New Insights on the Composition and the Structure of the Acellular Extrinsic Fiber Cementum by Raman Analysis

Tooth acellular extrinsic fibre cementum incremental lines in humans are formed by parallel branched Sharpey's fibres and not by its mineral phase

In humans, the growth pattern of the acellular extrinsic fibre cementum (AEFC) has been useful to estimate the age-at-death. However, the structural organization behind such a pattern remains poorly understood. In this study tooth cementum from seven individuals from a Mexican modern skeletal series were analyzed with the aim of unveiling the AEFC collagenous and mineral structure using multimodal imaging approaches. The organization of collagen fibres was first determined using: light microscopy, transmission electron microscopy (TEM), electron tomography, and plasma FIB scanning electron microscopy (PFIB-SEM) tomography. The mineral properties were then investigated using: synchrotron small-angle X-ray scattering (SAXS) for T-parameter (correlation length between mineral particles); synchrotron X-ray diffraction (XRD) for L-parameter (mineral crystalline domain size estimation), alignment parameter (crystals preferred orientation) and lattice parameters a and c; as well as synchrotron X-ray fluorescence for spatial distribution of calcium, phosphorus and zinc. Results show that Sharpey's fibres branched out fibres that cover and uncover other collagen bundles forming aligned arched structures that are joined by these same fibres but in a parallel fashion. The parallel fibres are not set as a continuum on the same plane and when they are superimposed project the AEFC incremental lines due to the collagen birefringence. The orientation of the apatite crystallites is subject to the arrangement of the collagen fibres, and the obtained parameter values along with the elemental distribution maps, revealed this mineral tissue as relatively homogeneous. Therefore, no intrinsic characteristics of the mineral phase could be associated with the alternating AEFC incremental pattern.

Stress exposure histories revealed by biochemical changes along accentuated lines in teeth

The regular incremental secretion of enamel and dentine can be interrupted during periods of stress resulting in accentuated growth lines. These accentuated lines, visible under light microscopy, provide a chronology of an individual's stress exposure. Previously, we showed that small biochemical changes along accentuated growth lines detected by Raman spectroscopy, coincided with the timing of medical history events and disruptions of weight trajectory in teeth from captive macaques. Here, we translate those techniques to study biochemical changes related to illness and prolonged medical treatment during early infancy in humans. Chemometric analysis revealed biochemical changes related to known stress-induced changes in circulating phenylalanine as well as other biomolecules. Changes in phenylalanine are also known to affect biomineralization which is reflected in changes in the wavenumbers of hydroxyapatite phosphate bands associated with stress in the crystal lattice. Raman spectroscopy mapping of teeth is an objective, minimally-destructive technique that can aid in the reconstruction of an individual's stress response history and provide important information on the mixture of circulating biochemicals associated with medical conditions, as applied in epidemiological and clinical samples.

Cementum is key to periodontal tissue regeneration: A review on apatite microstructures for creation of novel cementum-based dental implants

The cementum is the outermost layer of hard tissue covering the dentin within the root portion of the teeth. It is the only hard tissue with a specialized structure and function that forms a part of both the teeth and periodontal tissue. As such, cementum is believed to be critical for periodontal tissue regeneration. In this review, we discuss the function and histological structure of the cementum to promote crystal engineering with a biochemical approach in cementum regenerative medicine. We review the microstructure of enamel and bone while discussing the mechanism underlying apatite crystal formation to infer the morphology of cementum apatite crystals and their complex structure with collagen fibers. Finally, the limitations of the current dental implant treatments in clinical practice are explored from the perspective of periodontal tissue regeneration. We anticipate the possibility of advancing periodontal tissue regenerative medicine via cementum regeneration using a combination of material science and biochemical methods.

Incremental lines in human acellular tooth cementum - new insights by SEM analysis

BACKGROUND

Tooth cementum covers the surface of the root dentine and is produced and laid down in thin layers continuously throughout life. Functionally, different types of tooth cementum can be distinguished, which can be roughly divided into acellular (primary cementum) and cellular (secondary cementum) forms. One main type is acellular extrinsic fibre cementum (AEFC), which covers the cervical and middle third of the root. Light microscopic examinations of transverse sections of AEFC show lamellar patterns of alternating light and dark lines called growth or incremental lines. Following mammalian research, a seasonal rhythm of incremental line formation is also assumed in humans. Previous attempts at visualising incremental lines in the AEFC by scanning electron microscopy (SEM) were not particularly successful. The aim of the present study was to detect incremental lines in the AEFC and to analyse their underlying structure by SEM.

METHODS

For this purpose, non-embedded and resin-embedded transverse and longitudinal sections of three single-rooted teeth obtained from different patients were investigated. The thin sections were not pre-treated (e.g. by etching, grinding or coating).

RESULTS

Lamellar structures, which could be identified as incremental lines, were detectable in both transverse and longitudinal sections, with transverse orientation in the cross-section and longitudinal orientation in the longitudinal section. The lamellar pattern was created by broad fibre-rich layers alternating with narrow fibre-poor layers. The orientation of the collagen fibres changed from layer to layer from transverse to radial direction. The visibility of the layered structure discovered varied significantly.

CONCLUSIONS

The study demonstrate that it is possible, in principle, to detect incremental lines in AEFC and to identify their basic structure using SEM. Our results suggest that the density and orientation of the fibres play an essential role in the formation of incremental lines. Functional aspects seem to be of particular importance.

Short histological kaleidoscope - recent findings in histology. Part I

This article is a review of new advances in histology, concerning either classification or structure of different tissular elements (basement membrane, hemidesmosomes, urothelium, glandular epithelia, adipose tissue, astrocytes), and various organs' constituents (blood-brain barrier, human dental cementum, tubarial salivary glands, hepatic stellate cells, pineal gland, fibroblasts of renal interstitium, Leydig testicular cells, ovarian hilar cells), as well as novel biotechnological techniques (tissue engineering in angiogenesis), recently introduced.

Bone matrix quality in paired iliac bone biopsies from postmenopausal women treated for 12 months with strontium ranelate or alendronate

Bone quality is altered mainly by osteoporosis, which is treated with modulators of bone quality. Knowledge of their mechanisms of action is crucial to understand their effects on bone quality. The goal of our study was to compare the action of alendronate (ALN) and strontium ranelate (SrRan) on the determinants of bone quality. The investigation was performed on over 60 paired human iliac biopsies. Paired samples correspond to biopsies obtained from the same patient, one before treatment (baseline) and one after 12 months of treatment, in postmenopausal women with osteoporosis. Vibrational spectroscopy (Raman and FTIRM) and nanoindentation were used to evaluate the effect of both drugs on bone quality at the ultrastructural level. Outcomes measured by vibrational spectroscopy and nanoindentation are sensitive to bone age. New bone packets are distinguished from old bone packets. Thus, the effect of bone age is distinguished from the treatment effect. Both drugs modify the mineral and organic composition in new and old bone in different fashions after 12 months of administration. The new bone formed during ALN administration is characterized by an increased mineral content, carbonation and apatite crystal size/perfection compared to baseline. Post-translational modifications of collagen are observed through an increase in the hydroxyproline/proline ratio in new bone. The proteoglycan content is also increased in new bone. SrRan directly modulates bone quality through its physicochemical actions, independent of an effect on bone remodeling. Strontium cations are captured by the hydrated layer of the mineral matrix. The mineral matrix formed during SrRan administration has a lower carbonate content and crystallinity after 12 months than at baseline. Strontium might create bonds (crosslinks) with collagen and noncollagenous proteins in new and old bone. The nanomechanical properties of bone were not modified with either ALN or SrRan, probably due to the short duration of administration. Our results show that ALN and SrRan have differential effects on bone quality in relation to their mechanism of action.

Altered collagen chemical compositional structure in osteopenic women with past fractures: A case-control Raman spectroscopic study

Incidences of low-trauma fractures among osteopenic women may be related to changes in bone quality. In this blinded, prospective-controlled study, compositional and heterogeneity contributors of bone quality to fracture risk were examined. We hypothesize that Raman spectroscopy can differentiate between osteopenic women with one or more fractures (cases) from women without fractures (controls). This study involved the Raman spectroscopic analysis of cortical and cancellous bone composition using iliac crest biopsies obtained from 59-cases and 59-controls, matched for age (62.0 ± 7.5 and 61.7 ± 7.3 years, respectively, p = 0.38) and hip bone mineral density (BMD, 0.827 ± 0.083 and 0.823 ± 0.072 g/cm3, respectively, p = 0.57). Based on aggregate univariate case-control and odds ratio based logistic regression analyses, we discovered two Raman ratiometric parameters that were predictive of past fracture risk. Specifically, 1244/1268 and 1044/959 cm-1 ratios, were identified as the most differential aspects of bone quality in cortical cases with odds ratios of 0.617 (0.406-0.938 95% CI, p = 0.024) and 1.656 (1.083-2.534 95% CI, p = 0.020), respectively. Both 1244/1268 and 1044/959 cm-1 ratios exhibited moderate sensitivity (59.3-64.4%) but low specificity (49.2-52.5%). These results suggest that the organization of mineralized collagen fibrils were significantly altered in cortical cases compared to controls. In contrast, compositional and heterogeneity parameters related to mineral/matrix ratios, B-type carbonate substitutions, and mineral crystallinity, were not significantly different between cases and controls. In conclusion, a key outcome of this study is the significant odds ratios obtained for two Raman parameters (1244/1268 and 1044/959 cm-1 ratios), which from a diagnostic perspective, may assist in the screening of osteopenic women with suspected low-trauma fractures. One important implication of these findings includes considering the possibility that changes in the organization of collagen compositional structure plays a far greater role in postmenopausal women with osteopenic fractures.

Tooth-Supporting Hard Tissue Regeneration Using Biopolymeric Material Fabrication Strategies

The mineralized tissues (alveolar bone and cementum) are the major components of periodontal tissues and play a critical role to anchor periodontal ligament (PDL) to tooth-root surfaces. The integrated multiple tissues could generate biological or physiological responses to transmitted biomechanical forces by mastication or occlusion. However, due to periodontitis or traumatic injuries, affect destruction or progressive damage of periodontal hard tissues including PDL could be affected and consequently lead to tooth loss. Conventional tissue engineering approaches have been developed to regenerate or repair periodontium but, engineered periodontal tissue formation is still challenging because there are still limitations to control spatial compartmentalization for individual tissues and provide optimal 3D constructs for tooth-supporting tissue regeneration and maturation. Here, we present the recently developed strategies to induce osteogenesis and cementogenesis by the fabrication of 3D architectures or the chemical modifications of biopolymeric materials. These techniques in tooth-supporting hard tissue engineering are highly promising to promote the periodontal regeneration and advance the interfacial tissue formation for tissue integrations of PDL fibrous connective tissue bundles (alveolar bone-to-PDL or PDL-to-cementum) for functioning restorations of the periodontal complex.

Measuring incremental line width and appearance in the tooth cementum of recent and archaeological human teeth to identify irregularities: First insights using a standardized protocol

OBJECTIVE

Irregular incremental lines (ILs) in the tooth cementum were previously associated with pregnancy and certain diseases. This study aims to identify irregular ILs and assess their patterns and reproducibility.

MATERIALS

24 recent and 32 archaeological teeth from the nineteenth century with known birth history.

METHODS

Histological sections of tooth roots were microscopically assessed. The width and appearance of 16,605 ILs were measured according to a standardized protocol.

RESULTS

Irregular appearing ILs were present in earlier deposited ILs, which correspond to younger years in life. Irregular appearances decreased as the IL number increased, whereas irregular width was spread evenly across all ILs. Within-section reproducibility was relatively high for irregular appearance (intra class correlation close to 0.70 in recent and archaeological teeth) and irregular width (intra class correlation: recent: 0.49; archaeological: 0.58), whereas the across-section reproducibility was moderate.

CONCLUSIONS

Irregular width and appearance in ILs were identified successfully with within-section reproducibility. The moderate reproducibility across sections needs to be addressed in further studies by more systematic sampling of sections.

SIGNIFICANCE

The proposed protocol identifies irregularities in a reproducible manner and may suggest that irregular ILs could be used in paleopathology to identify pregnancies and diseases.

LIMITATIONS

The correlation between the identified irregular ILs and known pregnancies has not been assessed as part of this study.

SUGGESTIONS FOR FURTHER RESEARCH

The identified irregular ILs need to be validated by correlating them with known life history data.

Bone quality assessment of osteogenic cell cultures by Raman microscopy

The use of autologous stem/progenitor cells represents a promising approach to the repair of craniofacial bone defects. The calvarium is recognized as a viable source of stem/progenitor cells that can be transplanted in vitro to form bone. However, it is unclear if bone formed in cell culture is similar in quality to that found in native bone. In this study, the quality of bone mineral formed in osteogenic cell cultures were compared against calvarial bone from postnatal mice. Given the spectroscopic resemblance that exists between cell and collagen spectra, the feasibility of extracting information on cell activity and bone matrix quality were also examined. Stem/progenitor cells isolated from fetal mouse calvaria were cultured onto fused-quartz slides under osteogenic differentiation conditions for 28 days. At specific time intervals, slides were removed and analyzed by Raman microscopy and mineral staining techniques. We show that bone formed in culture at Day 28 resembled calvarial bone from 1-day-old postnatal mice with comparable mineralization, mineral crystallinity, and collagen crosslinks ratios. In contrast, bone formed at Day 28 contained a lower degree of ordered collagen fibrils compared with 1-day-old postnatal bone. Taken together, bone formed in osteogenic cell culture exhibited progressive matrix maturation and mineralization but could not fully replicate the high degree of collagen fibril order found in native bone.

Impaired mineral quality in dentin in X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a skeletal disorder arising from mutations in the PHEX gene, transmitted in most cases as an X-linked dominant trait. PHEX deficiency leads to renal phosphate wasting and hypophosphatemia, as well as impaired mineralization of bone and dentin, resulting in severe skeletal and dental complications. Dentin mineralization defects appear as characteristic, large interglobular spaces resulting from the lack of fusion of calculospherites in the circumpulpal region during the mineralization process. Here, we examined changes in the composition and structure of dentin using Raman spectroscopy on XLH human teeth, and using transmission electron microscopy on the dentin of Hyp mice (the murine model of XLH). The dentin of patients with XLH showed changes in the quality of the apatitic mineral, with greater carbonate substitution and lower crystallinity compared to the dentin of age-matched control teeth. In addition, ultrastructural analysis by transmission electron microscopy revealed a major disorganization of the peri- and intertubular structure of the dentin, with odontoblast processes residing within an unmineralized matrix sheath in the Hyp mouse. Taken together, these results indicate that like for bone and tooth cementum, there are impaired mineral quality and matrix changes in XLH dentin reflecting high sensitivity to systemic serum phosphate levels and possibly other local changes in the dentin matrix.

Incremental distribution of strontium and zinc in great ape and fossil hominin cementum using synchrotron X-ray fluorescence mapping

Cementum and the incremental markings it contains have been widely studied as a means of ageing animals and retrieving information about diet and nutrition. The distribution of trace elements in great ape and fossil hominin cementum has not been studied previously. Synchrotron X-ray fluorescence (SXRF) enables rapid scanning of large tissue areas with high resolution of elemental distributions. First, we used SXRF to map calcium, phosphorus, strontium and zinc distributions in great ape dentine and cementum. At higher resolution, we compared zinc and strontium distributions in cellular and acellular cementum in regions where clear incremental markings were expressed. We then mapped trace element distributions in fossil hominin dentine and cementum from the 1.55-1.65 million year old site of Koobi Fora, Kenya. Zinc, in particular, is a precise marker of cementum increments in great apes, and is retained in fossil hominin cementum, but does not correspond well with the more diffuse fluctuations observed in strontium distribution. Cementum is unusual among mineralized tissues in retaining so much zinc. This is known to reduce the acid solubility of hydroxyapatite and so may confer resistance to resorption by osteoclasts in the dynamic remodelling environment of the periodontal ligament and alveolar bone.

Tissue-specific mineralization defects in the periodontium of the Hyp mouse model of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a dento-osseous disorder caused by inactivating mutations in the PHEX gene, leading to renal phosphate wasting and hypophosphatemia, and impaired mineralization of bones and teeth. In the oral cavity, recent reports suggest a higher susceptibility of XLH patients to periodontitis, where patients present with impaired tooth cementum - a bone-like tissue involved in tooth attachment to the jaw bones and post-eruption tooth positioning - and a higher frequency of intrabony defects. In the present study, the pathobiology of alveolar bone and tooth cementum was investigated in the Hyp mouse, the murine analog of XLH. PHEX deficiency in XLH/Hyp dramatically alters the periodontal phenotype, with hypoplasia of tooth root cementum associated with a lack of periodontal ligament attachment and the presence of an immature apatitic mineral phase of all periodontal mineralized tissues. Challenging the Hyp periodontium in two surgical experimental models - ligature-induced periodontal breakdown and repair, and a model of tooth movement adaptation inducing cementum formation - we show that bone and cementum formation, and their healing, are altered. Bone and cementum mineralization appear similarly disturbed, where hypomineralized pericellular matrix surrounds cells, and where the protein osteopontin (OPN, a mineralization inhibitor) accumulates in a tissue-specific manner, most notably in the perilacunar matrix surrounding osteocytes. Although the pathobiology is different between XLH/Hyp bone and cementum, our results show a major XLH phenotype in oral mineralized tissues consistent with variations in patient susceptibility to periodontal disorders.

Defective Mineralization in X-Linked Hypophosphatemia Dental Pulp Cell Cultures

X-linked hypophosphatemia (XLH) is a skeletal disease caused by inactivating mutations in the PHEX gene. Mutated or absent PHEX protein/enzyme leads to a decreased serum phosphate level, which cause mineralization defects in the skeleton and teeth (osteomalacia/odontomalacia). It is not yet altogether clear whether these manifestations are caused solely by insufficient circulating phosphate availability for mineralization or also by a direct, local intrinsic effect caused by impaired PHEX activity. Here, we evaluated the local role of PHEX in a 3-dimensional model of extracellular matrix (ECM) mineralization. Dense collagen hydrogels were seeded either with human dental pulp cells from patients with characterized PHEX mutations or with sex- and age-matched healthy controls and cultured up to 24 d using osteogenic medium with standard phosphate concentration. Calcium quantification, micro-computed tomography, and histology with von Kossa staining for mineral showed significantly lower mineralization in XLH cell-seeded scaffolds, using nonparametric statistical tests. While apatitic mineralization was observed along collagen fibrils by electron microscopy in both groups, Raman microspectrometry indicated that XLH cells harboring the PHEX mutation produced less mineralized scaffolds having impaired mineral quality with less carbonate substitution and lower crystallinity. In the XLH cultures, immunoblotting revealed more abundant osteopontin (OPN), dentin matrix protein 1 (DMP1), and matrix extracellular phosphoglycoprotein (MEPE) than controls, as well as the presence of fragments of these proteins not found in controls, suggesting a role for PHEX in SIBLING protein degradation. Immunohistochemistry revealed altered OPN and DMP1 associated with an increased alkaline phosphatase staining in the XLH cultures. These results are consistent with impaired PHEX activity having local ECM effects in XLH. Future treatments for XLH should target both systemic and local manifestations.

Correction: New Insights on the Composition and the Structure of the Acellular Extrinsic Fiber Cementum by Raman Analysis

[This corrects the article DOI: 10.1371/journal.pone.0167316.].