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MASTER CAST:Should have reproduced details of:
- DBAs, functional width and depth of the sulci.Poured in in stone or 75% stone-plaster mix (strength).Clinician should scribe, on the Final impression the:
- position of the post-dam.- planned preservation of the peripheral roll.
Box out the land area relevant to the preserved peripheral roll, to have a quality cast with inscribed extent of the post dam.
Survey and outline the undercuts on master cast. There will be left and right anterior undercuts and slight
undercuts at the anterior aspects of the left and right tuberosites and mylohyoid ridges..
Some cast areas may require tin foil added to produce relief areas, or blocking of some undercut areas using plaster.
Master cast with peripheral border land and carved-out post-dam area
Preparing the Record Rims:Comprise bases & occlusal rims.Bases made of wax, thermoplastic resin or PMMA.Occlusal rims generally made of wax.Bases for occlusal rims / aesthetic control should be:
- Well adapted & conform closely to the master cast.- Stable, on the cast and in situ.- Free of voids or surface projections on fit surface.- Not > 1 mm thick over the residual ridge to prevent:
- it interfering with the setting of denture teeth.To impart rigidity parts of base be;
- 2 mm thick in the post-dam area of upper denture.- 2 mm thick in the lingual flange of lower CD
Easily removed from the cast.Smooth rounded form reproducing cast contours.
Record Bases & Rims (Contd):Incorporated a form of post-dam in the denture base.Restored functional width & depth of the sulci. Made of materials stable at oral temperature.Clinician should select the material to form the base.Wax bases do not provide stability per se:
- their usage is not encouraged. Thermoplastic resins tend to be brittle and also they:
- lack the versatility of PMMA.- no longer enjoy widespread usage.
Made of heat-cured, self-cured & VLC PMMA.Despite varying tissue-fit all provide adequate stability.Theoretically, heat-processed bases are superior.
Bases well-adapted, stable & finished to high quality. Failure to have a base fitting the cast is:
- the fault of the technician.Base fitting to the cast, but not the relevant arch:
- the fault often lies with the clinician.The posterior border of upper denture should displace
mucosa overlying the apo-neurosis of tensor palatini at the junction between hard and soft palates (Ah Line / Vibrating line).
Clinician knows details of palatal tissue displaceability. Clinician responsible to scribe the appropriate extent
& depth of post-dam using e.g a Le Cron Carver.Clinician to ensure scribing post dam appropriately.
Preparing a Base in VLC Resin:Smear DBAs of both casts with a thin layer of vaseline.Remove the plastic sheets from the VLC material.Do not cause the material to pull and become too thin. With fingers coated lightly with petroleum jelly, apply:
- VLC material completely over DBAs of upper cast. Let the material slump into the palatal vault area. Gently adapt the VLC to the cast. If an air pocket is trapped at the vault of palate, poke a
vent hole in the VLC, letting the air escape through the vent hole and re-adapt the material.
Then gently tap-tap the material in order to eliminate the hole & smooth the surface of the VLC.
With a wax spatula adapt material into entire peripheral roll.
Cut the excess material off at the external aspect of the land area of the cast.
Smooth the peripheral area of the VLC with index finger.Ensure that the peripheral roll of cast is completely filled. Work the excess VLC off & make it flush with the land area. Have the posterior aspect of upper record base extended
4mm. beyond the projected vibrating line. Thin the posterior aspect of upper record base to one-half
its original thickness with a forefinger coated in petroleum jelly.
Excess thickness of material in this area will result in acrylic shrinkage and pulling away of the record base.
For the mandibular base, cut a trapezoidally shaped piece of VLC material and adapt it to one side of the lower cast.
Fill and fit the VLC material to the facial peripheral roll just as done for the upper.
Fill and fit the material to the lingual roll just as done for the external peripheral roll.
Cut a second trapezoidally shaped piece of VLC material and adapt it to the other side of the mandibular cast.
Fill, fit, and trim the facial and lingual peripheral rolls just as done on the first side.
Any space in excess of 2mm. between the record base and the cast indicates that a new record base will be required.
Blend overlapping pieces at the midline by tapping them together.
Evaluate both base for adaptation, smoothness and peripheries and fit to cast.
Except the posterior aspect of maxillary base, there should be no thin areas of VLC (pink areas).
A uniform medium pink color indicates a consistent and proper thickness of the VLC record bases.
Place the casts and record bases into a VLC machine.Set the machine carousel at its lowest position and turn
the machine on for two minutes. After this first exposure, remove the casts and bases. Gently tease the record bases off of the casts. Replace bases upside down in machine for 6-mintutes.
After this second cure wash bases with soap & water.With acrylic bur, smoothen & blunt all peripheries.Fit them back onto their respective casts and adjust internal
aspects so that they fit snugly (no falling off & not requiring pressure to separate them.)
Make new base if space > 2mm at post-dam area. Draw vertical lines at the area of left & right second
bicuspids on both record bases. Connect these lines with a line drawn parallel to & 2mm.
above the anterior peripheral roll of each base plate.Draw a fourth line on the record bases, connecting the
vertical lines, 4mm. lingual to the crest of RR of each cast. Trim to thin VLC material within this rectangular outline to
paper thickness. (This make the setting of the anterior teeth easier).
Adding Wax Occlusal Rims to Record Bases:Confusion exist on how to make the upper rim/ACB. Useful guides to customizing occlusal rim not requiring too
much addition or removal at chair-side include:- Pre-extraction records (Biometric guides, Casts, Teeth, RPDs, IDs, CDs and Copy denture
techniques.- Measurements, Alma gauge, Alameter & Papilla-meter.
Similar guidelines also apply to lower rim but: - The 'Manchester rim' or the construction of the central-bearing apparatus reduces the potential for confusion over dimensional parameters.
Height of rim not higher than retro-molar pads.
Warm the mid-section, width-wise, of a piece of pink bite rim wax and break it into two halves.
Warm an end of this half piece and an end of a full piece of pink wax.
Slightly overlap and fuse the two ends together to form one elongated piece of wax.
Pass this wax through the flame of a properly adjusted Bunsen burner.
Several passes in all directions will render this wax uniformly soft.
Fold the wax in half lengthwise and then widthwise.Pass thru the flame again & fold in half length-wise. One side of wax block should be rounded & smooth.The other side should have all of the free wax sheet
ends laminated together.
Flame soften & bend wax-block into “U” shape lengthwise.
Push the laminated end firmly down onto the residual ridge area of the maxillary record base.
With fingers, mold the labial surface of the soft wax down as far as to the land area of the cast.
Center the body of wax over crest of maxillary ridge. Mold the lingual surface of the wax smoothly toward
the palatal surface of the record base. Visualize the wax & ensure that it is placed on the
base such that the anterior section of the denture will be oriented with a slight anterior sloping of the labial surface from cast land area to the occlusal surface.
The incisal edge of the maxillary wax rim should be 22mm from the land area as measured in the lateral incisor area.
Enough bulk of wax available to accommodate the above mentioned 22mm height anteriorly.
Posteriorly, occlus. surf. parallel to crest of upper RR. Create proper BL width of the occlusal plane:
- 3mm in area of anterior teeth.- 5mm. In bicuspid area & 7mm. In molar area.
Projected center of occlusal plane over crest of RR. Heat Hyde scraper to smoking.Take the wax rim base off the upper cast.Run the flat surface of the hot blade up and down the
facial surface of wax. Feather wax right to the edge of the record base.
Facial surface wax is smooth and has no voids. If voids are present, add wax to the defect with a
hot wax spatula. Wax in the anterio-facial region has a slight anterior
inclination.Wax in facial aspect of bicuspid & molar areas is
more upright. Heat a wax spatula to smoking & shape lingual wax
to a smooth, void-free inclined surface. The wax should feather right onto the palatial
surface of the Base. Occlusal portion of rim centered over RR. Have correct widths of occlusal surface of the rim.
Flatten occlusal plane with a smoking Hyde scraper. Be sure that the height is 22mm. from the lateral
incisor land area anteriorly.Plane of rim parallel to the mean foundation plane of
RR when viewed antero-posteriorly. Occlusal surface is flat bucco-lingually, uniform and
void-free. Posteriorly, cut distal aspect of upper rim at the mid-
point of second molar area. Have this posterior surface angled slightly toward the
anterior from the base interface to the occl. plane. • Finally, smooth the wax using a paper towel with
cold water. A piece of nylon mesh will also smooth wax nicely.
No wax, other than a slight film on the palatal and tuberosity aspects of the record base.
Smooth any wax flashing at the peripheral roll edges.
Repeat the same procedures for lower rim, except for the following variations:
- anteriorly, height of rim is18mm above land area.
- lingual surface of rim fitted down to lingual peripheral roll in the same manner as the facial aspect of rim is finished down to LB peripheral roll.
- occl. Surf. of rim on a flat plane from its anterior point of reference to its posterior left and right points of reference, one-half the height of the retro-molar pads.
- width of lower rim is same as the upper rim.
