Chapter 5 Dental Amalgam PDF

Chapter DENTAL AMALGAM 5 ntroduction Amalgam has been an accepted part of dental therapeutics for more than 150 years and is still used for the majority of direct posterior restorations. The reasons for its popularity lie in its ease of manipulation relatively low...

Chapter DENTAL AMALGAM 5 ntroduction Amalgam has been an accepted part of dental therapeutics for more than 150 years and is still used for the majority of direct posterior restorations. The reasons for its popularity lie in its ease of manipulation relatively low cost. a long life. Some concern has been raised about mercury toxicity from both biologic and an environmental point of view; however, it is believed that amalgam presents an acceptable risk-to- benefit ratio when properly used.  Overview Alloy: Alloy is a union of two or more metals Amalgam: Amalgam is an alloy in which mercury occurs as a main constituent. Dental amalgam: The dental amalgam is an alloy of mercury with silver, tin, and varying amounts of copper, zinc and other minor constituents. *** insert a video, about what is dental amalgam*** AMALGAM Amalgam is the most widely used permanent filling in dentistry. It is prepared by mixing the alloy with mercury. The reaction between mercury and alloy is termed an amalgamation reaction. It results in the formation of a hard restorative material of silvery – gray appearance Amalgam Use and Benefits Dental amalgam, in widespread use for over 150 years, One of the oldest materials used in oral health care. Its use extends beyond that of most drugs, and is predated in dentistry only by the use of gold. Dental amalgam is the end result of mixing approximately equal parts of elements  liquid mercury (43 to 54%)  an alloy powder (57 to 46%) composed of silver, tin, copper, and sometimes smaller amounts of zinc, palladium, or indium.  Amalgam MERCURY (Hg) – is a liquid at room temperature and it is able to form a workable mass when mixed with the alloy. The reaction between mercury and alloy is termed an amalgamation reaction. Dental amalgam has been used for many years with a large measure of success. It is the most widely used of all available filling materials.  Composition The composition of the alloy powder particles varies from one product to another. Composition of CONVENTIONAL AMALGAM ALLOY: Metal: Weight: Silver (Ag)............................ 40-60 Tin (Sn).................................27-30 Copper (Cu)..........................13-30 Zinc (Zn)................................2 Mercury (Hg).........................3 CLASSIFICATION OF AMALGAM According to the number of alloyed metals According to the shape of the particles According to the copper content of the alloy - Low copper alloys: contain less than 6% copper - High copper alloys: contain more than 6% copper According to zinc content - Zinc -containing alloys: contain more than 0.01% zinc - Zinc-free alloy: contain less than 0.01% zinc According to whether the alloy is unimixed or admixed Role of each metal in dental amalgam Role of each metal in dental amalgam  Composition 1. Silver: Increases strength, expansion and reactivity. Decreases creep. Corrosion products are AgCl and AgS. 2. Tin: Increases reactivity and corrosion. Decreases strength and hardness. Corrosion products are SnO, SnCl, and SnS. 3. Copper: Increases strength, expansion and hardness. Decreases creep. Corrosion products are CuO and CuS.  Composition 4. Zinc: Increases plasticity, strength and the Hg:alloy ratio. Decreases creep. Causes secondary expansion. Corrosion products are ZnCl and ZnO. 5. Mercury: Wets the alloy particles. Decreases strength if in excess amounts. Implicated in toxic and allergic reactions.  In Brief Silver......................................gives strength Tin……...…….……………….……workability Copper….....strength & corrosion resistance Zinc…………….………….prevents oxidation Effects on properties of an amalgam restoration imparted PROPERTY by ingredients. INGREDIENT Silver Tin Cooper Zinc Strength Increases Durability Increases Hardness Increases Expansion Increases Decreases Increases Flow Decreases Increases Decreases Color Imparts Setting time Decreases Increases Decreases Workability Increases Increases Cleanliness Increases  Advantages 1. High compressive strength and hardness 2. Ease of use 3. Excellent wear resistance 4. Easy to distinguish between amalgam and tooth structure 5. Convenience of manipulation 6. Fairly low cost.  Disadvantage s 1. Objectionable 2. Mercury hazard aesthetics (silver color) 3. Amalgam tattoo 4. Non -insulating filling material  Amalgam: properties 1. DIMENSIONAL CHANGES 2. STRENGTH 3. PLASTIC DEFORMATION (CREEP) 4. CORROSION 5. THERMAL PROPERTIES 6. BIOLOGICAL PROPERTIES 1. DIMENSIONAL CHANGES A large contraction would result in a marginal gap down which fluids could penetrate. A large expansion would result in the protrusion of the filling from the cavity. A freshly mixed amalgam is condensed into the cavity preparation, the ideal result is that the amalgam neither expands or contracts as it sets. Expansion could result in post-placement sensitivity or protrusion from the cavity, Contraction would leave gaps prone to leakage between the restoration and the tooth The net contraction or expansion of an amalgam is called its "dimensional change." 2. STRENGTH The strength of dental amalgam must be high enough to resist forces placed on the amalgam restoration in the mouth. The strength of dental amalgam is developed slowly. - 24 hours: 90% to reach a reasonably high value and continues to increase slightly for some time after that. - 1 hour: 40 to 60% maximum 15 – 20 minutes after placing the filling , the AMALGAM is relatively weak. It is necessary to instruct patients not to apply undue stress to their freshly placed AMALGAM fillings.  3. PLASTIC DEFORMATION Creep is(CREEP) a viscoelastic property Creep is a gradual dimensional change under load. Amalgam undergoes a certain amount of plastic deformation or creep when subjected to dynamic intra-oral stresses.  4. TARNISH AND Tarnish is a surface phenomenon that can result in a CORROSION discolored restoration. Tarnish, the chemical reaction between the amalgam and the oral cavity are restricted to the amalgam surface. Corrosion results from chemical reactions that penetrate into the body of amalgam. Corrosion is a matter which may significantly affect the structure and mechanical properties. The rate of corrosion is accelerated if the AMALGAM filling contacts a gold restoration. Smooth surfaces are less prone to concentration cell corrosion.  5. THERMAL PROPERTIES AMALGAM has a relatively high value of thermal diffusivity. Dentine is replaced by a good thermal conductor. The coefficient of thermal expansion value for AMALGAM is about three times greater than that for dentine. This results in considerably more expansion and contraction in the restoration than in the surrounding tooth when a patient takes hot or cold food or drink. Thermal expansion may cause microleakage around the fillings since there is no adhesion between AMALGAM and tooth substance. Microleakage plays an important part in initiating such lesions.  BIOLOGICAL PROPERTIES Certain mercury compounds are known to have a harmful effect on the central nervous system. Some studies have shown a higher concentration of mercury in the blood and urine of patients with AMALGAM fillings than those without. Another potential problem concerns allergic reactions, usually manifested as contact dermatitis. Mercury or freshly mixed AMALGAM should never be touched by hand. Mercury is readily absorbed by the skin.  Usage and preparation of The dental specialist has the direct responsibility for the amalgam correct preparation and use of amalgam. Incorrect use may produce a faulty restoration that can cause or contribute to the loss of a tooth. Therefore, the dental specialist must use extreme care in preparing a good mix of amalgam that will provide the best qualities obtainable from the alloy. ***insert a video about changing an amalgam restoration for composite resin restoration***  MANIPULATIVE VARIABLES The manipulating of AMALGAM involves the following sequence of events: 1. Proportioning and dispensing 2. Trituration 3 Condensation 4.Carving 5. Polishing ***insert a video about class 1 amalgam restoration*** 1. PROPORTIONING AND DISPENSING Alloy/mercury ratios vary between 5:8 and 10:8. Those mixes containing greater quantities of mercury are “wetter” and are generally used with hand mixing. Those mixes containing smaller quantities of mercury are “drier” and are generally used with mechanical mixing. - For example Spherical particle alloys, require less mercury to produce a workable mix. 1. PROPORTIONING AND DISPENSING For optimum properties, the final set amalgam should contain less than 50% mercury. The optimal final mercury content ranges from an average of 45% for lathe-cut materials to an average of 40% for spherical materials. TRITURATION The mixing or trituration of AMALGAM may be carried out by hand or in an electrically powered machine which vibrates a capsule containing the mercury and alloy. Trituration by hand is not extensively practiced in developed countries nowadays. Mechanical mixing is far more widely used - amalgamator. Trituration times 5 - 20 seconds are normal.  2. TRITURATION The advantages of mechanical trituration are as follows: 1. A uniform and reproducible mix is produced. 2. A shorter trituration time can be used. 3. A greater alloy/mercury ratio can be used. Amalgamator  3. ONDENSATION Material is condensed into the prepared cavity using a flat- ended steel hand instrument called an amalgam condenser. The technique chosen for condensation must ensure the following. 1. Adequate adaptation of the material to all parts of the cavity base and walls. 2. Good bonding between the incremental layers of amalgam 3. Optimal mechanical properties in the set amalgam by minimizing porosity and achieving a final mercury content of 44-48%.  3. CONDENSATION There should be a minimal time delay between trituration and condensation. If condensation is commended too late, the amalgam will have achieved a certain degree of set and adaptation, and final mechanical properties are all affected. There is a good correlation between the quality of an AMALGAM restoration and the energy expended by the operator who condenses it. It needs to use a high condensating force. Lower forces are required to condense spherical particle amalgams than lathe-cut materials.  Condensing Instruments Amalgam carriers and condensers are used for this purpose. 4. CARVING Soon after condensing the AMALGAM, the surface layer, which is rich in mercury, is carved away with a sharp instrument. If carving is delayed too long the material may become too hard to carve and there is a danger of chipping at the margins. 4. CARVING Example of Amalgam Carvers  5. POLISHING Polishing is carried out in order to achieve a lustrous surface having a more acceptable appearance and better corrosion resistance. The fillings should not be polished until the material has achieved a certain level of mechanical strength, otherwise there is a danger of fracture, particularly at the margins. Many products require a delay of 24 hours between placing and polishing.  5. POLISHING Example of AMALGAM polishing materials THANK YOU