what is the definition of adhesion?
substance capable of strongly and permanently holding two surfaces together
what are the two types of adhesion in densitry?
-mechanical (micromechanical interlocking)
- chemical (true) adhesion
both mechanisms of adhesion (micromechanical and chemical) can be found _______
simultaneously (common with dental adhesions)
what are the steps for a typical composite bonding?
conditioning
primer
adhesive
composite
what are the key steps/techniques for good bonding?
clean adherence
good wetting
intimate adaptation
bonding
complete curing
what is etching/conditioning used for?
removal or modification of smear layer
what can be used for etching?
- acids (37% phosphoric acid)
- calcium chelators (EDTA)- without demineralization of dentin
- functional monomers (10-MDP, 4-META, phenyl-P)
explain what enamels acid etching does?
- converts smooth surface into a rough surface
- creates micropores (5-500 um deep)
- increases surface energy and wettability
- prepares surface for micromechanical locking
explain what dentin acid etching does?
- opens the dentin tubules for resin infiltration (for acid etching bonding systems)
explain what a smear layer is
- cavity is preped and residual layer forms smear layer
- fills dentin tubules, forming smear plugs
- decreases dentin permeability
what are primers used for?
- to increase the diffusion of resin into moist/ demineralized dentin after etching
- similar to primers in paint and are usually air dried, not rinsed off
what are primers made of and what are common primers?
- usually a solution of monomers, organic solvents (alcohol/acetone), water and stabilizers
- common primers are HEMA and 4-META
what does it mean that primers are bi-functional agents?
contain monomers with a
- hydrophilic end with affinity for exposed collagen fibrils
- hydrophobic end with affinity for resin/adhesive
what is an adhesive resin?
- link between primer and composite
- solvent free (hydrophobic) low-viscosity resin that is applied over the primer that interacts and copolymerizes with the restorative material
what are some examples of adhesive resins?
unfilled or lightly filled monomers typically Bis-GMA, UDMA, TEGDMA
what are the three bonding strategies?
- etch and rinse (total etch)
- self etch
- universal
what does the etch and rise technique always use?
acid-etch step
explain the etch and rinse strategy
- oldest strategy
- either 2 or 3 step process
- etching + primer + bonding
- etching + primer/bonding
- wet bonding technique after acid etch
-primary adhesion mechanism is mechanical locking
explain the self etching strategy
- no acid etching
- primers contain functional monomers (carboxyl or phosphate) that can permeate and diffuse into dentin
- partial demineralization
- chemically interacts with hydroxyapatite
- either 1 or two step process
- acid/primer + adhesive (gold standard)
- acid/primer/adhesive
- primary adhesive mechanisms are mechanical locking/ chemical bond
how are self etching strategies classified?
based on aggressiveness:
- strong (pH < 1)
- intermediate (pH = 1.5)
- mild (pH = 2)
- ultramild (pH > 2.5)
what is universal/multi-mode adhesive and what is it available as?
- most simple-to-use and versatile adhesive
- available in ER (acid etching + universal bottle) mode and SE mode (universal bottle)
what are some challenges for dental adhesion?
- retention (bacteria and leaks)
- degradation of biomaterials (bad environmental condutions)
- technique (proper preparation)
- handling (proper material and lamp use
what can lack of retention cause?
sensitivity
failure
staining
2nd caries
inflammation
what is the first challenge in bonding to dentin?
- the presence of water and organic components lower the surface energy of dentin
- water keeps collagen expanded and retains spaces for resin infiltration
- dry collagen collapses and obstructs the resin from reaching the dentin
*** presence of moist/wet dentin is needed
