牙颌发育与全身发育是一致的。对于需要正畸治疗的儿童和青少年患者来说,判断患者的生长发育周期,有助于医生在最佳治疗时机给予患者及时的正畸治疗,这对于那些存在骨骼不调的患者尤为重要。而且了解患者的生长发育阶段也有助于正畸医生做出诊断,制订治疗计划,获得良好的正畸效果和稳定性。通常可以通过两种途径来评价生物学年龄:①临床评估,包括第二性征、身高、女孩的初次月经和男孩声音的改变;②用手腕部或颈椎X线片评估 [15-19] 。
一般来说,手腕部X线片是评价骨龄的金标准 [20] 。主要是通过手腕骨骼的钙化情况,了解生长发育阶段,评估生长发育潜能以及是否处于生长发育高峰期等。1972 年,Lamparski首次提出用颈椎来评价骨龄的标准,他发现在生长发育阶段,男性和女性颈椎的改变是相同的,但女性的颈椎会早于男性发生改变,通过颈椎来评价骨龄具有很高的临床可信度 [21] 。之后的很多研究也显示,颈椎的成熟度与个体骨骼的成熟度密切相关,通过颈椎来评价生长发育具有很高的有效性 [16-18,22-31] 。此外,由于正畸治疗需要常规拍摄头颅侧位片,而头颅侧位片上就有颈椎的显示,若是通过颈椎来评价生长发育,就能避免患者因为拍摄手腕部X线片而接受额外的放射线,所以越来越多的正畸医生开始接受颈椎分析法评价生长发育。
颈椎分析法主要是通过第二颈椎(C2)、第三颈椎(C3)和第四颈椎(C4)(图 1-9)的椎底和椎体的变化来评价生长发育。随着生长发育的不断进行,椎底会由平依次逐渐变凹,C3 和C4 椎体的高度会依次逐渐增加,由最初的梯形依次变为水平矩形、正方形和垂直矩形 [32] (图 1-10)。
图 1-9 头颅侧位片中第二、第三、第四颈椎的显示
通常使用Baccetti法 [33] 来评价颈椎的发育阶段,该方法将颈椎的变化分为了 6 个阶段(图 1-11)。
第一阶段(CS1):C2、C3、C4 的椎底均为平的,C3 和C4 的椎体为梯形。说明离生长发育高峰期还有 2 年左右。
第二阶段(CS2):C2的椎底变凹,C3和C4的椎体为梯形。说明离生长发育高峰期还有 1 年左右。
第三阶段(CS3):C2 和C3 的椎底变凹,C3 和C4 的椎体为梯形或水平矩形。说明生长发育高峰期即将到来。
第四阶段(CS4):C2、C3、C4 的椎底变凹,C3 和C4的椎体为水平矩形。说明在此阶段之前的 1~2 年为生长发育高峰期。
第五阶段(CS5):C2、C3、C4 的椎底仍然是凹的,C3和C4 的椎体至少有一个为正方形;如果不是正方形,剩余的其他椎体均为水平矩形。说明生长发育高峰期至少结束了1 年。
图 1-10 以第三颈椎为例,随着生长发育的进行,其椎底和椎体的变化(摘自Brent Hassel and Allan G. Farman [22] )
图 1-11 颈椎变化的 6 个阶段示意图(摘自Tiziano Baccetti,Lorenzo Franchi and James A. McNamara [33] )
第六阶段(CS6):C2、C3、C4 的椎底仍然是凹的,C3和C4 的椎体至少有一个为垂直矩形;如果不是垂直矩形,剩余的其他椎体均为正方形。说明生长发育高峰期至少结束了 2 年。
从以上 6 个阶段可以看出,生长发育高峰期处于第三和第四阶段之间,通过观察颈椎底和颈椎体的变化,我们能很好地预测生长发育。近年来的一些研究也显示,对于颈椎的一些轻微变化较难辨别,所以无法准确判断出生长发育高峰期 [19,34] 。但无论怎样,颈椎分析法作为一种评价生长发育的方法,在帮助正畸医生了解青少年患者的生长潜力方面,仍然具有一定的临床意义和参考价值。
总而言之,颌面部的生长发育在胎儿时期即开始,只有当颌面部的骨骼、软组织及牙齿协调生长和发育,才能出现“正常的面型”及“理想的咬合”。一旦这一生长过程出现不调,则会导致错 畸形的发生。因此,对颌面部正常生长发育过程的了解,有助于正畸医生对于错 畸形的诊断分析和最佳矫治计划的制订,有助于理解上、下颌骨矫治后的骨改建和最终形态变化,有助于预测患者矫治结束后的 面形态变化,从而在临床上更好地控制颌面部生长。
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