Dental Materials Science Flashcards
how does composite bond to tooth?
hybrid layer formed through DBA e.g. primer i.e. HEMA and resin i.e. bis-GMA. hydrophilic end of DBA bonds to wet dentine and fills dentinal tubules; hydrophobic end polymerises with bis-GMA resin. note that bond made is mechanical
how does GI bond to tooth?
by hydrogen and mineral bonds with collagen. calcium in tooth being chelated by COO in polyacid. complex reprecipitation of CaPO4 from apatite and calcium salts from GI onto/into tooth surface
how does amalgam bond to tooth
it doesn’t it is mechanically retained
why does a bond fail and what can happen
normally fails due to microleakage; oral fluids/bacteria/sugar enter restoration margins causing secondary caries which untreated can lead to pulpitis and eventually a necrotic pulp that can become purulent and drain gingivally or extra orally. treatment = extraction / antibiotics
amalgam composition + use
powder AgSnCu + Hg
liquid Hg
used for restoration of medium to large posterior cavities
RMGI composition + use
powder: polyaluminosilicate glass + barium glass // vacuum dried polyacrylic acid
liquid: polyacrylic acid// tartaric acid // water // photo initiator
use: light curing material that acts as a base/liner for deep restorations
composite - composition + use
- filler particles - quartz/glass and silica for hybrid
- resin - bis-GMA
- photo initiator - camphorquinone
- low weight dimethyacrylate - TEGDMA
- coupling agent - silane
use - primary caries / abrasion / erosion / failed restorations i.e. secondary caries / trauma
what is bis-GMA
bisphenol-A glycidyl methacrylate
is a difunctional molecule that allows for free radical addition polymerisation
composite vs flowable composite
composite = filled bis GMA resin flowable = unfilled bis GMA resin
CaOH compostion + use
base - CaOH, zinc oxide filler, plasticiser
catalyst - butylene glycol disalicylate, zinc oxide filler
use - prevents gaps, acts as a protective barrier
vitapex - composition + use
CaOH and iodoform
to fill root canals in paediatric pulpectomy
hardness
a material’s ability to resist scratching or surface indentation
compressive strength
ability to withstand direct pushing forces
thermal expansion
expansion of a material due to increased molecular vibrations as they absorb heat
creep
permanent deformation if a load is applied over a period of time even though the stress is below the elastic limit
brittleness
high stresses to cause a small strain - material breaks with little permanent deformation occurring beforehand
fracture
large force causes catastrophic destruction of material’s surface
deformation
applied force may cause a permanent change in material’s dimensions but won’t fracture it
why Cu enriched amalgam
higher earlier strength, less creep (so less ditching and marginal breakdown), higher corrosion resistance, increased durability of margins
why spherical particles in amalgam
require less Hg, have higher tensile strength, higher early compressive strength and easier to carve
tensile strength
resistance to breaking from a force acting to elongate
gamma 2 phase
weakest, most electronegative, least corrosion resistant
thermal expansion of amalgam
3x that of the tooth so may lead to microleakage
factors impacting strength of amalgam
corrosion undermixing too high Hg content low condensation pressure slow rate of packing
to reduce corrosion in amalgam
Cu enriched materials
polishing margins
avoiding galvanic cells
liners protect pulp from
chemical stimuli - unreacted chemicals in / pH of filling material
thermal stimuli - exothermic setting of composite / heat conduction of amalgam
bacteria + endotoxins
ease of use of cavity liners
should be command set
workable
easy to mix
thermal properties of cavity liner
low thermal conductivity
same TEC as tooth
diffusivity should be similar to conductivity
mechanical properties of cavity liner
high compressive strength, placement of filling without breakage, radiopaque, low solubility, marginal seal, cariostatic, biocompatibility
ZOE zinc oxide eugenol
involves chelation of zinc oxide with eugenol to form a matrix bonding unreacted particles - inhibits set of comp resin so don’t use
EBA - modified ZOE
modified ZOE with better compressive strength and lower solubility
hybrid layer
exists between dentine and the restorative material. has several constituents i.e. primer/adhesive (HEMA + bis-GMA), exposed collagen fibrils, demineralised dentine, resin tags penetrating down dentinal tubules
syneresis
loss of water
imbibition
uptake of water
what does pmma stand for
polymethylmethacrylate
if too much monomer in pmma
contraction porosity
if insufficient monomer in pmma
granularity
gaseous porosity which affects strength appearance roughens sensation to tongue and absorbs saliva
self cure v heat cure acrylic
self - increased accuracy but decreased mechanical properties
heat - stronger due to higher weight monomers. more commonly used
rmgi vs gic
rmgi has better physical properties // lower solubility // fluoride release // better translucency + aesthetics // better handling
gic has less polymerisation shrinkage
rmgi dual curing
on mixing - dissolution
light activation causes free radical methacrylate reaction to occur = resin matrix formed
acid base reaction occurs for several hours after
rmgi tri curing
on mixing - dissolution redox light activation - resin matrix formed redox continues for 5 mins acid base occurs for several hours final hardening may take days
3 phases of GIC setting reaction
dissolution
gelation
hardening
3 phases of GIC setting reaction
dissolution
gelation
hardening
properties of GIC
poor bond strength poor tensile strength lower compressive strength than composite higher solubility than composite usually seals well fluoride release for short time
mechanical properties of composite
smooth surface finish
technique sensitive
low setting shrinkage
thermal properties of composite
TEC poor compared to amalgam + GI
under cold stimuli composite can shrink away from cavosurface margins
requirements of DBA
flowability
intimate contact w dentine surface
adhesion to substrate
low viscosity
