quiz 2 dental materials

posterior region (closest to mandibular hinge axis)

where is occlusal force highest

decreases

how does the occlusal force change as it moves towards incisors

300-800 N

forces on first and second molars

300 N

average force on premolars

200 N

average force on cuspids

150 N

average force on incisors

oral tissue and restorative materials

in addition to the teeth what else is subjected to forced during normal use

force on removable generally lower

how does occlusal force on removable prosthetics differ from Natural Dentition and Fixed Dental Prostheses

65-235 N

range of force on removable partial dentures

100N

average force on molars and premolars with complete DENTURES

40 N

average force on incisors with complete dentures

stress

INTERNAL reaction to applied external force within a system or body

elongation/shrinkage

axial forces

torsion

twisting motion

strength

internal force that resists an externally applied force

stress

force per area

pascal (1 Pa= 1N/m2)

SI unit of stress

compressive strength

the capacity of a material to withstand axial loads without failure.

N/mm2

units of compressive strength

384

COMPRESSIVE strength of ENAMEL

189

compressive strength of amalgam

76

compressive strength of denture base resin

225

compressive strength of resin composite

10 MPa

tensile strength of enamel

25

tensile strength of porcelain

55

TENSILE strength of AMALGAM

48

tensile strength of denture resin

ductile

a material that can deform plastically (permanently) before breaking

elongation, compression, shear, torsion, bending

types of stress

elongation

deformation from a tensile force

proportional limit

highest stress at which the stress-strain curve is a straight line (stress is linearly proportional to strain)

elastic limit

maximum stress that a material will withstand without permanent deformation

yield point

point at which parallel line (strain) intersects stress-strain curve

yield strength

estimate of when a material will start to deform permanently, more important than ultimate strength in design and material selection

ultimate strength

maximum stress a material can withstand before failure

ultimate engineering stress

determined by: (max load tension/original cross-sectional area)

12 GPa

elastic modulus of dentin

elastic modulus

stiffness of material within elastic range, units MPa or GPa

34 GPa

ELASTIC MODULUS of ENAMEL

ceramic

brittle material that deform elastically until they break

metals

deform elastically and then plastically until they fail

polymers

rubber-like materials that deform elastically until bonds break and they deform both elastically and viscoelastically

resilience

resistance of material to elastic deformation

amount of energy necessary to deform material

what does resilience indicate

toughness

resistance of a material to permanent deformation or
fracture

amount of energy necessary to cause fracture

what is toughness an indication of

area under elastic portion of stress-strain curve

how is resilience measured

area under elastic and plastic portion of stress-strain curve

how is toughness measured

fracture toughness

proportional to energy consumed in plastic deformation and required for fracture

strength of material and distortion expected

what does three-point bending test determine

four-point bending

preferred measure of flexural modulus

139

FLEXURAL STRENGTH of resin COMPOSITE

17

FLEXURAL strength of high-strength stone

ultimate tensile strength

alternative method of testing brittle material determined through compressive testing

shear bond strength

measurement of how well one material bonds to another

push-out method

method of testing shear strength in which an axial load is applied to push one material through another.

static testing

continuous application of force at slow rates of loading

dynamic testing

cyclic loading (forced oscillation) or loading at high rates

impact test (charpy V notch CVN)

most common method of measuring toughness

Fatigue test

performed by alternating stress application below yield strength until fracture occurs

fatigue strength

stress level at which a material fails/fracture under REPEATED LOADING

endurance limit

stress level at which the specimen can be loaded an infinite number of times without failing

hardness

resistance to plastic deformation or penetration. function of applied load, strength of the material, and the surface area being indented

Hardness

used to predict the wear resistance of a material and ability to abrade opposing dental structures

shore (durometer) hardness test

macro indentation test for polymers

barcol hardness test

macro-indentation test for composite materials

knoop hardness test

used for measurement of small areas of brittle material

stress>bonding strength

when does gap formation occur in composite restorations

decrease sensitivity and risk of recurrent caries

benefits of bonding to dentin

stable esthetic result

benefit of bonding to enamel

stress distribution not uniform

why is bond strength of interface often not accurate

stress concentration around flaw or void

what causes debonding

flexural strength values

should be used when tensile strength values are not available