DMS Flashcards
what are some patient concerns about amalgam?
- aesthetics
- discolouration of tooth
- mercury poisoning
- metal allergy
- environmental impact
- pregnancy concerns
what reassurance can you give pt about amalgam use?
- has been used for many years
- v effective in purpose
- metal compound so mercury not the same as in elemental state
- mercury in very small amounts
what aspects of cavity prep allow for i) removal of all caries
ii)ensure restoration is fully cleansable
i) remove enamel to identify extent of lesion at adj and smooth enamel margins
progressively remove caries at adj and then circumferentially deeper. only then remove deep caries overlying pulp chamber.
ii) no overhangs, smooth margins, smooth occlusal surface
describe the mechanism by which composite bonds to dentine
acid etch: dentine conditioner.
- removal of smear layer
- decalcifies dentine
- exposes collagen network
dentine bonding agent: bivalent molecule. hydrophilic end bonds to dentine through penetration and micromechanical retention into dentine tubules and collagen. hydrophobic end bonds to resin in adhesive
What are the ideal properties of a denture base? (6)
dimensionally accurate high softening temperature high hardness biocompatible high thermal conductivity easy/inexpensive to make and repair
What are the constituents of PMMA?
powder -> benzoyl peroxide, PMMA particles, plasticisers, pigments, co-polymer
liquid -> methacrylate monomer, hydroquinone, co-polymer
benzoyl = initiator hydroquinone = inhibitor
Give 4 possible faults during production of acrylic baseplate and explain why they occur?
contraction porosity - too much monomer
gaseous porosity - monomer boiling in thicker areas
granularity - too little monomer
crazing- cooling too quickly, internal stress caused
4 advantages of CoCr as a denture baseplate
high softening temperature
high thermal conductivity
high youngs modulus YM -rigid
radiopaque
Give 4 disadvantages of CoCr as a denture baseplate
aesthetics
costly to make
difficult to modify
difficult to make
What undercuts are required for SS, Gold and CoCr clasps?
- 75 SS
- 5 gold
- 25 CoCr
What are the ideal properties of an impression material? (6)
no dimensional change high wettability high surface reproduction high tear strength good operator convenience acceptable taste and smell biocompatible compatible with lab materials/ gypsum
Name 2 non elastic impression materials
impression compound
impression paste
Give 4 types and names of elastomers
- polyether - impregum
- addition silicones - PVS
- condensation silicones - lab putty
- polysulfide -
Name 2 hydrocolloids
agar
alginate
Constituents of alginate
setting reaction
sodium alginate, calcium sulphate, trisodium phosphate
sodium alginate + calcium sulphate -> sodium sulphate + calcium alginate
2 pros and 2 cons alginate
:)
cheap
user friendly
high elasticity
:(
poor tear strength
poor storage - imbibition and syneresis
2 uses alginate
primary imps dentures
imps for study models
wash impression
3 advantages elastomeric impression materials over alginate
better tear strength
better accuracy
better surface reproduction
better storage - does not dry out
Pros of using RMGI as liner over GI liner
on demand set
higher mechanical strength
lower solubility
What is different about GI used for restorations over GI used as luting cement
shorter working time in filling GI
Luting cement used for metal post core
GI luting cement
Luting cement used for porcelain veneer
resin luting cement w/ silane coupling agent
Luting cement used for carbon fibre post
DUAL CURE comp resin cement
Ideal properties of luting cements (6)
high tensile strength high compressive strength easy to use thickness <25 microns RADIOPAQUE low solubility CARIOSTATIC
Negative of RMGI as luting cement
HEMA absorbs water + swells
cytotoxic to pulp
Process of bonding porcelain veneer?
etch with hydrofluoric acid, then use silane coupling agent to allow c=c bonds with comp resin cement
hydrophobic c=c from c-oh hydrophilic
Process of bonding non-precious metal?
sandblast with aluminium oxide
use MDP or 4META
Components of temp bond
ZOE based
base - zinc oxide, starch, mineral oil
accelator - EBA, eugenol, carnuba wax
How is zirconia retained?
micromechanical retention
cannot be etched therefore cannot be chemically bonded
Pros of lithium disilicate crowns
crystals stop crack propagation
high flexural strength
used for posterior crowns
Why apply vaseline on top of GI restorations
after hardening, fresh cement is highly prone to crazing and cracking due to drying of loose water particles.
