Outline Form

The outline form of the access cavity should be shaped correctly and positioned accurately to establish complete access for instrumentation, from cavity margin to the apical foramen. The internal anatomy of the tooth established by the pulp dictates the external outline form. The endodontic cavity preparations are therefore done in a reverse manner; from the inside of the tooth to the outside. Thus, the external outline form is established by mechanically projecting the internal anatomy of the pulp onto the external surface. This can be executed by drilling into the pulp chamber and then working with the bur from the inside of the tooth to the outside, cutting away the dentin of the pulpal roof and walls overhanging the floor of the chamber.

The factors of the internal anatomy that regulate the outline form of endodontic coronal cavities are:

i) Size of the pulp chamber.

ii) Shape of the pulp chamber.

iii) Number, position and curvature of the root canals.

Size of the Pulp Chamber

The size of the pulp chamber considerably affects the outline form of the access cavity. The preparation must be more extensive in a young patient unlike that in an old patient. The difference is so because with age the pulp recedes and the pulp chamber becomes smaller in all three dimensions. This

becomes extremely important in preparing the anterior teeth for younger patients who have large root canals and thus require larger instruments and filling materials.

Shape of pulp chamber of mandibular incisors

Shape of the Pulp Chamber

The shape of the pulp chamber should be accurately reflected by the finished outline form. Let us consider an example of a mandibular molar tooth. In this tooth, the floor of the pulp chamber is usually triangular in shape, owing to the triangular position of the orifices of the canals. This triangular shape is extended upto the walls of the cavity and out onto the occlusal surface. Thus, the final cavity outline form is generally triangular. Likewise, if you consider maxillary first premolar, the outline form of the endodontic coronal cavity in this tooth is narrow, elongated oval in bucco-lingual projection. This reflects the size and shape of the broad, flat pulp chamber of this particular tooth.

Number, Position, and Curvature of Root Canals

The cavity walls often have to be extended or modified to allow an unstrained instrument approach to the apical foramen, in order to instrument each canal efficiently without interference. This is particularly apparent in cases of curved canals. The outline form of the endodontic cavity is significantly affected when the cavity walls are extended to improve instrumentation. This change is for convenience in preparation, therefore, the convenience form regulates the outline form to some extent.