DMS Flashcards
adv of non-y2 amalgam
high corrosion resistance
more durable
less creep
compressive strength
longer rests
lower marginal breakdown and ditching
reduced post-op sensitivity
how do you remove y2 from amalgam structure
high copper alloy >=12%, allowing tin to preferentially react with copper instead of mercury
formation of Cu5Sn6 phase instead of y2
lathe cut particles
originally, why was it necessary to add zinc to amalgam
as a scavenger/oxidiser to remove oxygen during manufacturing process
prevent oxidisation of other metals
improve handling and longevity
what effect could occur in freshly placed amalgam rest as result of presence of zinc in amalgam
moisture contamination leading to gradual expansion, marginal discrepancies, fractures, microleakage
explain the mechanism of expanding zinc amalgam
moisture contamination
zinc and water react to form zinc hydroxide and hydrogen gas
build up of gas causes internal expansion of amalgam, causing dimensional change
symptom of zinc amalgam expansion
pulpal pain
what is amalgam setting reaction
ag3sn + Hg
Ag3Sn + Ag2Hg3 + Sn8Hg
adv of amalgam
high compressive strength
long lasting
cost effective
durable
ease of use
less technique sensitive
high abrasion resistance
disadv of amalgam
poor aesthetics
more destructive
high thermal expansion
high thermal conductivity
toxic mercury
adv of composite over amalgam
better aesthetics
reduced thermal expansion/conductivity
less destructive
biocompatible
chemical bonding with tooth
components of composite
filler particles =
silica, glass, quartz
resin =
BISGMA
camphorquinone =
initiator, light cure activated
low weight dimethacrylate =
TEDGMA
silane coupling agent
name different types of composite
flowable
bulk fill
hyrbid
microfilled
macrofilled
nano
what are clinical disadvantages of composite and how are they minimised
technique/moisture sensitive =
adequate isolation w cotton wools, dam
polymerisation shrinkage =
place in increments
adhesive bonding =
correct etch bond cure technique
indications for resin bonded bridge
favourable occlusion
good quality enamel abutments
large surface area abutments
short span
young
good OH
simplifies RPD
contraindications for resin bonded bridge
unfavourable occlusion
poor OH
long span
parafunction
heavily restored abutments
poor abutment alignment
perio involved
mobility
excess soft tissue loss
contact sports
how do you cement a porcelain bridge
panavia
etch with hydrofluoric acid
dual cure resin cement with 10MDP monomer
how do you cement a metal bridge
sandblast with alumina oxide
GIC cement
how is the surface of porcelain veneer treated in lab to improve adhesion
etched with hydrofluoric acid
silane coupling agent
if using composite resin cement, what material ensures good bond to porcelain
silane coupling agent
chemically, how does silane coupling agent work to ensure good bond to porcelain
chemical bond
silane chemical bond to porcelain, reactive group bonds w composite
silane reacts with silica on porcelain, forming siloxane bond
methacrylate group of silane bonds with composite resin by free radical polymerisation
when is silane coupling agent used in dentistry
fibre posts
ceramic
porcelain crowns
inlays/onlays
LiDiSi
when is a dual cure cement indicated
both light and self needed
where light will not be able to fully penetrate
porcelain/emax crowns onlays
fibre posts
what concerns do pt have about use of amalgam
poor aesthetics
toxic
mercury content
allergy
health risk
side effects
news
how to give pt reassurance on amalgam
may release small amounts of gaseous mercury
remains at safe level
isn’t enough for toxic effects
no evidence it has harmful health effects
extensive research + regulatory approval
use for decades
what aspects of cavity prep ensure
-> caries adequately removed
-> finished restoration margins are cleansable
high speed to full extent, clear ADJ, explore soft/stained
clear contact area, matrix band fully adapted and tight, tightly pack amalgam, anatomical features e.g. undercuts, Cavo-surface 90-120*
describe the mechanism composite bonds to dentine
acid etch 37% phosphoric to remove smear layer
demineralisation and creates microporosities
exposure collagen fibre
rough + increased bonding surface
bonding agent with hydrophilic monomers penetrate collagen network for infiltration for chemical bond
hybrid layer formation where dentine collagen fibres are penetrated by resin monomers, creates mechanical + chemical bond
polymerisation by light cure
creates mechanical interlocking from microporosities by etching
chemical bond from resin monomers
ideal properties of denture base
fracture resistance
high compressive strength, abrasion
biocompatible
dimensionally stable
good aesthetics
unaffected by oral fluids
constituents of PMMA
powder =
PMMA particles, benzoyl peroxide initiator, plasticisers, pigments, co-polymers
liquid =
MMA monomer, inhibitor hydroquinone, co-polymer
give 4 possible faults during PMMA production and explain why they occur
gaseous porosity = air trapped in mixing, not heated equally, fast curing
contraction porosity = too much monomer
granularity = too little monomer
crazing = internal stress due to fast cooling
undercuring = free monomer
adv of CoCr as a denture base
superior compressive strength/hardness
high wear resistance
smaller cross section needed
corrosion resistance
lightweight
disadv of CoCr as denture base
difficult to adjust, add teeth to
cost
aesthetics
what undercuts for SS, CoCr, Au clasps
cocr = 0.25
au = 0.5
ss = 0.75
ideal properties of impression material
dimensionally stable
accurate
ease of handling
biocompatible
adequate working/setting time
tear resistance
elastic recovery on removal
acceptable taste/smell
good flowabiltiy
surface detail reproduction
name 2 non-elastic impression materials
impression compound
impression paste
name 4 elastomers
polyether
addition silicone
condensation silicone
polysulphide
name 2 hydrocolloids
agar
alginate
what are the constituents of alginate
sodium alginate
calcium sulphate
silica, fillers, water
alginate setting reaction
sodium alginate + calcium sulphate
calcium alginate + sodium sulphate
adv of alginate
cheap
acceptable taste/smell
non-irritant
non toxic
ease of use
disadv of alginate
poor tear strength
not 100% elastic recovery
dimensionally unstable
limited detail accuracy
uses of alginate
primary imps
secondary imps
ortho study models
advantages of elastomeric impression
higher dimensional stability
better detail reproduction
reduced water sorption + shrinkage
GI composition
acid/liquid =
poly acrylic acid
base/powder =
calcium fluoroaluminosilicate glass, silica, alumina
describe the setting reaction of GI
dissolution =
H+ ions attack glass, ca/al/f ions released, leaves unreacted silica
gelation =
initial setting due to ca2+ ions crosslinking with poly acrylic acid by chelation with carboxyl group
hardening =
trivalent al increases crosslinking, al polyacrylate formation, takes few days
use of GIC
restorative
cavity liner
stainless steel crown cementation
metal onlay cementation
properties of GIC
fluoride release
ok aesthetics
thermal expansion similar to dentine
biocompatible
RMGI vs GI liner
rmgi better
- on demand set
- increased physical prop e.g. strength, resistance
- better bonding to dentine
why bad idea to use filler material GI as a luting agent
thicker, can stop correct seating
too viscous
increased fracture risk
less flexural strength
luting cement for metal post cure
GIC
luting cement for porcelain veneer
dual cure resin cement
carbon fibre post
dual cure resin cement
ideal properties of luting cement
good adhesion
biocompatible
low solubility
adequate working time
good mech props
why is RMGI not as good luting cement
contains HEMA which is cytotoxic
swells, no bonding with indirect
lower bond strength compared to resin
how do you bond a porcelain veneer
etch with hydrofluoric acid 4-9%
silane coupling agent
dual cure resin cement
how do you bond non-precious metal
surface prep via sandblast with aluminium oxide
GI cement
temp bond components
zinc oxide
eugoenol
resin
fillers
can you bond zirconia??
no
needs sandblasted with aluminium oxide
GIC cement
why are lithium disilicate crowns so strong
high crystalline content
interlocking crystals reinforce glass matrix and block crack propagation
high fracture resistance
400MPa flexural strength
