What are the benefits of dentine bonding agents? (4)
- allow for restorations to be bonded
- offer retention and a seal
- minimised need of micro mechanical retention makes tooth preparations more conservations
- designed to provide a sufficiently strong interface between restorative composites and tooth structure to withstand mechanical forces and shrinkage stress
What are the ideal functions of a DBA? (4)
- provide a strong, immediate and permanent bond to dentine
- seal the cavity and minimise leakage
- resistant to microbial/enzymatic degradation
- reduce the risk of recurrent caries
How do you bond to enamel?
Enamel is etched which roughness the surface and increases the surface energy allowing for micro mechanical retention
What do you need to overcome to bond to dentine? (3)
- smear layer (overcome by conditioning)
- possible insult to pulp (caused by low pH of acids)
- increased difficulty in bonding to organic components and water (primer and adhesive allow for the formation of a hybrid layer)
How does bonding occur?
Mainly micro mechanical through the formation of a hybrid layer
What is the basic composition of DBAs? (3)
- etchant (aka conditioner, primer)
- primer (aka coupling agent)
- adhesive
What does the etchant (aka conditioner, primer) do? (4)
- cleans the surface
- removes smear layer
- dissolves hydroxyapatite crystals
- roughens surface
Give 4 examples of etchant
- polyacrylic acid
- phosphoric acid
- citric acid
- EDTA
Is the primer hydrophilic or hydrophobic?
Hydrophilic
What does the primer do?
Makes surface of tooth more favourable for accepting a bond
What does primer contain? What does this do? What are the disadvantages of this?
Solvent that thins material and increases wetting
Solvents tend to be volatile which implies a biohazard risk
What does adhesive contain?
Unfilled or slightly filled resins to which hydrophilic molecules have been added
What does adhesive do?
- help in the formation of the hybrid layer( zone of resin reinforced dentine where resin penetrate microtubules to form micro tags)
- amphiphilic- hydrophilic particles (e.g HEMA) increase wetting to dental tissues, hydrophobic particles (e.g BIS- GMA) bind and copolymers with restorative materials
What are the different classifications by mechanism of adhesion/clinical step?
- three steps (etch>prime>bond) most time consuming and complex operative procedure but highest bond strength
- two steps 1 (etch> prime+ bond)
- two steps 2 (etch+prime>bond)
- one step- clinically easiest to use, acceptable bond strengths
What does universal bonding agent mean?
- capable of being used in whichever etching mode the operator considers appropriate
- may be used for direct and indirect restorations
- contains 10-MDP which bonds with hybrid layer and bonds ionically to calcium vis hydrophilic group incorporated in the molecule
What are the advantages and disadvantages of multi stage systems?
More technique sensitive and time consuming
Better bond strength
Better conditioning of enamel improves retention and marginal seal
What are the disadvantages of single stage systems?
- tend to have weaker acids so as not to damage the dentine in comparison to phosphoric acid. This means that the acid in these systems is too weak to condition enamel which compromises the marginal seal. This may be overcome by selectively etching enamel with phosphoric acid prior to using DBA to improve retention and marginal seal
- lack of compatibility with chemical cure composites as lower pH deactivated tertiary amine activator and a poorer dentinal seal.
- combining all materials into one bottle will also decrease stability of material and reduce the shelf life
What are the advantages of single stage systems?
- no post conditioning rinsing
- less sensitive to degree of dryness of dentine
- single unit dose packaging possible- reduced crosse infection
- consistent and stable composition
What does over etching enamel do?
Loss of excess enamel, loss of fluoride
What does over drying dentine do?
Collapsed dentinal tubules, decreased penetration of primer/adhesive and compromised bond
What does under drying dentine do?
Dilute the bonding agent and compromise bond/strength
What does under etching dentine do?
Smear layer compromises penetration and bond of DBAs
What does over etching dentine do?
Post op sensitivity
What does a filled DBA do?
Increase penetration of resin into dentinal tubules and increase the thickness of the hybrid layer improving mechnical properties
