Tissue contributions to sex and race: differences in tooth crown size of deciduous molars

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.

Dental age estimation using the Kvaal method-an evaluation of length and width ratios: a systematic review

This study aimed to systematically review the correlational accuracy between width ratios and length ratios based on the Kvaal methodology with chronological age. This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). The search strategy included ProQuest, PubMed, Science Direct, and Taylor and Francis and Willey online without time or language restriction using Kvaal method of age estimation as key words for the search up to December 2021. A team of two researchers independently selected the studies and extracted the data. The Covidence platform was used to systematically organize all titles. The full texts of eligible studies were analyzed. Risk of bias (RoB) was assessed using a modified (to the specific characteristics of this systematic review) checklist based on Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement checklist for observational studies. A total of 658 articles were initially reviewed, but 22 were selected for inclusion. The risk of bias was estimated to be unclear to low overall. Among the length ratios, ratio R showed a strong association with chronological age, followed by ratio P. For the width ratios, ratio B demonstrated a close association with chronological age, followed by ratio C. The results suggest that width ratios correlate better with chronological age than length ratios. This systematic review suggests the width ratios are more strongly associated with chronological age than the length ratios. Using a width ratio could serve as a convenient and rapid way to estimate dental age. Our results apply equally to all types of ethnic groups.

Parity, dental caries and implications for maternal depletion syndrome in northern Nigerian Hausa women

BACKGROUND

Female reproductive history, especially high parity, affects general health and may impact negatively on oral health. While parity has been positively linked to tooth loss, the specific association between parity and caries has not been adequately investigated.

AIM

To determine the association between parity and caries in a population of higher parity women. Influences of likely confounders (age, socio-economic status, reproductive parameters, oral health practices and sugar consumption between meals) were considered.

METHODS

This was a cross-sectional study involving 635 Hausa women of varying parity aged 13-80 years. Socio-demographic status, oral health practices and sugar consumption were obtained using a structured interviewer-administered questionnaire. All decayed, missing and filled teeth due to caries (excluding third molars) were noted, and tooth loss etiology was queried. Associations with caries were evaluated through correlation, ANOVA, post hoc analyses and Student's t tests. Effect sizes were considered for magnitude of differences. Multiple regression (binomial model) was used to investigate predictors of caries.

RESULTS

Hausa women had a high prevalence of caries (41.4%) despite low sugar consumption; nonetheless the overall mean DMFT score was very low (1.23 ± 2.42). Older, higher parity women experienced more caries, as did those with longer reproductive spans. Additionally, poor oral hygiene, use of fluoride toothpaste and frequency of sugar consumption were significantly associated with caries.

CONCLUSION

Higher parity (>6 children) was associated with higher DMFT scores. These results suggest that a form of maternal depletion, expressed as heightened caries susceptibility and subsequent tooth loss, occurs with higher parity.

Volumetric assessment of canines using post-mortem computed tomography (PMCT) for sexual dimorphism in a Malaysian population

Background

Recent research has explored volumetric assessment in three-dimensional (3D) imaging procedures for sexual dimorphism. The 3D techniques have enabled a more realistic, accurate, and non-invasive visualization of sex-related anatomical parameters, such as the size and shape of human teeth.

Aim

To perform sexual dimorphism based on dental tissue volumes of permanent left maxillary and mandibular canines in a Malaysian population.

Methods

A cross-sectional study was carried out on 220 post-mortem computed tomography (PMCT) scans of Malaysian subjects (114 males and 106 females) aged between 18 and 40 years old. The permanent left maxillary and mandibular canines were analysed based on the volume of their (I) enamel cap, (II) coronal dentine, and (III) root, as well as the combination between the three dental tissue volumes (DTV). 3D Slicer version 4.10.2 computer software was used to perform a semi-automated segmentation of the anatomic regions of interest of each tooth.

Results

The DTV of the permanent left maxillary and mandibular canines showed sexual dimorphism as the males presented larger DTV than females (p < 0.05). After binary logistic regression, the DTV revealed an overall sex classification rate of 60 to 74.1%. The DTV of the permanent left mandibular canine had more discriminant power to correctly classify males and females compared to the left maxillary canine.

Conclusions

The volumetric assessment of the dental tissues of the permanent left maxillary and mandibular canines could discriminate sex in the Malaysian population. Given the limited classification rate, this approach could act solely as a supplementary tool to existing sex estimation methods.

Hunter-Schreger Band configuration in human molars reveals more decussation in the lateral enamel of 'functional' cusps than 'guiding' cusps

OBJECTIVES

Enamel prism decussation, which manifests as Hunter-Schreger Bands (HSB), is considered a mechanism to mitigate crack propagation. During the chewing cycle, the 'functional' cusps that are involved in Phase II crushing and grinding experience more complex patterns of stress than do those that 'guide' the molars into occlusion (Phase I). This study examines HSB configuration in the lateral enamel of human molars to identify potential differences between these cusps as predicted from their functional distinctions.

DESIGN

Measurements were recorded from scanning electron micrographs of sections through the mesial cusps of unworn permanent molars. For each section, HSB packing density and the relative thickness of decussated enamel were quantified in the cuspal and middle segments of lateral enamel over the guiding and functional cusps.

RESULTS

No clear trend from first to third molars in HSB configuration was found in either jaw. In maxillary molars, the functional cusp displays higher HSB packing density in the cuspal and middle segments, and relatively thicker decussated enamel in the cuspal segment than does the guiding cusp. In mandibular molars, the functional cusp displays higher HSB packing density in the middle segment than does the guiding cusp, but no difference in relative thickness was found between them. Enamel of mandibular molars shows weaker decussation than maxillary molars.

CONCLUSIONS

The results suggest that guiding cusps are intrinsically more susceptible to crack propagation than functional cusps in human permanent molars. Structural factors such as enamel decussation should be considered when interpreting enamel chipping patterns in dietary contexts.

Age Estimation by Kvaal's Method Using Digital Panoramic Radiographs in the Saudi Population

Introduction

In forensic literature, estimating an individual's age has garnered a lot of attention. With increasing age, the size of the dental pulp cavity shrinks as a result of secondary dentin deposits. This could be used as a measure of age. Aside from morphological approaches, radiological approaches might be used to analyze this regression shift. Kvaal's method calculates the chronological age of individuals based on the age-pulp size relationship on periapical dental radiographs.

Purpose

This study aims to use Kvaal's method to estimate the chronological age of patients using digital panoramic radiographs and verify the validity of regression equations proposed by Kvaal et al. in the Saudi population.

Material and methods

A total of 74 digital orthopantomograms were randomly selected from Qassim University Dental Clinic in Saudi Arabia, ranging in age from 18 to 64 years (mean age 32 years). The radiographs were taken between 2018 and 2021 according to inclusion and exclusion criteria.

Results

When the Kvaal technique was applied to Saudi members, there was no statistically significant discrepancy between the estimated and chronological ages. The coefficient of determination R2 was highest when three mandibular teeth were evaluated together (0.752).

Conclusion

The most accurate indicator for age assessment was "M" (mean worth, all things considered) and "W L" (contrast among "Width" and "Length").

Crown dimensions of primary teeth-A systematic review and meta-analysis

Odontometrics, also known as metric traits, includes mesiodistal, buccolingual dimensions, and crown height. The purpose of this study was to assess pancontinental odontometric variations in the crown dimensions of primary teeth. Ten electronic databases were searched to identify studies that measured crown dimensions of primary teeth, published in English language, without year restriction up to July 2020. Studies included cross-sectional research measuring on casts, subjects, and on radiographs of healthy children. Meta-analysis was performed, and risk of bias was assessed using modified Newcastle-Ottawa Scale. Eighty-seven observational studies were included, with 24,634 participants (9487 males, 11,083 females; 19 studies lacked gender information). Only one study showed a low bias risk, whereas 81 and 5 studies had moderate and high risk, respectively. Sixty-five studies included for meta-analysis revealed heterogeneity in mean mesiodistal dimensions of maxillary first molars from Asia (I² -99.7%), buccolingual measurements of mandibular first molars from Europe (I² -99.9%), crown height of mandibular second molars from Africa and Europe (I² -79.8%). Among mesiodistal and buccolingual dimensions, Australians have larger while Asians have smaller teeth. Pertaining to crown height, very few studies could be found in the literature. This review highlights the variations in crown dimensions of primary teeth among populations.

Lingual bone thickness in the apical region of the horizontal mandibular third molar: A cross-sectional study in young Japanese

Background

Perforation of the lingual plate in the apical region of mandibular third molars will increase the risk of aberration and migration of the root tip and the risk of lingual nerve injury. The aim of this study was to analyze anatomical information, including relationships between the apical region of horizontally impacted mandibular third molars and lingual plates, in young Japanese.

Methods

Japanese patients, with horizontally impacted third molars, who underwent CT examination as a preoperative assessment for mandibular third molar extraction were included, and anatomical characteristics in the apical region of the right mandibular third molar were analyzed, in this study.

Results

A total of 121 patients were included based on the inclusion and exclusion criteria of this study. The mean and standard deviation of the bone thickness on the lingual side of the mandibular third molar in the apical region was 1.5 ± 1.6 mm, and the absence of lingual cortical bone in the apical region, namely, “perforation”, was observed in 44 patients. The statistical analysis revealed the predictors of cases with perforation as follows: gender, age, and the available space evaluated by Pell and Gregory classification.

Conclusions

This study clarified that “perforation” was sometimes observed in young Japanese, and that the predictors of those cases were as follows: gender, age, and the available space evaluated by Pell and Gregory classification.

Gender determination analysis using anthropometrical dimensions of 2D:4D, foot index and mandibular canine index

Introduction

Sex determination is a challenge for forensic experts during mass disasters. Teeth are an excellent source in both living and nonliving population, where bodies are mutilated beyond recognition. Mandibular canines can be employed for gender determination in such situations. Similarly, second-to-fourth digit ratio (2D:4D) and foot index (FI) are sexually dimorphic and differ in males and females. Mandibular canine index (MCI), 2D:4D and FI are considered quick, easy and reproducible methods for determining the sex of an individual.

Aim

This study aimed to determine the combined role of MCI, 2D:4D and FI in denoting gender identity and establish their correlation.

Materials and Methods

The present study comprised of 100 dental students (50 males and 50 females) of our institution, aged 19-25 years, with specific inclusion and exclusion criteria. The measurements were done using a Vernier caliper, a divider and a ruler, and MCI, 2D:4D and FI were calculated using their specific formulae. The calculated values of FI, MCI and 2D:4D were subjected to statistical analysis.

Results

There was a statistically significant difference observed between left MCI (P < 0.05), right and left 2D:4D and FI (P < 0.05). The results revealed that 2D:4D was less, whereas MCI and FI were higher in males than in females. The observed MCI was compared with standard MCI, and left MCI revealed higher sexual dimorphic characteristics (15.2%). Although the overall correlation between 2D:4D, FI and MCI was insignificant, the measurements were comparable.

Conclusion

This study indicated that the anthropometric dimensions of 2D:4D, FI and MCI can be used for sex determination independently with accurate results.

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.

Impact of population-specific dental development on age estimation using dental atlases

OBJECTIVES

The steady development and subsequent eruption of the dentition is particularly useful for the estimation of age in juveniles. There are few studies that examine and test methods on a population-diverse sample. Our goal is to test the Ubelaker () and London Atlas (2010) dental charts on a sample representing several different population backgrounds to infer if refinement for population-specific standards should be developed.

MATERIALS AND METHODS

The first and second authors examined panoramic radiographs of 335 individuals from the James K. Economides Orthodontic Collection blind to chronological age, sex, and ancestry and scored using both dental atlases.

RESULTS

The age of Native Americans and African Americans was generally overestimated, suggesting faster rates of development. European Americans and New Mexico Hispanics, while not always showing the highest success rates, generally were closer to the correct age than other ancestry groups. The overall success rate for Ubelaker () was 80.00% for both observers, while the London Atlas was significantly lower at approximately 21.79-23.28%. Accuracy rates did not differ significantly between ancestry groups, though patterns were evident regarding under- or over-estimation of age.

DISCUSSION

The present study demonstrates that incorrect age estimations were typically still within 1.5 years of the actual age. Ubelaker () had higher rates of success due to broader age ranges. The results suggest that though accuracy rates did not significantly differ, different developmental rates may affect age estimates and population-specific standards should be considered for known-ancestry individuals, while aging standards constructed from a diverse sample should be utilized for unknown-ancestry cases.

The effect of different geometric shapes and angles on the fracture strength of IPS e.max computer-aided designed ceramic onlays: An in vitro study

Statement of Problem:

The current ceramic onlay preparation techniques for cuspal areas involve the reduction of cusps following the cuspal anatomy and the removal of all sharp angulations. However, there is little research literature studying the effect of occlusal preparation angles. Furthermore, there is no recent literature on the effect of angulations on IPS e.max computer-aided designed (CAD) (e.max) ceramic onlays.

Purpose:

The purpose of this study is to investigate the effect of geometric cuspal angulation and different internal preparation angles on the fracture strength of e.max CAD ceramic onlays.

Materials and Methods:

Sharp (33° and 22°) and round (33° and 22°) preparations were tested, each group having 10 specimens. e.max ceramic onlays were milled, sintered, glazed, and then bonded onto geometric tooth models. Fracture strength was measured at the initial fracture with a universal testing machine. The load was applied laterally to the central fossa (2-point contact) and vertically to the cusp peak (1-point contact).

Results:

A reduced cuspal angulation of 22° resulted in a stronger ceramic onlay than a 33° angulation when laterally loaded (P = 0.001). The presence of sharp angles weakened the ceramic significantly for both the 22° preparation (P = 0.0013) and 33° preparation (P = 0.0304).

Conclusion:

This in vitro study found that preparation angles of 22° resulted in superior fracture strength during central fossa loading and that rounding the preparation resulted in significantly higher fracture strength when a cusp peak load was applied. When the cusp tip loading is applied, the preparation angle does not appear to influence the fracture strength.

In Vivo Electron Paramagnetic Resonance Tooth Dosimetry: Dependence of Radiation-Induced Signal Amplitude on the Enamel Thickness and Surface Area of Ex Vivo Human Teeth

In vivo L-band electron paramagnetic resonance tooth dosimetry is a newly developed and very promising method for retrospective biodosimetry in individuals who may have been exposed to significant levels of ionizing radiation. The present study aimed to determine the relationships among enamel thickness, enamel area, and measured electron paramagnetic resonance signal amplitude with a view to improve the quantitative accuracy of the dosimetry technique. Ten isolated incisors were irradiated using well-characterized doses, and their radiation-induced electron paramagnetic resonance signals were measured. Following the measurements, the enamel thickness and area of each tooth were measured using micro-focus computed tomography. Linear regression showed that the enamel area at each measurement position significantly affected the radiation-induced electron paramagnetic resonance signal amplitude (p < 0.001). Simulation data agreed well with this result. These results indicate that it is essential to properly consider enamel thickness and area when interpreting electron paramagnetic resonance tooth dosimetry measurements to optimize the accuracy of dose estimation.

Neanderthal and Denisova tooth protein variants in present-day humans

Environment parameters, diet and genetic factors interact to shape tooth morphostructure. In the human lineage, archaic and modern hominins show differences in dental traits, including enamel thickness, but variability also exists among living populations. Several polymorphisms, in particular in the non-collagenous extracellular matrix proteins of the tooth hard tissues, like enamelin, are involved in dental structure variation and defects and may be associated with dental disorders or susceptibility to caries. To gain insights into the relationships between tooth protein polymorphisms and dental structural morphology and defects, we searched for non-synonymous polymorphisms in tooth proteins from Neanderthal and Denisova hominins. The objective was to identify archaic-specific missense variants that may explain the dental morphostructural variability between extinct and modern humans, and to explore their putative impact on present-day dental phenotypes. Thirteen non-collagenous extracellular matrix proteins specific to hard dental tissues have been selected, searched in the publicly available sequence databases of Neanderthal and Denisova individuals and compared with modern human genome data. A total of 16 non-synonymous polymorphisms were identified in 6 proteins (ameloblastin, amelotin, cementum protein 1, dentin matrix acidic phosphoprotein 1, enamelin and matrix Gla protein). Most of them are encoded by dentin and enamel genes located on chromosome 4, previously reported to show signs of archaic introgression within Africa. Among the variants shared with modern humans, two are ancestral (common with apes) and one is the derived enamelin major variant, T648I (rs7671281), associated with a thinner enamel and specific to the Homo lineage. All the others are specific to Neanderthals and Denisova, and are found at a very low frequency in modern Africans or East and South Asians, suggesting that they may be related to particular dental traits or disease susceptibility in these populations. This modern regional distribution of archaic dental polymorphisms may reflect persistence of archaic variants in some populations and may contribute in part to the geographic dental variations described in modern humans.

Potential hominin affinities of Graecopithecus from the Late Miocene of Europe

The split of our own clade from the Panini is undocumented in the fossil record. To fill this gap we investigated the dentognathic morphology of Graecopithecus freybergi from Pyrgos Vassilissis (Greece) and cf. Graecopithecus sp. from Azmaka (Bulgaria), using new μCT and 3D reconstructions of the two known specimens. Pyrgos Vassilissis and Azmaka are currently dated to the early Messinian at 7.175 Ma and 7.24 Ma. Mainly based on its external preservation and the previously vague dating, Graecopithecus is often referred to as nomen dubium. The examination of its previously unknown dental root and pulp canal morphology confirms the taxonomic distinction from the significantly older northern Greek hominine Ouranopithecus. Furthermore, it shows features that point to a possible phylogenetic affinity with hominins. G. freybergi uniquely shares p4 partial root fusion and a possible canine root reduction with this tribe and therefore, provides intriguing evidence of what could be the oldest known hominin.

Evidence favoring a secular reduction in mandibular leeway space

OBJECTIVE

Researchers have documented secular trends in tooth size among recent generations. This study was a test for a change in mandibular leeway space.

MATERIALS AND METHODS

Dental casts from participants in the Denver Growth Study (23 boys, 22 girls; born in the 1930s) were compared with casts from a contemporary series of orthodontic patients (23 boys, 22 girls; born in the 1990s). All were phenotypically normal, healthy American whites.

RESULTS

Analysis of variance (accounting for sex) showed that the cumulative mandibular primary canine plus first and second primary molar size (c + m1 + m2) was slightly larger in the recent cohort (23.53 mm earlier vs 23.83 mm recent cohort; mean difference: 0.30 mm; P = .009), principally due to larger second primary molars (m2) in the recent cohort. In turn, the sum of the permanent canine and two premolars (C + P1 + P2) was significantly larger in the recent cohort (21.08 mm earlier vs 21.80 mm recent cohort; mean difference: 0.72 mm; P = .002). Larger teeth in the contemporary series produced a mean leeway space per quadrant of 2.03 mm versus 2.45 mm in the earlier cohort-a clinically and statistically significant reduction (P = .030). Some tooth types (primary second molar and permanent canine) were significantly larger in boys than in girls, but the sex difference in leeway space was not statistically significant.

CONCLUSION

Results suggest that mandibular leeway space is decreasing in 21st century American whites and may present a challenge to orthodontists in managing tooth size-arch length discrepancies.

MMP20 rs1784418 Protects Certain Populations against Caries

This work aimed to further evaluate the association of MMP20 rs1784418 C>T and dental caries experience with the hypothesis that MMP20 rs1784418 C>T is a risk factor for dental caries. 184 children 4-7 years of age had their caries experience determined and buccal cheek swabs collected for DNA extraction to test for association with the MMP20 rs1784418 C>T using standard statistical approaches. A meta-analytic approach was also implemented to compile previous discrepant reports of the same association. We found an association between MMP20 rs1784418 C>T and dental caries experience in primary dentition (p = 0.01). The meta-analysis showed that this association appears to favor individuals born in Brazil and not Turkey. MMP20 rs1784418 C>T appears to protect against dental caries, but its effects are likely to be more marked in certain populations.

Human enamel thickness and ENAM polymorphism

The tooth enamel development gene, enamelin (ENAM), showed evidence of positive selection during a genome-wide scan of human and primate DNA for signs of adaptive evolution. The current study examined the hypothesis that a single-nucleotide polymorphism (SNP) C14625T (rs7671281) in the ENAM gene identified in the genome-wide scan is associated with a change in enamel phenotype. African Americans were selected as the target population, as they have been reported to have a target SNP frequency of approximately 50%, whereas non-Africans are predicted to have a 96% SNP frequency. Digital radiographs and DNA samples from 244 teeth in 133 subjects were analysed, and enamel thickness was assessed in relation to SNP status, controlling for age, sex, tooth number and crown length. Crown length was found to increase with molar number, and females were found to have thicker enamel. Teeth with larger crowns also had thicker enamel, and older subjects had thinner enamel. Linear regression and generalized estimating equations were used to investigate the relationship between enamel thickness of the mandibular molars and ENAM SNP status; enamel in subjects with the derived allele was significantly thinner (P=0.040) when the results were controlled for sex, age, tooth number and crown length. The derived allele demonstrated a recessive effect on the phenotype. The data indicate that thinner dental enamel is associated with the derived ENAM genotype. This is the first direct evidence of a dental gene implicated in human adaptive evolution as having a phenotypic effect on an oral structure.

Primary tooth size asymmetry in twins and singletons

OBJECTIVES

To explore asymmetry values of antimeric deciduous tooth crown dimensions in three types of twins: monozygotic (MZ), dizygotic same-sex (DZ) and opposite-sex (OS) vs. single-born controls.

SETTING AND SAMPLE POPULATION

Mesiodistal and labio-lingual crown dimensions of second deciduous molars and mesiodistal canine and first molar crown dimensions of 2159 children at 6-12 years of age were evaluated, originating from the US cross-sectional Collaborative Perinatal Study from the 1970s, including altogether MZ (n = 28), DZ same-sex (n = 33) and OS (n = 39) pairs. Single born (n = 1959) were used as controls.

MATERIAL AND METHODS

Dental casts were measured for comparison of variance relationships calculated from antimeric teeth, exhibiting fluctuating (FA), and directional (DA) asymmetry using anova.

RESULTS

Significant differences appeared in MZ and OS girls in DA of deciduous canines, which gain size in the first and second trimester, and deciduous second molars, which finally stop crown growth during the early post-natal period. Significantly, increased FA values appeared for lower deciduous canines and second molars, indicating greatest environmental stress in OS girls, MZ girls and DZ boys. Twin girls had more fluctuating and directional crown asymmetry than twin boys, but in some dimensions, the twins were more symmetric than controls.

CONCLUSIONS

Transmembrane hormonal influence between opposite-sex twins, and late gestational stress factors, caused by placental malfunction and/or monochorionicity, may be involved in asymmetric growth of antimers, during critical periods of crown size gain.

Sex determination by tooth size in a sample of Greek population

Sex assessment from tooth measurements can be of major importance for forensic and bioarchaeological investigations, especially when only teeth or jaws are available. The purpose of this study is to assess the reliability and applicability of establishing sex identity in a sample of Greek population using the discriminant function proposed by Rösing et al. (1995). The study comprised of 172 dental casts derived from two private orthodontic clinics in Athens. The individuals were randomly selected and all had clear medical history. The mesiodistal crown diameters of all the teeth were measured apart from those of the 3rd molars. The values quoted for the sample to which the discriminant function was first applied were similar to those obtained for the Greek sample. The results of the preliminary statistical analysis did not support the use of the specific discriminant function for a reliable determination of sex by means of the mesiodistal diameter of the teeth. However, there was considerable variation between different populations and this might explain the reason for lack of discriminating power of the specific function in the Greek population. In order to investigate whether a better discriminant function could be obtained using the Greek data, separate discriminant function analysis was performed on the same teeth and a different equation emerged without, however, any real improvement in the classification process, with an overall correct classification of 72%. The results showed that there were a considerably higher percentage of females correctly classified than males. The results lead to the conclusion that the use of the mesiodistal diameter of teeth is not as a reliable method as one would have expected for determining sex of human remains from a forensic context. Therefore, this method could be used only in combination with other identification approaches.

Increased enamel hypoplasia and very low birthweight infants

Birth cohort studies of developmental defects of enamel (DDE) and early childhood caries (ECC) in very low birthweight (VLBW) and normal birthweight (NBW) infants are rare. In this birth cohort of 234 VLBW and 234 NBW infants, we report the incidence of ECC and DDE at 8 and 18-20 mos of corrected age. Infant medical and maternal socio-demographic data were abstracted from medical records at birth. Dental assessments for ECC and DDE (enamel hypoplasia, demarcated and diffuse opacities) were completed at 8 and 18-20 mos. The incidence of hypoplasia was significantly higher in VLBW compared with NBW infants (8 mos, 19% vs. 2%; 18 mos, 31% vs. 8%). The incidence of ECC (International Caries Detection and Assessment System: ICDAS ≥ 2) was 1.4% (8 mos) and 12% (18-20 mos) and was similar between the VLBW and NBW groups. At both ages, using a beta-binomial regression model to control for potential confounders (maternal and infant characteristics), we found increased risk for enamel hypoplasia among the VLBW infants compared with the NBW infants. African Americans had a lower risk for enamel hypoplasia at 18-20 mos. The VLBW infants should be monitored for ECC due to the presence of enamel hypoplasia.

Masculinization of the eruption pattern of permanent mandibular canines in opposite sex twin girls

The aim of this study is to explore the effect of prenatal androgenization on the clinical eruption of permanent teeth expressing dimorphism and bimaturism. The eruption curves of permanent teeth (except third molars), including those that make up the canine complex (permanent canines, lower first premolars), are compared among opposite sex twins (OS twins) relative to single-born boys and girls. The comparisons are made with regard to three phases of eruption (pierced mucosa, half- erupted, and completely erupted) from a cross-sectional sample of dental casts, using Kaplan-Meier survival and Cox regression analyzes. The casts were collected from 2159 school children from the US Collaborative Perinatal Project, including 39 pairs of OS-twins, of which 12 pairs (30.8%) were Euro-Americans and 27 pairs (69.2%) were of African-American ancestry. The eruption patterns of the incisors, upper first molars, and lower canines were found to be significantly masculinized (delayed) among OS twin girls. The differences in most other teeth were either not significant, or the number of observations of active eruption phases were too few, such as in the upper first molars and incisors, to yield strong evidence and meaningful results. The masculinization of the tooth eruption pattern in OS twin girls is intriguing because of the lower canine responses during puberty, as well as canine primordial formation during early fetal androgenization of their co-twin during the 8th to 14th gestational weeks. The present results offer a challenge for future research exploring tooth eruption mechanisms, and may also highlight some cases of delayed or ectopic canines, which are biased toward females.

Odontometric determination of sex at Mound 72, Cahokia

The mortuary context of Mound 72 at the Cahokia site is one of the most unusual ever described in prehistoric North America. Previous skeletal analyses suggested that four large mass graves within the mound contained only female skeletons. However, these findings were complicated by extremely poor bone preservation that limited the number of skeletal observations that could be made. Furthermore, most skeletons were aged in the 15-25 year range, a time when sexually dimorphic bony traits may still be developing. In this study, dental remains were used to examine sex in the four presumably all-female mass graves in Mound 72. Additional sources of information, including the original field/laboratory notes and new sexing data based on modern standards, were gathered to fully evaluate the dental estimates. Initially, discriminant function analysis was performed on odontometrics using the original Mound 72 sex assignment. Inconsistent results indicated that some of the skeletons may have been misclassified in the original analyses. To overcome this issue, discriminant function equations were generated using a large pooled skeletal sample from two sites in close temporal and geographic proximity to Cahokia. Application of the equations to Mound 72 revealed that each of the four mass burial groups contained individuals classified as male. These assignments were checked against the skeletal remains and the original field/laboratory notes. Discussion centers on how the results affect previous archaeological interpretations as well as the methodological considerations associated with this study.

Sexual dimorphism in permanent teeth of modern Greeks

Sex determination is considered an important step in reconstructing the biological profile of unknown individuals from a forensic context. Forensic anthropologists have long used teeth as an additional tool for sex determination as they resist postmortem destruction. In this case the use of population-specific data is necessary since sexual dimorphism varies between different populations. Currently there are no odontometric standards for determining sex in Greek populations. The purpose of this study is to examine the degree of sexual dimorphism in permanent teeth of modern Greeks. A total of 839 permanent teeth in 133 individuals (70 males and 63 females) from the Athens Collection were examined. Mesiodistal and buccolingual crown and cervical diameters of both maxillary and mandibular teeth were measured. It was found that males have bigger teeth than females and in 65 out of 88 dimensions measured, male teeth exceeded female teeth significantly (P<0.05). Canines were the most dimorphic teeth followed by first premolars, maxillary second premolar and mandibular second molar. Although other teeth were also sexually dimorphic they did not have a statistically significant difference in all dimensions. The most dimorphic dimension was buccolingual cervical diameter followed by buccolingual crown diameter. A comparison of sexual dimorphism in teeth between different populations showed that it differs among different groups. European population groups presented the highest degree of sexual dimorphism in teeth whereas Native South Americans the lowest.

Social inequalities in childhood dental caries: the convergent roles of stress, bacteria and disadvantage

The studies reported here examines stress-related psychobiological processes that might account for the high, disproportionate rates of dental caries, the most common chronic disease of childhood, among children growing up in low socioeconomic status (SES) families. In two 2004-2006 studies of kindergarten children from varying socioeconomic backgrounds in the San Francisco Bay Area of California (Ns = 94 and 38), we performed detailed dental examinations to count decayed, missing or filled dental surfaces and microtomography to assess the thickness and density of microanatomic dental compartments in exfoliated, deciduous teeth (i.e., the shed, primary dentition). Cross-sectional, multivariate associations were examined between these measures and SES-related risk factors, including household education, financial stressors, basal and reactive salivary cortisol secretion, and the number of oral cariogenic bacteria. We hypothesized that family stressors and stress-related changes in oral biology might explain, fully or in part, the known socioeconomic disparities in dental health. We found that nearly half of the five-year-old children studied had dental caries. Low SES, higher basal salivary cortisol secretion, and larger numbers of cariogenic bacteria were each significantly and independently associated with caries, and higher salivary cortisol reactivity was associated with thinner, softer enamel surfaces in exfoliated teeth. The highest rates of dental pathology were found among children with the combination of elevated salivary cortisol expression and high counts of cariogenic bacteria. The socioeconomic partitioning of childhood dental caries may thus involve social and psychobiological pathways through which lower SES is associated with higher numbers of cariogenic bacteria and higher levels of stress-associated salivary cortisol. This convergence of psychosocial, infectious and stress-related biological processes appears to be implicated in the production of greater cariogenic bacterial growth and in the conferral of an increased physical vulnerability of the developing dentition.

Evolutionary adaptations to dietary changes

Through cultural innovation and changes in habitat and ecology, there have been a number of major dietary shifts in human evolution, including meat eating, cooking, and those associated with plant and animal domestication. The identification of signatures of adaptations to such dietary changes in the genome of extant primates (including humans) may shed light not only on the evolutionary history of our species, but also on the mechanisms that underlie common metabolic diseases in modern human populations. In this review, we provide a brief overview of the major dietary shifts that occurred during hominin evolution, and we discuss the methods and approaches used to identify signals of natural selection in patterns of sequence variation. We then review the results of studies aimed at detecting the genetic loci that played a major role in dietary adaptations and conclude by outlining the potential of future studies in this area.

Dietary change and adaptive evolution of enamelin in humans and among primates

Scans of the human genome have identified many loci as potential targets of recent selection, but exploration of these candidates is required to verify the accuracy of genomewide scans and clarify the importance of adaptive evolution in recent human history. We present analyses of one such candidate, enamelin, whose protein product operates in tooth enamel formation in 100 individuals from 10 populations. Evidence of a recent selective sweep at this locus confirms the signal of selection found by genomewide scans. Patterns of polymorphism in enamelin correspond with population-level differences in tooth enamel thickness, and selection on enamel thickness may drive adaptive enamelin evolution in human populations. We characterize a high-frequency nonsynonymous derived allele in non-African populations. The polymorphism occurs in codon 648, resulting in a nonconservative change from threonine to isoleucine, suggesting that the allele may affect enamelin function. Sequences of exons from 12 primate species show evidence of positive selection on enamelin. In primates, it has been documented that enamel thickness correlates with diet. Our work shows that bursts of adaptive enamelin evolution occur on primate lineages with inferred dietary changes. We hypothesize that among primate species the evolved differences in tooth enamel thickness are correlated with the adaptive evolution of enamelin.

Predictors of variation in mandibular incisor enamel thickness

BACKGROUND

Interproximal reduction of mandibular incisor enamel often is performed as an adjunct to orthodontic alignment. The authors conducted a study to determine factors contributing to variations in incisor enamel thickness.

METHODS

The authors compared enamel thickness between mandibular central and lateral incisors, between mesial and distal surfaces, between male and female subjects (N=40 each) and between African-American and white subjects (N=40 each). The authors also evaluated correlations between overall tooth width and enamel thickness.

RESULTS

The authors found significantly greater enamel thickness in lateral incisors, on distal tooth surfaces and in black subjects (P<.0001 for each); they found no differences between male and female subjects. They found that wider teeth were associated with greater enamel thickness (P<.01) but that the amount of thickness varied greatly among subjects (range: 0.44-1.28 millimeters).

CONCLUSIONS

Thicker enamel was found on the distal aspect of lateral incisors, in black subjects and in wider teeth. The authors observed, however, that the variations in thickness are not fully explained by these factors alone.

CLINICAL IMPLICATIONS

If substantial enamel reduction is planned as part of dental treatment, the authors recommend that clinicians use calibrated radiographs to measure the thickness of their patients' enamel surfaces because of the extensive variation in enamel thickness among and within people.

Sexual dimorphism of the dental tissues in human permanent mandibular canines and third premolars

Methods of measuring tissue area from images of longitudinal thin tooth sections have been used to assess sexual dimorphism in the permanent dentition. The aim of this study was to demonstrate the extent of sexual dimorphism within the coronal tissue proportions of permanent mandibular canines and premolars, using area measurements of the enamel and dentine-pulp core. The sample consisted of embedded "half-tooth" sections from 45 individuals, all of known age-at-death and sex, collected from the St. Thomas' Anglican Church historic (1821-1874) cemetery site in Belleville, ON, Canada. The relative dentine-pulp area of the third premolars and canines displayed high levels of sexual dimorphism, as well as statistically significant mean differences between the sexes. The male canines and premolars have significantly more dentine than their female counterparts, as well as relatively more dentine with respect to overall crown size. The female canines and premolars have significantly more enamel relative to overall crown area than those of the males. These results suggest that relative area measures of crown tissues are more predictable measures of sexual dimorphism than absolute measures, and tissue proportions may remain constant despite intrasex variation in overall tooth crown size.

A practical genome scan for population-specific strong selective sweeps that have reached fixation

Phenotypic divergences between modern human populations have developed as a result of genetic adaptation to local environments over the past 100,000 years. To identify genes involved in population-specific phenotypes, it is necessary to detect signatures of recent positive selection in the human genome. Although detection of elongated linkage disequilibrium (LD) has been a powerful tool in the field of evolutionary genetics, current LD-based approaches are not applicable to already fixed loci. Here, we report a method of scanning for population-specific strong selective sweeps that have reached fixation. In this method, genome-wide SNP data is used to analyze differences in the haplotype frequency, nucleotide diversity, and LD between populations, using the ratio of haplotype homozygosity between populations. To estimate the detection power of the statistics used in this study, we performed computer simulations and found that these tests are relatively robust against the density of typed SNPs and demographic parameters if the advantageous allele has reached fixation. Therefore, we could determine the threshold for maintaining high detection power, regardless of SNP density and demographic history. When this method was applied to the HapMap data, it was able to identify the candidates of population-specific strong selective sweeps more efficiently than the outlier approach that depends on the empirical distribution. This study, confirming strong positive selection on genes previously reported to be associated with specific phenotypes, also identifies other candidates that are likely to contribute to phenotypic differences between human populations.

Carabelli's trait and tooth size of human maxillary first molars

Carabelli's trait is a morphological feature that can occur on the protocone of human maxillary molars. This study tests the hypothesis that Carabelli's trait is correlated statistically with the dimensions of the crown's four principal cusps or whether, as a cingular feature, the trait truly accretes onto an otherwise unaffected crown. Computer-assisted image analysis was used to measure the 6 intercusp distances and 12 angular relationships among cusp tips on the permanent first molar of 300 young adult American whites. Carabelli's complex was scored using an 8-grade ordinal scheme. Crown size was quantified in three ways, namely as 1) maximum mesiodistal and buccolingual diameters, 2) the 6 intercusp distances, and 3) the 12 angular cusp arrangements. There was no sex difference in the morphological expression of Carabelli's trait in this sample. Overall crown size and intercusp distances were significantly and progressively larger in molars with larger Carabelli's trait expressions. There are graded size responses between crown size (mesiodistal and buccolingual diameters), sizes of the four principal cusps, and morphological stage of Carabelli's complex, though the statistical relationships are appreciably stronger in males than females. Carabelli's trait occurs preferentially in larger molars. In contrast, angular (shape) relationships among cusp tips are not discernibly affected by trait size in either sex. There is the situation, then, that Carabelli's trait is developmentally correlated with crown size, but with no apparent alteration of cusp arrangements, suggesting that the increases are isometric across the occlusal table. Why the association is much weaker in females remains speculative, but these data provide yet another line of evidence that, within a population, tooth size is associated in a positive fashion with crown complexity.

Microstructure and chemical composition of primary teeth in children with Down syndrome and cerebral palsy

This study was designed to test the hypothesis that prenatal growth insults leave permanent signs in the developing primary teeth that can be identified in later life. To test this hypothesis we examined exfoliated and extracted lower second primary molars of children with Down syndrome (DS) and cerebral palsy (CP). Teeth of children with no adverse medical history were used as a control group. Informed consent of parents and children was obtained in all cases. On each tooth two thin sections were cut, one bisecting the mesial cusps and one bisecting the distal cusps. Using a light microscope, the width of prenatal enamel and postnatal enamel was measured on each section at standardized locations from the dentin-enamel junction (DEJ) with the neonatal line used to distinguish between prenatal and postnatal enamel. Chemical analysis of each section was carried out using an energy dispersive spectrophotometer (ESR). The Ca/P ratios of enamel and dentin for each cusp were calculated and intercusp and intergroup differences analysed using non-parametric statistical tests. The results showed that significantly less enamel was laid down prenatally in DS and CP teeth than in the control group and that the enamel of the mesial cusps in these groups was less highly mineralised than that of the controls. The results also showed that in DS teeth growth and mineralisation of all cusps was affected. Based on these findings we propose that analysis of exfoliated deciduous teeth in developmentally challenged children may help in identifying the onset and severity of growth insults in utero and its impact on later development.

Dentition of moustached tamarins (Saguinus mystax mystax) from Padre Isla, Peru, part 1: Quantitative variation

Analyses of dental variation in geographically restricted, wild populations of primates are extremely rare; however, such data form the best source for models of likely degrees of variation within and between fossil species. Data from dental casts of a geographically restricted population of moustached tamarins (Saguinus mystax mystax) from Padre Isla, Peru, document high levels of dental variability, as measured by coefficients of variation, in a nonsexually dimorphic species, despite its isolation and small population size. Like other primates, moustached tamarins show lower variability in the dimensions of the first molars and increased variability in the dimensions of the final molars in the toothrow. Moustached tamarins from Padre Isla have a distinctive pattern of variability in the remaining teeth, including more stable tooth lengths in the anterior and posterior portions of the toothrow, and more stable tooth widths in the midregion of the toothrow. High variability in incisor width may be due to age effects of a distinctive diet and pattern of dental wear.

Modern human molar enamel thickness and enamel-dentine junction shape

This study examines cross-sections of molar crowns in a diverse modern human sample to quantify variation in enamel thickness and enamel-dentine junction (EDJ) shape. Histological sections were generated from molars sectioned buccolingually across mesial cusps. Enamel cap area, dentine area, EDJ length, and bi-cervical diameter were measured on micrographs using a digitizing tablet. Nine landmarks along the EDJ were defined, and X and Y coordinates were digitized in order to quantify EDJ shape. Upper molars show greater values for the components of enamel thickness, leading to significantly greater average enamel thickness than in lower molars. Average enamel thickness increased significantly from M1 to M3 in both molar rows, due to significantly increasing enamel cap area in upper molars, and decreasing dentine area in lower molars. Differences in EDJ shape were found among maxillary molars in combined and individual populations. Sex differences were also found; males showed significantly greater dentine area, EDJ length, and bi-cervical diameters in certain tooth types, which resulted in females having significantly thicker average enamel. Differences in enamel thickness and EDJ shape within molars were also found among populations, although few consistent trends were evident. This study demonstrates that enamel thickness and EDJ shape vary among molars, between sexes, and among populations; these factors must be considered in the categorization and comparison of ape and human molars, particularly when isolated teeth or fossil taxa are included. Human relative enamel thickness encompasses most values reported for fossil apes and humans, suggesting limited taxonomic value when considered alone.

Sexual dimorphism in modern human permanent teeth

On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth.

Enamel thickness of deciduous and permanent molars in modern Homo sapiens

This study presents data on the enamel thickness of deciduous (dm2) and permanent (M1-M3) molars for a geographically diverse sample of modern humans. Measurements were recorded from sections through the mesial cusps of unworn teeth. Enamel is significantly thinner on deciduous than on permanent molars, and there is a distinct trend for enamel to increase in relative thickness from M1 to M3. The relatively thicker enamel of M2s and especially M3s can be related to the overall reduction in size of more distal molar crowns, which has been attained through a differential loss of the dentine component. Enamel tends to be thicker on the protocone than on the paracone, and thicker on the protoconid than on the metaconid, but its distribution is not wholly concordant with models that predict increased thickness as a means by which to counter heavier attritional loss on these "functional" cusps. Indeed, the thickness of enamel tends to be more variable on cusp tips and occlusal surfaces than over the lateral aspects of cusps. The proportionately thicker enamel over the lateral aspects of the protocone and protoconid more likely serves as a means to prolong functional crown life by preventing cusp fracture, rather than being an adaptation to increase the attritional longevity of wear facets. The present data suggest that the human dentition is not predisposed to develop a helicoidal wear plane through the disposition of molar enamel thickness.

Genetic analysis of crown size in the first molars using SMXA recombinant inbred mouse strains

Tooth crown size may be determined by both genetic and environmental factors. The aim of this study was to identify quantitative trait loci (QTLs) affecting dental crown size and determine whether there is genetic independence between upper and lower teeth, using SMXA recombinant inbred strains of mice. Mesiodistal and buccolingual crown diameters (MD and BL, respectively) of the upper and lower first molars (M(1) and M(1), respectively) were measured. For each trait, mean values of substrains showed a continuous spectrum of distribution. Genome-wide scan detected QTLs exceeding suggestive threshold levels for MD of M(1) (chromosomes 7, 13, and 17), BL of M(1) (chromosomes 8 and 13), MD of M(1) (chromosomes 7 and 13), and BL of M(1) (chromosomes 3 and 15). These findings suggest that tooth crown size is controlled by multiple genes, and that there is some independence of genetic control between M(1) and M(1).

Integrating the genotype and phenotype in hominid paleontology

Competing interpretations of human origins and evolution have recently proliferated despite the accelerated pace of fossil discovery. These controversies parallel those involving other vertebrate families and result from the difficulty of studying evolution among closely related species. Recent advances in developmental and quantitative genetics show that some conventions routinely used by hominid and other mammalian paleontologists are unwarranted. These same advances provide ways to integrate knowledge of the genotype into the study of the phenotype. The result is an approach that promises to yield a fuller understanding of evolution below the family level.