Recent advances in silver amalgam/ dental implant courses by Indian dental academy

RECENT ADVANCES IN SILVER AMALGAM ⇒

An ALLOY is defined for dental purposes as a metal containing two more elements, at least one of which is a metal, and all of which are mutually solvable in molten state.

⇒

DENTAL AMALGAM or SILVER AMALGAM is a special type of alloy that contains mercury as one of its constituents (Ag; Cu; Sn; and sometimes Zn).

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INTRODUCTION Silver Amalgam has been in use as a VERSITILE restorative

material since the beginning of 19 th century. The first dental silver amalgam was introduced into England by “Joseph Bell” in 1819 and was known as “BELLS PUTTY”.

- SIR REGNART because of his extensive study is considered as the FATHER OF AMALGAM. In the last several years, concern regarding MERCURY TOXICITY and greater interest in improved esthetics have encouraged a more away from Amalgam as a material of choice.

In spite of several challenges and of the encouraging data, it is probable that amalgam will be part of the Dental armamentarium for the next decade Amalgam has undergone drastic changes improvements in

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terms of composition; manipulation and safety in use. Amalgam though not pretty compared to the very appealing esthetic restorative materials is still being used as a material of choice in the posterior teeth by 92% of [Dentists clinical RESEARCH ASSOCIATES; 1997]; 96 are they wed to it? No; The reasons they use it so frequently are quite simple.

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Ease of manipulation.

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Less cost.

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Less time required.

Whereas resin based composites are: -

More technique sensitive.

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Less durability.

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Post-operative sensitivity.

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Microleakage.

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Secondary caries.

IMPROVEMENTS IN THE MATERIAL AND MANIPULATION -

It was not until 1960’s that formulations that differed from BLACK’s ALLOY WERE RECOGNIZED.

BLACK’s ALLOY Minimum of 65% Ag 29% Sn (Traditional low Cu)6% Cu 3% Hg 2% Zn

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The 1st divergence was brought by Innes and Youdelis in (1963).

This discovery did not receive much attention until 1970 when it was shown that high Cu-Amalgam were superior to low-CuAmalgams in resistance to marginal breakdown.

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Usually an alloy powder containing less than – 6% Cu  Low-Cu / traditional powder.

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Alloy containing greater than – 8 to 10%  Cu-high Cu amalgams.

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In contrast, the most recently adopted ISO standard (1986) specifies a chemical composition in wt% of a min of 40% Ag A max of

32% Sn 3% Cu 2% Zn 3% Hg

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The usage of high-Cu-Amalgams has become more common because of its superior clinical performance.

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1960’s Youdelis introduced high-Cu admixed / dispersant.

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Lathe cut (Ag-Sn) alloy

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Spherical (Ag-Cu) alloy (Eutectic)

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-

1974

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Asgar developed a new type of alloy for amalgam by preparing a powder from single Ag-Cu-Sn ternary alloy and called it as highCu-Single composition (OR) UNICOMPOSITION.

HIGH-Cu-ADMIXED ALLOY -

These alloys are often termed “Admixed Alloy” because the final powder is a mixture of at least two kinds of particles.

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Lathe cut; low Cu-(Ag-Sn) alloy; wt (30% to 55%) Spherical; Eutectic – (Ag-Cu) alloy.

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The spherical Ag-Cu particles mainly act as FILLERS to strengthen the amalgam matrix.

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When Hg-reacts with an admixed powder From Ag-Cu alloy  Ag dissolves.

Ag-Sn alloy  Ag and Sn dissolves in solution diffuses to the

surfaces of the Ag-Cu alloy and reacts with Cu  n phase (Cu6-Sn5) n crystals form around Ag-Cu unconsumed particles  and also contain γ1 crystals. γ1  matrix phase – that binds unconsumed particles together.

REACTION : Alloy particles (β+γ) and Ag-Cu eutectic + Hg  γ1 + n + unconsumed alloy of both types of particles; γ2 is virtually eliminated during the hardening reactions because of the high-Cu-content (12%). γ2  “crevices” / crevicular corrosion, γ2  SnHg - Sn causes corrosion; γ1  AgHg and γ-AgSn

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HIGH Cu-SINGLE COMPOSITION – 60% Ag; 27% Sn and 13% Cu by wt (13% to 30wt% of Cu). In addition, small amounts of Pd and indium are found in some of the marketed single composition alloy. 

Atomized particles have dendrite microstructures; consisting of lamella.



When Hg reacts  Ag-Sn phases and little Cu dissolves - in Hg  γ1 crystals.



γ1 acts as a matrix; that binds the partially dissolved alloy particles.



η crystals – are seen (meshed) on unconsumed alloy particles and may strengthen bonding between the alloy particles and γ1 grains.



η Crystals dispersed between γ1 grains may interlock γ1 grains.



THIS INTERLOCKING – improves Amalgam resistance to deformation.

REACTION: Ag-Sn-Cu alloy particles + Hg  γ1 + n + unconsumed alloy particles. γ2 eliminated ; forms if powder is not heat treated or if powder is treated too long at too high temperature.

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HIGH-Cu-AMALGAMS SHOWED IMPROVED MECHANICAL AND PHYSICAL PROPERTIES OVER LOWER-Cu-AMALGAMS Ranges of strengths and creep values of low Cu and High Cu amalgam (OHP) Amalgam

Comp. St. (MPa) 30 min 

Low-Cu

Tensile St. (MPa)

Elastic Modulus (GPa)

ISO CREEP (%)

1 hr 

24 hrs

124-200

310-390

53-62

20-40

0.70-3.70

High-Cu: (Admixed)

55-110

80-180

330-500

42-62

35-50

0.05-2.10

High-Cu: (Single)

70-210

100-320

320-570

34-64

30-60

0.03-0.04



High Cu Alloys exhibit

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Improved Marginal Integrity.

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Corrosion Resistance.

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Dimensional Stability.

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# resistance of the margins and bulk.

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Less mercury release.

SELECTION OF ALLOYS : Since numerous alloys of dental amalgam are available, selecting the best amalgam for use can be confusing.

CREEP AND COMPRESSIVE STRENGTH are 2 important factors to consider when making a selection.

Ex: An amalgam with an ISD creep value of less than 1.0% is likely to show.

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-

GOOD MARGINAL INTEGRITY FOR A LONG SPAN.

Early st (1hr) – compressive strength is another important factor.

Thus when you see the chart, high-Cu-Single alloys have much early st. than high-Cu-Admixed. 

Advantages: for immediate crown preparation can be polished 10 minutes after the end of trituritron without harmful effects.



ADMIX

High-Cu-alloys

on

the

other

hand

resist

condensation well therefore contain irregular particles; and are generally easier to adapt to cavity walls and exhibit less leakage.

DUNNE et al : I.D.J. (1997) 47; 131.

INDICATIONS FOR SILVER AMALGAM -

It seems sensible to restrict the use of Amalgam to clinical situations that justify its use.

They may include: 1) Large Cl-I and Cl-II cavities, involving more than the middle 3 rd of the occlusal surface of the posterior teeth, where indirect restorations are contraindicated.

2) Class II cavities where the cervical margin of the box finishes subgingivally / is composed entirely of dentin.

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3) Extensive cores, where the majority of coronal tooth structure is missing.

4) Where definite restorations must be placed but care or moisture cannot be controlled.

5) Where cost is a major patient concern and aesthetic unimportant.

CONTRAINDICATIONS FOR SILVER AMALGAM 1) Anterior teeth and clearly visible surfaces of posterior teeth.

2) Allergy to any component of Amalgam, proven by skin test, conducted by trained dermatologist.

3) Patient’s with proven amalgam – induced lichenoid lesions.

4) Remaining tooth structure requires support / would require extensive preparation to accommodate amalgam.

5) Treatment of incipient / early primary fissure caries.

POSSIBLE RESTRICTIONS IN USE OF SILVER AMALGAM 1) Amalgam should not be used during the first 3 years of a child’s life (German Health Authorities).

2) Amalgam should not be used in adults with kidney disease.

3) Amalgam usage was contraindicated in women of childbearing age.

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4) In patients who suffer from bruxism because Hg release from amalgam is greater during tooth grinding and chewing.

AMALGAMS SHOULD ONLY BE USED WHERE IT OFFERS CLEAR ADVANTAGES OVER OTHER MATERIALS (Advantages of Silver Amalgam over other tooth coloured Restorative materials): 1) COST EFFECTIVENESS: When compared to the esthetic restorative materials amalgam is highly cost effective and involves no lab fees.

Ex:If amalgam is

– 1X

Direct composite

– 2.5X

Direct composite

– Inlay 6X

Indirect composite – Inlay 8X Indirect Ceramic Inlay – 10X Gold Inlay

– 10X

Metal Ceramic

– 10X

CAD-CAM

– 10X+

2) TIME EFFECTIVENESS: Placement of an amalgam restoration takes only 20%-50% of the time taken when compared to esthetic restorative materials.

3) EASE OF PLACEMENT. 4) TRAINING CLINICAL RESEARCH AND EXPERIENCE:

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Because of the accumulated knowledge and research over 150 years all practitioners are fully trained in terms of use of amalgam.

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Whereas newer esthetic materials are still under research and still require complete understanding.

5) WEAR CHARACTERISTICS -

Amalgam exhibits physiological wear characteristic to those of tooth enamel whereas, GIC and LC GIC have very poor wear resistance.

6) DIMENSIONAL CHANGE: Modern alloys undergo very little dimensional change (some ¹ 0.2% by vol). In contrast conventional and (LC) GIC’s shrink by an order of magnitude greater as they set which cause post-operative sensitivity.

7) MARGINAL ADAPTATION : A particular advantage of amalgam is that marginal adaptation to cavity walls improved with time. This is due to the accumulation of corrosion products in the microspace (which is an unique feature).

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The recurrence of caries around amalgam restoration is low. This caries protective properties clinically proven but poorly understood.

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8) CLINICAL PERFORMANCE : The most important advantage offered by Amalgam is it’s clinical durability, especially when placed in large cavities subjected to occlusal forces.

9) OPERATOR SENSITIVITY : It is the least operative sensitive of all restorative materials. It is less affected by moisture contamination and dimensional change. Proper isolation during placement is necessary to provide a very durable restoration; contamination may still allow susceptibility for a short-term. This is in stark contrast to tooth coloured restorative materials which simply cannot be used where saliva, gingival fluid and blood are not completely controlled.

DISADVANTAGES OF SILVER AMALGAM IN COMPARISON WITH TOOTH COLOURED RESTORATIVE MATERIALS 1) LACK OF ADHESION TO THE TOOTH STRUCTURE : Since amalgam does not bond to the tooth structure, microleakage immediately following the insertion of the restoration is inevitable; whereas the tooth coloured restorative materials have clinical bond/micromechanical bond.

2) AESTHETICS : The appearance of amalgam is considered to be a drawback hence its use is limited to the posterior teeth.

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3) TOXICITY : The seemingly constant pronouncements about the toxic effects of Hg and the suggested link between dental amalgam and disease have confused and frightened public. While there is no scientific evidence whatsoever to support these claims they continue to flame the “ANTIAMALGAM FIRES”.

4) MARGINAL DETERIORATION : The ‘ditching’ around amalgam restorations are considered to be a stress / corrosion dependent defect occurring in areas subject to occlusal loading.

The magnitude and extent of ditching is directly proportional to creep properties. 

Secondary caries is one of the most important factors leading to replacement of Ag restoration. There was no significant difference

between

the

F-containing

amalgam

and

the

conventional amalgam with treatment of the cavity preparations with the 8% stannous fluoride solution on the inhibitory effect on the development of experimental cavity wall lesions in vitro.

O.D. : (1990) 15; 178-185.

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Admixed high-Cu Advantages: Longer WT

Single Cu  Increased strength  Increased strength expansion.

Less dimensional change Displace of matrix

Zn  Scavanger.

Easier finishing

Silver: Increased strength

Low condensation pressure

Increased expansion on setting.

Decreased creep and tarnish (whitens)

Disadvantages:

Sn : Controls reaction between Ag and Hg

Slower set

Decreased rate of reaction.

High Hg residual Higher creep condensation.

Decreased strength and hardness.

during

Decreased corrosion and tarnish.

Less easily strength Harder to finish POWDER COATED TECHNOLOGY This technology was developed in USA, Maryland at the National Institute of Standards and Technology. This is a more economic variant of cohesive gold. This powder can be then condensed under pressure to produce solid restorations. Hence oxidation of silver is the problem. Hence, if the powder particles are packed with tetra fluoroboric acid the oxides are dissolved and a restoration is obtained with properties inbetween cohesive gold and amalgam.

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ALLOYING ADDITIONS ADDITION OF INDIUM TO AMALGAM [OD; 1992; 17 : 196-202]. ⇒

Laboratory studies have shown that admixed indium improves the properties of dental amalgam, Youdelis (1979).

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Experimental study carried out by (1985) Johnson (where admixed indium was added to high-Cu-amalgam) showed that: 1) Less Hg was required for mixing.

2) Compressive strength increased upto 10%.

3) Improved resistance to creep and corrosion.

4) Reduced dimensional change on setting.

5) The alloy was not cytotoxic / hemolytic.

The 5-year clinical trials of Johnson showed that there were no

significant differences between. Indium containing and high Cu-Amalgam except that indium containing amalgam restorations incurred slight less break-down than high-Cu (Dispersalloy).

OD : 1992; Vol. 17 : 196-202. ⇒

ADDITION OF PALLADIUM (JOD; 1999 (27) 401-35) In 1997 Cherlin reported that 0.5 to 0.7wt% of palladium when

added to γ1 phase of amalgam resulted in 1) Decreased corrosion.

2) Increase in compressive strength.

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3) Increase in creep resistance.

4) Decreased in release rates of mercury vapour and ions.

5) Decreased transition of γ1 and β1. ⇒

Silver particles treatmented with alcohol: The alcohol removes the surface oxide layer improves the

adhesiveness of the silver particles to create a dense filling.

DRIVEN BY THE RECENT MERCURY FREE AMALGAMS 1.

MERCURY

CONTROVERSY

GALLIUM BASED ALLOYS : [DM (2000) Vol. 16, 97102].

Gallium was discovered in 1875. It is a metal with similar atomic

structures and characteristics to mercury and has a melting temperature of 29°C. Hence, by 1928 Puttkammer suggested gallium as a substitute for mercury.

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There were several reports in the 1950-60’s on efforts to develop a direct placement restorative material based on Gallium.

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Clinical restoration of a Ga-containing alloy were also placed, but no results were reported.

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Recently, 2 Ga based restorative alloys have become available.

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One developed in JAPAN

Other in AUSTRALIA

 Gallium Alloy

Galloy – has reviewed the ADA seal

GF II

of approval; FDA seal of approval NIDM acceptance in 96.

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Lab data on both alloys were promising.

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Toxicity was minimal.

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Handling characteristics were more different than Amalgam but acceptable.

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Mechanical and physical properties compared to amalgam.

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However, clinical studies showed mixed results.

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Many studies showed catastrophic failures of Ga – containing restoration.

Advantages: 1) Adapts well to the cavity walls.

2) Shows reduced initial marginal leakage (because of small setting expansion).

3) Mechanical properties such as compressive strength and creep are comparable to those of high-Cu amalgam.

DISADVANTAGES: 1) Handling characteristics of this paste is not favourable.

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2) It has to be manipulated and packed under alcohol to improve their handling.

3) Since mix is sticky Teflon coated instruments are required.

4) Working field should be absolutely dry during packing otherwise expansion occurs during setting (expansion exceeded 0.02% which is a limit set by ADA specification No. 1).

5) High level of corrosion is seen which causes loss of strength marginal disintegration and marginal # in “chunks”.

6) Uncontrolled growth of corrosion products led a) To dimensional change of 21.5%. b) Stress build up  caused.

1. Postoperative sensitivity.

2. Tooth fracture.

7) Whitening of Enamel and dentin margins because of gallium uptake.

8) Faster setting.

9) Poor biocompatibility.

10)Costly.

Since Ga reacts with moisture for upto 18 hours after placement forming corrosive products and expansion.

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⇒

They recommended encapsulating the restoration in resin during placement.

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A study carried out in 1993 showed that Galloy restorations from the oral fluids with a resin.

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reduced tarnish.

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Eliminated dimensional stability.

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Galloy using BIS-GMA based resin have shown acceptable clinical performance.

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Recently PAAMA – 2 as a sealing agent is being tried out.

As of now no reports on the long-term behaviour of these gallium

based alloys are currently available. Efforts are being directed towards the development of a more corrosion-resistant gallium alloy and a more biocompatible materials before it can be recommended and approved for clinical use.

POWDER COATED TECHNOLOGY 2.

DIRECT

FILLING

SILVER

ALTERNATIVE

TO

AMALGAM : QI 99, 30; 199.

The study investigated the wear resistance of Hg free Ag direct filling material and a dental amalgam.

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METHOD : A precipitated Ag powder was rinsed with dilute Fluoro boric acid and consolidated into a cohesive solid with a dental amalgam plugger at a load of 15N. RESULT : The Ag had: 1) A flexural strength, to that of amalgam 2) Smooth surface and hardening in Ag was obtained.

3) More resistance to wear-induced damage than amalgam.

The surface of Ag was more resistant than amalgam because of wear-induced work hardening.

4) Direct filling silver may be STRONG and wear resistant than amalgam.

DF silver has been developed based on temperature welding / cold welding if a precipitated Ag-based powder into a cohesive solid.

TO COMPENSATE FOR SOME OF THE DISADVANTAGES PRESENTED BY AMALGAM A CLINICAL TECHNIQUE THAT BONDS

AMALGAM

TO

ENAMEL

AND

DENTIN

WAS

INTRODUCED BY BALWIN as long back as 1897.

This adhesive amalgam restoration technique combines the good properties of amalgam with the principles of tooth structure preservation and marginal seal inherent to adhesive materials. The adhesive systems

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may obviate the need for protective basis and strengthen remaining tooth tissues weakened by disease and cavity preparations.

INDICATIONS [CLINICAL APPLICATIONS] -

In young, adult / aged patients

(Because resin adhesives can offer auxiliary retention, improve the marginal seal and protects the pulpal complex in all amalgam restorations) irrespective of the location a depth.

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For repair of restorations i.e. (to bond new to old amalgam) and to seal faulty margins in the old restorations).

In some clinical situations: However, use of a well-defined resistance form; Removal of weak walls, Reduction of cusps are recommended for reconstruction with Amalgam.

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Extensive carious lesions of the posteriors.

Advantages: The amalgam adhesive restoration technique offers advantages over non-adhesive treatment alternatives.

1) It is a treatment option for extensively carious posterior teeth, with a lower cost than either cast metal restorations / metal ceramic crowns.

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2) It allows the use of amalgam in teeth with low gingival- occlusal height (unlike conventional amalgam with pins amalgapin, inlays; onlays) etc.

3) It permits more conservative cavity preparations because it does not always require additional mechanical retention (unlike amalgam with pins; etc).

4) It eliminates the use of retentive pins and their inherent risks e.g.: periodontal perforation and pulpal exposure.

5) It reduces marginal leakage to minimum.

6) It reinforces tooth structure weakened by caries and cavity preparation.

7) It reduces the incidence of postoperative sensitivity commonly observed with amalgam restorations.

8) It reduces the incidence of marginal fracture.

9) It reduces the incidence of recurrent caries.

10)It allows definitive restorations of a tooth with a badly broken down crown in one clinical session.

11)It allows the biologic sealing of pulpodentinal complex.

LIMITATIONS AND DISADVANTAGES: The adhesive amalgam technique also has some limitations.

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1) It increases the time to perform a conventional amalgam and may be technique sensitive.

2) It requires practitioners to adapt to the new technique.

3) It increases the cost of amalgam restoration.

4) It makes the use of amalgam seem feasible in situations where it would not be indicated such for large restorations involving functional cusps.

5) It has not been in use long enough to allow a proper evaluation of its clinical performance.

TECHNIQUE -

Cavity preparations for bonded amalgam restorations may however still require an adequate form of resistance.

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The technique of employing the adhesives varies slightly among the different brands; however, the clinician must always follow a logical and previously established sequence.

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A rubber dam was to be applied to isolate the teeth.

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The carious lesions has to be removed with caries removal system caridex (etc) / a bur.

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Remove the unsupported enamel and finish the cavity preparation with adequate resistance form.

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The cavity preparations should be rinsed with a stream of H 2O and if a case is required usually GIC is opted because of its anticariogenic property.

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Then the surface is etched with 37% phosphoric acid for 20 seconds, rinsed with H2O for 30 seconds and then dried.

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Proper material and adequate wedging should be done.

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The etched enamel is painted with a thin coat of adhesive resin of individuals choice and manufacturers instructions are followed.

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Then the high-Cu-Amalgam was condensed by means of manual and mechanical condensation. After setting of the amalgam, the wedges and matrices were removed and the restorations carved to proper form.

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The rubber dam must be removed and then occlusion should be adjusted and restorations can be polished.

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CONCLUSION: -

Amalgam is a material of relatively low cost.

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Good clinical longevity.

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An amazing tolerance of manipulative variable.

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It is a material that is not likely to disappear from the clinical scene very soon in spite of attacks by certain factions.

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It has served many years and will continue to do so if we respect its advantages and shortcoming.

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