1. DENT 1200 Materials I Lesson 1 Structure and Properties of Materials

2. 1. 4 Criteria needed for the selection of materials in the mouth 1. Tooth 2. Patient preference 3. Dentist preference 4. Material properties Not poisonous Not harm or irritate tissue Resemble natural dentition Ease of use Function in limited access, wet conditions with poor visibility

3. 2,3,4. Force Stress Strain Force- push or pull on matter Stress- reaction within material compressive- push material together- bite down tensile- pulls material apart- sticky gum shearing- sliding over- scissors Strain- change produced due to stress

4. 3 types of force/stress Compressive, tensile, shearing

5. 5. Elasticity Ability of a material to be deformed under stress and resume origin shape when stress is removed. Ex: rubber band impression material

6. 6. Significance of Biting Forces Ave biting force on posterior teeth-170# On 1 cusp of 1 molar- 28000 PSI

7. 7. Thermal Changes Ever eat ice cream and drink coffee? Heat- expands, metal more than tooth cause pain or fracture due to pressure Cold- contracts, metal more than tooth cause microleakage Amalgam vs composite?

8. 8. Galvanism- an electrical property An electrical current between two different metals in the oral cavity, saliva is the conductor Causes: Tarnish- a discoloration Corrosion (rust) a chemical breakdown

9. 9. Solubility Degree to which a material dissolves in water

10. 10. Mechanical retention, adhesion, bonding Mechanical retention- uses shape (interlocking)to hold two things together that do not adhere, amalgam prep, called undercuts or dovetail Adhesion – force causing materials to join,ex: cements fill cracks, Factors: wettability, flow, viscosity, thickness Bonding- micromechanical adhesion, surface roughened with acid etch, bonding material flowed into roughened area and often light cured. Next layer of material chemically adheres to bonding agent.

11. 11. Vocab Crystalline- solid with definite pattern, melt pt. ex: amalgam, gypsum Amorphous- solid with no definite pattern, melt pt ex: glass, wax Organic- came from a plant or animal alginate, cotton, wax Inorganic- not from a plant or animal, nonliving, mineral. Ex: gypsum, amalgam