A mold and method for making reproducible patterns

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  • A mold and method for making reproducible patterns

    M. T. Barreto, D.D.S.,* and G. Mumford, D.D.S., M.D.S.** University of Connecticut, School of Dental Medicine, Farmington, Conn.

    I n various research projects several wax patterns similar in form, size, thickness, and design may be needed. This article describes a three-piece mold that allows such patterns to be reproduced with a minimum of time, effort, and frustration.

    FABRICATION OF TRAY

    1. Hollow a lucite rod 1% inches in diameter and 1% inches in length with a %-inch drill, transforming it to a cylinder closed at one end with a wall thickness of A inch. 2. Drill four pinholes 1% inches deep and equidis-

    tant from each other with a ?&inch drill. 3. Cut the cylinder in two halves perpendicular to

    the long axis. 4. Cement four %-inch dowels, split or solid, in the

    four holes of the bottom half with a cyanoacrylate cement. The top half should slide on the dowels with ease. 5. Cut the top half of the cylinder vertically in two

    so that two pinholes are in each piece (Figs. 1 and 2).

    PREPARATION OF DIE

    The master die (prepared tooth) could be of any material, that is, ivorine or extracted tooth, stone, epoxy resin, or silver-plated die. 1. Flatten or groove one side of the base, regardless

    of the material used, for each relocation of the die into the mold. 2. Wax up the prepared tooth. 3. Place a sprue on the center of the wax pattern

    parallel to the long axis of the tooth. The sprue should be about 25 mm long and about 3 mm in diameter (ready-made wax shapes, &gauge round, Kerr/ Sybron, Emeryville, Calif.).

    *Assistant Professor, Department of Restorative Dentistry. **Professor and Chairman, Department of Restorative Dentistry.

    Fig. 1. Finished three-piece container.

    Fig. 2. Finished three-piece container, open. Four split dowels were cemented on base. Two top halves slide with ease on dowels.

    286 FEBRUARY 1983 VOLUME 49 NUMBER 2 0022-3913/83/020286 + 03$00.30/O @ 1983 The C. V. Mosby Co.

  • MAKING REPRODUCIBLE WAX PATTERNS

    Fig. 5. Die in position in bottom half. Top halves are ready for placement on dowels.

    Fig. 3. Die waxed up, sprued, and placed in silicone to finish line.

    Fig. 6. Injecting molten wax inside mold.

    Fig. 4. Finished mold. Bottom half shows cemented dowels and silicone impression of base of die. Both top halves show shape of crown and sprue; arrow points to funnel of sprue channel to ease wax injection.

    POURING OF MOLD

    1. Fill the bottom half of the tray with a silicone impression material (RTU 630A and B, General Electric CIo., Silicone Products Dept., Water-ford, N.Y.).

    2. Sink the die into the tray up to the margin of the

    Fig. 7. Open mold after wax injection. Sprue and flush should be removed and margins checked and, if necessary, finished.

    THE JOURNAL OF PROSTHETIC DENTISTRY 287

  • Fig. 8. Mold and dies assembled for fabrication of a three-unit fixed partial denture.

    wax pattern (Fig. 3) and allow the silicone to set. 3. Lubricate with a silicone lubricant. 4. Place the two top halves in position and pour the

    same silicone over the wax pattern and sprue, filling the tray completely, with only the sprue extruding from the silicone. Allow the silicone to set.

    5. Separate the mold. 6. Cut the top part in two with a scalpel or razor

    blade following the slot on the tray. 7. Flare the sprue channel at the top to ease wax

    injection. The three-piece mold is now ready to start mass production (Fig. 4).

    MAKING WAX PATTERNS

    A plastic coping (Coping disks, 0.06~inch, Howme- dica, Inc., Chicago, Ill.) may be used. It is especially indicated where the pattern represents a PFM coping: in general, very thin, easy to distort or break. The plastic gives rigidity to the pattern and makes it easy to handle. Whenever plastic copings are used, a vertical

    Fig. 9. Three-unit fixed partial denture ready for investing. Notice V-shaped cuts in clear plastic copings filled with wax.

    V-shaped cut on the buccal surface is made and filled with wax allowing for investment expansion (Fig. 9).

    1. Place the lubricated die, with or without a plastic coping, in the mold (Fig. 5). 2. Insert molten wax with a wax injector into the

    mold (Fig. 6). If a wax injector is not available, a medicine dropper can be used.

    3. Cool the wax, open the mold, and remove the die and wax pattern (Fig. 7). Check the margins and finish if necessary.

    4. Invest the wax pattern. This system is especially useful when the research

    project calls for several fixed partial dentures of similar design (Figs. 8 and 9).

    Reprint requests to:

    DR. MARIA T. BARRETO SUNY AT STONY BRINK

    SCHOOL OF DENTAL MEDICINE

    STONY BROOK, NY 11794

    288 FEBRUARY 1983 VOLUME 49 NUMBER 2

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