Dentine bonding

Question 1

Structure of dentine

Answer 1

70% HAP
20% organic material, mainly collagen
10% water
Tubules around 1-5μm width
-get wider as they go down

Question 2

Why resin bond to dentine?

Answer 2

Eliminate marginal and internal gaps
Seal dentinal tubules
Enhance retention
Enhance strength

Question 3

Problems to bonding to dentine

Answer 3

Formation of a smear layer (area of debris from drilling)
Complex substrate (dentine)
Hydrophobic resins, hydrophilic dentine
Fluid flow into tubules

Question 4

Fixing the smear layer

Answer 4

Etch with an acid

• removes smear layer
• demineralises dentine
• unblocks and widens tubules

Question 5

Dentine conditioner

Answer 5

Usually 37% phosphoric acid, but not always
Creates demineralised surface layer ~4μm thick
-should be called the primer

Question 6

Hydrophilic dentine to hydrophobic resins

Answer 6

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

Question 7

Bifunctional monomer

Answer 7

Combines these 3 parts
-polar gp
-spacer
-methacrylate gp
This one is HEMA

Question 8

Dentine primers

Answer 8

A bifunctional monomer
-polar gp
-spacer
-methacrylate gp
A solvent or water to carry monomer deep into demineralised collagen

Question 9

Preventing fluid flow into tubules

Answer 9

We now have surface of hydrophobic methacrylate gps

Bond directly using methacrylate based resin`

Question 10

Dentine sealer

Answer 10

Methacrylate based
-Bis-GMA
-UDMA
Either light cured or chemically cured
Can contain some bifunctional monomer to aid bonding with primer

Question 11

3 stages to dentine bonding

Answer 11

1. Apply conditioner
   - removes smear layer and open tubules
2. Apply primer
   - bonds to hydrophilic collagen and HAP
3. Apply sealer
   - seals tubules and bonds to primer

Question 12

Anatomy of a dentine bond

Answer 12

Filled resin
Sealer
Hybrid layer

Question 13

Concerns with dentine bonding

Answer 13

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

Question 14

Wet dentine bonding

Answer 14

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!!

Question 15

Classification of dentine bonding agents

Answer 15

Type 1: etch, prime, seal
Type 2: etch, prime and seal
Type 3: Etch and prime, seal
Type 4: etch and prime and seal

Question 16

Type 1: 3 stage systems

Answer 16

Etch with dentine conditioner (32 or 35% H3PO4)
Prime
Seal (Bis-GMA and HEMA)

Question 17

Type 2: etch and rinse

Answer 17

Combined final 2 steps
Etch (then rinse)
Prime and seal (Prime&bondNT or Scotchbond1XT)
Follow instructions carefully

Question 18

Prime and bond NT

Answer 18

Uses acetone to carry primer and sealer into dentine
Acetone chases water out of dentine
Needs time and possibly air to evaporate the acetone

Question 19

Scotchbond 1 XT

Answer 19

Water and ethanol carry primer and sealer

Needs agitation to ensure primer and sealer get into dentine

Question 20

Type 3: self etching primers

Answer 20

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

Question 21

Type 4: all in one systems

Answer 21

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

Question 22

Xeno III (Dentsply)

Answer 22

Liquid A: HEMA, ethanol, water, aerosil, stabiliser

Liquid B: Pyro-EMA, PEM-F, UDMA, CQ, Stabiliser

Question 23

Which type to choose?

Answer 23

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