Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, Faculty of Medicine, University of Zurich, Zürich, Switzerland.
Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece.
Prog Orthod. 2017 Dec 18;18(1):44. doi: 10.1186/s40510-017-0198-5.
In the long-lasting debate of extraction versus non-extraction treatment, the impact of extractions on the skeletal vertical dimension remains rather unclear. The aim of this retrospective research study was to obtain a bias-free sample of morphologically similar borderline patients treated with or without extraction of the four first premolars and to retrospectively evaluate the vertical changes that occurred.
A borderline sample of 83 patients, 41 treated with four first premolar extractions and 42 treated without, was obtained by means of discriminant analysis applied to a previously investigated parent sample of 542 class I patients. The pretreatment and posttreatment cephalometric radiographs were analyzed digitally, and seven measurements were assessed for vertical skeletal changes. Also, average tracings between the two treatment groups were evaluated using the Procrustes superimposition method.
The variables of SN to Go-Gn and Y-axis showed adjusted intergroup differences of - 0.91° and - 1.11° (P = 0.04). Comparing the mean intra-group differences of all the variables simultaneously, a significant difference was found between the two treatment groups (overall P value = 0.04). In the extraction group, only the gonial angle showed a significant decrease (P = 0.01) while the overall P value evaluating the intra-group differences between pre- and posttreatment was significant (overall P value < 0.01). In the non-extraction group, the variable of N-ANS/N-Me showed a significant decrease (P = 0.02) and the overall P value evaluating the intra-group differences between pre- and posttreatment was also significant (overall P value < 0.01). Differences in treatment duration were assessed using a log-normal model and showed that extraction treatment lasted significantly longer than non-extraction treatment (P < 0.01).
The borderline group of patients identified by the discriminant analysis exhibited similar morphological characteristics at treatment's onset; therefore, the posttreatment changes could safely be attributed to the choice of extraction or non-extraction treatment and not to pre-existing differences. Treatment choice had an impact on the patients' vertical skeletal dimensions. Patients treated with four first premolar extractions showed a slight decrease in the vertical skeletal measurements, whereas non-extraction patient treatment showed a slight increase. The treatment time was also significantly higher in the extraction group.
在拔牙与不拔牙治疗的长期争论中，拔牙对骨骼垂直向的影响尚不清楚。本回顾性研究的目的是获得一组形态相似的边缘型患者的无偏样本，这些患者接受了或未接受四颗第一前磨牙的拔牙治疗，并回顾性评估发生的垂直向变化。
通过判别分析从之前调查的 542 例 I 类患者的母样本中获得了 83 例边缘型患者的样本，其中 41 例接受了四颗第一前磨牙的拔牙治疗，42 例未接受拔牙治疗。对治疗前和治疗后的头颅侧位片进行数字化分析，并对 7 项测量值进行评估，以了解垂直向骨骼的变化。此外，还使用 Procrustes 叠加法评估两组之间的平均轨迹。
SN 到 Go-Gn 和 Y 轴的变量显示调整后的组间差异为-0.91°和-1.11°（P=0.04）。同时比较两组之间所有变量的平均组内差异，发现两组之间存在显著差异（总体 P 值=0.04）。在拔牙组中，只有下颌角显示出显著的减小（P=0.01），而评估治疗前后组内差异的总体 P 值显著（总体 P 值<0.01）。在非拔牙组中，N-ANS/N-Me 变量显示出显著的减小（P=0.02），评估治疗前后组内差异的总体 P 值也显著（总体 P 值<0.01）。使用对数正态模型评估治疗持续时间的差异，结果表明拔牙治疗持续时间明显长于非拔牙治疗（P<0.01）。
通过判别分析确定的边缘型患者组在治疗开始时具有相似的形态特征；因此，治疗后的变化可以安全地归因于拔牙或不拔牙治疗的选择，而不是预先存在的差异。治疗选择对患者的垂直骨骼维度有影响。接受四颗第一前磨牙拔牙治疗的患者的垂直骨骼测量值略有减小，而接受非拔牙治疗的患者的测量值略有增加。拔牙组的治疗时间也明显较长。
