The influence of lower incisor angle on human masseter muscle activity

• Main Authors: Yu-Ling Chen, 陳玉玲
• Other Authors: Chi-Yang Tsai
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/71410197230311013001

碩士 === 臺北醫學大學 === 口腔復健醫學研究所 === 92 === Since Broadbent introduced standardized radiographic cephalometry at 1931, then be recommended to be used in the orthodontic field, cephalometric analysis started to develop. Tweed announced up to now well-known diagnostic triangle at 1954. He thought that the triangle formed by lower incisor axis, mandibular plane and Frankfort-horizontal plane was the basis for making treatment plan clinically: the angle formed by lower incisor axis and mandibular plane (IMPA) must be a right angle. This norm until now was still used by many orthodontists. Facial esthetics was chosen to establish the normal reference norms. But it needs to be proved that whether this right angle function properly or not. The aim of this study is to observe the relationship between IMPA and masseter muscle activity. By observing the change of electromyographic (EMG) data, we can establish the influence of IMPA on masseter muscle function. After the EMG data is processed and analyzed, we can discuss the status of IMPA angle on oral physiology. The results would be an index for clinical use by orthodontists. EMG maximum clenching values were measured from 20 healthy, dentate adult volunteers. We recorded the data when overall and anterior teeth were in contact with the custom-made bite registration material. We use the Ratio (MCVant /MCVall) to compare with IMPA and other cephalometric craniofacial morphology measurements by means of a nonparametric correlation analysis and Mann-Whitney U test. We could conclude that IMPA do not correlate with MCVant, MCVall and Ratio. The results showed that uprighting or proclination of lower incisors had no significance relationship with masseter muscle activity.