Correlation of Root Dentin Thickness and Length of Roots in Mesial Roots of Mandibular Molars

Introduction

The purpose of this study was to analyze the relation of tooth length and distal wall thickness of mesial roots in mandibular molars at different locations (ie, 2 mm below the furcation and at the junction between the middle and apical third).

Methods

Forty-five mandibular first molars were taken, and the length of each tooth was measured. Then, specimens were divided into three groups according to their length: group I–long (24.2 mm ± 1.8), group II–medium (21 mm ± 1.5) and group III–short (16.8 mm ± 1.8). mesial root of each marked at two levels - at 2 mm below the furcation as well as at junction of apical and middle third of roots. The minimum thickness of the distal root dentine associated with the buccal and lingual canals of the mesial roots was measured, The distance between the buccal and lingual canals and the depth of concavity in the distal surface of the mesial roots were also measured.

Results

Statistical analysis was performed by using analysis of variance and the Student-Newman-Keuls test. The minimum thickness of the distal wall of the mesiobuccal canal was significantly different (P < .001) between groups 1 (long) and 3 (short).

Conclusions

Distal wall thickness of the mesiobuccal root and distal concavity of the mesial root of mandibular first molars were found to be thinner in longer teeth compared with shorter teeth.     

Effect of enamel matrix proteins (Emdogain') on healing after re-implantation of "periodontally compromised" roots. An experimental study in the dog

OBJECTIVE: The present experiment was performed to assess whether Emdogain applied on the root surface of extracted teeth or teeth previously exposed to root planning can protect the tooth from ankylosis following re-implantation. MATERIAL AND METHODS: The experiment included two groups of dogs, including five animals each. The root canals of all mandibular third premolars (3 P 3) were reamed and filled with gutta-percha. A crestal incision was placed from the area of the second to the fourth premolar. Buccal and lingual full thickness flaps were elevated. With the use of a fissure bur, the crown and furcation area of 3 P 3 were severed in an apico-coronal cut. The distal and mesial tooth segments were luxated with an elevator and extracted with forceps. Group A: The mesial and distal segments of 3 P 3 were air dried on a glass surface for 60 min. The roots from the right side were conditioned and exposed to Emdogain application. The roots from the left side received the same treatment with the exception of Emdogain application. The mesial and distal tooth segments were re-implanted and the crown portions were severed with a horizontal cut and removed. The buccal and lingual flaps were mobilized and sutured to obtain complete coverage of the submerged roots. Group B: A notch was prepared in each root, 4-5 mm apical of the cemento-enamel junction. The area of the root that was located coronal to the notch was scaled and planned. The roots in the right side of the mandible were treated with Emdogain, while the roots in the left side served as controls. After 6 months of healing, the dogs were killed and blocks containing one root with surrounding tissues were harvested, and prepared for histological examination, which also included morphometric assessments. Thus, the proportions of the roots that exhibited signs of (i) replacement (ii) inflammatory and (iii) surface resorption were calculated. RESULTS AND CONCLUSION: It was demonstrated that healing of a re-implanted root that had been extracted and deprived of vital cementoblasts was characterized by processes that included root resorption, ankylosis and new attachment formation. It was also demonstrated that Emdogain treatment, i.e. conditioning with EDTA and placement of enamel matrix proteins on the detached root surface, failed to interfere with the healing process.     

滑动法关闭下颌拔牙间隙的力学行为有限元分析

目的模拟临床加载力系统,研究滑动法内收下前牙过程中,不同方向载荷作用下,牙及弓丝力学行为的变化。方法建立含有托槽、弓丝、前后牙牵引钩的下牙列及下颌骨有限元模型。连接前后牵引钩上的点来确定矫治力的方向。并通过改变牵引钩高度来改变矫治力的作用点和方向。分析计算每一组加载力对牙的三维瞬间移动趋势、牙周膜的单元应力、弓丝的节点最大位移。结果前后牵引钩高度的变化与各牙角位移及牙周膜应力间均有相关性(P<0.01),各牙在不同后牙牵引钩高度,均随着前牙牵引钩高度变化而产生不同的移动。①随着前牙牵引钩高度的增加,中切牙、侧切牙的移动趋势逐渐由近中舌侧倾斜变为近中唇侧倾斜;而尖牙则向远中舌侧倾斜;第二前磨牙由近中颊侧倾斜变为近中舌侧倾斜;第一磨牙则由近中舌侧倾斜变为远中舌侧倾斜,且近中根比远中根舌向倾斜角度要大。②全牙弓牙周膜的最大应力始终出现在侧切牙的唇侧根尖1/3处;而尖牙、第一磨牙的牙周膜最大应力分别集中在牙槽嵴顶、根分叉处。结论在临床治疗中,可通过改变牵引钩的高度来实现前后牙的不同移动趋势,在弓丝上弯制不同的序列以更好地控制支抗牙。     

Dentine removal in the coronal portion of root canals following two preparation techniques

AIM: To measure the root canal area and the reduction of the mesial and buccal/lingual wall thickness at the level of the coronal interference in mesial roots of mandibular molars after instrumentation with a crown-down or a simultaneous root canal preparation technique. METHODOLOGY: Twenty mesial roots of first mandibular molars with a moderate root canal curvature were embedded in resin and sectioned horizontally at the level of the coronal interference, using a modification of the Bramante technique. After scanning and processing, the sections were reassembled. One root canal of each root was prepared using ProTaper instruments, while Mtwo instruments were used in the other root canal of the same mesial root. After scanning and processing, the data obtained were analysed for two parameters: changes in root canal area after instrumentation (Delta A) and reduction of the mesial and buccal/lingual wall thickness (Delta T). The data were subjected to Student's t-tests for statistical analysis at a significance level of P < 0.05. RESULTS: No statistically significant differences were found between the two groups with respect to the changes in the areas (Delta A) at the level considered (P = 0.410). No statistically significant differences were noticed between the two groups for dentine thickness (Delta T) of both the mesial wall (P = 0.077) and the buccal or lingual wall (P = 0.171). CONCLUSIONS: There was no difference between the ProTaper and Mtwo groups for the amount of dentine removed.     

The morphological studies of root resorption of maxillary primary canines and their relation with the position of successive permanent teeth using Micro-CT

The purpose of this study is to clarify the root resorption of maxillary primary canines in relation to the development of successive permanent teeth. It was observed the maxilla of dry skulls of Indian children, using Micro-CT, and measured shortest distance between the root surface of maxillary primary canine and the bony crypt of maxillary canine. The bony crypt including successive canine was positioned almost directly above the root of primary canine and located superior to another bony crypts in the primary dentition stage. When the first molars reached the alveolar crest in addition to the primary dentition stage, the bony crypt of canine grew, showing the distal inclination of the superior margin and mesial inclination of the inferior margin. After the stage which is central incisors reached the alveolar crest, root resorption of primary canines was observed on the lingual side nearby the root apex and the bony crypt of canine was adjacent to the nasal cavity. It was quantitatively shown that the distance between the roots of primary maxillary canine and canine bony crypts reduced from central incisors reached the alveolar crest to lateral incisors reached that.     

Residual dentin thickness in bifurcated maxillary first premolars after root canal and post space preparation with parallel-sided drills

STATEMENT OF PROBLEM: The primary factor that determines the prognosis of endodontically treated and restored teeth is preservation of sound dentin. The potential of these teeth to fracture is directly related to the amount of dentin removed. PURPOSE: The purpose of this study was to measure residual dentin thickness of bifurcated maxillary first premolars, in vitro, after root canal and conservative post space preparation. MATERIAL AND METHODS: Human premolars (n=13) with bifurcation at the junction of cervical and middle root thirds were embedded in a muffle device and horizontally sectioned 2, 4, and 6 mm apically to the cement-enamel junction. Residual dentin thickness was measured at the buccal, lingual, mesial, and distal aspects, apically to the bifurcation, and at the buccal or lingual, mesial, and distal aspects, coronally to the bifurcation. This procedure was repeated at baseline, after endodontic preparation (K-40 file), and after preparing the post space (ParaPost drills Nos. 3 and 4). Residual dentin thickness was analyzed using 3- or 4-way repeated measures ANOVA (alpha=.05). RESULTS: Endodontic therapy and post preparation reduced more dentin in the bifurcation aspects of both roots compared to outer aspects (P=.001). Post space preparation jeopardized the roots due to a residual dentin thickness of less than the recommended minimum 1-mm thickness in 61% (lingual) and 77% (buccal) of roots. CONCLUSIONS: Lack of residual dentin thickness after post preparation implies that the use of posts in maxillary first premolars should be limited. When mandatory, it is recommended that the lingual root be used and the buccal root be avoided.     

Evaluation of resistance form for prepared teeth

Resistance form of preparations for which castings were made in a large dental laboratory was evaluated. Each preparation was also evaluated for the placement of grooves. Evaluation of resistance form was done by grasping the casting between thumb and index finger and attempting to roll the uncemented casting off the die with finger pressure. Each preparation was tested for resistance form in all directions (buccal, lingual, mesial, and distal), from a fixed point of rotation. Evaluation was by tooth groups: incisors, canines, premolar, and molars. The preparations were found to have resistance form in 96% of the incisors, 92% of the canines, 81% of the premolars and only 46% of the molars. Only nine of 294 preparations evaluated had grooves. Mesial or distal grooves provided resistance to buccal and lingual dislodgment, and buccal or lingual grooves provided resistance to mesial and distal dislodgment.     

A comparative study of dentin thickness of primary human molars

The aim of the present survey was to evaluate the dentin thickness of buccal, lingual, mesial and distal surfaces of first and second primary molars. These evaluations were done at the middle third of the crowns of twenty extracted non-carious primary teeth separated in two groups (first molars and second molars). Comparisons were performed within-groups and between-groups. The mean values of dentin thickness observed for first molars were 2430 mm (buccal), 1.869 mm (lingual), 1.655 mm (mesial) and 1.664 mm (distal). For second molars the dentin thickness presented 3.006 mm (buccal), 2730 mm (lingual), 2130 mm (mesial) and 2192 mm (distal). The dentin thickness was higher in the buccal surface in both groups (P<0.05; Wilcoxon Test), except for the lingual surface of second molars (P>0.05). No differences were observed between mesial and distal surfaces in both groups (P>0.05). Comparisons between-groups showed that the dentin thickness was higher in all surfaces of second molars (P<0.01; Mann-Whitney Test). It was concluded that there are differences in the dentin thickness between first and second primary human molars and within the different surfaces of such teeth.     

Assessment of root curvature and distance using computed tomography

The safety and efficacy of subgingival root surface instrumentation may be enhanced by optimized adaptation between instrument and treated surface. Thus, detailed knowledge of root geometry may allow advances in instrument design. The aim of this study was therefore to measure root radii of various tooth types as well as distances between tooth roots using computed tomography. Two hundred sixteen teeth in eight patients were studied, with cross sections of teeth at the level of the cemento-enamel junction (CEJ) being regarded as ellipses. The maximum radii of ellipses were calculated and averaged for each tooth surface within various tooth groups. In addition, the spacing between roots at CEJ level and 5 mm below the CEJ was measured. Mean radii varied from 1.09+/-0.50 mm (lower incisor, lingual) to 13.7+/-0.96 mm (upper molar, mesial). Radii of 1 mm to 6 mm were most frequently found at buccal, palatal, and lingual surfaces, whereas the majority of radii were between 2 mm and 11 mm at mesial and distal sites. Root distance varied between 1.04+/-0.49 mm (lower incisors, CEJ level) and 2.81+/-1.70 mm (lower molars, 5 mm below CEJ). The curvature of an instrument for root surface instrumentation should correspond to a radius of at least 11 mm to achieve maximum adaptation to the treated surface, and the width of the working end should be less than 1 mm to allow sufficient interdental instrumentation.     

A survey of approximal root concavities in an ethnic Chinese population

Eight hundred and forty teeth were surveyed, 60 approximal surfaces for each tooth type being studied. Approximal root concavities were completely absent in maxillary central incisors, in contrast with mandibular central incisors of which 73% had concavities on mesial surfaces and 93% on distal surfaces. Similarly, a markedly higher prevalence was found for mandibular lateral incisors and canines. However, mandibular first and second molars had fewer approximal concavities than their maxillary counterparts. In maxillary teeth, concavities were more frequent on distal surfaces, while for mandibular teeth no definite pattern was seen. In both maxillary and mandibular teeth, approximal concavities often started in enamel, extending down to the root surface. There were differences in the approximal root topography of Chinese teeth in comparison with other populations.     

青少年三根型下颌第一恒磨牙牙根外形解剖数据的锥形束CT测量分析

目的:利用锥形束CT测量青少年三根型下颌第一恒磨牙(PMFMs)牙根外形解剖数据,为牙周炎的预后判断和治疗提供理论支撑和临床指导.方法:选取175颗三根型PMFMs的锥形束CT影像学资料,记录牙齿发生情况、牙根长度、根柱长度、釉牙骨质界(CEJ)根方2 mm水平的根柱凹陷程度、根分叉穹窿顶点根方2 mm水平处的根分叉宽...     

无托槽隐形矫治拔牙病例的后牙不同轴倾度对牙齿三维力学影响

目的 研究无托槽隐形矫治技术拔除双侧上颌第一前磨牙病例整体内收前牙，后牙不同轴倾度时，各个牙齿的瞬时受力情况。方法 设置4组后牙不同轴倾度的上颌牙列，T1组后牙为正常牙合轴倾度，T2组后牙在T1组基础上后倾5°,T3组后牙在T1组基础上前倾5°,T4组后牙在T1组基础上前倾10°。拔除双侧第一前磨牙，整体内收前牙0.25 mm,在矫治器六轴力传感器测试平台上测量4组牙列中各个牙齿在三维方向的瞬时力。每组牙列设计12副隐形矫治器。结果 与T1组相比，T2组切牙伸长力减小，尖牙远中向力增加，后牙近中向力减小，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。与T1组相比，T3和T4组切牙舌向力和伸长力增大，尖牙远中向力增大，后牙近中向力也增大，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。结论 后牙后倾时利于前牙转矩的表达，有助于保护后牙支抗，但增加了磨牙的颊向力和伸长力。后牙前倾时，前牙更容易出现转矩丢失，覆牙合加深的现象。后牙越前倾，覆牙合越容易加深，后牙支抗容易丢失。     

New cavity forms in first deciduous molars which maximize dentin thickness between cavity and pulp chamber

Using a total of 60 human extracted first deciduous molars (30 upper molars and 30 lower molars), we contrived a variety of ideal cavities having dentin thicknesses below the cavity (subcavitary dentin) that measure approximately 1 mm in thickness from the pulp chamber at any point of measurement and also having a retentional groove prepared in such a way that detachment of a filling material is prevented. The transparent specimens prepared from the cavity-containing teeth were cut into serial sections of 93 microns. These sections were reconstructed using a personal computer. The thickness of dentin below the cavity was measured in randomly selected sections. Results obtained were as follows: 1. An ideal thickness of the subcavitary dentin was preserved for upper first deciduous molar by preparing a retentional groove lingually or by providing a dovetail-like shape to mesio-distolingual sides in the cavity; for lower first deciduous molar, any form of cavitation worked. 2. In the upper first deciduous molars, the margins of the cavity were displaced medially to the summits of the respective cusps 1.9 mm at the buccal side and 1.2 mm at the lingual side. In the lower first deciduous molars, the buccal margin medially measured 0.9 mm and the lingual margin measured 0.6 mm at the mesial side. At the distal side, the buccal and lingual margins measured 1.2 mm and 1.0 mm, respectively. 3. The ratio of cavity width to the distance between the summits of the buccal and lingual cusps was 1/3 in upper deciduous first molars and 2/5 in the lower first deciduous molars. 4. In the upper first deciduous molars, the depths of the buccal and lingual walls of the cavity at the center of the central groove were both 1.1 mm. In the lower first deciduous molars, the cavity formed with its center at the middle of the transverse ridge had a depth of 1.5 mm at the buccal wall and a depth of 1.7 mm at the lingual wall. The cavity formed with its center at the central fossa had a depth of 1.2 mm at the buccal wall and 1.1 mm at the lingual wall. 5. The width of the gingival wall in the proximal box measured 0.6-0.7 mm in upper and lower first deciduous molars.     

The external and internal anatomy of human mandibular canine teeth with two roots

Abstract— This study investigated the internal anatomy of 65 human mandibular canines with two well-defined roots. The teeth were decalcified and injected with gelatin coloured with india ink. Diaphanization was carried out using clear resin to allow permanent preservation. It was found that all mandibular canines with two roots had two root canals. Lateral canals were found in 68.9% of teeth and 19.7% had lateral canals at the bifurcation. The results of the external measurements (cusp tip to root apex) showed that the average buccal root length was 23.0 mm and the average lingual root length was 22.7 mm. The maximum and minimum buccal lengths were 26.7 mm and 17.9 mm respectively and the maximum and minimum lingual lengths were 27.2 mm and 17.1 mm respectively. The buccal root was the larger of the two in 47.7% of teeth and 43.1% had roots of equal size. The lingual root was larger than the buccal root in 9.2% of cases. Clinicians should be aware of the anatomical variation that exists for mandibular canines.     

蒙汉族人下颌切牙颈部牙体壁厚度对比研究

目的：通过对蒙古族和汉族人的下颌切牙颈部牙体壁厚度进行测量,对比其间的差异,为内蒙古地区下颌切牙牙体治疗和修复治疗提供解剖学依据。方法：筛选蒙古族和汉族128人的下颌切牙512颗,利用Newtom3G锥形束CT—三维头颅成像系统和NNT操作软件进行拍摄、重建并分别测量牙体颈部唇侧、舌侧、近中、远中牙体壁厚度,所得数据进行统计分析。结果：唇侧、近中、远中牙体壁的厚度蒙古族均大于汉族,差异具有统计学意义（P〈0.05）,舌侧壁厚度对比差异无统计学意义。结论：汉族和蒙古族36～45岁人群的下颌切牙颈部牙体壁厚度存在一定的差异,从而为口腔临床治疗提供一定的理论依据。     

Micro-CT扫描下颌乳中切牙釉质厚度的研究

目的：用Micro-CT扫描测量下颌乳中切牙釉质厚度,了解其牙冠不同部位牙釉质的厚度。方法：用Mi-cro-CT扫描41颗下颌乳中切牙,选取牙冠不同部位的扫描横断面,测量其牙釉质厚度。结果：下颌乳中切牙釉质厚度牙冠切端1/3处显示：唇面最厚（0.37±0.04）mm,依次为远中面（0.36±0.04）mm、近中面（0.30±0.04）mm、舌面（0.22±0.03）mm;牙冠颈部1/3处厚度依次为：唇面（0.24±0.04）mm、舌面（0.22±0.03）mm、远中面（0.22±0.04）mm,近中面最薄（0.14±0.04）mm。结论：下颌乳中切牙釉质厚度在牙冠不同部位分布存在不同程度的差异。     

Buccal bone plate thickness of the Asian people

Distances from the apex to the buccal bone plate were measured on the computed tomography (CT) images of 1806 teeth from 66 patients, using an image analyzer program (Image-Pro Plus, Ver. 4.0, Media Cybernetics). In the mandible, the mean distance from the distal apex of the mandibular second molar to the buccal bone plate was the largest distance measured, at 8.51 mm, followed by distance from the mesial root to the buccal bone (7.34 mm). In the mandibular first molar, the mean distal and mesial bone thicknesses were 5.18 mm and 4.09 mm, respectively. However, when there were two distal roots, the distance of the disto-lingual root to the buccal plate was found to be 9.52 mm, which constitutes the greatest measured thickness. In the maxillary buccal roots, the distances from the mesio-buccal and disto-buccal root of the second molar to the buccal bone plate were the largest, at 4.63 mm and 3.61 mm, respectively. The average distances from the palatal apex of the maxillary first and second molars to the buccal bone plate were 10.69 mm and 10.17 mm, respectively, while, from the palatal bone plate, average distances of 3.15 mm and 3.08 mm were measured. Special considerations, such as bony lid approach, lingual approach, or intentional replantation may be required, especially when a patient has a surgical need in the second molars and the disto-lingual root of the mandibular first molar, or in the palatal root of the maxillary molars.     

Root surface measurements of the mandibular first molar

The root surface area (RSA) per millimeter of root length was determined for 20 extracted mandibular first molars. The molars were cross-sectioned at 1-mm increments, and each section photographed, projected and measured with a calibrated opisometer. The RSA and per cent RSA were calculated for each 1 mm of root length (1-mm section), the root trunk and the individual roots. Also measured was the location of the root separations from the root trunk, the location of the first detectable root concavity, and the prevalence of "intermediate bifurcation ridges" (IBRs). Mean measurements indicated that the greatest RSA per millimeter of root length was 4 to 7 mm apical to the cementoenamel junction (CEJ) in the area of the furcation. Of the total RSA, 48.7% was located in the coronal 6 mm of a root (mean length, 14.4 mm). Root separation occurred 4.0 mm apical to the CEJ with no tooth having a root trunk longer than 6 mm. Buccal and lingual root concavities were first present 0.7 mm and 0.3 mm apical to the CEJ, respectively. Fourteen (70%) of the 20 teeth had IBRs. According to the mean measurements, the mesial root was larger than the distal root by a ratio of 1.0:0.88. Horizontal attachment loss of 6 mm affecting both the buccal and lingual surfaces of the mandibular first molar would have resulted in a through and through (grade 3) furcation involvement of all the teeth studied.     

Changes in root length from early to mid-adulthood: Resorption or apposition?

A significant number of adults are seeking orthodontic treatment, therefore, it is important to determine the normal changes in root length (resorption or apposition) that occur at this stage of maturation, specifically between early and mid-adulthood. The purpose of the study was to determine on a longitudinal basis the changes in root length between 25 and 45 years of age in a normative untreated population. Two sets of complete mouth surveys were available at early and mid-adulthood, on a total of 26 subjects (12 males and 14 females). Each set consisted of at least 18 periapical radiographs. On each set of radiographs, the roots of 28 teeth were measured including incisors, canines, premolars, and first and second molars, in both the maxillary and mandibular arches. Root length was measured as the perpendicular from the root apex to a line connecting the mesial and distal points of the cementoenamel junction of each tooth. A total of 1456 teeth (1664 roots) were measured; 672 teeth in males and 784 teeth in females. Allowable intraexaminer and interexaminer measurement variability was predetermined at 0.5 mm. Paired and Student t tests were used to determine: (1) whether significant changes occurred with age; (2) whether there were differences between males and females for the incisors, canines, premolars, and molars; and (3) whether there were differences between the right and left sides. Statistical significance was predetermined at P 相似文献   

Parallel post-space preparation in different tooth types ex vivo: deviation from the canal centre and remaining dentine thickness

AIM: To determine the deviation of parallel-sided twist-drills during post-channel preparation and relate this to tooth type and position. METHODOLOGY: Human teeth with single root canals were selected: maxillary second premolars (group i); maxillary lateral incisors (group ii); mandibular canines (group iii); mandibular first premolars (group iv; all groups n = 16). The teeth were reduced to 17 mm length by sectioning the crown, and the root canals prepared and filled. Microradiographs were made in two directions. The teeth were individually embedded in a gypsum jaw and placed in a phantom head. Two operators performed parallel post-space preparation (12 mm length, 1.25 mm diameter) to the following protocol: gutta-percha removal with Gates Glidden drills numbers 2 and 3 and post-space enlargement with parallel drills numbers 3, 4 and 5, consecutively. Subsequently, microradiographs were re-exposed. The original and post-operative microradiographs were digitized and superimposed, and deviation of the post-space from the filled canal and remaining dentine thickness measured. RESULTS: Overall, the mean deviation was 0.07 mm to the mesial (95% CI: 0.01-0.12), and 0.27 mm to the buccal (95% CI: 0.18-0.35). Group ii had significantly more buccal deviation than other groups (P = 0.004-0.008). A remaining dentine thickness of <0.5 mm occurred 16 times in 14 teeth, and of <1 mm occurred 97 times in 52 teeth. CONCLUSIONS: Deviation during parallel post-preparation was common, predominantly in mesial and buccal directions, especially in maxillary incisors. This deviation increased the risk of perforation considerably.