DMS Flashcards
What are the constituents of stainless steel and their proportions
- Iron – 72%
- Chromium – 18%
- Nickel – 8%
- Titanium – 1.7%
- Carbon – 0.3%
What is work hardening
- Work done at temperatures below recrystallisation temperature (such as bending, swaging or rolling)
- This causes slip so any dislocations in the lattice collect at grain boundaries
- This results in a stronger, and harder material
what is sintering (in regards to fabrication of a ceramic crown)
when the particles melt and fuse together as one mass
define springiness
the ability to undergo large deflections without permanent deformation
what are some disadvantages of self-cure PMMA
- water absorption can cause expansion
- poorer mechanical properties
- unreacted monomer can act as irritant
- poorer colour stability
what are some ideal properties of acrylic denture base
-high softening temp
- unaffected by oral fluids
- radiopaque
- non toxic, non irritant
- low density
- high strength, stiffness, hardness, toughness
why is mould liner used in fabrication of an acrylic denture
to prevent the penetration and adhesion of resin into the surface of the plaster mould
- it is usually a solution of sodium alginate
what is gaseous porosity and why does it happen?
when the temp exceeds boiling temp of PMMA before the polymerisation process is complete
–> should be carried out slowly to avoid
how is porcelain prepared in the lab to improve bonding
etched to hydrofluoric acid
what bonds porcelain to composite resin luting cement?
silane coupling agent
how does silane coupling agent act chemically
- one end forms strong bonds b/w the oxide groups on the porcelain
- the other end has C=C that bonds to the composite resin luting agent
when would youse use dual cured composite as a luting agent
when bonding to a metal, as light will not penetrate
i.e. when cementing most crowns, bridges, posts…
why would you do to a metal in a lab to prepare?
sandblast the metal surface
what chemical agent is used to bond metal?
MDP and 4-META
what metal can be use for an acid-etch retained bridge
non precious metal alloys e.g. CoCr, NiCr
What are the two main differences in composition between decorative and dental ceramic
Decorative ceramics contain Kaolin - makes it opaque in appearance
Dental ceramics need to be translucent so Kaolin is removed and feldspar and silica replace it
dental ceramics are glasses
Explain what the following terms mean with regard to optical properties of the materials
a. Translucency
b. Opalescence
Translucency is the relative amount of light transmission or diffuse reflection from a substrate surface through a turbid medium
The opalescence of dental materials is defined as the difference in chroma between the reflected and transmitted colours.
how does an alumina reinforced feldspathic core increase the strength of a ceramic crown
the alumina particles act as crack stoppers preventing cracks propagating through the material and causing fracture
what is a problem with alumina cored crowns
lacks flexural strength
what are the strongest crown types
monolithic block crowns - they are milled from a single block of material
key comparison between crowns with layered and monolithic block crowns
layered =better aesthetics BUT more likely to chip due to stresses between core and crown
For the same material a milled crown will be stronger than a built up or pressed crown. WHY?
the block will have been subjected to the ideal heat treatments to maximise tits properties and all blocks will be consistent
what are some problems with zirconia cored crowns
expensive equipment required
Potential for veneering porcelain to debond from core
what types of crowns are typically used in posterior teeth
Monolithic Zirconia
