Canine sexual dimorphism in crown and root dimensions: a cone-beam computed tomographic study.

The primary step in forensic odontological analysis is sex determination. The present study is one of the few studies that evaluated the accuracy of the combination of canine tooth root length and crown measurements for sex determination. The study sample comprised 196 cone-be am computed tomographic scans of individuals aged 20-80 years distributed in five age categories: 20-29, 30-39, 40-49, 50-59, and 60+ years old. Different parameters, such as width, length, and ratio measurements for the crown and root of each maxillary and mandibular canine tooth, were examined and recorded. The findings indicated that maxillary canines had greater sex dimorphism ability (87.3%) than mandibular canines (80.6%). Total tooth length and root length of maxillary canine were the most pronounced variables in the differentiation of sex groups. When the combination of the mandibular and maxillary measurements was considered, the accuracy for sex dimorphism was 85.7%. By using ratio variables, the accuracy was reduced to 68.9%. According to the findings of this study, total tooth length and root length are the most discriminant variables of canine teeth. These variables are more reliable sex indicators than crown measurements.

Shape variation in modern human upper premolars.

Morphological variation in modern human dentition is still an open field of study. The understanding of dental shape and metrics is relevant for the advancement of human biology and evolution and is thus of interest in the fields of dental anthropology, as well as human anatomy and medicine. Of concern is also the variation of the inner aspects of the crown which can be investigated using the tools and methods of virtual anthropology. In this study, we explored inter- and intra-population morphometric variation of modern humans' upper third and fourth premolars (P3s and P4s, respectively) considering both the inner and outer aspects of the crown, and discrete traits. We worked by means of geometric morphometrics on 3D image data from a geographically balanced sample of human populations from five continents, to analyse the shape of the dentinal crown, and the crown outline in 78 P3s and 76 P4s from 85 individuals. For the study of dental traits, we referred to the Arizona State University Dental Anthropology System integrated with more recent classification systems. The 3D shape variation of upper premolar crowns varied between short and mesio-distally broad, and tall and mesio-distally narrow. The observed shape variation was independent from the geographical origin of the populations, and resulted in extensive overlap. We noted a high pairwise correlation (r1 = 0.83) between upper P3s and P4s. We did not find any significant geographic differences in the analysed non-metric traits. Our outcomes thus suggest that geographical provenance does not play a determinant role in the shaping of the dental crown, whose genesis is under strict genetic control.

Digital measurement of deciduous tooth dimensions in China: A cross-sectional survey.

OBJECTIVE: Crown dimensions data of deciduous teeth hold anthropological, forensic, and archaeological value. However, such information remains scarce for the Chinese population. This multi-center study aimed to collect a large sample of deciduous crown data from Chinese children using three-dimensional measurement methods and to analyze their dimensions. DESIGN: A total of 1592 children's deciduous dentition samples were included, and the sample size was distributed according to Northeast, North, East, Northwest, Southwest and South China. Digital dental models were reconstructed from plaster dental models. Independent sample t test, paired t test, principal component analysis (PCA), and factor analysis (FA) were used to analyze the tooth crown dimensions. RESULT: 18,318 deciduous teeth from 1592 children were included. Males exhibited slightly larger values than females. The range of sexual dimorphism percentages for each measurement was as follows: mesiodistal diameter (0.40-2.08), buccolingual diameter (0.13-2.24), and maxillogingival diameter (0.48-3.37). The FA results showed that the main trend of crown dimensions changes was the simultaneous increase or decrease in mesiodistal diameter, buccolingual diameter and maxillogingival diameter in three directions. CONCLUSION: This is the first large-scale survey of deciduous tooth crown dimensions in China, which supplements the data of deciduous tooth measurement and provides a reference for clinical application.

Morphological differences between the first and second maxillary premolar crowns: A three-dimensional surface homologous modeling analysis.

OBJECTIVES: The current study used a three-dimensional (3D) surface homologous modeling to analyze the structure of maxillary first premolar (P1) and second premolar (P2) crowns, to identify any morphological differences between them, particularly in their cuspal structures. METHODS: The study sample comprised 27 male elementary and junior high school students from Chiba Prefecture, Japan. Plaster casts were collected and the 3D coordinates were used to measure the crown structures. Thereafter, principal component (PC) analysis was carried out using the 3D coordinates of the homologous models, containing 4498 anatomical data points, including 9 landmarks. RESULTS: The findings indicated that P1 was significantly larger than P2, despite both teeth exhibiting similar intercuspal distances. The homologous model analysis revealed that 61.5 % of the total variance could be explained up to the fourth PC. Overall size and shape in the mesiodistal and buccolingual directions were estimated using PC1 and PC2, respectively. Both components highlighted a shape factor, indicating that the buccal cusp was more well-developed than the lingual cusp in P1 compared to P2. CONCLUSIONS: The variations in the size of the mesial and distal premolar teeth and the relationships between the cusps in the completed tooth crowns can be explained using molecular biology developmental models.

Sexual dimorphism in the three-dimensional detailed crown structure of maxillary first premolars.

OBJECTIVES: Maxillary first premolars have a unique shape because of their curvature features, positional relationship of the cusps, and most prominent points, making them different from other teeth. This study aimed to quantitatively analyze the detailed three-dimensional morphometric structure of maxillary first premolars and sexual dimorphism. METHODS: The study participants were 60 elementary and junior high school students (30 boys and 30 girls) in Japan. The distance between landmarks was measured using the three-dimensional coordinates of plaster casts, and the data collected was statistically analyzed. RESULTS: Sexual dimorphism was greater in the lingual cusp, showing greater variation in size than the buccal cusp. Boys exhibited significantly larger relative distances in the mesiodistal and buccolingual directions than girls; particularly, regarding mesiodistal diameter of the central groove, mesial slope of the buccal cusp, and distal slope of the lingual cusp. These results may be due to a slight difference in the timing of secondary enamel knots between boys and girls during the developmental stage, which was reflected in the sexual dimorphism of the completed teeth. Curvature features, cusp positions, and most prominent points were considered individual traits because they were not interrelated. CONCLUSIONS: Subtle differences during the developmental stage may lead to sexual dimorphism of the completed crown. Furthermore, the morphological characteristics of the maxillary first premolars may be related to their location in the dental arch.

On the first Baryonychinae (Theropoda, Spinosauridae) teeth from South America.

We report the first occurrence in South America of spinosaurid specimens belonging to the clade Baryonychinae. The material comprises three tooth crowns recovered from the Lower Cretaceous (Berriasian-Valanginian) of the Feliz Deserto Formation, State of Sergipe, northeast Brazil. The three specimens have the typical conidont condition, displaying a fluted morphology, veined enamel texture and carinae extending to the cervix region, conditions similar to those shared among spinosaurid theropods. Furthermore, a notable feature is the presence of a serrated carinae composed of 6-7 diminutive denticles per millimetre, a key feature shared by baryonychine spinosaurids. Phylogenetic and multivariate analyses performed on dentition-based and crown-based datasets of theropod taxa confirm the relationship of the three tooth crowns described here with the well-supported spinosaurid clade. Our results retrieve the taxa which comprise the "classically" baryonychine clade as individual branches within a polytomy which includes the three tooth crowns and a subclade of spinosaurines (Spinosaurus + Angaturama/Irritator). Additionally, the discriminant and cluster analyses suggest that the materials are more similar to Suchomimus than to Baryonyx morphometrically, but clearly bearing similarities with baryonychines (sharing a similar morphospace). These new findings paleogeographically expand the occurrence of this clade to western Gondwana, and comprise one of the oldest spinosaurid records worldwide, which brings implications on hypotheses for the emergence and evolution of the clade. Furthermore, these new records indicate the presence of more than one spinosaurid taxon in the Lower Cretaceous deltaic paleoenvironment of the Feliz Deserto Formation.

Ancestry of victims of 1755 Lisbon earthquake based on tooth morphology.

The present investigation comprises the characterization of skeletal remains recovered from the 2004 archaeological excavations carried out in the Cloister's Southwest Wing of the Academy of Sciences of Lisbon, attributed to the 1755 earthquake. Among the remains, many teeth were found. Our goal is to use dental morphological characteristics to assess the geographic ancestry of the combined sample using the methods of biodistance and web-based application of the Arizona State University Dental Anthropology System 2. The crown and root traits of the ASUDAS were scored in a sample of 1068 disarticulated teeth, 65 skulls, 138 adult and 42 sub-adult jaws. Eight characteristics of 34 specimens (7 skulls and 27 jaws) were analyzed using rASUDAS2. Results demonstrate that 73.5% of this sample can be assigned to Western Eurasian ancestry, with the remaining 26.5% divided between Sub-Saharan Africa, non-Arctic and Arctic America, and East Asia. Euclidean and Bray-Curtis distance measures were used to put this Portuguese sample in a world context. From both distance matrixes, cluster analyses were used to generate dendrograms. Based on Bray-Curtis values, Portugal is closest to Western Europe, followed by India and Eastern Europe. For the tree based on Euclidean distances, India is the first to join Portugal, followed by Eastern and Western Europe. Therefore, on both an individual and group level, the Portuguese sample is most closely tied to Western Eurasia. However, there may be other ancestries in the sample, such as Sub-Saharan Africa, due to non-European migrants in Portugal along with the African slave trade to Brazil that reached its peak in 18th century Lisbon.

Three-Dimensional Analysis of the Pulp Chamber and Coronal Tooth of Primary Molars: An In Vitro Study.

The anatomical variability of primary molars promotes research to improve clinical restorative activity, forensic identification, and industrial development. The objective was to study the morphology of the pulp chamber and its three-dimensional relationship with the external morphology of the tooth. A total of 151 deciduous molars were collected and subjected to three-dimensional imaging analysis in order to determine dental crown (CV) and pulp chamber (PV) volumes, their ratio (VR), pulp chamber roof (PCR) and pulp chamber floor (PCF) area, the furcation length (FD), and morphological peculiarities. The data were compared using the Kruskal-Wallis test in SPSS 26 software. The statistical analysis determined statistically significant differences between the four groups of molars for all variables. Great anatomical variability was observed, especially in the maxillary first molar, the volumes were higher in the maxillary second molar and the highest risk of furcal perforation was seen in the mandibular first molar. Additionally, mandibular second molars with six pulp horns, and some different density images compatible with accessory canals and pulp stones were found. Based on the findings of this investigation, we confirm the great anatomical variability that exists between the maxillary and mandibular molars.

Genetic Correlation, Pleiotropy, and Molar Morphology in a Longitudinal Sample of Australian Twins and Families.

This study aims to expand our understanding of the genetic architecture of crown morphology in the human diphyodont dentition. Here, we present bivariate genetic correlation estimates for deciduous and permanent molar traits and evaluate the patterns of pleiotropy within (e.g., m1-m2) and between (e.g., m2-M1) dentitions. Morphology was observed and scored from dental models representing participants of an Australian twin and family study (deciduous n = 290, permanent n = 339). Data collection followed Arizona State University Dental Anthropology System standards. Genetic correlation estimates were generated using maximum likelihood variance components analysis in SOLAR v.8.1.1. Approximately 23% of deciduous variance components models and 30% of permanent variance components models yielded significant genetic correlation estimates. By comparison, over half (56%) of deciduous-permanent homologues (e.g., m2 hypocone-M1 hypocone) were significantly genetically correlated. It is generally assumed that the deciduous and permanent molars represent members of a meristic molar field emerging from the primary dental lamina. However, stronger genetic integration among m2-M1/M2 homologues than among paired deciduous traits suggests the m2 represents the anterior-most member of a "true" molar field. The results indicate genetic factors act at distinct points throughout development to generate homologous molar form, starting with the m2, which is later replaced by a permanent premolariform crown.

Three-dimensional digital evaluation of tooth symmetry and volume in patients with missing and peg-shaped maxillary lateral incisors.

INTRODUCTION: This study aimed to evaluate the 3-dimensional tooth crown symmetry and the crown volumes of maxillary and mandibular teeth in patients with unilateral or bilateral missing or peg-shaped maxillary lateral incisors. METHODS: Six groups were established for the possible clinical variations in patients with unilateral missing or peg-shaped maxillary lateral incisors, bilateral presence of these tooth anomalies, and a control group (CG) with normal lateral incisors. The study was conducted on digital dental models of 132 patients. The morphologic symmetry of the antimere teeth was investigated using 3-dimensional deviation analysis. Volumes of contralateral teeth were compared within and among groups for the maxilla and mandible. Furthermore, volumes of teeth were compared in missing and peg-shaped quadrants and quadrants of CG. Intergroup differences were tested using one-way analysis of variance and Kruskal-Wallis tests, whereas paired t and Wilcoxon tests were used for parametric and nonparametric variables, respectively, for intragroup comparisons. RESULTS: Significant deviations in symmetry of antimere teeth were not detected (P >0.05). The volumes of mandibular central and lateral incisors in missing or peg-shaped lateral incisor groups were smaller than in the CG (P <0.05). Per quadrant analysis, volumes of the maxillary central incisor and mandibular central incisors, canines, and first molars in quadrants with missing or peg-shaped lateral incisors were smaller than in the control quadrants (P <0.05). CONCLUSIONS: Neither unilateral nor bilateral presence of missing or peg-shaped maxillary lateral incisors affected the morphologic symmetry of antimere teeth but did affect tooth volume, especially in the mandibular arch.

An Analysis of Maxillary Anterior Teeth Crown Width-Height Ratios: A Photographic, Three-Dimensional, and Standardized Plaster Model's Study.

OBJECTIVE: To analyze the width and height ratios of maxillary anterior teeth at different crown levels through photographs, 3D, and plaster dental model techniques in a subset of the Pakistani population. Material and Methods. This clinical study consisted of 230 participants. The maxillary impression, standardized photographs, and models were constructed for crown width and height analysis. The SPSS version 25 was used for statistical analysis. Descriptive statistics were carried out for mean, standard deviation, and percentage calculation of teeth width and height, gender, and age of participants. Paired t-test analysis was carried out to compare the dependent variables (teeth size, width, and height ratios) with independent variables (techniques applied, side disparity). A p value of ≤ 0.05 was considered statistically significant. RESULTS: The mean width and height of maxillary anterior teeth obtained through photographs, 3D, and plater models were statistically different. The 3D dental model analysis showed reliable and accurate results. The mean width and height ratio of teeth were different on both sides of the arch. There was a significant difference (p = 0.001) in crown width-height ratios at different crown levels. CONCLUSION: The width and height ratios in the studied population were different at various crown levels. The dimensions of teeth varied from the incisal to the cervical part of the crown. Hence, rather than relying on a single, fixed ratio of 78% to 80% suggested by researchers for anterior teeth, the clinician should adopt different crown width-height ratios to restore teeth with the optimum esthetic outcome.

Symmetry of crown widths in subjects with unilateral maxillary lateral incisor agenesis.

PURPOSE: The aim of this study was to compare mesiodistal width and symmetry of maxillary and mandibular teeth in subjects with and without unilateral maxillary lateral incisor agenesis. PATIENTS AND METHODS: The study group consisted of 31 patients with unilateral maxillary lateral incisor agenesis (19 females, 12 males, mean age: 16.55 ± 5.24 years), and a control group of 31 patients (19 females, 12 males, mean age: 16.58 ± 4.41 years) without agenesis. Mesiodistal dimensions of all teeth except second molars were measured. Paired samples t­test and Wilcoxon signed-rank test were used for intragroup comparisons. Independent samples t­test was used for intergroup comparisons. RESULTS: In the study group, mesiodistal dimensions of maxillary canine, second premolar, first molar, mandibular second premolar and first molar teeth on the agenesis side were significantly smaller than on the contralateral side (p < 0.05). In the control group, no significant difference was seen in mesiodistal dimensions between right and left sides. In the study group, mesiodistal dimensions of all teeth on the lateral agenesis side were significantly smaller than on the control side (p < 0.05). On the side without lateral agenesis, all teeth except the maxillary and mandibular first molars and mandibular second premolar teeth were significantly smaller than on the control side (p < 0.05). Total mesiodistal dimensions of the maxillary teeth were significantly smaller on the lateral agenesis side than on the contralateral side (p = 0.001). Total tooth size of the study group was significantly smaller than for the control group (p < 0.05). CONCLUSION: Patients with unilateral maxillary lateral incisor agenesis might have asymmetries in tooth width and have smaller teeth than individuals without agenesis.

An initial investigation of dental morphology variation among three southern Naga ethnic groups of Northeast India.

OBJECTIVES: This study examines dental morphology trait prevalence among three southern Naga groups and compares them to 10 ethnic groups from other regions of South Asia to accomplish two objectives: assess the biological relationship of these Tibeto-Burman-speakers to speakers of non-Tibeto-Burman languages in other South Asian regions, and determine which traits distinguish northeast Indians from other South Asians. METHODS: Dental morphology traits were scored with the Arizona State University Dental Anthropology System. Tooth-trait combinations were evaluated for significant inter-trait correlation and intra-trait correspondence within dental fields. Comparisons were based on simple trait prevalence and with Smith's MMD. Affinities based on the former were accomplished with correspondence analysis and principal components analysis. Affinities based on the latter were undertaken with neighbor-joining cluster analysis and multidimensional scaling. RESULTS: After elimination due to inter-trait correlations and uniform prevalence, biodistances based on the remaining 17 tooth-trait combinations identify significant differences between northeast Indians and other South Asian ethnic groups due to high frequencies of shoveling on the maxillary incisors and Cusp 6 on the mandibular molars coupled with low frequencies of Carabelli's trait and Cusp 5 on UM1 and UM2, respectively. CONCLUSIONS: Patterns of biodistances obtained from dental morphology are consilient with those obtained from DNA indicating statistically significant differences between northeast Indians from members of ethnic groups of other regions of South Asia. Researchers should explore the sex-specific patterns. Biodistances should not be limited to "key" teeth within dental fields, for in almost every case traits present on mesial and distal teeth yield non-redundant information.

What is the effect of preterm birth on permanent tooth crown dimensions? A systematic review and meta-analysis.

BACKGROUND: The permanent tooth formation process may be disrupted in preterm infants with potential discrepancies in size and subsequent occlusal disturbances. OBJECTIVE: To systematically analyse and quantitively synthesize the available evidence regarding the impact of preterm birth on permanent tooth crown dimensions. SEARCH METHODS: Unrestricted searches in 6 databases and manual searching of the reference lists in relevant studies were performed up to March 2021 (Medline via PubMed, CENTRAL, Cochrane Database of Systematic Reviews, Scopus, Web of Science, ProQuest Dissertations and Theses Global). SELECTION CRITERIA: Observational studies investigating permanent tooth crown dimensions in preterm and control full-term born individuals. DATA COLLECTION AND ANALYSIS: Following study retrieval and selection, relevant data were extracted, and the Newcastle-Ottawa scale was used to assess the selection, comparability, and outcome domains. Exploratory synthesis and meta-regression were carried out using the random effects model. RESULTS: Three studies were located from the initially retrieved records and the assessments with the Newcastle-Ottawa scale identified issues regarding the selection and comparability domains. Overall, the mesiodistal and the buccolingual dimensions of the permanent teeth in both dental arches tended to be smaller in children born prematurely than full term children. Subgroup analyses showed statistically significant differences for the extremely preterm to control group comparisons for the incisors and the first molars. Meta-regression showed a modificatory effect of gestational age and racial background but not of birth weight and gender on tooth size. The quality of available evidence was rated at best as moderate. CONCLUSIONS: Premature birth could potentially be associated with reduced tooth-crown dimensions in some permanent teeth especially in children born extremely preterm. Although the results from these observational studies should be approached with caution until more information becomes available, the possible clinical implications in terms of diagnosis and treatment planning should be considered. REGISTRATION: PROSPERO (CRD42020182243).

Relative tooth size, Bayesian inference, and Homo naledi.

OBJECTIVES: Size-corrected tooth crown measurements were used to estimate phenetic affinities among Homo naledi (~335-236 ka) and 11 other Plio-Pleistocene and recent species. To assess further their efficacy, and identify dental evolutionary trends, the data were then quantitatively coded for phylogenetic analyses. Results from both methods contribute additional characterization of H. naledi relative to other hominins. MATERIALS AND METHODS: After division by their geometric mean, scaled mesiodistal and buccolingual dimensions were used in tooth size apportionment analysis to compare H. naledi with Australopithecus africanus, A. afarensis, Paranthropus robustus, P. boisei, H. habilis, H. ergaster, H. erectus, H. heidelbergensis, H. neanderthalensis, H. sapiens, and Pan troglodytes. These data produce equivalently scaled samples unaffected by interspecific size differences. The data were then gap-weighted for Bayesian inference. RESULTS: Congruence in interspecific relationships is evident between methods, and with many inferred from earlier systematic studies. However, the present results place H. naledi as a sister taxon to H. habilis, based on a symplesiomorphic pattern of relative tooth size. In the preferred Bayesian phylogram, H. naledi is nested within a clade comprising all Homo species, but it shares some characteristics with australopiths and, particularly, early Homo. DISCUSSION: Phylogenetic analyses of relative tooth size yield information about evolutionary dental trends not previously reported in H. naledi and the other hominins. Moreover, with an appropriate model these data recovered plausible evolutionary relationships. Together, the findings support recent study suggesting H. naledi originated long before the geological date of the Dinaledi Chamber, from which the specimens under study were recovered.

The human EDAR 370V/A polymorphism affects tooth root morphology potentially through the modification of a reaction-diffusion system.

Morphological variations in human teeth have long been recognized and, in particular, the spatial and temporal distribution of two patterns of dental features in Asia, i.e., Sinodonty and Sundadonty, have contributed to our understanding of the human migration history. However, the molecular mechanisms underlying such dental variations have not yet been completely elucidated. Recent studies have clarified that a nonsynonymous variant in the ectodysplasin A receptor gene (EDAR 370V/A; rs3827760) contributes to crown traits related to Sinodonty. In this study, we examined the association between the EDAR polymorphism and tooth root traits by using computed tomography images and identified that the effects of the EDAR variant on the number and shape of roots differed depending on the tooth type. In addition, to better understand tooth root morphogenesis, a computational analysis for patterns of tooth roots was performed, assuming a reaction-diffusion system. The computational study suggested that the complicated effects of the EDAR polymorphism could be explained when it is considered that EDAR modifies the syntheses of multiple related molecules working in the reaction-diffusion dynamics. In this study, we shed light on the molecular mechanisms of tooth root morphogenesis, which are less understood in comparison to those of tooth crown morphogenesis.

Advances in the identification of deciduous molar tooth germs.

In forensic anthropology, correct identification of human deciduous teeth is of paramount importance for age-at-death estimation and relies on detailed anatomical descriptions. Yet literature is scarce on indications: details on the morphology of molar tooth germs of fetuses and newborns, developing from multiple mineralized centers that will eventually coalesce, are scant. This paper presents new anatomical elements for practitioners to identify human molar tooth germs at early developmental stages. 126 deciduous molars from 22 modern skeletons of fetuses and newborns (with a known age-at-death ranging between 0 days and 2 months and 21 days postnatal), without reported or observed dental pathological signs, were selected from the Collezione Antropologica LABANOF (CAL) documented skeletal collection. Gross anatomical descriptions of the morphology and configuration of the centers were provided, considering the number of mineralized centers, the shape and the outline of the occlusal plane at different stages. Three different developmental stages were observed in the maxillary first and second molar and the mandibular first molar, whereas in the mandibular second molar four stages were observed. For each stage, we provide additional detailed morphological descriptions, sketches outlining the shape of the tooth germ, and a picture of the tooth; also, indications for siding the teeth are presented. This information can be used by forensic anthropologists and odontologists for a proper identification when tooth germs are not found in anatomical connection within the dental sockets. Further analyses that encompass more age groups on a larger sample would allow to map the entire crown development of deciduous molars.

Dimorphism in dental tissues: Sex differences in archaeological individuals for multiple tooth types.

OBJECTIVES: Dimorphism in the dentition has been observed in human populations worldwide. However, research has largely focused on traditional linear crown measurements. As imaging systems, such as micro-computed tomography (micro-CT), become increasingly more accessible, new dental measurements such as dental tissue size and proportions can be obtained. This research investigates the variation of dental tissues and proportions by sex in archaeological samples. MATERIALS AND METHODS: Upper and lower first incisor to second premolar tooth rows were obtained from 30 individuals (n = 300), from 3 archaeological samples. The teeth were micro-CT scanned and surface area and volumetric measurements were obtained from the surface meshes extracted. Dental wear was also recorded and differences between sexes determined. RESULTS: Enamel and crown measurements were found to be larger in females. Conversely, dentine and root measurements were larger in males. DISCUSSION: The findings support the potential use of dental tissues to estimate sex of individuals from archaeological samples, while also indicating that individuals aged using current dental aging methods may be underaged or overaged due to sex differences in enamel thickness.

Molar crown formation times of fossil orangutan molars from Guangxi, China.

OBJECTIVES: We aimed to investigate molar enamel development in fossil orangutans from Guangxi and shed light on the evolution of Asian great apes. MATERIALS AND METHODS: We collected 32 fossil orangutan molars, most of which were from Guangxi apothecaries and the Guangxi Daxin Heidong cave, and prepared histological sections of each molar. We then characterized aspects of dental development, including long period line periodicity, number of Retzius lines and lateral enamel formation time, cuspal enamel thickness, and enamel formation time. RESULTS: The long period line periodicity in fossil orangutans ranged from 9 to 10 days (mean, 9.09 days). The molar lateral enamel formation time ranged from 1.48 to 3.17 years (540-1,152 days). Cuspal enamel thickness in fossil orangutan molars ranged from 949 to 2,535 µm, and cuspal enamel formation time ranged from 0.64 to 1.87 years. Molar enamel formation time of fossil orangutans ranged from 2.47 to 4.67 years. DISCUSSION: Long-period line periodicity of fossil orangutans from Guangxi was within the variation range of extant orangutans, and the average long period line periodicity (9.09 days) of fossil orangutans from Guangxi in this study was lower than the values for extant orangutans (9.5 days) and fossil orangutans (10.9 days) from Sumatra and Vietnam. Orangutan enamel thickness may have gradually decreased from the Middle Pleistocene to Holocene. Crown formation time of fossil orangutans was slightly longer than that of extant orangutans, and the M1 emergence age of fossil orangutans from Guangxi was about 4-6 years. These findings might indicate the regional difference or evolutionary changes in orangutans since Pleistocene. Dental development of the Guangxi fossil orangutans were more similar to that of Asian Miocene apes, suggesting the closer evolutionary relationship of orangutans to Miocene Asian fossil apes.