Crystals in tooth enamel were analyzed by X-ray diffraction, XRD, using a 100 μm in diameter microbeam. A polished section of human tooth enamel was made, and the microbeam XRD patterns were obtained at six positions from the enamel-dentin junction region to the surface region. Although the apatite unit cell dimensions of the six positions were almost the same, the orientation of crystallites changed abruptly at the surface layer. It was noted that the crystallites aligned not only in their c-axis but also in their a-axis.

View full abstract

In dentin, phosphophoryn is a major non-collagenous protein for mineralization. The most part of phosphophoryn is electrostatically bound to type I collagen and hydroxyapatite, and the remaining small part of phosphophoryn is covalently bound to the collagen fibrils. Previously we reported that immobilized phosphophoryn induced mineral formation. Free-type phosphophoryn is known to inhibit spontaneous precipitation from the mineralization medium having high solution saturation. In this study we examined the interaction of the role between bound-type and free-type phosphophoryn in mineralization in vitro using the classical nucleation theory. The concentrations of 0.8-800 μg/3ml of free-type phosphophoryn were incubated with 0.1 mg of insoluble dentin collagen (2.64 μg of bound-type phosphophoryn) in the mineralizing solution that no spontaneous precipitation occurred. The interfacial tensions on hydroxyapatite nucleation for mixture of 2.64 μg of collagen-bound phosphophoryn with 0.8 μg, 8.0 μg, 80 μg, and 800 μ of free type phosphophoryn were calculated using the data on mineral induction time (the time lag before mineral induction occurs) and solution saturation. It was 91.5 ergs/cm² for 0.1 mg of insoluble dentin collagen having 2.64 mg of collagen-bound phosphophoryn. For 0.8 μg of free phosphophoryn added, it was 90.2 ergs/cm², 91.2 ergs/cm² for 8.0 μg of free phosphophoryn added, 91.7 ergs/cm² for 80 μg of free phosphophoryn added, and 99.2 ergs/cm² for 800 μg of free phosphophoryn added. Electron microscopic observation showed a difference in the shape of crystals induced by immobilized phosphophoryn between with and without free phosphophoryn. These indicated that inhibition of the apatite induced by immobilized phosphophoryn required a much greater amount of phosphophoryn free in solution. Therefore, free phosphophoryn appears to regulate the crystal growth that induced by immobilized phosphophoryn.

View full abstract

The effect of immobilized phosphate ester on hydroxyapatite formation was studied in vitro using metastable solutions that do not precipitate spontaneously. Phosphophoryn, an acidic phosphoprotein secreted by odontoblast in dentin, was used in this study. Increasing the solution saturation with respect to hydroxyapatite nucleation decreased the mineral induction time (the lag time until mineral formation). Progressive dephosphorylation (50% and 70%) of phosphophoryn by acid phosphatase prolonged the mineral induction time. 95% dephosphorylated phosphophoryn no longer induced mineral formation after 48 hours. The mineral induced by immobilized phosphophoryn was identified to be an apatite by micro-area X-ray diffraction. Using these data and classical nucleation theory, the interfacial tension between the immobilized phosphophoryn and apatite crystal formed on the surface of phosphophoryn was calculated. The interfacial tension on phosphophoryn containing 0.65 mmol phosphate per ml beads was relatively low (89.0 ± 2.0 ergs/cm²), similar to that on hydroxyapatite (91.0 ergs/cm²). Moreover, dephosphorylation of phosphophoryn increased the interfacial tension for hydroxyapatite nucleation to 91.6 ± 1.6 ergs/cm² for 50%-dephospphorylated phosphophoryn, and 96.0 ± 2.4 ergs/cm² for 70%-dephosphorylated phosphophoryn. These results indicate that phosphophoryn possesses a significant potential of apatite nucleation and induces apatite nucleation in a phosphate concentration-dependent manner.

View full abstract

The aim of this study was to enhance the demineralization-inhibiting effect in dentin using a mixture of zinc oxide and conventional glass-ionomer cement (GIC). In the experimental group. cavities in bovine dentin were filled with GIC mixed with zinc oxide (GIC-Z group). In the control group, cavities were filled with GIC alone (GIC group). Specimens were immersed in acidic solution at 37°C for 0, 3, 6 or 9 days. Dentin was then observed under contact microradiography (CMR) for demineralization. For day 9 specimens, mineral loss was measured and specimens were observed under scanning electron microscopy (SEM). In addition, ordinary dentin samples were also observed for normal dentinal tubules. Electron probe microanalysis (EPMA) was used to investigate zinc infiltration into day 9 specimens in the GIC-Z group. Concentrations of Mg²⁺, Ca²⁺ and F^- in the acidic solution were measured with day 9 specimens in both GIC-Z and GIC groups. Mechanical properties of compressive strength and disintegration rate were compared between the GIC-Z and GIC cements.
On CMR images, subsurface demineralized lesions were observed in days 3, 6 and 9 specimens. Total mineral loss did not differ substantially between day 3 and day 6 specimens. Mineral loss was slightly reduced with the day 9 specimen in the GIC-Z group. Scanning electron micrograph of the polished surface before acid treatment showed that all dentinal tubules were open. In micrograph of day 9 specimen in the GIC group, many dentinal tubules were closed. In micrograph of day 9 specimen in the GIC-Z group, most dentinal tubules were closed. By EPMA analysis, intensity of Zn was highest at the dentin face in the GIC-Z group. Concentrations of Mg²⁺ and Ca²⁺ in the acidic solution were significantly lower in the GIC-Z group than in the GIC group. No difference in F^- concentration was found between the two groups. Mechanical properties were not significantly different between the two groups.
In conclusion, addition of zinc oxide to GIC contributes to inhibit dentin demineralization without major changes in mechanical properties compared to GIC.

View full abstract

BACKGROUND: Sialolith is a pathological calcification found inside salivary glands, composed principally of apatite crystals. The purpose of this study was to investigate detailed structural properties to gain insight into the formation of sialolith. METHODS: A 45 mm long sialolith from a human submandibular gland was studied using micro-FTIR and three types of X-ray diffraction (XRD) techniques: i) conventional, ii) micro-focus, and iii) “selected-area XRD” (SA-XRD). RESULTS: The longitudinal section of the sialolith showed a stratified structure perpendicular to the long axis. XRD and FTIR showed that the bulk of the sialolith was composed of carbonate hydroxyapatite. Micro-XRD revealed that crystal orientation was slightly different in each incremental zone. “SA-XRD” showed that the average unit cell dimensions of apatite crystals were different for each zone. CONCLUSION: These results suggest that the stratified structure in the sialolith was a result of intermittent and incremental additional growth reflecting compositional changes in the microenvironment.

View full abstract