direct restorative materials Flashcards
what is a composite
2 or more materials combined
phases of composites
3 phases of composites:
Organic matrix – plastic monomer that polymerises –BisGMA normally
Inorganic filler – particles spread in the matrix that reinforce it
Can be macrofillers (poor finish due to big bumps),
hybrid (good for mechanical properties),
or microfillers (can be polished so very smooth but are weaker)
Coupling agent– promotes adhesion between filler and matrix – e.g. silane
composite pros and cons
Composite pros:
Aesthetics
Less tooth tissues removed compared to amalgam
Command set if light cured
Composite cons:
Uncured resin can leach out
Long time to place since incremental curing needed
Polymerisation shrinkage can increase risk of secondary caries
Doesn’t adhere intrinsically to enamel and dentine
Bonding of Composites
Enamel bonding -> wetting of enamel is impossible so we need to etch (enamel surface tension is lower).
(wetting allows thin and uniform layer)
30-50% phosphoric acid opens prism areas and then resin can flow inside and form resin tags (this allows chemical bonding!)
Dentine bonding -> you need 3 things in this order to bond:
Conditioner – acid that clears the smear layer (but opens tubules)
Coupling primer – acts as an adhesive
Sealer – bond that seals dentine tubules
Smear layer = denatured collagen and debris contaminated with bacteria
what is a cavity lining material
= an intermediate restorative material that lines a cavity. It is applied before the restoration and is permanent.
types of cavity lining materials
Cavity varnish 2-5μm – seals dentine, decreases microleakage, no strengthening purposes
Cavity liner <0.5mm– seals dentine, promotes pulp health, antibacterial action
Cavity base >0.75mm – thick mix placed in bulk, acts as dentine replacement, minimises need for lots of resto material, insulator, high strength
how do cavity lining materials set
These set by acid-base cement setting -> this reaction is never complete.
factors affecting set of cavity lining materials
Factors affecting set:
Particle size
Smaller the particle size, the greater the specific surface area and the faster the setting reaction.
Powder/liquid ratio
A higher powder content will give a faster set
Temperature
Increasing the temperature will increase the setting rate
The setting reaction is exothermic so it may further accelerate set
Moisture
options for cavity lining materials/ cements
- zinc phosphate cements
- zinc oxide eugenol cements ZOE
- zinc oxide non eugonel cements
- zinc polycarboxylate cements
- calcium hydroxide cements CaOH
- ethoxy benzoic acid
from QB->
1. Water-based: Zinc phosphate, zinc polycarboxylate, GIC, RMGIC
2. Resin-based: Composites, compomers, RMGIC, Panavia
3. Temporary: Zinc oxide eugenol (ZOE)
cavity lining materials/ cements
zinc phosphate cements
setting reaction | properties | uses
ZnO and phosphoric acid, p+l, exothermic setting reaction
Good strength
Quick hardening
Cheap
Good thermal insulator
Low initial pH so pulpal irritation
Brittle
No chemical adhesion
Used for luting cement for restos and ortho, thermal insulator, temporary resto material
cavity lining materials/ cements
Zinc oxide eugenol cements
setting reaction | properties | uses
ZnO and eugenol, 2 paste
Fast set
Easy to mix
Not irritant
Good thermal insulator and protects pulp from chemical irritation
Low strengths
Potential allergy to eugenol
Can’t be used under composites since it inhibits vinyl polymerisation
Used as thermal insulating base ( protects tooth from thermal sensitivity)
cavity lining materials/ cements
Zinc polycarboxylate cements
setting reaction | properties | uses
ZnO and polyacrylic acid
Low irritancy
Good chemical adhesion
Gains strength quickly
Lower compressive strength
Short working time
Used for luting and thermal insulating bases, ortho band luting
cavity lining materials/ cements
Calcium hydroxide cements
setting reaction | properties | uses
2 paste salicylate ester and Ca(OH)2
Alkaline so neutralises acid materials
Antibacterial
Easy handling and mixing
Good seal
Low strength
Weakened by moisture
Used for cavity lining, thermal insulating and in endo
ethoxy benzoic acid vs ZOE as a cavitity lining material
similar to ZOE but poor handling characteristics
cavity lining materials/ cements
when would zinc oxide non-eugonal cements be used
for pts that are allergic to eugonal
euogenol = clove oil
Composition and setting reaction of GICs
Composition
Powder – ionomer glass
Liquid – polyacrylic acid in aqueous solution
Setting reaction:
Dissolution – H+ ions from PAA attack glass and free other ions
Gelation and hardening – ions cause polymer chain entanglement
Final maturation – increase in strength
pros, cons and uses of GICs
GIC pros:
Fluoride release
No free monomer
Aesthetics
No shrinkage
GIC cons:
Weaker than composites/amalgam
Poor wear resistance at early stage
GICs are used for anterior restorations, cavity linings, luting cements, fissure sealants
list the modified GICs
GICs can be modified to make cermets, RMGIC, giomers, PAMCs:
properties of cerments, giomers, pamc
Cermets = more abrasion resistant and less brittle but worse F release and bond strength
Giomers = composite resin + glass ionomer particles as filler – still has fluoride release with the better properties of composites
PAMC (compomer)= polyacid modified composites, inferior mechanical properties to composite and undergoes shrinkage, but good handling properties
pros, cons, use of RMGICs
Pros -> good compressive strength, longer working time, less brittle
Cons -> shrinkage, unpolymerized HEMA leaching, swell in water after curing
RMGICs used for cavity linings, luting cements, restorative for primary teeth
amalgam compition and mechanical properties
Amalgams = when mercury is mixed with another metal
Amalgams can be low copper (3%) or high copper (20%)
Mechanical properties -> good compressive strength, wear resistance, mercury content must be less than 50% for strength to be good
disadvantages of amalgams
Non-adhesive (mechanical retention only)
Conducts heat and electricity (galvanic effects)
Poor aesthetics
Weak in thin sections
Marginal leakage can occur
Rule for UK – no amalgam for under 15s
compare GIC and RMGIC
RMGIC
has better aesthetics
has ability to use bonding agent
has better wear, polish, strength
BUT RMGIC shrinks and has a medium thermal expansion coefficient
whereas GIC TEC matches the tooth
both release fluoride
compare compomers and composite
all have good aesthetics and require bonding agents
they all have minimal fluoride release
composites can have macrofillers (poor finish due to big bumps), hybrid (good for mechanical properties), or microfillers (can be polished so very smooth but are weaker)
compomers are just modified GICs
polyacid modified composites, inferior mechanical properties to composite and undergoes shrinkage, but good handling properties
compare composite vs amalgam
composites have better aesthetics and don’t soley rely on mechanical retention ˙.˙ bonding agents available
but amalgams have better wear, polish and stregth
they also shrink less
but have contraindications in children, pregnant etc ˙.˙ mercury
