[Effect of hydroxyapatite based agents on the bonding properties of universal adhesives]

Objective: To study the effect of hydroxyapatite (HA) based agents on the bonding properties of universal adhesive with different application modes, and to provide evidence for the use of adhesives after desensitization treatment. Methods: Sixty impacted third molars were extracted and selected (acquired from Department of Oral and Maxillofacial Surgery, College of Stomatology, Xi'an Jiaotong University). Four third molars were used to prepare 1 mm thick dentin disks and treated with 1% citric acid to simulate sensitive tooth models. The dentin surfaces were observed by scanning electron microscope (SEM) after treating with no desensitization (control group), desensitized by HA based toothpaste Biorepair and Dontodent Sensitive respectively (desensitizing toothpaste A group and B group), or HA paste treatment (desensitizing paste group ) (n=2 per group). The remaining teeth were selected to expose the mid-coronal dentin and establish dentin sensitivity models. Then, the specimens were divided into 4 former groups and received corresponding treatment. Each group was randomly divided into 2 subgroups, and intermediately strong universal adhesive (G-Premio Bond) was applied on the desensitized dentin by either etch-and-rinse mode or self-etch mode. Resin-dentin slice specimens (n=4 per subgroup), microtensile specimens (n=20 per subgroup) and slice specimens (n=6 per subgroup) were prepared. The microstructure and nanoleakage of the adhesive interfaces were observed by scanning electron microscopy (SEM). The microtensile strength (bond strength) and fracture mode were tested and recorded. The water permeability of the adhesive interface was observed by laser scanning confocal microscopy (LSCM). Results: SEM showed that desensitizing toothpaste and desensitizing paste could partially or entirely occlude most of the dentin tubules. For the etch-and-rinse mode, the bond strength of specimens treated with toothpaste A [(40.98±4.60) MPa], toothpaste B [(40.89±4.64) MPa] and HA paste [(41.48±3.65) MPa] was significantly higher than that of the control group [(38.58±4.28) MPa] (F=3.89,P<0.05). There was no statistically significant difference in bond strength among the 4 subgroups for self-etch modes (F=0.48,P>0.05). After desensitization, the bond strength of the control group and desensitizing groups in the self-etch mode was significantly higher than that in the etch-and-rinse mode (P<0.05). The overall fracture modes were mixed failure and interfacial failure in the control group and desensitizing groups. SEM showed speckled silver-stained particles deposited along the bottom of the hybrid layer on the bond interface of etch-and-rinse mode, and there were few silver-stained particles deposited on the bond interface of self-etch mode. LSCM showed continuous linear penetration in the hybrid layer of etch-and-rinse mode subgroups and discontinuous linear penetration in the hybrid layer of self-etch mode subgroups. Conclusions: HA based desensitizers have no adverse effect on the bond strength of intermediately strong universal adhesive and show good bonding performance accompanied with the self-etch mode.

Damage to epitaxial GaN layer on Al2O3 by 290-MeV 238U32+ ions irradiation

Micro-structural characteristics and electrical properties of an n-type GaN epilayer on Al₂O₃ irradiated by 290-MeV ²³⁸U³²⁺ ions to various fluences were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution X-ray diffraction (HRXRD), and Raman scattering spectroscopy. AFM images show that the nano-hillocks generated, and the diameter and density of the nano-hillocks, increase obviously with increasing ion fluence, accompanied by an increase in surface roughness. SEM images display that the Al, O, and C elements appear on the GaN surface, along with a spiral-like, layered volcanic-cone structure formed at the highest-fluence irradiation. HRXRD reveals that the dislocation density increases, as the lattices gradually expand, and that Ga₂O₃ was produced with increasing ion fluence. Raman scattering spectra show that no N and Ga vacancies were produced, the free-carrier concentration decreases, while its mobility first increases and then exhibits a significant reduction with increasing ion fluence.

Short communication: Changes in fluorescence intensity induced by soybean soluble polysaccharide-milk protein interactions during acidification

Interactions between stabilizer and milk protein are believed to influence the stabilizing behavior of the milk system. We investigated changes in fluorescence intensity induced by interactions of soybean soluble polysaccharide (SSPS) and milk protein (Mp) during acidification. The fluorescence intensity (If) of Mp increased as pH decreased from 6.8 to 5.2. Compared with Mp alone, If of SSPS-Mp mixtures increased as the pH decreased from 6.8 to 5.2. We found that the If of the SSPS-Mp mixture decreased in a pH range from 5.2 to 3.6, which indicated a change in the polarity microenvironment around the Trp residues. We also found that the maximum emission wavelength (λmax) shifted from 337 to 330nm as pH decreased from 6.8 to 3.6, in further support of SSPS interacting with the polar portion of Mp during acidification. Furthermore, an excited monomeric molecule (pyrene exciplex) was found as a ground-state pyrene formed and a broad band was shown at about 450nm. The intensity ratio of the first peak to the third peak (I1:I3) of Mp increased slightly, and the ratio of intensity of pyrene exciplex to monomer (Ie:Im) decreased because pyrene molecules were located in a less hydrophobic microenvironment during acidification. However, the ratio of I1:I3 decreased clearly at pH below 5.6 and the ratio of Ie:Im showed the opposite trend in the SSPS-Mp mixture. Changes in intrinsic and exogenous fluorescence intensity confirmed that interactions of SSPS and Mp could change the polarity of the microenvironment and that SSPS probably interacted with the polar portion of Mp. These results could give insight into the behavior of stabilizers in acid milk products.