Abstract
A 33-year-old man was referred by a local dentist for autotransplantation of the right mandibular third molar to the site of the left mandibular first molar. Before the operation, dental-cone-beam computed tomography was performed to measure the dimensions of the graft tooth and the bone volume of the socket. The three-dimensional (3D) structure of the graft tooth was created from the 3D imaging data. A replica of the graft tooth was produced using a stereolithographic CAD/CAM system before autotransplantation. A socket of the appropriate size and structure was created and the graft tooth was extracted immediately before grafting. This procedure shortened the time needed to fit the graft tooth into the socket and reduced injury to the periodontal membrane. The postoperative outcomes of autotransplantation of the tooth were good.
Tooth autotransplantation allows the adjacent teeth to remain intact and is readily accepted by patients because the grafted tooth can be used similarly to a normal tooth. This procedure has been performed conventionally ; but its narrow indication range and the need for high technical expertize based on extensive clinical experience have limited its clinical use.
The authors produced a replica of a graft tooth from dental-cone-beam computed tomographic (CBCT) three-dimensional (3D) images, using a CT 3DX system (J. MORITA MFG. Co., Kyoto, Japan) and a stereolithographic system for autologous tooth grafting . CBCT analysis can be used to assess the detailed position of the mandibular canal and maxillary sinus as well as bone quality before surgery, thereby reducing operation-related risks. This procedure allows the bone volume of the socket and the structure of the graft tooth to be assessed before surgery, facilitating the identification of patients in whom tooth autotransplantation is indicated. The authors also devised a method to simplify the surgical technique by using implantation burrs and replica teeth; the results are described in this report.
Patient and methods
The patient was a 33-year-old man who was referred for autotransplantation of the right mandibular third molar to the site of the left mandibular first molar. The patient’s medical and family histories were not relevant to the present disorder.
Panoramic X-ray films showed that the root of the left mandibular first molar was intact, and the right mandibular third molar was partially erupted ( Fig. 1 A and B ). The CT 3DX system was operated at a tube peak potential of 80 kV, a filtration of 31 mm Al equivalents, and a tube current of 2 mA, with an imaging time of 17 s. A single 360° scan collected projection data from a cylinder (height 30 mm, 240 pixels or height 40 mm, 320 pixels; diameter 40 mm, 320 pixels) for image reconstruction. The effective dose (uSv) estimated by the ICRP 2007 recommendations was 29.62. CBCT images revealed that the right mandibular third molar had a single root, the apex of which came in contact with the mandibular canal. The root length was 10.59 mm, and the width of the cervical region was 10.40 mm ( Fig. 1 C).
To produce a replica of the right mandibular third molar, CBCT imaging data were obtained at a slice thickness of 0.25 mm, and a 3D model was constructed using 3D trabecular structure measurement software (R.2.02.12-S, RATOC Systems, Inc., Osaka, Japan) ( Fig. 2 A) . A 680 nm semiconductor laser was applied at a spot diameter of 0.15 mm, using a stereolithographic system (SCR8000HD, Denken Ltd. Co., Kyoto, Japan). Eight replicas were produced from the 3D model, using light-curing type UDMA resin (DeSolite). The incremental resin thickness was set at 0.1 mm ( Fig. 2 B). Reproducibility was assessed by comparing another extracted tooth with its replica before surgery (full length of extracted tooth: 14.0 mm and full length of replica tooth: 14.0 mm; cervical width of extracted tooth: 10.0 mm and cervical width of replica tooth: 10.5 mm). Although error apparently occurred at each stage of producing the CAD model and replica teeth, the total error was in the acceptable range .
On 27 September 2004, the left mandibular first molar was extracted with the patient under local anaesthesia. The tooth socket at the transplantation site was drilled by implantation burrs and adjusted to fit the replica produced beforehand. The fit of the socket and the replica, and the relations with the adjacent and opposing teeth were examined ( Fig. 3 A) . The right mandibular third molar was extracted and grafted immediately to the socket. Suturing and fixation were performed ( Fig. 3 B). Three weeks after surgery, the root canal was filled with a calcium hydroxide agent. Three months after surgery, the root canal was filled with gutta-percha points. Six months after surgery, prosthetic treatment was performed. About 4 years after surgery, the patient remains free of any abnormalities ( Fig. 4 A and B ).
