Bonding systems

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

due to structure of enamel - densely packed prism, highly mineralised, dry

phosphoric acid 35%

roughens enamel surface allows micromechanical interlocking of resins to enamel pits increases surface energy by removing surface contaminants leads to better wettability of enamel enamel rods after etching

dentine bonding agents - phosphorylated BIS-GMA or low viscosity Bis-GMA

• 20% oroganic, 70% inorganic, 10% water • full of permeable tubules - fluid pumped from pulp to dentine, making dentine wet • secondary and tertiary dentine are irregular and more mineralised • low surface energy • hydrophilic

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

dentine bonding agent and the dentine surface meshing and interlocking with minimum gaps

bonding at a molecular level mineralised: ionic bonding organic: covalent bonding

electrostatic or dipole interaction between bonding agent and substrate strength depends on contact angle and is a good indication of wettability of a solid

low surface energy substance with low surface energy liquid = does not spread high surface energy substance with low surface energy liquid = will spread

low surface energy so liquids/low viscosity resins do not spread

increase the surface energy of dentine and allow the composite resin to flow and stick

adhesive is absorbed onto the surface and penetrates dentine due to wetting by adhesive and surface energies absorbed component forms long polymer that meshes with the substrate

layer of organic debris that remains on the dentine surface after the preparation

• remove it and bond to “clean” dentine • incorporate it by penetrating it, infiltrating it with the bonding agent and stick it to the dentine below

conditioner primer adhesive

35% phosphoric acid * removes smear layer and opens dentinal tubules * decalcifies uppermost layer * collagen network in top of dentine is exposed

• hydrophilic end bonds to hydrophilic dentine and hydrophobic end bonds to resin • has a spacer group to make it long enough to be flexible when bonding • gives dentine high surface energy, making it hydrophobic

mixture of resins - Bis-GMA, HEMA * contains camphorquinone to enable light cure * penetrates the primed dentine which is now hydrophobic * forms a micromechanical bond within the tubules and collagen fibres - molecular entanglement

over-etching collapses the collagen fibres so resin cannot penetrate over-etching - too deep an etch and the primer cannot penetrate the full depth of the etch moisture dependent - too dry and the surface of dentine collapses, too wet and the primer is diluted

still a total etch techinque with same chemicals used primer and sealant are combined and applied to the etched, washed dentine and light cured

they do not remove the smear layer, it infiltrates it and incorporates into it it is not washed off and creates a hybrid layer

hybrid layer and resin that has entered tubules