Dental Ceramics Part II - Dental Materials

Have you ever wondered how ceramic bonds to metal. In this presentation we will look closely into metal ceramic bonds viz., chemical bonding, mechanical bonding, compression bonding, and covalent bonding. Once we understand the metal ceramic bonding, we will be looking into strengthening of ceramics. Under that, we will read about development of compressive stresses, reduction of crack, interruption of crack propagation and design modification

1. Dental ceramics part – 2 Dr.Shiva

2. Impression Cast Die cutting Die pin Die deching Die hardener Die spacer Die lubricant Wax pattern Sprue attachment Reservoir attachment Wax pattern to sprue former Ring liner Investment material Burn out Melting of alloy Placement of casting ring in centrifuge machine Quenching Sand blasting Finishing Ceramic build up Opaquer Dentin shade Enamel shade Translucent shade glazing Place in ceramic furnace

3. how does ceramic bond to metal??

4. CHEMICAL BONDING Primary mechanism Oxide layer between metal and ceramic Surface oxides dissolve from metal and dissolved by, the opaque layer (chemisorpition) & atomic contact with the metal surface for enhanced wetting and direct chemical bonding so metal and porcelain share electrons

5. MECHANICAL BONDING Irregular metal surface Ceramic flow into irregularities SANDBLASTING

6. COMPRESSION BONDING Mismatch in COTE between metal and ceramic

7. COVALENT BONDING Mutual exchange of electrons between the metal and ceramic

8. BOND FAILURE

9. STRENGTHENING OF CERAMICS

10. DEVELOPMENT OF RESIDUAL COMPRESSIVE STRESSES Bending forces Tensile forces

11. CHEMICAL TEMPERING Sodium is replaced with potassium Immersed in kno3 salt bath at 400 degrees for 4 hours . K ions 35% larger than sodium.

12. CHEMICAL TEMPERING

13. THERMAL TEMPERING THERMAL COMPATIBILITY/ COTE MISMATCH HEATED PORCELAIN QUENCHED OUTER LAYER COOLS RAPIDLY PRODUCING RIGID SKIN INNER CORE COOLS SLOWLY DEVELOPING STRESSES METAL(SHRINKS MORE) CERAMIC (SHRINKS LESS)

14. AUTO GLAZE ADD ON GLAZE Low fusion temp Equal COTE Selective heating More durable GLAZING

15. INTERRUPTION OF CRACK PROPAGATION DISPERSION OF CRYSTALLINE PHASE Al2O3 ALUMINOUS PORCELAIN Alumina is added which is strong.

16. INTERRUPTION OF CRACK PROPAGATION

17. TRANSFORMATION TOUGHENING Stress Unstable tetragonal Stable monoclinic ZIRCONIA BASED CERAMICS

18. Thank you