Figure 8-32. Trimmed maxillary and mandibular cast.
Prefabricated trays are made to fit everyone moderately well, but will not fit anyone very well. On the other hand, a custome tray provides a dentist with an impression material carrier that permits the dentist to make a more accurate impression that they could make using a stock (prefabricated) tray. The custome tray is made on a diagnostic cast. The dentist draws the border outlines of the proposed custom tray on the diagnostic cast, as shown in figure 8-33(A), and gives other directions, such as handle position and the need for vertical stops. You may then make the tray so it conforms to the design. Two of the most popular ways of making custom trays are self-curing resin dough method and the vacuum method. We will limit this discussion to the more frequently used dough method.
The dentist will usually prefer a custom tray that provides room for a controlled thickness of impression material. Spacers used to develop vertical tissue stops accomplish this purpose. The stops are made to hold the tray off the cast by a distance equal to the thickness of the spacer. When the spacer is removed and the tray is placed in the patient's mouth, the stops hold the inner surface of the tray out of contact with the patient's tissue. The subsequent space between the tray and tissue is then later filled with impression material.
Figure 8-33. Design and blockout for a custom tray.Continue Reading