Bonding to Teeth

Question 1

what are the ideal properties of a dental adhesive?

Answer 1

• provide a high bond strength to tooth tissues
• immediate high strength bond
• durable bond
• impermeable bond
• easy to use
• safe

Question 2

what does the etching of enamel provide?

Answer 2

• increased surface energy of the enamel
• therefor better wettability
• allows resin to adapt better to roughened surface

Question 3

what acid is most commonly used to etch enamel?

Answer 3

30% phosphoric acid

Question 4

why is bonding to dentine more complicated that bonding to enamel?

Answer 4

• dentine is WET (due to permeable tubules)
• dentine has a low surface energy
• dentine is hydrophilic whereas most bonding agents are hydrophobic

Question 5

what are the requirements of a dentine bonding agent?

Answer 5

• ability to flow
• potential for intimate contact with dentine surface
• low viscosity
• adhesion to substrate

Question 6

what is the effect of bonding agents to the surface of dentine?

Answer 6

dentine bonding agents INCREASE THE SURFACE AREA of dentine & allow composite to flow and stick to it

Question 7

what is the smear layer?

Answer 7

the smear layer is an adherent layer of organic debris that remains on the dentine surface after the preparation of the dentine during the restoration of a tooth

Question 8

what effect does etching have on the smear layer?

Answer 8

remove and/or modify the smear layer from dentine

Question 9

what is the function of phosphoric acid applied to dentine as a conditioner?

Answer 9

• removes smear layer
• opens dentinal tubules by removing smear plugs
• decalcifies the uppermost layer of the dentine

Question 10

in terms of bonding to dentine, what is the primer and how does it function?

Answer 10

• the primer is really the adhesive element
• its a coupling agent
• it contains a bifunctional molecule with a hydrophilic end to bond to dentine and a hydrophilic end to bond to resin

Question 11

what is a common coupling agent found in bonding primers? how does it work?

Answer 11

HEMA

- contains a C=C bone which opens and forms a strong covalent bone with the next resin layer

Question 12

in dentine bonding agents, how does the adhesive work?

Answer 12

• predominately hydrophobic
• penetrates the primed dentine which now has a hydrophobic surface
• forms a micromechanical bond within the tubules and exposed dentinal collagen fibres
• formed the HYBRID LAYER of collagen plus resin

Question 13

what can happen if the dentine is over etched?

Answer 13

• collapse of the collagen fibres so no resin can penetrate

- too deep an etch and primer cannot penetrate full depth