Construction of point-based mandibular median sagittal plane / 上海交通大学学报（医学版）

Objective: To develop a new point-based mandibular median sagittal plane (MMSP) by selecting from varied mandibular planes which were formed by combining bony landmarks derived from multiple regions of the mandible. Methods: Forty adult patients were evenly divided into two groups by the degree of chin deviation: mandibular asymmetric group (MA group) and mandibular symmetric group (MS group). Three dimensional (3D) mandibular models were rebuilt by Mimics 19.0 software. In this software, 3D coordinates of 4 central landmarks and 6 pairs of lateral landmarks were collected. Then 120 candidate planes were constructed by point-based method, and compared with the reference plane formed by the iterative closest point (ICP) algorithm. All the planes were reordered and screened by geometric indices such as angle, distance and area in MS group. In addition, the clinical symmetrical indices such as point-to-plane distance, surface area difference, volume difference, and 3D deviation ratio of screened planes were compared in MA and MS groups. Results: The candidate planes co-constructed with landmarks from three mandibular regions (symphysis, mandibular angle and coronoid process) were the top 5% of all the planes. Among them, no statistical difference between B-Cor-Golat plane (constructed with supramentale, coronoid superius and gonion lateralis) and ICP plane was found (P >0.05), while there were significant differences between the rest screened planes and the reference plane (P<0.05). Conclusion: The B-Cor-Golat plane can be used as the mandibular median sagittal plane to reflect the symmetrical degree of the mandible well.

Advances in determination of median sagittal plane of facial soft tissue / 中华口腔医学杂志

Facial symmetry is a crucial component of human facial esthetics. Along with the increasing pursuit of aesthetic, in recent years, more and more researchers have focused on facial asymmetry assessment, of which determining the facial median sagittal plane is the first and most important step, and it will directly affect the accuracy of asymmetry evaluation and clinical treatment outcome. Limited by technical means, the earlier studies of facial soft tissue asymmetry assessment were mainly based on midline from two-dimensional (2D) images. Along with the development of three-dimensional (3D) measurement and data analysis techniques, new methods such as 3D landmark-based method and mirror-original alignment method have become main trend nowadays. This article systematically reviews the methods of determination of median sagittal plane of facial soft tissue, elaborates the developments and the latest research progress in this field, and discusses the advantages and limitations of each method in order to provide reference for clinical application.

Influence of positional relationship between the long axis of the mandibular anterior teeth and the alveolar bone on the treatment design of dental implants / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study aimed at investigating and measuring the positional relationship between the long axis of the mandibular anterior teeth and the alveolar bone using cone beam computed tomography (CBCT) to provide reference data for implant treatment.</p><p><b>METHODS</b>From the CBCT image database, 150 cases of radiographic data were selected according to the inclusion criteria and then were divided into six groups: males' mandibular central incisors, males' mandibular lateral incisors, males' mandibular canines, females' mandibular central incisors, females' mandibular lateral incisors, and females' mandibular canines. The angle (β) formed by the long axis of the mandibular anterior teeth and the corresponding alveolar bone was measured and recorded. Based on the long axis of alveolar bone, if the teeth incline to the lingual side, the value of the angle (β) was positive; otherwise, the value was negative. The resultant data were analyzed by SPSS 19.0.</p><p><b>RESULTS</b>The β of the mandibular central incisors presented a mean value of 4.77° (range: -8.17°-16.10°) for male subjects and 5.38° (range: -5.63°-12.93°) for female subjects. The β of the mandibular lateral incisors exhibited a mean value of 6.12° (range: -2.87°-
17.57°) for male subjects and 5.81° (range: -7.70°-15.70°) for female subjects. Finally, the β of the mandibular canines presented a mean value of 5.01° (range: -8.13°-17.67°) for male subjects and 6.21° (range: -7.70°-17.87°) for female subjects. The percentages of the β between -10° and 10° of males' mandibular incisors, mandibular lateral incisors, and mandibular canines were 87.34%, 80.67%, and 88.00%, respectively and those of females were 90.67%, 82.66%, and 82.66%, respectively. Whether male or female, the percentages of the β between -10° and 10° of the mandibular anterior teeth were more than 80%. The β that inclined to the lingual was not more than 20° and to the labial did not exceed 10°.</p><p><b>CONCLUSIONS</b>The long axis of the mandibular anterior teeth was almost consistent with the long axis of the alveolar bone. Therefore, the positional relationship could be referred to make reasonable implants treatment plan.</p>