chemical reaction between amalgam and substances in saliva or food resulting in OXIDATION of amalgam
how do you prevent corrosion of amalgam?
using high copper alloys (no gamma 2 phase) or polish low copper amalgams
what is the purpose of merucry?
causes amalgamation and binds it all together
what is murcury's most dangerous form?
vapor
what componenets are needed to produce galvanism?
two dissimilar metals
what causes expansion in amalgam? 3
compostion of alloy particles
ratio of mercury-alloy powder (by weight)
saliva/moisture contamination
why do you need to polish amalgam?
to reduce the rate of corrosion
what does polishing remove? 4
surface tarnish
stains
flash
roughness
how does an amalgam get retention in a tooth? 3
bonded
undercut walls
mechanical retention
how do you detect overhangs
explorer
what is the relationship of zinc and corrosion of amalgam?
zinc INHIBITS corrosion by reducing oxidation of other metals
what are the three noble metals?
gold
platinum
palladium
which noble metal is the most corrosive resistant?
gold
which noble metal has good gorrosive resistance, increases hardness of alloy and is less expensive than gold?
palladium
____% noble = no gold requirement
25
high noble = ___ % noble/ _____% gold by weight
60
40
when is the best time of day to view esthetic materials?
midday
when viewing esthetic materials a natural _____ light is great
NORTH
fluorescent lights=_____ and incandenscent lights= _____
more blue light
more yellow light
t/f you want to take the shade in the light the patient is seen in most often
true
the dental unit light ______ shade brightness and _____ color intensity
INCREASE
DECREASE
what are the two fluoride RELEASING composites
glass ionomers
hybrid (resin-modified) ionomer
what are the componenets of dental compostie/resin materials?
organic resin matrix (Bis-GMA or bisphenol-A, glycidal methacrylate, UDMA-urethrane dimethacrylte)
inorganic SILICA filler
SILANE coupling agent
what are themost common filler particles?
silicate
quartz
glass
what is the purpose of fillers?
make resin stronger, reduce shrinkage and more wear resistant
what is added to resin for radiopacity?
barium stronium
the ____ the filler the stronger and more ____ ____ the resin will be
HIGHER
WEAR RESISTANT
what is the advantage of light cured composites over self cured composites?
light cured are LESS porous than self cured
what causes post op sensitivity in composties?
leakage, shrinkage (large composite increments)
t/f adjusting water/powder ration is only recommended to increase the working time of gypsum products
false-adjusting water/powder ration is NOT recommended-follow manufacturers instructions
what increases/decreases work and setting time?
water temperature
cold water=longer set
warm water=shorter set
how is the setting time affected by cold water? warm water?
cold water=longer set
warm water=shorter set
what is being described: beta, weaker, irregular, porous particle, used for diagnostic casts, more soluble than stone, white in color, W/P=.45
plaster (TYPE II)
what is being described: alpha, strongest, less water needed, less porous, better than plaster, working casts/study model, white or yellow color, takes less water to turn into dihydrate, W/P=.30
stone (TYPE III)
what are the four effects of air incorporated into gypsum?
air exposure ACCELERATES set
prolonged exposure RETARDS set
water absorption
surface irregularities
what is the initial set of regualr set gypsum?
7-9 minutes from start to mix
what is the working time for the intial set of gypsum?
6-8 minutes to pour impression
how can you tell if the initial set has begun with gypsum?
loss of glossy appearance
what type of reaction is the final set of gypsum?
exothermic reaction
how long must the regular set gypsum set before separation?
1 hour
at how many hours is the regular set gypsum 3x harder
24 hours
when can you disinfect regular set gypsum?
24 hours=3x harder
t/f failure to separate modle within 1 hour will have detrimental effects on characteristics of model
true
what impression material is used for: study models, preliminary impression for complete dentures, partial denture framework
opposing casts for crown and bridge treatments
reparis of partial and complete dentures, provisional restorations, custom trays for fluoride or bleaching, sports protector andnight guards, removable orthodontic appliances?
irreversible hydrocolloid
what is the most widely used impression material?
irreversible hydrocolloid
what is irreversible hydrocolloid impression material not good for? 5
crown and bridge
inlays
onlays
titanium remobable partial dentures
which impression material is agar?
reversible agar
what impression material is alginate?
irreversible hydrocolloids
what are the five elastic impression materials?
reversible (agar) hydrocolloid
irreversible (alginate) hydrocolloid
plysulfides (elastomer)
silicone rubber (elastomer)
polyether (elastomer)
what are the four types of inelastic impression materials?
type I gypsum
plaster
compound
zinc-oxide eugenol
what is used as a disinfectant for impression materials?
sodium hypochlorite and iodophors
how long should an impression be disinfected for before the pour?
10 minutes
what are the four purposes of diagnostic casts?
study model/diagnostic casts
reproduce preparations for final restoration
postive reproduction of teeth and tissues
impression=negation reproduction
how is gelation time increased or decreased?
temperature
what state is gelation if chilled? heated?
chilled=gle, semisolid (jell-o)
heated=reverse into a liquid suspension (sol)
what retards the set of gypsum products?
borax and agar
what are the ingredients of reversible hydrocolloid (agar)? 4
seweend extract
potassium sulfate
borax
alkyl benzoate
what is the antifungal in agar?
alkyl benzoate
what is the gel strengthener in agar?
borax
what are the ingredients of irreversible hydorcolloid (alginate)? 2
potassium or sodium alginate
seweed derivative
what is added to keep alginate from interfering with the set of gypsum productes?
postassium sulfate
how do you store an alginate impression before pouring?
rinse and disinfect 10 minutes
wrap impression in wet paper towel
place in ziploc bag expressed of air
how quickly should you pour an impression?
pour withing one hour
the sol to gel state is a ____ reaction ONLY, _____ dependent
physical
temperature
wghat happens during hysteresis when the reversible hydrocolloid is cooled?
turns to a solid or gel
what happens to the reversible hydrocolloid during syneresis when left standing?
gels contact and squeeze out, liquid forming an exudate on the surface (susceptible to imbibition-absorb moisture)
what are the three advantages to reversible hydrocolloids?
moist field
accuracy
inexpensive (exept for equipment(
what are the disadvantages of reversible hydrocolloids? 3
dimensionally unstable -pour immediately after disinfection
only ONE pour
deformation upon hard compression
what are the 2 advantages for irreversible hydrocolloids?
not temp dependent
popular for study models
what are the disadvantages for irreversible hydrocolloids?
