Non Surgical Root Canal Treatment of Unilateral Mandibular Fused Second and Third Molars: a Rare Occurrence

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Table of Contents

  • Introduction
  • Case Report
  • Discussion
  • Conclusion


Dental developmental anomalies are considered to be rare in clinical practice. Gemination and fusion are two developmental disturbances presented as the union of teeth. The union between affected teeth can be at the level of enamel, dentin, cementum, or pulp depending on the stage of tooth development before the merging of tooth germs takes place. Irregular tooth morphology of fused teeth involves union of epithelial and mesenchymal germ layers. The clinical management of teeth suffering from developmental anomalies is considered to be a complex procedure as it may result in malocclusion, esthetic complications, and several oral disorders. Diagnosis, treatment planning, and rehabilitation of such cases are often very challenging due to abnormal presentation of the crown and severely distorted root canal system anatomy. The aim of this article is to present a case of successful non surgical root canal treatment for a very rare developmental anomaly of fused second and third mandibular molars.

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Case Report

A 34 years old Caucasian female presented to the Endodontic Clinic, Faculty of Dentistry, Cairo University with spontaneous diffuse pain related to right mandibular area. Her medical history was not contributory. Clinical examination revealed the presence of fused crowns of mandibular second and third molars, with a deep cavity related to the crown of second molar (figure 1). Tooth was not sensitive to percussion. Periodontal probing revealed normal values of 1 mm on the buccal, lingual, and distal aspects and 2 mm on the mesial aspect. Radiographic examination showed two fused crown having separate pulp chambers with 3 separate roots; mesial root, middle root, and distal root with widening of the periodontal membrane space.

After the patient was provided an informed consent, the tooth was anesthetized and rubber dam isolation was done. Complete removal of carious enamel and dentin was performed using round bur size 3, followed by opening of access cavity using Endo Z bur in the mesial pulp chamber, which was completely necrotic without any signs of viable tissues or bleeding. Pathological pulp exposure was seen on the mesial wall of the distal pulp chamber, which was seen to be vital and irreversibly inflamed. Diagnosis of the fused molars was confirmed as, necrotic mesial root canal system and symptomatic irreversible pulpitis of the distal root canal system. Access cavity was done in the distal pulp chamber, followed by complete debridement using 2. 5% sodium hypochlorite (NaOCl) irrigation.

Scouting of the root canal system was done under dental loups magnification of 6X with the aid of the anatomical landmarks and the dentin map using K-file size 15 with 2% taper. 4 root canals where revealed, 2 in mesial root, 1 in the middle root, and 1 in distal root. Confirmation of the working lengths was done using Apex locator. Upon working lengths determination, cleaning and shaping procedure was done using controlled memory nickel titanium M-Pro rotary system (Innovative Materials and Devices, China). First file of tip size 18 and taper of 8% was introduced in the canals till 2/3 of the working length under torque of 3 N/m and speed of 400 rpm. K-file size 15 was introduced to the full working length to insure patency of the root canals. Second file of tip size 20 and taper of 4% was introduced to the full working length under torque of 1. 5 N/m and speed of 150 rpm, followed by the third file of tip size 25 and taper of 6% under the same speed and torque. The distal root canal was prepared using rotary M-pro file of tip size 35 and taper of 6%. Active ultrasonic irrigation was done using side vent needle using 2. 5% NaOCl and 17% EDTA (Figure 5). A confirmatory mastercone radiograph was done with gutta percha of size 25 and taper 6% in mesial canals and middle canal, and size 35 and taper 6% in distal canal.


Upon observation of the normal number of teeth in the oral cavity for this patient, the case presented here could be diagnosed as teeth fusion. The permenant dentition has a prevalence of fusion ranging between 0. 1- 1%, and the primary dentition ranging between 0. 5-2. 5%. Teeth affected by fusion are most probably anterior teeth and its usually unilateral. 12,13 Complex root canal anatomy of fused roots is considered very problematic when it comes to root canal treatment, as seen in this case report. The abnormal external morphology and malpositioning of affected tooth may cause difficulties with attempted rubber dam isolation. Fusions of molar teeth, or fusion involving supernumerary teeth, are considered particularly rare and may result in caries, periodontal disease and crowding. Clinically, In order to differentiate between germination and fusion, some authors have proposed that, when counting the teeth, a crown with developmental anomaly should be counted as a single tooth. The challenge to differentiate between a fused from a geminated tooth led Brook et al. to propose a new neutral term, referring to such anomalies as ‘double teeth’. Double teeth are usually asymptomatic and, if aesthetically acceptable, do not require treatment. Whenever such condition causes aesthetic and functional problems such as dental caries in grooves, periodontal problems associated with grooves in fusion zones, endodontic complications, asymmetries and malocclusions, therapy is inevitable. Treatment options include tooth extraction, hemisection and intentional replantation associated with endodontic and/or orthodontic treatment, crown reconstruction with fixed prostheses or composite resins. The presented case shows a rare anomaly of two fused crowns with separated pulp chambers, one common tooth trunk, and 3 roots with 5 root canals. Radiographic and clinical assessment are essential for the successful endodontic treatment of anomalous teeth20, because it is imperative to evaluate the altered anatomy correctly. Its success relies on the careful preparation of the access cavity and the cleaning, shaping, and three dimensional filling of the root canal system.


A Successful non surgical root canal treatment has been presented in this case report, by which massive developmental anomaly can be observed upon clinical and radiographic examination. Cone beam computed tomography plays an important role in such cases, but if it is not available, several radiographs must be taken coupled with operating under magnification to insure proper root canal treatment.

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