Dental Amalgam II PDF

‫بسم هللا الرحمن الرحيم‬  Faculty of Dentistry Dental Amalgam II By Prof. Essam Al-Wakeel  Significant properties ◼ ANSI/ADA requirements 1. One hour compressive strength > 80 MPa 2. Creep < 3% 3. Dimensional changes in 5 minutes to...

‫بسم هللا الرحمن الرحيم‬  Faculty of Dentistry Dental Amalgam II By Prof. Essam Al-Wakeel  Significant properties ◼ ANSI/ADA requirements 1. One hour compressive strength > 80 MPa 2. Creep < 3% 3. Dimensional changes in 5 minutes to one day ± 20 µm/cm. Faculty of Dentistry  Strength and stiffness ◼ Amalgam is strong in compression than in tension and has a relatively high modulus of elasticity. ◼ Tensile strength is about 1/8 of the compressive strength at day 1. ◼ More γ in the set amalgam increases strength. ◼ Spherical alloys have higher strength. Faculty of Dentistry  Dimensional changes ◼ In general, most amalgams contract or expand slightly during setting. ◼ Dissolution of γ causes contraction in the first 20 min. ◼ Formation of γ1 and ή phases causes expansion latter. Faculty of Dentistry  Delayed expansion ◼ It occurs in zinc-containing amalgam due to moisture contamination during manipulation of amalgam. ◼ Moisture may come from operator’s hand or the patient’s saliva. ◼ It occurs over a period of weeks and months ◼ Zn + H2O → ZnO + H2 Faculty of Dentistry  Creep Faculty of Dentistry ◼ The repeated chewing forces causes creep of amalgam. ◼ Unicompositional amalgam shows the lowest creep values. ◼ The presence of γ2 is associated with the higher creep rates in low copper amalgam. ◼ Creep is correlated with marginal breakdown (ditching) of the filling. Marginal breakdown  Tarnish and corrosion ◼ Amalgams often show tarnish and corrosion in the oral cavity. ◼ Corrosion causes increased porosity, reduced marginal integrity, loss of strength and release of intermetallic compounds. ◼ γ1 has the highest corrosion resistance and γ2 has the lowest. ◼ Corrosion products fill the gap between filling and tooth walls reducing microleakage.  Types of corrosion ◼ Due to heterogeneous structure ◼ Galvanic corrosion ◼ Concentration cell corrosion In low copper amalgam: γ2 + 1/2O2 + H2O + Cl- → Sn4(OH)6Cl2 + Hg In high copper amalgam Cu6Sn5 (ή) + 1/2O2 + H2O + Cl- → CuCl2 3Cu (OH) + SnO  Thermal properties ◼ Amalgam has high thermal diffusivity, so it requires a base or liner under it. ◼ Varnish in superfacial cavity, glass ionomer or zinc phosphate bases in moderate cavities and calcium hydroxide liner and base in deep cavities. ◼ Amalgam has a higher coefficient of thermal expansion, Three times than that of tooth. Microleakage  Manipulation of Dental Amalgam A. Selection of the alloy and mercury ◼ A high-copper amalgam is selected because a restoration with no gamma 2 (γ2) has better mechanical properties. ◼ Spherical alloy has higher strength. ◼ Fine particles produce smoother surface during carving and finishing. ◼ Pure mercury should be used. Faculty of Dentistry  B. Proportion of the alloy to mercury ◼ In the past, Hg-alloy ratio was 3 to 1 or 8 to 5. ◼ Squeezing was required to remove excess Hg. ◼ In 1960, Eames technique (no squeeze-cloth technique) was developed. ◼ Now, the Hg-alloy was low (1:1) and even less. ◼ The ratio can be adjusted using a mechanical dispenser or using capsules. ◼ Every 1% increase in the residual Hg above 60% will cause 1% decrease in compressive strength of the filling.  C. Mixing (trituration) ◼ Old technique: Trituration by mortar and pestle. ◼ Currently, mechanical mixing (amalgamators) ◼ Normal mix: appears shiny and separate as a single mass. ◼ Undermix: appears dull and crumbly. ◼ Overmix: appears soupy and stick to the inside of the capsule and the instruments. Amalgamators Amalgam (left: undermixed, center: normal mix, right: overmixed) Correctly triturated amalgam mass Ready amalgam mass  Cavity design and Carrying amalgam ◼ The cavity should be with sufficient depth particularly the isthmus part. ◼ Undercut is required to retain dental amalgam. ◼ Amalgam is dispensed into the isolated cavity using amalgam carrier. ◼ The cavity should be filled in increments. The amalgam being dispensed into the cavity  D. Condensation Purposes: 1. Compact the amalgam mix into a denser mass and eliminating voids. 2. Adapt amalgam to the tooth structure. 3. Express (squeeze out) excess mercury. Faculty of Dentistry  Condensation ◼ Irregularly-shaped alloy needs smaller condensers and greater force. ◼ Large condenser tips and smaller forces are needed with spherical alloys. ◼ Mechanical condensation can be performed using a mechanical device (impact or vibration). Used mostly with irregularly- shaped alloys when high condensation forces are required. Condensation of amalgam Overpacking of amalgam  E. Carving and burnishing ◼ Amalgam restoration is carved to produce the proper tooth anatomy using sharp carvers. ◼ Carving is done towards the margins of the tooth. ◼ Burnishing involves rubbing the surface of partially set amalgam with a smooth surface instrument (burnisher). ◼ It helps to achieve better adaptation to the cavity margins and eliminates microprosities. Carving amalgam Burnishing of amalgam  E. Carving and burnishing ◼ The disadvantage of burnishing is the disturbance of the microstructure of the surface layer resulting in weaker margins. ◼ In general, burnishing should not be done once amalgam reaches certain degree of hardness. Faculty of Dentistry  F. Finishing and polishing ◼ Final finishing and polishing should not be done until the amalgam is full set (at least 24 hours after condensation). ◼ Wet abrasive powder in a paste form and rubber cup are used. ◼ Final polish is done using a rotating soft brush. Finished amalgam Finished amalgam Advantages of dental amalgam Ease of manipulation. Acceptable marginal adaptation. High compressive strength. Technique insensitivity. Self Sealing. Good wear resistance. Low cost. Faculty of Dentistry  Disadvantages Faculty of Dentistry Some destruction of sound tooth tissue. Poor aesthetic qualities. Long-term corrosion. Galvanic response potential exists. Local allergic potential. Concern about possible mercury toxicity. High thermal diffusivity. Is Dental Amalgam a Safe Restoration???  Amalgam Safety ◼ It is controversial. ◼ Despite the toxicity of mercury, dental amalgam is a safe restoration. ◼ Hg can get access to the body through the skin, ingestion or lungs. ◼ The most dangerous form of Hg in dental clinic is Hg vapor.  Good Mercury Hygiene in Dental Clinics ◼ Premeasured capsules should be used. ◼ A mask should be worn during working with amalgam. ◼ Hg should be contained in stoppered bottles. ◼ Spills of Hg should be avoided. ◼ No touch technique should be used.  Good Mercury Hygiene in Dental Clinics ◼ Amalgam scrap should be stored under water in a closed container. ◼ Dental office should not be carpeted. No effective way for removing liquid mercury from carpeting. ◼ Use high evacuation system when finishing or removing amalgam. ◼ Working in a well-ventilated spaces with fresh air exchange.  Gallium Amalgam ◼ It was suggested as early as 1928 in Germany. ◼ Under development in Japan since 1956. ◼ The first commercial alloy was introduced in Tokyo in 1990 and called gallium alloy GF and then Gallium alloy GF II. ◼ The more recent alloy was introduced in Australia in 1995 and called Galloy.  Composition of Galloy ◼ Powder Ag (50%), Sn (25.7%), Cu (15%) and Pd (9%) and traces (0.3%), all by weight. ◼ Liquid Gallium (62%), indium (25%), tin (13 %) and traces 0.5%. Faculty of Dentistry  Handling characteristics ◼ Ga amalgams are more difficult to handle (because of their sticky nature). ◼ In most other respects, they are similar to spherical amalgam. ◼ They are technique sensitive. Faculty of Dentistry  Physical properties ◼ Comparable compressive strength and creep with silver amalgam. ◼ Lower corrosion resistance. ◼ Moisture contamination causes marked expansion (sometimes causes cracking of the tooth). Faculty of Dentistry  Evaluation of Ga Amalgam ◼ Gallium amalgam can be successfully used in simple cavities. ◼ Sealing the restoration before and after placement is mandatory to prevent excessive expansion. ◼ Handling properties need to be modified. ◼ More in-vivo studies are required before market distribution.  Amalgam Bonding ◼ Using resin bonding technology, amalgam is micromechanically bonded to dentin and enamel. ◼ The advantages of amalgam bonding include: 1. Amalgam retention 2. Tooth reinforcement 3. Reducing microleakage and post operative sensitivity.  Resin bonding System for amalgam ◼ Amalgambond resin-based adhesive is one of the first to find successes in the market. ◼ After application of the etchant and primer, the mixed amalgam is condensed into the adhesive. ◼ The resulting bond is almost half of that of composites. Faculty of Dentistry  AMALGAM BONDING Mechanical Interlocking AMALGAM BONDING SYSTEM Amalgam Reaction Product Matrix Residual Amalgam Alloy Amalgambond Plus (Parkell) ENAMEL or DENTAL DENTIN AMALGAM Interfacial Interlocking of phases  Although there is evidence that amalgam use is declining, it remains one of the choices for posterior direct restorations because of its ◼ Longevity ◼ Ease of placement ◼ Versatility Faculty of Dentistry Amalgam versus composite restorations