Preparation of space for posting: effect on thickness of canal walls and incidence of perforation in molars.

A total of 150 extracted maxillary and mandibular molars separated into six groups of 25 teeth each were prepared to the size of a 30 endodontic file. Numbers 2, 3, and 4 Peeso drills were used to produce a post cavity preparation in the root canals of these teeth. After use of each size of Peeso drill, the thickness of the canal walls was measured at two levels: the middle level, 4 mm from the canal orifice; and the apical level, 7 mm from the canal orifice. Mean thickness of all walls was determined for each tooth and drill size. The incidence of root perforations and strippings was recorded also. We found that distal roots of mandibular molars and palatal roots of maxillary molars are best suited for post cavity preparation. Most perforations and strippings occurred on the distal walls of mesial roots of mandibular molars or on the proximal walls of the buccal roots of maxillary molars.