Amalgam Restoration and Manipulation I PDF

Operative dentistry I AMALGAM RESTORATION AND MANIPULATION I Dr.Luluah K. Alhagas Assistant professor in operative dentistry department 2024 Lecture objectives: 1- Define dental amalgam restoration. 2- List advantages, disadvantages,indications, and contraindications of ama...

Operative dentistry I AMALGAM RESTORATION AND MANIPULATION I Dr.Luluah K. Alhagas Assistant professor in operative dentistry department 2024 Lecture objectives: 1- Define dental amalgam restoration. 2- List advantages, disadvantages,indications, and contraindications of amalgam restoration. 3-Identify dental amalgam classifications. 4- Identify dental amalgam composition. 5- Explain dental amalgam setting reaction. 6- Describe dental amalgam properties. Introduction to dental amalgam  Defined as a metallic restorative material composed of a mixture of silver–tin– copper alloy and mercury. The unset mixture is pressed (condensed) into a specifically prepared tooth cavity and contoured to restore the tooth’s form and function.  1. Ease of use. 1- Non-esthetic. 2-Less conservative (more removal of tooth structure 2. High strength. during tooth preparation). 3. Excellent wear resistance. 3-Non insulating. 4. Favorable long-term clinical research results. 4-More difficult tooth preparation. 5. Low cost. 5- Environmental concern. 1- used in posterior teeth 1- not used in esthetic areas (anterior teeth). restorations. 2- not used for mercury sensitive 2- used in large cavities. patients. 3-used in areas with limited 3-not used in small cavities. moisture control. 4- not used if composite restoration will 4- core build up for crowns. offer a better conservative restoration. Dental amalgam classification  Amalgam classification According to According to According to particle shape copper content zinc content  Requires less condensation. Spherical Easy in carving. Gives improper proximal contact. alloy Used in class I cavity. Lathe-cut Requires more condensation. Difficult in carving. alloy Gives proper proximal contact. Used in class II cavity. Admix alloy Has the advantages of spherical and lathe-cut alloy. Low copper alloy Less than 6% Cu High copper alloy More than 12% Cu Zinc containing alloy More than 0.01% Zn Zinc free alloy 0.01% or less Zn Dental amalgam composition Silver ( Ag) Increase strength and expansion Increase tarnish and corrosion resistance Tin ( Sn) Decrease strength and expansion Increase flow and creep Copper ( Cu) Increase strength Increase tarnish and corrosion resistance Zinc ( Zn) Prevent oxidization of other metal in the alloy Increase strength, and creep resistance Dental amalgam setting reaction Low copper amalgam ( conventional ) AgSn + Hg  AgSn + AgHg + SnHg   1 2 silver-tin silver-tin silver-mercury tin-mercury  Unreacted gamma 1 Gamma 1 ( strongest phase) 2 Gamma 2 ( weakest phase)  High copper amalgam AgSn + Ag-Cu + Hg  AgSg + AgHg + SnHg + Ag-Cu  eutectic  1 2 eutectic silver-tin Silver-copper silver-tin silver-mercury tin-mercury Silver-copper Ag-Cu + SnHg  AgHg + CuSn  Unreacted gammma 2 1  1 Gamma 1 ( strongest phase) 2 Gamma 2 ( weakest phase) eutectic Silver-copper tin-mercury silver-mercury Eutectic  Copper-tin Eta Dental amalgam properties  Dental amalgam properties Creep Tarnish Compressive Tensile Modulus of Dimensional & & strength strength elasticity changes flow corrosion  Dental amalgam properties 1- Compressive strength: Is the ability of material that can withstand force loaded toward an object. ( compression) Amalgam has high compressive strength range between 300-500 Mpa after 7 days, it depends on the amalgam type. Low copper amalgam has lowest compressive strength. Amalgam is weak under tensile and shear force.  Dental amalgam properties 2- Tensile strength: Is the ability of the material to withstand force lateral to an object. ( stretching) Amalgam has low tensile strength range between 48- 60 Mpa after 7 days, it depends on the amalgam type. Low copper amalgam has lowest tensile strength. High early tensile strength within the first 15 minuts can resist the fracture. High copper amalgam has the highest early tensile strength. Factors affecting the amalgam strength: 1- Temperature: Amalgam loses 15% of its strength when temperature raises from root temperature to mouth temperature. Amalgam loses 50% of its strength when temperature raises inside the mouth up to 60%. Ex: drinking hot beverage. 2- mercury content: High mercury content will decrease the strength up to 50% Low mercury alloy is recommended. *if mercury is too low it will produce rough and pitted surface. Factors affecting the amalgam strength: 3-Trituration: Effect of trituration on strength, depends on: - Type of amalgam alloy. - Trituration time. - Speed of the amalgametor. * under- trituration or over-trituration will affect the amalgam strength even with high or low copper amalgam. 4-condensation: - lathe-cut alloy needs more condensation for higher compressive strength. - Spherical alloy needs light condensation for higher compressive strength.  Dental amalgam properties 3- Modulus of elasticity: Dentin= Defined as measurment of material 15-20 Gpa elastic stiffness. Composite= Amalgam has modulus of elasticity 17-22 Gpa range between 20-50 Gpa. Amalgam = High copper amalgam is stiffer than low copper amalgam 20-50 Gpa Enamel= stiff 50-80 Gpa  Dental amalgam properties 4- Creep & Flow: Its time dependant plastic deformation of a material under static load. Flow measured during amalgam setting. Creep measured after amalgam setting. Creep will lead amalgam to flow to the margin and make it protruded out of the margin. This amalgam maybe weakened by corrosion and causing ditching around the amalgam margin. High copper amalgam has lower creep than low copper amalgam. Factors affecting the amalgam creep: 1- Amalgam composition: Presence of 2 in low copper amalgam will increase the creep. 2- Amalgam manipulation: In high copper amalgam, proper the condensation pressure and trituration time will decrease the creep.  Dental amalgam properties 5- Dimensional changes: It’s a property of a material that can changes its original shape and dimentions easily, under heat or chemical reaction. Amalgam has high dimensional changes and Amalgam should not high coeffiecent of thermal expansion. expand or contract The greatest dimentional changes in low copper more than 20 m/cm amalgam 19.7 m/cm. at 37 ℃ Which is equal to 0.1- 0.4 %  Dental amalgam properties Mechanism of Dimensional changes: When mercury is combined with amalgam alloy It will undergo 3 dimensional changes. 1- initial contraction Occurs for 20 minutes Contraction is up to 4.5 m/cm. 2- expansion 3- limited delayed contraction  Dental amalgam properties Delayed expansion : If zinc containing alloy contaminated with moistur during its manipulation in a cavity prepration. Will lead to gradual expansion of the amalgam after 3-5 days of setting and continue for months. And will reduce amalgam strength. This issue will cause: post operative sensitivty occlusal interference Expansion over margin This expansion may reach to 400 m/cm  Factors affecting the amalgam dimensional changes : 1- Mercury content: High mercury will give high expantion of amalgam restoration. 2- Trituration: Under-trituration, will lead to amalgam expansion. Over-trituration, will lead to amalgam contraction. 3- Condensation: Less condensation pressure, will lead to amalgam expansion.  Dental amalgam properties 6- Tarnish & Corrosion: Tarnish: Is the process by which a metal surface is discolored due to reaction to other chemicals ( sulfide, oxide, chloride,…), or poor oral hygiene, or acidic food. Amalgam surface appear dull or loss its luster If tarnish continued, it will produce corrossion.  Dental amalgam properties 6- Tarnish & Corrosion: Corrosion: Is the chemical or electrochemical process by which a metal surface is partially or completely dissoluted due to environmental attack. Amalgam surface appear deteriorated If corrosion continued, it will produce mechanical failure. Excessive corrosion can lead to: Increase porosity Reduce marginal integrity Loss of strength Release metalic producets in the oral environment Does amalgam have self sealing ability ?  Dental amalgam properties Summary High copper alloy Low copper alloy Compressive strength High compressive strength Low compressive strength Tensile strength Low tensile strength Lowest tensile strength Modulus of elasticity Stiff Less stiff Creep & Flow Less creep & Flow More Creep & Flow Dimentional changes Low dimentional changes High dimentional changes ( more dimentional stability) ( Less dimentional stability) Tarnish & Corrosion Less Tarnish & Corrosion More Tarnish & Corrosion Reference: Sturdevant art and science of operative dentistry Chapter 13 “introduction to amalgam restorations” Chapter 18 “ biomaterials” Thank You