To investigate whether the RW-splint could be used to guide or determine the CR position of the lower jaw so as to provide help for the later diagnostic design.

20 class Ⅱ^Ⅰ malocclusion patients were recruited in orthodontic department of Foshan Stomatological Hospital. They were treated by RW-splint for half a year before orthodontic treatment. The overjet of anterior teeth were recorded before and after treatment.

The overjet of anterior teeth was (6.792 ± 0.795) mm before treatment and (7.720 ± 0.930) mm after half a year's treatment. The overjet of anterior teeth had significant difference (t=6.319, P ＜ 0.01). The overjet change of anterior teeth between before treatment and half year after treatment was (0.928 ± 0.657) mm.

The RW-splint wearing before treatment can be used to guide or determine the mandible in the CR position.

To find out the existence of Mandibular Incisive Canal (MIC) through CBCT scanning and measure its 3D relationship with the surrounding tissue, so as to provide protection for the operation in submental area.

CBCT images of 100 patients were measured and three dimensionally reconstructed. The measurement include following items, the existence of the MIC; vertical and horizontal diameter of MIC; vertical distance from MIC to the mandibular buccal and lingual wall; to the root apex, to the inferior border of mandible and alveolar crest in corresponding points (the mandibular first premolar, canine and incisor).

the MIC was 100% visible in CBCT. The mean distance between MIC and buccal bone plate and lingual bone plate was 3.52 ± 0.54 mm and 5.37 ± 0.25 mm. The average distance from the inferior border of the mandible, the apex of the root and the crest of the alveolar bone was 10.44 ± 0.61 mm、10.57 ± 0.76 mm and 20.21 ± 0.83 mm relatively. The distance from MIC to the inferior border of the mandible in male was 10.70 ± 0.43 mm and 10.17 ± 0.63 mm in female, P＜0.05.

The detection rate of MIC is high and there are many variations. It was suggested that the location and size of the MIC should be checked in CBCT in each patient before operation, which is helpful to avoid surgical complications in submental area.

To compare the morphology of the crown roots of upper and lower canines in patients with skeletal Class Ⅰ, Ⅱ, and Ⅲ malocclusions by CBCT and to provide guidance for the clinical treatment of orthodontics.

Randomly selected patients with permanent occlusal malocclusion who had undergone CBCT and X - ray skull lateral radiographs were Classified according to the ANB angle size: group Ⅰ, group Ⅱ, and group Ⅲ. Three-dimensional reconstruction was used to obtain the median sagittal section images of the right upper and lower canines. The crown root angle, crown root deflection distance, and lip tangent angle at the center of the clinical crown were used as indicators for measurement and analysis with the use of AutoCAD software.

The difference in the crown-root skew distance between different sagittal face types, including upper canines (F＝3.335, P＝0.042), lower canines (F＝3.745, P＝0.029) crown root angles and upper canines (F＝3.312, P＝0.043), and lower canines (F＝3.641, P＝0.032), was statistically significant (P < 0.05). The crown root angle of the maxillary canine in group Ⅰ was larger than that in group Ⅱ, and the deflection distance of the crown root was negative and the absolute value was lager in group Ⅰ than in group Ⅱ (P < 0.05). The deflection distance was positive and greater in group Ⅲ than in groups Ⅰ and Ⅱ (P < 0.05). There was no significant difference in the maxillary canine crown-labial tangent angle between the different sagittal facial misalignment groups (P > 0.05).

Differences in the morphology of canines were found among subjects with skeletal Class Ⅰ, Ⅱ, and Ⅲ malocclusions. The root of the upper canine in Class Ⅰ malocclusions was relatively closer to the labial side of the crown than that in Class Ⅱ malocclusions. The root of the lower canine in Class Ⅲ malocclusions was the closest to the lingual side of the crown among the three Classes.

To compare the the rate of en-masse space closure with sliding mechanics between 3M SmartClip self-ligating brackets and 3M Gemini MBT twin brackets in the first premolar extraction patients.

20 Class I malocclusion patients who need first premolar extraction treatment were selected. One arch side of the second premolar and first molar were bonded with 3M self-ligating brackets and the other side bonded with Gemini MBT twin brackets. After leveling and alignment, 0.48 mm × 0.64 mm (0.019 inch × 0.025 inch) stainless steel wire and nickel titanium coil springs were used to close the space. An average rate of space closure per month (mm/month) was calculated in each side.

The median rates of tooth movement for the SmartClip bracket side (1.03 mm per month) and the Gemini MBT twin brackets side (1.00 mm per month) were not significantly different (t = 0.70, P = 0.48).

There was no significant difference in the rate of en-masse space closure between SmartClip brackets and Gemini MBT twin brackets.