Early life of Neanderthals.

The early onset of weaning in modern humans has been linked to the high nutritional demand of brain development that is intimately connected with infant physiology and growth rate. In Neanderthals, ontogenetic patterns in early life are still debated, with some studies suggesting an accelerated development and others indicating only subtle differences vs. modern humans. Here we report the onset of weaning and rates of enamel growth using an unprecedented sample set of three late (∼70 to 50 ka) Neanderthals and one Upper Paleolithic modern human from northeastern Italy via spatially resolved chemical/isotopic analyses and histomorphometry of deciduous teeth. Our results reveal that the modern human nursing strategy, with onset of weaning at 5 to 6 mo, was present among these Neanderthals. This evidence, combined with dental development akin to modern humans, highlights their similar metabolic constraints during early life and excludes late weaning as a factor contributing to Neanderthals' demise.

von Willebrand factor D and EGF domains regulate ameloblast differentiation and enamel formation.

Cell- and tissue-specific extracellular matrix (ECM) composition plays an important role in organ development, including teeth, by regulating cell behaviors, such as cell proliferation and differentiation. Here, we demonstrate for the first time that von Willebrand factor D and epidermal growth factor (EGF) domains (Vwde), a previously uncharacterized ECM protein, is specifically expressed in teeth and regulates cell proliferation and differentiation in inner enamel epithelial cells (IEEs) and enamel formation. We identified the Vwde as a novel ECM protein through bioinformatics using the NCBI expressed sequence tag database for mice. Vwde complementary DNA encodes 1773 amino acids containing a signal peptide, a von Willebrand factor type D domain, and tandem calcium-binding EGF-like domains. Real-time polymerase chain reaction demonstrated that Vwde is highly expressed in tooth tissue but not in other tissues including the brain, lung, heart, liver, kidney, and bone. In situ hybridization revealed that the IEEs expressed Vwde messenger RNA in developing teeth. Immunostaining showed that VWDE was localized at the proximal and the distal ends of the pericellular regions of the IEEs. Vwde was induced during the differentiation of mouse dental epithelium-derived M3H1 cells. Vwde-transfected M3H1 cells secreted VWDE protein into the culture medium and inhibited cell proliferation, whereas ameloblastic differentiation was promoted. Furthermore, Vwde increased the phosphorylation of extracellular signal-regulated kinase 1/2 and protein kinase B and strongly induced the expression of the intercellular junction protein, N-cadherin (Ncad). Interestingly, the suppression of endogenous Vwde inhibited the expression of Ncad. Finally, we created Vwde-knockout mice using the CRISPR-Cas9 system. Vwde-null mice showed low mineral density, rough surface, and cracks in the enamel, indicating the enamel hypoplasia phenotype. Our findings suggest that Vwde assembling the matrix underneath the IEEs is essential for Ncad expression and enamel formation.

A missense variant in specificity protein 6 (SP6) is associated with amelogenesis imperfecta.

Amelogenesis is the process of enamel formation. For amelogenesis to proceed, the cells of the inner enamel epithelium (IEE) must first proliferate and then differentiate into the enamel-producing ameloblasts. Amelogenesis imperfecta (AI) is a heterogeneous group of genetic conditions that result in defective or absent tooth enamel. We identified a 2 bp variant c.817_818GC>AA in SP6, the gene encoding the SP6 transcription factor, in a Caucasian family with autosomal dominant hypoplastic AI. The resulting missense protein change, p.(Ala273Lys), is predicted to alter a DNA-binding residue in the first of three zinc fingers. SP6 has been shown to be crucial to both proliferation of the IEE and to its differentiation into ameloblasts. SP6 has also been implicated as an AI candidate gene through its study in rodent models. We investigated the effect of the missense variant in SP6 (p.(Ala273Lys)) using surface plasmon resonance protein-DNA binding studies. We identified a potential SP6 binding motif in the AMBN proximal promoter sequence and showed that wild-type (WT) SP6 binds more strongly to it than the mutant protein. We hypothesize that SP6 variants may be a very rare cause of AI due to the critical roles of SP6 in development and that the relatively mild effect of the missense variant identified in this study is sufficient to affect amelogenesis causing AI, but not so severe as to be incompatible with life. We suggest that current AI cohorts, both with autosomal recessive and dominant disease, be screened for SP6 variants.

Amelogenin phosphorylation regulates tooth enamel formation by stabilizing a transient amorphous mineral precursor.

Dental enamel comprises interwoven arrays of extremely long and narrow crystals of carbonated hydroxyapatite called enamel rods. Amelogenin (AMELX) is the predominant extracellular enamel matrix protein and plays an essential role in enamel formation (amelogenesis). Previously, we have demonstrated that full-length AMELX forms higher-order supramolecular assemblies that regulate ordered mineralization in vitro, as observed in enamel rods. Phosphorylation of the sole AMELX phosphorylation site (Ser-16) in vitro greatly enhances its capacity to stabilize amorphous calcium phosphate (ACP), the first mineral phase formed in developing enamel, and prevents apatitic crystal formation. To test our hypothesis that AMELX phosphorylation is critical for amelogenesis, we generated and characterized a hemizygous knockin (KI) mouse model with a phosphorylation-defective Ser-16 to Ala-16 substitution in AMELX. Using EM analysis, we demonstrate that in the absence of phosphorylated AMELX, KI enamel lacks enamel rods, the hallmark component of mammalian enamel, and, unlike WT enamel, appears to be composed of less organized arrays of shorter crystals oriented normal to the dentinoenamel junction. KI enamel also exhibited hypoplasia and numerous surface defects, whereas heterozygous enamel displayed highly variable mosaic structures with both KI and WT features. Importantly, ACP-to-apatitic crystal transformation occurred significantly faster in KI enamel. Secretory KI ameloblasts also lacked Tomes' processes, consistent with the absence of enamel rods, and underwent progressive cell pathology throughout enamel development. In conclusion, AMELX phosphorylation plays critical mechanistic roles in regulating ACP-phase transformation and enamel crystal growth, and in maintaining ameloblast integrity and function during amelogenesis.

Comparative study of B content and δ11 B in the enamel of isolated teeth from brothers in the same family.

RATIONALE: The quantity of boron (B) and its isotopic ratios in tooth can provide information on dietary habits and oral health of individuals. These metrics are gradually being used in stomatology, environmental science and geochemistry. METHODS: This study measured the B concentration and δ11 B in the enamel of isolated teeth from brothers in the same family living in high-B-exposure areas at different times using inductively coupled plasma mass spectrometry (ICP-MS) and multicollector ICP-MS. RESULTS: The results demonstrate that B content in tooth samples of two brothers is related to the time of shedding. The earlier the time of shedding, the lower is the B content in tooth. The B content increased from 20.5 µg/g of the central incisor (6-7 years old) of the younger brother to 50.4 µg/g of the second molar (10-12 years old). And B content for the elder brother increased from 28.7 to 58.3 µg/g at the same positions. In the same family, the diet and environmental input of B is basically similar, and the B exposure is basically the same every year. The annual growth rate of B for the younger brother in this experiment is about 4.98 µg/g per year and that for the elder brother is about 4.93 µg/g per year. The δ11 B of shed teeth at different times from the same person is basically similar, but different from person to person. The δ11 B of shed teeth from the elder brother varies from 15.5‰ to 17.9‰ and from the younger brother varies from 5.2‰ to 6.7‰. The δ11 B is quite different for the brothers in the same family who had the same food and environmental intake of B. CONCLUSIONS: The experimental data confirmed the relationship between the information of B (B content and δ11 B) in shed teeth and B exposure. They provided an experimental basis using modern human teeth to apply B-isotope paleo-environmental significance.

An inconstant biorhythm: The changing pace of Retzius periodicity in human permanent teeth.

OBJECTIVES: Human tooth enamel retains evidence of growth in the form of Retzius lines. The number of daily growth increments between the regularly occurring lines defines their repeat interval, or periodicity. Retzius periodicity is often incorporated into enamel formation times, age-at-death reconstructions, or used to provide a basis from which to explore an underlying biorhythm. Biological anthropologists typically assume that RP remains constant within an individual and does not vary along the tooth-row. Here, we test that assumption. MATERIALS AND METHODS: RP was calculated from n = 223 thin sections of human permanent teeth from individuals of British and southern African origin. Forty individuals provided multiple teeth (n = 102 teeth) and a further 121 individuals each provided a single tooth. RESULTS: We report first evidence that RP of permanent teeth does not always remain constant within an individual. Of those individuals that provided multiple teeth, 42% (n = 17/40) demonstrated a decrease in RP along the tooth row, with most shifting by two or more days (n = 11). Across the entire sample, mean RP of anterior teeth was significantly higher than molars. Mean premolar RP tended to be intermediate between anterior teeth and molars. DISCUSSION: Our data do not support the assumption that RP invariably remains constant within the permanent teeth of an individual. Transferring RP from molars to incisors within an individual can result in a miscalculation of formation time and age-at-death by up to 1 year. Implications for biological anthropologists and the source of the underlying long period biorhythm are discussed.

Sex estimation of teeth at different developmental stages using dimorphic enamel peptide analysis.

OBJECTIVES: This study tests, for the first time, the applicability of a new method of sex estimation utilizing enamel peptides on a sample of deciduous and permanent teeth at different stages of mineralization, from nonadults of unknown sex, including perinates. MATERIALS AND METHODS: A total of 43 teeth from 29 nonadult individuals aged from 40 gestational weeks to 19 years old were analyzed. The sample included pairs of fully mineralized and just developing teeth from the same individual. The individuals were from four archaeological sites in England: Piddington (1st-2nd centuries AD), Coach Lane, Victoria Gate, and Fewston (all 18th-19th centuries). A method that identifies sex chromosome-linked isoforms of the peptide amelogenin from human tooth enamel was applied. The method utilizes a minimally destructive acid etching procedure and subsequent nano liquid chromatography tandem mass spectrometry. RESULTS: It was possible to determine the sex of 28 of the nonadult individuals sampled (males = 20, females = 8, undetermined = 1). Only one sample failed (CL9), due to insufficient mineralization of the sampled tooth enamel. Data are available via ProteomeXchange with identifier PXD021683. DISCUSSION: Sufficient peptide material to determine sex can be recovered even from the crowns of developing perinatal teeth that are not fully mineralized. The minimally destructive and inexpensive (compared to ancient DNA) nature of this procedure has significant implications for bioarchaeological studies of infancy and childhood.

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.

Assessment of physiological disturbances during pre- and early postnatal development based on microscopic analysis of human deciduous teeth from the Late Epipaleolithic site of Shubayqa 1 (Jordan).

OBJECTIVES: To study pre- and early postnatal tooth formation and to analyze the effects of physiological disturbances on enamel and dentin formation in deciduous teeth of infants from the Late Epipaleolithic (Natufian) site Shubayqa 1. MATERIALS AND METHODS: Ten deciduous teeth from six infants (ages at death between 21 and 239 days) were analyzed by light and scanning electron microscopy. RESULTS: Marked prism cross-striations and an abnormal wavy course of the prisms were recorded in pre- and postnatal enamel of all analyzed teeth. Single or multiple accentuated incremental lines were observed in prenatal enamel of nine teeth and in postnatal enamel of eight teeth. Accentuated Andresen lines and broader zones exhibiting an enhanced calcospheritic pattern were recorded in the pre- and postnatally formed dentin of nine teeth. DISCUSSION: The structural abnormalities in the pre- and postnatally formed enamel of the infants are considered indicative of chronic stress that negatively affected the activity of secretory ameloblasts. The structural aberrations in pre- and postnatal dentin denote that odontoblasts were also affected by this stress. The presence of single or multiple accentuated incremental lines in pre- and postnatal enamel is interpreted as reflecting (short-term) impacts of higher intensity superimposed on the chronic stress. Our findings suggest compromised maternal health affecting the late fetus and compromised health in newborns. Although limited by the small number of analyzed individuals, the present study contributes to the knowledge of maternal and early infant health conditions in Late Epipaleolithic populations.

Genetic variants in pachyonychia congenita-associated keratins increase susceptibility to tooth decay.

Pachyonychia congenita (PC) is a cutaneous disorder primarily characterized by nail dystrophy and painful palmoplantar keratoderma. PC is caused by mutations in KRT6A, KRT6B, KRT6C, KRT16, and KRT17, a set of keratin genes expressed in the nail bed, palmoplantar epidermis, oral mucosal epithelium, hair follicle and sweat gland. RNA-seq analysis revealed that all PC-associated keratins (except for Krt6c that does exist in the mouse genome) are expressed in the mouse enamel organ. We further demonstrated that these keratins are produced by ameloblasts and are incorporated into mature human enamel. Using genetic and intraoral examination data from 573 adults and 449 children, we identified several missense polymorphisms in KRT6A, KRT6B and KRT6C that lead to a higher risk for dental caries. Structural analysis of teeth from a PC patient carrying a p.Asn171Lys substitution in keratin-6a (K6a) revealed disruption of enamel rod sheaths resulting in altered rod shape and distribution. Finally, this PC-associated substitution as well as more frequent caries-associated SNPs, found in two of the KRT6 genes, that result in p.Ser143Asn substitution (rs28538343 in KRT6B and rs151117600 in KRT6C), alter the assembly of K6 filaments in ameloblast-like cells. These results identify a new set of keratins involved in tooth enamel formation, distinguish novel susceptibility loci for tooth decay and reveal additional clinical features of pachyonychia congenita.

Enamel multidien biological timing and body size variability among individuals of Chinese Han and Tibetan origins.

AIMS: To measure the number of days of enamel formation between periodic striae of Retzius growth lines, the Retzius periodicity (RP), and to compare this multi-day, or multidien rhythm, to body height and weight among people from Beijing, China and Lhasa, Tibet/China. SUBJECTS AND METHODS: Subjects requiring dental extractions from clinics in Beijing, China (N = 338) and Lhasa, Tibet/China (N = 227) provided a tooth and body size information. Multiple observers examined histological sections of the teeth and recorded RP. RP values were statistically compared to body height and weight. RESULTS: In Beijing and Lhasa samples, respectively, average height was 166.38 and 165.70 cm, average weight was 59.53 and 66.53 kg, and average RP was 7.47 and 7.69 d. Statistically significant differences were found between Beijing and Lhasa weight and RP means. Correlations for height and weight against RP were significant, but only comparatively strong for height. CONCLUSIONS: Supporting the negative correlation presented in previous studies, RP is negatively associated with height and weight among a large intraspecific sample of people from Beijing and Lhasa. RP represents a metabolic-mediated multidien biological timing mechanism responsible for the rate of cell proliferation and maintenance of the body.

A comprehensive survey of Retzius periodicities in fossil hominins and great apes.

Recent studies have provided great insight into hominin life history evolution by utilizing incremental lines found in dental tissues to reconstruct and compare the growth records of extant and extinct humans versus other ape taxa. Among the hominins, studies that have examined Retzius periodicity (RP) variation have come to contradictory conclusions in some instances. To clarify RP variation among hominins and better place this variation in its broader evolutionary context, we conduct the most comprehensive analysis of published RP values for hominins and great apes to date. We gathered all available data from the literature on RP data from extant humans, great apes, and fossil hominins and assessed their variation using parametric and nonparametric analyses of variance. We also performed phylogenetic generalized least-squares regressions of RP data for these taxa as well as a larger set of hominoids for which RP data have been published against data for body mass, encephalization, and mean semicircular canal radius (a proxy for metabolic rate). Our results show that modern humans have a mean RP significantly differing from that of other hominins. Pongo also is significantly different from nearly all other taxa in all analyses. Our results also demonstrate that RP variation among hominins scales with respect to body mass, encephalization, and semicircular canal radius similarly to other hominids but that modern humans and Pongo stand out in this regard. Operating within the hypothesis that RP reflects autonomic biorhythms that regulate multiple life history variables, our results reinforce the idea that Homo sapiens has evolved a life history distinct from other hominins, even from other members of Homo, and suggest that many of these life history differences may be driven by hypothalamic output from the brain.

Enamel thickness and growth rates in modern human permanent first molars over a 2000 year period in Britain.

OBJECTIVES: This study explores variation and trends in first molar enamel thickness and daily enamel secretion rates over a 2000 year period in Britain. METHODS: Permanent first molars (n = 89) from the Roman, Anglo-Saxon, and Medieval periods, as well as modern-day Britain, were analyzed using standard histological methods. Relative enamel thickness (RET) and linear measurements of cuspal and lateral thickness were calculated for mesial cusps. Daily secretion rates (DSRs) were calculated for inner, mid, and outer enamel regions in both cuspal and lateral enamel. Significant differences and trends were identified between samples using nonparametric statistical tests. RESULTS: Enamel thickness differed between some populations, but no temporal trends were identified. Early Anglo-Saxon molars had significantly thinner RET than both Late Anglo-Saxon (p < .00) and Medieval (p < .00) molars. Lateral enamel from the Roman molars was significantly thinner than the modern-day sample (p = .04). In contrast, a significant slowing trend in DSRs was observed across the more ancient to modern-day samples in every measured region except the mid-lateral enamel region. DISCUSSION: This study presents the first evidence for a gradual slowing in the daily rate that enamel is secreted in molars over the past 2000 years in Britain. However, this trend was not matched by consistent or significant positive or negative shifts in enamel thickness. These findings suggest that modern human molars of similar enamel thickness, from different modern and ancient populations, formed at different rates.

Enamel growth rates of anterior teeth in males and females from modern and ancient British populations.

OBJECTIVE: This study explored biological sex differences in the regional daily growth rates of human anterior enamel from modern and ancient populations in Britain. METHODS: Maxillary permanent incisors (n = 80) and canines (n = 69) from Roman, Anglo-Saxon, Medieval, and Modern day populations were analyzed using histological methods. Daily secretion rates (DSRs) were collected for inner, mid, and outer regions of cuspal and lateral enamel. Modern day samples were of known sex, archeological individuals had sex determined using standard osteological methods. Variation in DSRs between the sexes, both between and within populations, was sought using parametric and nonparametric tests. RESULTS: When all samples were pooled, there was no significant difference between males and females. Similarly no significant differences in DSRs were identified between male and females within each population. When DSRs were compared between the populations, DSRs decreased from the more ancient to the more recent populations for males, and for females. More interpopulation differences were observed in males. DISCUSSION: This study presents evidence for the relative consistency of enamel DSRs between male and female groups within each British population. Interpopulation analyses found DSRs slowed significantly between Roman and modern day populations for both sexes, with male DSRs showing the greatest variation between populations.

SATB1 establishes ameloblast cell polarity and regulates directional amelogenin secretion for enamel formation.

BACKGROUND: Polarity is necessary for epithelial cells to perform distinct functions at their apical and basal surfaces. Oral epithelial cell-derived ameloblasts at secretory stage (SABs) synthesize large amounts of enamel matrix proteins (EMPs), largely amelogenins. EMPs are unidirectionally secreted into the enamel space through their apical cytoplasmic protrusions, or Tomes' processes (TPs), to guide the enamel formation. Little is known about the transcriptional regulation underlying the establishment of cell polarity and unidirectional secretion of SABs. RESULTS: The higher-order chromatin architecture of eukaryotic genome plays important roles in cell- and stage-specific transcriptional programming. A genome organizer, special AT-rich sequence-binding protein 1 (SATB1), was discovered to be significantly upregulated in ameloblasts compared to oral epithelial cells using a whole-transcript microarray analysis. The Satb1-/- mice possessed deformed ameloblasts and a thin layer of hypomineralized and non-prismatic enamel. Remarkably, Satb1-/- ameloblasts at the secretory stage lost many morphological characteristics found at the apical surface of wild-type (wt) SABs, including the loss of Tomes' processes, defective inter-ameloblastic adhesion, and filamentous actin architecture. As expected, the secretory function of Satb1-/- SABs was compromised as amelogenins were largely retained in cells. We found the expression of epidermal growth factor receptor pathway substrate 8 (Eps8), a known regulator for actin filament assembly and small intestinal epithelial cytoplasmic protrusion formation, to be SATB1 dependent. In contrast to wt SABs, EPS8 could not be detected at the apical surface of Satb1-/- SABs. Eps8 expression was greatly reduced in small intestinal epithelial cells in Satb1-/- mice as well, displaying defective intestinal microvilli. CONCLUSIONS: Our data show that SATB1 is essential for establishing secretory ameloblast cell polarity and for EMP secretion. In line with the deformed apical architecture, amelogenin transport to the apical secretory front and secretion into enamel space were impeded in Satb1-/- SABs resulting in a massive cytoplasmic accumulation of amelogenins and a thin layer of hypomineralized enamel. Our studies strongly suggest that SATB1-dependent Eps8 expression plays a critical role in cytoplasmic protrusion formation in both SABs and in small intestines. This study demonstrates the role of SATB1 in the regulation of amelogenesis and the potential application of SATB1 in ameloblast/enamel regeneration.

Sonic Hedgehog Signaling and Tooth Development.

Sonic hedgehog (Shh) is a secreted protein with important roles in mammalian embryogenesis. During tooth development, Shh is primarily expressed in the dental epithelium, from initiation to the root formation stages. A number of studies have analyzed the function of Shh signaling at different stages of tooth development and have revealed that Shh signaling regulates the formation of various tooth components, including enamel, dentin, cementum, and other soft tissues. In addition, dental mesenchymal cells positive for Gli1, a downstream transcription factor of Shh signaling, have been found to have stem cell properties, including multipotency and the ability to self-renew. Indeed, Gli1-positive cells in mature teeth appear to contribute to the regeneration of dental pulp and periodontal tissues. In this review, we provide an overview of recent advances related to the role of Shh signaling in tooth development, as well as the contribution of this pathway to tooth homeostasis and regeneration.

Pig enamel revisited - Incremental markings in enamel of wild boars and domestic pigs.

The nature and periodicity of incremental markings in pig enamel is currently debated. To broaden the basis for a correct interpretation of growth marks in pig enamel, we analyzed their periodicity in teeth of wild boars and domestic pigs. For that, the numbers of enamel incremental markings were recorded in ground sections and compared with crown formation times for the respective teeth derived from literature data on tooth development and eruption in Sus scrofa. Our study revealed that laminations with a daily periodicity are the dominant incremental feature of pig enamel. In wild boar M3s, daily enamel secretion (apposition) rates ranged between a minimum of 6.1 µm in the inner and a maximum of 30.6 µm in the outer enamel. Long-period (supra-daily) incremental markings were present as perikymata at the outer enamel surface (OES). Contrary to the situation in primate enamel, in pig enamel the long-period incremental lines terminating in perikyma grooves were mostly structurally indistinguishable from the daily laminations. Typically, five sub-daily increments were present between successive laminations. The incremental pattern in pig enamel can be misinterpreted if the laminations are mistaken for long-period markings (striae of Retzius) and the sub-daily growth marks for daily prism cross-striations. The findings of the present study demonstrate the critical importance of correctly characterizing the incremental markings and their periodicity in enamel, and caution against an uncritical transfer of the interpretation of the nature of incremental markings in primate enamel to other mammalian taxa.

Mutations in the pH-Sensing G-protein-Coupled Receptor GPR68 Cause Amelogenesis Imperfecta.

Amelogenesis is the process of dental enamel formation, leading to the deposition of the hardest tissue in the human body. This process requires the intricate regulation of ion transport and controlled changes to the pH of the developing enamel matrix. The means by which the enamel organ regulates pH during amelogenesis is largely unknown. We identified rare homozygous variants in GPR68 in three families with amelogenesis imperfecta, a genetically and phenotypically heterogeneous group of inherited conditions associated with abnormal enamel formation. Each of these homozygous variants (a large in-frame deletion, a frameshift deletion, and a missense variant) were predicted to result in loss of function. GPR68 encodes a proton-sensing G-protein-coupled receptor with sensitivity in the pH range that occurs in the developing enamel matrix during amelogenesis. Immunohistochemistry of rat mandibles confirmed localization of GPR68 in the enamel organ at all stages of amelogenesis. Our data identify a role for GPR68 as a proton sensor that is required for proper enamel formation.

Age estimation using pulp/enamel volume ratio of impacted mandibular third molars measured on CBCT images in a northern Chinese population.

The present study aims to evaluate the relation between chronological age and the ratio of pulp volume (PV) to enamel volume (EV) of impacted mandibular third molars (IMTMs) by using cone-beam computed tomography (CBCT) images and an improved 3D image segmentation technique. A sample of CBCT images of IMTM was collected from 414 northern Chinese subjects (214 male and 200 female clinical patients) ranging in age from 20 to 65 years. The GrowCut effect image segmentation (GCEIS) module algorithm was used to calculate the PV and EV from CBCT images. The total sample was divided into a training group and validation group in a ratio of 7 to 3. The PV/EV ratio (PEr) in the training sample was used to develop a mathematical formula for age estimation as follows: age = - 5.817-21.726 × Ln PEr (p < 0.0001) (Ln, natural logarithm). The mean absolute error (MAE) and root mean square error (RMSE) were used to determine the precision and accuracy of the mathematical formula in the validation group and all samples. The MAEs in the male, female, and pooled gender samples were 9.223, 7.722, and 8.41, respectively, and the RMSEs in the male, female, and pooled gender samples were 10.76, 9.58, and 9.986, respectively. The precise and accurate results indicate that the PEr of IMTM in CBCT images is a potential index for dental age estimation and is possible to be used in forensic medicine.

Growth response of dental tissues to developmental stress in the domestic pig (Sus scrofa).

OBJECTIVES: To compare relative response of enamel, dentin and bone to developmental stressors between attritional and catastrophic mortality assemblages of pigs. MATERIALS AND METHODS: Heads from 70 Sus scrofa of known sex, weight and age comprising an attritional sample of 50 sick pen (SP) pigs that died prematurely versus 20 control pigs slaughtered at 6 months (Catastrophic assemblage). Hard tissue changes (alveolar bone thinning), abnormal bone formation (Harris lines) and re-modeling (auditory bullae) were recorded. Areas and volumes of coronal enamel and dentin were recorded from microCT scans with Avizo 6.3 and Geomagic Wrap. RESULTS: Attritional and catastrophic assemblages are metrically indistinguishable. Ages at death and tissue measures in the SP pigs are differentially distributed, necessitating partition into developmental outcome cohorts. SP "late death" pigs are of lesser physiological maturity than expected, free of disease, with large dental tissue dimensions, comparable to "Controls". SP "early death" pigs have 5% less dentin and enamel and chronic bone infection. Older cohorts of the SP "early deaths" mortality assemblage show progressively reduced enamel. SP pigs show dental evidence of reduced bone mass in the maxilla. DISCUSSION: Bone, dentin and enamel tissues, each, respond distinctively to developmental stressors. Bone mass evinces malnutrition not disease. Both dental tissue reduction and abnormal bone formation link to chronic infection. Paradoxically, reduced dentin mass signals lower survivorship while reduced enamel signals enhanced survivorship. Meaningful comparison of Attritional and Catastrophic assemblages necessitates recognition of developmental outcome cohorts, stratified by age at death and physiological maturity, to reveal heterogeneity of survivorship, tissue measures and lesions.