Kiwako Izumi

Assessment of the Relationship Between Impacted Mandibular Third Molars and Inferior Alveolar Nerve With Dental 3-Dimensional Computed Tomography

PURPOSE The purpose of this study was to assess the capacity of dental 3-dimensional computed tomography (3D-CT; limited cone-beam CT) to predict the exposure and injury of the inferior alveolar nerve (IAN) after mandibular third molar extractions. MATERIALS AND METHODS This study was a retrospective case series of patients who presented for extraction of mandibular third molars. Subjects eligible for study enrollment were those who underwent preoperative dental 3D-CT because the mandibular third molars were determined to be extremely close to the IAN on panoramic radiogram. The predictive variable was the anatomic relation of the IAN and third molar apices and was a binary variable, contact or noncontact. The primary outcome variable was IAN exposure, and the secondary outcome variable was IAN injury. RESULTS From January 2006 to August 2007, 1,853 mandibular third molars in 1,539 patients were extracted. Among them, dental 3D-CT was performed on 53 third molars in 47 patients. The mandibular third molars were judged to make contact with the mandibular canal on dental 3D-CT images in 35 cases (66%). Intraoperative IAN exposure was observed in 17 (49%) contact cases and 2 (11%) noncontact cases on dental 3D-CT images. Of 53 cases extracted after dental 3D-CT examinations, IAN injury occurred in 8 cases (15%). IAN exposure led to IAN injury in 36.8% of cases, whereas IAN injury occurred in only 2.9% of cases without IAN exposure. Although the incidence of IAN injury in the molar-canal contact cases was 23%, all 8 cases with IAN injury (100%) were included in these contact cases. CONCLUSION When viewing the anatomic relation between the IAN and mandibular third molar root apices using dental 3D-CT, contact of the 2 anatomic structures results in an increased risk for IAN exposure or injury.

The relationship between jaw deformity and scoliosis

ObjectivesTo analyze the relationship between lateral displacement of the mandible and scoliosis.MethodsFrom April 2002 through July 2003, we examined posteroanterior cephalometric radiographs and chest X-rays from 85 patients with jaw deformities and a control group of 20 patients with no jaw deformities. To measure the lateral shift of the mandible, we drew a horizontal baseline (X axis) on the cephalogram connecting the intersection of the external margins of the orbits and the most lateral points of the greater wings of the sphenoid. A vertical baseline (Y axis) was then marked perpendicular to the X axis, intersecting the ethmoid crista galli. Then, we measured the lateral displacement of the mandibular mentum from the Y axis. Displacement to the right was designated positive; that to the left was designated negative. Cobbs method was used to measure scoliosis curves on chest X-rays; the direction of the curve was designated similarly.ResultsOf the 85 patients with jaw deformity, 23 (27.1%) had a Cobb angle exceeding 10°. None of the control group had scoliosis exceeding 10°. No correlation was found between the direction of mandibular displacement and the direction of scoliosis.ConclusionThis study suggests a relationship between jaw deformities and scoliosis, as scoliosis was found in 27.1% of the patients with a main complaint of jaw deformity.

Three-dimensional Assessment of the Accuracy of Maxillary Repositioning by Le Fort I Osteotomy with Emphasis on Maxillary Backward Transference

Objective: To evaluate the accuracy of repositioning of the maxilla by Le Fort I osteotomy with emphasis on maxillary backward transference. Materials and Methods: Thirty patients with jaw deformity who underwent Le Fort I osteotomy were enrolled in the study. The patients were divided into 3 groups: backward transference group, in whom both molar regions were moved >2 mm in the posterior direction; forward transference group, in whom both molar regions were moved >2 mm in the anterior direction; and minor transference group, in whom both molar regions were moved <2 mm. The 3-dimensional position of the maxillary central incisor (U1) and both first molars (R6, L6) were measured on presurgical, surgical, and post-surgical dental models. The difference between planned and actual movements was analysed using Wilcoxon signed-rank test. Results: In the backward transference group, the maxilla was moved backward to excess, probably because of a preconception that forward movement after the operation due to occlusal force will occur. In the forward transference group, the maxilla was located more forward as a consequence of being excessively moved upwards. In the horizontal direction, influence of the operators position and the plate fixation method were thought to explain the differences between the backward transference group and the forward transference group. Conclusion: To perform the operation more precisely, additional reference points with a plane factor are needed for Le Fort I osteotomy. In the future, the infrared sensor might be useful and effective.