Dental Bonding Flashcards
what acid is commonly used for the acid- etch technique on enamel and how does it work
phosphoric acid
roughens the surface of enamel allowing applied resin into microporosities providing a mechanical lock - micro mechanical adhesion
enamel must be dry as moisture contamination can prevent resin flow
why is dentine bonding more complex than enamel
fluid pumps from pulp to dentine so surface always wet
permeable tubules
low surface energy
smear layer
how to dentine bonding agents work
they increase dentines surface energy to allow subsequent products placed on it to flow and stick
smear layer
layer of organic debris that remains on dentine surface during restoration preparation
total etch vs self etch in regards to smear layer
total etch - removes smear layer
self etch - incorporates smear layer
describe the 3 (2) phases of the total etch technique
1 - dentine conditioner / etch - usually phosphoric acid, removes the smear layer and exposes the collagen network, this is then washed off
2 - primer - bifunctional molecule with hydrophillic end to bond to dentine and hydrophobic end to bind with subsequent resins. example = HEMA
3 - adhesive - mixture of resins e.g Bis- GMA and HEMA, penetrates primed dentine surface which is now hydrophobic and forms micromechanical bonds with exposed tubules (molecular entanglement)
Resulting surface has higher surface energy)
(steps 2 and 3 often combined)
what are the main pros and cons of total etch and self etch
total etch = better bond but more technique sensitive
self etch = not as technique sensitive but bond not as strong
what bifunctional molecule is commonly used in self etch products
acidic methacrylate monomers
what is the mechanism of bonding in self etch
minerals are removed from dental hard tissues and replaced by resin which once mineralised mechanically interlocks in these porosities (molecular entanglement)
adhesion decalcification concept
interaction of molecules with hydroxyapatite
initially all acid monomers in self etch process bond to calcium in HA but whether they stay bonded depends on bond strength which depends on acid monomers pKa
