64 model cast bridge restoration. Selective opened partial retainer - definition

section

• what is FPD model cast duplication method

• what is needed to for this method?

• refractory model and casting process

• when is this used

• what is a risk

• what is FPD model cast duplication method

• another method for bridge fabrication. We use this method if we have to make a bridge restoration, but the preparation of the abutment teeth is very complicated

• dental technician will cast the bridge over the model, but according to this reason we need a model made of refractory material (able to withstand high temperatures of casting). Because for base metal alloys the temperature of casting is over 1000C and we need a model made of refractory material able to withstand these temperatures.

• what is needed to for this method?

• dental technician will cast the bridge over the model, but according to this reason we need a model made of refractory material (able to withstand high temperatures of casting). Because for base metal alloys the temperature of casting is over 1000C and we need a model made of refractory material able to withstand these temperatures.

refractory model and casting process

1. Initial Model:
   A first impression is taken and poured with plaster or dental stone to create the initial model.

2. Duplicating the Model:
   This model is duplicated using A-type silicone (commonly used today) or reversible hydrocolloid.
   The silicone is poured into a plastic mold around the gypsum model.
   Once set, the gypsum model is removed and the mold is filled with refractory (investment) material to create a heat-resistant duplicate.

3. Wax Application:
   The refractory model is dipped into a mixture of special waxes to create a smooth, sticky surface.
   The wax-up (retainers, pontic) is done directly on this model in full contour.
   Wax is later reduced on the vestibular surface and incisal edge to allow space for porcelain layering.

4. Spruing and Investing:
   Sprue formers and the crucible former are attached.
   The model is placed into a casting ring and invested with investment material.

5. Casting:
   After wax elimination, molten alloy is cast into the mold.
   The refractory model is destroyed during this step.

6. Finishing:
   The final bridge is removed and all adjustments, cleaning, and polishing are done on the original (first) model.

• when is this used

We use this method in a case of complicated teeth preparations on the abutment teeth or if we have to make very big or very long bridge restoration.

• what is a risk

If done normally in such cases there is a big risk of deformation of the wax pattern on the retainer therefore it is better to cast it directly on the refractory model.