Impression Materials Flashcards
function of impression materials
provide accurate replica of surface and shape of hard and soft oral tissues
impression definition
negative reproduction of tissues
dental stone definition
fill impression, produces positive replica [stone cast]
mucostatic materials
fluid materials that displace soft tissues slighty
e.g. give impresison of undisplaced mucosa
mucostatic material examples
zinc oxide eugenol ZOE
low viscosity alginates
mucocompressive materials
viscous material that record an impression of the mucosa under load]i.g give impression of displaced mucosa
mucocompressive material examples
impression compound, high viscosity alginates/elastomers
why wait before pouring cast after impression
advantageous to wait for a time before you pour the cast, to minimise permanent strain = deformation
elastic materials example group
hydrocolloids
hydrocolloids
2 phase system of fine particles, one dispered in another phase
alginate [non reversible]
agar [reversible]
alginate
hydrocolloid, non reverisble
sodium alginiate, calcium sulphate
hot water speeds up setting, crosslinking continues
adv and disadv of alginate
adv - ease of use, ok setting time
disadv - poor tear strength, avoid moisutre in storage
requirements of impresison material
acuracy;
flow [surfsce detail], no dimensional change, easy removal, no shape change in storage, easy to decontaminate, compatible with cast material, ease of use, short setting time, acceptable taste/smell
properties affecting;
viscosity, setting mechanism, thermal expansion coefficient ideally low, tear strength
elastomers examples
polysulphides, silicone, polyether
elastomer polyether
impregum
monophase impression material
need special tray, undergoes addition polymerisation
