BACKGROUND:Age and dental age are shown to have some limitations in predicting skeletal maturity. OBJECTIVE:To compare the mandibular length in boys and girls with Class I and Class II skeletal patterns by using the cervical vertebrae maturation, and to provide valid reference index for orthodontical treatment. METHODS:The lateral cephalograms of the 160 cases of Class I (40 males and 40 females) and Class II (40 males and 40 females) skeletal patterns, aged 8-15 years, were taken before orthodontic treatment. The sample was grouped according to stages of the cervical vertebrae maturation (Hasse and Farman method), and the mandibular length was measured separately. The results were statistical y analyzed by the independent-sample t test. RESULTS AND CONCLUSION:No matter you are a male or female, the mandibular length of Class I was greater than that of Class II at the early stages of growth and development. In the Class I pattern, the mandibular lengths of boys were greater than those of girls at accelerated, transition, and deceleration stages (P<0.05), whereas in the Class II pattern, the mandibular lengths of boys were greater than those of girls at accelerated, transition, and deceleration stages (P<0.05). The present results indicate a sexual dimorphism in the mandibular length at almost al stages of bone maturation, but the possibility of a later“catch up”growth period occurs on Class II girls. And this information has important orthodontic clinical implications.%背景：研究发现年龄和牙龄在预测骨骼成熟度方面有一定的局限性。 目的：采用颈椎骨成熟度评价系统比较处于生长发育期的骨性Ⅰ，Ⅱ类错牙合男性女性患者的下颌骨长度。 方法：选取在新疆医科大学第五附属医院口腔科就诊并拍摄头颅侧位片的160例年龄在8-15岁的Ⅰ类错牙合(男，女各40例)，Ⅱ类错牙合(男，女各40例)骨性错牙合畸形患者，采用颈椎骨成熟度评价法(Hasse和Farman法)对样本进行分期，然后分别测量其下颌骨长度，采用独立样本t检验对骨性Ⅰ，Ⅱ类错牙合男性女性患者的下颌骨长度进行比较。 结果与结论：在骨成熟度的早期，骨性Ⅰ类错牙合患者的下颌骨长度较骨性Ⅱ类错牙合患者长(P <0.05)；骨性Ⅰ类错牙合畸形患者在加速期、过渡期和减速期，男性患者下颌骨的长度比女性患者长(P <0.05)。骨性Ⅱ类错牙合畸形患者在加速期、过渡期和减速期，男性患者下颌骨的长度比女性患者长(P <0.05)。表明性别不同导致的下颌骨长度的差异性几乎存在于骨成熟度各分期，但对于骨性Ⅱ类错牙合女性患者而言，在生长发育后期会出现一段“显著增长期”。提示正畸医师正确利用这段时期进行矫治可以起到事半功倍的效果。
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