2. final impressions

which phase of dental Tx?

• examination and tx planning

• prelim design

• pt education and motivation

I

which phase of dental Tx?

• simple restoration

• endo Tx

• perio Tx

• extraction of hopeless teeth

• interim partial denture

II

which phase of dental Tx?

• final rpd design confirmed

• pre-prosthetic surgery if needed

• fixed partial denture and crowns

III

which phase of dental Tx?

• fabrication and delivery of rpd

• oral and written instruction 

• (main one discussed this lecture)

IV

which phase of dental Tx?

• post-insertion care

• periodic recall

• reinforcement of edu and motivation

V

final impressions happen (@ time) of phase IV fabrication fo the rpd

first visit

external casting of framework happens (@ time) of phase IV fabrication fo the rpd

between first and second visit

external processing of the denture happens (@ time) of phase IV fabrication fo the rpd

between third and fourth visits

what are the two impression materials for final impressions for rpds?

non-elastic and elastomeric

what are the two non-elastic impression materials?

rigid and thermoplastic

what are the four elastomeric impression materials?

hydrocolloids, polysulfides, polyether, silicone

which elastomeric impression material is used for stock and custom trays?

irreversible hydrocolloids

which elastomeric impression material is used for stock tray, custom tray AND altered cast technique?

silicone

which elastomeric impression material is used for custom tray and altered cast technique?

polysulfide 

which elastomeric impression material is also known as Mercaptan rubber base?

polysulfide

which elastomeric impression material is not the material of choice

polyether

which elastomeric impression material has these negative effects?

• low tear strength 

• less surface detail 

• not dimensionally stable 

• difficult control of length and width of impression borders (usually overextended impressions)

irreversible hydrocolloid

which elastomeric impression material has these positive effects?

• hydrophilic

• inexpensive

• pour well with stone

• pleasant taste and odor

irreversible hydrocolloid

which elastomeric impression material is used with lots of dentition left, usually Kenn Class III and IV - tooth supported? 

irreversible hydrocolloid 

which elastomeric impression material is also called alginate?

irreversible hydrocolloid

which elastomeric impression material has these negative effects?

• slow recovery from elastic deformation

• poor long-term dimensional stability (loss of reaction byproducts)

• unpleasant odors 

polysulfide

what does polysulfide’s negative effect of poor long term dimensional stability mean?

it is not to be used with lots of remaining dentition and undercuts

what does polysulfide’s negative effect of loss of reaction byproducts?

water is the byproduct; this requires it to rebound 7-15 minutes and pour w/in 30 min

which elastomeric impression material has these positive effects?

• high tear strength 

• long working and setting time (8-10 minutes)

• acceptable accuracy 

polysulfide

what is polysulfide’s long working and setting time ideal for?

border molding 

which elastomeric impression material is used a lot per the lecturer?

silicone

which elastomeric impression material has these positive effects?

• high accuracy 

• excellent dimensional stability 

• good tear strength

• inexpensive 

silicone

which elastomeric impression material negative effects?

• working time 3-5 min

silicone

which elastomeric impression material has these negative effects?

• short working time

• low flexibility, stiffness

• low tear strength 

polyether

which elastomeric impression material has these positive effects?

• good accuracy 

• hydrophilic meaning good wettability of tissue

polyether

which elastomeric impression material is hydrophilic and hydrophobic?

silicone

three ways to take final impression

• stock tray

• custom tray (maxilla and mandible)

• altered cast technique 

what are the goals of impressions?

to accurately record remaining teeth and full extension of edentulous areas (anterior and posterior, where major and minor connectors will sit)

what do you NEED to capture for maxilla?

ptyergohamular notches and entire palate

what do you NEED to capture for mandible?

buccal shelves, retromolar pads, facial vestibule, lingual vestibule

which mandible area is the area of the major connector?

lingual vestibule

what can stock trays be constructed from? perforation type?

metal or plastic; can be unperforated or perforated to help with retention of impression material 

which stick tray material is used with adhesive?

plastic

stock trays should be (BLANK)mm larger than outside surface of residual ridge to provide sufficient thickness or impression material and avoid tearing

5

what happens if the stock tray is too small?

• impression material will not support itself away from confines of the tray

• any area not covered by tray will not be recorded

where to add rope wax

on lingual side of border to add extension

what happens if the tray size is too big?

• results in overextended borders

• needs to be adjusted (possible w plastic trays)

how can stock trays be modified?

rope wax, modeling compound, or heating and opening plastic/thermoplastic trays

if properly dimensioned stock tray not possible fabricate custom tray when border modeling is important kenn class I and II

what kenn classes is border molding important?

kenn I and II

when do you use a stock tray?

when minimal border molding is required (kenn class III and IV) and/or short edentulous areas and minimal bone loss (otherwise flange is necessary)

describe the sequence to take impressions

• prepare and place impression material into the tray

• place material in oral critical areas (cingulum/occlusal rest preps)

• minimal border molding movements for edentulous areas

• remove impression and assess its quality

• disinfect and pour the impression with dental stone type V immediately

  • if you cannot pour, store in 100% humidity but pour within the hour

for tooth-supported impression what impression material can be used?

alginate

what do you assess for final impression quality?

• all anatomical landmarks 

• surface areas of major connectors entirely captured

• all aspects of abutment teeth were recorded (rests but also lingual and buccal aspects were reciprocal and retentive arms will be located)

is this the goal of tooth supported or tissue supported?

impress ridge in anatomical form meaning at rest without applying lots of pressure

tooth-supported

is this the goal of tooth supported or tissue supported?

impress ridge in functional form under slight pressure to gain more support from soft tissue and distributes force more evenly between the tissue and teeth for less post-op visits

tissue supported

tissue or tooth supported?

distal extension, no rigid posterior stop so during function partial denture moves towards tissue 

tissue supported 

tissue or tooth supported?

• at rest

• no pressure

• minimum support from edentulous ridge 

• more movement → abutment loosening

tooth 

tissue or tooth supported?

• in function

• under pressure

• maximum support from edentulous ridge

• overly displaced tissues can become inflamed, impaired accompanied with bone resorption 

tissue

when are final impressions using a custom tray recommended?

when

• impression cannot be taken w a stock tray due to anatomy (too large or too small, large tori, etc)

• need for border molding (class IV, flange to compensate for bone resorption AND tissue-supported situations)

stock tray or custom tray?

• less lab time

• less accurate

stock tray

stock tray or custom tray?

• more lab time

• more accurate

• good for anatomical limitations

custom tray

stock tray for which Kenn classes?

III and IV

custom tray for which kenn classes?

all but especially I and II