impressions & provis Flashcards
defn of impression
GPT 9TH edn
a negative imprint of hard and soft tissus in mouth, from which a positive reproduction can be formd
what factors of soft tissue management must be done before impression takign
TISSUE HEALTH
- tissue may not be in the optimum state due to active perio disease, tissue trauma during prep etc
MOISTURE CONTROL
- salivary ejector, cotton roll etc
- CR contaminates some APS (Zhermack brand)
GINGIVAL TISSUE DISPLACEMENT
- mechanical by retraction cords
- chemical by epinephrine, or aluminium chloride (Expasyl, but FL say dont like this)
- others by electrosurgery, soft tissue laser or rotary gingival technique
features of a good impression
- captures accurate details of tooth prep: no air bubbles, tears
- captures all teeth in arch to allow articulation of casts
- captures soft tissue surrounding prep
- no distortion, no drag
defn of a provisional restoration
gpt 9th ed
- to enhance esthetics, stabilisation and/or function for a limited period of time, after which it is to be replaced by a definitive dental prosthesis
- to assist in determination of therapeutic effectiveness of a specific tx plan or the form & function of a planned definitive prosthesis
requirements of a provi
BIOLOGIC
- protect pulp & tooth structure
- maintain periodontal health
- provide occlusal stability
- maintain tooth position
- insulation from thermal & bacterial insults
MECHANICAL
- resist functional load
- maintain inter abutment alignment
AESTHETIC
- color compatibility
- used as a guide to achieve optimum aesthetics in the definitive restoration , similar to try in stage for complete dentures. because beauty preferences are highly subjective, verbal description is vague, can use provi to communicate
ideal properties of provi
- biocompatible
- strong
- convenient handlign (sufficient working time, rapid setting time)
- dimensional stability (dont want it to shrink overtime)
- easy to contour and polish
what are the displacement techniques of gingival tissues
MECHANICAL
1) retraction cord
2) displacement paste eg Expasyl
- aluminium chloride containing paste
3) occlusal matrix impression technique
- index fabricated from a rigid material directly over prepped tooth and trimmed 1mm short of margin
- index seated over tooth preps with medium bodied impression material, ensuring apically directed flow of impression material ??? IDK LAH NVM
CHEMICAL
1) epinephrine
- seldom used due to risk of tachycardia if placed on lacerated tissue
2) ferric sulphate
3) aluminium chloride but this is hemodent…
4) potassium aluminium sulphate
5) astringent - hemodent
SURGICAL
1) rotary gingival curettage
2) excision with scalpel
3) electrosurgery
4) radiosurgery (cutting with radio waves)
classification of impression materials
INELASTIC
1) impression waxes - compound
2) impression plaster - type I gypsum
3) ZOE impression pastes
ELASTIC
split into hydrocolloids and elastomeric materials
HYDROCOLLOIDS
1) reversible
2) irreversible aka alginate
- sodium or potassium salts of alginic acid react chemically with calcium sulfate to produce insoluble calcium alginate
ELASTOMERIC MATERIALS
1) polysulfide
2) condensation polymerisation silicone
3) polyether
4) addition polyerimerisation silicone
properties of irreverisble hydrocolloids
- no by products
- poor dimensional stability due to high percentage of water
ADV
- rapid setting
- straightforward technique
DISADV
- poor accuracy and surface detail
- low dimensional stability
properties of reversible hydrocolloids
aka agar hydrocolloids
it is when there is a suspension of agar particules of water that can be liquefied on heating, and turned to gel on cooling
- agar changes from elastic gel to viscous fluid at elevated temps and this change is REVERSIBLE
properties
- setting time is on cooling
- no by products
- poor dimensional stability also because of high percentage of water
- very good accuracy
ADV
- if poured immediately, can produce cast of excellent dimensional accuracy and acceptable surface detail
- no custom tray required because accuracy is improved with increased bulk vs elastomeric materials accuracy improved with reduced bulk
- low material cost
- hydrophilic
- long working time
DISADV
- low tear resistance
– low dimensional stability
- special equipment needed eg conditioning unit
INDICATIONS
- multiple preps
- where moisture control is not achievable
PRECAUSTIONS
- must be poured immediately
- stone only
properties of polysulfide
mercaptan rubber + lead dioxide -> polysufide rubber + water
moa: cross linking
PROPERTIES
- setting time: 10-16min
- by product: water
- dimensional stability: poor bc of loss of water as a by product
- very good accuracy
ADV
- high tear resistance
- easier to pour than other elastomers
- low material cost
DISADV
- messy, stain risk
- unpleasant sulfide odor
- long settig time of 10 mins
- dimensional stability only fair because it gives off water as byproduct, causes dimensional contraction
- better dimensional stbaility and tear strength than hydrocolloid but worse than polyether and addition silicone
PRECAUTIONS
- must be porued within 1 hour
