Dental Materials Flashcards
Soncini 2007 : RCT of Amalgam vs Resin
- Results?
267 children randomized
- 5 years follow up
- Differences in longevity not statistically significant
- Compomer/resin was replaced significanly more frequently due to recurrent caries and required 7x as many repairs
Meta analysis of SSCs vs amalgams in primary teeth (Randall)
Failure rates of SSC 1.9 to 30%
failure rates of amalgams: 12-90%
1.5 to 2 failed amalgams for each failed SSC
**Cochrane Review no studies met inclusion criteria however, lean toward SSC placement
Function of filler
- Reduce polymerization shrinkage
- decrease coefficient of thermal expansion
- increase hardness (compressive strength)
- improve wear
- control transulcency
- need about 70% or more filler for the wear you need
Polymerization shrinkage:
Incremental filling reduces stress
- Bond strengths of >18 MPa needed to overcome polymerization shrinkage stress
- Less material, less shrinkage, therefore a base (GIC/RMGIC) reduces shrinkage stress
- Resins vary in polymerization shrinkage (2-6%) lower filled resins shrinkage more
Flowable resin composites
Lower filler volumes 45-70% same partical size as hybride, micro, minifilled composites, decreased viscosity/stiffness
- increased polymerization shrinkage, decreased viscosity, decreased wear resistance, decreased strength
- bond strength 8-10MPa
- most contain fluoride; effective release
- radiopacity is an issue
Glass Ionomer cements: advantages
- bond to dentin and enamel through chelation; no bonding agent required
- leaches F
- bio compatible w/connective tissue
- thermal expansion similar to enamel and dentin
- low setting shrinkage
- bond strength of .5-4 MPa to carious and on carious dentin
GIC disadvantages
- Technique sensitive- moisture imbibition/dessication
- bond sterngth less than that of composite/dentin bonding
Smear Layer
- about 1-5 microns thick; dentin chips, debris, partially denatured collagen
- partly porous, but dramatically reduces fluid flow from tubules
- weak attachment to dentin (6MPa)
- extends several microns into tubules
- permeability increased by primers
Dentinal tubule structure and its effects on bond strength
- Tubule diameter increases w/depth toward the pulp
- superficial dentin: relatively few tubules per surface area, less area for lateral diffusion of bonding agent
- bond strength decreases with progressive depth from DEJ because water in dentinal fluid competes with collagen for hydrophilic monomers; also, fluid dilutes concentration of monomer
Dentin sclerosis and effect on bond strength
- Sclerotic, caries affected dentin is denser in mineral content
- Reduced penetration of bonding agent
- Caries -affected dentin: additional/extended acid etching can increase tensile bond strength
Primer : what does it do? effect on dentin/collagen?
- Provides micro-mechanical retention to modified smear layer and dentin
- Primer wets/penetrates collagen meshwork, raises it to nearly original level, creates “hybrid layer” increases wetability of dentin
Adhesive :
Unfilled resin adhesive bonds w/primer and composite restorative material placed over it
What is the gold standard of etch to adhesive?
Two bottle etch and rinse system : etch-rinse-prime-bond is the gold standard for bonding agents.
- any simplification in procedure results in loss of bonding effectiveness
- Self etch products modify but do not remove the smear layer
Bonding in primary teeth
- Smear layer is removed more easily
- 25-30% thicker hybrid layer compared to permanent teeth
- Greater reactivity of primary dentin to acid conditioning; deeper demineralized zone may preclude complete penetration of primer and adhesive
- less time required for acid conditioning of primary teeth
- Microtensile bond strength of adhesive systems similar in permanent and primary dentin
Where are implants ‘best’ placed in a growing child?
Anterior mandible
