Composites: Bonding to Dentine

Question 1

Is tooth tissue hydrophobic or hydrophilic?

Answer 1

Hydrophilic

Question 2

Are most restorative materials hydrophobic or hydrophilic?

Answer 2

Hydrophobic

Question 3

What adhesive bonds can occur between tooth tissue and restorative material? (3)

Answer 3

• Micromechanical
• Molecular entanglement
• Chemical

Question 4

Which bond needs to be achieved for longevity between tooth tissue and restorative material?

Answer 4

Chemical bond

Question 5

What are some advantages of adhesives? (6)

Answer 5

• Better aesthetics
• Conservation of tooth tissue
• Reinforcement of weak tooth structure
• Reduced marginal leakage
• Reduced potential for pulp sensitivity
• Range of techniques

Question 6

What are the ideal requirements for adhesives? (5)

Answer 6

• Provide high bond strength to enamel and dentine
• Immediate and durable bond
• Prevent ingress of bacteria
• Safe to use
• Simple to use

Question 7

Composition of enamel structure by weight;

Mineral?
Organic material?
Water?

Answer 7

• 96% Mineral
• 1% Organic material
• 3% Water

Question 8

When would you need to bond a restoration to enamel? (2)

Answer 8

• Orthodontic appliances

- Bridges

Question 9

Comment on the surface tension of enamel compared to the adhesive resin

Answer 9

Surface tension of enamel is lower than that of the adhesive resin so perfect wetting cannot take place, (The resin will not flow/cover the enamel surface appropriately)

Question 10

What layer covers enamel?

Answer 10

Pellicle layer

Question 11

How can adhesion onto an enamel surface be achieved?

Answer 11

• Pellicle layer of enamel must be removed

- Enamel surface must be etched to raise surface tension

Question 12

How is the pellicle layer removed and enamel
etched?

What chemical is used for this?

Answer 12

• Using the acid-etch technique

- Using 30-50% phosphoric acid on the enamel surface

Question 13

What are the main effects of the acid etch technique? (4)

Answer 13

• Increased surface roughness
• Surface energy is raised
• Improved wettability
• Opens inner prism area for interlocking tag formation

Question 14

What visible appearance is present when adequate etching has been achieved?

Answer 14

When the enamel has a ‘frosty appearance’

Question 15

What is recommenced to apply after an acid-etch before you place a composite?

Answer 15

Recommended to apply a resin of low viscosity (eg. unfilled Bis GMA, or dentine adhesive resin)

Question 16

Name some dental procedures where the acid-etched enamel is used for (6)

Answer 16

• Fissure sealing
• Direct composite
• Ceramic veneers
• Resin bonded bridges
• Orthodontic brackets
• Periodontal splinting

Question 17

Why does a restorative resin have to be adhesively bonded to dentine?

Answer 17

To retain the restoration in the cavity and to
eliminate marginal gaps in order to prevent
bacterial microleakage

Question 18

Composition of dentine structure by weight;

Inorganic hydroxyapatite?
Organic material?
Water?

Answer 18

• 70% Inorganic HA
• 20% Organic material (Hydrated Collagen)
• 10% Water

Question 19

What happens when dentine is cut? (2)

Answer 19

• Fluid is pumped through the dentine tubules giving a wet surface
• Inorganic HA crystals are broken up, the collagen is stretched, torn, and smeared over the cut surface

Question 20

What is the organic material of dentine mostly composed of?

Answer 20

Hydrated collagen

Question 21

What are the 3 essential components of a dentine bonding agent?

Answer 21

• Conditioner
• Coupling agent
• Sealer

Question 22

What is the role of the conditioner in a dentine bonding agent?

What property of the conditioner allows it to do that?

Answer 22

Acidic so clears smear layer

Question 23

What is the role of the Coupling agent in a dentine bonding agent?

What molecule does it contain?

Answer 23

Used as the adhesive

Hydroxyethyl methacrylate (HEMA)

Question 24

What is the role of the Sealer in a dentine bonding agent?

What agents can be used as sealers?

Answer 24

Seals the dentine tubules

Unfilled Bis GMA or UDMA

Question 25

The interpenetrating layer of dentine and resin is referred to as?

Answer 25

The hybrid zone

Question 26

What are the bonds found in dentine adhesion? (2)

Answer 26

• Micromechanical

- Entanglement

Question 27

Explain the bonding between the dentine tubules and coupling agent

Answer 27

Molecular entanglement with OH groups of primer

Question 28

Explain the bonding between the coupling agent and the sealer

Answer 28

Methacrylate group of coupling agent chemically bonds to Methacrylate group of sealer

Question 29

Explain the bonding between the sealer and filled-composite material

Answer 29

Methacrylate group of sealer chemically bonds

to Methacrylate group on filled composite materials

Question 30

What will happen if there is excessive desiccation of dentine?

Answer 30

Post operative pulpal sensitivity and a poor bond

Question 31

If there is bond failure amongst dentine adhesion what may occur?

Answer 31

Pulpal inflammation leading to bacterial leakage

Question 32

What are some potential causes for adhesive bond breakdown? (4)

Answer 32

• Polymerisation shrinkage
• Differential thermal expansion and contraction
• Internal stresses from occlusal loading
• Chemical attack (hydrolysis)