Composites: Bonding to Dentine Flashcards
Is tooth tissue hydrophobic or hydrophilic?
Hydrophilic
Are most restorative materials hydrophobic or hydrophilic?
Hydrophobic
What adhesive bonds can occur between tooth tissue and restorative material? (3)
- Micromechanical
- Molecular entanglement
- Chemical
Which bond needs to be achieved for longevity between tooth tissue and restorative material?
Chemical bond
What are some advantages of adhesives? (6)
- Better aesthetics
- Conservation of tooth tissue
- Reinforcement of weak tooth structure
- Reduced marginal leakage
- Reduced potential for pulp sensitivity
- Range of techniques
What are the ideal requirements for adhesives? (5)
- Provide high bond strength to enamel and dentine
- Immediate and durable bond
- Prevent ingress of bacteria
- Safe to use
- Simple to use
Composition of enamel structure by weight;
Mineral?
Organic material?
Water?
- 96% Mineral
- 1% Organic material
- 3% Water
When would you need to bond a restoration to enamel? (2)
- Orthodontic appliances
- Bridges
Comment on the surface tension of enamel compared to the adhesive resin
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)
What layer covers enamel?
Pellicle layer
How can adhesion onto an enamel surface be achieved?
- Pellicle layer of enamel must be removed
- Enamel surface must be etched to raise surface tension
How is the pellicle layer removed and enamel
etched?
What chemical is used for this?
- Using the acid-etch technique
- Using 30-50% phosphoric acid on the enamel surface
What are the main effects of the acid etch technique? (4)
- Increased surface roughness
- Surface energy is raised
- Improved wettability
- Opens inner prism area for interlocking tag formation
What visible appearance is present when adequate etching has been achieved?
When the enamel has a ‘frosty appearance’
What is recommenced to apply after an acid-etch before you place a composite?
Recommended to apply a resin of low viscosity (eg. unfilled Bis GMA, or dentine adhesive resin)
Name some dental procedures where the acid-etched enamel is used for (6)
- Fissure sealing
- Direct composite
- Ceramic veneers
- Resin bonded bridges
- Orthodontic brackets
- Periodontal splinting
Why does a restorative resin have to be adhesively bonded to dentine?
To retain the restoration in the cavity and to
eliminate marginal gaps in order to prevent
bacterial microleakage
Composition of dentine structure by weight;
Inorganic hydroxyapatite?
Organic material?
Water?
- 70% Inorganic HA
- 20% Organic material (Hydrated Collagen)
- 10% Water
What happens when dentine is cut? (2)
- 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
What is the organic material of dentine mostly composed of?
Hydrated collagen
What are the 3 essential components of a dentine bonding agent?
- Conditioner
- Coupling agent
- Sealer
What is the role of the conditioner in a dentine bonding agent?
What property of the conditioner allows it to do that?
Acidic so clears smear layer
What is the role of the Coupling agent in a dentine bonding agent?
What molecule does it contain?
Used as the adhesive
Hydroxyethyl methacrylate (HEMA)
What is the role of the Sealer in a dentine bonding agent?
What agents can be used as sealers?
Seals the dentine tubules
Unfilled Bis GMA or UDMA
The interpenetrating layer of dentine and resin is referred to as?
The hybrid zone
What are the bonds found in dentine adhesion? (2)
- Micromechanical
- Entanglement
Explain the bonding between the dentine tubules and coupling agent
Molecular entanglement with OH groups of primer
Explain the bonding between the coupling agent and the sealer
Methacrylate group of coupling agent chemically bonds to Methacrylate group of sealer
Explain the bonding between the sealer and filled-composite material
Methacrylate group of sealer chemically bonds
to Methacrylate group on filled composite materials
What will happen if there is excessive desiccation of dentine?
Post operative pulpal sensitivity and a poor bond
If there is bond failure amongst dentine adhesion what may occur?
Pulpal inflammation leading to bacterial leakage
What are some potential causes for adhesive bond breakdown? (4)
- Polymerisation shrinkage
- Differential thermal expansion and contraction
- Internal stresses from occlusal loading
- Chemical attack (hydrolysis)
