1 Flashcards
Problem with alginate impression - viscosity.
Because of their high viscosities, these impression materials will often displace the soft tissues ofthe vestibules, resulting in an overextended impression and resulting cast
Prior to making the impression, the patient is instructed to
rinse his or her mouth with water to reduce the \iscosit' of the saliva
Prior to inserting the impression tray, the patient should be asked to
swallow to elim- inate excess saliva
Figure 6-8 Note that a “fatty” pad of tissue (A) is often
present in the distobuccal area of the mandibular arch and may fold over the retromolar pad (B) and become trapped in an impression.This fold can be minimized by lifting this tissue upward and away from the retromolar pad while seating the impression.
An irreversible hydrocolloid impression should be poured in dental .stone within
10 minutes
Retention nodules for a cast
stone “mountains” on the bottom of the cast that are then used to prop up the initial die in another blob of wet stone so as to create a good land area.
Wlicn properly shaped, the cast sbould also exhibit land areas around the vestibules and a base of approx- imately
12-13 mm (1/2 inch) in tliickness
The land area shotild be approximately
2-3 mm (1/8 inch) wide on the buccal and labial
land area should be about
5-6 mm (1/4 inch) wide in the posterior
For most patients, the labial and lingual flange lengths will be of
equal length unless the patient has had a surgical extension of the vestibular notch or severe bone loss.
When border molding before you trim
chill in ice water **only when using wax/heated material
VPS does not have the viscosity or rigidity of modeling compound and therefore cannot be used to
correct borders that are underextended by more than 4-5 mm.
Also if not supported by the impression tray, VPS cannot be depended on to form
tray fianges 2-3 mm in thickness
The buccal shelf areas are initially border molded and must be completed
individ- ually
The minimum thickness of a master cast should be
12-15 mm in the thinnest area.