On the Potential of Bulk Metallic Glasses for Dental Implantology: Case Study on Ti40Zr10Cu36Pd14.

Ti40Zr10Cu36Pd14 Bulk Metallic Glass (BMG) appears very attractive for future biomedical applications thanks to its high glass forming ability, the absence of toxic elements such as Ni, Al or Be and its good mechanical properties. For the first time, a complete and exhaustive characterization of a unique batch of this glassy alloy was performed, together with ISO standard mechanical tests on machined implant-abutment assemblies. The results were compared to the benchmark Ti-6Al-4V ELI (Extra-Low-Interstitial) to assess its potential in dental implantology. The thermal stability, corrosion and sterilization resistance, cytocompatibility and mechanical properties were measured on samples with a simple geometry, but also on implant-abutment assemblies' prototypes. Results show that the glassy alloy exhibits a quite high thermal stability, with a temperature range of 38 °C between the glass transition and crystallization, a compressive strength of 2 GPa, a certain plastic deformation (0.7%), a hardness of 5.5 GPa and a toughness of 56 MPa.√m. Moreover, the alloy shows a relatively lower Young's modulus (96 GPa) than the Ti-6Al-4V alloy (110-115 GPa), which is beneficial to limit bone stress shielding. The BMG shows a satisfactory cytocompatibility, a high resistance to sterilization and a good corrosion resistance (corrosion potential of -0.07 V/SCE and corrosion current density of 6.0 nA/cm²), which may ensure its use as a biomaterial. Tests on dental implants reveal a load to failure 1.5-times higher than that of Ti-6Al-4V and a comparable fatigue limit. Moreover, implants could be machined and sandblasted by methods usually conducted for titanium implants, without significant degradation of their amorphous nature. All these properties place this metallic glass among a promising class of materials for mechanically-challenging applications such as dental implants.

Effect of nanoclay addition on physical, chemical, optical and biological properties of experimental dental resin composites.

OBJECTIVE: To prepare organically modified montmorillonite (OM MMT) and assess mechanical, physical, chemical and biological effects of its introduction into resin-composites. METHODS: Natural MMT clay was modified by a methacrylate functionalized quaternary ammonium intercalating agent. Interlayer distance was measured by X-ray diffraction. Dental composites were then prepared with x=0, 1, 2.5, 5 or 7.5wt.% of OM MMT, (75-x) wt.% of silanated barium glass and 25wt.% of methacrylate based matrix). Relative weight loss was measured and the effect of the substitution on mechanical properties was studied by dynamic mechanical analysis and hardness tests. Properties of resin composites were evaluated in terms of water sorption, light transmittance, biological tests and by high-performance liquid chromatography (HPLC). RESULTS: Resin based composites with well-dispersed organically modified MMT were successfully prepared. There were no significant weight loss differences shown by TGA within all samples. The DMA analysis showed that the introduction of clays have a beneficial effect in increasing the storage and elastic modulus of composites. Clay presence was shown to interfere with the blue light transmittance, affecting Vickers hardness and water sorption levels. The amount of released monomers measured from extracts was below expected levels for this type of materials and biological tests show satisfactory cell compatibility. SIGNIFICANCE: This paper reports the successful functionalization of MMT by a methacrylate group and further incorporation in experimental dental composites. Physical and biological results show a potential interest to the application of nanoclays into dental resin composites.

Characterization of Mechanical Properties, Fluoride Release and Colour Stability of Dental Sealants

Objective: To compare the mechanical properties, fluoride release, colour stability and spreading characteristics of glass ionomer cement (GIC), compomer (CO), chemical (CR) and light-cured resin based (LR) fissure sealants. Material and Methods: Cylinders were prepared to determine mechanical properties by diametral tensile strength tests (stored for 24h in distilled water at 37°C) and fluoride release (24 hours, 3, 7 and 15 days; deionised water). Disk shaped specimens were prepared to determine colour stability (1 week in pigmenting solution; 37°C; CIE L*a*b*; ΔE). A simplified method of a spreading test was proposed to predict viscosity characteristics of the tested materials. Data were analysed using one-way ANOVA followed by T-test (p<0.05). Results: Results showed differences between materials regarding all tested properties. CO was statistically more resistant than the other materials (p<0.05), but no difference was observed between CR and LR. The fluoride release of GICs was significantly higher than the other materials (p<0.05). CO showed lower ΔE than the other materials in the following order: CO

Setting of commercial glass ionomer cement Fuji IX by (27)Al and (19)F MAS-NMR.

OBJECTIVES: To investigate the long term setting reaction in the glass ionomer restorative, Fuji IX, by monitoring the structural evolution of aluminium and fluorine species using (27)Al and (19)F MAS-NMR spectroscopy. METHODS: Fuji IX cements aged from 5min up to 3 months were prepared according to the manufacturer instructions from the commercial material. The (27)Al and (19)F MAS-NMR studies were carried out on powders made after terminating the setting reaction. RESULTS: (27)Al MAS-NMR results show conversion of aluminium from the glass phase, where it has coordination number four, Al(IV), into the cement matrix where it has a coordination number of six, Al(VI). At least two different Al(VI) species were detected at short ageing time cements. Assignment of these species is discussed and compared with the data from other sources. The possibility for a condensed aluminium species [Al(13)(OH)(24)(H(2)O)(12)](7+) to form is considered. The ratio of aluminium in the cement, Al(VI), to the remaining unreacted in glass has been evaluated by deconvolution of the spectra. Various theoretical ratios of aluminium species in the cement matrix to the unreacted ones remaining in glass have been estimated. The (19)F MAS-NMR spectra are identical for the glass and cements at the early times and contain a dominant signal assigned to Al-F-Sr(n). CONCLUSIONS: The data confirms that the conversion of aluminium is a diffusion-controlled process at early stage less than 1h and it is largely complete between 1 and 6h. The comparison with the experimental data shows that the majority of aluminium cations do not form tricarboxylates but are coordinated with one or two carboxylic groups and other ligands. Insufficient amount of water and excess of glass in this cement formulation affect glass degradation mechanism.

Variations of salivary flow rates in Brazilian school children.

The salivary flow rate (SFR) in healthy individuals may vary according to different factors. There is a scarcity of studies from different geographical areas that analyze SFR variations in children. The aim of this study was to verify stimulated salivary flow rate (SFR) variations in 6 to 12-year-old children, from four different public schools of Rio de Janeiro and correlate these data to gender, age, type of dentition, and health status. Clinical data were taken from the children's medical records that were kept at those schools. Oral examination and sialometry were performed in every child. Salivary flow rate was obtained by chewing-stimulated whole saliva under standard conditions. There were significant differences in SFR according to age (p = 0.0003). Six and 12-year-old children showed the lowest SFR, and when they were excluded from the analysis, no significant differences were found (p = 0.21). There were also significant differences in SFR among children from different public schools (p = 0.0009). The gender did not show any correlation to SFR, even when children were stratified by age (p = 0.36). Correlation between SFR and deciduous, mixed or permanent dentition was not found as well. These results show that the analyzed clinical variables did not seem to influence SFR in this children population.

Variations of salivary flow rates in Brazilian school children

O fluxo salivar (FS) em indivíduos saudáveis pode variar em função de diversos fatores. Dados sobre a análise das variações do FS em crianças de diferentes regiões geográficas são escassos na literatura. O objetivo deste trabalho foi estudar possíveis variações do FS em crianças de quatro escolas públicas do Rio de Janeiro, apresentando entre 6 e 12 anos de idade, além de correlacionar esses dados com gênero, idade, tipo de dentição e estado de saúde. A história médica das crianças foi obtida dos registros nas escolas. Em todas as crianças foram realizados exame bucal e sialometria. O FS foi obtido pelo método de saliva total estimulada mecanicamente, em condições padronizadas. Houve diferenças no FS em relação à idade (p = 0,0003). Crianças de 6 e 12 anos mostraram as menores médias de FS, mas quando estas crianças foram eliminadas da análise, não houve mais diferenças significativas no FS em relação à idade (p = 0,21). Houve também diferenças significativas nas médias dos FS entre as escolas (p = 0,0009). Não houve correlação do FS com gênero, mesmo quando as crianças foram agrupadas em relação à idade (p = 0,36). Também não houve correlação entre FS e as dentições decídua, mista ou permanente. Esses resultados mostram que na população de crianças estudada não houve influência das variáveis clínicas analisadas sobre o FS.