The relationship between maxillary length, differential maxillary impaction, and the change in maxillary incisor inclination.

A mathematical formula based on a geometric model is described that will permit greater accuracy in planning orthodontic treatment and orthognathic surgery for patients who require differential maxillary impaction.     

采用锥形束CT测量健康上前牙唇侧骨板形态及牙长轴倾角的变化

目的 采用锥形束CT（CBCT）图像数字化测量的方法,测量健康上前牙唇侧骨板厚度、釉牙骨质界（CEJ）到骨嵴顶距离及牙长轴倾角,并探讨可能的影响因素。方法 分析由Newtom VGI ^? CBCT机拍摄获得的345例CBCT影像,使用NNT软件分别在上颌中切牙、侧切牙和尖牙的正中矢状平面上测量CEJ下4 mm、根中点和根尖水平的唇侧骨板厚度,CEJ距骨嵴顶距离和牙长轴倾角,记录各牙位CEJ下4 mm水平唇侧骨板厚度≥1 mm的例数。结果 1）中切牙的牙长轴倾角,CEJ距骨嵴顶距离,CEJ下4 mm、根中点和根尖水平的骨板厚度均值分别为15.2°±6.2°、（1.5±1.0）mm、（0.8±0.4）mm、（0.6±0.4）mm和（1.3±0.7）mm;侧切牙和尖牙的上述5项测量值分别为16.2°±8.8°、（1.6±1.0）mm、（0.7±0.5）mm、（0.4±0.6）mm和（1.1±0.7）mm;19.0°±6.2°、（1.8±1.0）mm、（0.9±0.6）mm、（0.4±0.6）mm和（1.2±0.7）mm。2）345例患者中,中切牙、侧切牙和尖牙CEJ下4 mm水平骨板厚度≥1 mm者分别占28.3%、25.8%和42.7%。3）中切牙、侧切牙和尖牙CEJ到骨嵴顶距离与年龄高度相关,相关系数分别为0.42、0.50、0.62（P<0.01）。结论 健康上前牙唇侧骨板厚度较薄,CEJ到骨嵴顶距离随着年龄的增加而增加,牙长轴较牙槽突长轴舌倾,充分考虑这些特点有利于提高相关口腔治疗方案的安全性和预后。     

采用锥形束CT测量健康上前牙唇侧骨板形态及牙长轴倾角的变化

目的 采用锥形束CT（CBCT）图像数字化测量的方法,测量健康上前牙唇侧骨板厚度、釉牙骨质界（CEJ）到骨嵴顶距离及牙长轴倾角,并探讨可能的影响因素。方法 分析由Newtom VGI ^? CBCT机拍摄获得的345例CBCT影像,使用NNT软件分别在上颌中切牙、侧切牙和尖牙的正中矢状平面上测量CEJ下4 mm、根中点和根尖水平的唇侧骨板厚度,CEJ距骨嵴顶距离和牙长轴倾角,记录各牙位CEJ下4 mm水平唇侧骨板厚度≥1 mm的例数。结果 1）中切牙的牙长轴倾角,CEJ距骨嵴顶距离,CEJ下4 mm、根中点和根尖水平的骨板厚度均值分别为15.2°±6.2°、（1.5±1.0）mm、（0.8±0.4）mm、（0.6±0.4）mm和（1.3±0.7）mm;侧切牙和尖牙的上述5项测量值分别为16.2°±8.8°、（1.6±1.0）mm、（0.7±0.5）mm、（0.4±0.6）mm和（1.1±0.7）mm;19.0°±6.2°、（1.8±1.0）mm、（0.9±0.6）mm、（0.4±0.6）mm和（1.2±0.7）mm。2）345例患者中,中切牙、侧切牙和尖牙CEJ下4 mm水平骨板厚度≥1 mm者分别占28.3%、25.8%和42.7%。3）中切牙、侧切牙和尖牙CEJ到骨嵴顶距离与年龄高度相关,相关系数分别为0.42、0.50、0.62（P<0.01）。结论 健康上前牙唇侧骨板厚度较薄,CEJ到骨嵴顶距离随着年龄的增加而增加,牙长轴较牙槽突长轴舌倾,充分考虑这些特点有利于提高相关口腔治疗方案的安全性和预后。     

Effect of maxillary incisor angulation and inclination on arch length

This article discusses the quantitative effects of angulation of incisors on dental arch length. The incisors are approximated mathematically to rectangular shapes, which enables the authors to calculate the change in arch length when teeth are tipped and to describe graphically the effect of other influencing parameters. The authors demonstrate that the height and the width of a tooth crown can enhance or diminish the effect of angulation on arch length. In addition to angulation, dental arch length is also influenced by torque. A mathematic formula has been derived and the results are demonstrated numerically and graphically. The authors show that vertical positioning of the brackets plays an important role because torquing is a rotational movement around the center of the bracket slot. Hence, in calculating the effect of torque on dental arch length, one must consider different angles and axes than those discussed by Andrews.4 The interaction between angulation and inclination and its influence on dental arch length has been investigated. It has been found to cause little change in arch length.     

牙尖斜度对上颌全口义齿基托应力分布的影响

目的:探讨后牙牙尖斜度对上颌全口义齿基托应力分布状况的影响。方法:建立0°、20°、30°三种牙尖斜度的上颌全口义齿及其支持组织的三维有限元模型,分别在全牙列、前牙列、双侧及单侧后牙列加载下,分析基托内切牙乳突区、唇系带切迹区、后牙区的综合应力值大小。结果:全牙列加载下,基托内各区基本呈现较广泛的高应力值分布,且随牙尖斜度增加而加大。前牙加载下,牙尖斜度变化对基托内应力值影响较小。双侧或单侧后牙加载下,随牙尖斜度增加,后牙区应力值呈显著增大,对切迹区应力值亦有一定影响。结论:随牙尖斜度增加,基托各区内应力值均发生变化,且变化幅度与加载方式有关。     

The crown to root angle of maxillary central incisors in different incisal classes

The angulation of the maxillary central incisor crown to its root has been measured in 191 patients representing the four classes of incisor malocclusion. Significant differences were only found between Class II Division 1 and Class II Division 2 groups.     

Tip upturning and maxillary advancement: the UT angle

Improving facial aesthetics has been shown to be a strong motivational factor in patients who decide to undergo orthognathic surgery. The nose is a keystone of facial aesthetics and is thus of central importance in planning and executing orthognathic surgery. Authors present their way to forecast the tip projection in anterior advancement of the maxilla. In the sample, only patients who, after Le Fort I, needed an advancement of the maxilla (56 patients) were considered. For each patient, the upturning angle was measured before and 6 months after surgery. In all the cases, a good aesthetic and functional result was reached; there were no big complications. From this study, it is possible to note that the upturning angle decreased by 0.6 to 0.8 degree each millimeter of maxillary advancement.     

牙尖斜度对上颌第一磨牙牙体应力分布的影响

目的:探讨磨牙隐裂的生物力学机制。方法:建立上颌第一磨牙的三维有限元模型,根据隐裂与非隐裂上颌第一磨牙的牙尖斜度,确定模型的牙尖斜度。在600N垂直分散载荷和200N轴向、斜向、水平向载荷下,观察不同牙尖斜度时模型的应力变化。结果:隐裂模型的最大拉应力、最大压应力和最大Von Mises应力均高于非隐裂对照模型。随着载荷方向与牙长轴交角的增大,拉应力和Von Mises应力不断增大,水平向加载时拉应力最大。近中舌尖、近远中窝沟和腭侧牙颈部是主要的拉应力集中区。结论:同等加载条件下,牙尖斜度越大,应力峰值越高,磨牙隐裂的可能性越大,而水平向力是其主要因素。     

Effect of the inclination of a maxillary central incisor on periodontal stress

Abstract Objective: To determine the effect of labiolingual inclination of a maxillary central incisor on the magnitude and distribution of stresses within the periodontal space. Materials and Methods: Five three-dimensional finite element models of a right maxillary central incisor were created with 0°, 10°, 20°, 30°, and 40° inclination. Each incisor model was subjected to a 1?N lingual-directed force and 6-12?N·mm countertipping moment on the labial surface. The stress level within the periodontal ligament was calculated in terms of maximum principal stresses. Results: With increased inclination, compressive stresses tended to increase whereas tensile stresses tended to decrease. The location where compressive stress was prevalent changed from the midroot area to the apical area on the lingual side, while the area where tensile stresses were predominant changed from the midroot area to the cervical area on the labial side. Conclusion: There are more compressive stresses concentrated at the apex of incisors with a high degree of inclination than in incisors that are more upright. This may be associated with the higher clinical incidence of apical root resorption found in inclined maxillary central incisors.     

Craniographic examination of the condylar angle and the maxillary incisal palatal angle in Bedouin skulls

Craniographic registrations were used to examine 25 Bedouin skulls. The skulls were divided into three groups according to the anatomy and position of the maxillary incisor. Correlations between condylar guidance angle, maxillary incisal palatal angle, attrition, and flaring were investigated. No correlation was found between the condylar and maxillary incisal palatal angles. In the presence of severe attrition and/or flaring, the maxillary incisal palatal angle was reduced and mild reduction was also found in the condylar guidance angle. A strong correlation was found between the level of attrition and flaring.     

Accuracy of recording horizontal condylar inclination and Bennett angle with the Cadiax compact

This study assessed the accuracy of an electronic hinge axis tracing device (Cadiax compact) in measuring the horizontal condylar inclination (HCI) and the Bennett angle. The hinge axis movements were simulated with an articulator to which the hinge axis tracer was attached. On the articulator the pre-set HCI values were 20 degrees, 40 degrees and 60 degrees, the pre-set Bennett angles were 0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees. The maximum measuring errors ranged from 0 to 3.4 degrees (in average 1.2 degrees ) and yielded statistically significant differences between articulator setting and Cadiax compact measurement (P < 0.05) except the HCI of 40 degrees and the Bennett angle of 0 degrees. Because of the small range of the maximum measuring error the Cadiax compact represented reasonable accuracy for clinical application in anterior guidance restorations.     

上颌窦宽度及角度预测经牙槽嵴顶上颌窦底提升术骨移植稳定性的价值

目的: 探讨通过锥形束CT（CBCT）测量上颌窦宽度及角度,评估牙槽嵴顶上颌窦底提升术骨移植稳定性的价值。方法: 选取行经牙槽嵴顶上颌窦底提升术并同期种植的78例患者为研究对象。所有患者术前、术后6个月均行CBCT检查,测量上颌窦宽度、角度及根端骨吸收量。分析影响牙槽嵴顶上颌窦底提升术骨移植稳定性的因素,评估上颌窦宽度、上颌窦角度预测牙槽嵴顶上颌窦底提升术骨移植稳定性的价值。采用SPSS 18.0软件包对数据进行统计学分析。结果: 术后6个月种植体根端骨平均吸收量为（1.81±0.26）mm,其中,49例≤1.81 mm,29例>1.81mm。Logistic多因素回归分析显示,上颌窦宽度、上颌窦角度是影响牙槽嵴顶上颌窦底提升术骨移植稳定性的独立因素（OR：3.873、4.518,95%CI：1.594~9.412、1.859~10.979,P<0.05）。ROC曲线分析显示,上颌窦宽度、上颌窦角度及两者联合预测牙槽嵴顶上颌窦底提升术骨移植稳定性的AUC分别为0.764、0.742和0.908。结论: 上颌窦宽度和角度是影响牙槽嵴顶上颌窦底提升术骨移植稳定性的指标,两者联合预测术后骨移植稳定性效能良好。     

Axial-wall inclination angle and vertical height interactions in molar full crown preparations

OBJECTIVE: This study has been designed to evaluate the interaction of axial wall heights with inclination angles in full crown tooth preparations. The interaction of these parameters was related to the resulting preparation surface area. MATERIALS AND METHODS: A right regular pyramid was used to simulate a single mandibular molar preparation with known convergence angles and vertical heights. Various combinations of these two variables allowed the calculation of surface areas with a formula for the area of a pyramid and right triangles through trigonometric manipulations. The pyramidal model system had a 9-mm square base with vertical heights from 3- to 5-mm and single-side inclination angles from 2 to 25 degrees. The occlusal surface was a flat, square or rectangular surface and was included in the total area. RESULTS: A percentage of surface area lost or gained served as the dependent variables. The significance levels were set at 10.0% or greater magnitude of loss/gain in a surface area compared to the ideal 2 degree-level. Significant area loss was demonstrated in all alpha-level comparisons. The largest change was found in the 5-mm height grouping compared to the 3-mm height grouping, -36.6% difference between groups at the 2 degree-level. CONCLUSIONS: Axial single-side inclination angles greater than 10 degrees in 3- and 4-mm height-molars are detrimental to maximum surface area in full crown restorations. The 5-mm axial wall height with < or = 10 degree single wall has been shown to maximize the luting agent surface area between restoration and tooth structure.