Enamel, Dentine and Bonding

Question 1

The emergence of adhesive materials has revolutionised many aspects of preventative and restorative dentistry, it offers potential to:

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What are the three approaches to achieving attachment to tooth substance?

Answer 1

• seal vunerable pits and fissures
• conserve tooth tissue
• reduce/eliminate microleakage

Attachment processes:

• micromechanical attachments: acid etch and application of resins
• chemical adhesion to enamel/dentine: coupling agents/cements containing polyacids
• complex - involving wetting, penetration and formation of bound material of restorative substrate interface: modern dentine bonding agents

Question 2

Describe the contact angle:

Answer 2

• low angle = good wetting
• high angle = poor wetting

The contact angle shows the attraction between adhesive and adherend which lowers surface tension of adhesive so will flow into irregularities

Question 3

What did Buonocore discover in 1955?

Answer 3

• application of acid gel leads to selective decalcification of enamel prisms, so if a resin is applied to the area, this would result in micromechanical tags flowing down into the irregularities bonding the resin in place
• highest bond strength achieved: 20-25MPa

Question 4

What are the effects of acid etching?

List some factors affecting acid etch:

Answer 4

• increases surfae roughness microscopically
• increases enamel surface energy which removes surface contaminants, increases wetting and facilitates micromechanical retention

Factors affecting:

• etching time: must be enough for an effect, but not too long as allows precipitation of calcium and phosphate (smooth surface)
• washing: approx 60s to remove debris
• drying: to enable hydrophobic resin to penetrate and attach

Question 5

What do we want in an ideal dental adhesive?

Answer 5

• a high bond strength to enamel and dentine
• an immediate and durable bond
• a reliable bond
• prevent bacterial ingress
• be safe and simple to use

Question 6

Why is dentine bonding a problem?

Answer 6

Dentine is:

• hydrophilic (adhesives are hydrophobic)
• a vital tissue
• consists of inorganic and organic material
• after cavity prep, tubules are covered by a smear layer

Question 7

List component functions of dentine bonding materials:

Answer 7

Primers = dentine conditioners

• acids, alter surface appearance and characteristics of dentine

Coupling agents = Primers

• components that do the sticking

Sealers

• flows into dentinal tubules, seals dentine with surface layer rich in methacrylates (forms base of resin composite)
• ensures bonding to the resin in the composite

Question 8

Give examples of dentine conditioners and explain how they work:

Answer 8

eg. maleic, oxalic, phosphoric and nitric acids
- acid base reaction with hydroxyapatite
- open dentinal tubules
- demineralise surface dentine to a depth of 4 microns

Question 9

How do primers work?

What is the general formula of a primer?

What is the most popular volatile solvent?

WHy is it dangerous?

Answer 9

• act as adhesives
• bond hydrophobic composites to hydrophilic dentine
• M-R-X dissolved in volatile solvent
  where: M - methacrylate, R - spacer molecule, X - bond to dentine

HEMA:

• dermatological effects and penetrates rubber gloves
• bonds to hydroxyl of the apatite and amino groups of the collagen
• solvent enhances penetation by seeking and displacing water carrying the coupling agent with it

Question 10

What is the gold standard for bonding?

Answer 10

3 stage presentation:

ETCH, PRIME AND BOND