02 - structure & properties of dental materials

Question 1

What are common types of materials used in dentistry?

Answer 1

1) metals & alloys
- E.g Mercury for amalgams
- Alloy = mixture of different metals
- Crystalline structure
- Grain boundaries – place of transition between 2 alloys
- Fractures, corrosion & failure usually arise due to grain boundaries

2) polymers
- Molecules that are groups of monomers
- Advantage: easily manipulated & set rigidity due to polymerization
- Disadvantage: thermal stability, could be brittle
- E.g. dentures, molds
- Alginate, acrylic resin denture base material, GIC, waxes, silicone impression material, composite resin

3) ceramics
- Regular arrangement of crystals = ceramics
- irregular arrangement of crystals = glass
- control translucency of materials by controlling crystals
- difference between glass & ceramics is structure

4) composites
- Composite = two or more materials combined together
- Composite used in teeth is resin-based
- Each material forms its own phase
- Dental amalgams:
o 3 phases
o Also an alloy

Question 2

What are the 2 types of structures for dental materials?

Answer 2

1) Amorphous structure:
- Irregular structure, atoms in non-repeating units
- Polymeric based materials usually amorphous
- Don’t have definite melting temperature, gradually soften with increased temp
- EXAMPLES: wax, resins, ceramic crowns
- Amorphous SiO2 = glass
2) Crystalline structure:
- Highly ordered regular arrangement of crystals
- Crystal lattice (usually cubic)
- EXAMPLES: Au-Cu alloy crowns, other metals
- Crystalline SiO2 = quartz
- Pure ceramics – alumina, zirconia

Question 3

Give an example for the primary and secondary bonds.

Answer 3

1) Primary bonds -> very strong & high melting point
- covalent -> dental resin
- ionic -> gypsum structures & phosphate-based cement
- metallic -> amalgam

2) Secondary bond -> weaker, no sharing of electrons
- van der waals -> weak interatomic forces
- hydrogen bonding -> highly polar compounds.

Question 4

what are the chemical and physical properties of dental materials

Answer 4

1) Chemical
- Solubility
- Toxicity
- Reactivity
- Biodegradation
- Amalgams are susceptible to corrosion

2) Physical
- Temperature-related properties
- Electrical properties
- Optical properties
- Other properties