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Objective: Enamel laminations are closely spaced incremental lines that run parallel to Retzius lines or the developing enamel surface. Here, the timing of enamel laminations is calculated for naturally exfoliated deciduous molars (n = 111) from three modern-day populations (Aotearoa New Zealand, Britain and Canada)., Design: Teeth were sectioned using standard histological methods and examined using a high-powered microscope. Mean daily secretion rates (DSR) were calculated for the outer enamel of each molar in cuspal, lateral and cervical enamel regions. These DSRs were used to determine the periodicity of enamel growth across laminations in each region. Lamination periodicity was compared between populations and sexes, and within molars to assess the relationship between lamination periodicity and the angle between laminations and the outer surface., Results: Laminations were present in 57 % of all molars (n = 63 out of n = 111). Their presence did not vary between populations or by sex. A mean two-day periodicity was observed in cuspal and lateral outer enamel sampling regions. A mean one-day periodicity was observed in the cervical outer enamel. The angle of laminations relative to the outermost surface of the enamel was significantly related to the presence of laminations., Conclusions: A two-day periodicity for laminations indicates that this incremental marking is not a reliable proxy for a circadian 24-hour rhythm in human deciduous molars. The orientation of laminations was similar to Retzius lines but differed to the orientation of cross-striations., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: This study examines whether larger enamel prism diameters accommodate a greater enamel volume from the enamel-dentine junction (EDJ) to the outer-enamel surface (OES) in primate molars, and how prism size relates to enamel thickness and crown location., Design: We assessed variation in enamel prism diameter in relation to crown location and enamel thickness in catarrhine lower molars (n = 14 species) and one platyrrhine. Prism diameter and enamel thickness were recorded in four locations (lingual lateral; lingual cuspal; buccal cuspal; buccal lateral), using a buccal-lingual section through the centre of the mesial cusps. Ten prism diameter readings were collected at inner (near the EDJ), outer (near the OES) and middle (between the two locations) enamel for each location., Results: Mean prism diameter values for each species were similar (range: 4.06 µm to 5.81 µm). Prism diameter enlarged from inner to outer enamel, suggesting larger prisms help accommodate the increase in enamel volume from the EDJ to the OES. Average prism diameter does not associate with enamel thickness. Instead, cuspal positions had significantly smaller prism diameter at the EDJ than lateral positions, and larger prism sizes at the OES, leading to an overall similar prism diameter mean for all positions (Lingual lateral: 5.11 µm; Lingual cuspal: 5.04 µm; Buccal cuspal: 4.78 µm; Buccal lateral: 4.99 µm)., Conclusions: Our study revealed consistent average enamel prism diameters in various crown locations of lower primate molars, potentially contributing to the mechanical integrity and functional optimization of enamel in primates., Competing Interests: Declaration of Competing Interest The authors have no competing interest to disclose., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: Variation in enamel and dentine mineral concentration and total effective density can be reliably collected using Micro-CT scans. Both variables are suggested to reflect mechanical properties such as hardness and elastic modulus in dental tissues, meaning Micro-CT methods allow relative composition and mechanical properties to be collected non-destructively., Design: 16 lower molars from 16 Catarrhine primates were Micro-CT scanned alongside hydroxyapatite phantoms using standardized settings and methods to calculate mineral concentration and total effective density. Mineral concentration, total effective density and thickness of dentine and enamel were calculated for four cusps, representing each 'corner' of the tooth and four lateral crown positions (i.e., mesial, buccal, lingual and distal)., Results: The results show mean mineral concentration and total effective density values were higher in areas of thicker enamel, while the opposite was observed for dentine. Buccal positions had significantly higher mineral concentration and total effective density values than lingual areas. Cuspal positions had higher mean values than lateral enamel, for both dentine (mineral concentration cuspal: 1.26 g/cm 3 ; lateral: 1.20 g/cm 3 ) and enamel (mineral concentration cuspal: 2.31 g/cm 3 ; lateral: 2.25 g/cm 3 ). Mesial enamel had significantly lower values than other locations., Conclusions: These common patterns across Catarrhine taxa may be linked to functional adaptations related to optimization of mastication and tooth protection. Variation in mineral concentration and total effective density may also be associated with wear and fracture patterns, and can be used as baseline information to investigate the effect of diet, pathological changes and aging on teeth through time., Competing Interests: Declaration of Competing Interest None., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: To investigate the microstructure, elemental composition and mechanical properties of polar bear teeth., Design: Incisors, canines and fourth premolar teeth of two subadult male museum specimens were analysed. Teeth were measured, photographed, embedded in Epoxy resin, sectioned, polished and etched for scanning electron microscope (SEM) imaging, elemental composition and nanomechanical testing analyses., Results: The thickness of enamel ranged from 350-430 µm in canines, 220-330 µm in incisors and 320-510 µm in premolars. SEM images showed distinct transversely-oriented undulating Hunter Schreger bands from the enamel-dentine junction (EDJ) to the outer enamel surface. Enamel prisms had a hexagonal shape, with open prism sheaths. Prisms measured 6-8 µm in diameter. The EDJ was straight with no evidence of scalloping. Larger tubules adjacent to the EDJ were observed in the mantle dentine zone. Enamel Hardness and Elastic modulus values were higher in premolars (6.9 GPa and 269 GPa), followed by canines (6.5 GPa and 230 GPa) and incisors (4.9 GPa and 187 GPa). Dentine Hardness and Elastic modulus values were higher in canines. CaO and P 2 O 5 were the components with higher oxide weight percentage in both enamel and dentine., Conclusions: Understanding the microstructure, elemental composition and mechanical properties of polar bear teeth can help elucidate the biology and functional morphology of this globally threatened species and could be used as a proxy for studies with fossil ursids., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objective: To investigate and describe the variation in enamel daily secretion rates (DSRs) of naturally exfoliated deciduous molars (n = 345) from five modern-day populations (Aotearoa New Zealand, Britain, Canada, France, and Sweden)., Design: Each tooth was thin sectioned and examined using a high-powered Olympus BX51 microscope and DP25 digital microscope camera. Mean DSRs were recorded for the inner, mid, and outer regions of cuspal and lateral enamel, excluding enamel nearest the enamel-dentin junction and at the outermost crown surface., Results: Mean DSRs did not vary significantly between populations, or by sex. Cuspal enamel grew slightly faster than lateral enamel (mean difference 0.16 µm per day; p < 0.001). The trajectory of DSRs remained relatively constant from inner to outer cuspal enamel and increased slightly in lateral enamel (p = 0.003)., Conclusions: The DSRs of deciduous molars from modern-day children are remarkably consistent when compared among populations. While growth rates are faster in cuspal than lateral enamel, the trajectory of enamel formation changes only slightly from inner to outer regions. The trajectory of DSRs for deciduous molars differs to that of permanent molar enamel, which typically display a steep increase in matrix deposition from inner to outer enamel., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objectives: Tooth damage as a result of oral stereotypies is evident in captive orca, yet little research on the topic exists. This study examines the associations between dental pathology, sex, facility, duration of captivity and other factors in captive orca., Design: We evaluated mandibular and maxillary teeth from dental images of 29 captive orca owned by a US-based theme park. Each tooth was scored for coronal wear, wear at or below gum line and bore holes. Fractured and missing teeth were also noted. Summary statistics described the distribution and severity of pathologies; inferential statistics examined how pathologies differed between sexes, between wild-captured and captive-born orcas and between captive orca at four facilities. We also evaluated how dental pathology and duration of captivity were related., Results: Approximately 24% of whales exhibited "major" to "extreme" mandibular coronal tooth wear, with coronal wear and wear at or below gum line highly correlated. More than 60% of mandibular teeth 2 and 3 exhibited fractures. Bore holes were observed primarily among anterior mandibular teeth, with more than 61% of teeth 2 and 3 bearing evidence of having been drilled. Four of five orca with the highest age-adjusted tooth pathology indices were captive-born., Conclusions: Various dental pathologies were observed across all whales, with pathologies beginning at a young age. Oral stereotypies exhibited by captive orca contributed to the observed dental damage. By making dental and health records of captive whales publicly available, the theme park industry is uniquely positioned to provide further insight into dental pathology and resultant health consequences in captive orca., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

(1) Mammalian teeth play a major role in food acquisition and processing. While most mammals are heterodont and masticate their food, dolphins are homodont with simplified tooth morphology and negligible mastication. Understanding mechanical properties of dental tissues in dolphins is fundamental to elucidate the functional morphology and biomechanics of their feeding apparatus. This paper aims to study the hardness and elastic modulus of enamel and dentine in dolphins. (2) Teeth of 10 extant species (Inioidea and Delphinoidea) were longitudinally sectioned, polished and mounted in a UMIS nanoindenter. Indentations were performed from dentine to outer enamel. Hardness and elastic modulus were calculated using the Oliver-Pharr method. (3) Mean values of hardness and elastic modulus were similar on buccal and lingual surfaces. While dentine hardness was statistically similar among species, enamel hardness varied from 3.86GPa (±0.4) in Steno bredanensis (rough-toothed dolphin) to 2.36GPa (±0.38) in Pontoporia blainvillei (franciscana). For most species, there was a gradational increase in hardness values from inner to outer enamel. Enamel and dentine elastic modulus values clearly differed among species. In enamel, it ranged from 69.32GPa (±4.08) in the rough-toothed dolphin to 13.51GPa (±2.80) in Stenella coeruleoalba (striped dolphin). For most species, elastic modulus values were highest at inner and outer enamel. (4) Differences in mechanical properties between species, and within the enamel of each species, suggest functional implications and influence of ultrastructural arrangement and chemical composition., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

(1) Dental wear is a common phenomenon in mammals. Its occurrence is influenced by tooth anatomy, animal physiology, biomechanics and behaviour. So far, investigations of dental wear in cetaceans have been scanty and superficial. We compare the frequencies of occurrence, location and intensity of dental wear in some species of dolphins from southern Brazil, South Atlantic Ocean. (2) Teeth of ten species were evaluated using a stereoscopic microscope to identify wear facets, which were classified according to location, anatomical position and wear intensity. (3) Frequencies of dental wear were high for all species with exception of Delphinus capensis, with less than 50% of teeth worn. Simultaneous wear facets in the apex and lateral of teeth were more common than facets restricted to the apex or lateral faces. Wear on the dental crown was more common, but some species showed less frequent wear down to the cingulum or root level. Superficial wear seems to be the general trend for dolphins, but Stenella coeruleoalba and Pseudorca crassidens showed a higher frequency of severe wear. Only for Tursiops truncatus the frequencies of wear were significantly different between males and females. When considering the ontogeny of dental wear, only for T. truncatus and Stenella frontalis indexes of dental wear were correlated with body length. (4) Whether dental wear has implications or not in fitness and feeding behaviour, severely worn teeth may expose the pulp cavity and increase the susceptibility to local infections., (Copyright © 2012 Elsevier Ltd. All rights reserved.)