dental 3

Question 1

what are biomechanics

Answer 1

study of how biological material interacts and deforms when exposed to chemical, thermal and mechanical challenges

Question 2

what is force

Answer 2

measured in newtons (N)
is defined by 3 characteristics-
point of application 
magnitude
direction of application

Question 3

occlusal force

Answer 3

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

Question 4

forces on restoration

Answer 4

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)

Question 5

what is stress

Answer 5

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

Question 6

how is force measured

Answer 6

pascal of mega pascal Pa/MPa

1Pa = 1N/m2 = 1MN/mm2

Question 7

what is stregth

Answer 7

max stress a structure can withstand without sustaining a plastic strain. (yield strength)
or stress at the point of fracture. (ultimate stregth)

Question 8

what is strain

Answer 8

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

Question 9

how is strain calculated

Answer 9

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

Question 10

different types of strain

Answer 10

elastic

palastic

Question 11

what is elastic strain?

Answer 11

reversible
the object fully recovers to its original shape when the weight is removed
occurs when the stress is less the elastic limit

Question 12

what is plastic strain

Answer 12

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

Question 13

what is hardness

Answer 13

the resistance of a material to indentions or penetration

Question 14

brinell hardness test

Answer 14

indenter is a small hardened steel ball that is forced into the surface of a material under a specific load

Question 15

Vicker hardness test

Answer 15

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

Question 16

Knoop hardness

Answer 16

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

Question 17

Rockwell hardness test

Answer 17

used to determine the hardness of steel

uses different hardened steel balls and diamond cones and different loads

Question 18

shore a hardness

Answer 18

a test used to measure the hardness of rubber and soft plastics
scale between 0 and 100 units

Question 19

what is elasticity

elastic modulus

Answer 19

having a constant ratio of stress to strain
(elastic modulus)
stiffness of material within the elastic range
1 stress σ: 1 Strain ε

Question 20

what is yield strength?

Answer 20

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

Question 21

ultimate strength

Answer 21

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.

Question 22

fracture strength

Answer 22

stress at which a brittle material fractures.

Question 23

impact stregth test

Answer 23

the stress required for a fracture of a material under sudden maximum impact is measured by a sharpy type impact tester

Question 24

shear strength

Answer 24

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

Question 25

compressive strength test

Answer 25

test that mesures the loads that destroy the materials under the action of the crushing stresses

Question 26

flexural strength test

Answer 26

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.