Bonding
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what are the ideal properties of a bonding agent
strong bond to teeth, impermeable, durable, bond immediately
what properties of enamel make it easy to bond to
inorganic, high surface energy, dry
what is used for etching enamel
30% phosphoric acid
how does phosphoric acid work for etching enamel
removes calcium hydroxyapatite, creates a porous surface, characteristic etched pattern, allows the resin to flow in, increases critical surface energy, once resin flows in, can polymerise and cannot be pulled out
what is the name of adhesion for enamel bonding
micro mechanical adhesion
what makes bonding to dentine more difficult than enamel
it is more organic, has a dentinal fluid, this reduces the critical surface energy
what is critical surface energy
the tension of a fluids ability to flow on a surface and stick on this surface - high, good flow and stick, low poor flow and not sticking, surface must be higher than the liquid
what two ways can bonding to dentine occur
chemically or mechanically
what is mechanical bonding to dentine
similar to that of enamel, creating porous surface for resin to flow in and micro mechanically lock in
what is a surface wetting agent
an agent that increases the critical surface energy of a surface, to allow the flowability and adhesion of a liquid on the surface
how does surface wetting agent work in dentine
it is a bifunctional molecule - one end is hydrophillic and one end is hydrophobic. dentine is a hydrophillic surface but the resin is hydrophobic. therefore, this agent can flow on to the dentine surface and polymerise to make the dentine hydrophobic
what is the smear layer
the layer on dentine created during cavity preparation. normally full of bacteria and dentine - organic debris, interferes with adhesion
what are the 3 components in dentine bonding
conditioner, primer and adhesion
what is the conditioner used in dentine bonding
30% phosphoric acid, to remove calcium hydroxyapatite and increase porosity
what is the primer used in dentine bonding
normally HEMA, this is a bifunctional molecule with a hydrophobic and hydrophillic end. It contains C=C for covalent bond with the next resin layer and increases the surface energy. main adhesion molecule
what is the adhesion molecule used in dentine bonding
mix of Bis-GMA and HEMA. predominantly hydrophobic, creates a hybrid layer as it bonds to the dentine and the restorative material
what is adhesion known as in dentine
molecular entanglement and micro mechanical retention
what is the problem with moisture in bonding
too dry - collapse of collagen fibres, nothing to bond on to too wet - resin cannot flow properly, surface energy low
what is the problem with over etching
collagen collapse and the resin cannot penetrate as deep as the pores created
what steps can be simplified in practice of dentine bonding
combine prime and adhesion - prime and bond, scotchbond, still uses total etch technique
what is self-etchant technique
when one agent is used, containing etchant, primer and adhesion, reduces steps to reduce effects of poor moisture control