enamel bonding

Question 1

What is enamel composed of?

Answer 1

96% hydroxyapatite
1% organic proteins
3% water
Hexagonal rods of mineral (5micrometer diameter)
Prismatic arrangement perpendicular to tooth surface

Question 2

Why is enamel bonding useful?

Answer 2

Add composite to-
~improve appearance 
~mask out discolouration
~prevent further wear and tear
No extensive tooth prep
If bonding needs removing, tooth under is healthy

Question 3

Why do we acid-etch?

Answer 3

Increase surface roughness
~acid/base reaction prompts partial dissolution of hydroxyapatite
~loss of enamel prism periphery and prism core constituents
Raises surface energy
~acid removes pellicle (low SE, 28mJ/m^2) and exposes enamel (higher SE, 42mJ/m^2)
~typical SE of adhesive is 34-38mJ/m^2)
~higher surface tension encourages wetting
Acid removes surface contaminants

Question 4

How can acid etching aid enamel bonding?

Answer 4

Makes a retentive surface
Micromechanical bonding
Increases surface area and energy

Question 5

What should be considered clinically for acid etching?

Answer 5

Patient selection
~bonding area should be free of contaminants (elderly, kids, mentally ill) - proper isolation
Enamel prophylaxis
~clean w pumice and water slurry for 30s w bristle brush (remove plaque and pellicle)
Application
~gel or liquid applied w brush or cotton pledget
~mustn’t rub as it breaks retentive tags and weakens bond