Location of Triple-Negative Breast Cancers: Comparison with Estrogen Receptor-Positive Breast Cancers on MR Imaging

There has been a major need to better understand the biological characteristics of triple-negative breast cancers. Compared with estrogen receptor (ER)-positive cancers, several magnetic resonance (MR) imaging findings have been reported as characteristic findings. However, information regarding their location has not been described. Our study was to compare the location of triple-negative breast cancers with that of ER-positive breast cancers using magnetic resonance (MR) imaging. The locations of 1102 primary breast cancers (256 triple-negative and 846 ER-positive) in 1090 women (mean, 52.1 years) were reviewed using three-dimensional (3D) coordinates. The x-axis measurement was recorded as the transverse distance from the posterior nipple line; y-axis measurement as the anteroposterior distance from the chest wall; z-axis measurement as the superoinferior distance from the posterior nipple line. The association between breast cancer subtype and tumor location was evaluated using multiple linear regression analysis. Triple-negative breast cancers were significantly closer to the chest wall than ER-positive breast cancers in absolute (1.8 cm vs. 2.3 cm, P < .0001) and normalized (0.21 vs. 0.25, P < .0001) y-axis distances. The x- and z-axes distances were not significantly different between triple-negative and ER-positive breast cancers. Multiple linear regression analysis revealed that age, mammographic density, axillary nodal status, and triple-negative subtype were significantly associated with absolute and normalized distances from the chest wall (all P < .05). Our results show that triple-negative breast cancers have a tendency toward a posterior or prepectoral location compared with ER-positive breast cancers.     

拔除下颌第三磨牙对下颌角区形态影响的CBCT 研究

目的:探讨下颌第三磨牙的拔除会否造成下颌角区骨骼形态的变化以及这种变化对面型的影响。方法:30例因矫治需要拔除下颌第三磨牙的成人正畸患者,在拔牙前和拔牙后6个月拍摄CBCT片,采用三维测量软件mimics10.01测量下颌第三磨牙所在的下颌角区牙槽骨骨质的宽度、高度和长度,利用SPSS18.0统计软件分析前后数值有无差异。结果:下颌第三磨牙拔除前后下颌角区骨质宽度和高度减小,差异有统计学意义(P<0.05),下颌角区骨质前后向长度未见明显差异。结论:拔除下颌第三磨牙能从一定程度上减小下颌角区骨质高度和宽度,但是前后向长度度基本没有变化。     

A note on functional implications of morphological variation in the human mandible

This study was carried out on 56 mandibles belonging to skeletal remains recovered from archaeological excavations in Israel dated to 6.000 BP. or less, 2 Neandertal mandibles dating between 50.000–60.000 BP. and 2 early H. sapiens sapiens mandibles both dating to circa 92.000 yr BP. Mandibular body length, the distance from the anterior border of the symphysis to a line bisecting the first molar (distance 1), and the distance from the line bisecting the first molar to the mandibular angle (distance 2) were measured. Distance 1, showed little variation between specimens. However, distance 2 showed a significant difference between sexes and between early and late specimens. For all specimens examined there was a low nonsignificant correlation, between the length of the mandible and distance 1, while there was a high correlation between the length of the mandibular body and distance 2. There was little or no correlation between distance 1 and 2. We propose that the human mandible, as a lever arm, can be divided into two functional parts; an anterior part which shows little change over the last 90000 years, and a posterior part which differs in accordance with the length of the mandibular corpus. These changes in distance 2 appear to correlate to changes in body size and diet, suggesting that as proposed by Hylander (1988) chewing rather than incision has played the main role in evolutionary trends of the hominid mandible. This is also in accordance with mandibular growth during development where the lengthening of the jaw takes place mostly in the posterior part by remodeling in the ramus area (Enlow, 1990) both during individual development (ontogenesis) and through evolutionary changes (phylogenesis).     

Morphologic variation in the cranium and mandible of the white-tailed deer (Odocoileus virginianus): A comparative study of geographical and four biological distances

Several biological distances based on cranial and mandibular variation among breeding groups of white-tailed deer were calculated and compared with geographic distances among the groups. Distances based on epigenetic variation among ten groups were calculated using 16 non-metric variants of the cranium and mandible. Penrose's size and shape distances and Mahalanobis' D² distance were calculated for 11 groups; the calculations were based on seven skeletal and seven dental metric variables of the mandible. The biological distances were correlated with geographic distance as follows: the epigenetic distance, 0.74; Penrose's shape distance, 0.71; Penrose's size distance, 0.45; and Mahalanobis' distance, 0.37. All correlations were significant at the 0.01 level. The epigenetic and Penrose shape correlations were significantly higher than the Mahalanobis correlation. Because of the conditions under which the breeding groups were selected, it was assumed that genetic affinites among the groups would be a function of geographic distance. The results suggest that the epigenetic distance and Penrose's shape distance reflect genetic affinities among groups better than do the Penrose size and Mahalanobis distances.     

A new method to quantify liner deformation within a prosthetic socket for below knee amputees

Many amputees who wear a leg prosthesis develop significant skin wounds on their residual limb. The exact cause of these wounds is unclear as little work has studied the interface between the prosthetic device and user. Our research objective was to develop a quantitative method for assessing displacement patterns of the gel liner during walking for patients with transtibial amputation. Using a reflective marker system and a custom clear socket, evaluations were conducted with a clear transparent test socket mounted over a plaster limb model and a deformable limb model. Distances between markers placed on the limb were measured with a digital caliper and then compared with data from the motion capture system. Additionally, the rigid plaster set-up was moved in the capture volume to simulate walking and evaluate if inter-marker distances changed in comparison to static data. Dynamic displacement trials were then collected to measure changes in inter-marker distance due to vertical elongation of the gel liner. Static and dynamic inter-marker distances within day and across days confirmed the ability to accurately capture displacements using this new approach. These results encourage this novel method to be applied to a sample of amputee patients during walking to assess displacements and the distribution of the liner deformation within the socket. The ability to capture changes in deformation of the gel liner will provide new data that will enable clinicians and researchers to improve design and fit of the prosthesis so the incidence of pressure ulcers can be reduced.     

Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing

doi: 10.1111/j.1741‐2358.2011.00494.x
Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing Purpose: The aim of this study was to evaluate linear dimensional alterations of artificial teeth for complete dentures when using different investment and flasking techniques. Background: Dimensional changes in the vertical dimension may occur owing to changes in artificial teeth positioning caused by different investing and flasking techniques. Materials and methods: Thirty pairs of the complete dentures were manufactured and randomly divided into three groups (n = 10): (1) invested with type III stone in monomaxillary PVC flask; (2) invested with type III stone in bimaxillary PVC flask; and (3) invested with laboratory silicone in bimaxillary PVC flask. Dentures were polymerised by microwave, and 12 linear distances were measured before and after denture processing. Data were analysed by one‐way anova , considering manufacturing technique as the study factor. Tukey’s HSD was used as post hocanova (p = 0.05). Results: Most of the linear distances were comparable for all groups. All transversal maxillary and mandibular distances were higher for group 1 compared with groups 2 and 3 (p < 0.05), except the distance 3–6 for mandibular arch, in which no difference was found between groups (p < 0.05). Both maxillary diagonal distances were higher in group 1 (p < 0.05), and no differences were found among all groups for mandibular measurements. Conclusions: Double flasking technique independent on the investment material is shown to be the most effective method to reduce changes in artificial teeth positioning.     

A quantitative genetic analysis of localized morphology in mandibles of inbred mice using finite element scaling analysis.

We analyzed patterns of mandibular genetic and phenotypic morphological integration and the relationship of genealogy to interstrain molecular and morphological differences in ten inbred strains of mice. Positions of mandibular landmarks in two-dimensional space were used to construct a finite element mesh for each individual, then all individuals from the ten strains were compared to the average mandible from a standard strain (SEA/GnJ). Measures of size and shape associated with finite element scaling analysis were then used in a quantitative genetic analysis of mandibular variation. Significant genetic variation for mandibular size and shape was uncovered. Patterns of both genetic and phenotypic correlation for measures of landmark-specific sizes were consistent with models of morphological integration based on the developmental origin of parts of the mandible and on the effects of muscle attachment on mandibular morphology. Shape differences local to particular landmarks did not show these forms of morphological integration. Although interstrain distances based on local shape magnitudes were significantly correlated with genealogical relationship, distances based on local size differences were not. Even higher than the correlation of genealogy with distances based on local shape magnitude was the genealogical-molecular distance correlation. Patterns of morphometric mandibular variation corresponded to expected effects of epigenetic developmental processes. Also, when detailed shape differences were considered, morphology served as a rough guide to genealogy, although molecular distances showed a stronger relationship.     

Insulin-like growth factor-I stimulates acromegaly-like specific mandibular enlargement in rats.

To help us investigate the time course of mandibular enlargement in acromegaly or acrogiantism to determine the most suitable period for occlusal treatment in this disease, our aim was to develop a rat model of acromegaly (acrogiantism). In this study, prominent mandibular enlargement was induced by continuous subcutaneous infusion of human recombinant insulin-like growth factor-I (IGF-I) (640 microg/day) in 10-week-old male rats for 4 weeks (n = 6); the control sham-operated group was injected with saline alone (n = 6). Circulating human IGF-I was clearly detectable in the IGF-I group during the four-week administration period, while endogenous rat IGF-I levels decreased. Total IGF-I (human + rat) increased significantly during administration, returning to control levels afterwards. The length of every bone examined (mandible, maxilla, and femur) showed a significant increase compared to control rats, especially the mandible. Although the mandible did not continue to grow after discontinuation of IGF-I administration, it did not return to control size, unlike the maxilla and femur, and disharmonious jaw size (between maxilla and mandible) persisted even after circulating IGF-I levels normalized. These findings in our rat model suggest that mandibular occlusal treatment should only be considered for acromegalic (acrogiantic) patients after serum IGF-I levels have normalized and bone growth has ceased.     

The course of the inferior alveolar nerve in the normal human mandibular ramus and in patients presenting for cosmetic reduction of the mandibular angles

This study was undertaken to quantify the path of the inferior alveolar nerve in the normal human mandible and in the mandibles of patients presenting for cosmetic reduction of the mandibular angles. The goals were: (1) to provide normative information that would assist the surgeon in avoiding injury to the nerve during surgery; (2) to characterize gender differences in the normal population; and (3) to compare the course of the nerve in the normal population to its course in a group of patients who presented with a complaint of "square face." The study was based upon the computerized tomographic scans of 10 normal patients (six men, four women) and 8 patients (all women) complaining of "square face." Using AnalyzePC 2.5 imaging software, the mandibles were segmented and the position of the nerve was recorded within its osseous canal in the mandibular ramus on each axial slice in which it was identifiable. Distances were calculated between the nerve and the anterior, posterior, lateral, and medial cortices. The positions of the lateral ramus prominence and the lowest point on the sigmoid notch were also recorded. The position of the mental foramen was recorded in relation to the nearest tooth, and the three-dimensional surface distances from the foramen to the alveolar bone, the inferior border of the mandible, and the mandibular symphysis were determined. The distances from the entrance of the nerve into the mandible to the lateral ramus prominence and the lowest point on the sigmoid notch were calculated. Summary statistics were obtained, comparing differences in gender. The nerve was identifiable in each ramus over a mean distance of 12.7 mm. On average, the lateral ramus prominence was 0.3 mm higher on the caudad-cephalad axis than the point at which the nerve entered the bone, whereas the location of the lowest point on the sigmoid notch was 16.6 mm above the nerve. The average distances from the nerve to the anterior, posterior, medial, and lateral cortices were 11.6, 12.1, 1.8, and 4.7 mm, respectively. Gender differences were significant for all of these except the medial cortex to nerve distance. On average, the mental foramen exited the body of the mandible immediately below the second premolar and the average surface distances from the foramen to the symphysis, the most cephalad alveolar bone, and the inferior border of the body were 30.9, 14.2, and 19.3 mm, respectively. With regard to the patients presenting for mandibular angle reduction, there were a few statistically significant but small scalar differences from normal controls.     

Predictive functional ANOVA models for longitudinal analysis of mandibular shape changes

In this paper, we introduce a Bayesian statistical model for the analysis of functional data observed at several time points. Examples of such data include the Michigan growth study where we wish to characterize the shape changes of human mandible profiles. The form of the mandible is often used by clinicians as an aid in predicting the mandibular growth. However, whereas many studies have demonstrated the changes in size that may occur during the period of pubertal growth spurt, shape changes have been less well investigated. Considering a group of subjects presenting normal occlusion, in this paper we thus describe a Bayesian functional ANOVA model that provides information about where and when the shape changes of the mandible occur during different stages of development. The model is developed by defining the notion of predictive process models for Gaussian process (GP) distributions used as priors over the random functional effects. We show that the predictive approach is computationally appealing and that it is useful to analyze multivariate functional data with unequally spaced observations that differ among subjects and times. Graphical posterior summaries show that our model is able to provide a biological interpretation of the morphometric findings and that they comprehensively describe the shape changes of the human mandible profiles. Compared with classical cephalometric analysis, this paper represents a significant methodological advance for the study of mandibular shape changes in two dimensions.     

Mandibular growth in the rhesus monkey (Macaca mulatta)

Mandibular growth of 42 rhesus monkeys (Macaca mulatta) was analyzed quantitatively and qualitatively. Four groups of animals were defined according to dentitional age (i.e., infant, juvenile, adolescent, young adult). At each age growth was observed for a 24 week period. Since some animals were observed at more than one stage of development, 57 periods of growth were studied. The growth incremental data were collected by superimposing serial cephalograms on mandibular implants. Growth and remodeling of both the skeletal and dento-alveolar components of the rhesus mandible were greatest in the infant monkeys and were less in successive age groups. Posterior relocation of the ramus was noted in all age groups while bone deposition on the anterior and inferior borders of the mandibular body was greatest in the younger animals. The most pronounced dental changes also occurred in the younger animals while the dentitions of the adolescent and adult animals were generally more stable. This study demonstrates that the rate and direction of normal mandibular growth varies with the age of the animal. Furthermore, mandibular growth is quantified at four defined maturational levels to provide a set of values illustrating normal mandibular growth. These values can also be used as control data for experimental studies.     

Ontogenetic relationships between cranium and mandible in coyotes and hyenas

Developing animals must resolve the conflicting demands of survival and growth, ensuring that they can function as infants or juveniles while developing toward their adult form. In the case of the mammalian skull, the cranium and mandible must maintain functional integrity to meet the feeding needs of a juvenile even as the relationship between parts must change to meet the demands imposed on adults. We examine growth and development of the cranium and mandible, using a unique ontogenetic series of known‐age coyotes (Canis latrans), analyzing ontogenetic changes in the shapes of each part, and the relationship between them, relative to key life‐history events. Both cranial and mandibular development conform to general mammalian patterns, but each also exhibits temporally and spatially localized maturational transformations, yielding a complex relationship between growth and development of each part as well as complex patterns of synchronous growth and asynchronous development between parts. One major difference between cranium and mandible is that the cranium changes dramatically in both size and shape over ontogeny, whereas the mandible undergoes only modest shape change. Cranium and mandible are synchronous in growth, reaching adult size at the same life‐history stage; growth and development are synchronous for the cranium but not for the mandible. This synchrony of growth between cranium and mandible, and asynchrony of mandibular development, is also characteristic of a highly specialized carnivore, the spotted hyena (Crocuta crocuta), but coyotes have a much less protracted development, being handicapped relative to adults for a much shorter time. Morphological development does not predict life‐history events in these two carnivores, which is contrary to what has been reported for two rodent species. The changes seen in skull shape in successive life‐history stages suggest that adult functional demands cannot be satisfied by the morphology characterizing earlier life‐history stages. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

On the relative frequencies of hominid maxillary and mandibular teeth and jaws as taphonomic indicators

In southern African samples of early hominid remains, maxillary and mandibular teeth (deciduous-plus-permanent) have a virtually equal chance of accumulating in the dolomitic limestone cave deposits, of being preserved therein and recovered therefrom. Thus, of 1066 fossil teeth ofAustralopithecus spp. plusHomo habilis, 51.9 per cent are maxillary and 48.1 per cent mandibular. On the other hand, the East African sample of 847 early hominid, deciduous-plus-permanent teeth, departs more strikingly from a 1∶1 ratio: it comprises 41.0 per cent maxillary and 59.0 per cent mandibular teeth. It is inferred that mandibular teeth have a somewhat better chance of accumulating and being preserved in, and being recovered from, the open, fluvial, lacustrine and deltaic sedimentary environments of the East African sites. The dental proportions are approximately matched by the proportions of jaws. For example, the maxilla: mandible proportions at Koobi fora in northern Kenya are 33.0∶67.0 for teeth and 21.6∶78.4 for jaws. In other words, the preponderance in favour of mandibular remains is somewhat more marked in the case of jaws than of teeth, this distinction doubtless reflecting the more fragile bony structure of the maxilla and the sturdier construction of the mandible. This first study known to the author of the differential distribution of maxillary and mandibular teeth of the Plio-Pleistocene hominids leads the author to hypothesize that, where environmental conditions at the place and time of the death of the hominids have been non-destructive, non-dispersive, relatively mild and protective, maxillae and mandibles may be expected to have been conserved and recovered in approximately equal proportions—and likewise of maxillary and mandibular teeth. On the other hand, the more brutal and destructive the sedimentary environment and other taphonomic influences have been, at the place and time when the hominid individuals died, the more likely it is that the maxillary and mandibular remains of jaws and teeth will deviate from equality of proportions, generally at the expense of the maxillae and upper teeth. Hence, it is proposed that the upper jaw/low jaw ratio (Mx/Mn jaw ratio) and the maxillary teeth/mandibular teeth ratio (Mx/Mn dental ratio) may serve as two useful new gauges of the rigour of palaeo-ecological and taphonomic conditions.     

记安徽一鳄类化石

<正> 本文讨论的这一鳄类下颌骨化石标本是由本所安徽红层队采集于1970—1972年,它不具有通常鳄类所具有的下颌外窗,现记述于下。西贝鳄亚目 Sebecosuchia,Simpson 1937. 皖鳄科(新科) Wanosuchidae,fam.nov. 特征见本科代表属皖鳄属皖鳄属(新属) Wanosuchus,gen.nov.     

3D Mapping of Safe and Danger Zones in the Maxilla and Mandible for the Placement of Intermaxillary Fixation Screws

Intermaxillary (IMF) screws feature several advantages over other devices used for intermaxillary fixation, but using cone beam computed tomography (CBCT) scans to determine the safe and danger zones to place these devices for all patients can be expensive. This study aimed to determine the optimal interradicular and buccopalatal/buccolingual spaces for IMF screw placement in the maxilla and mandible. The CBCT volumetric data of 193 patients was used to generate transaxial slices between the second molar on the right to the second molar on the left in both arches. The mean interradicular and buccopalatal/buccolingual distances and standard deviation values were obtained at heights of 2, 5, 8 and 11 mm from the alveolar bone crest. An IMF screw with a diameter of 1.0 mm and length of 7 mm can be placed distal to the canines (2 - 11 mm from the alveolar crest) and less than 8 mm between the molars in the maxilla. In the mandible, the safest position is distal to the first premolar (more than 5 mm) and distal to the second premolar (more than 2 mm). There was a significant difference (p<0.05) between the right and left quadrants. The colour coding 3D template showed the safe and danger zones based on the mesiodistal, buccopalatal and buccolingual distances in the maxilla and mandible.The safest sites for IMF screw insertion in the maxilla were between the canines and first premolars and between the first and second molars. In the mandible, the safest sites were between the first and second premolars and between the second premolar and first molar. However, the IMF screw should not exceed 1.0 mm in diameter and 7 mm in length.     

Mandible Form Relative to the Main Food Type in Ladybirds (Coleoptera: Coccinellidae)

The Coccinellidae is an economically important family within the Coleoptera. Some members are phytophagous pests, but many are beneficial predators and valuable biocontrol agents. This study investigates the morphology of the mandibles of adult Coccinellidae in relation to diet. Using scanning electron microscopy on 86 species of Coccinellidae, it was found that the morphology of the mandibles was dictated by the general feeding method, and could only be used to indicate a phytophagous, mycophagous or carnivorous diet. Phytophagous Coccinellidae of the subfamily Epilachninae had mandibles with denticulate apical teeth and setae for feeding on leaf material. The mandibles of the mycophagous Psylloborini had secondary teeth on the ventral apical tooth for collecting fungal spores. The mandibles of carnivorous Coccinellidae and Scymninae had either a bifid or unidentate apex. The unidentate mandible seemed to be restricted to coccidophagous species. Many species also had a mandibular groove along which prey body juices were conducted. Although mandible morphology could be related to the overall feeding method, there was no relationship between specific diet or food taxon and mandible shape. Mandible shape does not appear to be especially restricting for changes in diet either in the ecological sense or over evolutionary time. Mandible morphology is of limited use in determining diet and host specificity in Coccinellidae that are being selected as potential biocontrol agents.     

Deletion of the Pitx1 genomic locus affects mandibular tooth morphogenesis and expression of the Barx1 and Tbx1 genes

Pitx1 is a bicoid-related homeodomain factor that exhibits preferential expression in the developing hindlimb, mandible, pituitary gland and teeth. Pitx1 gene-deleted mice exhibit striking abnormalities in morphogenesis and growth of both hindlimb and mandible, suggesting a proliferative defect in these two structures. Here, we studied the expression and regulation of Pitx1 in both mandible and developing teeth and analyzed tooth morphology, cell proliferation, apoptosis and expression of Pitx2, Barx1 and Tbx1 in dental tissues of Pitx1−/− mouse embryos. Pitx1 expression is restricted to the epithelium of the growing tooth anlagen. Tissue recombination and bead implantation experiments demonstrated that bone morphogenetic protein-4 down-regulates Pitx1 expression in both mandibular mesenchyme and dental epithelium. Deletion of the Pitx1 locus results in micrognathia and abnormal morphology of the mandibular molars. Although Pitx2 expression in teeth of Pitx1−/− embryos is not altered, expression of Barx1 decreased in the mesenchyme of the mandibular molars. Furthermore, Pitx1 deletion results in suppression of Tbx1 expression in dental epithelium. Taken together, these results indicate that independent genetic pathways in mandibular and maxillary processes determine tooth development and morphology.     

Model for the examination of evolutionary trends in tooth development

Through the use of serial computerized tomography (C-t) scans, two distinct developmental stages can be identified in mature teeth. C-t scans thus provide a non-destructive method for assessing growth within individual teeth, as well as for comparison of the development of modern and fossil teeth. The second deciduous molar (DM2) and first permanent molar (M1) resemble one another morphologically, despite differences in size and developmental rates. Thus, they provide an excellent model for studying variation in growth within an individual. To test the C-t method, we first examined a recent archaeological sample and then examined teeth from Skhul I. Serial C-t scans were used to compare two distinct developmental stages represented by the dentine-enamel junction (DEJ) and outer enamel surface (OES), respectively, in mandibular DM2 and M1 of 31 archaeological specimens. The difference in form and size between these two surfaces in and between teeth was calculated from intercusp distances measured at the DEJ and OES using the form distance matrix. Intercusp distances at the DEJ and OES of these teeth were then compared to their counterparts in the DM2 and M1 of Skhul I, taken here as representative of early anatomically modern Homo sapiens sapiens. Form differences between paired DM2 and M1 at the DEJ were smaller than those at the OES, supporting the hypothesis that differences between the two teeth increase throughout development. The increase in intercusp distances from the DEJ to OES was found to reflect the angulation of cusps relative to one another, rather than enamel thickness. Form differences between the Skhul DM2 and M1 were smaller than those observed in the recent series, and the recent M1 differed more than the DM2 from its fossil counterpart. The similarities found between the Skhul permanent and deciduous teeth and the recent DM2, may reflect a similar growth pattern. This would contribute to earlier crown completion in the fossil M1. Am. J. Phys. Anthropol. 102:283–294, 1997 © 1997 Wiley-Liss, Inc.     

A Cone-Beam Computed Tomographic Study on Mandibular First Molars in a Chinese Subpopulation

The purpose of this study was to conduct a cone-beam computed tomographic (CBCT) investigation on the root and canal configuration of the mandibular first molars, especially the morphology of the disto-lingual (DL) root, in a Chinese subpopulation. A total of 910 CBCT images of the mandibular first molars were collected from 455 patients who underwent CBCT examinations as a preoperative assessment for implants or orthodontic treatment. The following information was analyzed and evaluated: tooth position, gender, root and root canal number per tooth, root canal type of the mesial root(s) and distal root(s), angle of the DL root canal curvature, distance between two distal canal orifices in the teeth with DL root, and angle of disto-buccal canal orifice–disto-lingual canal orifice–mesio-lingual canal orifice (DB-DL-ML). Most of the mandibular first molars (64.9%, n = 591) had two roots with three root canals, and most of the mesial root canals (87.7%, n = 798) were type VI. The prevalence of the DL root was 22.1% (n = 201). The right side had a higher prevalence of DL root than the left side (p<0.05). Additionally, the curvature of the DL root canal were greater in the bucco-lingual (BL) orientation (30.10°±14.02°) than in the mesio-distal (MD) orientation (14.03°± 8.56°) (p<0.05). Overall there was a high prevalence of DL root in the mandibular first molars, and most of the DL roots were curved in different degrees. This study provided detailed information about the root canal morphology of the mandibular first molars in a Chinese subpopulation.