In the Begg Technique, factors controlling the anterior intrusive force provided by the archwire have yet to be fully clarified. The rationale for bite opening with very light forces, the effect of Class II elastics on intrusive Force magnitude and the intrinsic qualioy of "Australian" wire in bite opening are examined in this paper. A formulais is presented which allows the intrusive force that archwir exert in different individuals to be predicted. The values derived from the formula were compared with cose model measurements. it was found that the intrusive force of the archwire was afreeted by the length of th e indi vidual dental arch. The magnitude of this in trusive force was seen to increase gradually during the period of bite opening and appeared to be related to the use of Class II elastics. The study revealed factors which aiffected the magnitude of the intrusive force.

The purpose of this study was to compare orthodontic treatment outcomes in Chinese patients with borderline problems treated with and without extractions. Methods: Records of 39 borderline patients treated at the Faculty Clinic of the Peking University Orthodontic Department were evaluated retrospectively by 5 associate professors. Sixteen patients had been treated without extractions, and 23 had 4 first or second premolars extracted. Each judge evaluated the posttreatment records independently for tooth alignment, overbite, overjet, midline symmetry, lateral occlusion, and facial profile, and rated them on a scale from 1 to 5. Results: The only statistically significant difference between the extraction and nonextraction groups was for facial profile, with the judges preferring the extraction profiles. Fifteen soft-tissue cephalometric variables were measured to determine the source of the difference, and 6 showed statistically significant differences. When profile changes from pretreatment to posttreatment were examined, significant differences in treatment-associated changes between extraction and nonextraction groups were all related to the lower lip and chin. Conclusions: In this sample of Chinese borderline orthodontic patients, Chinese clinicians had a statistically significant preference for the facial profiles of the extraction patients, but no statistically significant preferences for tooth alignment, overbite, overjet, midline symmetry, or posterior occlusion. Extraction treatment increases the inclination of the chin and reduces protrusion of the lower lip compared with nonextraction treatment, and this might explain the difference.

目的 探讨安氏Ⅱ1类错畸形在用常规固定矫治器进行减数治疗后硬组织侧貌突度的变化趋势及其稳定性。方法 随机提取30例经拔除4个双尖牙用常规固定矫治器治疗的安氏Ⅱ1类青少年错畸形患者的X光片为研究对象，以3人重复定点的方法对样本的治疗前、治疗后、随访期（治疗后4年左右）的头颅侧位片进行计算机头影测量，并对这三期的硬组织侧貌变化情况进行配对t检验。结果 正畸治疗前后，上颌及上切牙突度均发生有统计学意义的减小（P<0.05P<0.001）；而下颌骨突度基本没有变化。四年后复查显示，所有测量项目均有不同程度的复发。结论 Ⅱ1 类错减数治疗后侧貌突度的改变主要为上颌及上前牙突度的减小，其中上前牙突度及唇倾度的改变最为显著，且即使在少量复发后，仍与治疗前的测量结果保持显著的临床及统计学意义的差别。

目的 调查正畸医师临床判断拔牙或不拔牙治疗设计的一致性。方法 本研究选用了在北大口腔正畸科完成正畸治疗的样本一（55名患者）和未完成治疗的样本二（90名患者）的治疗前诊断资料，请本科室5位副高职称的正畸专科医师根据患者的牙模型、X线片及面颌像进行拔牙、不拔牙或临界这3种情况的临床判断，并进行描述性统计分析。结果 如果以5人完全一致的判断为标准，样本一中的符合率只有30.9%，但如果以3人以上判断一致为标准，则符合率可以高达96.3%。样本二中，5人完全一致的判断符合率只有21.1%，而3人以上一致的判断符合率为80%。在以上两组中正畸专家们挑出的临界病例的比例分别占25.5%和35.6%。合并两样本统计5位医师判断拔牙的比率，分别为57%、56%、46%、41%和32%。结论 虽然正畸专家们对拔牙还是不拔牙的选择在大多数情况下可以取得共识，但仍有相当比例的错　畸形可能处于拔牙或不拔牙两可的临界状态。而不同正畸医师对拔牙与否的倾向性具有明显的个体差异。

目的：调查上切牙内收过程中牙槽骨的增生与吸收情况。方法：以55例拔牙治疗病例治疗前、治疗后、及随访期的头颅侧位片为研究样本，测量他们在这3个阶段切牙的位移以及其牙根前方和后方牙槽骨的厚度变化及牙槽突总厚度的变化情况。测量方法采用腭结构重叠法，以治疗前的前颅底平面为参照平面建立同一坐标系，双人定点取均值的方法在计算机上完成测量及重叠计算。结果：上切牙阻力中心治疗后向腭侧移动了1.8mm（P<0.001），向上移动了0.4mm（P>0.05）。阻力中心水平的唇侧牙槽骨厚度增加了0.2mm（P<0.01），腭侧牙槽骨厚度减小了0.8mm（P<0.001）；随访期切牙阻力中心向唇向复发了0.8mm（P<0.01），阻力中心水平的唇侧牙槽骨厚度相应减小了0.2mm（P<0.05），但腭侧牙槽骨厚度却并没有明显的增加。结论：在上前牙唇腭侧向移动的过程中，牙槽骨的生物学改建是以骨吸收为主，骨增生十分有限。