Field test of quantum key distribution over aerial fiber based on simple and stable modulation.

We have developed a simple time-bin phase encoding quantum key distribution system, using the optical injection locking technique. This setup incorporates both the merits of simplicity and stability in encoding, and immunity to channel disturbance. We have demonstrated the field implementation of quantum key distribution over long-distance deployed aerial fiber automatically. During the 70-day field test, we achieved approximately a 1.0 kbps secure key rate with stable performance. Our work takes an important step toward widespread implementation of QKD systems in diverse and complex real-life scenarios.

Surface roughness and gloss alteration of polished resin composites with various filler types after simulated toothbrush abrasion.

Background/purpose: Few studies have focused on the influence of simulated toothbrush abrasion on the surface qualities of novel nanofilled and nanohybrid composites. The aim of the study was to evaluate the surface roughness and gloss values of resin-based composite (RBC) materials with various filler types before and after simulated toothbrush abrasion. Materials and methods: One nanofilled (Filtek Z350 XT [FT3]), two nanohybrids (Harmonize [HM] and Clearfil Majesty [CM]) and one microhybrid (Filtek Z250 [FT2]) were evaluated. Twelve specimens of each material were made and polished with silicon carbide sandpapers. Initial surface roughness and gloss values were measured as negative controls. Then, all specimens were subjected to simulated toothbrush abrasion on a custom-made apparatus. After 2000, 4000 and 8000 cycles, the surface roughness and gloss values of all specimens were tested. One additional specimen from each group was selected for scanning electron microscope (SEM) analysis. Results: For FT3, Ra and GU values did not significantly change until after 8000 cycles during the process of toothbrushing (P > 0.05). For HM, CM and FT2, the Ra and GU values significantly decreased after 4000 and 8000 cycles of toothbrush abrasion (P < 0.05). After 8000 cycles of toothbrush abrasion, FT3 presented the lowest surface roughness and highest gloss values of all materials (P < 0.05). SEM images showed that surface textures and irregularities corresponded to the results of surface roughness and gloss. Conclusion: Surface roughness and gloss after simulated toothbrush abrasion were material dependent. Nanofilled resin composite presented the lowest Ra values and highest GU values.

Polymerization shrinkage and shrinkage stress of bulk-fill and non-bulk-fill resin-based composites.

Background/purpose: Bulk-fill resin-based composites (RBCs) are a new class of restorative materials, and polymerization shrinkage (PS) is concerned due to their single increment up to 4 mm. The aim of this study was to evaluate the PS and shrinkage stress (SS) of bulk-fill RBCs in vitro. Materials and methods: Three bulk-fill RBCs and three conventional non-bulk-fill RBCs were selected. The PS was determined with Acuvol volumetric shrinkage analyzer by calculating the specimen volume variation before and after light irradiation. The SS was investigated using universal testing machine method with a polymethyl methacrylate rod as a bonding substrate. The force generated during the polymerization process was detected by a load cell linked to a computer. SS was calculated by dividing the maximum stress force by the area of the rod. Results: The mean PS of various RBCs ranged from 1.72% to 2.13%. All PS results of bulk-fill RBCs were comparable to their conventional counterparts. Sonicfill 2 (SF2) and Harmonize (HM) showed the lowest PS (p < 0.05; Tukey HSD test). Medians of SS results ranged from 0.55 MPa to 0.67 MPa. All SSs of bulk-fill RBCs were comparable to their conventional counterparts. SF2 showed significantly lower SS than Tetric N-Ceram (TN) and Tetric N-Ceram Bulk Fill (TNB) (p < 0.0083; post hoc comparisons with Bonferroni adjustments). A moderate, positive correlation was observed between PS and SS with Pearson's correlation (r = 0.446, p = 0.013). Conclusion: Both PS and SS are material dependent. A moderate, positive correlation between PS and SS is found with new bulk-fill RBCs and their conventional counterparts.

Effects of heat treatment on metal-ceramic combination of selective-laser-melted cobalt-chromium alloy.

STATEMENT OF PROBLEM: Components fabricated by selective laser melting (SLM) deform because of residual stress, but heat treatment allows the release of that stress and avoids deformation. Although dental cobalt-chromium (Co-Cr) alloy has been specifically designed for SLM, the effects of heat treatment on the metal-ceramic combination of SLM Co-Cr restorations require investigation. PURPOSE: The purpose of this in vitro study was to evaluate the effects of heat treatment on the metal-ceramic combination of SLM Co-Cr alloy. MATERIAL AND METHODS: Following ISO 9693:2012, Co-Cr metal strips (Solibond C Plus cast alloy and SLM powders; YETI Dental) were fabricated with a dimension of 25×3×0.5 mm by casting and SLM. The SLM specimens were divided into 3 subgroups (n=15 for each subgroup). Two subgroups were subjected to heat treatment at 880°C (SLM-880) and 1100°C (SLM-1100). The third subgroup was not subjected to heat treatment and served as a control (As-SLM). Cast specimens (n=15) also acted as a control. A porcelain layer with a thickness of 1.1 mm was fired to the central area (3×8 mm) of each specimen. The 3-point bend test was used to evaluate the metal-ceramic bond strength (τb). The fractured metal surfaces were examined by the naked eye, using a digital camera, and also using a scanning electron microscope. The area fraction of adherence porcelain (AFAP) was determined by measuring the atomic percentage of silicon using energy-dispersive x-ray spectroscopy (EDS). One-way ANOVA and the Kruskal-Wallis test, followed by the Mann-Whitney test (α=.05), were used for statistical analysis. RESULTS: The 1-way ANOVA found no significant difference in the bond strength among the 4 groups. The EDS analysis indicated that specimens in the groups receiving heat treatment (SLM-880 and SLM-1100) showed higher AFAP values than those in the As-SLM group (P<.05). The SLM-880 also showed significantly higher AFAP values than the SLM-1100. Compared with the cast group, significant differences in AFAP values were also observed, and the specimens in the order of highest to lowest AFAP values were SLM-880>cast>As-SLM; no significant difference was found between the SLM-1100 and cast groups. CONCLUSIONS: Heat treatment at 880°C and 1100°C did not affect the metal-ceramic bond strength of Co-Cr alloy made by SLM but did improve the porcelain adherence. SLM-fabricated and heat-treated Co-Cr alloy shows comparable or more porcelain adherence than cast specimens.

[Effect of Polident denture cleansers on the properties of heat-polymerized denture base acrylic resin].

OBJECTIVE: To study the change in properties of heat-polymerized acrylic resin after using one denture cleanser. METHODS: In the study, 20 disk-shaped (50.0 mm×0.5 mm) and 40 rectangular (34.0 mm×13.5 mm×1.3 mm) specimens prepared from heat-polymerized acrylic resin were randomly divided into four groups. The specimens were exposed to one of the three treatments as follows: Group 1 was without any treatment, Group 2 was exposed to air, Group 3 to distilled water, and Group 4 to Polident. The 4 exposures lasting 8 hours were conducted daily and repeated for 30 days. The color stability of heat-polymerized acrylic resin was determined by visual methods. The flexural strength and bonding strength of acrylic resin were measured using a universal testing machine. All the results were analyzed using ANOVA. RESULTS: The flexural strength test of acrylic resin demonstrated significant differences between Group 4 and Group 1 (P<0.05), there were no significant differences among Group 1, Group 2 and Group 3. No significant differences were found in other properties of the test materials. CONCLUSION: Long-term use of polident could alter the physical and mechnical properties of heat-polymerized acrylic resin. It may be related to the accelerating aging of resins caused by certain chemicals in denture cleansers. Polident may have some adverse effects on denture materials for decreasing flexural strength of heat-polymerized acrylic resin after 30-day immersion.

[Study on the properties of self-adhering flowable composite].

OBJECTIVE: This study was designed to investigate the properties of self-adhering flowable composite by comparison with self-etching adhesive and traditional composite. Moreover, the effect of additional etching process on the bond strength of dentin was investigated. METHODS: Totally 90 bovine incisors were prepared to expose the dentin, and then divided into three groups (Group A, Group B and Group C). A, B and C were treated with flowable composite, flowable composite and self-etching adhesive, traditional composite and self-etching adhesive respectively. These groups were further divided into two subgroups, without additional etching process(i.e. A1, B1 and C1) and with additional etching process (i.e. A2, B2 and C2). The bond strength of those samples was measured and the results were analyzed with a one-way ANOVA. RESULTS: The shear bond strength of A1 [(3.39±1.71 ) MPa] was lower than B1 [(21.58±4.50) MPa],and there is significant difference (P<0.05) between them. There is no significant difference (P>0.05) between B1 and C1 [(19.31±6.79) MPa]. After additional etching process, the shear bond strength of A2 [(6.75±3.54) MPa] was higher than A1. As for self-etching adhesive, the shear bond strength of B2 [(16.56±7.39) MPa] was lower than B1 (P<0.05) and C2 [(11.31±5.54) MPa] was lower than C1 (P<0.05). CONCLUSION: The bond strength of self-adhering flowable composite was lower than that of flowable composite with self-etching adhesive. There was no significant difference between bond strength of flowable composite with self-etching adhesive and traditional composite with self-etching adhesive. However, the additional etching process would decrease bond strength of self-etching adhesive and increase the coefficient of variation of measured results.

Comparison between a silorane-based composite and methacrylate-based composites: shrinkage characteristics, thermal properties, gel point and vitrification point.

A silorane-based composite was compared against methacrylate-based composites in terms of shrinkage characteristics, thermal properties, gel point, and vitrification point. Shrinkage strain was measured using a laser triangulation method. Shrinkage stress was measured using a stress analyzer. Heat flow during photopolymerization was measured using photo-DSC. Statistical analysis was performed using one-way ANOVA and Tukey's test (p=0.05). Silorane exhibited significantly lower shrinkage strain than the methacrylate-based composites. It also presented the lowest stress values during light exposure, but the highest maximum stress rate after light exposure. It showed the highest heat flow rate, and it took the longest time to reach gel and vitrification points. Silorane demonstrated improved performance over the methacrylate-based composites with delayed gel and vitrification points as well as reduced shrinkage strain and stress. However, a high quantity of heat was liberated during the curing process, causing silorane to show significantly higher stress rate (p<0.05) than the methacrylate-based composites after light exposure.

[A new dynamic approach to monitoring dental composite curing kinetics].

OBJECTIVE: To employ a laser triangulation method for measuring the dynamic shrinkage of composite resins during polymerization, and to investigate the maximum shrinkage rate (S(max)) and the time at maximum shrinkage rate (t(max)). METHODS: A novel experimental set-up based on laser triangulation was utilized which was capable of real-time shrinkage strain measurements. Uncured composite was condensed into a PTFE mould and irradiated for 40 s. The laser signals obtained from lateral composite surfaces were monitored using a laser triangulation measuring system and were converted into the displacement of the tested surface. The volumetric shrinkage derived from the linear shrinkage was calculated by multiplying 3. Total volumetric shrinkage (%S) of the five restorative materials (AP-X, Charmfill, Charisma, Durafill VS, and Herculite Precis) was measured using three methods (laser triangulation method, Acuvol, and buoyancy method). S(max) and t(max) were measured using the laser triangulation method. Statistical analyses were done using the two-way ANOVA (P<0.05) and post hoc test. RESULTS: The highest shrinkage value was measured by Acuvol, followed by laser method, and the lowest was by buoyancy method. All the three methods of measuring %S generated the same, statistically secured ranking for the five light-cured restorative materials: DurafillVS < AP-X < Herculite Precis < Charisma < Charmfill. %S measured by laser triangulation method varied between 2.06% and 3.37%. S(max) varied between 4.39 µm/s and 29.25 µm/s. t(max) varied between 0.77 s and 1.59 s. Significant differences in S(max) (F=734.87,P<0.01) and t(max) (F=53.24,P< 0.01) for five composite resins were found. CONCLUSION: Laser triangulation method offers several advantages over the conventional methods of measuring polymerization shrinkage. It is simple, compact, non-invasive and suitable for measuring the dynamic polymerization shrinkage in real time without delay. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of visible-light-cure materials.

[Evaluation of laser triangulation method for measurement of post-gel shrinkage and post-vitrification shrinkage in composite resins].

OBJECTIVE: To employ a laser triangulation method for measuring post-gel and post-vitrification polymerization shrinkage of composite resins. METHODS: A novel experimental set-up capable of measuring real-time shrinkage strain was utilized. Total shrinkage of the five composite resins was measured. The measurements of post-gel and post-vitrification linear shrinkage as a function of the gel-point and vitrification transition point were also carried out in the study. RESULTS: Gel point of the five composite resins ranged from 0.77 s to 1.59 s, while vitrification transition point ranged from 1.99 s to 6.33 s. Post-gel shrinkage ranged from 33.35 µm to 53.18 µm and post-vitrification shrinkage ranged from 16.43 µm to 30.58 µm. Total shrinkage ranged from 39.25 µm to 64.84 µm. Significant differences in the gel point and vitrification transition point among the five composite resins were found (P < 0.01). Significant differences in the post-gel shrinkage, post-vitrification shrinkage and total shrinkage among the five composite resins were found (P < 0.01). The ranking of post-gel and post-vitrification shrinkage of these composite was different from that of their total shrinkage. CONCLUSIONS: Laser triangulation method is suitable for measuring clinically significant post-gel and post-vitrification shrinkage.