To evaluatethe detection rate, typing, and therapeutic effect of second mesiobuccal canals (MB2) of first molars under dental operating microscope.

88 maxillary molars with the presence of MB2 through cone beam computed tomography (CBCT) were collected, in which 68 were received root canal treatment and 20 were received root canal retreatment because of the missing canal of MB2 respectively. The type of mesiobuccal root canal in the former 68 maxillary molars were analyzed under CBCT. The 68 maxillary molars were divided into 2 groups, with 34 in each group. The experienment group received treatment under dental operating microscope, while the control group under naked eyes. MB2 detection rate, treatment and retreatment effect between two groups were compared. The latter 20 maxillary molars were also seperated into 2 groups, in which 10 cases were treated under microscope and 10 cases were treated under naked eye. The effect of retreatment was observed.

The type of mesiobuccal root canal in 68 maxillary molars under CBCT were mainlytype Ⅱ and type Ⅲ, with the proportion of 77.9% (53 cases) and 22.1% (15 cases) respectively. The detection rate of MB2 in the experimental group was 100%, and 91.2% (30 cases) in the control group, a statistical difference can be found between 2 groups (P＜0.05). 97.5% (33 cases) of the experimental group was successfully treated, and 79.4% (27 cases) for the control group (P＜0.05). The success rate of retreatment under microscope was 60% (6 cases), which was significantly higher than that of the naked eye (P＜0.05). In 3-month and 6-month follow-up, the treatment effect in experimental group was significantly better than the control group (P＜0.05).

Dental microscope can help to increase MB2 detection rate and improve treatment and retreatment effect.

To investigate the anatomical features of alveolar bone in gummy smile patients with cone beam computed tomography (CBCT), and provide the reference for miniscrews implanted in anterior alveolar crest.

A total of 63 cases of adults with gummy smile were selected for the study and the CBCT data of jaw bones were obtained. The mesiodistal interradicular distances, buccal-lingual thickness and buccal cortical bone thickness were measured at three different level which included 4 mm, 6 mm and 8 mm above the alveolar crest.

The mesiodistal interradicular distances increased along with distance between measure level and alveolar crest. (P ＜ 0. 05). The interradicular distance were the least when measured between central incisor and lateral incisor (P ＜ 0. 05). The interradicular space between central incisors presented the least buccal-lingual thickness (P ＜ 0. 05). No significant differences were observed between the other thicknesses of anterior interradicular spaces (P ＞ 0. 05). The buccal cortical bone thickness increased along with distance between measure level and alveolar crest (P ＜ 0. 05). The thicknesses were the least between central incisors while the most between lateral incisor and canine (P ＜ 0. 05).

The mesiodistal interradicular distances, buccal-lingual thickness and buccal cortical bone thickness are found increased with the height level. Given the most bone mass and cortical bone thickness, canine and lateral incisor interval can be recommended as the place for the miniscrews inserting.