P2Y2 receptor elevates intracellular calcium concentration in rabbit eye suprachoroid

Effects of ATP on the intracellular free calcium ion concentration ([Ca2+]i) in the rabbit eye suprachoroid were investigated by means of fura-2 microfluorophotometry. ATP application (10 to 100 microM) elicited a dose-dependent biphasic [Ca2+]i-increase: a fast phase typically peaking within 30 s and a following slow plateau phase, which lasted during the presence of ATP. The slow plateau phase was markedly diminished by removal of extracellular Ca2+, whereas the fast phase remained. An inhibitor of Ca2+ release from the sarcoplasmic reticulum (TMB-8), an endoplasmic Ca2+-ATPase inhibitor (thapsigargin) and a phospholipase C (PLC) inhibitor (U-73122) diminished the fast phase. A P2 receptor antagonist (Suramin) inhibited the ATP-induced [Ca2+]i-response. The potency order of ATP and related substances in producing the [Ca2+]i-elevation was UTP approximately equals ATP>ATP-gamma-S>ITP>ADP. beta,gamma-MethyleneATP, 2-methylthioATP and UDP evoked no response. This order is consistent with the P2Y2 receptor characteristics. Cross-desensitization between ATP and UTP excludes the co-existence of the other types of receptors. In conclusion, the ATP-induced [Ca2+]i-elevation in the rabbit eye suprachoroid was elicited by the Ca2+ release from the PLC-dependent, thapsigargin-sensitive intracellular Ca2+ storage sites by activating P2Y2 nucleotide receptors.     

Stress distribution prevents ischaemia and bone resorption in residual ridge

Objective

Intensive mechanical stress and/or inflammation are known to induce alveolar bone resorption. This study investigated whether a distribution of mechanical stress would reduce residual ridge resorption or improve ischaemia.

Design

Thirty rats were divided into six experimental groups (n = 5). The control group received no intentional stimulation, but rats in the experimental groups wore denture stimulators made of acrylic resin or a soft lining material. The stimulator transmitted masticatory pressure to the rats’ palates for four weeks. The four types of soft lining materials investigated in this study dispersed the applied pressure, with compressive stress ranging from 20.8 to 90.8 kPa. Volumes of blood flow and bone resorption of denture foundations were measured every week for 4 weeks. Statistical evaluation of these results was performed using two-way ANOVA and Holm-Sidak test within 5% error limits.

Results

Non-viscoelastic material clearly induced bone resorption and ischaemia of denture foundations, while viscoelastic materials reduced these phenomena to different extents according to their viscoelastic properties. Ischaemia in the alveolar ridge preceded residual ridge resorption, because the amount of residual ridge resorption and blood flow rate showed a simple linear regression.

Conclusion

Animal model of this study suggested that a distribution or reduction of mechanical stress could improve blood flow and decrease alveolar ridge resorption.     

Analysis of chemical interaction of 4-MET with hydroxyapatite using XPS

Each dental adhesive contains a specific functional monomer that determines its actual adhesive performance to tooth tissue. 4-methacryloxyethyl trimellitic acid (4-MET) is well-known as one of the functional monomers mostly available and consequently widely used in commercial adhesives. We therefore characterized the chemical interaction of 4-MET with hydroxyapatite (HAp) using X-ray Photoelectron Spectroscopy (XPS). XPS revealed that the peak representing -COO- of 4-MET shifted to a lower binding energy, when 4-MET was adsorbed onto HAp. Deconvolution of this shifted peak disclosed two components with a peak representing unreacted carboxyl groups and ester groups, and a peak suggesting chemical bonding of other carboxyl groups to Ca of HAp. XPS spectra of HAp treated with 4-MET also disclosed the surface to be enriched in calcium and decreased in phosphorus, indicating that phosphorus was extracted at a relatively higher rate than calcium. It can thus be concluded that true chemical bonding of 4-MET with calcium present in HAp occurred, as it was proven using XPS.     

Effect of presilanization filler decontamination on aesthetics and degradation resistance of resin composites

Filler-matrix coupling determines, to a large extent, the mechanical strength and clinical longevity of dental composites. The aim of this study was to examine how far a methodology to decontaminate filler prior to silanization may improve aesthetic performance in addition to physico-mechanical properties such as degradation resistance. It was reported that filler particles are surrounded and wrapped by a film that consists of multiple layers of silane molecules. X-ray photoelectron spectroscopy, however, revealed that silanization of filler particles largely depended upon siloxane bridge (Si-O-Si) formation between the silica surface and the silane molecule rather than on intermolecular bonding between adjacent silane molecules. In this study, we showed that filler decontamination resulted in a higher translucency, thereby providing a better aesthetic potential. In addition, experimental composites produced following presilanization decontamination of filler revealed a higher Vickers hardness value and a diametral tensile strength that was resistant to degradation by thermo-cycling.     

Effect of self-etching primer containing N-acryloyl aspartic acid on enamel adhesion.

OBJECTIVES: A previous study demonstrated that N-acryloyl aspartic acid (N-AAsp) aqueous solution is useful as a self-etching primer for dentin adhesion. The purpose of this study was to evaluate whether N-AAsp solution can be used for enamel etching, when compared with phosphoric acid. METHODS: N-AAsp was synthesized by the reaction of DL-aspartic acid and acryloyl chloride. The experimental self-etching primers were prepared by dissolving N-AAsp in water at various concentrations up to 20 wt%. The tensile bond strength of resin to bovine enamel was measured after the enamel was treated with the N-AAsp primers. The 40 wt% H(3)PO(4) was used for comparison. The treated enamel surfaces and the resin-enamel interfaces were also observed with a scanning electron microscope. RESULTS: The tensile bond strength to enamel increased linearly with the increasing N-AAsp concentration and reached the same value as that to enamel etched with 40 wt% H(3)PO(4) when N-AAsp concentration was 20 wt%, even though the etching ability of 20 wt% N-AAsp was inferior to 40 wt% H(3)PO(4). Regardless of the concentration of N-AAsp, the bond strength to enamel was the same as that to dentin reported in our previous study. SIGNIFICANCE: The 20 wt% N-AAsp aqueous solution showed enamel bonding equivalent to 40 wt% H(3)PO(4) in addition to the advantage of eliminating the rinse step with water. Based on the results obtained in this study along with those obtained in a previous study, it was concluded that 20 wt% N-AAsp aqueous solution is a promising self-etching primer to simultaneously treat enamel and dentin.     

Marginal gap formation and fluoride release of resin-modified glass-ionomer cement: effect of silanized spherical silica filler addition

The purpose of this study was to investigate the effects of silanized spherical silica fillers (SF) on the immediate and 24-hour marginal gaps of resin-modified glass-ionomer cement (RMGIC) in tooth cavities. In correlation with marginal gap formation in the tooth cavity, these influencing factors were also examined: marginal gap and setting shrinkage of cement in the Teflon mold, as well as the shear bond strength to tooth substrate. Moreover in correlation with caries prevention, fluoride release was examined too. In this investigation, the fillers were mixed into the RMGIC powder (Fuji II LC EM). Untreated spherical silica filler (UF)-added RMGIC was used as a comparison. When compared with the control (i.e., original RMGIC), the addition of SF significantly decreased immediate marginal gap in tooth cavities and setting shrinkage in Teflon mold up to 63% and 66% respectively. Fluoride release was significantly reduced too. Apart from these results, this study showed that addition of 5 wt% SF increased the shear bond strength to human enamel and dentin.     

Degree of immobilization of synthetic RGDS(PO(3)H(2))PA peptides on titanium surfaces

The purpose of this study was to characterize the chemical interaction between titanium surfaces and the peptide RGDS(PO(3)H(2))PA (P-RGD) synthesized from RGD peptide (RGD) and o-phospho-L-serine (P-Ser), and to determine the degree of peptide immobilization on the titanium surface. X-ray photoelectron spectroscopy showed that the adsorption amount of RGD was significantly smaller than those of P-Ser and P-RGD (p<0.05). Furthermore, although it appeared that P-RGD bonded to the surface, ultrasonic rinsing with water caused it to dissociate, releasing RGD and leaving only S(PO(3)H(2))PA bonded to the surface. These findings show that although it remains difficult to obtain a stable P-RGD layer, the phosphate functional group greatly improves immobilization of the molecule on titanium surfaces.     

Effect of adhesive primer developed exclusively for heat-curing resin on adhesive strength between plastic artificial tooth and acrylic denture base resin

Despite progress in the development of denture base resin and artificial tooth materials, dental clinics are still plagued with artificial teeth falling off the denture base--due to poor bond strength--after denture delivery. Against this background, this study sought to examine the effect and durability of an adhesive primer developed exclusively for heat-curing resin on the adhesive strength of heat-curing denture base acrylic resin to plastic artificial tooth. Test specimens were divided into four groups according to the treatment method of the artificial tooth's test bonding surface: air abrasion, adhesive primer application, adhesive primer application after air abrasion, and pretreatment only (control). After heat curing of acrylic resin onto the bonding surface, shear test was performed for two storage periods: 24-hour versus 100-day water storage. From the results obtained, it was revealed that the evaluated adhesive primer was significantly effective in increasing adhesive strength between artificial tooth and acrylic resin, although specimens were stored in water for 100 days.     

Flexural properties of eight flowable light-cured restorative materials, in immediate vs 24-hour water storage

This study evaluated the flexural strength, flexural modulus, modulus of resilience and water sorption of eight flowable light-cured restorative materials compared with two conventional restoratives (as control). Forty specimens of each material were made. Twenty specimens were immediately flexural tested, while the remaining 20 were weight-measured and immersed in distilled water in a 37 degrees C incubator. After 24 hours, the samples were weight-measured again to identify water sorption and they were flexural tested. The findings were statistically analyzed using t-test, one-way ANOVA, Tukey test and Pearson's Product-Moment Correlation. The results of the flexural strength test were also analyzed using Weibull statistic. All flowable light-cured restorative materials except Palfique Estelite Low Flow exhibited immediate flexural strength values between the conventional ones. All flowable light-cured restorative materials showed 24-hour flexural strength values between the conventional ones. The Weibull modulus for immediate flexural strength of the materials varied from 6.37 to 15.23, while for 24-hour flexural strength, the strength varied from 8.10 to 14.30. In both conditions, all flowable light-cured resin composites showed lower flexural moduli but higher modulus of resilience than the conventional ones. The water sorption of all resin composites was lower than the flowable light-cured compomer. There was a distinct relation (r=-0.84, p<0.01) between the increasing ratio in modulus of resilience and the amount of water sorption.