Intro to composite resins Flashcards
Components of composite resin
- Resin matrix - BisGMA
- Inorganic filler particles - barium/borosilicate/strontium glass
- coupling agents - silane
- initiators
3 features of filler particles which benefit the restoration
- increase strength
- decrease linear coefficient of thermal expansion
- offer radiopacity
Why is post op sensitivity common in composite resin restos?
due to polymerization shrinkage which causes the resto to pull at the margins and cause leakage
Marginal relationship of amalgam-enamel = _____
Marginal relationship of composite-enamel = ____
Marginal relationship of amalgam-enamel = BUTT-TYPE JOINT
Marginal relationship of composite-enamel = ADHESIVE INTERFACE
What is a butt type joint?
two pieces of material are joined simply by placing their ends together. ie. no adhesion
As compared to amalgam preps, bonding of composite to enamel allows for:
- more conservative prep design
- less reliance on mechanical retention
- less removal of unsupported enamel
Simplified 3 main steps in composite restos:
- etch
- primer/bond
- composite
Two step total etch procedure:
- Etchant applied to preparation (15 sec enamel, 10 sec dentin)
- etchant is washed off with water for 10 seconds and lightly dried (do not dessicate dentin)
- Bonding agent applied to prep with microbrush (light cured for 10 seconds)
- Composite is incrementally placed (20 second light cure per increment)
Synonym of etchant:
conditioner
Following etching, what should the appearance of enamel and dentin be?
- enamel: white and chalky
- dentin: no change
What is generated on the surface of enamel by etchant?
microporosities. These increase SA for adhesion and increases surface energy to enhance penetration of bond into enamel surface
Conditioned dentin results in:
-removal of SMEAR LAYER, resulting in enhanced bond between tooth and composite resin
what is the smear layer?
- thin layer on dentin surface that has received instrumentation
- comprised of loosely bound debris, collagen and HA crystals
Major difference between total etch and self etch
In self etch, the smear layer is not removed and a hybrid layer is created when material is added to the tooth.
-Also, total etch uses higher acid content than self-etch
How many generations of dental adhesive exist?
8 gens
dental adhesive is classified based on 4 things:
- generation (8)
- Mode of application
- Number of clinical steps
- Etching pattern (total vs self etch)
How many clinical steps are involved in 3rd, 5th and 8th generation adhesive?
3rd - 3 (E+P+B)
5th - 2 (E+PB)
8th - 1 (EPB)
Bond enters microporisities of enamel and create long projections called __ ___
resin tags
RDT stands for:
remaining dentin thickness
What relationship is there with bond strength and RDT?
As RDT decreases, the concentration of dentinal tubules increases and so does peritubular dentin. These contain higher organic content (therefore more H2O) and thus bonding to dentin becomes increasingly unreliable.
Bond strength to ____ dentin is stronger than with ___ dentin
Bond strength to INTERTUBULAR dentin is stronger than with PERITUBULAR dentin
3 things that happen as RDT decreases:
- concentration of dentinal tubules increases
- peritubular dentin:intertubular dentin increases
- Resulting bond decreases
Goals of adhesive/bond
- seal enamel-composite interface
- increase retention
- decrease leakage at enamel-composite interface
4 types of composite resins
- flowable
- microfill
- macrofill
- hybrid
Filler content in the 4 types of composite resins
- flowable - lowest
- Microfill - low
- Macrofill - high
- a. mcrohybrid - high filler loading
