Intro to Dental materials slides Flashcards
Is the stress on the stress-strain curve when it ceases to be linear
Proportional Limit
Yield Strength is…
Is the stress at some arbitrarily selected value of permanent strain
The Elastic Modulus is…
a measure of
the stiffness of a material The Elastic Modulus is the slope of the stress-strain curve in the initial
straight-line portion
Ultimate Strength is…
the stress at which the fracture occurs.
Denture base should be constructed from a rigid material for two reasons:
- Load distribution
2. To be used in thin sections without bending
The Yield strength of human enamel is…
344 Mpa
The Yield Strength of composite are…
138-172 Mpa
Average of biting forces: For molars***
580 N
Average of biting forces: Bicuspids ***
310 N
Average of biting forces: Cuspids***
220 N
Average of biting forces: Incisors***
180 N
Patients with restorations and prosthesis decreases the biting forces by**
50-80%
Stress is…
is the internal action to the external applied force
Stress =
=Force/Area
For a given force, the_______ the area over which is applied, the______ the value of the stress
smaller
larger
Strain is…
Is the change in length per unit length of a material produced by stress.
Strain = Deformation/Length
elastic strain is…
Temporary
Plastic strain is…
Permanent
Ultimate compressive strength for human enamel?
400 MPa
Ultimate Tensile strength for gold alloys?
414-828 MPa
Ultimate tensile strength for nickel-chromium alloy?
421 MPa
Elongation and Compression is?
The amount of deformation that a material can resist before rupture and is reported as the percent of elongation when the material is under tensile stress or the percent of compression when it is under compressive stress.
The percent of elongation and compression are measures of
ductility and malleability, respectively.
Percent of Elongation—>
Ductility
Percent of Compression—>
Malleability
indicate the brittleness of the material.
Ductility, and Malleability
In general, alloys with elongation less than 5% are considered
brittle
Alloys with elongation higher than 5% are considered
ductile
Toughness:*****
Energy necessary to fracture a material
Resilience:*****
Energy required to deform a material permanently
The resilience has a particular importance in the evaluation of:
- Orthodontic wires, for the expected amount of work from a spring to move a tooth.
- Acrylic denture teeth: they are more resilient than porcelain so, they absorb most of the masticatory forces & transmit less force to the ridge
The hardness of dental materials is
reported in…
Knoop hardness
A material is considered hard if it
strongly resists indentation by a
hard material such as diamond.
Galvanism Results from the
presence of dissimilar metals in the mouth
is a measure of the body’s response to an
specific material.
Biocompatibility
The linear thermal expansion is expressed as a
coefficient of
thermal expansion
coefficient of thermal expansion for Wax
300-1000
coefficient of thermal expansion for Human teeth
10-15
coefficient of thermal expansion for Composites
25-68
coefficient of thermal expansion for Gold alloy
12-15
coefficient of thermal expansion for Amalgam
22-28
coefficient of thermal expansion for Porcelain
8
Thermal conductivity of Dental amalgam
0.055
Thermal conductivity of Gold alloys
0.710
is a measure of
the affinity of a liquid for a
solid as indicated by
spreading of a drop.
Wettability