Enamel

Question 1

What is the composition of enamel?

Answer 1

96% hydroxyapatite (mineral)
1% organic proteins
3% water

Question 2

What is the structure of enamel?

Answer 2

• Hexagonal rods of mineral
• Prismatic arrangement perpendicular to tooth surface
• Naturally covered in pellicle and usually plaque

Question 3

What is acid etching enamel?

Answer 3

Micromechanical bonding
Need to make a retentive surface
Increase surface area

Question 4

What % of phosphoric acid should be used for etching of enamel and what are the two different etching times?

Answer 4

Use ~35% phosphoric acid
~40s etch for fresh enamel
~20s for burred or milled enamel

Question 5

What are the 3 steps to prevent mistakes of enamel bonding?

Answer 5

Patient selection

Enamel prophylaxis

Application of etchant

Question 6

What patients should not be chosen for the acid etch tecnique?

Answer 6

The bonding area must be kept free of contaminants such as saliva or water

Patients who will re-wet the dried surface should not be selected for the acid etch technique

• don’t use if dentine is exposed
• isolate with rubber dam

Question 7

How would you get the materia/resin to bond to enamel and not the pellicle or plaque on surface?

Answer 7

Clean with a slurry of pumice and water for 30s using a bristle brush

• wash thoroughly to remove debris and dry

Question 8

How to apply the etchant?

Answer 8

• 35% phosphoric acid
• gel or liquid
• apply with cotton pleget
• don’t rub the etchant onto the surface
• wash etched surface to remove salts and excess acid
• surface of tooth drys to frosty white appearance

Question 9

What is adhesion?

Answer 9

The force that binds two dissimilar materials together when they are brought into intimate contact

Question 10

What can enamel bonding be used for?

Answer 10

Improve appearance of teeth
Mask out discolouration
Prevent further wear and tear

Question 11

How does acid etching modify enamel?

Answer 11

1. Increase roughness of surface - partial dissolution of HA, loss of enamel periphery (distorted)
2. Raises surface energy - acid removes pellicle and exposes underlying surface of enamel which has a higher surface energy. Acid also raises surface tension encouraging wetting and removes surface contaminants.

Question 12

Why does the bonding area have to be kept free of saliva/water?

Answer 12

Saliva and water = polar
Resin = non polar
Prevents resin bonding to enamel surface