dental 3 Flashcards
what are biomechanics
study of how biological material interacts and deforms when exposed to chemical, thermal and mechanical challenges
what is force
measured in newtons (N) is defined by 3 characteristics- point of application magnitude direction of application
occlusal force
max occlusal force ranges from 200N-3500N
the max force is in the posterior region close to the mandibular axis and decreases towards the incisor
molar- 400N-800N
premolar-300N
canine-200N
incisor-150N
increases by 22N annually in children
forces on restoration
partial restoration has a force ranging- 65N-235N
complete removable restoration- 40N-100N
When deciding restoration consider-
location in the arch,
opposing dentures
the force-generating capacity of the patient (can depend on age, gender, muscle)
what is stress
when force is applied on a constrained body and the body resists the force. the internal reaction has an equal magnitude and the direction of application is opposite to the external force applied
how is force measured
pascal of mega pascal Pa/MPa
1Pa = 1N/m2 = 1MN/mm2
what is stregth
max stress a structure can withstand without sustaining a plastic strain. (yield strength)
or stress at the point of fracture. (ultimate stregth)
what is strain
change in length per unit initial length
when a material is subject to tensile stress and it temporarily becomes longer, the temporary increase in length is called strain
relative deformation of an object subjected to stress
how is strain calculated
change in length divided by original length = a percentage
stress and strength are both proportional to a load applied when the cross-section area is kept the same
different types of strain
elastic
palastic
what is elastic strain?
reversible
the object fully recovers to its original shape when the weight is removed
occurs when the stress is less the elastic limit
what is plastic strain
the permanent deformation of the material that does not decrease when the force is removed
occurs when the stress is greater than the proportional or elastic limit
what is hardness
the resistance of a material to indentions or penetration
brinell hardness test
indenter is a small hardened steel ball that is forced into the surface of a material under a specific load
Vicker hardness test
square pyramid-shaped diamond that leaves a square diamond shaped indention on the surface being tested
hardness is determined by measuring the diagonals of the square and taking an average of 2 dimensions
Knoop hardness
the indentor is also made of the diamond but has 1 diagonal which is much longer than the other.
also only 1 diagonal is measured
Rockwell hardness test
used to determine the hardness of steel
uses different hardened steel balls and diamond cones and different loads
shore a hardness
a test used to measure the hardness of rubber and soft plastics
scale between 0 and 100 units
what is elasticity
elastic modulus
having a constant ratio of stress to strain
(elastic modulus)
stiffness of material within the elastic range
1 stress σ: 1 Strain ε
what is yield strength?
the stress at which a material deforms plastically and there is a defined amount of permanent damage
of greater importance than ultimate strength because the material is deformed permanently
ultimate strength
max stress a material can withstand before failure
determined by the max load in tension/cross-section area of an alloy
alloys that are stressed to near ultimate strength are useless as they are already past the yield strength.
fracture strength
stress at which a brittle material fractures.
impact stregth test
the stress required for a fracture of a material under sudden maximum impact is measured by a sharpy type impact tester
shear strength
used to investigate the forces of adhesion among materials
probe body consists of 2 glued together material.
in the machine forces that destroy the adhesion are produces
compressive strength test
test that mesures the loads that destroy the materials under the action of the crushing stresses
flexural strength test
measures the load that destroys the material when applied perpendicularly to a longitudinal axis of a sample.
stress on upper surface is compressive and lower surface is tensile.
