DMS 2 Flashcards
What is used to etch enamel
37% phosphoric acid
name 3 reasons why dentine bonding is more complex than enamel
- fluid pumps from pulp to dentine floor of cavity so surface always wet
-permeable tubules - smear layer
- hydrophillic
- low surface energy
wettability
- what is it
- whats used to measure it
ability of a liquid to maintain contact with a solid surface
contact angle is used to measure wettability
critical surface energy
liquid must have a lower surface energy than the surface it is being placed on for it to flow and stick
(non stick pans have a very low surface energy so nothing sticks)
smear layer
layer of organic debris that remains on dentine surface after restoration preparation
total etch vs self etch in regards to smear layer
total etch - removes
self etch - incorporates
discuss dentine and dentine bonding agents with regards to critical surface energies
wet dentine has a low surface energy
if composite applied to this it would not stick
dentine bonding agents increase dentine surface energy - they are dentine wetting agents
describe the process of total etchand bond on dentine
(often reduced to 2 steps e.g prime and bond used in GDH)
1. etching dentine - removes smear layer, decalcifies outermost layer (washed off)
2. prime - bifunctional agent, hydrophillic end to bind with dentine and hydrophobic end to bind with subsequent resin
3. bond (adhesive) - mixture of resins, penetrates primed dentine which now has a hydrophobic surface, forms micromechanical bond within tubules and exposed dentine collagen fibres (molecular entanglement) - formation of hybrid layer
hybrid layer
micromechanical bond between dental adhesive system and demineralised dentinal collagen
(resin material penetrating into dentinal tubules)
demineralised collagen intertwined with cured adhesive monomer
configuration factor
ratio of bonded surfaces to unbonded surfaces
what impact does a high configuration factor have when placing a composite restoration
high configuration factor increases polymerisation contraction stress which increases risk of restoration failure
discuss stress-strain curve
- definition of stress and strain
- what does it define
stress - force per unit area (measured in pascals)
strain - change in length compared to original length (shown as ratio or percentage)
- curve defines rigidity of material
elastic modulus
measures resistance of material to elastic deformation
steep slope on stress strain curve = rigid
ISO 4049 test
test used to determine depth of cure
(cylinder of composite cured, scrape away soft composite, divide remaining hard composite depth by 2)
hardness ratio test
test used to determine depth of cure
cylinder of composite cured
surface of cylinder hardness determined and compared to other points
at 80% of surface value - this is depth of cure
