The Influence Of Anterior Crossbite On The Positions Of Teeth And The Relationship Between Anterior Crossbite And Tooth Morphology

Scholars have different views about the early treatment of skeletal crossbite, which may be difficult to be treated only by orthodontics and have to undergo an operation after growing-up. The crossbite of anterior teeth may influence teeth positions. There maybe have some relationship between the abnormality of anterior occlusion and teeth morphology. This research aims to provide evidence of early treatment of anterior crossbite. This thesis contains two parts below:The first part: Investigating the mesiodistal dimensions of the teeth crown in permanent dentition of Chinese teenagers.In order to measure the mesiodistal dimensions of the crown in permanent dentition of Chinese teenagers, 224 teenagers' models in permanent dentition with class I molar relationship were measured and statistically analyzed. Mesiodistal crown dimensions: U6>U1>U3>U4>U2>U5, L6>L4>L5>L3>L2>L1, second molar excluded. The dimensions were analyzed in comparison with the data in 1959, and research into transformation of mesiodistal crown dimensions in permanent dentition during the long history. The averages of mesiodistal crown dimensions increased comparatively to the numerical values that Huiyun Wang offered, except for the mandibular first molar. Conclusions: (1)The mesiodistal crown dimensions of teenagers in the contemporary increases with the improvement of nutrition. (2) Various environmental factors influence the mesiodistal dimension of the teeth crown. (3)Biological variations between mandible and maxilla may lead to the more augment of teeth size in maxilla than in mandible.The second part: the influence of anterior crossbite on positions and morphology of teeth.81 teenagers in permanent dentition with anterior crossbite were chosen in group 1 and 95 teenagers in permanent dentition without anterior crossbite were selected in group 2 as control. Then, the teeth positions and morphology of both groups were compared. Results: (1) The percentage of ill-positioned teeth in maxillas was significantly higher in group 1 (14.0%) than that in group 2 (8.8%)(P<0.05).(2) The ill-positioned teeth with higher percentage in maxillas of group 1 were Iabially-displaced canines, palatally-displaced lateral incisors and palatally-displaced or impacted second premolars. (3)The mandibular teeth in group 1 showed a rather lower percentage of ill-position (0.9% for group 1, 3.5% for group 2, P<0.05).In other words, the patients with anterior crossbite are liable to have ill-positioned teeth in maxillas, but often have good order teeth in mandibles. ㏕he patients with anterior crossbite are apt to have conical lateral incisors (0.6% for group 1, 0.1% for group 2, PO.05). Conclusions: The possibility of ill-positioned teeth and heteroplasia teeth in maxillary increases in the patients with anterior crossbite. Therefore, anterior crossbite not only has the influence upon maxilla but also has the influence upon upper teeth. Those patients should be given orthodontic treatment as early as possible.