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The Dental Cast (Pouring of the Cast (Method ( Rinse disinfectant from…
The Dental Cast
Pouring of the Cast
MUST BE
DISINFECTED
(soak in hypochlorite for 60 seconds)
Instruments required
Impression, mixing bowl, spatula, gypsum, weighing scale, measuring cylinder, wax knife, lecron, vibrator, flat tile
Gypsum products
Type 1 -- Impression plaster (POP)
Type 2-- Model or lab plaster (POP)
Type 3 -- Laboratory stone
Type 4 -- Die stone (silky rock)
Components of cast pouring
Filling impression of anatomic portion
Forming base by mounding on a smooth tile
Method
Rinse disinfectant
from impression; shake/ blast off excess water
Outline
extent of cast o the impression with pencil/ marker
Use lab knife to
remove excess impression material
that will interfere with the pouring of the model
For mandibular arch, be sure to remove excess material from the tongue area
Mix gypsum material
(POP or dental stone)
Add powder to water
(measure accordingly)
Mix
till smooth (manual/ vacuum mix)
Debubble
if it is a rubber base impression
Use
Vibrator
Press tray handle against vibrator (low/ medium speed)
Use spatula to pick up about 1tsp of mixed material.
Allow mix to flow into distal of the most posterior tooth
while impression is vibrated so that the material flows towards the anterior teeth
Turn tray on its side
to provide continuous flow of material
13.
Continue to add gypsum
in small increments until occlusal/ incisal surfaces are filled
After anatomy portion is filled, use larger increments to fill the entire impresion (turn off the vibrator)
When filled,
place lightly over vibrator to coalesce
. (over-vibration causes bubbles)
Set poured impression aside to harden somewhat
Pouring the base
After initial set,
mix some new gypsum
material
Place mix in a mound on
plexiglas tile
and shape to approx
5x5cm and 2.5cm thick
Invert fim, poured impression onto base
Position so that occlusal plane of posterior teeth is parallel with table top, midline is at the centre of the base
Use spatula to smoothen the 2 parts together, remove excess
Base should be about 1cm thick at the thinnest portion
Leave to set for 45-60 minutes before separating impression
Trim and smoothen cast
Finish
Accuracy
Appearance
Sulcus preserved
Landing all around (1-2mm)
Anatomical Features
All casts
Residual ridges
Vestibules/ sulcus
(maxillary buccal, mandibular lingual)
Frenum/ fremae
: maxillary labial, maxillary buccal, mandibular labial, mandibular buccal, lingual
Maxillary cast
Tuberosities
Rugae
Incisive papilla
Hamular notch
Posterior border of hard palate
Fovea palatinus
Median palatine raphe
Torus palatinus (if present)
Mandibular Cast
Retromolar pads
Buccal shelf
Mylohyoid ridge
Torus mandibularis (if present)
Genial tubercles
Classification of Edentulous Saddles
Purpose
Gives clues to the
treatment and design problems
of a particular case
Location and number of edentulous spans
Type of support required
: Tooth/ mucosa/ tooth an mucosa
Facilitates discussion between dentists and communication with technicians
Kennedy Classification
What is its?
Anatomical classification which describes the number and distribution of edentulous areas present
CLASS 1
Bilateral edentulous areas
located
posterior to the remaining natural teeth
(bilateral free end saddles)
Undercut often present on distal surface of the abutment tooth
CLASS 2
Unilateral edentulous area
located posterior to the remaining natural teeth (
unilateral free end saddle
)
CLASS 3
Unilateral
edentulous area with
natural teeth remaining both posterior and anterior to it
(posterior bounded saddle)
Modifications
Each extra bounded saddle is a modification
First classify the main saddle. Other edentulous spans will then be mods
Class 4 has no modifications
CLASS 4
A
single but bilateral
(crossing the midline edentulous area located
anterior
to the remaining teeth
Applegate's rules for applying Kennedy Classification
Classification should
follow rather than precede extraction
If
3rd molar
is missing and
not to be replaced
, it is
not considered
in the classification
If the
3rd molar
is present and to be
used as in abutment
, it is
considered
in the classification
If the 2nd molar is missing and not to be replaced, it is not considered in the classification
THE MOST POSTERIOR EDENTULOUS AREA DETERMINES THE CLASSIFICATION
Edentulous areas other than those determining classification are called modification spaces
The extent of the modification is not considered, only the number
there is
NO MODIFICATION IN CLASS 4
The Dental Cast
Primary Cast (study/ diagnostic)
Diagnosis
Treatment planning
Special trays
Presentation aid
Usually poured in plaster of paris or lab stone (or both)
Master Cast (working)
Fabrication of prosthesis
Must have accurate details
Usually poured in lab stone or silky rock
Parts of the Cast
Anatomic portion
Teeth, oral mucosa and muscle attachment
Art portion
Base, landing
