bonding systems Flashcards
what are the properties of dental adhesive?
high bond strength to tooth tissues immediate high strength bond durable bond impermeable bond easy to use safe
why is bonding to enamel easy?
the structure of enamel heterogeneous structure -densely packed prismatic highly mineralised (95% organic) -more like rock/stone than bio tissue dry
describe the acid etch technique
enamel prisms filled with imperfectly packed hydroxyapatite crystals
surface modified by application of acid
acid roughens surface producing etched pattern
roughened surface allows micromechanical interlocking of resin filling materials
etched surface increases surface energy of enamel surface by removing surface contaminants leading to better wettability of enamel
better wettability allows resin to adapt better to roughened enamel surface
what is the requirement for enamel etch technique and why?
enamel must be dry
moisture contamination will prevent flow of resin into etched surface
what is the acid normally used in etching?
30-50% phosphoric acid
what are the 2 types of resin put on top of enamel etch?
low viscosity bis-GMA to penetrate into rough surface and light cured
higher viscosity composite resin filling material on top
describe the composition of dentine
20% organic 70% inorganic (HA) 10% water permeable tubules fluid pumps from pulp floor of cavity making surface wet inconsistent material -aged more mineralised low surface energy hydrophilic, most bonding agent hydrophobic
what are the requirements of a DBA?
ability to flow potential for intimate contact w dentine surface low viscosity adhesion to substrace -mechanical -chemical -van der waals
describe mechanical dentine bonding
same as enamel
dentine bonding agent and dentine surface meshing and interlocking with minimum gaps
what type of bond does mineralised dentine have?
ionic
what type of bond does organic dentine have?
covalent
what is van der waals adhesion based on?
electrostatic or dipole interaction between bonding agent and substrate
what does the strength of a van der waals interaction depend on?
contact angle
-indicates wettability of a solid by a specific liquid
what is critical surface energy?
surface tension of a liquid that will just spread on the surface of a solid
what surface energy must a liquid have compared to the surface it is being placed on for it to flow and stick?
lower surface energy
why will a low SA spread on a higher SA substrate?
leads to a lower SA of the material as a whole
what SA does wet dentine have?
lower than composite filling materials
how do you get composite resin to stick to dentine?
make the surface of the dentine have a higher critical energy than the composite