United Kingdom Edition
Telescope or double crowns Part 1 of precision dental prosthetics with highly engineered connections. By Ulrich Heker, Master Dental Technician & Verena Tunn- Salihoglu, dentist, Aberdeen, Scotland
n this first of two articles we will discuss the technical side of the telescopic dentures before presenting the clini-
cal side in the second part. Telescope prosthesis or double crowns are a proven option
for the prosthetic treatment of dramatically reduced dentition (fewer teeth might serve in some cases as an alternative to im-
plants). However, the production of such a prosthesis demands high technical skills on the side of the dentist and the dental tech-
D E N T S P LY A C A D E M Y W E B I N A R P R O G R A M M E
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nician. Of equal importance is a good communication between dentist and technician. These are the main keys to a successful case. The telescopic attachment consists of two parts: 1. The primary (inner) crown, or coping, which is permanently fixed to the anchor teeth, and is preferably made out of a precious metal, a high gold alloy. 2. The secondary (outer) crown implemented in to the prosthesis, made out of the same alloy. The usual type of double crown system next to the conus type is the parallel telescopic crown. They are named due to the fact that all surfaces from the primary (inner) and the secondary (outer) telescopic are not only parallel to each other but also parallel to the axis of each incorporated tooth. However in the case of a conus telescopic system a 4 degree angle of both telescopes to the axis of the tooth is aimed for, provided by the exact preparation of the dentist. Indications Double crowns can be used in the following situations: where there is a strongly depleted dentition uncertain prognosis of individual teeth in a periodontally damaged jaw (existing bone depletion, increased loosening of the anchor teeth) with a suboptimal distribution of the remaining teeth for the retention of removable bridges
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The almost universal applicability is characteristic for this anchoring system. Telescopic crowns can be applied as claspfree connecting elements with purely periodontally and periodontally-gingivally supported partial prostheses. The pros and cons of double crowns Advantages of the telescopic system: • a predominantly axial loading of the pillars leading to a favourable distribution of force protection of the anchor teeth from decay • the option of primary splinting for the securing and fixing of loose teeth • integrated tilt-avoidance • a straightforward ability to extend the prosthesis even up to a full denture the aesthetic advantage as no clasps are used the beneficial and straightforward treatment and control of the parodontium and the internal coping •can be used as a cost effective alternative to implants Disadvantages of the telescopic system: • requires a high technical effort • correspondingly higher costs • over sizing of the secondary crowns if the pile has not been efficiently reduced
United Kingdom Edition
• in comparison to a PMF crown higher tooth substance loss in preparation can only be coated/ veneered with composites How double crowns work Physical principles The patient expects the prosthesis to be easily inserted and removed. At the same time, the prosthesis has to be sufficiently attached so that it cannot be leveraged off by motion during speech and eating. In order for these conditions to be met, you need certain physical preconditions. These are explained below.
October 25-31, 2010
higher levels the patient can often not remove the prosthesis.
be removable without difficulty whilst not loosening at the wrong moment or due to sticky foods. The criteria must remain valid over a longer period of wear.
Achieving the correct friction of the individual telescopic components is only possible with considerable experience and skill by both parties technically involved; the dentist and the dental technician, and their interdisciplinary communication. The success also depends on the precision of each step
Note: The force required for removal of the prosthesis: 250–300 P is regarded as acceptable to patients. The maximal force required for removal should not exceed 650 P, as with
Telescope during insertion
In order to achieve a hold between the primary and secondary telescopic, these have to fit in a particular manner. There are three different types of fit: 1. a clearance fit, in which there is still a small bit of give/play 2. the medium fit, in which there is a large tolerance or oversizing before the joining of the components (which gives totally useless telescopic crowns) 3. the pressure fit, where the components are tight and interact such that friction is created during fitting
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On the principle that both crown pieces have to join exactly and without obstruction, parallel telescopic crowns are always pressure fittings; this is why telescopic crowns are preferably made from precious alloys, because of their high elasticity. The importance of friction The inner and outer telescopes are joined together by friction. Stated simply, the friction is due to the interaction between the surface layers of the inner and outer telescope. The binding forces of the telescopic crowns are therefore a consequence of this friction. Friction in telescopic crowns is a value that is difficult to measure. It is principally dependent on the technical construction of the crown, which is influenced by the following factors: • the number of the planned telescopic crowns • the length of the friction surfaces of the individual tooth and also the sum of all available telescopes • the placement of the friction surfaces relative to one another. Only oppositely facing parallel surfaces can provide the required friction with the elasticity of the materials, which is why gold alloys are generally used • the quality of the work A prosthesis has to be prepared in such a way that the patient can insert it without difficulty. Additionally, it must provide the feeling of fitting firmly. The
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22.09.2010 9:44:51 Uhr
24 Clinical ß
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on good communication and technical skill on both the dentists and the technical laboratory’s part.
and each detail. Conclusion to Part 1 We have given you an overview of the technical aspects of telescopic prostheses or double crowns and their almost universal applicability. The basic priciples of how they work and the importance of achieving the right level of friction are described. Success is dependent
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Copies upper jaw polishes for modelling the outer crowns
In the next article of “Part 2 of precision dental prosthetics with highly engineered connections” we will illustrate the clinical side to the telescopes or double crowns, i.e. the planning and preparation required. DT
Single Telescope with retention, showing primary and secondary telescope
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1. Becker, H: Einflüsse des umgebenden Mediums auf das Haftverhalten teleskopierender Kronen. Zahnärztl Welt 91, 54, (1982). 2. Becker, H: Wirkungsmechanismus der Haftung teleskopierender Kronen. Zahnärztl. Prax 34, 281 (1983). 3. Böttger, H: Das Teleskopsystem in der zahnärztlichen Prothetik. JA Barth, Leipzig 1961. 4. Diedrichs, G: Ist das Teleskopsystem noch zeitgemäß? Zahnärztl. Welt 99, 78 (1990). 5. Goslee, H: Principles and Practice of Crown and Bridge Work Dental Items of Interest Publishing Co., New York 1923. 6. Hedegard, B: Die Mitarbeit des Patienten – ein Planungsfaktor. Zahnärztl. Welt, Ref.88, 680 (1979). 7. Jacoby, W, Gasser, F: Nachträgliche Haltverbesserung von Teleskopkronen. Quintessenz 24, 59 (1973). 8. Jüde, HD, Kühl, W, Roßbach, A: Einführung in die zahnärztliche Prothetik. 5.Aufl. Deutscher Ärzte- Verlag, Köln 1996. 9. Kammertöns, H: Haftreibungsprüfung an Teleskop- und Konuskronenarbeiten. Quintessenz Zahntech 14, 11 (1988). 10. Krämer, A, Weber, H: Präzisionselemente in der Teilprothetik Teleskopierende Systeme. Zahnärztl Mitt 80, 2328 (1990). 11. Mack, H: Die teleskopierende Verankerung in der Teilprothetik. Quintessenz Zahntech 9, 17 (1983). 12. Peeso, FA: Crown and Bridgework. Henry Kimpton, London 1924. 13. Schreiber, S: Die Verankerung von Teilprothesen mit Teleskopkronen. Dtsch Zahnärztl Z 14, 983-988 (1959). 14. Schwanewede von, H, Anderseck, E: Proteza Teleskopowa – Die Teleskopprothese im stark reduzierten Lückengebiß. Prot Stom 35, 166 (1985). 15. Stüttgen, U, Hupfauf, L: Kombiniert festsitzend – abnehmbarer Zahnersatz. In: Horch, H-H, Hupfauf, L, Ketterl, W, Schmuth,G, (Hrsg): Praxis der Zahnheilkunde 6 (Teilprothesen), 2. Aufl. Urban & Schwarzenberg, München Wien – Baltimore 1988, S.163. 16. Wupper, H: Zur Biomechanik verschiedener Verankerungssysteme – Grundsätze zur Indikation von Geschieben, Stegen und Teleskopen. Zahnärztl Welt 95, 36 (1986).
About the author
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Ulrich Heker is the owner-manager of Ulrich Heker Dental Laboratory founded in 1996 with the strap line TEETH ‘R’ US. As a qualified master craftsman (German Master Dental Technician) since 1991, he has over 26 years’ experience both at the bench and in running a successful business. Ulrich lives in Mülheim on the river Ruhr and is an accomplished ‘westernstyle’ rider in his spare time. Ulrich is fluent in English and can easily be contacted at: http://www.germansmile.info, or you can email Ulrich@ Teethrus.de Verena Tunn- Salihoglu,was born close to Stuttgart, Germany. During her training at the Albert-LudwigsUniversity in Freiburg, Germany, she developed a keen interest in prosthodontics,, especially in partial dentures and telescopes. Now her main interest is the integration of holistic dentistry on a high precision dental quality level. Verena is fluent in English and can easily be contacted at: oldmachardental@ gmx.com
Part Two of a row of articles.