BONDING TO TEETH OSCE

Question 1

why is bonding to enamel easier than bonding to dentine?

Answer 1

Enamel is highly inorganic and dry

Question 2

what is normally used to etch enamel and dentine?

Answer 2

35% Phosphoric Acid

Question 3

what happens when enamel is etched?

Answer 3

The acid roughens the enamel surface and increases the surface energy by removing contaminants
- better wettability of enamel allows resin to adapt into the roughness

Question 4

what is the composition of dentine?

Answer 4

20% organic (mostly collagen)
70% inorganic (mostly hydroxyapatite)
10% water

Question 5

why is dentine so hard to bond to?

Answer 5

dentine is WET (because of permeable tubules) and has a LOW SURFACE ENERGY
- presence of smear layer also makes it hard to bond to

Question 6

why will composite materials not stick to wet dentine?

Answer 6

because wet dentine has a LOWER SURFACE ENERGY than composite materials
- for composite to stick, you have to make the dentine surface energy higher than that of the composite material

Question 7

what is the main purpose of dental bonding agents?

Answer 7

they INCREASE THE SURFACE ENERGY of dentine which allows composite to flow and stick to the surface

Question 8

what is the Smear Layer?

Answer 8

an adherent layer of organic debris that remains on the dentine surface after preparation (usually contaminated with bacteria)

Question 9

what does Acid Etching do to dentine?

Answer 9

REMOVES THE SMEAR LAYER

- opens dentinal tubules by removing smear plugs

Question 10

how is the HYBRID LAYER formed?

Answer 10

• dentine is etched and the smear layer/smear plugs are removed
• primer is able to flow into demineralised dentine and form a micro mechanical bond (collagen + resin)