Clinical and laboratory technology of orthopedic treatment

by combined cast crowns
The most advanced prosthesis design for the restoration of anatomical crowns front teeth is cast crown with veneer from plastic. It has several significant advantages over the combined stamped crown:

1. Cast frame of artificial combined crowns is more rigid than stamped. It is less susceptible to elastic deformation, thus making it more reliable fastening of facing material.

2. Cast frame can be made in the form of a cap, densely covering the prepared tooth stump. Lack of contact hard tissues with plastic, as well as accuracy of fit to the tooth exclude harmful effects of plastics and provide more reliable fixation prosthesis.

3. In the case of treatment by cast crown abutment tooth can be prepared from the shoulder. This allows us to minimize the impact of plastic on the edge periodontium (plastic ends on the ledge, not immersed in the gingival pocket and not deformed gingival attachment).

4. Manufacture of the cap with the shoulder makes it possible to increase the layer of plastic in the cervical area, which improves the aesthetic qualities of the prosthesis. Through a thin layer of plastic can shine metal, and small thickness facing its color is usually different from the other sections of labial surface.

5. The means of fixing plastic liners, which are used in the manufacture of cast crowns, are more reliable than stamped.

6. Cast combined crowns have the advantage in orthipedic treatment of tooth defects, when the missing part of the tooth restored cast suspension or facing material on the cast cap. In these cases stamped combined crowns are less resistant to chewing pressure.

7. Cast combined crowns are the most convenient desing for support of cast bridge.

The main problem that must be addressed in the design of the cast combined crowns, is to create a secure attachment for the plastic facing. Prepared tooth stump is fully covered by a cast cap, which is constructed for mounting plastic.

Fig.2.Cast simplified design combined crown

The design, developed by Mate, provides for the preparation of the tooth has a labial gum shoulder, but the crown is constructed so that the shoulder was based not only the edge of the cast cap, but also part of a facing material.

The author first used the principle of split cap and a slit-like space for going down in it facing material. Original is also a technique to obtain cast frame.

Fig.3. Cast combined crown by Mate.

More appropriate, according to N.Kirsten (1961), a complete closure of the tooth prepared on the scarp metal seals. In this case, the tooth is completely isolated from contact with plastic. To maintain the same holding power cladding is recommended to simulate a straight shoulder on the cap. Even more reliable, in our opinion, they grip in the formation of a shoulder at an angle less than 90°. Emerging from this undercut along with the strengthening of plastic in the slit-like space on the cutting edge contributes to a strong fixation facing material.

Fig.4. Cast combined crown by Н.Kirsten (1961)

The location of the metal on the cutting edge makes it difficult to obtain the necessary transparency and color of facing in this place. At the same time shortening the metal canopy crown weakens. In this connection searches for the most rational design of combined of cast crowns were continued. So, in order to avoid weakening of the crown for shortening the cutting edge, Ch.Miller proposes to build robust retention points for the plastic facing, using plastic beads.

Fig.5. Cast combined crown by Ch.Miller