers in dental technology in South Africa. He was a brilliant young man with a passion for dental materials and for his students. Peter has always had a mind for research, and it came as no surprise when Peter announced that he was going to join his friend in Boston, USA just a few years later. Between Dec 14 & 23, 1984 several US newspapers carried the news of a new scientific breaktrough: Ceramic Teeth! The New Straits Times read: “High-tech ceramics may revolutionise dentistry. In the wake of the space shuttle and dinner plates, your teeth may be the next thing made of glass-ceramics.” “This will completely change dentistry. “ said Dr Kenneth Malament of Boston, one of the first dentists to use the product and who has used it on hundreds of teeth, the newspaper reported. And how true those words turned out to be!

ramic dental restorations, were produced. The product was developed by Corning Ware and marketed by Dentsply. It was call Dicor - combination of the names of the two companies involved. Dicor Pyroceram was introduced to the market in 1984 and in 1988 Peter Adair patented his concept. Dicor castable ceramic was made up of a tetra silicic fluormica-containing material. It had a CTE of 7.2 and a flexual strength of 152Mpa. According to Wolfram Holand and George H. Beall in their book, Glass Ceramic Technology, Dicor produced the first machinable ceramic called Dicor MGC – mica glass ceramic. The flexual strengh of this product was 216 Mpa and it was available in a light and dark colour. Peter went on to write numerous research articles and was involved with Dicor for a number of years. In later years Peter returned to South Africa where he stayed until his death.

The newspapers reported that an innovative dental techncian from Boston named Peter J. Adair approached Corning Ware with the idea that glass-ceramics might be used to manufacture dental crowns and bridges. Peter found a ceramic material in the Corningware catalogue that had properties similar to human tooth enamel in hardness, texture and light reflextion. In addition the material could be cast, making it ideal for use in the lost wax casting process. Experimantation started and before long the first ever, all ce-

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The Process:

Dicor castable ceramic was made up of a tetra silicic fluormica-containing material. It had a CTE of 7.2 and a flexual strength of 12Mpa. Essentially the restoration was waxed up, invested and cast using the same lost wax casting technique as for metals. The investment ring was burnt out and held at 900C. A special “electric muffle casting machine” was used. The glassy ingots became liquidy and castable after a holding time of 6 minutes at 1370C. A certrifulgal casting process were used, spinning for 4 minutes.

The material:

Dicor castable ceramic was made up of a tetra silicic fluormica-containing material. It had a CTE of 7.2 and a flexual strength of 152Mpa. According to Wolfram Holand and George H. Beall in their book; Glass Ceramic Technology, Dicor produced the first machinable ceramic called Dicor MGC –mica glass ceramic. The flexual strengh of this product was 216 Mpa and it was available in a light and dark colour.

After devesting the restoration was heat treated in a special furnace. This process was called ceraming. During the ceraming process controlled crystallization occured. There were two important aspects in the process. Firstly the formation of crystal nucleation called nucleation, and secondly, the process of crystal growth, known as crystalliza

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tion. Nuclei were formed by keeping the casting at a temperature between 750°–850°C for a period of 1 to 6 hours. After nucleation the temperature was increased to the crystallization point between 1000°– 1150°C which was maintained for a period ranging from 1 to 6 hours, until the desired level of glazing was obtained. The number of crystals, their growth rate and size depended on the time and temperature of the creaming treatment. The ceraming process had two destinct benefits: it created a relatively opaque finish from the initially transparent crown, and it significantly increased the fracture resistance and strength of the ceramic.

to obtain the correct colour, later frameworks were created which was layered with porcelain. Something that is noticable reading though stacks of articles on this product is the preparation method prescribed for Dicor Castable Ceramics. A reduction of 1.5 to 2mm was required with no sharp edges or undercuts. A shoulder or deep champher with a rounded gingivo-axial line angle was needed and no knife, beveled or feather edges could be used. In essence, nothing has changed and the requirements of an all ceramic.

Initially full contour crowns were made and stained

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lOOSING YOUR HOME AND LABORATORY IN A

On Thursday November 20, 2014 Joggie Herbst, a dental technician and lab owner from Pretoria lost his home and lab in a devastating fire. The SADTJ contacted Joggie and asked him to share with us what happened on that fateful day. On Thursday November 20, 2014 Joggie Herbst, a dental technician and lab owner from Pretoria lost his home and lab in a devastating fire. The SADTJ contacted Joggie and asked him to share with us what happened on that fateful day. “While at a concert I got a phone call from my neighbor telling me that my house was on fire” Joggie told us. “I rushed home and as I took the last turn I saw thick black smoke filling the air. Confusion made place for shock as I realized it wasn’t just a small fire, my entire house and Dental Laboratory where going up in flames.” . Joggie remembers how he stood in disbelieve and watched how

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thick black smoke, billowed from had prepared was gone together his house and lab. In short bursts with the furniture the stored in our the reality of the situation hit house. And of course I thought of him. He realized that all his ma- the work that had to go out to my terial belongings where being de- clients the next day….” stroyed……going up in smoke and disappearing into the night sky. “After the smoked cleared, all that “The flames quickly spread and we were left with, was the inconvedestroyed everything. I remember nience caused by having lost the standing amongst the fire hoses; complete inventory of our house people running back and forth, and my lab. Not to mention the hassle of replacing it all.” some asking if I was okay.” Joggie reported that in the months Panic struck with the realization that followed, he and his family exof all that he has lost. “I thought perienced moments of tears, moabout the content of my house ments where they felt like giving and business that was lost forev- up and moments where they felt er. My daughter’s wedding was in totally un-grounded. There is no two weeks and everything that we simple answer to the question of

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what to do when you lose your entire house and business. After a incident like this there is a lot of work that needs to be done in order to put your life back together again. Claiming from insurance can be challenging especially when it involves the magnitude of Joggie’s case. “The best thing to do is to be open and learn.” Joggie said. Investigation determined that the cause to the fire was electrical and started in one of the bedrooms where a laptop was plugged in. Most house fires are caused by cellphone chargers, laptops and hair straighteners according to the investigating officer.

Joggie’s house and lab has been rebuild and they moved back on May 28, 2015. Joggie is grateful for his new life but as he said: ”It came at quite a cost.” “We have risen, and we are changed people. It is hard to explain the effects that such a traumatic experience has on one’s life. Sometimes that makes us feel very lonely, and other times, deeply connected.”

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Unlocking the future of digital workflow, new materials, and communication devices By Pam Johnson and Jason Mazda Originally Published in IDT© 2015 to AEGIS Publications, LLC. All Rights Reserved. Used with Permission of the Publishers

If there were a single secret word that would allow access to what the future of dentistry has in store for the next 5, or fewer, years, that password would have to be “technology.” Few, if any, segments of the dental industry have been left untouched by some form of computer-driven science. From caries detection and digital impressioning at chairside to virtual communication and automated manufacturing technology in the laboratory, every diagnostic and restorative phase of dentistry is being enhanced by computer-chip technology. These rapid technological advancements are not only having a profound impact on the day-to-day routine of dentists and laboratory owners and managers, but they are also reshaping how companies in the dental space both big and small operate within the dental business environment. Once siloed with distinct brands available exclusively through the company or a select distributor, the lines between the big-brand companies continue to blur as even the largest of them finds it necessary to work with one another in order to gain access to new materials and new technologies or strategically expand its product distribution lines. In recent months, Heraeus Kulzer and Dental Wings, Straumann and Amann Girrbach, Sirona and Align Technologies, Dentsply and Ren-

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ishaw, Shofu and Merz, and Nobilium and EOS all have announced strategic partnerships, distribution agreements, buyouts, or mergers to gain greater footholds in a competitive environment that is forcing companies to change how they do business. Likewise the explosion of new technologies launched on the market in recent months is forcing dental laboratories to rethink their positions in the marketplace. New product lines have opened up to a digital workflow, new materials may offer a competitive advantage, and improved automated equipment and communication devices will enhance production efficiencies and speed throughput. Also, new concept technologies and materials are breakthroughs for the industry and will impact how restorative products are made and what they are made of in the future. In March, the editors for Inside Dental Technology attended the International Dental Show (IDS) 2015 and saw many of the new innovations that will be introduced to the US market in upcoming months. In this article, we wanted to provide some perspective for what we saw, what we heard, and what we perceived as trends that will impact the industry for years to come.

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Digital Dentures Everywhere

If there is one technology trend that is taking the dental industry by storm, it is finding solutions that will transition the manufacture of full-arch dentures from conventional manual techniques to a digital workflow. “Many companies offered their own twist on the digital denture solution,” says IDS attendee Chris Brown, BSEE, Manager of Aclivi Consulting/Technical Services in Pinckney, Michigan. “This will be one of the emerging markets available for laboratories and clinicians to use for delivering dentures and removables.” The process of creating a complete digital solution has encountered several obstacles. The first has been the inability of current digital impressioning technology to digitally capture the necessary landmarks of the edentulous arch to accurately design a well-fitting and functional prosthetic. The second has been the development of open-architecture, non-proprietary CAD software that would provide access for the majority of laboratories owning scanning/CAD technology to participate in a digital workflow. A third obstacle that specifically targets manufacturers of 3D printing technology has been the development of FDA-approved materials for long-term use in the mouth. Also, the problem of setting denture teeth has lingered, which for most processes introduced is still manual. Only two companies currently provide a digital solution. AvaDent has successfully demonstrated the ability to mill a full arch from a single block of FDA-approved material complete with denture teeth, and Heraeus Kulzer with the Pala Digital Denture system uses a proprietary process to finish the final denture. Central to any solution to the digital removable process is the software. With the introduction of CAM software by 3Shape and exocad, laboratories using CAD technology powered by these two scan/ software companies now have or will soon have the ability to digital design full-denture solutions. This breakthrough has spurred manufacturers of milling and 3D printing technologies to develop at least partial solutions for the full digital process. Recently three companies, VITA, Dental Wings, and Dreve, announced they plan to bring together VITA’s expertise in denture teeth, Dreve’s 3D printing capabilities, and Dental Wings’ CAD software in a collaborative effort to develop a digital workflow for full-denture cases. This also shows promise for the future.

For those using subtractive technology, Wieland Dental and Amann Girrbach both announced solutions for milling a complete denture base. Wieland introduced the Zenotec Select Ion mill, equipped with an 8-disc material changer and ionization system that directs ionized compressed air onto the material and tools during the milling process to neutralize the static electricity of particles when milling acrylic materials and producing full-arch dentures, bite templates, try-ins, surgical guides, occlusal splints, and PMMA restorations. CAD design includes a tooth library with sample setups using digital versions of Ivoclar Vivadent and Candulor denture teeth. The denture base is milled from IvoBase CAD PMMA and available in several shades, and the denture teeth are set by hand. A unique feature of Amann Girrbach’s denture milling solution is the elimination of trimming the denture teeth by hand. The ridge lap surfaces of the teeth can be adapted to the alveolar ridge in the CAD software and then, using a special denture tooth holder designed for use in the Ceramill Motion 2, the denture tooth surfaces can be trimmed via milling technology. The Amann Girrbach system uses Heraeus Kulzer’s Pala denture teeth and a specialized denture tooth holder developed by Heraeus Kulzer for use in the Ceramill Motion 2. Eventually, Amann Girrbach plans to incorporate other tooth lines into the workflow for a wider range of customization and esthetics. Straumann also showcased a prototype of an inhouse denture milling unit although it is too early for any further information. The company has also made a big play for providing laboratories with in-house production capabilities, which will be covered later in this article. Several 3D printing solutions are also forthcoming from companies such as Bego, Stratasys, and Valplast. Bego introduced a 3D-printed solution that will be available in the fourth quarter of this year for printing a denture try-in combined with conventional denture fabrication techniques once the try-in is approved. Stratasys also had on display a printed full-denture try-in in color and complete with teeth produced by the company’s new Objet Dental Selection printer. Also, Valplast announced plans to release a full-denture solution later this year, which will feature a new library of denture teeth, plus printing and milling solutions for the final prosthetic.

“Many companies offered their own twist on the digital denture solution,”

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3D Printing Technologies

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dditive manufacturing is a technology that is being watched very closely by many major industries around the world due to the scalability of the technology as well as the promise of new materials that target specific industries. Still in its infancy in dentistry, 3D printing is beginning to show its versatility and advantages.

This year a milestone was achieved by the introduction of Stratasys’ new Objet Dental Selection printer. Using inkjet-style print heads, this new printer can produce a single job in multiple colors and shades of color as well as in multiple textures or multiple jobs requiring a combination of colors and textures. This makes it possible to print clear plastic jaw models with high-definition tooth, root, and nerve anatomy directly from CBCT scans using 3Shape software or print hard models with gingiva-colored soft tissue-like material for evaluating accurate function of implant restorations. For smaller, less complex 3D printing needs, several companies introduced small-footprint devices. Whip Mix introduced a line of compact printers, the smallest of which was the size of two oversized Rubix’s cubes. Though they are not yet available on the US market, Vice President of Sales and Marketing Anne Steinbock indicated they would be introduced in the near future. Called Veriprint, this technology builds in

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multiple layers in stacks up to 7 cm in height. Three models were on display: the Veriprint 100 for printing wax patterns, temporaries, and ginigival masks; the 200 for printing wax patterns, drill guides, models, implant trays, temporaries, and gingival masks; and the larger 300 for orthodontic appliances. Among the new 3D printing companies entering the dental arena was California-based Asiga with its Pico 2 and Pro75 FreeForm SAS (Slide and Separate) technology. This desktop printer produces minimal support material that has to be removed for its printed wax pattern crowns, bridges, partials, inlays, and onlays. In March, the French company Prodways opened a distribution and support center in Minneapolis, Minnesota for its industrial-sized ProMaker L series printers. Well-established in other industries, Prodways utilizes MOVINGLight®, a proprietary technology based on moving the build material and UV LED curing technology simultaneously for high-resolution precision models, wax patterns, and other complex structures in a variety of hybrid materials. Keep your eye out for a company called Carbon3D. This company was not at the IDS but has developed what it calls CLIP technology, which is said to “grow” parts instead of printing them layer-by-layer. CLIP stands for continuous liquid interface production and uses the interaction of UV light and oxygen to continuously grow objects from a pool of resin. The process is said to offer unprecedented quality and much greater speed than current technologies.

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M

Milling Technologies

ost interesting this year is the introduction of a laser milling technology unveiled by Dental Wings. Instead of using burs to grind a block of ceramic, polymer, or glass material, this new “milling” concept uses laser ablation technology. Very high-intensity laser pulses are used to vaporize small amounts of material with each pulse and with extreme precision. A built-in scanner compares what is being milled to the CAD design to ensure that the restoration meets the quality-control standards of the design. Currently, the unit can produce inlays, onlays, crowns, bridges, and veneers. The advantages of this technology beyond the “closed loop” quality-control process are that no after-market costs such as additional burs, cutting coolant, or compressed air are needed to operate. Because the laser beam is one-tenth the diameter of the smallest known CAM bur, the technology can produce restorations with features and resolution not possible with CNC manufacturing. In terms of milling technology, the most surprising is the play both Heraeus Kulzer and Straumann are making for the in-house milling arena. Lying dormant on the digital landscape and fixed side of dental technology for many years, Hereaus Kulzer came to life this year with its Pala Digital Denture platform and the introduction of the Cara DS scanner 3.2 and Cara DS mill 2.5. The company also announced plans to distribute the Dental Wings DLMS laser milling unit. The compact scanner is plug and play with an integrated PC and software. It allows scanning multiple teeth simultaneously as well as selective scanning of the gingiva, wax-ups, and check bites. The Cara DS mill on display is a small-footprint device with no further information available, but the unit did have a denture base mounted inside, if that is any indicator of its versatility. Straumann has strayed from its centralized production-only stance and partnered with Amann Girrbach to make its play into providing laboratories with inhouse milling technology. Although the milling units will first be introduced in central Europe starting in the fourth quarter of 2015, the company plans to expand distribution to other regions. Called the CARES® M Series, the 5-axis milling unit is a wet/dry mill for producing a range of prosthetics from inlays, onlays, veneers, and single crowns to bridges and screw-retained restorations. Supported by CARES Visual software and scanning technology, the mill will be offered with the new CARES desktop scanner

for laboratories entering the digital workflow or as a standalone for laboratories already equipped with a scanner. Among the other notable new milling technologies or advancements are Zirkonzahn’s two new milling units. The M4 is designed with an extra-large milling area to handle the processing of 10 models out of large specialized resin blocks. The new M6 unit incorporates a robotic “arm” for the automatic changing of up to 14 material blanks or 49 milling tools. Both will be available to the market soon. Zimmer introduced the Zfx Inhouse 5-axis wet/dry mill, which it calls the new industrial standard in compact size. It is suitable for milling various materials from zirconia, ceramic, and composite to PMMA, wax, cobalt chrome, and titanium. Schutz Dental unveiled the Tizian Cut 5.2 milling machine, a compact tabletop unit that it says can mill nearly all materials that are used in dental technology with its wet and dry options. Schutz calls the machine “extremely future-proof” due to its digital workflow integration. “The smaller, compact 5-axis mills that mill everything are exciting,” says IDS attendee Jessica Birrell, CDT, who owns Capture Dental Arts in Saratoga Springs, Utah. “As a smaller laboratory, if we are going to invest in a mill, we want it to do as much as possible.”

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Newest in Material Technology Two years ago the big story on new material introductions was the launch of millable lithium silicates by VITA, Glidewell, and Dentsply. This year it was the introduction of pressable lithium disilicates from Shofu, Zubler, and the Chinese company Upcera. Shofu’s Vintage LD pressable system boasts 400 MPa and four levels of translucency and comes complete with Vintage LD porcelain and LF stains. Zubler’s conceptPress lithium disilicate is billed by the company as the most stable on the market at 420 MPa. Offered in three opacities and three pellet sizes, the press system is supported by DC Ceram 9.2 layering porcelain and the Vario Press 300.e furnace, specially designed to process lithium disilicate ceramics. Anaxdent in partnership with Cendres+Metaux will be the exclusive distributor of a breakthrough new material in the US called Pekkton® ivory. This next-generation high-performance polymer has a compressive strength of 246 MPa and offers shock-absorbing characteristics similar to that of human bone, making it optimal for use in implant dentistry. Pressable and millable, this new highly biocompatible material offers myriad long-term solutions for crown and bridge frameworks and implant-supported restorations.

Another permanent 3D-printed breakthrough material this time on the removable side of dentistry was unveiled by Valplast. Not yet on the market, this will be a Class II printable resin material that offers the ability to produce the first permanent denture base directly from 3D printing. Other notable materials introduced include GC America’s millable CerasmartTM nano-ceramic block, Jensen Dental’s high-translucency Imagine full-contour zirconia with a strength of 769 MPa, Kuraray Noritake’s KATANA ST (Super Translucent) and UT (Ultra Translucent) zirconia as well as multi-layered versions of both, and DT Technologies’ high-translucency CubeX2 with a flexural strength of 720 MPa. “An exciting twist at IDS was the new zirconia materials being shown and introduced,” Brown says. “The higher translucency zirconia could very well be a game changer. Giving up a little strength in exchange for great translucency likely will be well received.”

“The higher translucency zirconia could very well be a game changer. Giving up a little strength in exchange for great translucency likely will be well received.”

Other breakthroughs are being made in the research and development of 3D printing materials that can be used for permanent restorations. One that may be coming from Bego sometime in the near future is a crown and bridge framework material. The company’s new Varseo 3D printer currently uses a self-contained cartridge system of eight different resin materials for producing splints, CAD/Cast® frameworks, surgical guides, and try-in denture bases. But tucked away in the company’s press materials was a reference to a

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“permanent” 3D-printed crown and bridge solution. Upon questioning at the Bego IDS press conference about this material and later at the Bego booth, it was revealed the material is a printable composite that can be layered and is in its second year of in vivo testing. If clinical testing proves positive, this would be the first material produced by 3D printing technology for use in long-term crown and bridge frameworks.

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Next-Generation Communication Technology A report on new innovations would not be complete without an update on digital impression scanning technology and devices designed to facilitate communication among team members. Faster, smaller, easier to use are the buzz words for impression scanning technology. “Digital impression scanners are becoming more affordable, but the product is also improving with innovations such as touchscreen technology,” says IDS attendee Pinhas Adar, CDT, MDT, owner of Adar Dental Network in Atlanta, Georgia. “The result is that in the future there will be a streamlined, digital production workflow available to a wider range of professionals.” Only one new player surfaced this year, and that was GC Europe with the new Aadva IOS. Not yet available in the US, the open-architecture Aadva features a slim, lightweight handpiece that requires no powder to use and can create a digital impression ready to send directly to the laboratory in under 5 minutes via the Cloud

for access by all team members.

3Shape was not shy about unveiling its newest entry the Trios Pod, a combination 3D color digital impression scanner and intraoral camera combined with the company’s tooth shade measurement system. The Trios now comes in a lighter-weight pen-grip design that can plug into any USB port for operation rather than the cart. The scan speed has been increased even further to yield a full arch in under a minute as demonstrated by co-founder Tais Clausen. Dental Wings’ DWIO impression scanner offers clinicians fast scan speed and keeps their attention on the patient rather than the computer screen to ensure capture accuracy by incorporating a green/ red LED on the handgrip to indicate whether the device is capturing data. The curved scan head with its 5 miniature 3D scanners allows less rotation to capture buccal and lingual information. The metal

scanner is similar in size, shape, and weight to existing dental handpieces. A further innovation is the no-touch computer screen to prevent cross-contamination in the operatory. The clinician can rotate the scan data and direct all functionality in mid-air without touching the screen. iTero slimmed down its new intraoral scanner, called the iTero Element, by 40% and decreased the weight for ease of use. The company also revamped the software to be more intuitive. The scan speed has been increased with integration of a new image sensor that also allows color scanning. Align Technology and Sirona Dental also announced a collaborative agreement that allows users of the CEREC Omnicam digital impression scanner and CEREC Ortho Software 1.1 to submit digital impressions to Align for orthodontic therapy. Other updates include Carestream’s integration of its CS 3500 digital impression scanner with exocad software through its patient browser for exporting scan data to the laboratory complete with color information in an open-file format. To aid communication between the operatory and laboratory, Sirona introduced the Sirona Connect app for the iPad and iPhone. It allows dentists and technicians to track their orders online. Laboratory owners can receive immediate notification of new cases being submitted to the laboratory. They can review the case in the app and accept it remotely. Whip Mix also introduced an iPad app that aids placement of the arch in the articulator. The dentist takes a facial picture, measures the width of the tooth, and chooses the point of contact. That file is sent to the laboratory, where the technician can line up the model and articulator based on the iPad image of the patient’s mouth.

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Originally published by Du Toit Mook Accountants and Auditors, and repulished with permission

ONLINE ACCOUNTING: AN INVALUABLE TOOL FOR YOUR BUSINESS

Technology just never stops. In recent years, there has been a growing trend towards online accounting in first world countries. It is now available locally but so far has been used mainly by technologically savvy people. Online accounting offers considerable benefits particularly to Small and Medium Enterprises (SMEs) who can now get control of this important part of their business. How does it work? Online accounting software seamlessly integrates many of your daily routines into your accounting system. Consider a credit note – a clerk investigates a claim and once satisfied sends it to the sales manager to authorise. He can authorise it online, your customer is emailed the credit note and your accounting records – sales, stock and debtors – are automatically updated. Let’s say the business owner is waiting for a flight at O.R. Tambo airport. With his laptop, he can run a month-to-date profit and loss report, see how the margin is holding up and run reports he has designed. For example, a sales person may be on a non-performance warning and the owner can design

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and run a report on this person’s sales to date. Instead of waiting three to four weeks for the accountant to run month end reports, they are now instantly available. Why use online accounting? • The quicker you get data, the quicker you can react. A debtor may be slow paying but finding out about this four weeks after month end could be the difference between collecting the money or writing off a bad debt. • It’s relatively simple to use. Staff from owners to clerks can be quickly trained to use the system. This is empowering as you can effectively control this part of the business instead of being overly reliant on your in-house accountant. • Online accounting is getting increasingly cost effective. In addition you will need less bookkeeping staff which can be a considerable saving. • As your in-house accountant becomes less needed for run-of-the-mill functions, you can now get more expert advice on how to interpret your accounting data. You can also obtain strategic input such as should I outsource distribution, what is the real cost of my sales force etc. Effectively, your business can move up to another level. The online accounting landscape is starting to develop in South Africa and the people who get in early will have a competitive advantage. Speak to your external accountant as to how you can investigate the benefits of online accounting.

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DEBT PRESCRIPTION RELIEF FOR CONSUMERS “Debt, noun. An ingenious substitute for the chain and whip of the slave driver” (Ambrose Bierce) We are all aware how consumer debt has risen in the past several years, especially for the lower paid and poorer sections of the community. As employers, you no doubt have staff who seem to be perennially in debt. A recent amendment to the National Credit Act has outlawed attempts by debt collectors to trade in or attempt to get consumers to pay prescribed debt. Background A debt prescribes if, for three years (note: three years is the prescription period for most commercial debt but there are different prescription periods for taxes due, judgments, mortgage bonds etc.) • No payment is made, • The debtor has not acknowledged that a debt is owed, • The creditor has not summonsed the debtor. What has been happening is that debt collectors have been “harassing” consumers for prescribed debt. This includes not just the original amount owed but also interest due and the debt collector’s fees. A debtor is entitled to raise prescription as a defence (if the debt has prescribed), in which case, the debt collector is not entitled to pursue the matter. However, until now the onus has been on the debtor to know his or her rights. The trend of debtors being “harassed” has been exacerbated by companies selling their debt claims to other collection agencies who have been extremely aggressive in their collection practices.

The new amendment provisions No longer must debtors raise the defence of prescription themselves. It is now illegal for debt collection entities to collect prescribed debt. It is also prohibited to sell prescribed debts to other debt collection agencies. In addition, debt collection firms are obliged to inform debtors if they sell their existing debts. This will prevent many of the unfair practices of debt collection businesses. Employers - ensure your employees are aware of changes to the National Credit Act and understand that they do not have to pay prescribed debt.

“Debt, noun. An ingenious substitute for the chain and whip of the slave driver” (Ambrose Bierce)

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TAX FREE SAVINGS ACCOUNTS LAUNCHING

1 MARCH

A GOOD DEAL? The Treasury department has been encouraging individuals to save more for several years and is following up on this by launching tax free savings accounts (TFSAs) on 1 March this year. How will it work? It is for individuals and allows them to invest R30,000 per annum until a threshold of R500,000 is reached. Thus a couple will be able to invest up to R 1 million but it will take more than 18 years to get to this limit. Parents can it seems also invest in TFSAs for their children – a family with three children could save R150,000 per annum per family. The advantage of this is all income received is tax free. This includes dividends (where 15% withholding tax is normally deducted), interest and capital gains. There will be no restrictions on withdrawals from this fund as opposed to retirement funding and it would seem that one of the rationales for TFSAs is that individuals needing to access money will draw on their TFSA and leave their retirement funding intact. The penalties for withdrawal will be kept low and withdrawals are to be paid out within seven to thirty two business days depending on the type of investment.

The net for investments is fairly wide and you may use unit trusts, endowments, fixed deposits, bonds and certain exchange traded funds. Treasury want to see simplicity, transparency and suitability in the products allowed. Funds that charge performance fees are excluded from participating in TFSAs and fees charged are to be reasonable. Penalties Failure to comply with the regulations will result in the TFSA losing its tax free status. What do the returns look like? Projections done by investment analysts show that TFSAs should produce returns slightly more favourable than retirement saving products. For investors who only want interest bearing products, the return should be nearly double that of similar non TFSA products due to the tax saving. Over the next few months most financial institutions will be launching TFSAs. This promises to be an attractive product for serious long term investors.

It will not be possible to transfer existing investments into TFSAs as the intention of this measure is to encourage new savings. From 1 March 2016, individuals will be allowed to move existing TFSAs to other TFSAs. Who can issue TFSAs and what type of investments can be used in TFSAs? Banks, long term insurers, managers of collective investments schemes/unit trusts, government, mutual banks and co-operative banks may set up TFSAs.

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EMPLOYERS:

TAKE NOTE OF THE GARNISHEE JUDGMENT

PAIA

REMEMBER THE DECEMBER DEADLINE Certain Small and Medium-Sized Enterprises were given until the end of 2015 to submit a PAIA manual in terms of the Promotion of Access to Information Act. This is a reminder not to forget to submit the manual to the South African Human Rights Commission. As this is a relatively simple process, there is a small cost of compliance for business. Businesses that were exempted until 31 December 2015 are those with less than fifty employees or turnovers lower than prescribed. These turnovers vary from R25 million per annum for wholesale and retail traders to R2 million for farming operations.

RETIREMENT REFORMS POSTPONED: WHAT YOU SHOULD DO NOW

There has been a considerable media spotlight on government’s intention to reform retirement funding. This has now been postponed as there is no agreement on proposals. It is worth taking advice on maximising your contributions in the meantime. The thrust of government’s approach is to limit the taxable amount of contributions that can be made to retirement funding which will effectively penalise high net worth individuals.

E

molume IT’S THAT TIME OF YEAR AGAIN: TAX SEASON 2015 nt attachment orders (EAOs), more widely known as garnishee orders, came under fire recently in the Western Cape High Court. Creditors have been getting garnishee orders issued by court clerks (and not magistrates) and they have often gone to courts hundreds of kilometres from where the debtors live. There is no requirement that the clerk of the court should review how the garnishee order would affect the economic circumstances of the debtor - in at least one instance, virtually the whole of an employee’s earnings were subject to deduction. Once a clerk of the court has authorised a garnishee order, employers are obliged to deduct the amount stated on the order from the relevant employee’s wages. The Court was scathing about these EAOs and declared them unconstitutional and unlawful. That they were issued a long distance from the debtors’ home effectively denied these people the ability to appeal the order, a breach of their right of access to justice. The judge also held that judicial oversight must occur with garnishee orders i.e. a magistrate must authorise an EAO. What should employers and employees do? Garnishee orders should be reviewed by employers in the light of this judgment. The fact that the Justice Department has agreed to abide by this judgment indicates there will almost certainly be changes to the law, and in fact the Department has announced its intention to effect amendments as a matter of urgency. Employees should be encouraged to seek legal advice on whether their particular garnishee order is

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IT’S THAT TIME OF YEAR AGAIN:

TAX SEASON 2015 “I just filled out my income tax forms. Who says you can't get killed by a blank?” (Milton Berle) The 2015 tax season opened with much fanfare on 1 July. The fanfare was justified as more than 67,000 returns were submitted by the 2nd. Are you liable to pay tax? This is the threshold at which you become liable for income tax -

The tax exemption for interest income is R23,800 (if you are less than 65) or R34,500 if you are 65 or older. What’s with the Populated Fields? When completing your tax return online, you will see that some of the data fields have been automatically filled in. It is worth checking that these amounts have been correctly entered. If you need to claim other deductions, such as car allowance, make sure you have the necessary supporting documentation (in this case a log-book), as SARS will want to see this. If you go to a SARS branch to complete your return, you will need to bring all supporting documents, plus your ID. If you use eFiling, you will be required to upload these supporting documents with your tax return. The same goes for other income you receive – for example if you receive business income, then the annual financial statements will need to accompany your return. Get expert advice from your accountant and make sure you get your return in on time and that it is accurate to avoid penalties and interest.

Do you have to submit a tax return? Liability to pay tax is one thing; liability to put in a tax return is another. It will save you time and stress if you don’t need to complete a tax return. If you are a natural person and • You earn R350,000 p.a. or less from a single source and o PAYE has been deducted, and o This amount was paid as a salary with no allowances, or • You earn less than R23,800 in interest (if less than 65 years old) or R34,500 in interest if aged 65 or over, or • You are a non-resident with dividend income. • Then you do not need to complete a tax return. Remember if you are due a refund, you will lose it if you don’t put a return in. If in doubt speak to your accountant. How much interest can you earn tax free?

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Your deadlines • By post or depositing it in a SARS drop box – 30 September 2015 • Electronically at a SARS branch (non-provisional taxpayers) – 27 November 2015 • Non-provisional taxpayers on eFiling – 27 November 2015 • Provisional taxpayers on eFiling – 29 January 2016. Be careful: As usual there are scams about If someone contacts you saying they can get you a tax refund, and particularly if they request a percentage of any refund obtained, be very suspicious. Also remember, SARS will never ask you for your personal banking details or your PIN number. Make use of the SARS “Report a Scam” facility on their web-site (http://www.sars.gov.za/TargTaxCrime/ Pages/Scams-and-Phishing.aspx?k=).

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Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

Canan BURAL1, Esin AKTA�2, Günnur DENIZ3, Ye�im 0NL0<;ER<;l4, Gülsen BAYRAKTAR5 1- DDS, PhD, Assistant Professor, Department Prosthodontics, Istanbul University, Faculty of Dentistry, Istanbul, Turkey. 2- MsC, PhD, Assistant Professor, Department of Immunology, Institute of Experimental Medicine, Istanbul University, Istanbul, Turkey. 3- MsC, PhD, Professor, Department of Immunology, Institute of Experimental Medicine, Istanbul University, Istanbul, Turkey. 4- DMD, Professor, Department of Biochemistry, Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey. 5- DDS, PhD, Professor, Department of Removable Prosthodontics Istanbul University, Faculty of Dentistry, Istanbul, Turkey. Corresponding address: Dr. Canan Bural - Istanbul University, Faculty of Dentistry - Department of Removable Prosthodontics - Capa, 34390 - Istanbul - Turkey - Phone: +90212 414 20 20 (ext: 30256) - Fax: +90212 525 35 85 e-mail: cbural@istanbul.edu.tr

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ABSTRACT Objectives: Residual methyl methacrylate (MMA) may leach from the acrylic resin denture bases and have adverse effects on the oral mucosa. This in vitro study evaluated and correlated the effect of the leaching residual MMA concentrations ([MMA] on in vitro cytotoxicity of L-929 fibroblasts. Material and Methods: A total of 144 heat-polymerized acrylic resin specimens were fabricated using 4 different polymerization cycles: (1) at 74ºC for 9 h, (2) at 74ºC for 9 h and terminal boiling (at 100ºC) for 30 min, (3) at 74ºC for 9 h and terminal boiling for 3 h, (4) at 74ºC for 30 min and terminal boiling for 30 min. Specimens were eluted in a complete cell culture medium at 37ºC for 1, 2, 5 and 7 days. [MMA] in eluates was measured using high-performance liquid chromatography. In vitro cytotoxicity of eluates on L-929 fibroblasts was evaluated by means of cell proliferation using a tetrazolium salt XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4methoxy-6-nitro)benzenesulphonic acid) assay. Differences in [MMA] of eluates and cell proliferation values between polymerization cycles were statistically analyzed by Kruskal- Wallis, Friedman and Dunn’s multiple comparison tests. The correlation between [MMA] of eluates

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and cell proliferation was analyzed by Pearson’s correlation test (p<0.05). Results: [MMA] was si%nificantly (p:50.001) hi%her in eluates of specimens polymerized with cycle without terminal boiling after elution of 1 and 2 days. Cell proliferation values for all cycles were si%nificantly (p/0.01) lower in eluates of 1 day than those of 2 days. 8he correlation between [MMA] and cell proliferation values was negative after all elution periods, showing si%nificance (p/0.0;) for elution of 1 and 2 days. MMA continued to leach from acrylic resin throughout 7 days and leaching concentrations markedly reduced after elution of 1 and 2 days. Conclusion: Due to reduction of leaching residual MMA concentrations, use of terminal boiling in the polymerization process for at least 30 min and water storage of the heat-polymerized denture bases for at least 1 to 2 days before denture delivery is clinically recommended for minimizing the residual MMA and possible cytotoxic effects. Key words: Acrylic resins. Denture bases. Methylmethacrylate. Cytotoxicity. Cell proliferation. Chromatography, high pressure liquid

INTRODUCTION Heat-polymerization is the most widely used method of polymerization for acrylic resin denture base fabrication and usually is accomplished in a heated water-bath10,12,26. The nature and duration of the conditions to which the molded acrylic resin subjected is described as the polymerization cycle14,26. The conventional method of polymerization cycle is a long, slow-temperature water-bath polymerization where the heat-polymerization of acrylic resin is processed for 9 h at 74ºC26. There are also post- polymerization cycles such as terminal boiling at 100ºC for durations of 30 min (short-term) or longer than 1 h (long-term)10,12,14,32. Furthermore, it has been reported that total polymerization time shorter than 2 h is widely preferred than the long polymerization cycles3. Although there has been several reported variations of polymerization temperature and time, the conversion of monomer is not complete and this might result in unreacted, residual monomer in the denture base acrylic resin2-5,10,12,14,25. Methyl methacrylate (MMA) was the predominant residual monomer in the acrylic resin32. In addition, it has been stated that the residual MMA content might change due to polymerization method4,5,31 and cycle10,12,14,25,32. Denture base is in continuous contact with the great part of the oral mucosa. It is important to evaluate the effect of the residual monomer, which has been shown to leach into water21,31,32, saliva2,4,30 or artificial saliva20, on the oral mucosa that is adjacent to the denture base. Leaching residual monomer have been suggested as potentially high enough to cause irritation of oral mucosa, irritation or even an allergic reaction. This might especially

be important for patients with infected= in>amed or lacerated mucosa11,23. In vitro cytotoxic effects of denture base acrylic resins have also been attributed to the leaching components4,8,15,17-19,22-24,30. Although there are a number of reports of in vitro cytotoxicity of denture base acrylic resins, which were processed with various polymerization methods and cycles8,11,16-19,22-24,30, there is no available study that correlated in vitro cytotoxicity and the leaching concentrations of residual MMA ([MMA] ) of heatpolymerized denture base acrylic resin, processed with different polymerization cycles. The aims of the present study were to evaluate 1) [MMA] , 2) in vitro cytotoxicity, 3) the correlation between the leaching [MMA] and in vitro cytotoxicity of heat- polymerized specimens, polymerized with different polymerization cycles after elution in a cell culture medium for 1, 2, 5 and 7 days. The hypothesis was that terminal boiling would reduce the leaching [MMA] and in vitro cytotoxicity of heat-polymerized denture base acrylic resin.

MATERIAL AND METHODS Specimen preparation Stainless steel discs (1 mm thick x 10 mm diameter)22-24 were conventionally molded in Type II dental stone (Moldano, Heraus Kulzer, Germany) with a powder/liquid ratio of 100 g/30 mL under aseptic conditions. Flasks were kept under hydraulic pressure (Kavo Elektrotechnisches Werk, GmBH, Allgäu, Germany) of 2 atm for 45 min. Heat-polymerizing, PMMA based denture base acrylic resin (Meliodent Heat-cure Denture Jase MaterialN Qeraus Uulzer VmJQYZo.= Qanau= Germany) without cadmium was tested in the

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present study. Acrylic resin was mixed in accordance with manufacturers’ recommendations, with a powder/liquid ratio of 23.4 g/10 mL for 60 s at room temperature (23±2ºC). After 5 min of doughing time, unpolymerized resin was packed in molds and then >asks were kept under hydraulic pressure of 2 atm for 45 min. Heat-polymerization was performed in thermostatically controlled water bath (Kavo EWL Typ 5506; Kavo Elektronisches Werk) with 4 different polymerization cycles (Figure 1). After completion of the polymerization cycles= the >asks were cooled at room temperature (23±2ºC) for 2 h. Specimens were transferred into sterile centrifuge tubes (TPP Centrifuge Tubes, Switzerland), containing 50 mL of distilled water at room temperature (23±2ºC) and then ultrasonically cleaned (Metu Elektromekanik; Ultrasonic Cleaner, Istanbul, Turkey) for 5 min1619. Thirty six (n=36) acrylic resins specimens were fabricated for each polymerization cycle with a total of 144 specimens. Eluate preparation Complete cell culture medium without serum11 was used as elution medium. Eluates of specimens were prepared by placing 3 disks into a sterile vial with 9 mL11,17 of Dulbecco's modified ea%le medium (DMEM)/ F-12 (Biological Industries, Haemek, Israel) supplemented with 1% antibiotics solution (100 IU/mL penicillin, 100 μg/mL streptomycin, 25 μg/ mL Amfoterisin-B; Biological Industries), 1% vitamin solution (MEM-Vitamins Solution 100X; Biological Industries), 2% non-essential amino acid solution (MEM-Eagle non-essential amino acid solution 100X; Biological Industries), and 1% L-Glutamine (L-Glutamine Solution; 200 mM, Biological Industries). The DMEM was maintained at pH 7.3 by adding 25 mM HEPES (HEPES BUFFER; Biological Industries)7. The ratio of surface area of the discs to the volume of culture medium was 0,626 cm2/mL and was within the range 0.5-6.0 cm2/mL as recommended by the International Standards Organization (ISO) 10993-513. Specimens were eluted with complete cell culture medium at 37ºC for 1, 2, 5 and 7 days in a humidified atmosphere of ;0 ZO , 95% air. After each elution period, the eluates were removed and the specimens were transferred into new vials and fresh cell culture medium. Cell culture media without acrylic resin specimens were also incubated Known serial concentrations of 1, 2, 3, 5 and 10 μmol/L (standards) of MMA dissolved in methanol was analyzed and a calibration curve (Figure 2) was

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obtained using chromatographic MMA peak at retention time of 10.22 min (Figure 3). Eluates were diluted with methanol (1:5 v/v) and injected into column with 10 μL volume. Peak area of each eluate was put into equation obtained from the calibration curve (Figure 2) and [MMA] in to serve as negative controls11,16-19. Eluates were filtered for sterilization and 100 fetal calf serum (FCS Heat-inactivated; Biological Industries) were added. Eluates were stored at -20ºC until the determination of the concentration of leaching residual MMA and in vitro cytotoxicity tests. Determination of leaching residual MMA concentration ([MMA] ) each eluate was expressed as μmol/L. Twenty-four chromatographic analyses for each polymerization cycle and 6 for each elution period with a total of 96 analyses were performed. Cell culture L-929 murine fibroblasts (American Type Zulture Zollection= ZZL 1 fibroblast= NZ8Z clone 929) were used in the study. Cells were cultured [MMA] in eluates was determined using High in 75 cm2 culture flasks (TPP, Tissue Culture Performance Liquid Chromatography (HPLC) with the HPLC pump (Waters 600 E, Millford, MA, USA) equipped with a gradient controller (Waters Model 600), autosampler (Waters 717 plus), tunable UV- Vis detector (Waters 486) and a reversed phase C18 with stainless steel analytical column (μ Bondapak 3.9x300 mm, 10 μ particle size, 125 Aº). The analysis was performed at room temperature (23±2ºC) under the following conditions: chromatographic grade methanol (Merck, KGaA, Darmstadt, Germany)/distilled water (1:1) mobile phaseN 0.8 mL/min >ow rate and detection at 220 nm. Dish, Switzerland) with the complete cell culture medium described above and incubated at 37ºC in a humidified atmosphere of ;0 ZO , 95% air. Cell proliferation Cell proliferation was assessed using a colorimetric assay system (XTT Cell Proliferation Kit; Biological Industries) which measures the reduction of a tetrazolium component, XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium] bis(4-methoxy-6-nitro) benzenesulphonic acid) into soluble formazan product by the mitochondria of viable cells. This assay kit contains a XTT reagent and an activation solution. 5x103 cells were plated in each well of 96 well-

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Code H1 H2 H3 H4a

Polymerization cycle at 74ºC, for 9 h at 74ºC, for 9 h at 74ºC, for 9 h at 74ºC, for 30 min

+ + +

at 100ºC, for 30 min at 100ºC, for 3 h at 100ºC, for 30 min

(Conventional) (Short-term terminal boil) (Long-term terminal boil) (Short-term polymerization)

a recommended polymerization cycle by the manufacturer

Figure 2- Standard calibration curve for methyl methacrylate (MMA)

Figure 3- High performance liquid cromatography chromatogram of methyl methacrylate (MMA) and characteristic peak at approximately 10.22 min of retention time.

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plates and incubated at 37oZ in a humidified atmosphere of ;0 ZO , 95% air for 24 h. 100 μL of eluates were added to each well and further incubated for 24 h7,19. 5 mL of XTT reagent were mixed with 0.1 mL activation solution in accordance with manufacturer’s instructions to obtain a solution which will react with cells. 50 μL of reaction solution were added to each well and incubated at 37oZ in a humidified atmosphere of ;0 and 7 days are presented in Table 1. For elution of 1 and 2 days, leached [MMA] of long-term terminal boiling cycle (Q3) was significantly (p:50.001) lower than polymerization cycles with no terminal boiling (H1) and short-term polymerization with short-term terminal boiling (H4). For elution of 5 and 7 days, leached [MMA] of shortterm terminal boiling cycle (Q2) was significantly lower than the cycles with no terminal boiling (Q1) (p:50.0;) and longterm terminal boiling cycle (Q3) (p:50.0;)= respectively. CO , 95% air for 2 h. Twenty-four cell proliferation Leached [MMA] reduced significantly (p/0.01) for measurements for each polymerization cycle and six for each elution period with a total of 96 measurements were performed. After incubation, colorimetric absorbance was measured at 450 nm (reference wavelength at 670 nm) using a microtiter plate reader (Universal Microplate Reader ELX 800; Bio-Tek Instruments Inc., Winooski, VT, USA). Cell proliferation was expressed as a percentage of negative controls7,11,16-19. Data were analyzed statistically using GraphPad Prisma Version 3 (San Diego, California, USA) polymerization cycle with no terminal boiling (H1) between elution of 1 and 2 days and increased significantly (p/0.0;) in long-term terminal boiling cycle

(H3) between elution of 2 and 7 days. Cell proliferation Mean and standard deviation of cell proliferation values of each polymerization cycle after elution of specimens for 1, 2, 5 and 7 days are shown in Table 2. For elution of 1 and 2 days, cell proliferation values of long-term terminal boiling cycle (H3) were significantly higher than cycles with no [MMA] and cell proliferation values between the terminal boiling (H1) (p<0.01) and short-term polymerization cycles were analyzed with Kruskal-polymerization with short-term terminal boiling Wallis test and the change in [MMA] and cell (H4) (p<0.05). Cell proliferation values changed proliferation values within the cycles were analyzed with Friedman tests. Posthoc comparisons were performed by Dunn’s multiple-comparisons test. The correlation between [MMA] in eluates and cell The correlation between leached [MMA] and cell proliferation values were analyzed by Pearson’s correlation test at si%nificance level of 0.0;.

RESULTS Leaching [MMA] Mean and standard deviation values of [MMA] of each polymerization cycle after elution of 1, 2, 5 proliferation values was negative after elution of 1, 2, 5 and 7 days. The correlation was statistically significant at elution of 1 day (r=-0.573, p<0.01) and 2 days (r=-0.491= p:50.0;). 8he correlation was also negative with no statistically significance at elution of 5 days (r=-0.116, p>0.05) and 7 days (r=-

Table 1- Mean residual ± standard deviation methyl methacrylate [MMA]r values at the end of days 1, 2, 5 and 7 of elution. The same letters indicate the statistically significant difference between cycles (p�0.05)

Cycle

H1 H2 H3 H4

36

Day 1 6.45±2.27a,e 2.29±0.89 0.92±0.40a 4.39±1.66a

Elution (μmol/L) Day 2 3.23±1.16b 1.69±0.55 0.71±0.39b,f 2.12±0.51b

Day 5 3.41±1.04c 2.02±3.66c 2.66±3.62 3.54±0.96

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Day 7 4.04±1.19 2.38±2.02d 5.87±2.56d,f 4.70±1.13


Table 2- Mean cell proliferation (%) at the end of days 1, 2, 5 and 7 of elution. The same letters indicate the statistically significant difference between cycles (p�0.05)

Cycle

H1 H2 H3 H4

Day 1 6.45±2.27a,e 2.29±0.89 0.92±0.40a 4.39±1.66a

Elution (μmol/L) Day 2 3.23±1.16b 1.69±0.55 0.71±0.39b,f 2.12±0.51b

Day 5 3.41±1.04c 2.02±3.66c 2.66±3.62 3.54±0.96

Day 7 4.04±1.19 2.38±2.02d 5.87±2.56d,f 4.70±1.13

DISCUSSION As far as the existing scientific data on in vitro cytotoxicity of denture base materials are concerned= there is no available study that identifies or quantifies the leachin% component in eluates of test specimens. 8his study showed and quantified that residual MMA leached into eluates. It was observed in this study that in vitro cytotoxicity changed depending on the leached [MMA] . In finding of differences in [MMA] between long-term (H3) and shortterm (H2 and H4) terminal boiling cycles. An another interestin% findin% was that leached [MMA] of the short polymerization cycle together with short-term terminal boiling (H4) were lower than the polymerization cycle with no terminal boiling (H1), observed after 1 and 2 days of elution. Present findings support the results of previous studies3,5,12,14,25,32 that indicate the use of a terminal boiling stage at least for 30 min in other words, increased [MMA] in the eluates the heat-polymerization to minimize the leaching produced reduced cell proliferation, thus increasing in vitro cytotoxicity. The hypothesis of this study was accepted, since terminal boiling reduced the leaching of [MMA] , which in turn decreased the in vitro cytotoxic effects of heat-polymerized denture base resin. Salivary concentrations of substances might diffuse from denture base acrylic resin2,4,20,21,30,32 and show cytotoxic effects22, depending on the time and the refreshing saliva. At the end of each elution period, eluates were collected and the tubes were re-filled with fresh culture medium11,22. This in vitro experimental design was preferred to simulate the in vivo removal of saliva into gastrointestinal tract by swallowing and salivary refreshment. It has been shown that leached residual MMA reduced when the polymerization temperature and time were increased10,12,32, depending on the decreased residual MMA content21,29. In the present study, the use of terminal boiling produced residual MMA.

In the present study, XTT assay was used for the cell proliferation measurements. The reasons for use of XTT assay are higher sensitivity, production of a water soluble dye that simplifies the analysis and provides faster determination than other methods. The use of soluble formazans, such as XTT, has been suggested to eliminate the error- prone solubilization step which is required for the microculture tetrazolium assays which employ MTT6,9,27. According to the ISO13 (1999) 10993-5 standard, the de%ree of cytotoxic effect is classified as noncytotoxic when cell proliferation is more than 75%, slightly cytotoxic when 50 to 75%, moderately cytotoxic when 25 to 50% and highly cytotoxic when less than 25%. Use of a terminal boiling stage has been previously attributed to produce improved cytotoxicity due to reduced residual monomer levels15,18. The finding of negative correlation marked reductions in [MMA] of eluates. The between leaching [MMA] and cell proliferation results of previous studies10,12,14,25,32 that reported the reduction in residual monomer content with increased terminal boiling time supports the present values indicates that leaching residual MMA content affects in vitro cytotoxicity of heat-polymerized acrylic resin. Within the polymerization cycles tested, the non-cytotoxic effect (the highest cell proliferation values) was determined in the cycles with short- (H2) and longterm (H3) terminal boiling. However, this trend was observed at some elution periods and the degree of cytotoxicity produced by all the polymerization cycles tested was counted as sli%htly cytotoxic on L-929 fibroblasts at elution of 7 days. A previous study1 has reported higher cell survival rates of 92%, 82%, 83% 91% and 92% for heat-polymerized specimens after elution of 1 h, 1, 3, 5 and 7 days, respectively. The differences in cytotoxicity levels might be due to differences in the experimental designs, such as elution conditions or cell proliferation assay. In vitro cytotoxicity of denture base acrylic resins were previously described mostly after 1 to 2 days

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of elution7,8,16-19,22,23. There are also few studies1,11,24,28,30 that investigated the in vitro cytotoxicity of denture base materials eluted for longer periods than 2 days of elution. In the present study, the shortest experimental period was 1 day for elution. The main reason for choosing this period was that the ISO13 (1999) 10993-5 standard recommends a minimum of 24 h for elution (extraction) process. There is only one report1 of elution for 1 h of denture base acrylic resins. However measurement of earlier periods mi%ht provide additional scientific data about leaching mechanism of residual components and in vitro cytotoxic effects of denture base acrylic resins. It is important to note that the non-significant polymerized prosthetic appliances. The results from in vitro cytotoxicity tests cannot be directly applied to in vivo conditions. However, in vitro measures play an important role in the analysis of denture base acrylic resins. Testing of dental materials by cell culture methods is relatively simple to perform, reproducible, controllable and cost effective12. In vitro tests may provide vital information about the biological behavior of dental materials in a simplified system that minimizes the effect of confounding variables. The results of cytotoxicity tests have limitations with regard to their applicability to their clinical use. The materials used in dentures are subjected to changes in the moist environments of the oral cavity18. Therefore, findings of in vitro or in vivo tests cannot be extrapolated to the clinical setting15. Further studies should focus on the identification of the leaching components or their derivatives in the moist environment. The correlation between leaching components and their effects on different cellular mechanisms may be interesting topics of future investigations.

CONCLUSION Under the experimental protocol and within the limitations of this in vitro study, it can be concluded for heat-polymerized denture base acrylic resin: • Residual MMA leached into cell culture media. • Polymerization temperature and time can changes in [MMA] (except H3) between elution affect the leaching concentrations of residual MMA. • Residual MMA continued to leach throu%hout 7 days of elution periods and leaching concentra tions markedly reduced after elution of 1 and 2 days • Reduction in residual MMA results in reduced in vitro cytotoxicity. • 8he choice of a polymerization cycle with at least 30 min of terminal boiling may minimize the increasing trend in [MMA]

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on the same days. For leached residual MMA and in vitro cytotoxicity. elution of 5 and 7 days, the lowest cytotoxic effect was observed in long-term polymerization cycle with short-term terminal boiling (H2). Although no ACKNOWLEDGEMENTS This study was supported by The Research values of this polymerization cycle was observed between the elution periods, this cycle has produced Support Unit of Istanbul University as the project no T-412/08032004. the lowest leaching [MMA] values and cytotoxic effect. The possibility of presenting [MMA] values REFERENCES 1- Ata SO, Yavuzyilmaz H. In vitro comparison of the cytotoxicity of acetal resin, heat-polymerized resin, and auto-polymerized resin as denture base materials. J Biomed Mater Res B Appl Biomater. 2009;91:905-9. 2- Austin AT, Basker RM. The level of residual monomer in acrylic denture base materials with particular reference to a modified leaching [MMA] into liquid cell culture media and method of analysis. Br Dent J. 1980;149:281-6. 3- Austin AT, Basker RM. Residual monomer levels in denture slightly cytotoxic effects, water storage of at least1 to 2 days can be recommended to minimize the risk potential of toxic or adverse effects of heat-bases. The effects of varying short curing cycles. Br Dent J. 1982;153:424-6. 4- Baker S, Brooks SC, Walker DM. The release of residual monomeric methyl methacrylate from acrylic appliances in the human mouth: an assay for monomer in saliva. J Dent Res. 1988;67:1295-9. ;- Jayraktar V= Vuvener J= Jural Z= Uresin Y. In>uence of polymerization method, curing process, and length of time of storage in water on the residual methyl methacrylate content in dental acrylic resins. J Biomed Mater Res B Appl Biomater. 2006;76:340-5. 6- Bean TA, Zhuang WC, Tong PY, Eick JD, Chappelow CC, Yourtee DM. Comparison of tetrazolium colorimetric and 51Cr release assays for cy

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totoxicity determination of dental biomaterials. Dent Mater. 1995;11:327-31. 7- Bouillaguet S, Shaw L, Gonzalez L, Wataha JC, Krejci I. Long- term cytotoxicity of resin-based dental restorative materials. J Oral Rehabil. 2002;29:7-13. 8- Cimpan MR, Cressey LI, Skaug N, Halstensen A, Lie SA, Gjertsen BT, et al. Patterns of cell death induced by eluates from denture base acrylic resins in U-937 human monoblastoid cells. Eur J Oral Sci. 2000;108:59-69. 9- Goodwin CJ, Holt SJ, Downes S, Marshall NJ. Microculture tetrazolium assays: a comparison between two new tetrazolium salts, XTT and MTS. J Immunol Methods. 1995;13;179:95-103. 10- Honorez P, Catalan A, Angnes U, Grimonster J. The effect of three processing cycles on some physical and chemical properties of a heat-cured acrylic resin. J Prosthet Dent. 1989;61:510-7. 11- Huang FM, Tai KW, Hu CC, Chang YC. Cytotoxic effects of denture base materials on a permanent human oral epithelial cell line and on primary human oral fibroblasts in vitro. Int J Prosthodont. 2001;14:439-43. 12- Huggett R, Brooks SC, Bates JF. The effect of different curing cycles on levels of residual monomer in acrylic resin denture base materials. Quintessence Dent Technol. 1984;8:365-71. 13- International Organization for Standardization. ISO 10993-5: biological evaluation of medical devices - Part 5: Tests for in vitro cytotoxicity. Geneva: ISO; 1999. 14- Jagger RG. Effect of the curing cycle on some properties of a polymethylmethacrylate denture base material. J Oral Rehabil. 1978;5:151-7. 15- Jorge JH, Giampaolo ET, Machado AL, Vergani CE. Cytotoxicity of denture base acrylic resins: a literature review. J Prosthet Dent. 2003;90:190-3. 16- Jorge JH, Giampaolo ET, Vergani CE, Machado AL, Pavarina AC, Carlos IZ. Biocompatibility of denture base acrylic resins evaluated in culture of L929 cells. Effect of polymerisation cycle and post- polymerisation treatments. Gerodontology. 2007;24:52-7. 17- Jorge JH, Giampaolo ET, Vergani CE, Machado AL, Pavarina AC, Carlos IZ. Cytotoxicity of denture base resins: effect of water bath and microwave postpolymerization heat treatments. Int J Prosthodont. 2004;17:340-4. 18- Jorge JH, Giampaolo ET, Vergani CE, Machado AL, Pavarina AC, Carlos IZ. Effect of post-polymerization heat treatments on the cytotoxicity of two denture base acrylic resins. J Appl Oral Sci.

2006;14:203-7. 19- Jorge JH, Giampaolo ET, Vergani CE, Pavarina AC, Machado AL, Carlos IZ. Effect of microwave postpolymerization treatment and of storage time in water on the cytotoxicity of denture base and reline acrylic resins. Quintessence Int. 2009;40:e93100. 20- Koda T, Tsuchiya H, Yamauchi M, Hoshino Y, Takagi N, Kawano J. High-performance liquid chromatographic estimation of eluates from denture base polymers. J Dent. 1989;17:84-9. 21- Koda T, Tsuchiya H, Yamauchi M, Ohtani S, Takagi N, Kawano J. Leachability of denture-base acrylic resins in artificial saliva. Dent Mater. 1990;6:13-6. 22- Lefebvre CA, Knoernschild KL, Schuster GS. Cytotoxicity of eluates from light-polymerized denture base resins. J Prosthet Dent. 1994;72:644-50. 23- Lefebvre CA, Schuster GS. Biocompatibility of visible light-cured resin systems in prosthodontics. J Prosthet Dent. 1994;71:178-85. 24- Lefebvre CA, Schuster GS, Marr JC, Knoernschild KL. The effect of pH on the cytotoxicity of eluates from denture base resins. Int J Prosthodont. 1995;8:122-8. 25- Lung CY, Darvell BW. Minimization of the inevitable residual monomer in denture base acrylic. Dent Mater. 2005;21:1119-28. 26- Phoenix RD. Denture base resins. In: Anusavice KJ, ed. Phillips’ science of dental materials. 11th ed. China: Saunders Elsevier; 2003. p:721-57. 27- Roehm NW, Rodgers GH, Hatfield SM, Glasebrook AL. An improved colorimetric assay for cell proliferation and viability utilizing the tetrazolium salt XTT. J Immunol Methods. 1991;142:257-65. 28- Sheridan PJ, Koka S, Ewoldsen NO, Lefebvre CA, Lavin MT. Cytotoxicity of denture base resins. Int J Prosthodont. 1997;10:73- 7. 29- Stafford GD, Brooks SC. The loss of residual monomer from acrylic orthodontic resins. Dent Mater. 1985;1:135-48. 30- Tsuchiya H, Hoshino Y, Tajima K, Takagi N. Leaching and cytotoxicity of formaldehyde and methyl methacrylate from acrylic resin denture base materials. J Prosthet Dent. 1994;71:618-24. 31- Vallittu PK, Miettinen V, Alakuijala P. Residual monomer

content and its release into water from denture base materials. Dent Mater. 1995;11:338-42. 32- Vallittu PK, Ruyter IE, Buykuilmaz S. Effect of polymerization temperature and time on the residual monomer content of denture base polymers. Eur J Oral Sci. 1998;106:588-93.

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REDEFINING THE DENTIST-LABORATORY RELATIONSHIP IN THE AGE OF DIGITAL DENTISTRY

Lee Culp, CDT

This article first appeared in Dental Economics magazine, June 2015. Reprinted with permission of Dental Economics and PennWell Corporation.

T

he arrival of the new millennium seemed to be the catalyst for change in digital dentistry-several different CAD/CAM systems have been introduced as restorative dentistry solutions since then, though it has taken slightly longer than anticipated to integrate this technology into daily practice. Today's chairside and laboratory-based CAD/CAM systems are used to design and manufacture implant abutments, bars, zirconia restorations, all-ceramic and composite full-contour crowns, inlays, and veneers that may be stronger, better-fitting, and more esthetic than restorations fabricated using traditional methods. As restorative dentistry evolves and incorporates digital imaging, computer design, and robot-created restorations, our perceptions and definitions of the dental laboratory must evolve as well. In order to fully understand these concepts, we must first define what a laboratory is. Initially, we might say that a laboratory is the place that a dentist sends impressions to be processed into restorations, which are then sent back for adjustment and delivery. This definition fits well with the traditional concept of a dentist-laboratory workflow. However, just as the Internet has forever changed the landscape of communication, electronic CAD/CAM restoration files catalyzed significant change in the way we view and structure the dentist- laboratory relationship.

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Let us imagine first that our laboratory is not a place, does not have walls, and exists only in the talents of the two partners in the restorative process-the dentist and technician. The equipment they use to create the restoration may be located next to the chair or in a dental laboratory. Their "laboratory" is actually nothing more than a workflow, which is flexible to the degree that abilities, access, and equipment allow. The primary decision is the timing of the hand-off from one partner to another. Moreover, a dentist who can use optical intraoral scans for impressions and who often chooses CAD/CAM restorations as the best patient treatment option has, I believe, more freedom in the timing of the hand-off to the technician partner. The laboratory is no longer a place; it is, to a large degree, a virtual and fluid entity.

of dental models.

In some instances, it makes sense for the dentist to independently prepare, design, and finish the restoration chairside during a single visit using the obvious advantages of a clinical CAD/CAM system. Other times, it is advantageous to engage the services of the restorative partner (i.e., a dental technician), because he or she possesses the skill and, perhaps more importantly, the time to create restorations that either demand more complex characterization or can be more efficiently created by someone other than the dentist.

Using the 3Shape restorative design software, the implant abutments and final Zenostar zirconia restorations were designed simultaneously. This allowed their designs to be tailored to best create the proper function, esthetics, and emergence profile for optimum tissue health and esthetics. This restoration was also designed to be screw-retained for removal for follow-up inspection (figures 3-4).

In the conventional indirect restorative process, the procedure begins with the usual steps: The clinician prepares the case according to the appropriate guidelines, makes an impression, and sends these and other critical information to the laboratory. After the laboratory receives all the materials from the dentist, the impression is poured, the models mounted, and the dies trimmed. These models are then used to fabricate appropriate restorations-either layered, pressed, milled, cast, or combinations. Even though this application offers many advantages to the dentist-technician team, it still requires taking intraoral impressions using conventional techniques, sending these impressions to the laboratory for the creation of stone models, and fabricating traditionally created dental restorations. In this article, we would like to explore the next phase in the evolution of the dentist-technician working relationship. Our patient was in need of a restoration to replace the missing posterior in the maxillary right quadrant. We elected not to use a conventional workflow that would have required impressions, implant impression analogs, the creation of stone models to produce a laboratory-fabricated set of implant abutments and the final restoration. Instead, we chose a completely digital method that did not require the use of traditional impression materials or the fabrication

Once the implants were deemed ready for the restorative phase, a digital impression was created using the 3Shape Trios intraoral scanner, the maxillary-mandibular arches were scanned, and the implant positions were virtually referenced with the use of "scan flags" that were placed into each implant and scanned to create our digital file. These were then sent to the laboratory through a communication portal (figure 1). Upon the laboratory’s receipt of the data file, the scans were uploaded into the design software, and the implants were identified for the correct implant type, size, and position (figure 2).

Upon completion of the design work, the design file for the Zenostar zirconia restoration was sent to the in-laboratory milling center for fabrication, while the custom implant abutments were sent to a milling center that specializes in titanium milling. While the implant abutments were being fabricated, our team completed the Zenostar full-contour zirconia bridge. When the implant abutments were shipped back to the laboratory, we checked for fit accuracy, and then sent both the implant abutments and Zenostar zirconia restoration to the prescribing dentist (figure 5). Upon the laboratory’s receipt of the data file, the scans were uploaded into the design software, and the implants were identified for the correct implant type, size, and position (figure 2). Using the 3Shape restorative design software, the implant abutments and final Zenostar zirconia restorations were designed simultaneously. This allowed their designs to be tailored to best create the proper function, esthetics, and emergence profile for optimum tissue health and esthetics. This restoration was also designed to be screw-retained for removal for follow-up inspection (figures 3-4). Upon completion of the design work, the design file for the Zenostar zirconia restoration was sent to the in-laboratory milling center for fabrication, while the custom implant abutments were sent to a milling center that specializes in titanium milling. While the

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Figure 1: Intraoral scan uploaded into design software

Figure 2: Manual alignment of implant scan flags

Figure 3: Design of custom implant abutments, Zenostar zirconia bridge, and screw access holes

Figure 4: Completed design of abutments and restoration

Figure 5: Completed screw-retained implant restoration

Figure 6: Facial view of final restoration

Figure 7: Occlusal view of final restoration

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implant abutments were being fabricated, our team completed the Zenostar full-contour zirconia bridge. When the implant abutments were shipped back to the laboratory, we checked for fit accuracy, and then sent both the implant abutments and Zenostar zirconia restoration to the prescribing dentist (figure 5). Upon the laboratory’s receipt of the data file, the scans were uploaded into the design software, and the implants were identified for the correct implant type, size, and position (figure 2). Using the 3Shape restorative design software, the implant abutments and final Zenostar zirconia restorations were designed simultaneously. This allowed their designs to be tailored to best create the proper function, esthetics, and emergence profile for optimum tissue health and esthetics. This restoration was also designed to be screw-retained for removal for follow-up inspection (figures 3-4).

Lee Culp, CDT, is the CEO of Sculpture Studios, a dental laboratory, education, research, and product development center specializing in new and innovative digital dental technologies and their applied applications to diagnostic, restorative, and surgical dentistry. He is a leading resource and inventor for many of the materials, products, and techniques used in dentistry today, and holds numerous patents for his ideas and products. Jonathan Ferencz, DDS, is a clinical professor of postgraduate prosthodontics at New York University.

Equity Dental

Upon completion of the design work, the design file for the Zenostar zirconia restoration was sent to the in-laboratory milling center for fabrication, while the custom implant abutments were sent to a milling center that specializes in titanium milling. While the implant abutments were being fabricated, our team completed the Zenostar full-contour zirconia bridge. When the implant abutments were shipped back to the laboratory, we checked for fit accuracy, and then sent both the implant abutments and Zenostar zirconia restoration to the prescribing dentist (figure 5). The screw-retained implant abutments and the final restoration were all created without the use of impression materials or the fabrication of dental models. The implant restoration was placed with very minimal adjustment to the occlusal surface; no adjustment was required to the interproximal contact (figures 6-7). The dental profession currently regards CAD/CAM technology as just a machine that fabricates full-contour ceramic restorations or frameworks. Digital dentistry and the digital dental team represents a totally new way to diagnose, plan treatment, and create functional esthetic restorations in a more productive and efficient manner. CAD/CAM dentistry will only further enhance the dentist-assistant-technician relationship as we move together into this new era of patient care.

Zumax Magnification Loupes R 6500.00 LED Illumination R 7750.00 Desk top Lab Microscope (10x; 20x) Desk top Lab Microscope (7x – 45x)

R 12 000.00 R 24 000.00

Orders:

David 0834587041 david@equitydental.com Photo credits: Figures 1-4 are courtesy of Lee Culp; figures 5-7 are courtesy of Dr. Jonathan Ferencz.

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Comparative analysis of

transmittance

for different types of commercially available

zirconia & lithium disilicate materials

Husain Hatim Harianawala1*, Mohit Gurunath Kheur1, Sanjay Krishnaji Apte2, Bharat Bhanudas Kale2, Tania Sanjeev Sethi1, Supriya Mohit Kheur3 Rangoonwala College of Dental Sciences, Pune, Maharashtra, India Centre for Materials for Electronics Technology, Pune, Maharashtra, India 1

2

3

D.Y.Patil Dental College, Pune, Maharashtra, India

Corresponding author: Husain Hatim Harianawala Department of Prosthodontics M.A.Rangoonwala College of Dental Sciences & Research Center, Maharashtra, India Tel. 919833683432: e-mail, husain.harianawala@gmail.com Received 9 May, 2014 / Last Revision 26 June, 2014 / Accepted 7 August, 2014 Š 2014 The Korean Academy of Prosthodontics

KEY WORDS:

Aesthetics; Lithium disilicate; Translucency; Transmittance; Zirconia

PURPOSE.

Translucency and colour stability are two most important aspects for an aesthetic dental restoration. Glass ceramic restorations are popular amongst clinicians because of their superior aesthetic properties. In the last decade, zirconia has generated tremendous interest due to its favorable mechanical and biological properties. However, zirconia lacks the translucency that lithium disilicate materials possess and therefore has limitations in its use, especially in esthetically demanding situations. There has been a great thrust in research towards developing translucent zirconia materials for dental restorations. The objective of the study was to evaluate and compare the transmittance of a translucent variant of zirconia to lithium disilicate.

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MATERIALS AND METHODS.

Two commercially available zirconia materials (conventional and high translucency) and 2 lithium disilicate materials (conventional and high translucency) with standardized dimensions were fabricated. Transmittance values were measured for all samples followed by a microstructural analysis using a finite element scanning electron microscope. One way analysis of variance combined with a Tukey-post hoc test was used to analyze the data obtained (P=.05).

RESULTS.

High translucency lithium disilicate showed highest transmittance of all materials studied, followed by conventional lithium disilicate, high translucency zirconia and conventional zirconia. The difference between all groups of materials was statistically significant. The transmittance of the different materials correlated to their microstructure analysis. CONCLUSION. Despite manufacturersâ&#x20AC;&#x2122; efforts to make zirconia significantly more translucent, the transmittance values of these materials still do not match conventional lithium disilicate. More research is required on zirconia towards making the material more translucent for its potential use as esthetic monolithic restoration. [ J Adv Prosthodont 2014;6:456-61]

INTRODUCTION The success of a dental restoration depends upon a num- ber of factors such as the material chosen, its mechanical properties, anatomical form, surface texture, translucency and colour. The most common aesthetic restorative materi- al used in day to day practice for crown and bridge work is porcelain fused to metal (PFM) because of its excellent mechanical properties.1 However, the much superior aes- thetic outcome of metal-free ceramic restorations has led to their increasing popularity, especially in the anterior regions of the mouth.2 The major drawbacks of porcelain fused to metal resto- rations are lack of aesthetics, the possibility of metal aller- gies and the delamination of the veneering porcelain. In order to overcome the unaesthetic metallic hue seen in PFM restorations, dental research began to be directed towards metal-free ceramic restorations to improve the aes- thetic outcome. Research and development led to the devel- opment of many metal-free ceramic systems, wherein ceramic substructures were introduced which were subse- quently veneered with porcelain providing relatively superi- or aesthetics.1 However; these newer ceramics are prone to failures owing to their poor mechanical properties.3,4 Glass ceramics with leucite and lithium disilicate rein- forced crystals have proven to be successful aesthetic options in the anterior aesthetically demanding regions of the jaw.5 However, these restorations cannot withstand the mechani- cal load of more than one pontic in the anterior region and are contraindicated in the load bearing posterior regions because of their poor flexural strength.6 The search for a material with mechanical properties similar to PFM, superior biocompatibility and aesthetics similar to glass ceramics has led to the rapid evolution of dental zirconia. 3 mol% yttrium stabilized tetragonal zirco- nia polycrystalline (3Y-TZP) ceramics have gained tremen- dous popularity as

restorative materials as a result of their excellent mechanical properties,3,4,7 good biocompatibility, and relatively good aesthetic properties.7 However, the conventionally available 3Y-TZP restora- tions are quite opaque owing to the large grain size and the presence of porosity which is evident at the microstructural level of these materials.8,9 The esthetic outcomes with these restorations are not as superior to lithium disilicate and leu- cite reinforced ceramics.7 Newer translucent varieties of zir- conia have been developed recently, with the objective of improving their transmittance, so that they can be used in esthetically demanding clinical situations. Studies done on these newer materials have shown that they are more translucent than conventional zirconia and demonstrated approximately two thirds more flexural strength than lithium disilicate.10 Use of translucent zirconia has the potential to eliminate delamination of the veneering ceramic, which has been known to be a common clinical problem and also reduce the amount of tooth preparation required.11 This study was undertaken to evaluate the light transmittance of this trans- lucent variety of 3Y-TZPs at different wavelengths and compare it to lithium disilicate.

MATERIALS AND METHODS Four groups of materials were prepared and evaluated in this study. Group 1- Conventional zirconia (Metoxit Dental Pre-Sintered Zirconia Blocks, High Tech Ceramics, Liechtenstein Lot No. 0019481), Group 2High translucen- cy zirconia (Metoxit Dental Pre-Sintered Zirconia Blocks, High Tech Ceramics, Liechtenstein Lot No. 0019832), Group 3- Conventional lithium disilicate (IPS e.max LT Shade A2, Ivoclar Vivadent, Liechtenstein Lot No. P83594.) and Group 4- High translucency lithium disilicate (IPS e.max HT Shade A2, Ivoclar Vivadent, Liechtenstein Lot No. P76936). 12 circular discs of 1 millimeter thickness

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and 1 centimeter diameter were fabricated for each group. The linear sintering shrinkage for the batch of conven- tional pre-sintered zirconia batch was 21%. The pre-sin- tered zirconia was milled using diamond discs and sintered diamonds attached to a mandrel into discs of 1.28 mm height and 1.2 cm diameter. These discs were then sintered as per the manufacturer’s guidelines. The thickness of the pre-sintered samples and samples post sintering were veri- fied using a digital vernier calliper (0-200 mm, Aerospace, China). Following finishing and polishing, the dimensions of all the samples were maintained at 1mm thickness and 1cm diameter, with a variation up to +/- 0.01 mm. A similar procedure was followed for fabrication of samples of the high translucency zirconia using a pre-sin- tered high translucency zirconia block. A cobalt chromium mould having height of 1 mm and diameter 1 cm was used for fabrication of wax patterns for the lithium disilicate samples. The mould was CAD-CAM milled from a block of cobalt chromium (Cobalt-Chromium alloy-d.Sign, Ivoclar Vivadent, Asia). The thickness of the wax patterns was verified using a digital vernier calliper. The patterns were then invested and pressed as per the manufacturer’s instructions. After the pressing was com- pleted the ring was divested and cleaned using 1% hydrofluoric acid in an ultrasonic cleaner. The discs were then fin- ished using porcelain finishing burs and their dimensions were reconfirmed. The dimensions were kept exactly the same as those of the zirconia samples. The high translucen- cy lithium disilicate samples were prepared following the same protocol. Transmittance is a measure of the fraction of incident light at a specified wavelength that passes through a sample. The translucency of dental porcelains can be studied by measuring direct transmission (when light goes through without a change in direction or quality), total transmission (combination of direct and diffuse light transmission) and spectral reflectance (fraction of incident light that is reflect- ed at an interface such as porosity). The transmittance of the samples was

measured using a dual beam UV- Spectrophotometer equipped with an integrating sphere (Beckman Acta C III UV-visible spectrophotometer, Beck- man Instruments, Inc., Irvine, CA9266, USA)(Fig. 1). Air was used as the reference. Diffuse light transmittance mea- surements were made from the 200 nm to 800 nm wave- length range . A black cardboard sample holder (1.25 cm ×1.25 cm × 4.5 cm) with a central orifice of 8.5 mm diame- ter was used to position the specimens in front of the sphere holder (Fig. 2). Data was recorded with a computer connected to the spectrophotometer, and a graph of light transmittance percentage per nanometer was obtained by using Origin 6.1 software (Microcal Software Inc., North- ampton, MA, USA) for each ceramic specimen. Digital readings at 525Å were recorded and used for the calculations.

Fig. 2. Sample holder with 8.5 mm slot placed in the. UV spectrophotometer. One way analysis of variance (ANOVA) test was used for multiple group comparisons followed by TukeyPost Hoc test for group wise comparisons. Field emission scanning election microscope (FSEM (JEOL JSM 7600F Field Emission Scanning Election Microscope) was used to study the microstructure of both the zirconia and lithium disilicate material.

Fig. 3. Samples of Group 1 - 4 arranged sequentially from left to right held against daylight.

Fig. 1. UV spectrophotometer

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Table 1. Transmittance values (Angstrom units –Å) for various groups studied Group

N

Group 1 Conventional Zirconia 12 Group 2 High translucency zirconia 12 Group 3 Conventional Lithium disilicate 12 Group 4 High translucency Lithium disilicate 12 *HS = Highly Significant.

C

SD

ANOVA F

P

0.06510558 0.14396933 0.15873866 0.20775941

0.00368295 0.13083695 0.00551693 0.00864425

289.373 579.870 36.864 725.119

0.000 HS 0.000 HS 0.000 HS 0.000 HS

Table 2. Tukey-Post Hoc test (Pairwise comparison) Conventional zirconia Conventional zirconia - Zirconia high translucency - Conventional lithium disilicate - Lithium disilicate high translucency -

*HS = Highly Significant.

Zirconia Conventional Lithium disilicate high Lithium High translucency disilicate translucency 0.0HS 1.1HS 0.000HS - 1.2HS 0.000HS - - 0.000HS - - 0.000HS

RESULTS The transmittance values for the samples from all groups and their comparisons are presented in Table 1. Trans- mittance values were highest for Group 4 (high translucen- cy lithium disilicate) showing mean transmittance values of 0.207759. Group 3 (conventional lithium disilicate) had mean transmittance value of 0.158738 which was marginal- ly higher than Group 2 (high translucency zirconia samples) whose mean value was 0.143969. Group 1 samples (conventional zirconia) had the least values of 0.065015. The relative translucency of the different groups of samples is represented in Fig. 3. High translucency lithium disilicate showed highest direct transmittance values which were statistically highly significant (P=.000)(Table 2). Conventional lithium disili- cate showed transmittance (P=.000) values higher than highly translucent zirconia which was statistically significant (P=.000). Conventional zirconia had the least transmittance (P=.000). Scanning electron microscopy (SEM) of the high trans- lucency zirconia samples showed nano sized crystals, with the external outline of the crystals depicting a polyhedral structure. Minimal nano sized porosity was seen. The grain sizes varied ranging from 50 nm to 400 nm for the high translucency zirconia samples (Fig. 4) as compared to the conventional zirconia which showed diffuse porosity rang- ing from 200 nano microns to 1.5 microns (Fig. 5).

Fig. 4. Scanning electron microscopic image of high translucency zirconia.

Fig. 5. Scanning electron microscopic image of conventional zirconia.

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Fig. 6. Scanning electron microscopic image of commercially available lithium disilicate. The lithium disilicate samples on scanning electron microscopy showed that the crystals were well merged with the matrix (Fig. 6). The crystals could not be differentiated from the matrix. Arrangement of the crystals was irregular with some spacing seen. The high translucency lithium disilicate samples showed well aligned parallel crystals with no spacing. The white spots seen are the colouring dopants (Fig. 7).

DISCUSSION The translucency of the core is one of the most important determinants of the aesthetic properties of metal-free ceramic restorations.12,13 The zirconia core is not as translu- cent as other dental metal-free ceramic materials such as glass-ceramics.14,15 Therefore, by increasing the translucency of the zirconia core, the aesthetic properties of a dental restoration can be improved. The ultimate aim is to elimi- nate the use of veneering porcelain, thereby eliminating the problem of porcelain delamination16 and enabling the clini- cian to employ more conservative tooth preparation designs. The translucency of dental ceramics can be evaluated through direct transmission, total transmission and via spectral reflectance. Total transmission increases with increasing wavelength of light as mentioned by the Rayleigh scattering equation. The transmittance of all the samples were studied at a wavelength of 525 Å in accordance with Brodbelt’s methodology of studying translucency of dental porcelains.17 Translucency of dental porcelains is known to be affect- ed by various factors such as grain boundaries, pores, sec- ond-phase of component, and light scattering from rough surfaces.18 The translucency of glass ceramics depends largely on the amount of crystals within the glassy matrix14,19 and the

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Fig. 7. Scanning electron microscopic image of high translucency lithium disilicate. size of the particles compared with the incident light wavelength.20 Another factor that interferes with light transmission is the difference in the refractive index between the crystals and the glassy matrix. The refractive index is measured as the amount of reduction in the speed of light when passing through a medium. Leucite (1.51) and lithium (1.55) have similar refractive indices to the glassy matrix (1.50).15 Presence of porosity in these glass ceramics tends to have a higher influence on the light trans- mission than the crystals themselves. The mismatch between the refractive indices of the air porosity (1.00) and that of the glassy matrix may lead to a significant light scattering effect.15 High translucency lithium disilicate showed the highest transmittance values (0.207759Å). This could be attributed to the refractive index of the lithium disilicate glass crystals matching to that of the glassy matrix. The absence of porosity prevents scattering of the light, thereby improving transmittance values. A linear well-organized crystalline structure was seen with the high transmittance glass ceram- ics. The significantly lower transmittance values for the conventional lithium disilicate may be attributed to the irregular arrangement of the crystals leading to increased scattering and reflectance. The significantly superior mechanical and biological properties of 3 mol% yttrium stabilized zirconia along with its biocompatible features have resulted in its increasing popularity amongst clinicians and researchers. Polycrystalline materials are known to show high transmittance when the grain sizes are small and uniform in size with minimal porosity.18 Dopants such as alumina are added to improve the phase stability and to reduce ageing. However the pres- ence of alumina because of its different refractive index to zirconia increases the scattering of light and reduces the translucency.

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Lowest transmittance values (0.065015 Å) were seen with conventional zirconia. This is attributed to the pres- ence of porosities larger than 50 nano microns which affect transmittance21 (Fig. 5). The high translucency zirconia showed a significant increase in transmittance values (0.143969 Å) over that of conventional zirconia. This is due to the significantly reduced frequency and size of the porosity seen with this newer material (Fig. 4). The material also showed a more uniform grain size and configuration than the conventional zirconia. Conventional lithium disilicate showed higher transmit- tance values (0.158738 Å) than the high translucency zirco- nia (0.143969 Å). This difference was statistically signifi- cant. Lithium disilicate restorations with opaque cores are currently used for cases wherein the tooth to be restored is non-vital or discoloured to mask the hue of the prepared stump.22,23 Zirconia having similar optical properties can be a better substitute for glass ceramic restorations because of its superior mechanical properties. The aesthetic demands of clinicians and patients have led manufacturers to improve upon the translucency of zir- conia and lithium disilicate ceramics. This study clearly demonstrates that the high translucency zirconia and lithi- um disilicate have significantly more transmittance than the conventional variants. This can be attributed to the manu- facturing procedures of these materials. Some of the meth- ods documented in the literature for obtaining more dense, less porous, more translucent zirconia are hot isostatic press- ing, microwave sintering, spark plasma sintering etc.9,18,24 However despite the significant improvement in transmit- tance, high translucency zirconia is still below par when compared with today’s aesthetic gold standard material, lith- ium disilicate. One of the greatest drawbacks of zirconia restorations compared to lithium disilicate is the tendency for delamina- tion of veneering ceramic from the core.16 The ability of bonding lithium disilicate to tooth structure is also an ad- vantage over zirconia restorations. Monolithic restorations used popularly today are not as esthetic as core veneered zirconia restorations or lithium disilicate restorations. The authors believe that if the translucency of zirconia could be increased, thereby favorably reducing its refractive index values from 2.2 to that of the aesthetic glass ceramics whose refractive index is 1.5, the need for using veneering ceramic can potentially be eliminated.9 This would permit life like restorations with larger spans providing aesthetics similar to glass ceramics. This would also reduce the amount of tooth preparation required, thus help conserve more tooth structure. It will broaden the horizons for use of zirconia as laminates and veneers.

CONCLUSION Within the limitations of the study, it can be concluded that high translucency lithium disilicate is the most translucent material amongst the materials studied. High translucent zirconia is significantly more translucent than conventional zirconia. However, the increase in transmittance achieved with high translucency zirconia is significantly less com- pared to even conventional lithium disilicate. Further research is needed on improving the microstructural fea- tures of zirconia materials in order to enhance their translucency.

REFERENCES 1. Kelly JR, Benetti P. Ceramic materials in dentistry: historical evolution and current practice. Aust Dent J 2011;56:84-96. 2. Durán P, Villegas M, Fernández JF, Capel F, Moure C. Theoretically dense and nanostructured ceramics by pres- sureless sintering of nanosized Y-TZP powders. Mater Sci Eng A 1997;232:168-76. 3. Chen YM, Smales RJ, Yip KH, Sung WJ. Translucency and biaxial flexural strength of four ceramic core materials. Dent Mater 2008;24:1506-11. 4. Tinschert J, Natt G, Mautsch W, Augthun M, Spiekermann H. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. Int J Prosthodont 2001;14:231-8. 5. Mizrahi B. The anterior all-ceramic crown: a rationale for the choice of ceramic and cement. Br Dent J 2008;205:251-5. 6. Raigrodski AJ. Contemporary materials and technologies for all-ceramic fixed partial dentures: a review of the literature. J Prosthet Dent 2004;92:557-62. 7. Conrad HJ, Seong WJ, Pesun IJ. Current ceramic materials and systems with clinical recommendations: a systematic re- view. J Prosthet Dent 2007;98:389-404. 8. Dias MC, Piva E, de Moraes RR, Ambrosano GM, Sinhoreti MA, Correr-Sobrinho L. UV-Vis spectrophotometric analysis and light irradiance through hot-pressed and hot-pressed-ve- neered glass ceramics. Braz Dent J 2008;19:197-203. 9. Tsukuma K, Yamashita I, Kusunose T. Transparent 8 mol% Y2O3–ZrO2 (8Y) Ceramics. J Am Ceram Soc 2008;91:813-8. 10. Chen YM, Smales RJ, Yip KH, Sung Wj. Translucency and biaxial flexural strength of four ceramic core materials. Dent Mater 2008;24:1506-11. 11. Sailer I, Fehér A, Filser F, Lüthy H, Gauckler LJ, Schärer P, Franz Hämmerle CH. Prospective clinical study of zirconia posterior fixed par

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tial dentures: 3-year follow-up. Quintessence Int 2006;37:685-93. 12. Rosenstiel SF, Land MF, Fujimoto J. Contemporary Fixed Prosthodontics. 4th ed. St. Louis; Mosby; 2006. p. 262-643. 13. Yu B, Ahn JS, Lee YK. Measurement of translucency of tooth enamel and dentin. Acta Odontol Scand 2009;67:57-64. 14. Heffernan MJ, Aquilino SA, Diaz-Arnold AM, Haselton DR, Stanford CM, Vargas MA. Relative translucency of six all-ce- ramic systems. Part I: core materials. J Prosthet Dent 2002; 88:4-9. 15. Heffernan MJ, Aquilino SA, Diaz-Arnold AM, Haselton DR, Stanford CM, Vargas MA. Relative translucency of six all-ce- ramic systems. Part II: core and veneer materials. J Prosthet Dent 2002;88:10-5. 16. Kelly JR, Tesk JA, Sorensen JA. Failure of all-ceramic fixed partial dentures in vitro and in vivo: analysis and modeling. J Dent Res 1995;74:1253-8. 17. Brodbelt RH, O›Brien WJ, Fan PL. Translucency of dental porcelains. J Dent Res 1980;59:705. 18. Kim MJ, Ahn JS, Kim JH, Kim HY, Kim WC. Effects of the sintering conditions of dental zirconia ceramics on the grain size and translucency. J Adv Prosthodont 2013;5:161-6. 19. Antonson SA, Anusavice KJ. Contrast ratio of veneering and core ceramics as a function of thickness. Int J Prosthodont 2001;14:316-20. 20. Zhang Y, Griggs JA, Benham AW. Influence of powder/liq- uid mixing ratio on porosity and translucency of dental por- celains. J Prosthet Dent 2004;91:128-35. 21. Alaniz JE, Perez-Gutierrez FG, Aguilar G, Garay JE. Optical properties of transparent nanocrystalline yttria stabilized zir- conia. Opt Mater 2009;32:62-8. 22. Succaria F, Morgano SM. Prescribing a dental ceramic materi- al: Zirconia vs lithium-disilicate. Saudi Dent J 2011;23:165-6. 23. Vichi A, Louca C, Corciolani G, Ferrari M. Color related to ceramic and zirconia restorations: a review. Dent Mater 2011; 27:97-108. 24. Johnson LD. Microwave and plasma sintering of ceramics. Ceram Int 1991;17:295-300.

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Questionnaires Comparative analysis of Effect of leaching residual methyl transmittance for different types methacrylate concentration on in of commercially vitro cytotoxicity of heat available zirconia lithium polymerized denture base disilicate materials. acrylic resin processed with Question 1 different polymerization cycles. The aesthetic outcome of 3 mol % yttrium stabilized tetragonal zirconia polycrystalline (ZY – TZP) are superior to that of lithium disilicate and leucite reinforced ceramics. A True B False

Question 2 The translucency of dental porcelains can be studied by: A Use of a microscope B Placement under a range of very bright lights C Measuring direct transmission, total trans mission and spectral reflection D All of the above Question 3 At what wave length was the transmittance of samples studied? A 358 Å B 689 Å C 1009 Å D 525 Å Question 4 The absence of perosity prevents scattering of light, therefor improving the: A Strength B Shade C Transmittance value D High Shine Question 5 Which material had the lowest transmittance value? A Conventional zirconia B High translucency lithium disilicate C High translucency zirconia D Conventional lithium disilicate

Question 1 At which temperature does the terminal boiling take place? A 30 ºC B 75 ºC C 100 ºC D 74 ºC Question 2 What kind of acrylic was used to perform the study? A Exel denture bas material B Vertex heat-cure denture base material C Meliodent heat-cure denture base material D None of the above Question 3 For elution of days five and seven, leached methyl methacrylate of short-term terminal boiling cycle was significantly higher than the cycles with no terminal boiling. A True B False Question 4 The use of terminal boiling stage has been previously attributed to produce improved cytotoxicity due to residual monomer levels. A True B False Question 5 The ISO (1999) 10993-5 standard recommends a minimum time period for the elution process to be a valid experiment. This minimum time period is: A 3 hours B 14 hours C 24 hours D 30minutes

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Vol 5 issue 3  

Journal dedicated to the subject of Dental Technology with CPD articles for South African Dental Technicians/Technologists.

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