Local Irradiation of Mouse Tooth Germ Gives Insight into the Direct Effects of Irradiation on Root Development.

To elucidate the mechanism underlying the failure of root formation after irradiation, we established a method of local irradiation of the molar tooth germ and demonstrated that radiation directly affected dental root development. In the current study, to locally irradiate the lower first molars of 5-day-old C57BL/6J mice, we used lead glass containing a hole as a collimator. We confirmed that our local irradiation method targeted only the tooth germ. The irradiated root was immature in terms of apical growth, and dentin formation was irregular along the outside of the root apices. Moreover, calcified tissue apically surrounded Hertwig's epithelial root sheath, which disappeared abnormally early. This method using a local irradiation experimental model will facilitate research into radiation-induced disorders of dental root formation.

Biomineralization of Collagen-Based Materials for Hard Tissue Repair.

Hydroxyapatite (HA) reinforced collagen fibrils serve as the basic building blocks of natural bone and dentin. Mineralization of collagen fibrils play an essential role in ensuring the structural and mechanical functionalities of hard tissues such as bone and dentin. Biomineralization of collagen can be divided into intrafibrillar and extrafibrillar mineralization in terms of HA distribution relative to collagen fibrils. Intrafibrillar mineralization is termed when HA minerals are incorporated within the gap zone of collagen fibrils, while extrafibrillar mineralization refers to the minerals that are formed on the surface of collagen fibrils. However, the mechanisms resulting in these two types of mineralization still remain debatable. In this review, the evolution of both classical and non-classical biomineralization theories is summarized. Different intrafibrillar mineralization mechanisms, including polymer induced liquid precursor (PILP), capillary action, electrostatic attraction, size exclusion, Gibbs-Donnan equilibrium, and interfacial energy guided theories, are discussed. Exemplary strategies to induce biomimetic intrafibrillar mineralization using non-collagenous proteins (NCPs), polymer analogs, small molecules, and fluidic shear stress are discussed, and recent applications of mineralized collagen fibers for bone regeneration and dentin repair are included. Finally, conclusions are drawn on these proposed mechanisms, and the future trend of collagen-based materials for bone regeneration and tooth repair is speculated.

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.

Blurred time resolution of tooth dentin serial sections.

OBJECTIVES: The growth of tooth dentin is incremental, so its formation represents a dietary record in early life. With archeological skeletons, applying sequential stable isotope analysis to the horizontal sections of tooth dentin has revealed weaning patterns and dietary changes that took place during childhood. However, the assignment of ages to dentin serial sections (DSSs) is problematic due to the changing extension rate and oblique growth layers of dentin, and these effects have not been quantified. This study presents a mathematical model for investigating the corresponding age range of the horizontal DSSs of human permanent incisors, canines, and molars. METHODS: Parameters describing the tooth dentin microstructure were taken from previous studies, and dentin growth patterns were modeled. The model was implemented as the R package MDSS. RESULTS: The developed model shows that the true corresponding age of the sections differed by a few years on average from the estimated age with equal temporal divisions, that the model gave values extending across a wide range, and that these differences become large for sections formed at older ages. The stable isotope ratio of the sections presented an aggregate representation of possibly complex dietary changes across a few years, and dietary changes over short times, such as several months, could not be accurately reconstructed even when using a finer horizontal sectioning method. CONCLUSIONS: These results demonstrate that DSSs correspond to an unexpectedly wider (i.e., three to four times) and different (i.e., -2 to 0.5 years on average) age range than previously assumed and that complicated patterns of dietary change blur in the isotopic trajectory of the sections. Alternative experimental methods, such as imaging-assisted oblique sampling, should be used to retrieve an accurate and precise sequential dietary record from tooth dentin.

Combinations of propolis and Ca(OH)2 in dental pulp capping treatment for the stimulation of reparative dentin formation in a rat model.

Background: Caries in the dental pulp result in inflammation and damage to the pulp tissue. During inflammation of the pulp, various inflammatory mediators and growth factors are released, including IL-8, IL-10, TLR-2, VEGF and TGF-ß through the NF-kB pathway. In the present study, therapy for pulpal caries was performed through pulp capping by giving a combination of propolis and calcium hydroxide (Ca(OH)2). This treatment was expected to stimulate the formation of reparative dentin as an anti-inflammatory material to prevent pulp tissue damage. Methods: 28 Wistar rats were divided into four groups and treated with Ca(OH)2 with or without the addition of propolis for either 7 or 14 days. Immunohistochemical examination was used to determine the expression of IL-8, IL-10, TLR-2, VEGF, TGF-ß in the four treatment groups. Results: The group treated with a combination of propolis and Ca(OH)2 for 7 days showed that the expression of IL-10, IL-8, TLR-2, VEGF, TGF-ß increased significantly compared to the treatment group treated with only Ca(OH)2. The expression of IL-10, TLR-2, TGF-ß, VEGF increased in the treatment group treated with propolis and Ca(OH)2 for 14 days, while the expression of IL-8 in the decreased significantly. Conclusions: Administration of a combination of propolis and Ca(OH)2 has efficacy in the pulp capping treatment process because it has anti-bacterial and immunomodulatory properties. The results show that it is able to stimulate the process of pulp tissue repair through increased expression of IL-10, TGF-ß, VEGF, TLR -2 and decreased expression of IL-8.

Biological clocks and incremental growth line formation in dentine.

Dentine- and enamel-forming cells secrete matrix in consistent rhythmic phases, resulting in the formation of successive microscopic growth lines inside tooth crowns and roots. Experimental studies of various mammals have proven that these lines are laid down in subdaily, daily (circadian), and multidaily rhythms, but it is less clear how these rhythms are initiated and maintained. In 2001, researchers reported that lesioning the so-called master biological clock, the suprachiasmatic nucleus (SCN), halted daily line formation in rat dentine, whereas subdaily lines persisted. More recently, a key clock gene (Bmal1) expressed in the SCN in a circadian manner was also found to be active in dentine- and enamel- secretory cells. To probe these potential neurological and local mechanisms for the production of rhythmic lines in teeth, we reexamined the role of the SCN in growth line formation in Wistar rats and investigated the presence of daily lines in Bmal1 knockout mice (Bmal1-/- ). In contrast to the results of the 2001 study, we found that both daily and subdaily growth lines persisted in rat dentine after complete or partial SCN lesion in the majority of individuals. In mice, after transfer into constant darkness, daily rhythms continued to manifest as incremental lines in the dentine of each Bmal1 genotype (wild-type, Bmal+/- , and Bmal1-/- ). These results affirm that the manifestation of biological rhythms in teeth is a robust phenomenon, imply a more autonomous role of local biological clocks in tooth growth than previously suggested, and underscore the need further to elucidate tissue-specific circadian biology and its role in incremental line formation. Investigations of this nature will strengthen an invaluable system for determining growth rates and calendar ages from mammalian hard tissues, as well as documenting the early lives of fossil hominins and other primates.

Histological and developmental insights into the herbivorous dentition of tapinocephalid therapsids.

Tapinocephalids were one of the earliest therapsid clades to evolve herbivory. In acquiring derived tooth-to-tooth occlusion by means of an exaggerated heel and talon crown morphology, members of this family have long been considered herbivorous, yet little work has been done to describe their dentition. Given the early occurrence of this clade and their acquisition of a dentition with several derived features, tapinocephalids serve as an important clade in understanding adaptations to herbivory as well as macroevolutionary patterns of dental trait acquisition. Here we describe the histology of tapinocephalid jaws and incisors to assess adaptations to herbivory. Our results yield new dental characters for tapinocephalids including a peculiar enamel structure and reduced enamel deposition on the occlusal surface. These traits are convergent with other specialized herbivorous dentitions like those found in ornithischian dinosaurs and ungulates. Furthermore, these results demonstrate that while acquiring some specializations, tapinocephalids also retained plesiomorphic traits like alternate, continuous replacement. We interpret these findings as an example of how different combinations of traits can facilitate a derived and specialized dentition and then discuss their implications in the acquisition of a mammal-like dentition.

Osteoadherin serves roles in the regulation of apoptosis and growth in MC3T3­E1 osteoblast cells.

Small leucine­rich proteoglycans (SLRPs) are a class of proteoglycans that are characterized by small protein cores and structures of leucine­rich repeats. SLRPs are expressed in most extracellular matrices and share numerous biological functions that are associated with binding of collagens and cell surface receptors. Osteoadherin (also termed osteomodulin) is encoded by the Omd gene and is a keratan sulfate proteoglycan of the class II subfamily of SLRPs. Osteoadherin is highly expressed in mineralized tissues, including bone and dentin; however, it's precise roles remain unknown. The present study determined the Omd expression levels and investigated the effects of over­ and under­expression of osteoadherin in osteoblastic cells. Omd mRNA expression increased with osteoblast differentiation in MC3T3­E1 cells. In C2C12 cells, Omd mRNA expression was induced by bone morphogenetic protein (BMP)2. Reporter assays similarly demonstrated activation of the Omd gene promoter following co­transfection with Smad1 and Smad4, which are intracellular signaling molecules of the BMP2 signaling pathway. Overexpression of Omd increased the viability and decreased caspase 3/7 activity in MC3T3­E1 cells. By contrast, following transfection with small interfering RNA for Omd, viable cell numbers were decreased and caspase 3/7 activity was increased. Furthermore, overexpression of Omd reduced the expression of CCN family 2 in these cells. These results demonstrate that Omd expression is regulated during osteoblast differentiation, and that the protein product osteoadherin serves roles in the apoptosis and growth of osteoblast cells.

Protocols for Studying Formation and Mineralization of Dental Tissues In Vivo: Extraction Protocol for Isolating Dentin Matrix Proteins from Developing Teeth.

The organic material in developing dentin is 90% type I collagen and 10% non-collagenous proteins. The key to understanding dentin biomineralization is to study how these proteins collectively precipitate and organize hydroxyapatite crystals. The first step in characterizing the proteins within a mineralizing matrix is to efficiently extract and isolate the essential molecular participants and elucidate their structural and biochemical properties. In this study, we expanded previous approaches to develop an improved strategy for the extraction of extracellular matrix proteins from the dentin of developing teeth. Proteins in dentin powder were sequentially extracted in the order Tris-guanidine buffer, HCl-formic acid solution, acetic acid-NaCl solution, Tris-NaCl buffer, and a second Tris-guanidine buffer. Individual fractions were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), by gelatin or casein zymography, and by Western blot analysis using dentin sialoprotein (DSP)- or dentin glycoprotein (DGP)-specific antibodies. This approach was used to purify assorted porcine dentin non-collagenous proteins.

Dentinogenesis and Tooth-Alveolar Bone Complex Defects in BMP9/GDF2 Knockout Mice.

Tooth development is regulated by sequential and reciprocal epithelium-mesenchymal interactions and their related molecular signaling pathways, such as bone morphogenetic proteins (BMPs). Among the 14 types of BMPs, BMP9 (also known as growth differentiation factor 2) is one of the most potent BMPs to induce osteogenic differentiation of mesenchymal stem cells. The purpose of this study was to examine potential roles of BMP9 signaling in tooth development. First, we detected the expression pattern of BMP9 in tooth germ during postnatal tooth development, and we found that BMP9 was widely expressed in odontoblasts, ameloblasts, dental pulp cells, and osteoblasts in alveolar bones. Then, we established a BMP9-KO mouse model. Gross morphological examination revealed that the tooth cusps of BMP9-KO mice were significantly abraded with shorter roots. Micro-computed tomography and three-dimensional reconstruction analysis indicated that the first molars of the BMP9-KO mice exhibited a reduced thickness dentin, enlarged pulp canals, and shortened roots, resembling the phenotypes of the common hereditary dental disease dentinogenesis imperfecta. Further, the alveolar bone of the BMP9-KO mutants was found to be shorter and had a decreased mineral density and trabecular thickness and bone volume fraction compared with that of the wild-type control. Mechanistically, we demonstrated that both dentin sialophosphoprotein and dentin matrix protein 1 were induced in dental stem cells by BMP9, whereas their expression was reduced when BMP9 was silenced. Further studies are required to determine whether loss of or decreased BMP9 expression is clinically associated with dentinogenesis imperfecta. Collectively, our results strongly suggest that BMP9 may play an important role in regulating dentinogenesis and tooth development. Further research is recommended into the therapeutic uses of BMP9 to regenerate traumatized and diseased tissues and for the bioengineering of replacement teeth.

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.

Effect of attenuation of fibroblast growth factor receptor 2b signaling on odontoblast differentiation and dentin formation.

Attenuation of fibroblast growth factor receptor (FGFR) 2b signaling suppresses the differentiation of oral epithelial stem cells to ameloblasts, their survival and viability remaining unaffected; however, its effect on dentin formation is unknown. This study aimed to clarify the effect of attenuation of FGFR2b signaling on odontoblast differentiation and dentin formation. Initially, we used a murine rtTA transactivator/tetracycline promoter system for inducible and reversible attenuation of FGFR2b signaling in adult mice. Experimental animals overexpressed soluble FGFR2b (sFGFR2b), and wild-type controls were selected from the same litter (WT group). Histological analysis of CMV mice confirmed the obliteration of the enamel and ameloblast layer, and micro CT analysis revealed a significant increase in dentin thickness in CMV mice rather than in WT mice (P < 0.05). On analyzing the expression of dentin-related differentiation factors, DSPP, nestin, and OCN were upregulated in CMV mice compared to WT mice after 2 weeks of attenuation of FGFR2b signaling. Thereafter, on overexpressing sFGFR2b in dental pulp stem cells, RUNX2 and ALP were upregulated; however, DSPP, nestin, and OCN were downregulated in CMV mice compared to WT mice. The present results show that attenuation of FGFR2b signaling in the oral epithelium specifically induced odontoblast differentiation and promotes early-stage dentin calcification in dental pulp tissue.

Numerical investigations of bone remodelling around the mouse mandibular molar primordia.

The formation of the alveolar bone, which houses the dental primordia, and later the roots of tooth, may serve as a model to approach general questions of alveolar bone formation. In this respect, this study aimed to investigate the potential interactions between the alveolar bone formation and tooth eruption by using finite element (FE) methods, and to figure out whether the expanding tooth systems induce shear stresses that lead to alveolar bone formation. 3D geometric surface models were generated from the 3D histological data of the heads of mice (C57 Bl/6J) ranging from stages embryonic (E) to postnatal (P) stages E15 to P20 using the reconstruction software 3-Matic. Bone, dentin, enamel and dental follicle around the primordia were generated and converted into 3D FE models. Models were imported into the FE software package MSC.Marc/Mentat. As material parameters of embryonic dentine, pulp, enamel, dental follicle, and bony structures basically are unknown, these were varied from 1% to 100% of the corresponding known material parameters for humans and a sensitivity analysis was performed. Surface loads were applied to the outside surface of dental follicle ranging from 0.1 to 5.0N/mm2. The validity of the model was analysed by comparing the activity pattern of the alveolar bone as determined in the histological study with the loading pattern from the numerical analysis. The results show that when varying the surface loads, the distribution of shear stresses remained same, and while varying the material properties of the hard tissues, the location of highest shear stresses remained stable. Comparison of the histologically determined growth regions with the distribution of shear stresses computed in the numerical model showed a very close agreement. The results provide a strong proof to support Blechschmidt's hypothesis that the bone in general is created under the influence of shear forces.

Activation of αSMA expressing perivascular cells during reactionary dentinogenesis.

AIM: To examine the contribution of perivascular cells expressing αSMA to reactionary dentinogenesis. METHODOLOGY: An inducible, Cre-loxP in vivo fate-mapping approach was used to examine the contribution of the descendants of cells expressing the αSMA-CreERT2 transgene to reactionary dentinogenesis in mice molars. Reactionary dentinogenesis was induced by experimental mild injury to dentine without pulp exposure. The Student's t test was used to determine statistical significance at *P ≤ 0.05. RESULTS: The lineage tracing experiments revealed that mild injury to dentine first led to activation of αSMA-tdTomato+ cells in the entire pulp chamber. The percentage of areas occupied by αSMA-tdTomato+ in injured (7.5 ± 0.7%) teeth were significantly higher than in teeth without injury (2 ± 0.5%). After their activation, αSMA-tdTomato+ cells migrated towards the site of injury, gave rise to pulp cells and a few odontoblasts that became integrated into the existing odontoblast layer expressing Col2.3-GFP and Dspp. CONCLUSION: Mild insult to dentine activated perivascular αSMA-tdTomato+ cells giving rise to pulp cells as well as a few odontoblasts that were integrated into the pre-existing odontoblast layer.

The role of bone morphogenetic proteins 2 and 4 in mouse dentinogenesis.

OBJECTIVE: The bone morphogenetic proteins (BMPs) play crucial roles in tooth development. However, several BMPs retain expression in the dentin of the fully patterned and differentiated tooth. We hypothesized that BMP signaling therefore plays a role in the function of the differentiated odontoblast, the job of which is to lay down and mineralize the dentin matrix. DESIGN: We generated mice deficient in Bmp2 and 4 using a dentin matrix protein 1 (Dmp1) promoter-driven cre recombinase that was expressed in differentiated odontoblasts. RESULTS: The first and second molars of these Bmp2 and Bmp4 double conditional knockout (DcKO) mice displayed reduced dentin and enlarged pulp chambers compared to cre-negative littermate controls. DcKO mouse dentin in first molars was characterized by small, disorganized dentinal fibers, a wider predentin layer, and reduced expression of dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP1), and bone sialoprotein (BSP). DcKO mouse odontoblasts demonstrated increased type I collagen mRNA production, indicating that the loss of BMP signaling altered the rate of collagen gene expression in these cells. Bmp2 and Bmp4 single Dmp1-cre knockout mice displayed no discernable dentin phenotype. CONCLUSIONS: These data demonstrate that BMP signaling in differentiated odontoblasts is necessary for proper dentin production in mature teeth.

On the Modes of the Formation of the Exoskeleton in Early Jawless Vertebrates (Osteostraci, Agnatha).

Based on recently obtained original and published data on the fine structure of the external skeleton of osteostracan agnathans (Osteostraci, Agnatha), possible modes of the formation of their hard cover in the course of the horizontal growth of the exoskeleton are characterized. The developmental models for the formation of various configurations of cephalothoracic shields typical for osteostracans are revealed. It is shown that, in the morphogenesis of the hard cover of this group of early vertebrates, a significant part of the variants of the exoskeleton horizontal growth characteristic of early vertebrates are observed.

Validation of Growth Layer Group (GLG) depositional rate using daily incremental growth lines in the dentin of beluga (Delphinapterus leucas (Pallas, 1776)) teeth.

Counts of Growth Layer Groups (GLGs) in the dentin of marine mammal teeth are widely used as indicators of age. In most marine mammals, observations document that GLGs are deposited yearly, but in beluga whales, some studies have supported the view that two GLGs are deposited each year. Our understanding of beluga life-history differs substantially depending on assumptions regarding the timing of GLG deposition; therefore, resolving this issue has important considerations for population assessments. In this study, we used incremental lines that represent daily pulses of dentin mineralization to test the hypothesis that GLGs in beluga dentin are deposited on a yearly basis. Our estimate of the number of daily growth lines within one GLG is remarkably close to 365 days within error, supporting the hypothesis that GLGs are deposited annually in beluga. We show that measurement of daily growth increments can be used to validate the time represented by GLGs in beluga. Furthermore, we believe this methodology may have broader applications to age estimation in other taxa.

Uncovering neurodevelopmental windows of susceptibility to manganese exposure using dentine microspatial analyses.

BACKGROUND: Associations between manganese (Mn) and neurodevelopment may depend on dose and exposure timing, but most studies cannot measure exposure variability over time well. OBJECTIVE: We apply temporally informative tooth-matrix biomarkers to uncover windows of susceptibility in early life when Mn is associated with visual motor ability in childhood. We also explore effect modification by lead (Pb) and child sex. METHODS: Participants were drawn from the ELEMENT (Early Life Exposures in MExico and NeuroToxicology) longitudinal birth cohort studies. We reconstructed dose and timing of prenatal and early postnatal Mn and Pb exposures for 138 children by analyzing deciduous teeth using laser ablation-inductively coupled plasma-mass spectrometry. Neurodevelopment was assessed between 6 and 16 years of age using the Wide Range Assessment of Visual Motor Abilities (WRAVMA). Mn associations with total WRAVMA scores and subscales were estimated with multivariable generalized additive mixed models. We examined Mn interactions with Pb and child sex in stratified models. RESULTS: Levels of dentine Mn were highest in the second trimester and declined steeply over the prenatal period, with a slower rate of decline after birth. Mn was positively associated with visual spatial and total WRAVMA scores in the second trimester, among children with lower (< median) tooth Pb levels: one standard deviation (SD) increase in ln-transformed dentine Mn at 150 days before birth was associated with a 0.15 [95% CI: 0.04, 0.26] SD increase in total score. This positive association was not observed at high Pb levels. In contrast to the prenatal period, significant negative associations were found in the postnatal period from ~ 6 to 12 months of age, among boys only: one SD increase in ln-transformed dentine Mn was associated with a 0.11 [95% CI: - 0.001, - 0.22] to 0.16 [95% CI: - 0.04, - 0.28] SD decrease in visual spatial score. CONCLUSIONS: Using tooth-matrix biomarkers with fine scale temporal profiles of exposure, we found discrete developmental windows in which Mn was associated with visual-spatial abilities. Our results suggest that Mn associations are driven in large part by exposure timing, with beneficial effects found for prenatal levels and toxic effects found for postnatal levels.

Do Mid-Crown Enamel Formation Front Angles Reflect Factors Linked to the Pace of Primate Growth and Development?

Enamel formation front (EFF) angles represent the leading edge of enamel matrix secretion at particular points in time. These angles are influenced by rates of enamel extension (the rates at which tooth crowns grow in height), rates of enamel matrix secretion and the angles that prisms make with the enamel-dentine junction. Previous research suggests, but has not yet established, that these angles reflect aspects of primate biology related to their pace of growth and development, most notably brain and body size. The present study tested this possibility on histological sections using phylogenetically-controlled and Bonferroni-corrected analyses spanning a broad taxonomic range. Ten species were represented in the analysis of anterior teeth; 17 in the analysis of posterior (postcanine) teeth (with varying sample sizes). Also, tested was the relationship of EFF angles to striae of Retzius periodicity (long period growth rhythms in enamel) and degree of folivory, as both factors are related to primate developmental rates. Finally, several analyses were conducted to investigate whether tooth size (operationalized as EDJ length) might mediate these relationships. Central results are as follows: (1) Relationships between EFF angles and brain weight (anterior teeth) and between EFF angles and body mass (anterior and posterior teeth) are statistically significant and (2) Mid-crown EFF angles are not statistically significantly related to EDJ lengths. These results suggest that tooth size does not mediate relationships between EFF angles and brain weight/body mass and are discussed with respect to underlying enamel growth variables (especially rates of enamel extension and secretion). Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:125-139, 2018. © 2017 Wiley Periodicals, Inc.

Age estimation using Olze's method in an adult Brazilian population.

OBJECTIVES: Age estimation is important to set an anthropological profile in human remains, as well as in legal issues where the suspect or victim doesn't have documents that prove the real age. The age estimation, in adults, is a challenge, and it can be analyzed through some dental stages. This study aimed to test Olze's method in a Brazilian sample composed by adults, aged between 20 and 70 years old, both sex. METHODS: For experiments, 306 orthopantomography from Brazilian individuals between 20 and 70 years were selected. The dental involution through four different dental parameters were classified and the correlation between chronological age and the estimated age was examined by means of a multiple regression analysis. RESULTS: The results showed that up to 41 years old, the correlation between real age and the interval obtained was considered strongly positive (R = 0.8-1), and the percentage of matching was 78.78% for men and 71.21% for women. From 42 years old up, the correlation between real age and the estimation was considered null (R = 0) for both sex, and the percentage of matching was 17.24% for men and 6.89% for women. CONCLUSION: It could be concluded that the method is effective for age estimation up to 41 years old, but has limitations to be used over this age in Brazilian people.