Tooth Microstructure Research Articles

Effects of Acid Etching on the Microstructure and Stiffness of Human Teeth

Abstract The mechanical properties of acid-etched enamel and dentin are important for understanding tooth erosion and developing innovative dental restorative materials. In this study, the microstructure and mechanical properties of both enamel and dentin were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to quantify the impact of acid etching. SEM images demonstrated that enamel rods have a diameter of approximately 5 μm, while dentinal tubules have a diameter of around 2 μm. After acid etching, the intertubular and peritubular regions were exposed, with the peritubular regions showing a thickness of approximately 1 μm. AFM measurements showed that the stiffness of enamel at the bottom, middle, and top layers is 26.28±4.24 GPa, 32.03±8.68 GPa, and 23.94±3.53 GPa, respectively. For dentin, the stiffness is 16.28±2.76 GPa at the bottom layer and 17.59±5.33 GPa at the middle layer. AFM morphology and stiffness maps illustrated the microstructures of enamel rod and sheaths, as well as dentin tubules in both unetched and acid-etched tooth sections. The stiffness of the acid-etched enamel rod and peritubular dentin decreased by 7-fold and 3.6-fold, respectively, compared to the unetched enamel rod and peritubular dentin.

Oxygen self-sufficient nanodroplet composed of fluorinated polymer for high-efficiently PDT eradicating oral biofilm

Oral biofilm is the leading cause of dental caries, which is difficult to completely eradicate because of the complicated biofilm structure. What's more, the hypoxia environment of biofilm and low water-solubility of conventional photosensitizers severely restrict the therapeutic effect of photodynamic therapy (PDT) for biofilm. Although conventional photosensitizers could be loaded in nanocarriers, it has reduced PDT effect because of aggregation-caused quenching (ACQ) phenomenon. In this study, we fabricated an oxygen self-sufficient nanodroplet (PFC/TPA@FNDs), which was composed of fluorinated-polymer (FP), perfluorocarbons (PFC) and an aggregation-induced emission (AIE) photosensitizer (Triphenylamine, TPA), to eradicate oral bacterial biofilm and whiten tooth. Fluorinated-polymer was synthesized by polymerizing (Dimethylamino)ethyl methacrylate, fluorinated monomer and 1-nonanol monomer. The nanodroplets could be protonated and behave strong positive charge under bacterial biofilm acid environment promoting nanodroplets deeply penetrating biofilm. More importantly, the nanodroplets had extremely high PFC and oxygen loading efficacy because of the hydrophobic affinity between fluorinated-polymer and PFC to relieve the hypoxia environment and enhance PDT effect. Additionally, compared with conventional ACQ photosensitizers loaded system, PFC/TPA@FNDs could behave superior PDT effect to ablate oral bacterial biofilm under light irradiation due to the unique AIE effect. In vivo caries animal model proved the nanodroplets could reduce dental caries area without damaging tooth structure. Ex vivo tooth whitening assay also confirmed the nanodroplets had similar tooth whitening ability compared with commercial tooth whitener H2O2, while did not disrupt the surface microstructure of tooth. This oxygen self-sufficient nanodroplet provides an alternative visual angle for oral biofilm eradication in biomedicine.

Comparative study on the effects of different polishing methods on tooth surface microstructure and roughness following initial periodontal treatment.

To investigate the effects of different polishing methods on the surface microstructure and roughness of teeth following initial periodontal treatment. Teeth were divided into three groups (silica onegloss, polishing disc, and polishing strip) in vitro. Tooth surface microstructure was characterized via scanning electron microscopy. Roughness was measured by profilometry and laser scanning confocal microscopy (LSCM). According to the in vitro results, one group was chosen for further clinical trials. Effects of the chosen polishing method on patient plaque control and satisfaction were assessed via plaque staining and visual analog scale (VAS). Electron microscopy results revealed that the polishing disc group had smoother roots and crowns than did the other two groups. Roughness analysis revealed that the crown roughness with the polishing disc and silica onegloss was lower, and the root roughness with the polishing disc was the lowest (p < .05) The LSCM results showed that the pigment deposition depth with the polishing disc and silicon onegloss in the crowns and roots were significantly lower than those with the other two methods (p = .000). The polishing effect of the polishing disc was best among the three groups. Clinical trials were performed to verify the polishing disc effects. Plaque staining results showed that the decrease in plaque in the polishing disc group was greater than that ofthe rubber cup group (p = .020), which was similar to the results of LSCM. The VAS results showed that the polishing disc made teeth feel smoother, similar to the results of the roughness detection, and the procedure was more comfortable (p < .05). However, there was no significant difference between the two groups regarding foreign body sensation during pronunciation (p = .178). Combining in vitro and in vivo evaluations, the use of a polishing disc following periodontal treatment yielded superior polishing effects on teeth and was better accepted by patients.

Lower hardness than strength: The auxetic composite microstructure of limpet tooth.

The limpet tooth is widely recognized as nature's strongest material, with reported strength values up to 6.5 GPa. Recently, microscale auxeticity has been discovered in the leading part of the tooth, providing a possible explanation for this extreme strength. Utilizing micromechanical experiments, we find hardness values in nanoindentation that are lower than the respective strength observed in micropillar compression tests. Using micromechanical modeling, we show that this unique behavior is a result of local tensile strains during indentation, originating from the microscale auxeticity. As the limpet tooth lacks ductility, these tensile strains lead to microdamage in the auxetic regions of the microstructure. Consequently, indentation with a sharp indenter always probes a damaged version of the material, explaining the lower hardness and modulus values gained from nanoindentation. Micropillar tests were found to be mostly insensitive to such microdamage due to the lower applied strain and are therefore the suggested method for characterizing auxetic nanocomposites. STATEMENT OF SIGNIFICANCE: This work explores the micromechanical properties of limpet teeth, nature's strongest biomaterial, using micropillar compression testing and nanoindentation. The limpet tooth microstructure consists of ceramic nanorods embedded in a matrix of amorphous SiO2 and arranged in a pattern that leads to local auxetic behavior. We report lower values for nanoindentation hardness than for compressive strength, a unique behavior usually not achievable in conventional materials. Utilizing micromechanical finite element simulations, we identify the reason for this behavior to be microdamage formation resultant of the auxetic behavior, sharp indenter tip and lack of ductility of the limpet tooth microstructure. This formation of microdamage is not expected in micropillar compression tests due to lower locally imposed strain.

A preliminary analysis of dental microstructure in Hamipterus (Pterosauria, Pterodactyloidea).

The toothed members of Pterosauria display an extremely wide range of tooth morphologies that supported a variety of feeding habits. Histological studies on the teeth of different pterosaur clades are potentially valuable in understanding the development of their tooth diversity. In this study, we used histological sections and scanning electron microscopy to describe and interpret the tooth microstructure of Hamipterus (Pterodactyloidea). Our analysis is based on seven teeth of Hamipterus (six isolated and one from a skull) from the Lower Cretaceous collected in Hami, China. Our results show that the enamel on the tooth crown is thin (~25 μm) in Hamipterus and covers only approximately half of the tooth crown. This thin enamel of the Hamipterus tooth makes it vulnerable and often becomes damaged during taphonomic and diagenetic processes. The radicular pulp inside the conical-shaped root shows a spindle space with a small foramen at the bottom, while the coronal pulp shows a small tunnel (100-140 μm in diameter). We estimate that the small teeth of Hamipterus likely took approximately 80 days to form. Furthermore, the tooth has Andresen lines, which represent 7-15 days period. For stable articulation of the tooth in the alveolus, the thick cellular cementum is concentrated on the lingual side of the root. The acellular cementum (~40 μm thick) layer runs from the root to the partial tooth crown.

Ex-vivo analysis of demineralisation on irradiated teeth using optical coherence tomography

Head and neck cancer patients are prone to dental caries after radiotherapy. An ex-vivo study was conducted to assess the feasibility of optical coherence tomography (OCT) to detect tooth demineralization due to caries in irradiated teeth. Thirty-nine human molar teeth were subjected to caries lesion induction through irradiation (Group 1), pH cycling (Group 2–1), and both (Group 2–2). The OCT signal attenuation coefficient, µR was assessed and validated against microhardness test and scanning electron microscope (SEM). The µR for Group 1 increased from 10 Gy to 40 Gy, and subsequently decreased after irradiated to 50 Gy and 60 Gy due to damaged enamel microstructure. In Group 2–1, the µR decreased with duration of pH cycling from day 1 to day 14 due to the increase of porosity in enamel layer. However, the µR showed decreasing trend from day 14 to day 28 of pH cycling, resulted from mineral deposition in the enamel layer. Although no significant difference was found in the µR between Group 2–1 and 2–2, SEM of Group 2–2 demonstrated visually higher porosity and larger gaps between microstructures. Irradiation may accelerate caries damage to tooth microstructure by increasing its porosity and brittleness, but larger sample size may be needed to further prove the effect. OCT could potentially be used for early detection of tooth demineralization in vivo based on the measurable µR changes for all groups which are shown negatively correlated with microhardness value (p < 0.05).

Comparative microstructural study on the teeth of Mesozoic birds and non-avian dinosaurs.

Although it is commonly considered that, in birds, there is a trend towards reduced dentition, teeth persisted in birds for 90 Ma and numerous macroscopic morphologies are observed. However, the extent to which the microstructure of bird teeth differs from other lineages is poorly understood. To explore the microstructural differences of the teeth of birds in comparison with closely related non-avialan dinosaurs, the enamel and dentine-related features were evaluated in four Mesozoic paravian species from the Yanliao and Jehol biotas. Different patterns of dentinal tubular tissues with mineralized extensions of the odontoblast processes were revealed through the examination of histological sectioning under electron microscopy. Secondary modification of the tubular structures, forming reactive sclerotic dentin of Longipteryx, and the mineralization of peritubular dentin of Sapeornis were observed in the mantle dentin region. The new observed features combined with other dentinal-associated ultrastructure suggest that the developmental mechanisms controlling dentin formation are quite plastic, permitting the evolution of unique morphologies associated with specialized feeding behaviours in the toothed birds. Proportionally greater functional stress placed on the stem bird teeth may have induced reactive dentin mineralization, which was observed more often within tubules of these taxa. This suggests modifications to the dentin to counteract potential failure.

The Preliminary Investigation of the Effect of Caries on the Extension of Dentin Cracks

Dentin is part of the structural composition of the teeth and consists of intertubular dentin (ITD), peritubular dentin (PTD) and the dentinal tubules. The interaction of the three components provides significant strength and durability to the dentin. Caries is a dental disease caused by bacteria, which can damage the microstructure of teeth and lead to teeth damage or even fracture. It is necessary to investigate the mechanism of teeth damage from the perspective of fracture mechanics. In order to study the effect of caries on crack extension, this study uses finite element simulation (FEM) to establish a monophasic dentin model, a bidirectional dentin model, and a dentin model with different caries degrees to compare and analyze the crack extension under the same magnitude of displacement load. The experimental results reveal the influence of different caries degrees on crack extension, which is important for exploring the damage and fracture mechanism of teeth and the design of bionic teeth.

Revelation of microcracks as tooth structural element by X-ray tomography and machine learning

Although teeth microcracks (MCs) have long been considered more of an aesthetic problem, their exact role in the structure of a tooth and impact on its functionality is still unknown. The aim of this study was to reveal the possibilities of an X-ray micro-computed tomography (muCT) in combination with convolutional neural network (CNN) assisted voxel classification and volume segmentation for three-dimensional (3D) qualitative analysis of tooth microstructure and verify this approach with four extracted human premolars. Samples were scanned using a muCT instrument (Xradia 520 Versa; ZEISS) and segmented with CNN to identify enamel, dentin, and cracks. A new CNN image segmentation model was trained based on “Multiclass semantic segmentation using DeepLabV3+” example and was implemented with “TensorFlow”. The technique which was used allowed 3D characterization of all MCs of a tooth, regardless of the volume of the tooth in which they begin and extend, and the evaluation of the arrangement of cracks and their structural features. The proposed method revealed an intricate star-shaped network of MCs covering most of the inner tooth, and the main crack planes in all samples were arranged radially in two almost perpendicular directions, suggesting that the cracks could be considered as a planar structure.

Impact of different types of storage media on enamel surface roughness and granularity distribution of avulsed teeth (In vitro study)

Background: To investigate the effect of different types of storage media on enamel surface microstructure of avulsed teeth by using atomic force microscope.Materials and methods : Twelve teeth blocks from freshly extracted premolars for orthodontic treatment were selected . The study samples were divided into three groups according to type of storage media :A-egg white , B- probiotic yogurt , and C-bovine milk . All the samples were examined for changes in surface roughness and surface granularity distribution using atomic force microscope, at two periods: baseline, and after 8 hours of immersing in the three types of storage media. Results: Milk group had showed a significant increase in the mean of the roughness values at the test period, while the egg white and the probiotic yogurt groups showed decrease in the surface roughness at the test period. No significant changes was found in the grain size of enamel surface of the avulsed tooth in any types of three storage media at eight hours interval. The use of egg white and probiotic yogurt to store the samples may be beneficial in that they contain various ions and proteins that fill up enamel valleys, while the longer periods of milk exposure encourage the bacteria to continue fermenting lactose, resulting in continual acid generation and increased demineralization. Conclusion : Milk group demonstrated the highest roughness values, while the egg white group demonstrated the lowest roughness values of the teeth. No significant changes in the grain size of enamel surface of the tested teeth in any types of three storage media at eight hours interval .

&lt;strong&gt;The effect of acidulated phosphate fluoride (APF) gel against erosion on enamel microstructure of primary teeth which soaked with Citrus aurantifolia &lt;/strong&gt;

ABSTRACTIntroduction: Erosion is a common dental problem that is especially prevalent in children due to the increasing consumption of acidic food and beverages. APF gel is believed to be effective in reducing the demineralization effect of the teeth as well as escalating the remineralization process. This research aims to determine and evaluate the effectiveness of 1.23% APF gel as a preventive agent for the erosion of tooth enamel, specifically in deciduous teeth. Methods: This type of research is true experimental research. The population of this research would be primary teeth extracted from children, using a purposive sampling technique with inclusive and exclusive criteria. A total amount of 5 maxillary primary central incisors were extracted and cleaned. APF gel was applied repetitively on the left side of the teeth for 4 minutes every hour, whereas the right side was left as it is. Samples were then analyzed using a scanning electron microscope (SEM). A qualitative and subjective analysis regarding the micromorphological features of the erosion can be done. Result: The side of teeth without APF gel application has a greater erosion rate compared with teeth with APF gel application. The tooth which is demineralized shows a honeycomb structure of the interprismatic enamel. As for the dentinal tubules, teeth without APF gel application have a bigger opening of dentinal tubules, going up to 7.868 micrometers in size compared to teeth with APF gel application (1-2 micrometers). Conclusion: The application of professional acidulated phosphate fluoride (APF) gel on deciduous teeth even when soaked in Citrus aurantifolia, is proven to be effective in preventing dental erosion.Keywords: acidulated phosphate fluoride (APF) gel; citrus aurantifolia; dental erosion; primary tooth

Microstructural characteristics and seasonal growth patterns observed in Metoposaurus krasiejowensis teeth

The tooth microstructure of Metoposaurus krasiejowensis was studied to observe external morphology, internal microstructure (comprising dentine structure and directional porosity as possible predatory adaptations) and enamel/enameloid mineral composition. Scanning electron microscopy (SEM) observation and thin-section inspection by light microscope enabled us to recognize a directional porosity in the tooth cross-sections, interpreted here as a part of the labyrinthodont structure displayed by temnospondyls and related groups. This network of canals is highly complicated and reveals a three-dimensional structure. The teeth present different cross-sections based on the distance from the tip, with a wide, circular, reinforced base and lateral compressed, directional cuspidal section with cutting edge. Interestingly, the internal structure observed in M. krasiejowensis teeth exhibit a peculiar variation of internal structure of temnospondyl teeth, as the convoluted canal-like structure seems to be irregular and appears in the upper section of teeth, while teeth bases show a regular structure with a pulpal cavity circled by pores. Furthermore, bands of incremental growth marks interpreted as Andresen lines, characterized by pronounced colour variation, were observed with strong implications for seasonal growth patterns in dentine. Additionally, a significant proportion (1.43–2.73%) of fluoride was observed as a component of enamel by scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) point and mapping analyses, suggesting a fluorapatite mineralogy of enamel.

A combined experimental-numerical approach for life analysis and modeling of polymer-based ternary nanocomposite gears

The life assessment of polyoxymethylene (POM), POM/carbon black (CB), and POM/CB/nano precipitated calcium carbonate (NPCC) ternary nanocomposite gears was carried out using experimental and numerical techniques. The gear life tests were conducted under constant loading up to failure. Finite element analysis (FEA) was utilized to calculate contact and root stress values. The characterization tests indicated the proper particle-polymer adhesion and the uniform distribution of nanoparticles in the matrix. According to experimental gear tests, POM/CB/3NPCC gears showed the highest lifetime at all applied loads, attributed to synergetic reinforcing effects of CB and NPCC in the POM matrix. The SEM examination of tooth microstructure displayed a smooth surface, characterized by minor indications of surface crack, plastic flow, and debris formation, with the application of 1.5 and 3 wt% NPCC, against pristine POM. The finite element analysis of gears indicated that the single tooth area, during teeth contact, was shorter than the theoretical value. In addition, the contact and root stress values were higher for nanocomposite gears than pristine POM. The experimental and numerical data were applied to obtain the stress-life diagrams for pristine POM and POM nanocomposites and propose a model for life prediction of the gear samples.

Dental Tissue Volumes in Mice with Osteogenesis Imperfecta

Osteogenesis imperfecta (OI), commonly known as brittle bone disease, has long been known to cause significant dental problems that affect patients over the course of their lives, including increased dental fractures, discolored teeth, and malocclusion.At the molecular level, OI is a disorder of the type I collagen protein. Insufficient amounts or misshapen forms of this protein lead to disruptions in the microstructure of bone and teeth tissues.Dentin, the hard tissue which comprises the bulk of the tooth and absorbs shock forces during chewing, develops on a matrix of type I collagen. Thus, collagen abnormalities in OI lead to less organized and less stable dentin.Further, the teeth in people with OI tend to exhibit dentin hypertrophy, in which increased amounts of dentin are deposited at the interior of the tooth. In humans with OI, dentin hypertrophy tends to develop shortly after the eruption of teeth into the oral cavity.Enamel, unlike dentin, develops on a matrix of non‐collagenous proteins, and is thought to develop normally in OI. However, abnormalities in the underlying dentin in OI can frequently lead to enamel fractures. Finally, the teeth in people with OI have often been noted to be smaller than those of people without OI.Mice are the most commonly used animal model for dental development. However, differences in dental tissue volumes in OI have not yet been studied in mice.The objective of this study is to compare dental tissue volumes at different developmental stages in teeth from mice with and without OI. We hypothesize that both juvenile and young adult mice with OI will have smaller dental tissue volumes than mice without OI.To test this hypothesis, three‐dimensional models of teeth from OI mice (n = 10) and wild type mice (n = 10) were created from microCT scans taken at weaning age (week 4 after birth) and young adulthood (week 16 after birth). Dental tissue volumes were measured using 3D Slicer.Mann‐Whitney U tests showed that at week 16, mice with OI had significantly lower dental volumes compared to mice without OI for upper molars, lower molars, upper incisors, and lower incisors (p &lt; 0.05). Additionally, at week 4, mice with OI had significantly smaller lower molars, upper incisors, and lower incisors (p &lt; 0.05). There was no significant difference between the two groups in upper molar size among the week 4 mice.At week 16, the OI mice had significantly lower volumes of dentin compared to the mice without OI in the upper and lower molars (p &lt; 0.05), but not in the upper or lower incisors. At week 4, the OI mice had significantly lower volumes of dentin compared to the mice without OI in the upper and lower incisors and lower molars (p &lt;0.05), but not the upper molars.There were no significant differences between the two groups in enamel volume at either timepoint.These results demonstrate that mice with OI have smaller overall dental volumes compared to mice without OI, consistent with the human OI phenotype of smaller teeth.This research will provide important insights into the development of the dental phenotype in OI. The use of a mouse model to investigate dental tissue volumes represents a novel direction for OI research. Establishing the validity of the mouse model will allow future researchers to further characterize the effects of this disease on early dental development using methods, such as CT scans, that cannot be practically or ethically performed in young human patients.

Skeletal remains of the oldest known pseudocoracid shark Pseudocorax kindlimanni sp. nov. (Chondrichthyes, Lamniformes) from the Late Cretaceous of Lebanon

A new fossil mackerel shark, Pseudocorax kindlimanni sp. nov. (Lamniformes, Pseudocoracidae), is described from the Cenomanian Konservat-Lagerstätte of Haqel, Lebanon. The new species is based on the most complete fossil of this group to date, which comprises an associated tooth set of 70 teeth, six articulated vertebral centra, numerous placoid scales and pieces of unidentifiable mineralized cartilage. The dentition of P. kindlimanni sp. nov. is marked by a high degree of monognathic heterodonty but does not exhibit the characteristic “lamnoid tooth pattern” known from other macrophagous lamniform sharks. In addition, P. kindlimanni sp. nov. shows differences in tooth microstructure and vertebral centrum morphology compared to other lamniform sharks. These variations, however, are also known from other members of this order and do not warrant the assignment of Pseudocorax outside the lamniform sharks. The new fossil is the oldest known pseudocoracid shark and pushes the origin of this group back into the Cenomanian, a time when lamniform sharks underwent a major diversification. This radiation resulted not only in high species diversity, but also in the development of a diverse array of morphological traits and adaptation to different ecological niches. Pseudocorax kindlimanni sp. nov. was a small, active predator capable of fast swimming, and it occupied the lower trophic levels of the marine food web in the Late Cretaceous.

Enamel microstructure of permanent and deciduous teeth of notoungulate Toxodon: development, functional and evolutionary implications

Enamel microstructure of permanent and deciduous teeth of notoungulate Toxodon: development, functional and evolutionary implications

On the vital role of enamel prism interfaces and graded properties in human tooth survival.

Teeth of omnivores face a formidable evolutionary challenge: how to protect against fracture and abrasive wear caused by the wide variety of foods they process. It is hypothesized that this challenge is met in part by adaptations in enamel microstructure. The low-crowned teeth of humans and some other omnivorous mammals exhibit multiple fissures running longitudinally along the outer enamel walls, yet remain intact. It is proposed that inter-prism weakness and enamel property gradation act together to avert entry of these fissures into vulnerable inner tooth regions and, at the same time, confer wear resistance at the occlusal surface. A simple indentation experiment is employed to quantify crack paths and energetics in human enamel, and an extended-finite-element model to evaluate longitudinal crack growth histories. Consideration is given as to how tooth microstructure may have played a vital role in human evolution, and by extension to other omnivorous mammals.

Tooth microstructure and feeding biology of the brittle star Ophioplocus januarii (Echinodermata: Ophiuroidea) from northern Patagonia, Argentina

Ophioplocus januarii is a common brittle star on soft and hard substrates along the Argentinian and Brazilian coasts. Based on stomach contents, tooth microstructure and field observations we identified its food. Opposed to previous suggestions, O. januarii appears to be a microphagous species feeding on macroalgal fragments (found in 60.0 % of the analyzed stomachs with content), plant debris (28.0 %), animal cuticle structures (13.0 %), and unidentifiable material (30.7 %). Less frequent items found were foraminiferans, ostracods, an amphipod, a juvenile bivalve, and other crustaceans. Electronic microscope revealed digested material, diatoms and small crustacean appendices. Thus, O. januarii is an omnivorous species, feeding mainly on algae, complemented opportunistically with other items. Suspension feeding was observed in the field. It has an fenestrated arrangement intermediate between the previously described uniform and compound teeth.

Microstructural and compositional variation in pacu and piranha teeth related to diet specialization (Teleostei: Serrasalmidae)

In any vertebrate group, tooth shape is known to fit with a biological function related to diet. However, little is known about the relationships between diet and tooth microstructure and composition in teleost fishes. In this work, we describe the external morphology, internal microstructure and elemental composition of the oral teeth of three representative species of the family Serrasalmidae having different feeding habits (herbivorous vs. omnivorous vs. carnivorous). We used backscattered-electron imaging and low vacuum environmental scanning electron microscope to compare the organization and mineralization of tooth layers as well as energy dispersive X-ray microanalysis and Raman microspectrometry to investigate the elemental composition, Ca/P ratio and mineralogy of the most superficial layers. Oral teeth of each serrasalmid species have the same internal organization based on five distinctive layers (i.e. pulp, dentine, inner enameloid, outer enameloid and cuticle) but the general tooth morphology is different according to diet. Microstructural and compositional variation of the cuticle and iron-enrichment of superficial layers were highlighted between herbivorous and carnivorous species. Iron is more concentrated in teeth of the herbivorous species where it is associated with a thicker cuticle explaining the more intense red-pigmentation of the cutting edges of oral teeth. The iron-enrichment is interpreted as a substitution of Ca by Fe in the hydroxyapatite. These traits are discussed in the light of the evolutionary history of the family. Further considerations and hypotheses about the formation and origin of the mineralized tooth layers and especially the iron-rich superficial layers in teleost fishes are suggested.

Predatory behaviour in mosasaurid squamates inferred from tooth microstructure and mineralogy

Dental morphology, microstructure and chemistry provide unique insights into various aspects of the evolutionary history and ecology of extinct clades. However, most studies have focused exclusively on the morphological aspects of teeth, while there are significantly fewer detailed accounts of tooth microstructure and mineralogy. Here we provide a full description of the enamel and dentine microstructure of mosasaurid squamates based on an assessment of isolated teeth belonging to two distantly related mosasaurid taxa, i.e., a russellosaurinan and a mosasaurine, from the ?Coniacian–Santonian and Maastrichtian of Belgium. The obtained data are further explored with regard to their value for inferences of mosasaurid predatory behaviour. SEM observations have shown that the Schmelzmuster consists of columnar enamel with an outer layer of parallel crystallites; transmitted light observations have further revealed the presence of mantle dentine cushioning between enamel and orthodentine, and electron microprobe analyses have demonstrated the unaltered enamel chemistry and heterogeneous diagenetic alteration of dentine. Columnar enamel allows minute movements without rupture under bending stress, and together with the presence of shock-absorbing mantle dentine and possibly elevated Fe contents in the enamel, which increase its hardness and enhance acid resistance, it is suggestive of a good ability of the teeth to withstand severe mechanical damage. Such properties of teeth indicate adaptation to shaking and tearing large and resisting prey.