Comparison of Restorative Materials Flashcards
What ways can resin composites be cured
Chemically Cured
Light Cured
How are chemically cured resin composites often mixed
two paste ting
Why might mixing be difficult for two paste resin composites
The pastes are very viscous
What might the incorporation of bubbles into the mixing pastes cause
You will compromise the mechanical properties as the bubbles act as a point where the stresses will concentrate and can cause cracks
What are some disadvantages of using a two paste resin composite system
- Mixing is difficult
- May incorporate air bubbles
- Discolouration with time
- Homogenous mix is not easy to get - due to viscosity
- Degree and time of polymerisation varies throughout the mass
What will be affected by the disadvantages of two paste resin composites
Youngs modulus and strength
What are the advantages of using one paste light cured resin composites
- Minimal porosity
- Less discolouration
- Virtually command set
- Rapid polymerisation
What are some of the disadvantages of one paste light cured resin composites
- Light sensitive during application
- Thin inhibited layer -due to oxygen in air
- Limited depth of cure
- Cure in increments
- Retina damage from curing light
What can be used to prevent the thin inhibited top layer on resin composites
Cellulose strip on top
What is the machine called to mix amalgams
Amalgamators
Why are manual mixing methods for amalgams not often used anymore
A lot more exposure to mercury vapour, but in capsules the mercury and alloy are less exposed and you also get a better mix off
What are the oil based acid base cements also called and give examples
Phenolate bonded cements
e.g. Zinc Oxide Eugenol (ZOE) and Calcium Hydroxide
Describe the features of the mixing for phenolate bonded acid base cements
Easy to mix,
Long working tie
Quick set in the mouth due to temperature and presence of moisture in oral cavity
Why are phenolate bonded acid base cements quick to set in the mouth
Due to temperature and presence of moisture in oral cavity
What are some types of the polycarboxylate bonded acid base cements
Zinc Polycarboxylate cements
Glass Ionomer cements
How do zinc phosphate acid base cements need to be mixed
On a cooled slab
Small increments
Over a large area
Why do zinc phosphate acid base cements need to be mixed on a cooled slab and over a large area
The reaction is very exothermic so you can slow the setting and prolong the working time
Large area to allow better mixing and dissipate any heat into the cool slab
How would decreasing powder/liquid ratio of zinc phosphate acid base cements affect the properties of the cement
Decreased compressive strength
Increased solubility
Increased initial acidity
Increased setting time
How would increasing the rate of powder incorporation of zinc phosphate acid base cements affect the properties of the cement
Decreased compressive strength
Increased solubility
Increased initial acidity
Decreased Setting time
How would increasing the mixing temperature of zinc phosphate acid base cements affect the properties of the cement
Decreased compressive strength
Increased solubility
Increased Initial acidity
Decreased setting time
How would water contamination of zinc phosphate acid base cements affect the properties of the cement
Decreased compressive strength
Increased solubility
Increased initial acidity
Setting time can go up or down depending on when water is added
List the acid base cements from most acidic to least acidic
Zinc phosphate cement Glass ionomer cement Zinc polycarboxylate cement ZOE cement Calcium hydroxide cement
AY BAWS CAN I HABE DE NOTE PLZ
Over the first few minutes of setting the cements their pH will increase
In terms of thermal conductivity which cement is similar to dentin
Zinc oxide eugenol
In terms of thermal diffusivity what cement is similar to dentin
Glass ionomer cements
List Amalgam, zinc phosphate, ZOE, GIC and composite from most to least thermally conductive
Amalgam Composite Zinc phosphate GIC ZOE
List Amalgam, zinc phosphate, ZOE, GIC and composite from most to least thermally diffusive
Amalgam Composite ZOE Zinc phosphate GIC
What cement has similar thermal expansion properties to the tooth
GICs
List Amalgam, composites, GICs and ZOE from highest thermal expansion to lowest
Composites
ZOE
Amalgam
GIC
List Calcium hydroxide, composite, zinc phosphate, amalgam, ZOE, zinc polycarboxylate and glass ionomer from highest to lowest compressive strength
Amalgam (stronger than enamel and dentin)
Composite (sometimes stronger than enamel and dentin)
Glass Ionomer
Zinc Phosphate
Zinc Polycarboxylate
ZOE
Calcium hydroxide
What is the compressive strength of enamel and dentin
Enamel - 350 MPa
Dentin - 270 MPa
List Calcium hydroxide, composite, zinc phosphate, amalgam, ZOE, zinc polycarboxylate and glass ionomer from highest to lowest tensile strength
Amalgam Composite Zinc polycarboxylate Zinc phosphate Glass ionomer Zinc oxide eugenol Calcium hydroxide
What are the tensile strengths of enamel and dentin
enamel - 10MPa
dentin - 40 MPa
How do composites and amalgams compare in terms of aesthetics
Composites are much better but the colour matched shades can discolour
Amalgams are grey and metallic and can turn black if tarnished as sulphides form
How long to amalgam and composite fillings last
Amalgam = 12 years Composites = 5-7 years
What are the biocompatibility issues of amalgams
They contain mercury and are potentially toxic
Rare cases of allergy
What are the biocompatibility issues of composites
Composites can leach components that are potential carcinogens
How do amalgams and composites compare in terms of wear
Composites wear more than amalgam
What types of wear are there
Abrasive
Fatigue
Corrosive
Where does wear occur to the highest extent
at the cusp contact points
How do amalgams and composites compare in terms of shrinkage
Amalgams shrink less - 0.02-0.2%
Composites undergo polymerisation shrinkage - 2-3% leads to marginal leakage
Which direction does shrinkage occur in self cure composites
Towards the cavity walls
Which direction does shrinkage occur in bulk light cure composites
Towards the lateral walls but away from the base of the cavity so yeh not good
How can be minimise the shrinkage problems of bulk light cure composites
Incremental light curing
Why are composites more likely to form secondary caries
Due to the shrinkage factor and bruh composites have quite a large risk of these.
How do composites and amalgams compare in terms of cavity preparation
Composites require less removal of tooth structure
Amalgam requires more removal to give adequate retention (undercuts)
What should be the size of the increments of composites
2mm.
How long does it take to place composite fillings compared to amalgams
20 mins for amalgam
30 for composite due to increments, etching, bonding etc
How do composites and amalgams compare in terms of pulp protection
- Composites are thermal insulators but can cause chemical irritation due to leakage
- Amalgams conduct heat so can cause reversible pulp damage without clinical symptoms
Compare ZOE and CH as cavity liners
- Both long working time, sharp set in mouth
- Water accelerates set of both cements
- ZOE stronger and less soluble than CH
- ZOE has a calming effect on inflamed tissue
- CH is alkaline - antibacterial
- CH stimulates secondary dentin formation
- The eugenol in ZOE inhibits curing of composites
List these filling materials from highest to lowest in terms of fluoride release : Resin-modified glass ionomer, Compomers, Glass ionomers and Composites
Glass ionomer
Resin-modified glass ionomer
Compomers
Composites
List these filling materials from highest to lowest in terms of strength of mechanical properties
Composites
Compomers
Resin-modified glass ionomers
Glass ionomers
The table on the last page of this lecture is quality if you want to see some comparisons
Honestly should probably have a look at it
