Bonding

Question 1

What are the ideal properties of a dental adhesive?

Answer 1

Easy to use
Biocompatible
High bond strength
Durable
Impermeable
Immediate high bond strength

Question 2

What is etch?

Answer 2

This is 37% phosphoric acid which is used to prepare dentine and enamel for bonding

Question 3

What is an example of a DBA?

Answer 3

Bis-GMA
HEMA

Question 4

Describe the structure of enamel

Answer 4

Highly mineralised structure that consists of enamel prisms with imperfectly packed hydroxyapatite crystals
It is composed of:
- Hydroxyapatite (inorganic structure)
- Water
- Proteins (amleogens)

Question 5

Describe the structure of dentine

Answer 5

Structure composed of dentine tubules surrounding by a collagen matrix. It is composed of:
- hydroxyapatite
- water
- collagen

Question 6

How do we bond to enamel?

Answer 6

Enamel is hydrophobic and already has a high surface energy so bonding is relatively straightforward
we use etch (37% phosphoric acid) which roughens the enamel surface and removes and surface contamination - this further increases enamels surface energy and allows micro mechanical interlocking of the resin fillers

enamel must be dry to allow the resin to flow (As resin is hydrophobic)

Question 7

How do we bond to dentine?

Answer 7

Dentine bonding more complex as dentine in hydrophilic and comp resin is hydrophobic

We must use numerous different agents to increase the surface energy of dentine and make dentine hydrophobic to allow bonding to occur

firstly we use (tissue conditioner) etch (37%) phosphoric acid which opens the dentinal tubules and aids in removal of the smear layer (layer of organic debris formed one cut dentine). We then rinse the etch of with water which results in an exposed collagen network of tubules - the outer layer right now is demineralised but under layers still hydrophobic so bonding wont yet work

then we use a primer such as 4-META, HEMA which acts as a coupling agent that has a bifunctional molecule that has a hydrophobic end and hydrophilic end. The hydrophobic end bonds to they hydrophobic dentine ad the hydrophilic end is on the surface ready for bonding - the molecule must be long and flexible to improve bond strength

finally we use a bonding agent (adhesive) such as Bis-GMA which penetrates the primed dentine and forms a micro mechanical bond in the tubules and exposed collagen - the dentine is now ready for bonding

Question 8

What happens if dentine is over etched?

Answer 8

Collapse of collagen fibres = resin cant penetrate

Question 9

What happens if dentine/enamels is too wet?

Answer 9

Composite is hydrophobic so wont flow and micro mechanically interlock - bond failure