FIXED PROS - Materials used for Cementation Flashcards
describe what a cement is
a material which sets into a paste through a setting reaction
what is the purpose of dental luting cements? (4)
- to provide a link between fixed prothesis and supporting prepared tooth structure
- provides a seal
- acts as a barrier to bacterial microleakage
- holds tooth and restoration together through mechanical, chemical or mechanochemical.
what is getting cemented to what?
dentine is getting cemented to either: metal, porcelain or composite
describe the steps of cementing.
- isolate and dry prep
- clean and dry restoration
- mix cements
- place layer of cement in restoration
- seat firmly, apply pressure so excess can flow out
give an example of a temporary luting cement.
zinc oxide/eugenol
give 5 examples of permanent luting cements.
- zinc phosphate
- zinc polycarboxylate
- gic
- composite resin
- rmgic
describe zinc phosphate - how it sets, what form it is in and its thickness.
- sets by acid-base reaction
form:
- powder - 90% zinc oxide, 10% magnesium oxide
- liquid - 67% phosphoric acid + Al+ Zn
- water present to control ionisation of acid and rare of setting
film thickness = less than 25 micrometer
describe zinc phosphate - strengths, compressive, tensile, modulus of elasticity
strength - more powder:liquid = stronger
- very strong, very stiff
compressive - 80-110MPa
tensile - 5-7MPa
modulus of elasticity - 13GPa
does zinc phosphate chemically or mechanically bond?
mechanically
when would zinc phosphate be used?
- long term
- posts
- metal inlays, onlays
- metal and all-ceramic crowns
- fixed bridges
- amalgam, composite or GIC cores
describe GIC - how it sets, what it consists of and its compressive strength.
- acid-base reaction
- aluminium fluorosilicate glass
- liquid copolymers of weak polyalkenoic acids
strength = 90-230MPa
do GIC chemically or mechanically bond to the teeth?
chemically :)
describe RMGIC - how does it set, what is the end result of setting.
acid-base reaction
- powder: fluoroaluminosilicate glass
- liquid: polyalkenoic acids with mod pendant methacrylate
result
- metal polyacrylate salt + polymer
what is the setting of RMGIC called?
photochemical initiation of free radical polymerisation
with RMGIC, compare the compressive strength and tensile strength to other cement types.
higher compressive and tensile stregth than Zn phosphate, polycarboxylate and GIC
- lower than composite
describe film thickness of RMGIC
= low
compare RMGIC to GIC
- RMGIC = less soluble - more resistant to water attack
- higher compressive and tensile strength
- both adhesive to enamel and dentine
- both release fluoride
how is RMGIC able to be non-soluble?
the addition of HEMA
- hydrophilic property
- has potential for dimensional change
why is RMGIC a worry in terms of biocompatibility?
- has free monomers present
- toxicity
- HEMA is also a known allergen to irritate the eyes
give an example of a RGMIC. why is it different to other RGMIC’s?
RelyX - prev known as Vitremer
- can set without light activation = a dark cure
- self-adhesive - no need for etch, prime or bond
what do resin composite cements consist of?
BISGMA resin + methacrylate
50-70% glass/silica
how do resin composite cements cure?
photochemical polymerisation = dual cure
5 advantages to resin composite cements
- various shades and opacities
- micromechanical adhesion
- high compressive strength
- resistant to tensile fatigue
- insoluble in oral
1 major disadvantage to resin composite cements
polymerisation shrinkage
what are the uses of resin composites?
aesthetics
ceramic restorations
porcelain restorations
metal alloys
fibre reinforced composites
give 2 examples of what may be components of resin composite materials that are able to bond well with metals.
superbond
contains 4-META - react with metal surface to give good bonds
MDP - panavia active monomer
give 3 advantages to MDP and 3 disadvantages
advantages
- bond well to sandblasted non-precious and tin-plated surface
- good physical properties
- bonding = water resistant
disadvantages
- weak bond to dentine
- technique sensitive
- air inhibited
why may the use of resin composite be contra-indicated if a temporary cement containing eugenol is used prior?
eugenol can inhibit the polymerisation of composite = compromised bond strength and setting
= they are not compatible materials
what is the effect of resin composite having a high filler content?
- increased viscosity
- reduce flow
= increase film thickness
what must be the 4 properties of an ideal luting cement?
- biological
- mechanical
- aesthetic
- working
describe what is meant by ideal biological properties
- biocompatible
- no interaction with oral tissues/fluids
- non-toxic
- low allergic potential
- inhibits caries
- prevents microleakage
what 2 things are to be considered regarding aesthetic?
- will the colour stay stable
- is it radio-opaque
what is considered regarding the working properties of the cement?
- does it have low film thickness
- does it have viscosity
why is low film thickness important for cement? what is the ideal thickness?
- lower = more retention
- gives close relationship between restoration and tooth surface
- ideal thickness = 25micrometer
why is low viscosity important?
- low viscosity
= small particles - more flow of cement
- reduce aggregation of particles
how can micro fractures lead to failure?m
microfracture
- microleakge
- bacterial ingress
- bacterial disease
or micro fracture can lead to catastrophic failure
- entire restoration has come off the tooth
Composite has the most ideal..
working time
solubility
RGMIC has the most ideal..
setting time
solubility
least microleakage
Zinc Phosphate has the most ideal…
thickness
elastic modulus
least pulp irritation
ease to remove excess
retention
