Dowel system for waxing denture construction
pontics in &bud
Roberto von Krammer K., Cirujano-Dentista Santiago,
his article describes a technique using a special dowel to facilitate the waxup of pontics in fixed partial denture construction. In the dowel system, a pin dowel (Fig. 1) is first placed in the impression and is later replaced in the cast by a pontic dowel (Fig. 2) upon which the pontic is waxed. The pin and pontic dowels have identical shank measurements to make them interchangeable in the cast. The advantage of the dowel system is that the pontics are carved on a firm base and can be easily removed for ready access to all surfaces in carving. They may be carved independently from the retainers.
PROCEDURE FOR DOWEL SYSTEM 1. Make an impression of the prepared arch with elastic impression material. 2. Determine the location of the future pontics in the impression. In the center of each of these zones, insert a pin dowel with its plastic sheath (Figs. 3 to 5). Use of the plastic sheath allows for easy removal of both the pin and pontic dowel from its seat in the cast and/or allows the use of the dowel system with electroformed casts. The pin dowels must be inserted following the path of insertion of the future fixed partial denture. If the shoulder end of the pin dowel does not fit exactly to the ridge, flow molten wax between them. 3. Pour the stone cast. When set, separate the cast from the impression (Fig. 6). Remove the pin dowels, and replace them with pontic dowels (Fig. 7). 4. Mount the casts on the articulator and reduce the pin dowels if necessary to allow 2 to 3 mm of space between the top of the dowel and the opposing occlusal surfaces (Fig. 8). 5. Wax the retainers in the usual manner (Fig. 9).
Fig. 1. Front (lefrl and back views of pin dowel.
Waxing the pontics 1. Cover media.
a separating Fig. 2. Front (left) and back views of pontic dowel.
The C. V. Mosby
Fig. 6. Cast has been separated from impression. Note that long axes of pin dowels coincide with those of preparations. Fig, 3. Arroros point at sites chosen in impression placement of pin dowels.
Fig. 4. Pin dowels have been inserted into elastic impression media at points selected previously.
strated. Pontics of any type may be substituted the pontic dowel.
Separating the pontics from the dowel
Fig. 5. Pin dowels with their plastic sheaths. 2. Cover the coronary portion of the pontic dowel with a thin layer of sticky wax (Fig. 10). 3. Complete the final waxup with inlay wax (Figs. 11 and 12j. In this technique, an all-wax pontic is demon-
When the pontic is cast independently: 1. Remove the waxed pontic from the cast. 2. Warm the end of a cotton pliers. 3. Grasp the dowel with the warmed pliers; when the wax is sufficiently heated, pull the pontic away from the dowel. 4. Retouch the dowel’s insertion point. The pontic is now ready for casting. When the pontics and retainers are to be cast in one piece: 1. Join the pontics and retainers with molten wax. 2. Lift the entire assembly from the cast. 3. Remove the dowels as indicated previously.
ALTERNATE This obtained
DOWEL SYSTEM PROCEDURE
technique is used when the cast is not from an elastic impression or when the
Fig. 10. Starting waxup
Fig. 8. Length of pontic dowels has been adjusted interocclusal space available.
Fig. 11. Finished
Fig. 9. Retainers have been waxed up. dentist prefers to select the site for the placement of the pontic dowel on the cast rather than in the impression. The pin dowel is not used in this procedure.
Technique 1. Determine the location of the pontics on the cast, and make a pencil mark in the center of each of these sites. 2. Drill holes of a diameter greater than the dowel into the cast on the points previously marked. The holes must coincide with the path of insertion of the future restoration, and their depth must be equal to the length of the pontic dowel. 3. Fill the holes with self-curing acrylic resin. 4. Lubricate the pontic dowels. Insert them into the resin filled holes to their shoulders and allow to set. The acrylic resin, once it has hardened, provides a seat for the pontic dowels. 5. Wax the pontics as previously outlined.
Fig. 12. Completed
waxup of fixed partial denture.
SUMMARY The use of special dowels is described as a means of facilitating the waxup of pontics in fixed partial denture construction.