Lower third molar fused with a supernumerary tooth: diagnosis and treatment planning using Cone-Beam Computed Tomography

Fusion is the union of two developing dental germs, resulting in a single large dental structure. It involve two normal dental germs or the germ of a normal tooth with a germ of a supernumerary one. Supernumerary teeth are additional teeth of the normal series which may occur in any region of the dental arch, althoug they are more common in the maxilla than in the mandible. This article presents a case of fusion between a third molar and a supernumerary tooth, in which a surgical intervention was carried out, with the objective of removing the dental elements. The panoramic radiography was complemented by the Donovan´s radiographic technique, but because of the proximity of the dental element to the mandibular ramus, it was not possible to have a final fusion diagnosis. Hence, the Cone-Beam Computed Tomography which provides precise three-dimensional information, was used to determinate the fusion diagnosis and also to help in the surgical planning.

牙融合是指两个发育中的牙胚（dental germ）发生联合，最终形成单个较大的牙体结构。该病变可由两个正常牙胚联合形成，也可由正常牙胚与多生牙牙胚联合所致。多生牙是指牙列中额外萌出的正常形态牙齿，可发生于牙弓的任何区域，但在上颌骨的发生率高于下颌骨。本文报告1例第三磨牙与多生牙发生融合的病例，该病例实施了外科手术以摘除患牙。本病例先采用曲面体层摄影（panoramic radiography）结合多诺万放射摄影技术进行检查，但由于患牙毗邻下颌支（mandibular ramus），无法最终确诊为牙融合。因此，本研究采用可提供精准三维影像信息的锥形束计算机断层扫描（Cone-Beam Computed Tomography，CBCT）来确诊牙融合，并辅助制定手术方案。