Week 7- fundamental concepts of enamel and dentin adhesion Flashcards
fundamental mechanism of enamel resin adhesion
formation of resin microtags in enamel surface
enamel adhesion made possible by
acid etch which makes enamel surface irregular
purpose of acid etch
makes enamel surface irregular -> resin penetrates surface -> polymerize and are then attached to enamel
the state in which two surfaces are held together by interfacial forces that consist of valence forces, interlocking forces, or both
adhesion
4 mechanisms of adhesion
mechanical adsorption diffusion electrostatic (MADE)
mechanical adhesion
interlocking of adhesive with irregularities in surface of substrate or adherend (enamel?)
absorption adhesion
chemical bonding between adhesive and adherend forces
primary (ionic, covalent)
secondary (H bonds)
valence forces
diffusion adhesion
between mobile molecules such as adhesion of two polymers through diffusion of polymer chain ends across interface
electrostatic adhesion
electrical double layer at interface of a metal with a polymer that is part of total bonding mechanism
4 types of dental adhesion
mechanical
adsorption
diffusion
combination of the above
microtags
small tags form across end of each rod
macrotags
tags form between enamel rods
what differentiates GI from resin based composite materials?
do not need to etch enamel/dentin with phosphoric acid gel
“self adhesive”
mechanical dental adhesion
penetration of resin and formation of resin rags with tooth structure
adsorption dental adhesion
chemical bonding to inorganic component (HA) or organic components (collagen I) of tooth structure
diffusion dental adhesion
precipitation of substances on tooth surface to which resin monomers can bond chemically or mechanically
what is critical for good adhesion?
close contact between adhesive and substrate (enamel or dentin)
adhesive failure
- cohesive failure in substrate
- cohesive failure within adhesive
- adhesive failure @ interface of substrate and adhesive
adhesive restoration technique uses
17 different things bonding, sealing, recontouring of teeth, improve retention for PftM or metallic crowns bond all ceramic restorations cavity restorations (class I-VI) bond ortho brackets & perio splints desensitize exposed root surfaces repair existing restorations
morphological patterns of acid etching - type I
dissolution of prism cores but keep prism peripheries
morphological patterns of acid etching - type II
dissolution of prism peripheries but keep cores
morphological patterns of acid etching - type III
not related to prism morphology
phosphoric acid concentration for etching
30-40%
etching time
15-60 seconds
bond strength
20-50 MPa
low end estimate of bond strength to resist contraction stresses
17MPa
Dentin adhesion relies on
penetrations of adhesion monomers into collaged network left exposed by acid etching
what makes etching dentin difficult?
dentin tubules with collagen and liquid
smear layer
after preparing tooth structure, remaining residual organic and inorganic components form layer of debris that fills dentin tubule orifices
removal results in fluid flow into exposed dentin - interferes with adhesion
ratio between # bonded surfaces and unbonded surfaces
Configuration (C) factor
stress relief within a 3D bonded restoration is limited by its
C-factor
class I restoration C-factor
5 ; results in stress relief due to limited flow from only one free surface
what may act to offset polymerization shrinkage effects?
water absorption by resin
microleakage around dentin margins is potentiated by
difference in linear coefficient of thermal expansion between substrate (tooth) and restoration
improves enamel seal:
extension of cavosurface bevel of enamel
______ usually sufficient to prevent formation of marginal gaps by polymerization contraction stresses
enamel bond strengths
loading and unloading of restored teeth can lead to:
damage or marginal gaps
how to remove smear layer?
acid etch
options for resin-dentin bonding
3 step etch and rinse adhesives
- phosphoric acid etching gel, rinse
- primer containing reactive hydrophilic monomers in ethanal, acetone, or water
- unfilled/filled resin bonding agent
acid etch acts to
remove smear layer
demineralize intertubular and peritubular dentin
expose filigree of collagen fibers
it is desirable for substrate to have ______ surface energy
high
after etching, dentin is left with ______ surface energy
low
what effect does primer in 3 step process have?
increases surface tension of dentin
what happens when primer and bonding resin applied?
penetrate intertubular dentin and form resin-dentin interfusion hybrid zone and resin tags = good bonding
two step etch and rinse adhesive
- etch
2. primer and adhesive in same bottle
water trees associated with:
porosities in adhesive layer
microleakage
passage of bacteria and toxins between restoration margins and tooth prep walls
bacteria can lead to pulpal irritation
interfacial gap
develops when dentin adhesive system does not adhere immediately to dentin substrate
bacteria can penetrate this gap
when all restoration margins are in enamel, quality and integrity of the bond remain:
unchanged
OR
degraded by hydrolysis
nanoleakage
small porosities in hybrid layer or hybrid/mineralized dentin transition layer allow penetration of little particles of silver nitrate dye
spotted pattern in hybrid layer or reticular pattern in adhesive layer (the RA says SHhhh) result from:
nanoleakage
