Dentine bonding Flashcards
Structure of dentine
70% HAP 20% organic material, mainly collagen 10% water Tubules around 1-5μm width -get wider as they go down
Why resin bond to dentine?
Eliminate marginal and internal gaps
Seal dentinal tubules
Enhance retention
Enhance strength
Problems to bonding to dentine
Formation of a smear layer (area of debris from drilling)
Complex substrate (dentine)
Hydrophobic resins, hydrophilic dentine
Fluid flow into tubules
Fixing the smear layer
Etch with an acid
- removes smear layer
- demineralises dentine
- unblocks and widens tubules
Dentine conditioner
Usually 37% phosphoric acid, but not always
Creates demineralised surface layer ~4μm thick
-should be called the primer
Hydrophilic dentine to hydrophobic resins
We can bond hydrophilic dentine with -OH gps, -COOH gps, -P(OH)3 gps
-these bond with amino gps in collagen and hydroxyl gps in HAP
We can bond hydrophobic resins with methacrylate gps
Use spacer to stick them together
Long enough to prevent rigidity and allows both ends to bond freely
Bifunctional monomer
Combines these 3 parts -polar gp -spacer -methacrylate gp This one is HEMA
Dentine primers
A bifunctional monomer -polar gp -spacer -methacrylate gp A solvent or water to carry monomer deep into demineralised collagen
Preventing fluid flow into tubules
We now have surface of hydrophobic methacrylate gps
Bond directly using methacrylate based resin`
Dentine sealer
Methacrylate based -Bis-GMA -UDMA Either light cured or chemically cured Can contain some bifunctional monomer to aid bonding with primer
3 stages to dentine bonding
- Apply conditioner
- removes smear layer and open tubules - Apply primer
- bonds to hydrophilic collagen and HAP - Apply sealer
- seals tubules and bonds to primer
Anatomy of a dentine bond
Filled resin
Sealer
Hybrid layer
Concerns with dentine bonding
Eliminate marginal gap?
-as they polymerise, molecules together take up less space: area of shrinkage
-there is a marginal gap
-may also be internal gap, can cause pain
Wet dentine bonding
Wet dentine bonding
If you dry dentine thoroughly the collagen collapses
Volatile solvent in prier chases water out of collagen and brings in the bifunctional monomer
No need to dry thoroughly!!
Classification of dentine bonding agents
Type 1: etch, prime, seal
Type 2: etch, prime and seal
Type 3: Etch and prime, seal
Type 4: etch and prime and seal
Type 1: 3 stage systems
Etch with dentine conditioner (32 or 35% H3PO4)
Prime
Seal (Bis-GMA and HEMA)
Type 2: etch and rinse
Combined final 2 steps
Etch (then rinse)
Prime and seal (Prime&bondNT or Scotchbond1XT)
Follow instructions carefully
Prime and bond NT
Uses acetone to carry primer and sealer into dentine
Acetone chases water out of dentine
Needs time and possibly air to evaporate the acetone
Scotchbond 1 XT
Water and ethanol carry primer and sealer
Needs agitation to ensure primer and sealer get into dentine
Type 3: self etching primers
Combines 1st two stages of 3 stage system
Acidic monomers that etch and prime
Smear layer is dissolved, but not removed
No need to rinse or dry - more consistent results
Weak etching of enamel can lead to marginal staining
-can prevent parginal staining by pre-etching enamel with phosphoric acid
-this turns technique back into 3 stage technique
Type 4: all in one systems
Condition, prime and seal all in one Simplest system to use Weakest bond strength Very clever chemistry e.g. Xeno III (Dentsply) mathacrylate --> water --> phosphoric acid ester groups
Xeno III (Dentsply)
Liquid A: HEMA, ethanol, water, aerosil, stabiliser
Liquid B: Pyro-EMA, PEM-F, UDMA, CQ, Stabiliser
Which type to choose?
Type 1s are most difficult to use and require excellent technique
Type 2s almost equally difficult and bond strength generally worse
Type 3s quite simple to use and have good bond strength
Type 4s unpredictable as still quite new
