Materials Science Forum Vols. 587-588

Abstract: This study analyzed immediate implantation and immediate loading of chemical mechanical polished (CMP) and resorbable blast media (RBM) SSIII OSSTEM dental implants histometrically. The 1st, 2nd, 3rd, and 4th mandibular premolars were extracted from five adult dogs. Immediate implantation was performed in the fresh extraction sockets. Each dog received two types of implant: CMP and RBM. The first premolar was submerged, whereas the second, third, and fourth were not submerged. The implants were splinted using acrylic resin and subjected to immediate loading. After 4 months, X-rays were taken and analyzed. The animals were euthanized and processed histologically to obtain non-decalcified sections. Longitudinal ground sections of each implant were made, and histometry was analyzed under light microscopy. No significant difference was found between the control and experimental groups based on immediate loading (p > 0.05) and implant surface (p > 0.05). The implant survival rate and implant-to-bone contact rate after immediate loading were similar to those of submerged implants. The CMP and RBM dental implants did not differ in terms of implant survival rate and implant-to-bone contact rate.

Abstract: We investigated the in vitro formation of apatites and other biologically relevant calcium phosphates, in particular the influence of temperature and pH in the nature of the mineral phases. With this purpose several calcium phosphates were synthesized under controlled conditions, in presence of atmospheric CO2. The results obtained suggest that both factors under study, temperature and pH, have major influence in the nature of the mineral phases obtained.

Abstract: Mineralization experiments on glasses of the Si-Ca-P-Mg system were carried out for 7 days in carbonated simulated inorganic plasma (CSIP) buffered with CO2/HCO3 -. This method enables physiological buffering of the solution within the 7.3–7.4 pH interval by maintaining a HCO3 - concentration between 24 and 27 mmol.L-1, which is the normal concentration range in blood plasma. XRD, SEM/EDS and FTIR were used to characterise the glass surfaces. All glasses exhibited an apatite-like deposit whose Ca/P ratio was dependent on glass composition.

Abstract: Hydroxyapatite (HA) is widely used as a bone repair material. The use of microwave radiation as energy source for powders densification opens new opportunities for sintering HA at lower temperatures than by conventional sintering (electric furnace). The aim of this work was to compare the densification behaviour of a commercial hydroxyapatite powder under microwave and conventional heating conditions through evaluation of the elastic properties of the resulting sintered materials. The effect of green density, sintering temperature and dwell time on the Young’s modulus E (measured by the impulse excitation of vibration method) of microwave sintered HA was evaluated by using the Taguchi method. Under the set of controlled parameters investigated, green density was the most significant factor affecting E. It was verified that the highest E values obtained with each sintering process are similar (104 and 105 GPa for microwave and conventional sintering, respectively). These values were obtained at 1250°C for 2 h in conventional sintering and at 1200°C for 10 min with microwave sintering. This illustrates the advantage of microwave processing on energy and time savings over conventional sintering.

Abstract: Porous κ-carrageenan based composites with potential application in bone tissue engineering have been prepared by in situ co-precipitation of nanoparticles of calcium phosphates, followed by thermally induced gelification and freeze-drying. The scaffolds showed macroporous structure with interconnected porosity. The variation of the biopolymer concentration affected the microstructure and compressive mechanical performance of the composites. The in vitro bioactivity was assessed by soaking the composites in simulated body fluid (SBF) and the formation of an apatite layer on their surface was found.

Abstract: This paper investigates the rheological behaviour of chitosan solutions crosslinked with different concentrations of genipin at body temperature and physiological pH. The effect of the crosslinker concentration on the rheological properties of hydrogels was evaluated. The oscillatory time sweep was used to analyze the dynamics of G’ during in situ gelation experiments enabling the determination of the gelation time. Additionally, the stress and frequency sweeps were employed to measure G’ of cured hydrogels. The solutions of chitosan crosslinked with genipin at physiological conditions were found to form relatively strong elastic gels for all the concentrations, when compared to pure chitosan. A significant reduction on gelation time was achieved. This behaviour shows that these formulations are able to be produced in situ and thus constitute promising matrices for cells and bioactive molecules encapsulation.

Abstract: When preparing β-tricalcium phosphate (β-TCP), it is difficult to industrialise traditional methods because of the problem of particle aggregation. In this paper, β-TCP was prepared by calcining calcium-deficient hydroxyapatite (CDHA) powders obtained by the wet precipitation method at pH=6 and 40 °C, together with additions of poly (ethylene glycol) (PEG), in order to prevent powder agglomeration. The effect of the Ca/PEG mass ratio on the particle size distribution and the morphology of the resulting powders was evaluated. For comparison purposes, one powder without PEG addition was also synthesized. All synthesized powders were characterized by means of X-ray diffraction analysis, particle size analysis and scanning electron microscopy prior and after calcination in static air at 1000 °C for 15 h. Single-phase β-TCP powders have been obtained by calcining CDHA powders in the temperature range of 850°C-1150°C. It was also found that increasing the PEG content in solution decreased the particle size distribution of the agglomerated particles and the β→α-TCP transition temperature. A plausible explanation consistent with these experimental findings is proposed.

Abstract: This study focus on the synthesis of Ca-deficient apatites (CDA) by using the wet chemical precipitation method in demineralised water solutions at pH=7 and synthesis temperature of 90 °C. Upon calcination at 1000°C, the resulting HAP powders decomposed leading to the formation of small amounts of β-TCP. Surprisingly, under some conditions, minor amounts of α- TCP were also formed at 1000°C together with β-TCP. The appearance of α-TCP is favoured by the absence of mineral ions in the precipitation medium, which in turn depends on the purity of the water used. Factors affecting the formation of both β-TCP and α-TCP are discussed.