Introduction to DMS Flashcards
what does the behavior of dental materials affect
selection preparation placement performance patient expectations
what indicates that a material is safe
CE mark
what are the different types of restorative materials
amalgam composites glass ionomer cements composers porcelain
what are the different impression materials
impression compound
impression paste
hydrocolloids
elastomers
what is the hydrocolloid impression material
alginate
what are the elastomers
polysulphides
polyethers
silicones
what are the different metals/alloys
amalgam cobalt chromium titanium gold stainless steel
what is composite like initially and finally
initially flows out of a cartilage - low to high viscosities available
finally sets with margins and hardens
what is impression material (polyether) like initially
initially flows into a tray and low viscosity
finally undergoes a setting reaction to become firm and stable
where is stainless steel used
denture base
orthodontic appliances
when is cobalt chromium used
partial dentures
what are the different properties of materials
mechanical, chemical, physical
what may forces applied to materials cause it to do
stretch/compress
deform (temp or permanent)
fracture
what is the equation for force
F = mass (kg) x gravitational acceleration
what are the types of forces
compressive
tensile
shear
what is the equation for stress
force/unit area
what is the equation for strain
change in length/original length
what is the definition of stress
force per unit cross sectional area that is acting on a material
what is the definition of strain
fractional change in the dimension caused by the force
what happens if the stress and strain exceed the maximum value that the material can withstand
fracture is most likely
what is the proportional limit
it is up until the proportional limit that stress and strain are linearly related
what is youngs modulus
measure of stiffness/rigidness of a material
what are the different mechanical properties
hard/soft
brittle/ductile
strong/weak
rigid/flexible
what are the mechanical properties of enamel
brittle
rigid
strong
hard
what are materials subjected to
biting
grinding/chewing
removal
how does biting affect materials
compressive force applied to upper tooth when biting. Can the tooth withstand the force or will it fracture?
how does grinding/chewing affect materials
tooth slides along the surface of the other. Frictional forces are experienced. Will tooth surface be abraded resulting in the loss of layers of enamel?
what is the typical biting force
500 to 700N (50-70kg)
how can materials be subject to removal
the material needs to adhere to enamel or it will be removed by masticatory forces – the forces will overcome the bond between material and tooth structure. This is through shear force
how do the mechanical properties of enamel and dentine compare
Enamel is more rigid than dentine as it has a higher EM. The fracture stress of enamel is greater than dentine.
how does amalgam stay in the tooth
through mechanical retention
what kind of cavity design does amalgam require
undercut
what kind of cavity design does composite require
minimal design
how does composite stay in the tooth
adhesive retention
what is the purpose of the undercut design
keeps the material in place as without it the material would just fall out as there is no bonding between the amalgam
what are the different material failure mechanisms
fracture hardness abrasion abrasion resistance creep deformation debond impact
how does fracture occur
large force causes catastrophic destruction of material’s structure
the biting forces are gradually increased
what is hardness
ability of surface to resist indentation (KHN)
what is abrasion
material surface removal due to grinding
what is abrasion resistance
ability to withstand surface layers being removed, so compromising surface integrity
what is fatigue
repetitive ‘small’ stresses causing material fracture
what is creep
gradual dimensional change due to repetitive small forces
what is deformation
an applied force may cause a permanent change in material’s dimensions (but not fracture it!)
what is impact
large sudden forces causes fracture
what is a hardness test
The hardness is determined by measuring the depth of the indenter penetration or by measuring the size of the impression left by an indenter.
what happens in abrasion
In abrasion the tooth grinds and slides along the opposing tooth surface and the tooth surface is abraded which can result in the loss of material in surface layers or a roughened surface
what happens in fatigue
Most failures are not due to the application of a single load (force) but instead when repeated loads are applied, small flaws (cracks) in a material grow (propagate) allowing fracture when only a relatively small force is applied.
how does creep occur
low level forces continually applied
amalgam protrudes around the margins
exposed amalgam vulnerable to fracture
how does permanent deformation occur
Applying stress to a material that results in a releasing stress that is greater than the elastic limit results in permanent deformation, dL
how are orthodontic appliances removed
shear force is applied to separate the bracket/bonding material from tooth surface
how can impact effect dentures
the impact can cause them to either split down the middle or for surface cracks to form
what are the other mechanical properties
ductility/brittleness
tear strength
what are the chemical properties
- setting mechanism
- setting time
- corrosive potential
what are the physical properties
- viscosity
- thermal conductivity
- thermal expansion
- density
- radiodensity
what are the ideal properties
Each dental material has its own properties, when evaluating a material, compare its performance with the ideal properties
how does the oral environment effect materials
saliva
temperature variations
pH variations
oral bacteria
