Is the postretention relapse of maxillary and mandibular incisor alignment related?

Previous studies suggest a poor association between initial and postretention pattern of incisor irregularity. One explanation may be that the incisor movements are limited by the boundaries provided by the incisors in the opposite arch. If so, postretention malalignment of the maxillary and mandibular incisors may be related. To test this hypothesis, long-term postretention study models of 96 patients with acceptable occlusion at the time of appliance removal were examined. The occlusal surfaces of the postretention study models were photocopied, and tooth anatomical contact points were digitized. An algorithm was used to fit the dental arch to the digitized points. The amount of incisor rotation and anatomical contact point displacement of maxillary and mandibular anterior teeth, relative to their respective dental arches, were computer generated. Overbite, the number of occlusal contact points in the anterior segment, and concavity of the lingual surfaces of the maxillary incisors were recorded manually. Statistical analyses demonstrated a significant association (P <.05) between the overall irregularity of the maxillary and mandibular incisors. The association did not differ among subgroups that were stratified according to overbite or number of occlusal contacts. No associations were found for the overall amount of incisor rotation in the 2 arches (P >.05). The amount and direction of displacement of antagonistic pairs of maxillary and mandibular central incisors were also associated (P <.05), but not the amount and direction of rotation (P >.05). The lingual configuration of the maxillary incisors did not affect the pattern of mandibular incisor malalignment.     

Dental crowding in primary dentition and its relationship to arch and crown dimensions among preschool children of Davangere

The purpose of the present study was to evaluate dental crowding in the deciduous dentition and its relationship to the crown and the arch dimensions among preschool children of Davangere. Stratified randomized selection of one hundred, 3-4 year old healthy children with all primary teeth erupted was done and divided into two groups. One group had children with anterior crowding in both the arches while the other had spacing. Alginate impressions of the upper and lower arches were made and the study casts were obtained. The tooth and arch dimensions were determined. Mesiodistal dimensions of all the teeth were significantly larger in the crowded arch group. However, the buccolingual dimensions of the maxillary right central incisor, mandibular lateral incisors and the maxillary molars and the crown shape ratio of maxillary lateral incisors, mandibular canines and mandibular right second molar was statistically different. No significant correlation was found between the arch width and the presence of crowding of deciduous dentition. The arch depth of the spaced dentition was greater when compared to the crowded ones. The arch perimeter of the crowded arches was significantly less than the spaced arches.     

上下颌唇挡对替牙晚期儿童牙(牙合)的影响

目的研究上下颌唇挡同时应用对替牙晚期儿童牙(牙合)的影响.方法选择替牙晚期上下牙列轻度或中度拥挤患儿12例,上下颌均采用唇挡治疗8个月,进行治疗前后X线头影测量分析和模型测量分析,并对治疗前后的测量值变化进行配对t检验.结果唇挡治疗后,SNA、SNB分别增加1.02°和0.97°(P＜0.05),上下切牙前移均是牙冠向近中倾斜,而根尖相对固定的控制性倾斜,旋转中心接近根尖.上下磨牙远中倾斜效果不同,上磨牙远中倾斜直立,旋转中心接近牙冠;下磨牙远中倾斜移动,旋转中心接近阻抗中心;上颌磨牙间牙弓宽度、牙弓周径分别增加4.12mm和5.09mm(P＜0.01),下颌磨牙间牙弓宽度、牙弓周径分别增加4.07mm和6.86mm(P＜0.01).结论在儿童生长发育高峰期,唇挡可有效地引起上下颌牙弓横向和纵向变化,减轻或解除上下牙弓拥挤.     

Critical assessment of a device to measure incisor crown inclination.

The aims of this study were to critically assess the use of a disposable device--the tooth inclination protractor (TIP)--to record incisor crown inclination and to compare its reliability and validity with that of traditional cephalometric radiographic analysis. The sample comprised 30 dental students with lateral cephalometric radiographs and dental casts. Four examiners were trained and calibrated to digitize radiographs and to use intraoral (on patients and dental casts) and extraoral (on dental casts) TIPs. The following angles were measured on the radiographs: maxillary incisor to maxillary plane, mandibular incisor to mandibular plane, maxillary incisor to occlusal plane, and mandibular incisor to occlusal plane. Measurements were also made with the TIP: maxillary incisor to occlusal plane and mandibular incisor to occlusal plane. All techniques were reliable between examiners. There were statistically significant systematic differences between the TIP and the radiographic assessments. The following differences were found. The TIP tended to record maxillary incisor crown inclination an average of 14 degrees less than maxillary incisor to maxillary plane. The TIP tended to record mandibular incisor crown inclination as similar to mandibular incisor to mandibular plane. The TIP recorded mandibular crown inclination 19 degrees less than mandibular incisor to occlusal plane. The disposable TIP was shown to be a simple, inexpensive, reliable, and valid method of assessing incisor inclination.     

Crown angulation measured by laser scanner

The aim of this study was to measure the crown angulation of Japanese subjects with normal occlusion using a laser scanner to minimize human error. Twenty study models with normal occlusion were scanned by laser scanner. Crown angulations of each tooth in scanned 3D dental images were measured according to Andrews’ procedure. In Andrews’ procedure, a plane was established along the mesiodistal contact points of each tooth. The crown angulations of each tooth were measured by projecting the facial axis of the clinical crown (FACC) and a vertical line from the occlusal plane, and the mean and standard deviation were calculated. In maxillary teeth, the canine crown angulation was highest at about 7°, thus indicating a mesial tip, which was seen in all teeth except the second molar. In mandibular teeth, the second molar crown angulation was highest at about 7°, thus indicating a mesial tip, and only the lateral incisor exhibited slight distal tip, while all the remaining teeth exhibited mesial tip. Standard deviations for the maxillary and mandibular teeth ranged from 2.5° to 8°. The standard deviation of the maxillary and mandibular second molars was particularly large.     

江苏地区正常的牙及牙弓测量研究

目的 测量125名江苏地区正常人群的模型,建立江苏地区正常牙及牙列指数的平均值。方法 选取正常模型125副(男61副,女64副),用电子游标卡尺测量牙冠宽度、牙弓宽度及长度、腭盖高度,对测量结果进行统计分析。结果 江苏地区正常人群的牙冠宽度、牙弓宽度及长度、腭盖高度均为男性大于女性,Bolton指数及Pont指数无性别差异。上下颌6个前牙牙冠宽度总和、全部牙冠宽度总和具有相关性,上颌中切牙与上颌前段牙弓宽度之间亦存在相关性,且建立了直线回归方程。结论 牙冠形态、牙列指数存在种族、地区和性别的差异,临床上应参照本民族、本地区的标准。     

Changes in the maxillary and mandibular tooth size-arch length relationship from early adolescence to early adulthood. A longitudinal study

The purpose of this study was to determine the association between the changes in maxillary and mandibular tooth size-arch length discrepancies (TSALD) and various dentofacial variables for 18 male and 14 female subjects with normal occlusion. All subjects were participants in the Iowa Longitudinal Growth Study and records were evaluated at two stages of dental development: stage I, when the permanent second molars initially erupted into occlusion (X age = 13.3 years); and stage II, at early adulthood (X age = 26.0 years). The following sets of variables were evaluated: mesiodistal crown diameters of single and groups of permanent teeth, dental arch widths and lengths, curve of Spee, maxillary and mandibular anterior and total crowding or spacing, anterior tooth rotations, and various cephalometric dentofacial parameters. Student's t test were used to compare subjects with the most and least changes. Regression analyses also were used to assess the relationships between these parameters and the changes in the maxillary and mandibular tooth size-arch length relationship. The most consistent finding from the t test comparisons is the significantly greater reduction in the available arch length in the group with the most TSALD at early adulthood. No other variables were found to be consistently different in the comparisons between the two groups. The results of the regression analysis indicated that a number of dentofacial variables are associated with the changes in the maxillary and mandibular TSALD--for example, the mesiodistal diameter of different teeth and the changes in anterior and posterior facial heights. The clinical implications of the present findings are discussed.     

Delayed eruption of mandibular primary central incisors in a child with severe lingual inclination and their spontaneous movement to appropriate positions

We previously reported a quite uncommon case of delayed eruption of primary mandibular bilateral incisors with severe lingual inclination identified in a Japanese girl aged 2 years 8 months. An intraoral examination demonstrated the tooth crown morphology of the primary mandibular incisors in the lingual submucosal area, while radiographic examinations of the affected teeth revealed what appeared to be a standard root morphology and the permanent successors located close to the affected teeth. We decided to perform periodical examinations at least until the roots of the permanent successors were sufficiently formed and here report recent findings in this case. At 2Y10M, the edge of the tooth crown of the primary mandibular left central incisor had emerged into the oral cavity and one-third of the tooth crown was identified at 2Y11M. Thereafter, the tooth crown of the primary mandibular right central incisor was identified under the mucosa at 3Y1M. A periapical radiograph taken at 3Y7M demonstrated formation of the permanent successors under development. At 3Y10M, nearly the entire part of the tooth crowns of both affected teeth had emerged and then they started to move gradually in a labial direction. At 4Y2M, the crowns of the affected were nearly within the dental arch, while periapical radiograph images showed straight roots for the affected teeth and the developing permanent successors. We intend to continue to perform periodical examinations to follow the development of the permanent successors until eruption.     

Permanent mandibular incisor with multiple anomalies - report of a rare clinical case

Permanent mandibular central incisor is rarely affected by tooth shape anomalies of crown and root. Co-occurrence of multiple anomalies in a permanent mandibular central incisor is extremely rare. This paper reports an unusual concurrent combination of multiple dental anomalies affecting both the crown and root of a permanent mandibular left central incisor - talon cusp, dens invaginatus, short root anomaly and macrodontia -, which has not previously been reported together. Case management is described and implications are discussed. The dentist should be aware of these rare entities in order to provide an accurate diagnosis and management for which detailed examination of the tooth both clinically and radiographically is very important.     

Solitary median maxillary central incisor in association with hemifacial microsomia: A rare case report and review of literature

Solitary median maxillary central incisor (SMMCI) is a rare dental anomaly. It is estimated to occur in 1:50,000 live births. The SMMCI tooth differs from the normal central incisor in that the crown form is symmetric and it develops and erupts precisely in the midline of the maxillary dental arch in both primary and permanent dentitions. Presence of SMMCI with hemifacial microsomia (HFM) is a very rare clinical condition. We report a case of HFM in a male of Indian origin who presented with SMMCI in both primary and permanent dentitions. The association of HFM with SMMCI may be due to defective development of neural crest cells and/or lack of space in maxilla.     

The mesiodistal crown diameters of primary dentition in Indonesian Javanese children

Dentition analysis of primary teeth is necessary for recognising and correcting occlusal problems in every stage of dental development to enable normal adult occlusion. To do this, normative data of mesiodistal tooth crown diameters from the same ethnic population are needed. The aims of this study were to gather normative data of mesiodistal crown diameters of primary dentition in Indonesian Javanese children and to compare this normative data with published data of other ethnic populations. Dental casts of 160 males and 137 females with acceptable occlusion, aged 3.25-6.58 years, were taken in Yogyakarta, Indonesia. Mesiodistal diameter was measured as the distance between the anatomic contact points using calipers with accuracy to within 0.05 mm. Each measurement was taken twice on different occasions. The results indicated that the magnitude of asymmetry between right and left teeth was larger in distal teeth within a tooth field, larger in males than females, and larger in mandibular than maxillary teeth. The stability of mesiodistal tooth crown diameters was less in males than in females, and was most prominent in the mandibular central incisor. Sexual dimorphisms were found in, the lateral incisor and first molar in the maxilla, and the canine, first and second molars in the mandible. Compared with other ethnic populations, Indonesian Javanese falls between Hong Kong Chinese and Australian Aboriginal.     

Objective assessment of occlusal and coronal characteristics of untreated normals: a measurement study.

To determine whether tooth shape and position are constant within tooth types, dental casts of 68 Indians (age range, 10-32 years; mean, 18.72 years) were analyzed. The casts were selected from a larger sample and met the following criteria: Class I molar and canine relationships; overjet and overbite within normal limits; well-related vertical, transverse, and anteroposterior relationships with pleasing profiles and well-aligned arches; and no supernumerary teeth or large restorations. None of the subjects had received orthodontic treatment, and all were in good health and exhibited normal growth. Crown angulation, inclination, offset of maxillary molar, curve of Spee, crown facial prominence, horizontal crown contour, and vertical crown contour were assessed. Means, standard deviations, and standard errors were calculated. The measurements were compared with Andrews's data on 120 nonorthodontic normal occlusion casts. The Student t test was used to determine the significance of differences between the 2 sets of data. It was found that teeth of the same tooth type have similar values of horizontal and vertical crown contours. Values for inclination, angulation, and relative prominence were also similar. Hence, we concluded that tooth shape and position are constant for each tooth type. The data from this study were comparable with Andrews's findings. However, from this study, it would be safe to presume that all teeth except the maxillary second molars require alterations in the bracket base inclination value, and that the maxillary lateral incisor, canine, second premolar, and second molar, and the mandibular canine, require alterations in angulation values.     

Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis

The dental casts and cephalometric records of forty-three patients exhibiting bilateral congenital absence of maxillary lateral incisors were evaluated to determine the nature and extent of any concurrent craniofacial and dental anomalies. The effects of bilateral orthodontic space closure were evaluated on a subsample of twenty-two cases. The data revealed normal dental arch length, arch width, overjet, and overbite, while significant tooth size discrepancies were found in several anterior and posterior teeth. Craniofacial deviations from normal included smaller maxillary length, smaller mandibular length, smaller anterior cranial base, and nasal bone. Vertical facial dimensions, both anterior and posterior, were significantly less, as was the mandibular plane angle. Soft-tissue examination revealed a 10 degrees greater nasiolabial angle, which was increased a further 5 degrees as a result of a mean incisor retraction of 1.5 mm during space closure. The craniofacial anomalies noted in the present sample were similar to those seen in persons with clefts and may reflect a common etiology related to a developmental disturbance during fusion of the facial processes in utero. In the treatment of patients with bilateral congenital absence of maxillary incisors, mechanotherapy designed to open the mandibular plane, increase the vertical dimension, and move the maxillary posterior teeth forward is recommended in order to prevent worsening the Class III tendency and to minimize maxillary incisor and upper lip retraction. Most cases will require significant mesiodistal reduction in tooth size in order to achieve an optimal occlusion.     

Multidisciplinary solution for an avulsed upper central incisor: case report

Abstract – This case report refers to an 18‐year‐old female who suffered from dental trauma when she was 7 years old caused by a bicycle accident. Her maxillary right central incisor was avulsed, and the left one was extrusively luxated. The left central incisor was correctly repositioned and immobilized with a semi‐rigid splint. The right one could not be found. She presented with class II malocclusion and severe negative arch‐length discrepancies in both arches. The treatment objectives were the following: recover smile esthetics by replacing the maxillary right central incisor, correct the class II relationship, and optimally reduce mandibular and maxillary crowding. Extractions of the maxillary left lateral incisor and the lower right first bicuspid were performed; thus, the maxillary right lateral incisor would function as a maxillary right central incisor, the canines would function as lateral incisors, and the first bicuspids would function as canines. This allowed for the malocclusion to be corrected while simultaneously reestablishing the smile esthetics, without the use of an osseointegrated implant. A good occlusion with coincident upper and lower midlines was achieved. After orthodontic therapy, the patient underwent periodontal surgery to improve her gingival margins. Subsequent teeth bleaching was performed, and the patient received six porcelain veneers. A combination of orthodontic space closure and prosthetic rehabilitation may be the best treatment option after severe traumatic tooth loss.     

Horizontal impaction of primary mandibular bilateral central incisors identified in 2-year-8-month-old girl

A girl aged 2 years and 8 months came to our clinic for consultation with regard to unerupted primary mandibular bilateral central incisors. An intraoral examination revealed that the teeth had not emerged into the oral cavity and showed a tooth crown morphology similar to that of the primary mandibular incisors, which appeared in the lingual submucosal area outside of the mandibular dental arch. Periapical radiographs demonstrated that the tooth crowns of both affected teeth were severely displaced to the lingual side. Computed tomography examinations were performed to clarify the three-dimensional positions of the affected teeth and their permanent successors, which revealed that the affected teeth were located in their estimated positions and had a standard root morphology. In addition, the permanent successors, which had not initiated root formation, were located close to the affected teeth. We decided to postpone extraction of the affected teeth and perform periodical examinations until the roots of the permanent successors are sufficiently formed. At the age of 2 years and 10 months, the edge of the tooth crown of the primary mandibular left central incisor was found emerged into the oral cavity. According to her parents, the patient did not complain of the emerging edge and no abnormal conditions were observed around the tooth.     

Angle Ⅰ类错畸形患者的庞特指数对比的相关分析

目的：比较正常庞特指数与AngleI错畸形庞特指数之间的差异,分析错畸形切牙牙冠与磨牙宽度之间的关系。方法：选取Angle I错畸形患者40例,取上下颌硅橡胶模型,使用三维扫描仪进行三维扫描,然后使用计算机正畸设计软件OrthoRx V3.20建立三维模型并进行数据处理,在模型上选取测量标志点对各项指标进行测量,最终应用spss17.0统计软件分析AngleI错与正常之间差异。结果：AngleI错畸形上颌庞特指数与以往研究一致,下颌前磨牙和磨牙间庞特指数有显著性差异。结论：AngleI错畸形患者上颌骨各部的发育比例与正常颌基本一致,下颌畸形形成因素较复杂,需要根据个体情况适当扩展牙弓宽度。     

Degeneration of tooth germ in the developing dentition of the gray short-tailed opossum (Monodelphis domestica)

The aim of this study was to examine the developmental aspects of the dental lamina and the tooth germ of the marsupial opossum (Monodelphis domestica), and to clarify the dental formula of this animal. Specimens were 12-, 16-, and 18-d-old opossums. 3-D reconstructions were constructed from frontal serial sections. In these animals, the tooth germs of the deciduous maxillary and mandibular canine, deciduous third premolar and first molar, and the deciduous maxillary first incisor and second molar had a successional dental lamina and a replacement tooth germ. The tooth germ of the deciduous maxillary fourth incisor and the mandibular first incisor were reduced. The dental lamina was continuous in each jaw except for the deciduous maxillary first incisor. The first dentition (deciduous dentition) remained as the permanent dentition on the deciduous maxillary first incisor, and the deciduous maxillary and mandibular canine and first molar. The maxillary fourth incisor and the mandibular first incisor were the second dentition (successional dentition). Only the deciduous third premolars were replaced. These results showed monophyodonty caused by both deciduous and replacement tooth germ degeneration.     

101例中国东北汉族上颌中切牙几何特征的研究

目的：研究上颌中切牙临床冠近远中径、切龈径与唇面形态,为前牙美学修复提供参考。方法：选取前牙列完整自愿者101例,测量左上中切牙近远中径、切龈径;并按尖圆、方正、卵圆形记录唇面总体形态,按平直、圆突、反圆弧记录切缘形态;以平坦、圆突记录唇面突度。按性别和年龄分组,SPSS 13.0分析研究结果。结果：经两独立样本T检验,壮年组的切龈径较青年组有所增加,但差异无统计学意义;男性切龈径大于女性,性别差异P〈0.05,有统计学意义;近远中径、近远中径/切龈径比值,青年与壮年组、男女两性差异均无统计学意义。经卡方检验,中切牙唇面形态构成比性别差异无统计学意义。结论：男性中切牙切龈径较女性长。中切牙形态与性别没有必然关系。     

影响上颌中切牙单个种植修复体龈乳头高度的因素分析

目的分析影响上颌中切牙单个种植修复体龈乳头高度的因素，探讨促进种植修复美学效果的相关因素。方法选择16例上颌中切牙单个种植修复患者（30个龈乳头），通过分析临床资料、口内照片、X线片和研究模型，得到龈乳头高度及相关因素数据，采用多重线性回归方法进行分析。结果16例患者中切牙种植修复体龈乳头高度为（4．01±1．85）mm，影响龈乳头高度的相关因素按作用由大到小的排列顺序为：种植修复体外冠接触点高度、邻近天然牙邻面牙槽嵴顶高度、邻近天然牙邻面牙槽嵴顶到外冠接触点的垂直距离、种植修复体外冠邻面凸度、种植体基台与邻牙牙根距离、冠根长度比例、种植修复体邻面牙槽嵴顶高度、种植修复体外冠唇面凸度、探诊深度。结论中切牙种植修复体龈乳头高度受多种因素影响。     

错(牙合)畸形尖牙、双尖牙组与其它组牙的相关分析

目的：研究错牙合、正常牙合的尖牙、双尖牙组与其它组牙的相关性，为尖牙、双尖牙组的预测提供科学依据。方法：选用５组不同类型错牙合和正常牙合，每组男女各３０人，共３６０人，应用ＹＭ－２１１５三维测量仪测量牙齿最大近远中径，进行有关的相关性统计分析。结果：正常牙合的尖牙、双尖牙组与下切牙组高度相关，符合Ｍｏｙｅｒｓ预测机理，但错牙合的尖牙、双尖牙组一般与同牙列的切牙加第一磨牙组高度正相关。结论：临床上对错牙合尖牙、双尖牙组的预测不能简单等同于正常牙合。