dentine bonding

Question 1

What is dentine?

Answer 1

Second hardest tissue 
Main supporting structure of teeth
70% hydroxapaptite
20% organic material (collagen)
10% water
Contains dentinal tubules of 1-5micrometers in width (30k-40k)

Question 2

What is a conditioner?

Answer 2

Modifies characteristics of substance so bond can be created
Modifies smear layer by dissolving hydroxyapatite and opening tubules
Usually acids
Creates demineralised surface layer ~4micrometers thick

Question 3

What is a coupling agent/primer?

Answer 3

Intermediary substance able to bond to substrate and adhesive
Hydroxyl, carboxyl and phosphates can bond to hydrophilic dentine
~amino in collagen
~hydroxyl in hydroxyapatite
Methacrylate bonds to hydrophobic resin

Question 4

What is a spacer?

Answer 4

Molecule long enough to prevent rigidity and allow both ends to bond freely

Question 5

What does a coupling agent have?

Answer 5

The polar group
The spacer
The methacrylate group
Eg. HEMA- HydroxyEthylMethAcrylate
Polar end faces hydrophilic dentine and methacrylate end faces hydrophobic resin
Carried in a solvent or water to flow deep

Question 7

What are the problems with bonding to dentine?

Answer 7

Complex/heterogeneous
Permeable and dynamic
Low surface energy
Forms a smear layer
Hydrophilic/hydrophobic
WETTING
POLYMER SHRINKAGE

Question 8

Ongoing research reducing shrinkage?

Answer 8

Filler particles
New monomer systems (siloranes)
Curing in small intervals

Question 9

Don’t dry thoroughly?

Answer 9

~collagen collapses if too dry

~solvent that carries primer displaces any water so allows good penetration

Question 10

What are the classifications of dentine bonding agents?

Answer 10

Type 1- Etch. Prime. Seal.
Type 2- Etch. Prime and Seal.
Type 3- Etch and Prime. Seal.
Type 4- Etch, Prime and Seal.

Question 11

What are the pros and cons of the classifications?

Answer 11

Type 1- difficult to use, need excellent technique
Type 2- difficult and poor bond strength
Type 3- simple and good bond strength
Type 4- new and unpredictable

Question 13

What is a sealer?

Answer 13

Substance that flows into dentinal tubules creating a methacrylate-based layer- ensures adhesion
Eg. Bis-GMA or UDMA
Either light cured or chemically cured