Dental Materials Flashcards
what are the types of amalgam?
conventional
high copper
what is the composition of conventional amalgam?
65% silver 29% tin 6% copper 2% zinc 3% magnesium
what is the composition of high copper amalgam?
40% silver 32% tin 30% copper 2% zinc 3% magnesium
what are the types of alloy morphology that amalgam can come in?
lathe cut
spherical
what is the action of the silver tin compound in the amalgam?
undergoes setting reaction
what is the action of the copper in the amalgam?
strengthens
what is the action of the zinc in the amalgam?
scavenger for oxygen
when does amalgam reach its final strength?
24 hours
what is creep?
amalgam flows manifesting as protrusions at the restoration margins
= produces fractures and ditching
what causes creep?
gamma 2 phase
corrosion of the alloy causes mercury to escape into the crevice = causing expansion
what benefits do corrosion products give?
marginal seal
what removes mercury from the amalgam?
packing and condensation
what are the benefits of bonded amalgam?
reduced prep needed
reduced marginal leakage and post op sensitivity
reinforced tooth structure
what is the composition of the resin matrix in composite?
methacrylate/dimethacrylate monomers - BISGMA
comonomers - TEGMA
what is the action of the TEGMA?
controls viscosity
what is the action of the C to C double bond in composite?
allows free radical polymerisation
what are siloranes?
contain oxiranes = ring opening polymerisation
what is cationic curing?
camphorquinone causes ring opening polymerisation
what is the filler in composite?
quartz, silica, glasses - aluminasilicate, boro silicate, barium oxide
what is the coupling agent in composite?
gamma silane
in what ways can composite be activated?
chemical
light - camphorquinone
what does camphorquinone do?
yields necessary free radicals to start polymerisation
generated by quartz halogen lights `
what is the job of the coupling agent?
transfers stess generated under occlusal loading from rigid brittle filler to ductile polymer matrix
what is the job of the filler?
shock absorber
what are the 4 types of composite?
conventional
microfilled
hybrid
nanocomposites
what is the difference in flowable composite compared to conventional?
less filler
what is GI?
ion leachable glass and polycarboxylic acid
what is the composition of the powder to liquid GI?
p - sodium aluminasilicate glass + 20% CaF
l - aqueous solution of acrylic acid copolymer and tartaric acid to control the set
what is the set reaction of powder and liquid GI?
acid base reaction
what is the set reaction of powder and water GI?
p - sodium aluminasilicate glass + 20% CaF, vacuum dried polyacid
what does hand spatulation when mixing GI cause?
increased air incorporation
increased porosity
how does GI bond to tooth surface?
by calcium ions
how does GI bond to collagen?
H bonding - metallic ion bridging
how can you boost the tooth to GI bond?
citric acid - removes smear layer
polyacrylic acid - increases bond strength
what are the properties of GI?
F release and uptake brittle poor abrasion resistance acid eroded non radiopaque
what is a cermet?
silver pelletized mix of glass and metal particles
radiopaque
f release
increased strength
what is RMGIC?
modified composite
giomers
RMGIC
what is modified composite?
filler of aluminasilicate glass = encourages F release
light cured free radical polymerisation
what is a giomer?
filler = aluminasilicate glass pre reacted with polyacid is pre reacted with glass polyalkenaote complex
what is the composition of RMGIC?
p - ion leachable glass
l - methacrylate resin - polymerisation set, polyacid - acid/base reaction, HEMA - allows acid and resin to coexist, water - ionisation for acid/base reaction, polymerisation activators and stabilisers
when you start to mix P and L of RMGIC what happens?
acid base reaction starts
light activation sets off polymerisation
chemical activators - moves more rapidly
what can happen to RMGIC’s?
shrinkage
expansion in water
why is adhesion of RMGIC’s limited?
lack of free acid
lack of sufficient ionic character
lack of mobility of active species
what is the make up of a phosphoric acid cement?
p - ZnO and other metallic oxides
l - aqeous solution of phosphoric acids and buffers of aluminasilicate phosphate and zinc phosphate
how to phosphoric acid cements set?
sets at surface of powder
rapid and exothermic
what are the properties of phosphoric cement?
low pH/MW = highly irritant thermal and electrical insulator strong radiopaque good compatibility not obtundant non adhesive - no coronal seal
what is a variant of phosphoric cement?
silicophosphate cements
p - aqueous phosphoric acid and buffers
l - zinc oxide and aluminasilicate glass
stronger, less soluble, leaches F
what is the composition of copper cement?
p - zinc oxide, black copper oxide
l - zinc oxide, aluminosilicate glass
what is the composition of zinc oxide eugenol?
p - ZnO and hydrogenated resin, accelerator - zinc oxide and aluminosilicate glass
l - eugenol and olive oil to control viscosity
how does zinc oxide eugenol set?
chelation
what are the properties of zinc eugenol?
beneficial irritancy bacteriocidal due to zinc radiopaque zinc incompatible with resin composites non adhesive - no coronal seal insulator obtundant
what is orthoethoxybenzoic acid?
stronger than zinc oxide eugenol
p - quartz
l - orthoethoxybenzoic acid/eugenol
what is the composition of chemically activated calcium hydroxide?
glycol salicylate
zinc oxide calcium hydroxide
what is the composition light activated calcium hydroxide?
how is it activated?
what increases its rate of set?
methacrylate monomer - BISGMA mixed with HEMA
polymerisation activation
moisture increases rate of set
what are the properties of calcium hydroxide?
high pH - beneficial irritancy high pH - bacteriocidal insulates radiopaque compatible not strong and no seal
what is the composition of polycarboxylates?
p = zinc oxide l = aqueous solution of polyacrylic acid
how do polycarboxylates set?
acid base reaction
what are the properties of polycarboxylates?
acidic - high MW = reduced penetration and mildly irritant F = bacteriostatic stong, insulative, compatible adhesive no seal, not obtundant
what are the properties of GI?
high mw = mild irritant
bacteriostatic due to F release
insulates
strong, adhesive, compatible
what 3 ways can adhesion be achieved by?
- micromechanical attachment - etch/resins
- chem adhesion to enamel and dentine - coupling agents/cements
- complex - wetting, penetration - modern bonding agents
what is acid etch?
acid gel
selective decalcification of enamel prisms
micromechanical tags into which bonding resin can flow
what are the effects of acid etch?
increased surface roughness
increased enamel surface energy - removes surface contaminants, increases wetting, facilitates micromechanical attachment
what happens if you etch for too long?
calcium phosphate re precipitate
why do you wash away etch?
remove debris
why do you dry after washing etch away?
enable hydrophobic resin to penetrate and attach
what is a primer?
dentine conditioner acid maleic acid, oxalic acid, phosphoric acid, nitric acid acid/base reaction with hydroxyapatite opens tubules
what is a coupling agent?
primer
sticks
bonds hyrophobic material to hydrophillic dentine
HEMA
what is a sealer?
sealant flows into tubules and seals dentine with methacrylates, ensures bond
BISGMA
TEGMA
what are the benefits of ormocers as opposed to composites?
less shrinkage
no residual monomers
what are the types of impression materials?
non elastic - impression compound/plaster, zinc oxide and eugenol pastes
elastic - hydrocolloids - reversible//irriversible
synthetic elastomers - polysulphides, silicone rubbers, polyethers
what are hydrocolloids?
colloidal suspension of polysulphides in waterb
soluble or gel
what is agar?
complex polysaccharide from seaweed gel
borax - gives body
potassium sulphate - counteracts retardent effects of gypsum
what are the advantages of agar?
disadvantages?
A- reversible, takes up moisture
D - complicated equipment, cost, cross infection
what are alginates made up of?
Na/K salt of alginic acid
CaSO42H2O - source of Ca for cross linking
sodium phosphate - controls working time
inert filler - body for manipulation
how does sodium phosphate control the working time?
limits the availability of calcium ions
