Ageing of calcium silicate cements for endodontic use in simulated body fluids: a micro‐Raman study

To evaluate bioactivity properties, a calcium silicate experimental cement (wTC) and a phosphate‐doped wTC cement (wTC‐TCP) were aged for different times (1–180 days) at 37 °C in two simulated body fluids, i.e. Dulbecco's phosphate buffered saline (DPBS) and Hank's balanced salt solution (HBSS). The cements were analyzed by micro‐Raman spectroscopy to investigate the presence of calcium phosphate deposits and the composition changes as a function of the storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). After 1 day of ageing in DPBS, the two cements already showed a different behavior: only the surface of wTC‐TCP cement showed the band at 965 cm⁻¹, suggesting the formation of a detectably thick calcium phosphate deposit. The trend of the I₉₆₅/I₉₉₀ Raman intensity ratio indicated the formation of a meanly thicker apatite deposit on the wTC‐TCP cement until 90 days. After 60 days of ageing in DPBS, the thickness of the apatite deposit on wTC and wTC‐TCP was about 200 and 500 µm, respectively, whereas at 180 days, the two cements did not appear significantly different (thickness of about 900 µm). The bioactivity of both cements in HBSS was less pronounced than in DPBS, according to the lower phosphate concentration of HBSS; at the same time, higher amounts of calcite were found on the surface of both cements. The wTC‐TCP cement showed a higher bioactivity in this medium also; after 180 days, the thickness of the apatite deposit on wTC and wTC‐TCP was < 50 µm and about 100 µm, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Synchrotron‐based X‐ray diffraction of the lead apatite series Pb10(PO4)6Cl2–Pb10(AsO4)6Cl2

A number of compounds of the pyromorphite–mimetite solid solution series were synthesized at room temperature and analyzed with infrared spectroscopy and powder X‐ray diffraction. High‐resolution high‐quality powder diffraction data were obtained by means of the state‐of‐the‐art instrument at the 11‐BM beamline of the Advanced Photon Source at Argonne National Laboratory, Argonne, IL, USA. The unit‐cell dimensions, atomic position and atomic displacement parameters, as well as site occupancy for analyzed phases, were refined by the Rietveld method and reported herein for the first time. The results of this study indicate that the pyromorphite–mimetite series is continuous in near‐Earth‐surface environments. Detailed structural changes caused by P⁵⁺–As⁵⁺ substitutions in minerals from the pyromorphite–mimetite solid solution series are reported.     

Measurements of Energetic States Resulting from Ion Exchanges in the Isomorphic Crystals of Apatites and Bioapatites

Developments in the field of nanostructures open new ways for designing and manufacturing innovative materials. Here, we focused on new original ways of calculating energy changes during the substitution of foreign ions into the structure of apatites and bioapatites. Using these tools, the energetic costs of ion exchanges were calculated for the exemplary cases known from the literature. It was established that the most costly were ion exchanges of some cations inside apatites and of anions, and the least costly exchanges in tetrad channel positions. Real energy expenses for bioapatites are much smaller in comparison to mineral apatites due to the limited involvement of magnesium and carbonates in the structure of hard tissues. They are of the order of several electron volts per ion. The rigorous dependences of the energy changes and crystallographic cell volumes on the ionic radii of introduced cations were proved. The differentiation of the positioning of foreign ions in locations of Ca(I) and Ca(II) could be calculated in the case of a Ca-Pb reaction in hydroxyapatite. The energetic effects of tooth aging were indicated. The ability of energy change calculation during the ion exchange for isomorphic substances widens the advantages resulting from X-ray diffraction measurements.     

Termal decomposition of carbonated calcium phosphate apatites

The thermal stability of AB-type carbonated calcium phosphate apatites prepared by precipitation from aqueous media was studied. The behavior of powders was investigated using temperature programmed XRD, infrared spectroscopy and thermogravimetry. In N₂ atmosphere, two successive peaks of decarbonatation with maxima at about 700 and 950°C occurred. This behavior is explained by different substitution modes for carbonates in the apatite. The decarbonatation peaks were shifted to higher temperature under CO₂ (around 900 and 1150°C). The analysis of the thermal stability allowed further densification of carbonate apatite ceramics without important carbonate loss. This revised version was published online in July 2006 with corrections to the Cover Date.     

Raman spectra of apatites: La10−x Si6−y (Al,Fe)y O26±δ

Raman spectra of eight polycrystalline apatites of the general formula La_10−xSi_6−yM′_yO_{26 ± δ} with M′ = Al or Fe were obtained at 300 K. Raman spectra of La₁₀Si₄Fe₂O₂₆ and La_9.83Si_4.5Al_1.5O₂₆ were investigated in the range 80–1000 K and 80–623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO₄ tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm⁻¹ when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al‐ and Fe‐substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm⁻¹ for La₁₀Si₄Fe₂O₂₆ is replaced by a strong band at 868 cm⁻¹, suggesting that SiO₄ tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so‐called two‐mode behavior. The occurrence of FeO stretching vibrations 150 cm⁻¹ lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe⁴⁺ species. Copyright © 2006 John Wiley & Sons, Ltd.     

From biomimetic apatites to biologically inspired composites

Hydroxyapatite is an elective material for bone substitution. In this outline of our recent activity the crucial role of nanostructured ceramics in the design and preparation of ceramic scaffolds will be described, focussing on our more recent interest in biomimetic apatites, in particular apatites containing HPO₄^2– CO₃^2– and Mg²⁺ which are similar to the mineral component of bone. The paper describes such nanostructured products and, in particular, innovative synthetic techniques capable of yielding powders with higher reactivity and bioactivity. However, so far the characteristics of artificial bone tissues have been shown to be very different from those of natural bone, mainly because of the absence of the peculiar self-organizing interaction between apatites and the protein component. This causes modification of the structure of apatites and of the features of the overall composite forming human bone tissue. Therefore, attempts to mimic the features and structure of natural bone tissue, leading toward so-called bio-inspired materials, will be speculated upon. New techniques used to reproduce a composite in which a nanosize blade-like crystal of hydroxyapatite (HA) grows in contact with self-assembling fibres of natural polymer will be presented. In this specific case, the amazing ability of biological systems to store and process information at the molecular level, nucleating nanosize apatites (bio-inspired material), is exploited.     

FT-IR microscopic imaging of calcified deposit of rotator cuff tendonitis: A pilot study and a randomised identification of the compositional components after extrusion from tendon to muscle

Fourier transform infrared (FT-IR) microspectroscopy with mapping system was applied to identify and evaluate what difference in the distribution and compositional components of the calcified deposit of rotator cuff tendonitis after dislocation from tendon to muscle. A 49 year-old female patient suffered from severe shoulder pain was enrolled in this study. Diagnostic high-resolution ultrasonography (HRUS) was initially carried out to verify the calcific tendonitis. The calcified deposits were then examined by histopathologic assessment and FT-IR microspectroscopy. Diagnostic HRUS reveals that the calcified deposits were observed in the subscapularis tendon and infraspinatus muscle of the shoulder for this patient. FT-IR microspectroscopic imaging results clearly indicate that both IR spectra of the calcified deposits in tendon and muscle were almost the same as that of the IR spectrum of hydroxyapatite except the peak at 873 cm⁻¹. It is also found that the peak intensity at 1030 cm⁻¹ for tendon sample was somewhat more intense than that of the peak at 1031 cm⁻¹ for muscle sample, implying that the calcified sample in the tendon seems to be mature than that in the muscle. The second-derivative IR spectra of two calcified samples exhibit two specific sharp peaks at 880 and 872 cm⁻¹, indicating that the type A and type B carbonated apatites were markedly co-existed in both calcified deposits of tendon and muscle even the calcified deposit was dislocated from tendon to muscle. These carbonated apatites presented in the calcified deposits of either tendon or muscle of the shoulder were also consistent with the nodular or nodular nodular-cystic morphology of calcified plaque of the shoulder after HRUS examination.     

Advanced Statistical Optimization of Parameters of Synthesis Process of Oxygenated Carbonated Apatite

The synthesis process of oxygenated carbonated apatite was optimized by an advanced statistical planning of experiments. Full factorial design of 24 experiments was used to find the effects of five principal parameters: pH of the reaction medium, atomic ratio Ca/P of the reagents, concentration of the calcium solution (Ca²⁺), temperature of the reaction medium (T) and duration of the reaction (D), with fixing the H₂O₂ composition at 30% and stirring to 600 turns/min. Studied responses were the atomic ratio Ca/P, % O₂, % O₂ ^2? and % CO_{3 2?}. Optimum synthesis parameters were found to be pH = 7.38, Ca/P = 1.647, [Ca2+] = 0.636 M, T = 40°C and D = 1 h. The prediction responses were Ca/P = 1.575, % O₂ = 0.76, % O₂ ^2? = 0.50 and % CO₃ ^2?= 1.84. The actual experimental results were in agreement with the prediction.