Flashcards in Dental Materials Deck (293)
What are 3 areas in why temp. is important in dentistry?
1. Use of drill
2. Exothermic setting reactions: can't do in mouth
3. Effect of hot/cold on restoration
Why is knowing temp. important?
Temp change may alter properties of material
What is heat of fusion?
Energy required to convert 1g of material from solid to liquid at melting temp.
What is thermal conductivity?
Quantity heat/second passing through a 1cm thick substance w/ cross section of 1cm2 w/ temp. inc. of 1 degrees
I.e. ease with which heat is transferred through a material
What is the clinical significance of thermal conductivity?
Large amalgam filling close to pulp may be sensitive to hot/cold thus use a non-mental cement between tooth and filling to insulate
Metal denture base material will more closely follow temp. of oral mucosa
What is specific heat?
Quantity of heat required to heat 1g material by 1 degrees
What is thermal diffusivity?
Measure of transient heat flow: how long does cold end of material take to heat up?
Rate of transfer of heat from hot side to cold side of material
What is the clinical relevance of thermal diffusivity?
Good inlay, crown, amalgam have low specific heat but high thermal conductivity thus if close to pulp may get thermal shock
What is thermal expansion coefficient?
Change in length of material for a 1 degree change in temp.
What is the clinical significance of thermal expansion?
Tooth and material will expand and contract due to hot/cold
Could result in breaking of marginal seal of inlay/filling
What electrical conductivity and resistivity?
Ability of material to conduct electrical current
Why is electrical conductivity and resistivity important?
Correlation between electrical conductivity and change in physical and mechanical properties of material
E.g. gold alloys: change in resistivity changes internal crystal structure
What is electromotive force?
Difference in electrical potential that gives rise to current
What is the electromotive series?
List of metals ordered in dec. tendency to oxidise in solution
What is galvanism?
Induction of current due to chemical reaction
Why is galvanism important in dentistry?
If 2 fillings of different electronegativities touch will cause short circuit which if near the pulp will cause pain
Why does amalgam have a high copper content?
Copper-tin complex much harder and less corrodible than tin-mercury
How do GICs bond to enamel?
Bind to Ca2+ in enamel
Carboxyl group plays role in setting reaction and bonding mechanisms
What is solubility?
Of inorganic salt: number moles of pure solid that will dissolve in 1L solvent at given temp
Compare solubility of hydroxyapatite and fluoroapatite
FA less soluble than HA: remains supersaturated for longer than HA even at lower pH
What are the 6 optical factors important in DMs?
4. Surface finish
5. Refractive index
What are the 6 thermal factors important in DMs?
1. Heat of fusion
2. Thermal conductivity
3. Thermal diffusivity
4. Specific heat
6. Thermal expansion
What are the 3 electrical factors important in DMs?
1. Conductivity and resistivity
2. Electromotive force
What are the 3 chemical factors important in DMs?
2. pH and solubility
Natural or synthetic material that interfaces w/ living or biological tissue
Ability of material to elicit an appropriate biological response, in given application, in body/mouth
What is biocompatibility dependent on?
Biological response required
Interaction w/ OC
What are the 4 main reasons for restorations?
3. Tooth loss
4. Revisions: repair failed restoration
Define safe in terms of DMs
Must not cause any local or systemic adverse reactions