Cephalometric evaluation of the effects of the Twin Block appliance in subjects with Class II, Division 1 malocclusion amongst different cervical vertebral maturation stages

ABSTRACT Objectives: To evaluate the cephalometric changes in skeletal, dentoalveolar and soft tissue variables induced by Clark's Twin Block (CTB) in Class II, Division 1 malocclusion patients and to compare these changes in different cervical vertebral maturation stages. Methods: Pre- and post-treatment/observation lateral cephalograms of 53 Class II, Division 1 malocclusion patients and 60 controls were compared to evaluate skeletal, dentoalveolar and soft tissue changes. Skeletal maturity was assessed according to cervical vertebral maturation stages. Pre- and post-treatment/observation mean changes and differences (T2-T1) were compared by means of Wilcoxon sign rank and Mann-Whitney U-tests, respectively. Intergroup comparisons between different cervical stages were performed by means of Kruskal-Wallis test and Mann-Whitney U-test (p ≤ 0.05) . Results: When compared with controls, there was a significant reduction in ANB angle (p < 0.001), which was due to a change in SNB angle in CS-2 and CS-3 (p < 0.001), and in SNA (p < 0.001) and SNB (p = 0.016) angles in the CS-4 group. There was significant increase in the GoGn-SN angle in CS-2 (p = 0.007) and CS-4 (p = 0.024), and increase in Co-Gn and Go-Gn amongst all cervical stages (p < 0.05). There was significant decrease in U1-SN and increase in IMPA amongst all cervical stages (p < 0.05). There was significant retraction of the upper lip in CS-3 (p = 0.001), protrusion of the lower lip in CS-2 (p = 0.005), increase in nasolabial angle in CS-4 (p = 0.006) and Z-angle in CS-3 (p = 0.016), reduction in H-angle in CS-2 (p = 0.013) and CS-3 (p = 0.002) groups. When pre- and post-treatment mean differences were compared between different cervical stages, significant differences were found for SNA, SNB and UI-SN angles and overjet. . Conclusions: The Twin-Block along with the normal craniofacial growth improves facial esthetics in Class II, Division 1 malocclusion by changes in underlying skeletal and dentoalveolar structures. The favorable mandibular growth occurs during any of the cervical vertebral maturation stages, with more pronounced effect during CS-3 stage.

摘要
研究目的：评估克拉克双垫矫治器（Clark's Twin Block，CTB）对安氏Ⅱ类1分类错牙合畸形患者的骨骼、牙-牙槽骨及软组织变量的头影测量变化，并对比不同颈椎骨成熟分期（cervical vertebral maturation stages）下的上述差异。
研究方法：选取53例安氏Ⅱ类1分类错牙合畸形患者与60例健康对照者的治疗前、后（或观察前、后）头颅侧位片，对比分析其骨骼、牙-牙槽骨及软组织的形态变化。基于颈椎骨成熟分期评估受试者的骨骼成熟度。分别采用Wilcoxon符号秩检验与Mann-Whitney U检验，比较组内治疗前后（或观察前后）的平均变化量及组间差异（T2-T1）；采用Kruskal-Wallis检验及Mann-Whitney U检验开展不同颈椎分期的组间比较（检验水准p ≤ 0.05）。
研究结果：与对照组相比，受试者ANB角显著减小（p < 0.001）；其中CS-2、CS-3分期患者的该变化源于SNB角的改变（p < 0.001），CS-4分期患者则同时伴随SNA角（p < 0.001）与SNB角（p = 0.016）的变化。CS-2分期（p = 0.007）与CS-4分期（p = 0.024）患者的GoGn-SN角显著增大；所有颈椎分期患者的Co-Gn与Go-Gn长度均显著增加（p < 0.05）。所有颈椎分期患者的U1-SN角显著减小、IMPA角显著增大（p < 0.05）。CS-3分期患者上唇显著内收（p = 0.001），CS-2分期患者下唇显著前突（p = 0.005）；CS-4分期患者鼻唇角显著增大（p = 0.006），CS-3分期患者Z角显著增大（p = 0.016）；CS-2（p = 0.013）与CS-3（p = 0.002）分期患者的H角显著减小。对不同颈椎分期的治疗前后平均差异进行比较后发现，SNA角、SNB角、U1-SN角及覆盖（overjet）存在显著组间差异。
研究结论：双垫矫治器联合正常颅面部生长，可通过调控骨骼与牙-牙槽骨结构的变化，改善安氏Ⅱ类1分类错牙合畸形患者的面部美观度。良好的下颌生长可发生于任意颈椎骨成熟分期，其中以CS-3分期的改善效果最为显著。