Dental Biomaterials Flashcards
Tensile force
pulls objects apart
Shear force
pushes one part on an object in one directions and another part in the opposite direction with a twisting or rotating motion
Stress
internal force that resists the applied force, and can resist the external force up to the point of fracture.
ultimate strength
highest stress that can be borne by the object before it fractures or breaks
fracture strength
point where an object breaks
ductility
ability to withstand deformation under stress before fracturing or breaking
brittleness
ability to fracture or break before deformation occurs
malleability
ability to be compressed without fracturing
strain
deformation of material in response to stress, the change in shape and size
Elastic deformation
the object recovers after stress is released
proportional limit
point of the stress/strain diagram at which stress and strain are directly proportionate to one another. At this point, if stress is removed there is no deformation
yield point
the point just before the material is permanently deformed
galvanism
a direct current of electricity especially when produced by chemical action
EX: fork touching a metal restoration causing a shock feeling
thermal conductivity
ability of heat to spread
coefficient of thermal expansion
change in volume and length of an object in response to a change in temperature
The higher the coefficient of expansion, the ______ the degree of contraction and expansion
greater
microleakage
leakage of fluid and bacteria that occurs at the interface of the tooth and the restoration margins due to the difference in the coefficient between the tooth and the material.
percolation
movement of fluid in the microscopic gap of the restoration margin as a result of differences in expansion and contraction of the tooth and the restoration with temperature change.
retention
ability for a material to maintain position without being displaced under stress
mechanical bonding
material penetrates into irregularities (pores on tooth structure) and interlocks mechanically.
wetting
degree to which the liquid adhesive spreads over the surface
the better the spread, the more retention.
cohesion
force of attraction between LIKE kinds of atoms and molecules within a material, resulting in a tenacious bond.
Adhesion
force of attraction between UNLIKE atoms and molecules on two different surfaces when brough into contact with each other
hue
color
chroma
intensity of color
value
lightness or darkness of color
opacity
light is absorbed by object
modulus of elasticity
measures the stiffness of an elastic material.
elastic limit
maximum stress that a material can withstand without being permanently deformed
hardness
measure of resistance to indentation when a compressive force is applied
Moh’s hardness scale
compares minerals and their ability to scratch another mineral
Knoop hardness
examines the indentation caused by a diamond point under a microscope
reversible hydrocolloid: agar agar
material is heated, converted into sol, and cooled to become a gel.
Can be reused multiple times and provides better details than alginate.
Irreversible hydrocolloid: aliginate
less accurate impression material than agar/rubber
polysulfide, silicone, polyether, and vinyl materials
hydrophobic
more rigid and provides better details than alginate
used for inlay, onlay, crown, bridge, and secondary (final) impressions
syneresis
loss of water mostly by evaporation
imbibition
ability to absorb water
gypsum in dentistry
calcium sulfate hemihydrate, obtained by a water evaporation process called calcination
most common material used for replication in dentistry.
Plaster
type 2
irregular porous particles. High setting expansion and low compressive strength.
requires more water
Stone
type 3
less irregular particles
low setting expansion and higher compressive strength. Used for study models
Diestone
type 4 and 5
non porous, smoothest, and dense particles.
Highest compressive strength.
Used for crowns and bridges.
What kind of reaction occurs with a hemihydrate and water
exothermic
T or F: all gypsum expands upon setting
true
wet strength
strength when excess water is present
dry strength
strength when excess water is removed.
Can a clinician accelerate the setting time of gypsum products by adding borax to it?
no, borax is considered a retardant.
Potassium sulfate acts as an accelerator
direct restoration
material is placed directly onto a prepared tooth
done in one appointment
indirect restoration
restoration is placed after it is fabricated in the lab
takes more than one appointment.
inlay
lies withing the cusp of a tooth
onlay
covers one or more cusp tips
Characteristics of gold
resists tarnishing
resists corrosion
highly resistant to fractures and is durable
may cause galvanic shock
thermal expansion is CLOSEST to the natural tooth surface.
Characteristics of porcelain
strong and durable
produces dentures, PFM crowns, bridges, veneers, onlays, and inlays
provides excellent match to natural teeth color, intensity, and translucency.
Do not use acidulated fluoride
Characteristics of composite
major component is dimethylacrylate (bis-GMA)
needs polymerization
can be light-cured or self cured.
poor conductor of heat and electricity
good flow
resistant
do not use acidulated fluoride
Components of amalgam
40-60% silver
27-30% tin
13-30% copper
1% zinc set with mercury.
Silver
enables setting expansion and causes an increase in strength and resistance to corrosion
copper
increases strength.
Minimized corrosion, tarnish, creep, and sensitivity.
Tin
mat cause setting contraction whereas copper improves strength, minimized corrosion, and tarnish, brings down creep, and brings down cases of marginal leakage.
Zinc
brings down the oxidation of other alloys in the metal. It has been proved that zinc-containing amalgams have a longer life when compared to non-zinc amalgams.
indium
strong, especially during compression
similar compressive strength to enamel.
inexpensive
undesirable traits of amalgam
lower tensile and shear strength
corrodes
creeps
galvanism
overhangs
low-copper amalgam
lower strength
high copper amalgams
higher strength, corrosion-resistant
lathe-cut amalgams
powder composed of small shavings
spherical amalgams
particles in the form of small spheres
Admixed alloy amalgams
mixture of lathe-cut and spherical alloys, produces better contacts
Ceramic
also called dicor
more durable for inlays compared to composite
What is the purpose of cements/liners/bases/varnishes
to protect the tooth and provide better retention
Cements
retain restorations in the mouth and provide thermal insulation near the pulp.
Bases
insulate and protect the tooth
substitute dentin removed
provide thermal and chemical protection and can resist condensation forces
liners
seal dentinal tubules and protect against leakage of irritants present in the saliva and restorative materials
CANNOT resist compressive forces.
Zinc oxide-eugenol (ZOE)
combo of zinc oxide powder and eugenol liquid
Zinc oxide-eugenol use
used as a liner for its sedative effect to the pulp called obtundent
Used for temporary fillings
can be used as impression material for complete dentures
Zinc phosphate
zinc oxide powder and phosphoric acid liquid combined causing an exothermic reaction.
polycarboxylate (durelon)
mainly used for permanent cementation of ortho bands and brackets.
does not release heat
Glass ionomer (KETAC-CEM)
binds to dentin and releases fluoride
Commonly used in Class 5 restorations
Resin
Mostly made up of bisphenol A- glycidyl methacrylate (BIS-GMA)
commonly used as a cement to retain restorations
Calcium hydroxide
used as a liner or base, or root canal filling material
stimulates the production of reparative dentin
Varnish
cavity liner applied under gold/amalgam restorations. Numbs pain, blocks penetration of chemicals, and seals dental tubules to prevent transfer of heat/cold
Conditioning/ etching
removes the smear layer and creates more pores for mechanical bonding
37% phosphoric acid
Finishing
removes excess materials and produces smooth surfaces
