Читать книгу Fundamentals of Fixed Prosthodontics - James C. Kessler - Страница 112

Every restoration must be able to withstand the constant occlusal forces to which it is subjected. This is of particular significance when designing and fabricating a fixed partial denture because the forces that would normally be absorbed by the missing tooth are transmitted, through the pontic, connectors, and retainers, to the abutment teeth. Abutment teeth are therefore called upon to withstand the forces normally directed to the missing teeth in addition to those usually applied to the abutments.

If a tooth adjacent to an edentulous space needs a crown because of damage to the tooth, the restoration usually can double as a fixed partial denture retainer. If several abutments in one arch require crowns, there is a strong argument for the selection of a fixed partial denture rather than a removable partial denture.

Whenever possible, an abutment should be a vital tooth. However, a tooth that has been endodontically treated and is asymptomatic, with radiographic evidence of a good seal and complete obturation of the canal, can be used as an abutment. However, the tooth must have some sound, surviving coronal tooth structure to ensure longevity. Even then, some compensation must be made for the coronal tooth structure that has been lost. This can be accomplished through the use of a dowel core or a pin-retained amalgam or composite resin core.

Teeth that have been pulp capped in the process of preparation should not be used as fixed partial denture abutments unless they are endodontically treated. There is too great a risk that they will require endodontic treatment later, with the resultant destruction of retentive tooth structure and of the retainer itself. This is a situation that is better handled before the fixed partial denture is made.

The supporting tissues surrounding the abutment teeth must be healthy and free from inflammation before any prosthesis can be contemplated. Normally, abutment teeth should not exhibit mobility because they will be carrying an extra load. The roots and their supporting tissues should be evaluated for three factors:

1 Crown-root ratio

2 Root configuration

3 Periodontal ligament area