An evaluation of guidelines for the apical enlargement of maxillary premolars.

A newly proposed set of experimental guidelines for the final size of apical enlargement was evaluated by instrumenting filling and evaluating a series of extracted maxillary premolars. The guidelines were applied to differing anatomical configurations of this type of tooth, and to teeth in which instrumentation terminated at various distances from the foramen. Comparison was made with the conventional guideline of enlarging to three sizes greater than the first instrument that binds, with instrumentation to 0.5 mm from the foramen. All teeth were vacuum injected with India ink and dried, mechanically enlarged according to the experimental or conventional guidelines, and examined for the presence of apically extruded debris. The teeth were then filled, cleared, and visually inspected for the condition of preparation in the apical portion. For the conventional guideline, preparation was generally judged as poor, and debris was usually forced through the foramen. With the experimental guidelines, adequate preparation was obtained for most canal configurations at 0.5 and 1 mm from the foramen, and at 1 mm the incidence of extruded debris fell sharply. Anatomical conditions possibly contraindicating the experimental guidelines were found and characterized.