Bonding Systems

Question 1

what are the properties of dental adhesives

Answer 1

• provide a high bond strength to tooth tissues
• immediate high strength bone
• durable bond
• impermeable bond
• easy to use
• safe

Question 2

why is enamel bonding easy

Answer 2

structure of enamel - heterogenous, densely packed and prismatic

highly mineralised and dry

Question 3

describe the acid etch technique in relation to enamel bonding

Answer 3

• long enamel prisms are filled with imperfectly packed hydroxyapatite crystals
• this surface can be modified by application of acid
• the acid roughens the surface of the enamel producing a characteristic etched pattern

Question 4

why is acid etching used for enamel bonding

Answer 4

• roughened surface allows micro mechanical interlocking of resin filling materials
• etching also increases the surface energy of the enamel surface by removing surface contaminants leading to better wettability of the enamel
• better gettability allows the resin to adapt better to roughened enamel surface
• enamel must be dry for this to work

Question 5

why does enamel need to be dry for bonding

Answer 5

moisture contamination will prevent the flow of resin into the etched surface

Question 6

what does wettability mean

Answer 6

ability of a liquid to maintain contact with a solid surface

Question 7

what is used for enamel acid etching

Answer 7

variety of organic and inorganic acids, in practice a 30-50% aqueous solution of phosphoric acid is normally used

Question 8

what bonding agent is applied to the etched enamel surfaec

Answer 8

low viscosity bis-GMA resin or any one of the dentine bonding agent resins (often phosphorylated bis-GMA)

Question 9

how are bonding agents applied to the etched enamel surface

Answer 9

applied to etched and dry enamel surface, penetrate into the rough surface and then be light cured

Question 10

what % phosphoric acid is usually used to etch enamel

Answer 10

35%

Question 11

what are the advantages of using phosphoric acid as an etching agent

Answer 11

straight forward bond
strong acid etches well
resin can flow into the roughness

Question 12

why is bonding to dentine more complicated

Answer 12

the composition of dentine is 20% organic, 70% inorganic and 10% water and is full of permeable tubules

fluid pumps up from the pulp to dentine floor of any cavity which makes the surface wet
aged dentine is more mineralised, dentine near the pulp has more tubules and increases the moisture content

dentine is hydrophilic whereas most simple bonding agents are hydrophobic

low surface energy

Question 13

what are some requirements for dentine bonding agents

Answer 13

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

Question 14

what is bonding to dentine actually achieved by - ie what is the mechanism

Answer 14

dentine bonding agent and dentine surface mesh and interlock with minimal gaps
easy to see microscopically