Flashcards in Dental Materials Deck (293)
What is a bond?
Interaction between atoms
What 3 bonds are primary bonds?
Describe covalent bonds
Strongest: 4-6 eV
Atoms share electrons to achieve noble gas configuration
Least reactive bond
Electron orbital overlap forms molecular orbital w/ shared electrons
Directional and rigid
Describe ionic bonds
Strong electrostatic (>1.5) interactions: 3-4 eV
Results in formation of ions: cations and anions
Non-directional as ions interact w/ any ions in vicinity
Describe metallic bonds
Non-directional, relatively weak 0.5-2 eV
Overlapped orbitals of metallic atoms forms electron gas
Electron has and metallic cations: electrostatic integration
What bonds are secondary bonds?
Describe secondary bonds
No electron sharing
Charge induced dipole interactions
Physically and chemically homogenous part of system/material that has clear boundaries
Define phase transition
Change from one phase to another
e.g. solid -> gas sublimation
What is a phase diagram?
Presentation of stability and phase transitions for a system/material of phases in equilibrium at range of temps.
Why are phase diagrams useful?
Identify phase against the composition at a given temp
What is the eutectic point?
Lowest melting point of system: lower than constituents and may other mixture of them
Describe crystalline solids
Consist of crystals
Form crystalline lattice: ordered (symmetric and periodic) and specific arrangements of atoms
Describe non-crystalline solids
Disordered solids, contain no crystals
Inorganic, rapidly quenched: glass
Phase transition specific for non-crystalline solids
Describe the phase transitions in non-crystalline solids
Glass transition: change in viscosity/rigidity from brittle to rubbery w/ inc. temp
Crystallisation (devitrification): conversion to crystalline solids if heated up to specific temp
What is polymerisation?
Synthesis of polymers from monomers
What are the 2 types of polymerisation?
Describe condensation polymerisation
Reaction between 2 molecules producing larger molecule and water/small molecule byproduct
Byproduct has to be removed during polymerisation
Describe addition polymerisation
Reaction between 2 molecules giving larger molecule with no byproducts
Monomers added 1 by 1 per chain to active site on growing chain
What is the most common type of addition polymerisation?
Free radical polymerisation
What is the Thiokol reaction?
Condensation polymerisation that forms polysulphide polymers
Used in base paste of polysulphide impression materials
How is 2-polyglycolic acid synthesised and what is its function?
Synthetic, absorbable, suture material
Biodegrades back to acid in 60-90days
What is a free radical?
Molecules w/ an unpaired electron
How is methyl methacylate synthesised and how is it used?
Used as denture base
How are free radicals formed?
When initiation decomposes into 2 highly reactive free radicals in presence of monomers
What is the common initiator?
What are the 4 stages of free radical polymerisation?
1. Activation: formation of FRs from initiators
2. Initiation: FR attacks monomer units
3. Propagation: chain growth, monomer units add together
4. Termination: 2 growing chains meet, FRa combine forming stable covalent bond
What are the 3 ways in which FRs are formed in dentistry?
2. Room temp
Describe heat formation of FRs
Usually powder/liquid, 2-paste or 1-paste
When mixed and heated, BP splits into FRs
FRs attack double bonds in monomers