SEM analysis of tooth enamel

SEM analysis contains researches of tooth enamel surfaces of two populations. First group of samples is tooth enamel of prehistorically ancestor from Vucedol and the second group of samples is enamel of modern Croatian citizen. Even on small number of human teeth samples from cooperage site of Vucedol (3,000 BC) and today's Croatian people, we can conclude about chewing biometry of prehistorically ancestors and today's modern Croatian people, comparing interspecifically the morphology of enamel microdefects. With the interspecific comparison of morphology changes on tooth occlusal surfaces, we can connect the size and shape of abrasive particles and diet with microdefects of tooth enamel.     

Stress analysis of irradiated human tooth enamel using finite element methods

The objectives of this project were to use finite element methods to determine how changes in the elastic modulus due to oral cancer therapeutic radiation alter the distribution of mechanical stresses in teeth and to determine if observed failures in irradiated teeth correlate with changes in mechanical stresses. A thin slice section finite element (FE) model was constructed from micro CT sections of a molar tooth using MIMICS and 3-Matic software. This model divides the tooth into three enamel regions, the dentin-enamel junction (DEJ) and dentin. The enamel elastic modulus was determined in each region using nano indentation for three experimental groups namely – control (non-radiated), in vitro irradiated (simulated radiotherapy following tooth extraction) and in vivo irradiated (extracted subsequent to oral cancer patient radiotherapy) teeth. Physiological loads were applied to the tooth models at the buccal and lingual cusp regions for all three groups (control, in vitro and in vivo). The principal tensile stress and the maximum shear stress were used to compare the results from different groups since it has been observed in previous studies that delamination of enamel from the underlying dentin was one of the major reasons for the failure of teeth following therapeutic radiation. From the FE data, we observed an increase in the principal tensile stress within the inner enamel region of in vivo irradiated teeth (9.97 ± 1.32 MPa) as compared to control/non-irradiated teeth (8.44 ± 1.57 MPa). Our model predicts that failure occurs at the inner enamel/DEJ interface due to extremely high tensile and maximum shear stresses in in vivo irradiated teeth which could be a cause of enamel delamination due to radiotherapy.     

Additional criteria for EPR dosimetry using tooth enamel

Currently, EPR measurements are based on the assumption that odontogenesis (the series of events between the bud formation stage until the complete maturation of the tooth) is finished as soon as the tooth erupts. Consequently, it is also assumed that the hydroxyapatite concentration of the enamel (source of free radicals) does not depend on tooth age. However, the present work provides evidence that odontogenesis does not end after tooth eruption but continues for several years after eruption. Fifty-nine molars and pre-molars were analyzed by EPR spectroscopy. Tooth enamel samples were irradiated with different doses of gamma radiation from a 60Co source. The resulting EPR signals were evaluated in terms of posteruption tooth age and tooth position. It was found that, except for wisdom teeth, the concentration of the dosimetric EPR free radicals increased with tooth age after eruption and became constant after a certain period. A mathematical equation was developed to describe this effect as a function of tooth age, tooth position and applied dose. The results suggest that EPR measurements obtained on young teeth should be interpreted carefully unless data are available that would allow one to describe the effect of posteruptive enamel maturation on the EPR estimated dose quantitatively. Little or no correction is needed for older teeth. Since only a limited number of young teeth were available for the present study, further studies are needed to clarify the situation and quantify this effect.     

Morphogenetic roles of perlecan in the tooth enamel organ: an analysis of overexpression using transgenic mice

Perlecan, a heparan sulfate proteoglycan, is enriched in the intercellular space of the enamel organ. To understand the role of perlecan in tooth morphogenesis, we used a keratin 5 promoter to generate transgenic (Tg) mice that over-express perlecan in epithelial cells, and examined their tooth germs at tissue and cellular levels. Immunohistochemistry showed that perlecan was more strongly expressed in the enamel organ cells of Tg mice than in wild-type mice. Histopathology showed wider intercellular spaces in the stellate reticulum of the Tg molars and loss of cellular polarity in the enamel organ, especially in its cervical region. Hertwig's epithelial root sheath (HERS) cells in Tg mice were irregularly aligned due to excessive deposits of perlecan along the inner, as well as on the outer sides of the HERS. Tg molars had dull-ended crowns and outward-curved tooth roots and their enamel was poorly crystallized, resulting in pronounced attrition of molar cusp areas. In Tg mice, expression of integrin β1 mRNA was remarkably higher at E18, while expression of bFGF, TGF-β1, DSPP and Shh was more elevated at P1. The overexpression of perlecan in the enamel organ resulted in irregular morphology of teeth, suggesting that the expression of perlecan regulates growth factor signaling in a stage-dependent manner during each step of the interaction between ameloblast-lineage cells and mesenchymal cells.     

Camel molar tooth enamel response to gamma rays using EPR spectroscopy

Tooth enamel samples from molar teeth of camel were prepared using a combined procedure of mechanical and chemical tooth treatment. Based on electron paramagnetic resonance (EPR) spectroscopy, the dose response of tooth enamel samples was examined and compared to that of human enamel. The EPR dose response of the tooth enamel samples was obtained through irradiation to gamma doses from 1 Gy up to 100 kGy. It was found that the radiation-induced EPR signal increased linearly with gamma dose for all studied tooth enamel samples, up to about 15 kGy. At higher doses, the dose response curve leveled off. The results revealed that the location of the native signal of camel tooth enamel was similar to that of enamel from human molars at 2.00644, but different from that of enamel from cows and goats. In addition, the peak-to-peak width (ΔH _pp) for human and camel molar teeth was similar. It was also found that the response of camel enamel to gamma radiation was 36% lower than that of human enamel. In conclusion, the results indicate the suitability of camel teeth for retrospective gamma dosimetry.     

Mineral-organic-matrix relations in tooth enamel

X-ray and electron diffraction patterns show that β-pleated-sheet polypeptide chains are predominantly oriented approximately perpendicular to the c-axes of developing enamel apatite crystallites. This spatial relation suggests a specific role for enamelins in controlling crystal growth.     

The evolution of dinosaur tooth enamel microstructure

The evolution of tooth enamel microstructure in both extinct and extant mammalian groups has been extensively documented, but is poorly known in reptiles, including dinosaurs. Previous intensive sampling of dinosaur tooth enamel microstructure revealed that: (1) the three‐dimensional arrangement of enamel types and features within a tooth—the schmelzmuster—is most useful in diagnosing dinosaur clades at or around the family level; (2) enamel microstructure complexity is correlated with tooth morphology complexity and not necessarily with phylogenetic position; and (3) there is a large amount of homoplasy within Theropoda but much less within Ornithischia. In this study, the examination of the enamel microstructure of 28 additional dinosaur taxa fills in taxonomic gaps of previous studies and reinforces the aforementioned conclusions. Additionally, these new specimens reveal that within clades such as Sauropodomorpha, Neotheropoda, and Euornithopoda, the more basal taxa have simpler enamel that is a precursor to the more complex enamel of more derived taxa and that schmelzmusters evolve in a stepwise fashion. In the particularly well‐sampled clade of Euornithopoda, correlations between the evolution of dental and enamel characters could be drawn. The ancestral schmelzmuster for Genasauria remains ambiguous due to the dearth of basal ornithischian teeth available for study. These new specimens provide new insights into the evolution of tooth enamel microstructure in dinosaurs, emphasizing the importance of thorough sampling within broadly inclusive clades, especially among their more basal members.     

Effect of microstructure upon elastic behaviour of human tooth enamel

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral–protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle.     

Amelogenesis: Transformation of a protein-mineral matrix into tooth enamel

During enamel formation, the organic enamel protein matrix interacts with calcium phosphate minerals to form elongated, parallel, and bundled enamel apatite crystals of extraordinary hardness and biomechanical resilience. The enamel protein matrix consists of unique enamel proteins such as amelogenin, ameloblastin, and enamelin, which are secreted by highly specialized cells called ameloblasts. The ameloblasts also facilitate calcium and phosphate ion transport toward the enamel layer. Within ameloblasts, enamel proteins are transported as a polygonal matrix with 5 nm subunits in secretory vesicles. Upon expulsion from the ameloblasts, the enamel protein matrix is re-organized into 20 nm subunit compartments. Enamel matrix subunit compartment assembly and expansion coincide with C-terminal cleavage by the MMP20 enamel protease and N-terminal amelogenin self-assembly. Upon enamel crystal precipitation, the enamel protein phase is reconfigured to surround the elongating enamel crystals and facilitate their elongation in C-axis direction. At this stage of development, and upon further amelogenin cleavage, central and polyproline-rich fragments of the amelogenin molecule associate with the growing mineral crystals through a process termed “shedding”, while hexagonal apatite crystals fuse in longitudinal direction. Enamel protein sheath-coated enamel “dahlite” crystals continue to elongate until a dense bundle of parallel apatite crystals is formed, while the enamel matrix is continuously degraded by proteolytic enzymes. Together, these insights portrait enamel mineral nucleation and growth as a complex and dynamic set of interactions between enamel proteins and mineral ions that facilitate regularly seeded apatite growth and parallel enamel crystal elongation.     

Nanotribological characterization of tooth enamel rod affected by surface treatment

Tooth enamel is a hybrid organic–inorganic bionanocomposite comprised predominantly of enamel rods. Understanding the effects of anti-caries treatment on the biomechanical properties of these rods is essential in developing effective caries prevention strategies. Calcium fluoride-like deposits play an important role in caries prevention and their nanotribological properties have a direct effect upon their long-term effectiveness. Accordingly, this study utilizes a variety of techniques, namely nanoindentation, nanoscratch tests, nanowear tests and atomic force microscopy (AFM), to characterize the mechanical and tribological properties of single enamel rods before and after topical fluoride application. The results show that the CaF₂-like deposits formed on the enamel surface following fluoride application increase the coefficient of friction of the enamel rods, but decrease their critical load and nanohardness. As a result, the nanowear depth of the treated enamel surface is around six times higher than that of the native enamel surface under an applied load of 300 μN. Following the removal of the surface deposits, however, the modulus of elasticity and wear depth of the underlying enamel surface are found to be similar to those of the original enamel surface. However, a notable increase in the surface roughness is observed.     

Biosynthesis and characterization of rabbit tooth enamel extracellular-matrix proteins.

Tooth enamel biomineralization is mediated by enamel proteins synthesized by ameloblast cells. Two classes of proteins have been described: enamelins and amelogenins. In lower vertebrates the absence of amelogenins is believed to give rise to aprismatic enamel; however, rabbit teeth, which apparently do not synthesize amelogenins, form prismatic enamel. The present study was designed to characterize the enamel proteins present in rabbit tooth organs and to gain an insight into the process of biomineralization. Rabbit enamel extracellular-matrix proteins were isolated and characterized during sequential stages of rabbit tooth organogenesis. The biosynthesis of enamel proteins was analysed by metabolic 'pulse-chase' experiments as well as mRNA-translation studies in cell-free systems. Our results indicated that rabbit enamel extracellular matrix contains 'amelogenin-like' proteins. However, these proteins are not synthesized as typical amelogenins, as in other mammalian species, thus suggesting that they are the processing products of higher-molecular-mass precursors. An N-terminal amino acid sequence of 29 residues, considered characteristic of mammalian amelogenins, was present in the rabbit 'amelogenin-like' proteins. By using anti-peptide antibodies to this region, similar epitopes were detected in all nascent enamel proteins, including enamelins. These studies suggest that the N-terminal sequence might be characteristic of all enamel proteins, not only amelogenins.     

Retrospective dosimetry using OSL of tooth enamel and dental repair materials irradiated under wet and dry conditions

Following a radiological or nuclear emergency event, there is a need for quick and reliable dose estimations of potentially exposed people. In situations where dosimeters are not readily available, the dose estimations must be carried out using alternative methods. In the present study, the optically stimulated luminescence (OSL) properties of tooth enamel and different dental repair materials have been examined. Specimens of the materials were exposed to gamma and beta radiation in different types of liquid environments to mimic the actual irradiation situation in the mouth. Measurements were taken using a Ris? TL/OSL reader, and irradiations were made using a ⁹⁰Sr/⁹⁰Y source and a linear accelerator (6 MV photons). Results show that the OSL signal from tooth enamel decreases substantially when the enamel is kept in a wet environment. Thus, tooth enamel is not reliable for retrospective dose assessment without further studies of the phenomenon. Dental repair materials, on the other hand, do not exhibit the same effect when exposed to liquids. In addition, dose–response and fading measurements of the dental repair materials show promising results, making these materials highly interesting for retrospective dosimetry. The minimum detectable dose for the dental repair materials has been estimated to be 20–185?mGy.