DMS Flashcards
describe how to bond to enamel
37% phophoric acid - etch/conditioner
acid roughens surface of the dry enamel, allowing micrmechanical interlocking of resin filled materials
etching inc the suface energy of the enamel suface- imrpove wettability - allows resin to adapt better
3 types of bond to dentine
mechanical - molecular entanglement
chemical -
vand der Waals (electrostatic interaction)
why do we need DBA
dentine is hydrophillic with low surface energey
DBA is required to inc surface energy
how do DBAs work
inc surface energy of dentine
* allow comp resins to flow and stick to surface
also primer/coupling agent - bifunctional molecule with hydrophilic and hydrophobic end
* hydrophillic end bonds to dentine and hydrophobic end bonds to comp resin
contain spacer groups allowing for flex during bonding and may contain filler particles to inc strength
HEMA, 4 META, MDP
smear layer
adherent layer of organic debris that remain on the dentine surface after tooth prep
0.5-5um thick
removed by dentine conditioners (etch) or penentrated by self-etching primers
adhesion-decalcification concept
interaction of bonding materials with HA
minerals removed from dental hard tissues replaced by resin which, when mineralised mechachinally interlocks in these porosities
* molecular entaglement
cavity liner Vs base
liner <0.5mm
base is thicker
function of cavity liner
3
protect pulp from chemical and thermal stimuli
prevent microleakage (bacteria and endotoxins)
* prevent gaps/voids/air blows
palliative function (reduce symptoms)
indications for when to place a liner
- deep cavities and direct restoratioins
- close to pulp
- pulpitis like symptoms
- small pulp exposures
examples of cavity liners
CaOH
GIC/RMGIC
ZnO
how does CaOH set
chelation reaction between ZnO and butyl glycol disilicylate
CaOH
adv
disadv
adv - bactericidal, forms tertiary dentine, quick set, radiopaque, easy to use
disadv - low compressive strength, unstable and soluble in oral fluids
GIC
adv
bonds to tooth
releases fluoride
ZnO cement examples
5 types; adv and diasdv
ZnPO4 - cheap, easy to use, non adhesive, non cariostatic
Zn polycarboxylate - ZnPO4 but bonds to tooth
ZOE - low strenght, highly soluble
RMZOE - inc comp strenght, lower solubility
EBA ZOE - reduced solubility, inc strength
dental ceramic
solid material compromising of inorgaic compound of metal, non metal and metalloid atoms primariliy held in ionic and covalent bonds
less kaolin and more feldspar than decroative ceramics
feldspar
how are feldspathic ceramics formed
fluxing agents lowers fusion and softening temp of glass
formed from leucite when heated to 1150-1550C
powder melts together to form crown, powder and water mixed and applied to die, heaters in furnance causing sintering
features of conventional felspathic ceramics
4 adv and diadvs
best aesthetics
smooth surface
chemcially stable
high comp strength
high hardness - can damage opposing natural teeth
low tensile strength
low flexural strength
low fracture resistancen
static fatigue
time dependent reduction in strength even in absence of applied load
likely due to hydrolysis of is-O groups within the material over time in acqueous enviroments
function of metal cored ceramic
inc fracture resistance and toughness
how are metal cores bonded
metal oxides
helps eliminate defects/cracks on the porcelain surface, micro mechanical, chemical bonds, stressed skin effects
examples alloys and ideal properties of MCC metal/alloys
6
CoCr, NiCr, AgPd, high gold allow, low gold alloy
high bond strength
high hardness
high elastic modulus
similar thermal expansion coefficient to porcelin
should avoid discolouring porcelain
features of alumina cores
strong
opaque
excellent aesthetics
relatively cheap
what do alumina particles act as
alumina cores
crack stoppers
preventing cracks propagating through material and causing fracture
where can alumina cored MCCs be used
single posterior crown
what type of zirconia is used and descrive the benefit of this type
ytteria stabilised zirconia
normal zirconia mooclinic crystal at room temp - if crack begins when stress crack tip reaches critical level, crystal transforms to monoclinic structure
causes slight expansion of materials adn closes up crack tip
properties of zirconia cores
where can they be used
very hard
strong
tough
best aesthetics
crowns and bridges throughout mouth
properties of zirconia cores
where can they be used
very hard
strong
tough
best aesthetics
crowns and bridges throughout mouth
how are silica containg ceramics luted to teeth
etched with hydrofluroic to produce a retentive suface
ethced surface can be bonded to using a silane coupling agent and bonded to totoh using a bonding agent
how are zirconia cored ceramics luted to teeth
no silica and not affected by acid (inert fitting surface)
strong enough to be self supporting and can be luted with conventional cements
impression material
def
material used to produce an accurate negative replica of the suface and shape of hard and soft oral tissues
mucostatic
displace soft tissues slightly and give an impression of undisplaced mucosa
mucocompressive
materials the record an impression of mucosa under load and give an impression of displaced soft tissue
ideal properties of IM
accuracy
low viscosity
good surface detail
good surface wetting
able to be disinfected
non toxic and non irritant
complete elastic recovery
low settting shrinkage
flexible
low stiffness
ideal elastic behaviour
upon removal
material reaches max amount of strain almost instantly
max strain held during removal
when fully removed, materal instantly return to original strain and returns to pre removal shape
observed elastic behaviour (viscoelastic)
upon and during removal
material strain gradually iinc to just below the max amount of strain
when fully remove materials return to almost the initial strain
results in permanent strain/deformation and a permanent change in dimension
possible problems in imp taking
poor bond to tray (no adhesive)
lack of occlusal detail (inadequate setting)
ledges
drags
air blows
voids
delimitation
seating error
suface inhibition
inconsistent mixing and surface contamination
alginate
material type
irrversible hydrocolloid
elastic
mucostatic
features of alginate
non toxic/non irritant
adquate setting time
easy to use
adequate flow
good elastic recovery
poor tear strength
poor stability
components of alginate
6
sodium alginate
trisodium phophate
calcium phophoate
filler
flavourings
colours
setting reaction of alginate
sodium alginate + calcium sulphate -> calcium alginate + sodium sulphate
polyether e.g.
impregum
impregum
elastomer
polyehter
mucostatic - RIGID when set
addition silicone
polyether
elastic elastomers
mucostatic
how are elastomers formed
polymerisation with cross linking of polymer chains
generating elastic properties
features of impregum
adequate tear resistance
hydrophillic - good if poor moisture control
dimensionally stable
good accuracy
non irritant/toxic
rigid when set - avoid undercuts, hard to remove
long set time
features of addition silicones
good elastic recovery
reduced shrinkage
high dimensional stabilty
accurate
variety of forms - light, medium body PVS
good tear resistance
non irritant/toxic
hydrophobic - dry teeth to avoid air blows
expensive
investment materials
types
Refractory material used to surround the wax pattern during the procedure of fabricating the metallic permanent restoration. Forms the mould into which the alloy is cast after the wax has been eliminated
Gypsum-bonded, phosphate-bonded, silica-bonded
ideal features of investment materials
Expand, porous, strong, smooth surface, chemically stable, easy to remove from cast, easy to use, cheap
components of investment materials
Binder (form coherent mass),
refractory component (withstands high temp, gives expansion)
indications for gypsum bonded investment materials
and types
Create study models and casts,
record position and shape of teeth,
treatment planning,
diagnostic wax up,
prostheses construction
Plaster, stone, improved stone (densite)
indications for gypsum bonded investment materials
and types
Create study models and casts,
record position and shape of teeth,
treatment planning,
diagnostic wax up,
prostheses construction
Plaster, stone, improved stone (densite)
features of gympsum bonded investment materials
Low hardness,
low strength,
very brittle,
porous,
dimensionally adequate,
stable,
adequate for fine detail reproduction,
convenient setting time
setting reaction for gympsum bonded investment material
factors that dec setting time
(CaSO4)2.H2O -> 2CaSO4.2H2O
Increased powder, spatulation, impurities, temperature, chemical additives (potassium sulphate; borax increases setting time)
hydroscopic expansion
Water molecules attracted between crystals by capillary forces, forcing crystals apart.
Increased by low powder/water ratio, increased silica content. higher water temp, longer immersion time
lost wax technique
Sprue, wax pattern, invest, set, wax burnt out leaving space, expansion, molten alloy cast under pressure, trapped gases escape, cooling to room temp, alloy shrinkage, de-vestment
types of luting agents
conventional cements (ZnO based)
GIC
comp resins
self adhesive comp resins
ideal features of luting agents
low viscosity
easy to use
radiopaque
good aesthetics
low/no solubilitiy
biocompatible
cariostatic
good mech properties
indications for comp luting agents
indirect composites
porcelin
metals (precious and non)
thick so light not penetrate fully
indications for dual cure comp luting agents
fibre posts
comp inlays
porcelain inlays
thick so light not penetrate fully
indication for light cure comp luting agents
veneers
indications for GIC luting agents
MCC
metal posts
zirconia crowns
gold
types of metal cooling
consequences of each
2
quenching/fast cooling - more nuclei, more grains, small and fine grains
slow cooling - fewer nuclei, fewer grains, large coarse grains
why are small fine metal grains better
high elastic limit
inc UTS and hardness
dec ductility
dislocations
metal
imperfections/defects in metal lattic
weak points which lead to an alteration of lattice structure and shape
resistable, occur due to slip
accumulate at grain boundaries
impeded dislocation movement
causes
inc elastic limit
inc UTS
hardness
dec ductility and impact resistance
cold working
metal
work hardening/strain hardening
work been on metal/alloy at low temp - below recyrstallisation temp
causes slip - leading to stronger harder metal
e.g. bending, rolling, swaging
cold working effect on mech properties of metal
inc elastic limit, UTS, hardness
dec ductility, impact strength and corroision resistance
strengthening metal by plastic deformation, dislocations interact and create obstructions in cystal lattice, resistance to dislocation formation develops
annealing
metal
heating of metal/alloy so that greater thermal vibration allow migration of atoms and atoms rearrange
stress relief annealing
metal
eliminates internal stresses caused by cold work by allowing atms to rearrange within grains
recrystallisation
occurs when metal/alloy is heated
leads to smaller equi-axed grains reducing EL, UTS, hardness and inc ductility
spoils benefits of cold working but allows for further cold working
alloys
adv
improved mechanical properties
lower melting points
solid solution
common lattice structure containing two metals that are soluble in one another
subsitutional - atomes of 1 metal replace other in crystal lattice; randomed or ordered
interstitial - atoms are markedly different in size and smaller are located in sapces of larger atoms
types of alloy cooling
2
slowly - metal atoms diffuse through lattice, ensuring grain composition is homogenous but large grains
rapidly - prevents atoms diffusion through lattice, causes coring as composition varies throughouot grain (undesirable) - smaller grains impeded dislocation
homogenising annealing
alloys
reverse coring
reheats alloy to allow atoms to diffuse and cause grain composition to become homogenous
composition and function of stainless steel
72% Fe - forms steel
18% Cr - chromium oxide layer inc corroision resistance
7% Ni - improves UTS and corrosion resistance
1.7% Ti - corrosion resistance
0.3% C - forms steel
what makes steel stainless
> 13% Cr
properties of stainless steel
light
#resistance
corrosion resistance
high thermal conductivity
impact strength
abrasion resistance
thin in cross section
can # if overworked, mechanical abrasion, fatigue or weld decay
PMMA setting reaction
free radical addition polymersiation reaction
activation - of initiator to provide free radicals
initiation - free radicals break C=C bonds in monomer and transfer free radical
propagation - growing polymer chain
termination - polymerisation
constiuents of PMMA
powder
* bezyoyl peroxide iniator
* pre polymerised PMMA beads
* co-polymers
* pigments
liquids
* methacrylate monomer
* inhibitor
* co-polymers
properties of PMMA
high softening temperature - but avoid boiling water
high termal conductivity
rigid
aesthetics
adeqaute thermal expansion
good abrasion resistance
low fracture toughness
insoluble in oral fluids
cheap
easy to repair
non irritant
gaseous porosity
monomer boiling
causes gas bubbles in PMMA
contraction porosity
insufficient pressure during processing or too much monomer
polymerisation shrinkage causes voids
constituents of amalgam
liquid mercury
silver, tin, copper, zinc
types of amalgam and which is best
Traditional
Copper-enriched - increased strength and hardness >6%
particle types types
* Lathe-cut
* Spherical (less mercury, higher tensile and early compressive strengths, less sensitive to condensation, easier to carve)
setting reaction for amalgam
Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
Copper enriched:AgSnCu + Hg -> AgSnCu + gamma-1 + Cu6Sn5
Weak strength, poor corrosion resistance.
Copper-enriched removes gamma-2 phase, making it stronger and causing less creep
Silver copper is mixed with gamma-2 to make it stronger and less corrosive.
Other methods to reduce corrosion includes polishing margins and avoiding galvanic cells
check
setting reaction for amalgam
Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
powder+liquids -> unreacted particles (gamma)+ gamma1 + gamma2
Copper enriched:AgSnCu + Hg -> AgSnCu + gamma-1 + Cu6Sn5
Gamma2 =Weak strength, poor corrosion resistance.
Copper-enriched removes gamma-2 phase, making it stronger and causing less creep
Silver copper is mixed with gamma-2 to make it stronger and less corrosive.
Other methods to reduce corrosion includes polishing margins and avoiding galvanic cells
check
indications and contraindications for amalgam
Moderate and large-sized cavities in posterior teeth, ability to seat matrix and wedges around tooth, moisture control not brilliant
Anterior teeth, aesthetics paramount, mercury sensitivity, inability to produce retentive cavity, pregnant, child
advantages and disadvantages for amalgam
User-friendly, strong, durable, good LT clinical performance, radiopaque, high elastic modulus, high
hardness, cheap
Poor aesthetics, no bond to tooth, high thermal diffusivity, destructive prep, marginal breakdown, tooth discolouration, ditching (LT corrosion at margin), lichenoid reactions, amalgam tattoo
why are amalgams now zinc free
Zinc is a scavenger during production - preferentially oxidises and slag formed/removed.
Materials are now zinc-free due to the reaction of zinc with saliva/blood: Zn + H2O -> ZnO + H2
* Bubbles of hydrogen gas is formed within amalgam.
* Pressure build-up causes expansion. Downward pressure causes pulpal pain. Upward pressure causes the restoration to sit proud of the surface/protrude
3 types of composite resin
Conventional,
microfine,
hybrid (best - compromise)
components of composite
5
Filler particles - improve mechanical properties, aesthetics, abrasion resistance, reduce PCS. Glass silica/quartz
Resin - bifunctional molecules that undergo free radical addition polymerisation - bis-GMA
Light activator - photo-active atom catalyst that initiates polymerisation of resins when activated by blue light (430-490nm) - camphorquinone
Low weight dimethacrylates - adjust viscosity and reactivity of resin monomer. TEGDMA
Silane coupling agent - bifunctional molecule binding resin and filler particles
indications and contraindications for composite
Anterior teeth, where aesthetics important, cores, veneers, indirect inlays/onlays, luting agents, class III, IV, V restorations,
Moisture control impossible, limited tooth structure remaining, posterior teeth with limited finances
advantages and disadvantages of composite
Good aesthetics, conservative prep, support for remaining tooth tissue, good bond to tooth, low thermal conductivity, good LT clinical performance, no galvanism
PCS (causing micro leakage, etc.), marginal integrity, post-op sensitivity (due to PCS, contraction, insufficient cure - prevent by <2mm increments), low fracture toughness, high elastic deformation, technique sensitive, hydrolytic breakdown, limited depth of cure, high thermal expansion coefficient
components of GIC
Polyacrylic acid,
tartaric acid,
silica,
alumina,
calcium fluoride
alumnium fluoride
setting reaction for GIC
MO,SiO2 + H2A -> MA + SiO2 + H2O
Dissolution. Acid added to solution; hydrogen ions interact and attack the glass surface, causing glass ions to be released/leached out. This leaves silica gel around unreacted glass
Gelation. Initial set. Calcium ions crosslink with the polyacid by chelation with the carboxyl groups, forming calcium polyacrylate. Calcium ions are bivalent, so can react with two molecules
Hardening. Trivalent aluminium ions ensure good crosslinking with an increase in strength - takes up to 7 days
indications and contraindications for GIC
Temporary restoration, luting agent, shallow cervical restorations, where moisture control difficult, dressing, FS, ortho cement, cavity base/liner
Definitive restoration of large posterior cavities, where composite can be placed
adv and disadv of GIC
Relatively good aesthetics, fluoride release/reservoir, stable strong bond to enamel and dentine, low micro leakage, good thermal properties, no setting contraction
Brittle, poor wear resistance, initial moisture susceptibility, poor handling characteristic s, not excellent aesthetics, susceptible to acid attack and drying out over time 8. Ion exchange with calcium in enamel and dentine and hydrogen bonding with collagen in dentine
how does GIC bond to tooth tissue
ion exchange with calcium in enamel and dentine and hydrogen bonding with collagen in dentine
CHELATION
components for RMGIC
Fluoro-alumino-silicate glass, barium glass, pigments
poly acrylic acid, HEMA, tartaric acid, camphorquinone, H2O
types of RMGIC
Dual cure - acid base, light activation
Tri cure - acid base, light activation, redox reaction
RMGIC vs GIC
advantages - Better aesthetics, better handling properties, better strength
disadv - PCS, exothermic setting reaction, reduced strength if unreacted monomer (if not light cured)
RMGIC vs Composite
adv - Easier to use, less moisture sensitive, fluoride reservoir
disadv - Reduced strength, worse aesthetics
