Spectroscopic imaging of mineral maturation in bovine dentin

Confocal Raman data analysis of tufts and spindles at the human dentin-enamel junction

OBJECTIVE

The aim of this article is to analyze the chemical mapping of tufts and spindles of the human dental enamel using confocal Raman microscopy measuring length, structuration and composition of spindles and tufts.

DESIGN

we used Raman diffusion, based on the interaction between photons and optic phonons, to reveal chemical bound. Adult molars were selected and longitudinally sectioned. Areas of 120 * 120 μm were scanned near the dentin-enamel junction and grooves. Spectra were collected and phosphate and proteins peak intensities images were reconstructed, related to HPA concentration. Images of Phosphate (PO₄^3-, 960 cm^-1) and protein (CH, 2800/3000 cm^-1) intensities have been reconstructed. K-mean cluster has been calculated to compare centroid spectra from enamel, dentin and tuft or spindle.

RESULTS

intensity profile revealed spindles as less mineralized areas than enamel, from 5 to 10 µm large. In the groove of molar, long tufts were found, more than 150 µm.

CONCLUSIONS

Confocal Raman microscopy is a very interesting tool to characterize chemically secondary structure of enamel. The size of a tuft in the groove allows us make the hypothesis that they could play a role in long term resilience of mechanical stress.

Identification of a protein-containing enamel matrix layer which bridges with the dentine-enamel junction of adult human teeth

OBJECTIVE

To investigate the ultrastructure and chemical composition of the dentine-enamel junction and adjacent enamel of minimally processed third molar tooth sections.

DESIGN

Undecalcified human third molar erupted teeth were sectioned and etched with 4% EDTA or 37% phosphoric acid prior to visualization by scanning electron microscopy. Confocal Raman spectroscopy was carried out at 50 μm and more than 400 μm away from the dentine-enamel junction before and after mild etching.

RESULTS

A novel organic protein-containing enamel matrix layer was identified for the first time using scanning electron microscopy of etched bucco-lingual sections of crowns. This layer resembles a three-dimensional fibrous meshwork that is visually distinct from enamel "tufts". Previous studies have generally used harsher solvent conditions which likely removed this layer and precluded its prior characterization. The shape of the organic enamel layer generally reflected that of sheath regions of enamel rods and extended from the dentine-enamel junction about 100-400 μm into the cuspal enamel. This layer exhibited a Raman CH stretching peak at ∼2931 cm(-1) characteristic of proteins and this signal correlated directly with the presence and location of the matrix layer as identified by scanning electron microscopy.

CONCLUSIONS

The enamel protein layer was most prominent close to the dentine-enamel junction and was largely absent in cuspal enamel >400 μm away from the dentine enamel junction. We hypothesize that this protein containing matrix layer could provide an important biomechanical linkage between the enamel and the dentine-enamel junction and by extension, with the dentine, of the adult tooth (246 words).

Application of polychromatic µCT for mineral density determination

Accurate assessment of mineral density (MD) provides information critical to the understanding of mineralization processes of calcified tissues, including bones and teeth. High-resolution three-dimensional assessment of the MD of teeth has been demonstrated by relatively inaccessible synchrotron radiation microcomputed tomography (SRµCT). While conventional desktop µCT (CµCT) technology is widely available, polychromatic source and cone-shaped beam geometry confound MD assessment. Recently, considerable attention has been given to optimizing quantitative data from CµCT systems with polychromatic x-ray sources. In this review, we focus on the approaches that minimize inaccuracies arising from beam hardening, in particular, beam filtration during the scan, beam-hardening correction during reconstruction, and mineral density calibration. Filtration along with lowest possible source voltage results in a narrow and near-single-peak spectrum, favoring high contrast and minimal beam-hardening artifacts. More effective beam monochromatization approaches are described. We also examine the significance of beam-hardening correction in determining the accuracy of mineral density estimation. In addition, standards for the calibration of reconstructed grey-scale attenuation values against MD, including K(2)PHO(4) liquid phantom, and polymer-hydroxyapatite (HA) and solid hydroxyapatite (HA) phantoms, are discussed.

Micro-attenuated total reflection spectral imaging in archaeology: application to Maya paint and plaster wall decorations

Fourier transform infrared (FT-IR) attenuated total reflection (ATR) imaging has been successfully used to identify individual mineral components of ancient Maya paint. The high spatial resolution of a micro FT-IR-ATR system in combination with a focal plane array detector has allowed individual particles in the paint to be resolved and identified from their spectra. This system has been used in combination with micro-Raman spectroscopy to characterize the paint, which was found to be a mixture of hematite and silicate particles with minor amounts of calcite, carbon, and magnetite particles in a sub-micrometer hematite and calcite matrix. The underlying stucco was also investigated and found to be a combination of calcite with fine carbon particles, making a dark sub-ground for the paint.

Secondary ionization mass spectrometry imaging of dilute stable strontium labeling in dentin and enamel

The labeling of the zones of active mineralization in bone and tooth is usually achieved with calcium-binding fluorescent dyes. However, these compounds are labile and mostly lost during the maturation process of the growing tissue. Here we labeled mouse teeth using injections of dilute strontium (SrCl(2), 500 microg/ml), a trace element that is naturally incorporated in hydroxyapatite, and resolve the subtle induced compositional changes using secondary ion mass spectrometry (SIMS) imaging and analysis. Entire hemi-mandibules sampled at 14 and 28 days after birth are embedded in resin and polished along longitudinal sections. SIMS chemical imaging reveals the double Sr labeling both in dentin and enamel of molar teeth as two stripes with excess Sr concentration parallel to the dentino-enamel junction. In order to quantify the variations of the strontium/calcium ratio (Sr/Ca), two international standards were sintered and measured along with the samples. The concentration of Sr in the two stripes is about 300 microg/g, which corresponds to an enrichment factor of about 1.3-1.4 relative to the natural baseline. These results show that SIMS provides rapid and quantitative imaging of small abundances of stable isotopes in growing mineralized tissues with a sensibility that is at least two orders of magnitude higher than classical X-rays microanalysis.

Mucopolysaccharidosis type I (Hurler syndrome): oral and radiographic findings and ultrastructural/chemical features of enamel and dentin

Mucopolysaccharidosis type I (Hurler syndrome, MPS I-H) is an autosomal recessive inborn error of metabolism due to deficient alpha-L-iduronidase enzyme activity and is characterized by accumulation of incompletely degraded glycosaminoglycans that generally lead to impairment of organ and body functions. This report presents oral, dental, and radiographic findings in a boy who presented with MPS I-H. Nine of the patient's primary teeth were extracted and investigated using scanning electron microscopy, x-ray diffraction analysis, and Fourier transform infrared spectroscopy. Compared with the teeth of otherwise healthy patients, MPS I-H-affected dentin was characterized by extremely narrow dentinal tubules, whose direction followed an irregular wave-like pattern. The enamel-dentin junction was defective, as evidenced by microgaps, and the enamel displayed irregular arrangement of prisms. The additional novel observation was made that the protein structure of enamel and dentin changed in MPS I-H-affected teeth. Also, an increase was observed in the relative mineral/matrix ratio of MPS I-H-affected dentin, indicating that its protein content had decreased in comparison with normal dentin.

Changes in matrix phosphorylation during bovine dentin development

Phosphorylation of the organic matrix proteins of dentin is important for the initiation of mineralization, but its relevance in later mineralization stages is controversial. The objective of this study was to analyze changes in the total matrix phosphate content during dentin development and to identify their origin. Amino acid and total matrix phosphate analyses of microdissected developing mantle and circumpulpal fetal bovine dentin specimens were performed. The amino acid composition showed few changes during mantle and circumpulpal dentin maturation. However, the total matrix phosphate content showed a significant, positive correlation with tissue maturation in both mantle and circumpulpal dentin, with a two- and a three-fold increase, respectively, being observed. The data indicate that changes occur in the pattern of phosphorylation of matrix proteins during dentin maturation, which we suggest may play a functional role in later stages of tooth mineralization.

Adaptations in the mandible and appendicular skeleton of high and low bone density inbred mice

The appendicular skeletons of high [C3H/HeJ (C3H)] and low [C57BL/6J (B6)] density inbred mice have been shown to differ in morphology, mechanical properties, and cellular activity. The focus of the current study was to (1) characterize the mandibular bone formation rate (BFR/BS), bone mass, indentation modulus (IM), and hardness of C3H and B6 mice and (2) investigate the relationship of the mechanical properties in three skeletal sites: mandible, femur, and tibia. Specimens from 17-week-old female C3H and B6 (n = 15/group) mice were obtained. Mandibular bone mass was estimated from the lateral-view area (LVA) and transverse cross sections. BFR/BS was measured in the mandibular section distal to the third molar. In addition, bone blocks from the distal surface of the third molar and the femoral and tibial midshaft were obtained for mechanical testing. BFR/BS, cortical area, and LVA were greater (P < 0.001) in C3H mandibles. IM was approximately 2 GPa higher in the C3H mandible (P > 0.05), femur (P < 0.001), and tibia (P < 0.01). Mandibular IM was lower (P < 0.05) than the femoral and tibial IM within each inbred mouse. IM was not significant between C3H and B6 mandibles. However, the magnitude of the difference ( approximately 12%) in the mandible was similar to the difference in the appendicular skeleton. This mandibular bone phenotype is similar to that observed in the appendicular skeleton of these distinct inbred mice.

Maturational changes in dentin mineral properties

In this study the changes in properties of the maturing mantle and circumpulpal dentin were quantitatively analyzed. Sections from six fetal bovine undecalcified incisors were used. Regions of mantle and circumpulpal dentin of sequential maturation stages were identified on spectroscopic images acquired by Fourier Transform Infrared Imaging. Spectroscopic parameters corresponding to mineral properties at these stages were analyzed and reported as a function of distance from the cervix of the incisor, the latter representing tissue age. Mineral parameters were correlated with distance from the cervix. Values of these parameters in mantle and circumpulpal dentin were compared. A multi-phasic pattern of changes was found for all the parameters examined, with most of the alterations occurring in the initial maturation period. The patterns of temporal variation in mantle and circumpulpal dentin mineral properties show distinct developmental stages and were not identical for the two dentin compartments. The study showed that mineral maturation in dentin is not a linear process and that mantle dentin is developmentally distinct from circumpulpal dentin, presenting at certain stages different physicochemical events during the maturation of the tissue.

Lateral distribution of ultrasound velocity in horizontal layers of human teeth

The speed of ultrasound at 20 MHz differs inside human teeth depending on which tissues are involved. At least two out of four dental tissues exhibit variations in the longitudinal velocity (CL). The aim of this in vitro study is to describe the laterally varying propagation velocity of tangentially propagating longitudinal waves. At a distance of 5 mm from the crown reference, the CL is determined using longitudinal sections and a pulse-echo technique. Several graphs are combined to account for the corono-apical decrease in CL and the laterally varying CL distribution along horizontally adjacent relative tooth width portions. The laterally increasing CL of 21 specimens at radial locations rises from 2900 to 4000 m/s. A mathematical evaluation reveals an optimal horizontal formula of the form CL(5 mm) = a + bX2 ln(X), where X is the standardized lateral parameter relative to individual tooth width w, which is compensated for offsets. Individual residuals and a, b coefficients of the corresponding approximations are provided. Individual mean errors range from 7 m/s (SD=6 m/s) to 92 m/s (SD=79 m/s). The lower contour of the envelope curve of all CL distributions is described by taking up a formerly introduced equation [J. Acoust. Soc. Am. 116, 545 (2004)].

Infrared spectroscopic characterization of mineralized tissues

Vibrational spectroscopy (Infrared and Raman), and in particular micro-spectroscopy and micro-spectroscopic imaging has been used to characterize developmental changes in bone and other mineralized tissues, to monitor these changes in cell cultures, and to detect disease and drug-induced modifications. Examples of the use of infrared micro-spectroscopy and micro-spectroscopic imaging are discussed in this review.