Abstract : Purpose : Our aim was to assess the prevalence and root and root canal morphology of mandibular first molars in a Japanese population using dental cone beam computed tomography (CBCT).

 Materials and methods : We analyzed CBCT images of 279 mandibular first molars from 141 patients. Numbers of roots and root canals, and root canal configurations were evaluated according to Vertucci's classification. The distance from the distolingual (DL) canal orifice to the distobuccal (DB), mesiobuccal (MB), and mesiolingual (ML) orifices for mandibular molars with a DL root were evaluated.

 Results : Most of the mandibular first molars (41.9%) had two roots with three root canals, and most of the mesial root canals (38.4%) were type Ⅳ. The prevalence of three-rooted mandibular first molars was 23.6%, with a bilateral incidence of 18.4%. There was significantly greater incidence of three-rooted molars on the right side of the mandible than on the left (p<0.01). The mean inter-orifice distance from the DL canal to the DB, MB, and ML canals of the three-rooted mandibular first molar were 2.7, 4.2, and 3.4 mm, respectively.

 Conclusions : Our results revealed that in this Japanese population, the prevalence and root and root canal morphology of the mandibular first molar were consistent with previously reported data. The present study also demonstrated that CBCT is a useful diagnostic tool for investigating root canal morphology.

Abstract : A patient was a 12-year-old boy. Both the maxillary right central incisor and left lateral incisor with dens invaginatus showed periapical lesions. The lesions healed 20 months after root canal treatment.

 The maxillary left first molar also showed dens invaginatus ; there have been very few reports of dens invaginatus on maxillary first molars. This unique case was found by CBCT images.

Abstract : Nickel-titanium files can be used to prepare curved canals, but cannot penetrate the original canals if a previous dentist modified the root canal morphology. Negotiation, patency, and glide path before nickel-titanium instrumentation are important for success. This case report introduces a novel technique for negotiating root canals. Negotiation was performed by the novel technique using clockwise and counter-clockwise motion of the engine in three cases. This technique was effective in cases of a ledge in retreatment, a canal not easy to access, and challenging anatomy.

Abstract : This case report describes the procedures and prognosis of internal adhesive treatment and intentional replantation for maxillary premolars with crown/root fracture. Two cases with buccal and lingual fragments caused by crown/root fracture are presented : one was a vital tooth and the other was a non-vital tooth. The teeth were extracted and stored in commercial balanced saline solution. The two fragments were repositioned, and the fracture surface was removed from the internal canal using a micromotor with a long carbide bar until the bar was visible. The cavity was dried using a capillary suction tip and treated with dentin conditioner. Dual-cure core resin and a 0.9-mm U-shaped orthodontic wire were used to fill and reinforce the root canal cavity. The end of the root apex was retrofilled with composite resin and replanted in the socket. The patient's prognosis was favorable and the teeth retained occlusal function at the 3-year follow-up. Our results showed that intentional replantation after internal adhesive treatment with dual-cure resin and a metal wire is an effective and practical treatment for crown/root fracture of maxillary premolars.