ABSTRACT
This study was performed to evaluate the effects of microstructural change of zirconia surface on tensile bond strength with resin cement. The zirconia partially sintered block was cut into a size of 18 × 18 × 7 mm, and then the Zirface slurry (DMAX, Daegu, Korea) containing 15% and 30% zirconia was applied and followed by sintering at 1530 ℃ for 2 hours. Resin cement (PermaCem 2.0, DMG, Hamburg, Germany) was applied on zirconia specimen and polymerized to prepare an 18 × 18 × 14 mm block. In addition, for comparison of bond strength, specimens were prepared for the group that was polished and the group that was blasted at 3 atm using 110 µm alumina. Thereafter, all blocks were cut into a cross-sectional area of 1.0 × 1.0 mm to prepare 12 specimens. The specimens were immersed in distilled water at 37 ℃. for 10 days for aging treatment. A holder for tensile testing was attached to each of the specimens, and then a tensile force was applied at a crosshead speed of 0.5 mm/min to measure the fracture load. The fracture surfaces of each test piece was observed with a high-resolution field emission scanning electron microscope. Through the above tests, the following results were obtained. 1. On the blasted surface, zirconia grains were locally removed but on the Zirface treated surface, a porous microstructure was created on the zirconia surface. 2. Arithmetical mean deviation from the mean line ra was the highest in the blasted group and the lowest in the polished group, and as a result of Tukey analysis, there were statistically significant differences between all test groups (P<0.05). 3. The maximum tensile bond strength was 18.8±5.4 MPa in the Zirface 30% group, and as a result of Tukey analysis, there was a statistically significant difference from the other test groups (P<0.05). 4. As a result of observing the fracture surface after the tensile test with a high-resolution field emission scanning electron microscope, in the Zirface 30% group, cohesive fracture and interfacial fracture in the resin was observed, but the other test groups showed the interfacial fracture pattern. In conclusion, within the limits of this study, treating the zirconia surface with Zirface 30% to form a porous microstructure can contribute to the improvement of the bond strength between zirconia and resin cement.
ABSTRACT
Background/Aims@#There is no study assessing the effect of changes of secondhand smoke (SHS) exposure and new-onset hypertension. We investigated the effect of a change of SHS exposure status on new-onset hypertension in self-reported and cotinine-verified never smokers. @*Methods@#Out of individuals enrolled in the Kangbuk Samsung Health Study between 2011 and 2016, 87,486 self-reported and cotinine-verified never smokers without hypertension at baseline visit were included with a median follow-up of 36 months. Individuals were divided into four groups on the basis of their SHS exposure status at baseline and at follow-up: no, new, former, and sustained SHS exposure groups. @*Results@#The incidence rates per 10,000 person-year of new-onset hypertension in no, new, former, and sustained SHS exposure groups were 84.7, 113.3, 102.0, and 123.7, respectively (p < 0.001). A multivariable Cox-hazard analyses showed that new and sustained SHS exposure groups increased their hazard ratio (HR) for new-onset hypertension compared to no SHS exposure group (HR, 1.31; 95% confidence interval [CI], 1.08 to 1.60 for new SHS exposure group; and HR, 1.24; 95% CI, 1.06 to 1.45 for sustained SHS exposure group). However, being part of the former SHS exposure group did not increase the risk of new-onset hypertension (HR, 0.91; 95% CI, 0.81 to 1.03). @*Conclusions@#This study showed that either new, or sustained SHS exposure, but not former SHS exposure, increased the risk for new-onset hypertension in self-reported never smokers verified as nonsmokers by urinary cotinine. These findings show the possibility that changing exposure to SHS even for a relatively short period can modify the risk of new-onset hypertension in self-reported and cotinine-verified never smokers.
ABSTRACT
This study was performed to evaluate the effects of microstructural change of zirconia surface on tensile bond strength with resin cement. The zirconia partially sintered block was cut into a size of 18 × 18 × 7 mm, and then the Zirface slurry (DMAX, Daegu, Korea) containing 15% and 30% zirconia was applied and followed by sintering at 1530 ℃ for 2 hours. Resin cement (PermaCem 2.0, DMG, Hamburg, Germany) was applied on zirconia specimen and polymerized to prepare an 18 × 18 × 14 mm block. In addition, for comparison of bond strength, specimens were prepared for the group that was polished and the group that was blasted at 3 atm using 110 µm alumina. Thereafter, all blocks were cut into a cross-sectional area of 1.0 × 1.0 mm to prepare 12 specimens. The specimens were immersed in distilled water at 37 ℃. for 10 days for aging treatment. A holder for tensile testing was attached to each of the specimens, and then a tensile force was applied at a crosshead speed of 0.5 mm/min to measure the fracture load. The fracture surfaces of each test piece was observed with a high-resolution field emission scanning electron microscope. Through the above tests, the following results were obtained. 1. On the blasted surface, zirconia grains were locally removed but on the Zirface treated surface, a porous microstructure was created on the zirconia surface. 2. Arithmetical mean deviation from the mean line ra was the highest in the blasted group and the lowest in the polished group, and as a result of Tukey analysis, there were statistically significant differences between all test groups (P<0.05). 3. The maximum tensile bond strength was 18.8±5.4 MPa in the Zirface 30% group, and as a result of Tukey analysis, there was a statistically significant difference from the other test groups (P<0.05). 4. As a result of observing the fracture surface after the tensile test with a high-resolution field emission scanning electron microscope, in the Zirface 30% group, cohesive fracture and interfacial fracture in the resin was observed, but the other test groups showed the interfacial fracture pattern. In conclusion, within the limits of this study, treating the zirconia surface with Zirface 30% to form a porous microstructure can contribute to the improvement of the bond strength between zirconia and resin cement.
ABSTRACT
Background@#No study has assessed association between cigarette smoking and new-onset diabetes mellitus (NODM) incidence using two different smoking classification systems: self-reported questionnaire and urine cotinine. The objective of this longitudinal study was to evaluate NODM risk using the above two systems in Korean adults. @*Methods@#Among individuals enrolled in Kangbuk Samsung Health Study and Cohort Study who visited between 2011 and 2012 at baseline and 2014 at follow-up, 78,212 participants without baseline diabetes mellitus were followed up for a median of 27 months. Assessment of NODM incidence was made at the end of follow-up period. Cotinine-verified current smoking was having urinary cotinine ≥50 ng/mL. @*Results@#Percentages of self-reported and cotinine-verified current smokers were 25.9% and 23.5%, respectively. Overall incidence of NODM was 1.5%. According to multivariate regression analyses, baseline self-reported current smoking (relative risk [RR], 1.33; 95% confidence interval [CI], 1.07 to 1.65) and cotinine-verified current smoking (RR, 1.27; 95% CI, 1.08 to 1.49) increased NODM risk compared to baseline self-reported never smoking and cotinine-verified current non-smoking. Higher daily amount and longer duration of smoking were also associated with increased NODM risk (P for trends <0.05). In particular, selfreported current smokers who smoked ≥20 cigarettes/day (RR, 1.62; 95% CI, 1.25 to 2.15) and ≥10 years (RR, 1.34; 95% CI, 1.08 to 1.67) had the highest RRs for NODM. These results remained significant in males, although there was no gender interaction. @*Conclusion@#This longitudinal study showed that baseline self-reported and cotinine-verified current smoking were associated with increased risks of NODM, especially in males.