Chapter 4 J: Composite Resins Flashcards
Why was there an initial rejection of the usage of composite resin in the posterior sectors?
- the effectiveness of the previous materials
- the already known problems of cr
What are the 5 components of CR?
- Organic matrix
- Inorganic particles
- Binding agents
- Polymerisation initiator
- Other: des, radio-opaquers
Bis-GMA polymer is a?
Organic matrix
Silicon dioxide is a?
Inorganic particle that improves physio-chemical properties
Silanes are?
Binding agents
Camphorquinone and lucirin are?
Polymerisation initiators
How do camphorquinone and lucirin work and what’s their disadvantage?
- camphorquinone has a yellow color, activated by the light in the dental chair
- lucirin is transparent and is activated by a different wavelength
- when mixed together they produce a white color but the properties become worse
Problems with CR could be due to the ___ or the ___?
Material or technique
What causes the fatigue of CR?
Due to the repeated impact of the antagonist cusp and thermal changes (expansion and contraction)
What causes wear of the CR? And how is it being improved?
- due to occlusion, brushing, and food (acidic)
- diminished due to improvement of inorganic fillers (hybrids)
What is the most serious problem of CR?
Polymerisation shrinkage
How much of the mass volume shrinks during polymerisation?
2.7-7.1%
Where is most of the shrinkage?
On the surface
Consequences of polymerisation shrinkage are?
- micro-filtration
- gap formation
- cuspal deflection
- enamel cracks and fractures
Gap formation causes?
Hypersensitivity
Pulp necrosis is due to __ not CR?
Bacterial contamination
Degree of conversion is?
The percentage of polymerised resin
Degree of polymerisation
There’s always unpolymerised monomer
3 factors that affect degree of conversion:
- Oxygen (CR touching oxygen can’t polymerise)
- Fillers (microfillers should be polymerised into thinner layers)
- Dyes (the darker —> the harder to polymerise, less light passes through)
OFD
Microfillers improve:
A. Color change
B. Resistance
C. Surface roughness
D. Biocompatibility
C
Self-cured resins tend to?
Darken
Light cured resins tend to?
Clarify
Filling defects are most common in?
Class II
Defects of polymerisation/curing depend on: (3 factors)
- State and quality of light (470nm)
- Obstacles in light’s path (Enamel is more translucent than dentin)
- Application technique: it’s convenient to apply the focus as close as possible and in a perpendicular position (lambert’s law)
Possible reasons for fracture of material
- Insufficient thickness
- Excessive occlusion (bruxists)
- Inadequate support
EII
T or F: CR have a similar thermal conductivity compared to dentin and enamel
T
What causes hypersensitivity with CR?
Movement of fluids within the dentinal tubules
How to avoid bacterial contamination
Removing all carious lesions
Achieving a perfect seal
Composite was used in the anterior sector since the?
60’s
