牙周膜减阻牵张移动上下颌尖牙的三维有限元分析

目的 分别建立牙周膜减阻牵张成骨术远移尖牙的上下颌三维有限元模型,探讨在尖牙远移过程中上下颌尖牙及牙周组织的应力分布和位移情况,为临床应用提供理论依据.方法 通过64排螺旋CT扫描,获得样本的颞下颌关节（TMJ）、上下颌骨、上下颌牙列的DICOM数据文件,建立上下颌牙周膜牵张成骨术远移尖牙的三维有限元模型.分别于尖牙颊侧及腭侧加载近远中向的牵引力,观察尖牙、牙周组织应力分布情况和位移趋势.结果 上下颌尖牙最大瞬时位移部位均位于牙冠1/3,从尖牙牙冠到根尖逐渐减少;最大瞬时位移数值：上颌尖牙＞下颌尖牙;支抗牙均未见明显位移.上、下颌尖牙最大等效应力部位：上颌集中于尖牙远中牙槽嵴顶略偏颊侧处,下颌最大等效应力主要集中在尖牙远中牙槽嵴顶偏舌侧处;最大等效应力：上颌尖牙＞下颌尖牙.结论 牙周膜减阻牵张成骨术可以有效减少支抗丧失的风险.上下颌尖牙在减阻牵张过程中有远中倾斜移动趋势;其中上颌尖牙远移时有颊向旋转趋势,下颌尖牙远移时有舌向旋转趋势,应用减阻牵张辅助尖牙远移过程中应控制尖牙的旋转移动或加以适当的纠正.     

Canine eruption in patients with complete cleft lip and palate

OBJECTIVE: To describe erupting maxillary canine positions in patients with bone-grafted alveolar clefts. SAMPLE: The sample consisted of 101 cleft sites from patients with complete unilateral or bilateral cleft lip and palate who had early (< or =9 years) or late (>9 years) secondary alveolar bone grafts. METHODS: Canine position was assessed using panoramic radiographs taken before and after alveolar bone grafts. Vertical canine positions were assessed using the long axis of the maxillary permanent canine relative to a 90 degrees vertical reference line. Lateral canine positions were defined using the relationship between the canine tip and the midplane of the lateral incisor root. Anomalous lateral incisors were recorded. Statistical analysis included Student's t tests and chi-square tests. RESULTS: Patients with alveolar clefts had a 20-fold increased risk for canine impaction, based on erupting canine positions. Abnormal vertical canine positions decreased following early and late alveolar bone grafts (p < .05), whereas abnormal lateral canine positions increased following late alveolar bone grafts (p < .01). Of the cleft sites with altered canine positions, 61% also had a lateral incisor anomaly. Based on canine position, the non-cleft-side canine had the same risk for impaction as the cleft-side canine. CONCLUSIONS: Patients with alveolar clefts have a significantly higher risk for canine impaction compared with patients without clefts. Timing of alveolar bone grafts and lateral incisor anomalies influenced the risk for canine impaction. An alveolar bone graft should be planned in accordance with maxillofacial development, including the eruption of teeth adjacent to the cleft.     

Relation between lingual contour of upper canine clinical crown and mandibular movement. Relative position between upper and lower canine

Upper canine protects molar teeth from occlusal trauma by controlling lateral movement of mandible and discluding. Hence, it is expressive to find relative position between lingual contour of upper canine and lower canine. The authors have investigated relative position between clinical crown of upper and lower canine with rectangular coordinates system established on the trace in a labiolingual section of clinical crowns of upper and lower canine. As a result, the authors arrived at the following conclusion: 1. Significant difference between right and left side wasn't found in relative position between upper and lower canine clinical crown (p less than 0.05). 2. Items of upper canine hadn't relevance to items of lower canine. 3. Over bite had significant relevance to 4, 6, and 7. But overjet hadn't relevance to the other items.     

Factors that relate to treatment duration for patients with palatally impacted maxillary canines.

The objectives of this study were to determine the relationship between the initial position of a palatally impacted maxillary canine (as seen on a panoramic radiograph) and the duration of orthodontic treatment and to determine whether a difference in treatment duration existed between patients with bilateral palatally impacted canines and patients with unilateral impaction. A total of 47 adolescent subjects were chosen (9 subjects with unilateral impactions and 18 subjects with bilateral impactions). All subjects had full fixed orthodontic appliances placed. The treatment duration of this group was compared with that of a control group with similar characteristics but without the impacted canine. The results showed that the average duration of treatment was 22.4 months for the control group, 25.8 months for the unilateral-impacted group, and 32.3 months for the bilateral-impacted canine group. The length of treatment for the impacted canine sample was related to the age of the patient at the start of treatment; younger patients required a longer treatment. The younger the patient, the more severely impacted the canine. The bilateral-impacted canine group had at least 1 canine that was more severely impacted than the impacted canine in the unilateral-impacted group. If the canine was impacted less than 14 mm from the occlusal plane, treatment duration averaged 23.8 months; if the canine was impacted more than 14 mm from the occlusal plane, treatment duration averaged 31.1 months.     

Clinical evaluation of a low-friction attachment device during canine retraction

OBJECTIVE: The present study used a split-mouth design to compare the amount of canine movement and the retraction time between brackets with Clear Snap and brackets with stainless steel ligature wires for three different levels of retraction force. MATERIALS AND METHODS: A sample of 30 patients was used. After initial leveling, the canine was retracted using a 50-g (n = 10), 100-g (n = 10), or 150-g (n = 10) closed-coil spring. The canine on one side was chosen at random, and Clear Snap was attached to the bracket during the retraction period. The other side was used as a control. The amount of canine retraction was measured with a digital vernier caliper. Statistical analysis was performed by analysis of variance. RESULTS: The average canine retraction time was approximately 2 to 3 months less in all experimental groups (50, 100, and 150 g) compared to the control group. In the control group, 150 g resulted in a shorter duration of canine retraction compared to 50 g. There was no significant difference in the duration of canine retraction among the experimental groups. A greater amount of mean total canine movement was observed in all experimental groups compared to the control groups. CONCLUSION: A shorter duration of canine retraction time was observed with Clear Snap attached when compared with the control. The authors suggest that with the use of Clear Snap, less than 50 g of force may effectively retract a canine.     

Canine ectopia: report of two cases

Transmigration of mandibular canine is a rare elusive phenomenon described in dental literature. The eruption of such transmigrated canines is even rarer. Two rare cases one of midline mandibular canine and the other of transmigrated mandibular canine across the midline and erupted distal to the opposite lateral incisor are presented. The transmigrated canine maintained its nerve supply from the original site. It is suggested that on routine evaluation of orthopantomograms when the dentist finds an excessive mesial inclination of the unerupted mandibular canine at 8-9 years associated with proclination of lower anteriors. increased axial inclination of the unerupted canine and an enlarged symphyseal cross section area of the chin, it is best to keep such a patient under routine evaluation.     

Transitory pre-eruptive malposition of a maxillary canine: report of a case

The ectopical eruption of the maxillary canine has been related to many causative factors. This paper shows a transient pre-eruptive abnormal position of a maxillary canine in a 9-year-old boy. The change from the normal position of the canine occurred coincidentally with the inflammation of the adjacent lateral incisor due to injury. The canine returned to a normal path after treatment and healing of the lateral incisor.     

The effect of tooth position on the image of unerupted canines on panoramic radiographs

The purpose of this study was to evaluate whether panoramic tomograms, which are routinely used in orthodontic practice, can provide adequate information to localize an impacted canine. The effect of changes in position and inclination of an impacted canine on orthopantomograms was investigated in an experimental set-up. An upper canine was removed from a human skull and replaced in a positioning system, enabling simulated positional variations in impactions. In comparison with the image of a contralateral well-aligned canine, the length of the impacted tooth always decreased or remained unchanged, whereas the tooth width increased or remained unchanged. The angulation of the image was unaffected by varying the position of the impacted canine, but altered when the inclination of the tooth in a sagittal or frontal direction was changed. If there was any transversal shift of the impacted canine on the orthopantomogram, it was always towards the mid-sagittal plane. The curvature of the tooth increased after dorsal inclination and decreased after ventral inclination (in comparison with the contralateral well-aligned canine).     

Surgical-orthodontic treatment of the upper canine retention

Combined surgical and orthodontic treatment of upper canine retention showed thorough development during the past decade. Depending on the axial position of the unerupted canine there are three methods for their alignment. When the axis of the unerupted canine is near vertical making a mucosal window is enough for deliberation of the crown. When the unerupted canine is covered by bone a palatinal or buccal corticotomy is necessary for the accessibility of the crown. When the unerupted tooth is positioned near horizontally redressment force or removal is advisable. Combined surgical and orthodontic method for alignment of unerupted canine may achieve excellent cosmetical and functional results.     

Autotransplantation of maxillary canine following removal of compound odontome: a case report

Obstruction remains as an important cause of failure in the eruption of a tooth. In this article, a 15-year-old girl was presented with retained upper left primary canine (63) and first primary molar (64), while the contralateral permanent canine (13) and premolars (14 and 15) have erupted. Upon radiographic examination, a mass which was diagnosed later to be compound odontome was detected. The treatment consisted of surgical removal of the odontome, extraction of the primary canine (63) and left permanent canine (23), and transplantation of the permanent canine (23). The management of this case and the literature related to autotransplantation are discussed.     

Early predictive variables for upper canine impaction as derived from posteroanterior cephalograms

The aim of this study was to identify a model of cephalometric variables for early diagnosis of the displacement of upper permanent canine and early prognosis of upper canine impaction. Postero-anterior (PA) cephalograms of 43 subjects (22 males and 21 females) with different types of malocclusions in the mixed dentition were analyzed at the time of first observation (mean age 8 years and 5 +/- 9 months). All subjects were reevaluated at the mean age of 14.3 years. At this time the sample was divided into 2 groups according to the presence of canine impaction: nonimpacted canine group (31 subjects) and impacted canine group (12 subjects). Stepwise variable selection on the measurements at the time of first observation identified 2 predictive variables on PA cephalograms, ie, the distance between the center of the canine crown and the midsagittal plane (A3cc to Cg Vertical) and the distance between the jugal process and the midsagittal plane (J to Cg Vertical). The closer the canine crowns to the midsagittal plane and the larger the posterior portion of the hemimaxilla, the higher the probability of canine impaction. Discriminant analysis assigned a classification power of 95.3% to the predictive model. On the basis of the equation generated by the multivariate statistical method, impaction of the maxillary canine for each new case at the age of 8 years can be predicted. The importance of PA cephalograms in the diagnosis and prediction of canine eruption disturbances is emphasized.     

单个链状橡皮圈弹力结扎牵引尖牙远移的临床观察

目的　比较单个链状橡皮圈弹力结扎与传统的弹力橡皮圈牵引尖牙远中移动的效果。方法　随机选择16例因正畸需要拔除上颌双侧第一双尖牙患者 ,用方丝弓矫治器排齐牙列换上 0 .0 4 6cm(0 .0 18英寸 )的澳丝后 ,以上颌第一磨牙为支抗 ,在患者上颌牙弓的右侧用单个链状橡皮圈弹力结扎 ,左侧用传统正畸弹力橡皮圈牵引尖牙远中移动。比较两种方法牵引尖牙远中移动的速度和支抗丧失的程度。结果　单个链状橡皮圈弹力结扎与传统的弹力橡皮圈牵引尖牙远中移动的速度无显著性差异 (P >0 .0 5 ) ,第一磨牙前移的距离无显著性差异 (P >0 .0 5 )。结论　单个链状橡皮圈弹力结扎可代替传统的弹力橡皮圈用于牵引尖牙远中移动。     

Unerupted canine without median diastema

summary The eruption of the canine is known to be a factor for diastema closure. In this study the relative changes in the orientation of the unerupted canine were assessed using the orthopantomographs of 9854 patients who sought consultation between April 1984 and March 1993. A total of 38 canines in 32 patients, all aged 11 years or older, were identified as unerupted canines. The features of the patients with unerupted canine showed no significant relation to diastema closure status, but some patients had unerupted horizontal or inverted canine without diastema even in the absence of a history of orthodontic treatment, suggesting the presence of a mechanical force due to some phenomenon other than canine eruption as a factor in diastema closure.     

Combined orthodontic-surgical management of a transmigrated mandibular canine

The presence of an impacted mandibular canine is one of the most difficult challenges that an orthodontist will meet. Orthodontic treatment is planned on an individual basis after thoroughly considering the patient’s overall facial and dentoskeletal characteristics; the duration, risks, and costs of treatment; patient preferences; and the orthodontist’s experience. This article reports an orthodontic treatment of a boy, age 12.9 years, with an impacted mandibular canine in the permanent dentition that was successfully managed. Radiographic analysis indicated a transmigration of the mandibular right canine. The orthodontic treatment plan included extraction of the deciduous right canine followed by surgical exposure and ligation of the permanent canine. Eruption was properly guided, and the correct position of the tooth was achieved. This challenging treatment approach is described in detail, including the mechanics used to align the impacted canine.     

上颌埋伏尖牙CT影像分型系统的建立和分析

目的 利用螺旋CT三维重建技术建立适合上颌埋伏尖牙的影像学分型系统。方法 选择102例上颌埋伏尖牙患者为研究对象,共121颗上颌埋伏尖牙。所有患者均接受标准的螺旋CT扫描,数据均导入MIMICS 10.01软件采用表面遮盖成像法进行三维重建。通过对121颗上颌埋伏尖牙的三维空间位置进行分析建立上颌埋伏尖牙的影像学分型系统。结果 本研究建立了一个上颌埋伏尖牙的三维CT影像学数据库。研究结果显示在X轴方向上,最常见的分型是牙尖近中伴根尖正常。在Y轴方向上,样本中所有埋伏尖牙只存在3种分型即根尖均处于高位,牙尖分别处于高、中、低位。在Z轴方向上,最常见的分型是牙尖和根尖均处于唇侧,约占总数的三分之一。结论 本研究利用螺旋CT建立了一个适合上颌埋伏尖牙的三维影像学分型系统,具有一定的临床诊断价值。     

A case of supernumerary primary and permanent canines

A case of supernumerary primary and permanent canines is presented. A 9Y4M-old boy was referred to our clinic for consultation regarding a maxillary supernumerary primary canine. An oral examination showed 2 primary canines with a similar morphology between the maxillary left lateral incisor and first primary molar. The primary canine in the opposite quadrant had the appearance of a fused-tooth, with composite resin restoration seen in the border. Orthopantomography revealed that permanent successors were present for each primary tooth in the maxillary left region, whereas only a single permanent canine was developing in the opposite quadrant. The 2 primary canines in the maxillary left region were extracted at 9Y4M. The mesially located permanent canine emerged into the oral cavity at 10Y1M and was extracted at 10Y9M. At 12Y2M, the other permanent canine located in the distal position had nearly reached the occlusal plane and the maxillary right permanent canine had arrived at the occlusal plane. Dental age was evaluated by assessing the tooth formation stages in 4 orthopantomographs taken between 8Y5M and 12Y2M, and found to be nearly the same as chronological age. However, the dental ages of the maxillary left permanent canine that had erupted earlier than the one located distally and of the left permanent canine were approximately 1 year behind chronological age. In addition, the dental age of the left permanent canine located distally was 2.5 years behind until the patient reached the age of 10Y9M, after which tooth development was accelerated following extraction of the mesially located permanent tooth.     

Finite element analysis of rapid canine retraction through reducing resistance and distraction

Objective

The aims of this study were to compare different surgical approaches to rapid canine retraction by designing and selecting the most effective method of reducing resistance by a three-dimensional finite element analysis.

Material and Methods

Three-dimensional finite element models of different approaches to rapid canine retraction by reducing resistance and distraction were established, including maxillary teeth, periodontal ligament, and alveolar. The models were designed to dissect the periodontal ligament, root, and alveolar separately. A 1.5 N force vector was loaded bilaterally to the center of the crown between first molar and canine, to retract the canine distally. The value of total deformation was used to assess the initial displacement of the canine and molar at the beginning of force loading. Stress intensity and force distribution were analyzed and evaluated by Ansys 13.0 through comparison of equivalent (von Mises) stress and maximum shear stress.

Results

The maximum value of total deformation with the three kinds of models occurred in the distal part of the canine crown and gradually reduced from the crown to the apex of the canine; compared with the canines in model 3 and model 1, the canine in model 2 had the maximum value of displacement, up to 1.9812 mm. The lowest equivalent (von Mises) stress and the lowest maximum shear stress were concentrated mainly on the distal side of the canine root in model 2. The distribution of equivalent (von Mises) stress and maximum shear stress on the PDL of the canine in the three models was highly concentrated on the distal edge of the canine cervix.

Conclusions

Removal of the bone in the pathway of canine retraction results in low stress intensity for canine movement. Periodontal distraction aided by surgical undermining of the interseptal bone would reduce resistance and effectively accelerate the speed of canine retraction.     

Transmigration of mandibular canines: a report of six cases and a review of the literature

BACKGROUND: The transmigration of a mandibular canine is a rare phenomenon, the etiology of which is not clear. The literature on this rare condition is reviewed, and six cases of transmigrated mandibular canines are presented. REPORT: Panoramic radiographic examination of six patients revealed each patient had one impacted transmigrated mandibular canine. Of the six impacted teeth, the left mandibular canine was involved in four instances and the right in two. In one case the transmigrated canine was associated with a dentigerous cyst. SUMMARY: Transmigration of the mandibular canine is a rare event, and early radiographic examination of the patient is important for treatment. In addition, future studies may lead to a better understanding of this rare anomaly and improvement of the classification criteria.     

牙间隔骨外科改建加速尖牙移动的临床疗效评价

目的　应用牵引装置牵引牙周韧带加速尖牙的移动。方法　选取临床上需拔除第一双尖牙后退尖牙的双颌前突正畸患者 13例 ,共 2 2颗尖牙 ,拔除第一双尖牙的同时 ,配合牙槽骨小手术 ,削弱尖牙远中移动的骨阻力 ,放置自制的牵引装置 ,牵引尖牙向远中的拔牙间隙 ,尖牙后退之前和之后均拍摄头颅侧位定位片和牙片。结果　 2 2颗尖牙在 3周内后退移动 6 .2 7mm ,第一磨牙近中移动 0 .84mm ,患者无明显疼痛。放射学检查显示 :尖牙的牙根吸收少 ,在牵张过程中和牵张后 ,在尖牙近中的牙周韧带中有新骨产生并迅速改建 ,牵张后 3个月牙槽骨逐渐成熟 ,已不能区分新旧牙槽骨。结论　通过牵引牙周韧带3周内完成尖牙的后退移动 ,尖牙的牙根吸收少 ,磨牙的支抗丧失少 ,患者无明显疼痛 ,临床应用安全。     

Prediction of breadth of permanent canines and premolars in the mixed dentition.

Multiple stepwise regression was used in the selection of mixed dentition variables capable of predicting the total breadth of the unerupted permanent canine and premolars. The material consisted of 77 children. Stone casts were made before and after eruption of the canine and premolars. At the first examination when the children were, on the average, 10 years old, intraoral roentgenograms were obtained of the canine and the premolars. To predict the total breadth of the upper canine and premolars the buccolingual breadth of the upper first permanent molar and measurements on roentgenograms of the breadths of the upper canine and premolars proved most useful. In the prediction of the total breadth of the lower canine and premolars the best results were obtained with measurement of the breadths of the teeth in the roentgenograms. The breadth of the incisors proved less useful as a predictor of the breadths of unerupted canines and premolars.