Materials Science 1 Flashcards
¢ Synthetic Biomaterials
Composites
Silicone Impression Materials
¢ Natural Biomaterials
Alginates
Hydrocolloids
¢ Tissue-engineered Biomaterials
Stemcells
Replacement tissues (Growing a Tooth from a Bud)
Promising but still a generation away (>20yrs) ¢ 4 yrs to create a coronal portion of a tooth
¢ Cost effective and accelerated
Metals
Hard
Ductile – Tough Strong
Ceramics
Hard
Brittle Strong
Polymers
Soft
Ductile - Tough Weak
Processing characteristics
Metals and Ceramics Have High Processing Temperatures
¢ Polymers tend to Have Lower Processing Temperatures
¢ Polymers Tend to be used as Direct Processing Materials
METALLIC BONDS
metallic elements have 1,2,3 electrons in their outer shell ¢ electrons are key to metallic bonds ¢ electrons are loosely bound to nucleus ¢ electrons have free mobility thermal and electrical conductivity ductility-bend without breaking
Ductile
Ductile- atoms can slide - in essence a more uniform atom size.
Less uniform atom size
Stronger less ductile
CHARACTERISTICS OF CERAMIC BONDS
¢ ionic and covalent bonds associated with ceramics ¢ both are stronger than metallic bonds
¢ covalent >ionic
¢ ionic bonds - electron donor and electron acceptor ¢ covalent bonds-equally shared electrons
¢ non mobile ions
MICROSTRUCTURE OF CERAMICS
Mixture of metallic and non-metallic elements
¢ Most common ceramics in dentistry are 3 metallic oxides (SiO2,
Al2O3, K20)
¢ Crystalline (long range order) crystalline silicate-quartz or crystobilite
¢ Noncrystalline (short range order no long range) or amorphous silicate-glass
¢ Most dental ceramics are semicrystalline or polycrystalline
¢ SiO4 tetrahedron is the building block
MICROSTRUCTURE OF DENTAL PORCELAIN
¢ SiO4 tetrahedron is the building block
¢ primarily a glass with some crystalline residuals
noncrystalline or amorphous silicate-glass
crystalline silicates
¢ Quartz or crystobilite ¢ Leucite (not Lucite)
¢ Processed by Sintering or Melting at High Temperatures
CHARACTERISTIC POLYMER BONDS
¢ Covalent bonds
¢ High molecular weight
¢ Long molecules composed principally of nonmetallic elements (organic chemistry C,O,N,H)
Free Radicals Will Initiate
Methacrylate Polymerization
CQ (Yellow) absorbs visible light. Interacts with
DMAEMA To Generate Free Radicals.
RESIN MATRIX
Monomers ¢ Initiator
hasten free radical reaction
¢ Direct Placement requirements
Flowable Material Stable Material
Trigger for Setting Rapid Setting
Room Temperature Setting Reaction
Metals – Indirect
High Processing Temperatures Exception: Amalgam
Ceramics – Indirect
High Processing Temperatures Exception: Cements
Polymers – Direct
Low Processing Temperatures Exception: Indirect Composites