福建省北部儿童乳牙近远中径的测量研究

目的 获得福建省北部地区儿童各个乳牙的近远中径正常值范围。方法获取福建省建瓯市政和县的374名4～8岁儿童的口腔模型，对各个乳牙牙冠的近远中径进行测量和分析。结果多数乳牙牙冠近远中径存在显著性性别差异，而左右侧同名牙近远中径的差异无统计学上显著性意义。结论所获取的乳牙的近远中径的数据为我国乳牙解剖学提供了资料，并对临床修复有一定的参考价值。     

恒尖牙双尖牙近远中径预测方程

目的：为口腔正畸临床混合牙列间隙分析提供简捷,便利的诊断依据。方法：在模型上测量牙冠近远中径,对测量值进行直线回归与相关分析。结果：下切牙与尖牙,双尖牙近远中径存在直线相关关系。结论：建立了汉族人群上,下颌尖牙双尖牙近远中径观测方程。     

第二磨牙和第三磨牙近远中径的预测

目的　为口腔正畸诊断中全牙列间隙分析提供理论依据。方法　随机选取 14 0名 18岁至2 5岁全牙列牙冠完全萌出 (包括第三磨牙 )的汉族青年 ,其中男 6 0人 ,女 80人。在牙模型上测量所有牙冠的近远中径和后牙颊舌径。利用SAS计算机软件 ,对测量值进行统计分析。结果　建立了汉族人第二磨牙和第三磨牙的多元回归方程。结论　第二磨牙或第三磨牙未萌时 ,应采用本研究所得方程预测其近远中径。     

下切牙先天缺失与牙颌畸形关系的分析研究

目的：探讨下恒切牙先天缺失情况及其与牙颌畸形的关系以及下尖牙近远中径的变化。方法：从962名门诊正畸病人中选取下颌恒切牙缺失的病例27名，并测量下前牙牙冠的近远中径。结果：下颌恒切牙先天缺失96％是中切牙，92％伴有前牙深覆He，下尖牙无显著性增大。结论：下颌中切牙先天缺失与前牙深覆He的形成有密切关系，下尖牙无代偿性增大。     

上颌第一双尖牙牙冠周径测量及其影响因素

目的探讨上颌第一双尖牙牙冠的周径与其颊舌径、近远中径、对角距离等解剖标志间的关系,为制作和选择带环提供参考依据.方法收集12～25岁患者拔除的100只离体上颌第一双尖牙,利用游标卡尺对上颌第一双尖牙进行测量,分析、观察牙冠周径与颊舌径、近远中径、对角距离的关系,列表总结并作统计学处理.结果上颌第一双尖牙牙冠周径与其颊舌径、近远中径关系最为密切(P<0.01).结论可通过测量上颌第一双尖牙颊舌径来推算牙冠周径.     

上颌第一前磨牙3根1例

患者女，14岁，因正畸需要拔除4个第一前磨牙。在20g/l。利多卡因局麻下顺利拔除24。离体牙检查：牙冠为双尖形，[牙合]面颊舌径大于近中远中径，共有3个牙根。在根长1/2处分为颊，舌2根，而颊根在距根尖1/3处又分为近中颊根和远中颊根。     

牙体牙髓-正畸方法联合处理恒上前牙冠根折的临床观察

目的：观察牙体牙髓－正畸方法联合处理恒上前牙冠根折的临床疗效。方法：21颗冠根折的恒上前牙，在完善根充后，利用正畸方法对患牙牙根进行垂直He向牵引，达到理想牙冠修复条件，在此基础上进行牙冠延长术和修复治疗。结果：21颗患牙垂直He向移动距离2mm-5mm，所需时间4周－8周；三年复查，部分患牙牙齿或牙龈相对位置有轻微变化，所有患牙根尖周正常。结论：牙体牙髓－正畸方法联合处理恒上前牙冠根折，作为修复治疗的辅助方法有效可行，但18岁以下的患者需延长牵引后的保持时间，并用临时冠进行过渡性修复。     

口腔多用测距仪的研制及应用

为解决口腔科临床精确测量有关参数的方法问题，作者自行研制了“口腔多用测距仪”。该仪器采用了位移传感技术，精度可靠，操作简单方便，易于口腔外直接读数并配装有可互换的颌间垂直距离和正畸专用测量工作头。应用该仪器对２５名１８～２５岁的健康受试者，进行了颌间垂直距离和牙冠指数测量，结果表明颌间垂直距离为６８．３４±１．０８ｍｍ，中切牙冠长为１１．５２±０．１２ｍｍ，冠宽为６．３１±０．１１ｍｍ。口腔多用测距仪为临床、科研提供了一种较先进的测量手段。     

影响切牙大小的遗传和环境因子的特点

目的：将双生子研究方法与因子分析法相结合，探讨影响切牙大小的遗传和环境因子的特点，为相关错He畸形的临床实践提供指导，为基因定位作好准备。方法：收集6岁－12岁女性双生子82对，通过DNA指纹图进行卵型诊断。采取口腔模型，测量切牙牙冠的近远中径和唇舌径，进行因子分析。结果与结论：（1）识别出下切牙唇舌径的遗传总控制因子。（2）对于切牙大小，遗传作用的对称性明显，环境作用多呈局部性，也可表现一定的对称性，但不及遗传作用明显。（3）在遗传上，同一牙齿的近远中径和唇舌径相互独立，受制于不同的作用因子。     

三种测量技术应用于口腔正畸模型测量中的比较研究

目的 对应用于正畸治疗中的三种正畸模型测量技术进行可靠性对比研究,并分析三种方法的差异.方法 采用手工直接测量、数码近摄测量、三维激光扫描测量三种方法对100副牙颌模型上每个牙的牙冠近远中径分别测量,并将三种测量值进行统计学分析.结果 三种测量技术之间无显著性差异;但三维激光扫描测量方法具有其他两种测量方法所不具有的优点.结论 三种测量技术都可进行准确的模型测量,三维激光扫描技术因其具有的优点而有广泛的临床应用前景.     

Is the Buccolingual Crown Diameter for Transverse Malocclusions?

OBJECTIVE: We investigated whether there is a correlation between the buccolingual crown diameter and cusp tip distance and if that can be considered a factor influencing the formation of a transversal malocclusion. MATERIALS AND METHODS: The buccolingual crown diameters and cusp tip distances of all premolars and first molars of 102 normal dentitions and 123 dentitions with a transverse malocclusion were measured and examined for significant differences. We also investigated whether there were differences in size between the genders and between left and right sides. RESULTS: General differences in buccolingual crown diameters ranged from 0.3 mm to 0.6 mm, and in cusp tip distance from 0.4 mm to 0.7 mm. Buccolingual crown width was generally greater in boys than girls, whereas we observed no statistically significant difference in cusp tip distances. Comparison of left and right sides revealed no significant difference. We were able to statistically prove the correlation between buccolingual tooth diameter and cusp tip distance. CONCLUSIONS: The results suggest that larger teeth with a greater cusp tip distance offer a more favorable prerequisite for the appearance of regular transversal occlusal relations than those with a smaller distance. The buccolingual crown width and its corresponding cusp tip distance seem important for initial contact with the antagonists, and may be regarded as a factor that determines whether or not a crossbite develops.     

Dentition and occlusion development in African American children: mesiodistal crown diameters and tooth-size ratios of primary teeth

PURPOSE: The aim of this study was to evaluate the mesiodistal primary tooth size diameter and posterior sagittal tooth-size ratio in an African American population and compare to existing African American and European American norms. METHODS: A sample of 1,124 African American children, 564 males and 560 females, was used to record crown size diameters employing indirect (cast) and direct (intraoral) measurement techniques. RESULTS: African American males showed larger crown diameters than African American females for each of the 5 classes of primary teeth (a=0.05 level). Sexual dimorphism averaged 3.5% in the maxilla and 3.2% in the mandible. When inter-racial primary crown size comparisons were made between African American and European American children, African American males showed larger mean crown diameters for each class of primary teeth compared to European American males. The inter-racial comparisons in crown diameters of females showed fewer statistically significant differences in primary teeth classes. When crown size comparisons of the primary dentition's posterior segments were made, African American males and females showed a larger primary posterior sagittal tooth-size-ratio compared to European American children. CONCLUSIONS: While intra- and inter-racial sex differences exist in the primary teeth of African American and European American children, with few exceptions, the mesiodistal crown size differences and sexual dimorphism appear to be larger for the African American population. African American children show a larger primary posterior sagittal tooth-size ratio (0.96) compared to European American children (0.94).     

上颌第一乳磨牙临床牙冠的计算机辅助测量

目的:收集华北地区上颌第一乳磨牙形态数据,分析其形态特征。方法:使用3d扫描仪对116名儿童重建上颌第一乳磨牙,使用Creo 2.0测量软件测量牙冠最大近远中径、颊舌径、冠指数、冠面积、冠周径、冠高等。结果:获得了华北地区上颌第一乳磨牙冠周径频数表和各检测项医学参考值范围。最大近远中径、颊舌径、冠面积、颌面周径、最大周径男性大于女性(P<0.05),左右两侧各检测项差异均无统计学意义(P>0.05)。结论:该研究提供了更适合中国北方儿童第一乳磨牙形态的基础数据。     

Tooth crown size in human females with 45,X/46,XX chromosomes

Permanent tooth sizes in 15 Finnish females with a 45,X/46,XX chromosome constitution were measured and compared with those of normal females, first-degree female relatives and 45,X females. Mesiodistal crown diameters of the 45,X/46,XX mosaic females were smaller than those of normal females but similar to those of females with pure 45,X chromosome constitution. Labiolingual crown diameters of the 45,X/46,XX mosaics were near normal, being consistently larger than those of 45,X females. The mesiodistal crown sizes are consistent with a decrease in enamel thickness in 45,X/46,XX mosaic females. The difference in labiolingual dimension between teeth of 45,X/46,XX mosaic females and 45,X females may relate to a gradual normalization of growth when normal 46,XX cells are mixed with defective 45,X cells.     

A comparison of mesio-distal crown dimensions of the permanent teeth in subjects with and without fluorosis

This investigation was undertaken to compare the mesio-distal crown dimensions of the permanent teeth in subjects with and without fluorosis. For this study, 25 pairs of study models cast immediately from alginate impressions of children from each of the two groups were evaluated. Their mean ages were 13.9 +/- 1.6 and 13.9 +/- 1.4 years, respectively. A dental vernier calliper was used to record the maximum mesio-distal dimensions. Analysis of the study models showed that there were no statistically significant differences between the left and right sides (P > 0.05). The results indicated that the mesio-distal crown diameters were consistently larger in the subjects with non-fluorotic permanent teeth. With the exception of the mandibular first premolars, there were no statistically significant differences in the mesio-distal crown diameters of the two groups.     

不同包埋材料对基底合金铸造收缩影响的实验研究

目的　比较不同包埋材料、不同包埋方法以及不同金属冠高度对铸造金属全冠收缩的影响,指导临床选择较为合适的材料和方法。方法　制作相同直径和厚度,高度分别为4 mm、6 mm和8 mm的全冠蜡型各96 个。选用3种磷酸盐包埋材料分别进行有圈包埋和无圈包埋,铸造后测量铸件边缘内径,对数据进行统计学分析。结果　(1)不同包埋材料对基底合金的铸造收缩的影响存在差异(P<0·01)。用水调拌的X-20 Chrome包埋材料铸件表现出较大的体积收缩率。GILVESTⅡS包埋材料和贺利氏包埋材料的膨胀能较好补偿合金的铸造收缩,铸件有较好的精密度。(2)不同包埋方法对基底合金的铸造收缩存在显著影响。无圈包埋的基底合金的铸造收缩小于有圈包埋。(3)不同冠高度对基底合金铸造收缩的影响无显著差异(P>0·05)。结论　不同包埋材料对铸造收缩影响不同,无圈包埋时的铸造收缩小于有圈包埋。     

Characterization of maxillary central incisor: novel crown–root relationships

Objectives

The periodontal biotype includes crown features of the maxillary central incisor (MCI), whereas root measures have been less studied. The aim of our study was to morphologically characterize MCI and search relationships between crown and root measures.

Material and methods

One hundred-fifty MCIs were used. On each tooth, several crown and root reference points were marked and the following measures were done: On crown: mesio-distal (MD?=?major, md?=?minor), axial (crown length, cervical convexity) and buccolingual diameters (Cbl); On root: mesio-distal (Rmd) and buccolingual diameters (Rbl); and tooth length. A ratio between md and MD was made in order to assess dental forms. Root diameter prediction was assessed by means of multiple and single linear regression analyses, with variable selection by backward method. Reliability of measurements was estimated by the Pearson correlation coefficient.

Results

Dental form groups were: Stout type 56.67 %, Intermediate type 22.67 %, and Strangled type 20.67 %. A significative association was found between Rbl and Cbl (p?=?0,000), Rmd with md (p?=?0.000), and Rmd with MD (p?=?0.000). The results allow predicting root diameters through crown measures.

Conclusions

There is a direct relationship between crown and root features, which allows the prediction of root diameters with a high accuracy (95 %), regardless of tooth form.

Clinical relevance

The morphometric data assess tooth diameters more accurately and could improve treatment planning, offering a more comprehensive approach to the periodontal biotype concept.     

Molar intercuspal dimensions: genetic input to phenotypic variation

Molecular studies indicate that epigenetic events are important in determining how the internal enamel epithelium folds during odontogenesis. Since this process of folding leads to the subsequent arrangement of cusps on molar teeth, we hypothesized that intercuspal distances of human molar teeth would display greater phenotypic variation but lower heritabilities than overall crown diameters. Intercuspal distances and maximum crown diameters were recorded from digitized images of dental casts in 100 monozygotic and 74 dizygotic twin pairs. Intercuspal distances displayed less sexual dimorphism in mean values but greater relative variability and fluctuating asymmetry than overall crown measures. Correlations between intercuspal distances and overall crown measures were low. Models incorporating only environmental effects accounted for observed variation in several intercuspal measures. For those intercuspal variables displaying significant additive genetic variance, estimates of heritability ranged from 43 to 79%, whereas those for overall crown size were higher generally, ranging from 60 to 82%. Our finding of high phenotypic variation in intercuspal distances with only moderate genetic contribution is consistent with substantial epigenetic influence on the progressive folding of the internal enamel epithelium, following formation of the primary and secondary enamel knots.     

Tooth-size reduction associated with occurrence of palatal displacement of canines

This study investigates mesiodistal crown size of the maxillary and mandibular incisors of patients with palatally displaced canines (PDC). Pretreatment dental casts of orthodontic patients with PDC of 1 or both maxillary canines (N = 31; M10:F21) were collected. This PDC sample was matched according to age and sex with pretreatment dental casts from unaffected orthodontic patients. For the PDC and matched control samples, maximum mesiodistal crown diameters were recorded for the 4 incisors on the left side only. The results showed that, on average, the mesiodistal crown diameters for the maxillary and mandibular incisors measured smaller in the PDC sample than in the control sample. These findings of statistically significant tooth-size reductions associated with PDC occurrence indicate a generalized pattern of reduced tooth size as a characteristic associated with the PDC anomaly. Further, the presence of generalized tooth-size reduction in cases with palatally displaced canines helps explain why most orthodontic treatment plans for PDC patients are of the nonextraction type.