intro Flashcards
what indicates a material is safe?
a CE mark
what are the 5 restorative materials available?
amalgam composite glass ionomer cements compomers procelain
what 4 impression materials are available?
impression compound impression paste hydrocolloids -alginate elastomers -polysulphides -polyethers -silicones
what is the purpose of impression materials?
record position, shape and dimention of dentition
what metals/alloys are available?
amalgam cobalt chromium titanium gold stainless steel
describe porcelain?
similar appearance to enamel so suits anteriors
ceramic veneers common
-material bounded to tooth aesthetically satisfying, hard, rigid, not always most appropriate
describe composite resin
initially flows out of cartridge low to high viscosities finally sets within margins hardens
describe amalgam?
not aesthetic
good for substantial restorations
describe impression materials
initially flows into tray low viscosity finally undergoes setting reaction firm, stable
what is gypsum?
dental stone
allows studying and making appliances
what is ppma?
dentures acrylic resin
high quality
polymethylmethacrylate
when is stainless steel used?
denture base
strong enough to withstand biting forces
orthodontic appliance
can be adjusted easily for ideal fit
when is cobalt chromium used?
partial denture
able to withstand engagement and disengagement over long period
What consequences can happen when a force is applied to a material?
Stretch/compress -depends how force applied Deform -temporary/permanent Fracture -failure
What are the 3 types of force?
Compressive
Tensile
Shear
-parallel to surface object is attached
What is the formula for stress?
Force/unit area
What is the formula for strain?
Force/unit area
What is the formula for rigidity? (elastic modulus)
Stress/strain
What are the 8 possible mechanical properties?
Hard, soft, strong, weak, rigid, flexible, brittle, ductile
What are the mechanical properties of enamel?
Brittle, hard, strong, rigid
What force does biting apply to teeth?
Compressive
-to upper tooth
What forces are experienced when grinding/chewing?
Tooth slides along surface of the other
Frictional forces
What is the consequence of biting (compressive forces)
fracture
What is the consequence of grinding/chewing?
abrasion
Why do restorative materials have to be adhered to enamel?
If not they will be removed by masticatory force
What restorative material required an undercut?
amalgam
How does amalgam achieve retention?
undercut-mechanical
How does composite resin achieve retention?
adhesive
What are the requirements of a filling material?
Must be pliable, to fit shape of interest, must set to form hard, strong material
What is the failure mechanism of fracture?
Large force causes catastrophic destruction of materials structure
What is the failure mechanism of hardness?
Ability of surface to resist indentation
What is the failure mechanism of abrasion?
Material surface removal due to grinding
- tooth grinds/slides along opposing tooth surface
- loss of material surface layers, roughened surface
What is the failure mechanism of abrasion resistance?
Ability to withstand surface layers being removed, so compromising surface integrity
What is the failure mechanism of fatigue?
Repetitive small stresses cause material fracture
What is the failure mechanism of creep?
Gradual dimensional change due to repetitive small forces
What is the failure mechanism of deformation?
Applied stress causes permanent change in materials dimensions
What is the failure mechanism of de-bond?
Applied forces sufficient to break material-tooth bond
What is the failure mechanism of impact?
Large, sudden force causes fracture
Why is a rough surface bad?
can act as plaque trap
where is de-bonding commonly used?
in removal of orthodontic appliance
-shear force used to separate bracket/bonding material from tooth surface
what chemical properties should be considered?
setting mechanism
setting time
corrosive potential
what physical properties should be considered?
viscosity thermal conductivity thermal expansion density radiodensity
