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Objectives: This study aimed to investigate the effects of ECIG smoking on color stability of simulated veneers made from lithium disilicate glass ceramics.Materials and methods: 24 specimens of lithium disilicate glass ceramic veneers were exposed to aerosols which are flavored and non-flavored with nicotine content (0, 6 and 12 mg). Six specimens were prepared for each group IPS E.Max press high translucent ceramic discs. Vacuum Induction Device was used to simulate smoking in vivo. Color measurement was performed on the specimens before and after exposure to ECIG aerosol using a calibrated spectrophotometer.Results: According to Two Way ANOVA, both flavor and nicotine contents have significant effect on color change (P <0.0001). Regarding specimens exposed to e-liquid, flavorless 0 mg. nicotine group showed the lowest value 1.044 (±0.044), while flavored 12 mg. nicotine group showed the highest values 2.369 (±0.034). As for specimens which exposed to e-liquid, flavorless group lowest value 1.197 was found, while flavored group showed the highest values 1.868. Regarding specimens which exposed to e-liquid, group which exposed to 0 mg nicotine showed the lowest value 1.268 (±0.233), while group exposed to 12 mg nicotine showed the highest values 1.868 (±0.524). Conclusion:Study showed that exposure to flavored and non-flavored ECIG aerosol of different nicotine concentrations has a significant effect on the color of lithium disilicate glass ceramic veneers. Higher concentrations of flavored nicotine had visually perceptible color changes and were deemed clinically unacceptable.

Background The aim of this study was to assess the impact of abutments with angled screw access channel on the retention of zirconia crowns. Methods Seven implant replicas were inserted in epoxy resin blocks. Fourteen zirconia crowns for central incisor tooth were digitally fabricated and cemented to titanium bases (Ti-bases) with resin cement. Titanium bases were categorized into 2 groups (n = 7). Control group (Group STA) included straight screw access channel abutments. Study group (Group ASC) included angled screw access channel abutments. Following aging (5 °C-55 °C, 60 s; 250,000 cycles, 100 N, 1.67 Hz), the pull-off forces (N) were recorded by using retention test (1 mm/min). Types of failure were defined as (Type 1; Adhesive failure when luting agent predominantly remained on the Ti-base surface (> 90%); Type 2; Cohesive failure when luting agent remained on both Ti-base and crown surfaces; and Type 3; Adhesive failure when luting agent predominantly remained on the crown (> 90%). Statistical analysis was conducted by using (IBM SPSS version 28). Normality was checked by using Shapiro Wilk test and Q-Q plots. Independent t-test was then used to analogize the groups. Results Mean ± standard deviation of retention force records ranged from 1731.57 (63.68) N (group STA) to 1032.29 (89.82) N (group ASC), and there was a statistically significant variation between the 2 groups (P < .05). Failure modes were Type 2 for group STA and Type 3 for group ASC. Conclusions The retention of zirconia crowns to abutments with a straight screw access channel is significantly higher than abutments with angled screw access channel.

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