Prof. Alsayed Abdel Hafez BDS, MD , PhD Zagazig University

Dental Amalgam. Prof. Alsayed Abdel Hafez BDS, MD , PhD Zagazig University.

Items to be covered. Definition Composition Packaging of amalgam Classification Amalgamation reaction Significant properties Manipulation Gallium amalgam.

Definition. Amalgam is an alloy of mercury with one or more other metals. Dental amalgam is an alloy of mercury and silver-tin. Ag- Sn + Hg → Dental Amalgam Amalgam is the material of choice for a low cost restoration of posterior teeth . Uses Class I, II and V (posterior) restorations. Core material. Filling of apices of roots after apicectomy ..

Composition I. Powder. Essential elements: Silver, tin and copper Ag- Sn : Conventional amalgam contains at least 65 wt % Ag, 29 wt % Sn and less than 6 wt % Cu. Purposes of Constituents in Amalgam: Silver : Increase strength and setting expansion Decrease flow and creep and setting time . Tin: Facilitates the amalgamation reaction by its high affinity to Hg. But decrease strength and expansion (weakest link amongst the alloy). Copper (Cu): Increase strength, Decrease creep & tarnish and corrosion resistance..

Composition I. Powder (other elements). Zinc (Zn): 0.01 wt % - not exceeding 1 wt %. Role 1. Acts as a scavenger (prevents oxidation of the other elements during manufacturing the alloy. 2. Helps amalgamation reaction with mercury. 3. Amalgam alloy without zinc is more brittle. It causes delayed expansion in the presence of moisture. Zn reacts with water and hydrogen gas is released during amalgam setting reaction. Indium : Reduces mercury vapor from restoration. Palladium : Reduces tarnish and corrosion..

Copper anc. Composition II. Liquid. Amalgam liquid (mercury) Mercury is added to promote the amalgamation reaction and give the final plastic mass which will be ready to condensed in the prepared cavity Increase setting expansion ,creep and setting time Decrease resistance to tarnish and corrosion strength.

abstract. 4/11/. Packaging of amalgam alloy. Powder Tablets Capsules.

Classification of Dental Amalgam Alloy:. According to particle shape Lath-cut (irregular) . Prepared by placing the annealed ingot in a milling lath- cutting machine to produce the desired particle size Spherical . Prepared by atomization. Admixed (Mixed). The admixed alloy has Ag-Cu spherical particles and lath-cut conventional particles (Ag- Sn )..

Low copper amalgam (conventional or traditional amalgam). <6 wt% Cu.

1. Zinc containing amalgam. It has > 0.01 wt% Zn..

I. Low Copper. Ag3Sn (γ) + Hg → Ag2Hg3 (γ1) + Sn7Hg (γ2) + γ.

γ (Ag3Sn): 27%-35%, hardest & strongest.. γ1 (Ag2Hg3): 54%-56%, hard & strong..

I. Strength and stiffness. Properties. Strong in compression than in tension..

Properties. III. Tarnish and corrosion γ 1 has the highest corrosion resistance and γ 2 has the lowest. ✔ Corrosive products fill the gap between filling and tooth walls reducing microleakage ( self sealing restoration ). Types of corrosion a- Galvanic corrosion due to heterogeneous structure b- Concentration cell corrosion In low copper amalgam γ 2 + 1/2O 2 + H 2 O + Cl - → Sn 4 (OH) 6 Cl 2 + Hg In high copper amalgam Cu 6 Sn 5 ( ή ) + 1/2O 2 + H 2 O + Cl - → CuCl 2 3Cu (OH) + SnO.

Properties. I V. Thermal Properties High thermal diffusivity base (glass ionomer or zinc phosphate) or liner calcium hydroxide) under it. Varnish is used in super facial cavity. Higher coefficient of thermal expansion, three times than that of tooth. V. 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..

Properties. VI. Dimensional changes - Modern amalgams mixed with mechanical amalgamators usually have negative dimensional changes . - Dissolution of γ causes contraction in the first 20 min. - Formation of γ 1 and ή phases causes expansion latter. VII. 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 + H 2 O → ZnO + H 2.

Manipulation of amalgam (Lab). A. Selection of the alloy and mercury - A high-copper amalgam is selected - Spherical alloy has higher strength. - Fine particles produce smoother surface during carving and finishing. - Pure mercury should be used. 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. - The ratio can be adjusted using a mechanical dispenser or using capsules..

Equipment's used with amalgam restoration. Amalgamator Amalgam capsules Amalgam carrier Amalgam condenser Amalgam carver Burnisher Band and matrix for class II restoration.

C. Mixing (trituration) Old technique Trituration by mortar and pestle. Currently, mechanical mixing (amalgamators) - Normal mix : appears shiny and separate as a single mass. - Under mix: appears dull and crumbly. - Over mix: appears soupy and stick to the inside of the capsule.

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. - 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..

E. Carving and burnishing - 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. - 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..

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 is used. - Final polish is done using a rotating soft brush..

Advantages. Ease of manipulation. Acceptable marginal adaptation (Self Sealing). High compressive strength. Technique insensitivity . Good wear resistance. Low cost..

Disadvantages. Needs removal of sound tooth tissue. Poor aesthetic qualities. Long-term corrosion. Galvanic response potential exists. Concern about possible mercury toxicity. High thermal diffusivity..

Safety Recommendations for Dental amalgam. Usage of premeasured capsules . Wearing masks during working with amalgam. Hg should be contained in stoppered bottles . Spills of Hg should be avoided. No carpets in Dental. Use high evacuation system when finishing or removing amalgam. Working in a well-ventilated spaces with fresh air exchange..

GALLIUM ALLOY. - The first commercial alloy was introduced in Tokyo in 1990 and called gallium alloy - 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%..

GALLIUM ALLOY. Handling characteristics Ga amalgams are more difficult to handle (because of their sticky nature). They are technique sensitive and similar to spherical alloy in properties. Physical properties Comparable compressive strength and creep with silver amalgam. Lower corrosion resistance. Moisture contamination causes marked expansion (sometimes causes cracking of the tooth). 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..

Thank You.