intro to dental material science Flashcards
what is the dental procedure
- examination
- diagnosis
- treatment plan (which material is suitable, how to use material, explain options to patient, select material)
what is the effect of dental materials
- selection = adequate, best type
- preparation = cavity design, tooth surface
- placement = technique, increments, curing
- performance = quality of fit, longevity
- patient expectations = aesthetics, durability
what does the dental material need to have to be safe
- a CE mark = an essential requirement, show material is safe
why just you not assume new materials are good
manufactures are constantly making new materials, but art doesn’t mean that they are better
- should read about material before using it
what are different types of restorative materials
- amalgam
- composite
- glass ionomer cements
- compomers
- porcelain
what are different types of impression materials
- impression compound
- impression paste
- hydrocolloids = alginate mainly
- elastomers = polysulphides, polyethers, silicones
what are different types of metals/alloys
- amalgam
- cobalt chromium
- titanium
- gold
- stainless steel
what are challenges in choosing materials
- so many materials to choose form
- constant changes to products and names
- range of brands
what is porcelain used for
veneers
what is composite resin
used for restorations
- can come in cartridge or nozzle
- low to high viscosities available
how do impression materials work
- record dentition in negative replica
- flows into trays at low viscosity
- undergoes setting reaction - becomes firm, stable
- gypsum (dental stone) = gives positive replica
what is PMMA
a denture base material
what are the mechanical properties of the materials
- force applied to material
- stress
- strain
- elastic modulus
what are some mechanical forces materials are subjected to
- biting, chewing, grinding
what may happen to the material from the force applied to it
- stretch/compress = depends on how force is applied
- deform/ change shape = temporarily (during application) or permanently
- fracture = failure
what types of force can be applied to the material
- compressive = squeeze material
- tensile = stretch
- shear = object bonded to another surface and apply force along parallel line of object
what is stress
force acting on an area
what is strain
change in length/original length
what is the stress-strain curve
- most materials have one
- FS = fracture stress
- star = proportional limit (up to here stress and strain are proportional)
- elastic modulus is in mega pascals (its the slope)
what is the elastic modulus
- also called Young/s modulus
- is the rigidity/stiffness of the material
what are the 4 mechanical properties and their opposites
- hard / soft
- strong / weak
- rigid / flexible
- ductile / brittle
what mechanical properties does enamel have
- hard
- strong
- rigid
- brittle
what is the typical biting force
- is a compressive force applied to upper tooth when biting
- typical biting force = 500 to 700N
what type of forces are grinding/chewing
- shear forces
- tooth slides along surface of another
- frictional forces are applied
- shear forces can remove restorations (material needs to adhere to enamel or it will be removed by masticatory forces)
what is the differences between enamel and dentine
- enamel is more rigid than dentine
- fracture stress is higher in enamel
- enamel FS = 262MPa, dentine = 234MPa
- enamel PL = 235 MPa, dentine = 176MPa
- enamel EM = 33.6 GPa, dentine = 11.GPa
how does material influence cavity design
- shape for amalgam quite distinctive compared to composite = needs to be bigger, splays outwards towards base of cavity
- composite will bond to tooth, amalgam has mechanical retention = amalgam has no bond to tooth surface, needs undercut cavity shape to stay in place
- material must be pliable, to fit shape of interest, must set to form a hard, strong material
how can the material fail
- fracture =large forces applied cause destruction go material structure
- hardness = not hard enough to withstand forces
- abrasion = material surface removed from grinding
- fatigue = repetitive small forces cause fracture
- creep = gradual shape change from small forces
- de-bond = forces sufficient to break material-tooth bond
- impact = large, sudden force causes fracture
what is abrasion resistance
ability to withstand surface layers being removed, so compromising surface integrity
what is the hardness test
- stainless steel with weight on top of the point (indentor)
- leave on surface of material for certain amount of time
- hard material will have a very small indentation, soft material will have large indentation (notch)
- hardness is about surface, not strength
what is abrasion
- tooth grinds/slides along opposing tooth surface
- tooth surface is abraded- loss of material surface layers/material can fall off
- causes roughened surface
what is fatigue
- most failures are not due to the application of a single load
- not just from one stress, but lots of little stresses over time
- when repeated loads are applied, small forces in a material grow allowing fracture
what is creep
- repetitive small forces cause a dimensional change
- from compressive forces
how is permanent deformation caused
- applying stresses greater than elastic limit
- once released this stress it will not recover as its past the elastic limit of the material
- causes permanent change in shape
how are impression materials not permanently changed on removal
- they will have some elasticity
- when removing the tray, the material will have an elastic strain as its removed and will then have elastic recovery once removed
- with the best material, can get 99.5% elastic recovery (never 100%)
what causes debonding
- shear forces
- to remove orthodontic appliances, shear forces are applied to separate the bracket material from tooth surface
what are some other mechanical properties
- ductility
- brittleness
- tear strength
what are chemical properties of materials
- setting mechanism
- setting time
- corrosive potential
what are physical properties of a material
- viscosity
- thermal conductivity
- thermal expansion
- density
- radiodensity
what should you do when evaluating a material
compare its performance to the ideal properties
how can the oral environment affect the materials
- saliva
- temperature variations
- ph variations
- oral bacteria
why is there more in vitro evidence than in vivo evidence for materials
- gathering clinical evidence is time consuming, costly and limited in scope
- means there is less robust evidence for the performance of dental materials in vivo
