Original Article
Association between adult mandibular third molar and retromolar space: a three-dimensional study
Guo Xueqiang, Liu Xinqiang, Wang Zheng, Zhao Rui, Kong Lei
Published 2021-06-20
Cite as Chin J Orthod, 2021, 28(2): 74-79. DOI: 10.3760/cma.j.cn115797-20200422-21203
Abstract
ObjectiveTo investigate the size of mandibular retromolar space, and its relation with the status of the third molar.
MethodsUsing cone-beam computed tomography, the right posterior retromolar region were measured in three dimensions in 86 adult patients with a skeletal Class Ⅰ normodivergent pattern. All patients were divided based on the different status of the right third molar. Distance between second molar crown to the anterior border of the ramus was measured at the crown level and 2 mm apically lower level along the posterior occlusal line (POL, which connects the buccal cusps of the mandibular first and second molars). Distance between second molar root to lingual inner cortical bone was measured at levels of 2 mm, 4 mm, 6 mm, 8 mm and 10 mm apically to the CEJ border along the POL, respectively.
ResultsIn all groups (no third molar group, normal eruption group, horizontal impaction group, mesial impaction group, and vertical impaction group) the distance at the crown levels were significantly larger than that at root levels. Among all measurement levels, the space measured in normal eruption group and vertical impaction group were no less than that in the other three groups (no third molar group, horizontal impaction group and mesial impaction group).
ConclusionsWhen considering the distalization of mandibular molars, more attention should be directed to the lingual cortical bone of the mandible. The diagnosis accuracy of cone-beam computed tomography is higher compared with that of two-dimensional radiographs. In addition, different status of third molars, whether eruption of impaction, can also affect molar distalization.
Key words:
Retromolar space; Third molar; Molar distalization
Contributor Information
Guo Xueqiang
Department of Orthodontics, The Affiliated Hospital of Qingdao University, School of Stomatology of Qingdao University, Qingdao 266003, China
Liu Xinqiang
Department of Orthodontics, The Affiliated Hospital of Qingdao University, School of Stomatology of Qingdao University, Qingdao 266003, China
Wang Zheng
Department of Orthodontics, The Affiliated Hospital of Qingdao University, School of Stomatology of Qingdao University, Qingdao 266003, China
Zhao Rui
Department of Orthodontics, The Affiliated Hospital of Qingdao University, School of Stomatology of Qingdao University, Qingdao 266003, China
Kong Lei
Department of Orthodontics, The Affiliated Hospital of Qingdao University, School of Stomatology of Qingdao University, Qingdao 266003, China
平面(以及从下颌
平面向根方2 mm的平面)处第二磨牙牙冠到升支前缘的最短距离。牙根层面的测量以釉牙骨质界为参考，在其根方2、4、6、8、10 mm的水平面上沿POL线测量第二磨牙牙根与下颌骨舌侧内层骨皮质的最短距离。
畸形则是一种不错的选择。正畸医生可以使用种植支抗实现牙列整体远移，并可避免前牙唇倾、磨牙升高等不利的影响。然而，磨牙远移的量会受到磨牙后间隙大小的影响，尤其是下颌[3]。以往常以曲断片和侧位片测量磨牙后间隙，但这些测量方式存在着影像重叠、不能从三维方向上准确分析磨牙后区的实际解剖结构等问题[4,5]。而使用CBCT(cone-beam computed tomography)对磨牙后区进行三维方向的分析，可以弥补以上不足，不失为一种更可靠的方法[6]。近年来有学者对下颌磨牙后间隙的研究认为下颌磨牙远中移动的解剖限制是下颌骨舌侧内层骨皮质，而非传统观点认为的下颌升支前缘[7]。为此，本实验采用CBCT对成人下颌磨牙后区大小进行测量，并分析其与第三磨牙萌出/阻生状态可能存在的关系，以期为临床下颌磨牙远移提供相应的理论支持。
