intro to DMS Flashcards
CE mark
indicates a material is safe if used correctly
force
something that causes another object to be influenced
measured in newtons
what are the 3 types of force discussed in dentistry
compressive - ‘crushed’
tensile - ‘stretched’
shear - ‘pushed’
stress
force per unit area (unit area = contact point on object subject to force)
measured in pascals
strain
change in length compared to original length of that material
can be shown as a ratio or a percentage
proportional limit
point at which stress to strain ratio stops being proportionate to one another
above this point - permanent deformation , below this point elastic recovery
stress - strain curve
axis = stress (MPa) against Strain (percentage or ratio)
shows how much stress is needed to cause a certain amount of strain
this defines rigidty/ elastic modulus of the material
fracture stress
point at which material fractures
seen at the end of stress strain curves
elastic modulus (youngs modulus)
indicates rigidity
calculated via YM = stress over strain (ratio)
e.g 250 MPa stress and 1% strain = 250/0.01 = 25GPa
abrasion
frictional wear from an external source seeing loss of material surface layers, can lead o a roughened surface which can act as a plaque trap, most common cause = too much force when tooth brushing
fatigue
repeated small stresses over a long period of time leaving micro cracks that can potentially lead to fracture
creep
gradual change in shape (deformation) that can lead to fracture
deformation
material changes shape, seen when stress exceeds elastic limit
blacks cavity class i
pit and fissure caries
blacks cavity class ii
posterior approximal
