The effect of adding silver nanoparticles on the color stability of feldspathic porcelains.

Background: This study aims to investigate the color stability of feldspathic porcelains with different concentrations of silver nanoparticles (AgNPs). Materials and Methods: In this experimental study, feldspathic porcelain disks with AgNPs of 0 parts per million (ppm), 250 ppm, and 500 ppm were used (sample size = 180). These ceramic discs were subjected to thermocycling in tea, orange juice, and artificial saliva. The optical parameters of disks were measured before and after being immersed in the solutions. Then, the color change (ΔE 00) of the samples was measured by using the CIEDE 2000 formula. The data were analyzed by one-way analysis of variance (ANOVA) and Tukey's post hoc test. The level of significance was determined to be 0.05. Results: The results of the ANOVA test show that there was a significant difference in ΔE 00 (P ≤ 0.05). The maximum ΔE 00 was visible in the samples with AgNPs 0 ppm that were exposed to orange juice, and the minimum ΔE 00 was related to the disks with AgNPs 500 ppm in artificial saliva. Conclusion: Based on the results of this study, adding AgNPs to feldspathic porcelain increases the color stability of the ceramic discs.

Evaluating the color stability of 3D-printed resins against various solutions.

The purpose of this study was to investigate the effect of different solutions on the optical behavior of two types of 3D-printed resin (Detax and Asiga). The samples were randomly divided into 4 groups of cola, orange juice, tea and artificial saliva (control group) in the form of 14 x 10 mm blocks with a thickness of 1.5 ± 0.3 mm (10 samples in each group). By spectrophotometric device, the color of the examined samples was recorded in the CIE system and in three parameters *L (brightness), a* (red-green) and b* (blue-yellow) as the initial record. The color difference of the samples was recorded on 7 and 30 days after immersion as a secondary record. After that, using the formula, the color difference (ΔE) were calculated. T-test also was used to analyze the data. There was no significant difference between the amount of ΔE on 7th and 30th days after exposure to artificial saliva and cola and on 7th days after exposure to orange juice and tea. But on the 30th day, a significant difference was found in orange juice and tea drinks (p<0.05), so that the value of ΔE in Asiga printer was lower than Detax. ΔE changes in orange juice solution were more than other drinks. On the 30th day of immersion in tea drinks and orange juice, Asiga printer had significantly less color difference than Detax printer.

Effect of Adding Silver Nanoparticles on the Flexural Strength of Feldspathic Porcelain.

AIM: This study aimed to evaluate the impact of silver nanoparticles (AgNPs) on the flexural strength of feldspathic porcelain. MATERIALS AND METHODS: Eighty bar-shaped ceramic specimens were prepared in five groups, including a control group and four case groups containing 5, 10, 15, and 20% w/w of AgNPs. Each group consisted of 16 specimens. Silver Nanoparticles were synthesized by a simple deposition method. Three-point bending test was used in the universal testing machine (UTM) machine to evaluate the flexural strength of the specimens. The fractured surface of the ceramic samples was analyzed under scanning electron microscopy (SEM). In order to analyze the data obtained, one-way analysis of variance (ANOVA) and Tukey tests were used (p <0.05). RESULTS: The results implied that the average flexural strength of the samples in the control group was 90.97 MPa and for the experimental groups reinforced with 5, 10, 15, and 20% w/w of AgNPs were 89, 81, 76, and 74 MPa, respectively. CONCLUSION: The addition of AgNPs with a certain amount (up to a concentration of 15% w/w) without reducing the flexural strength improves the antimicrobial properties of the materials used and ultimately improves its quality for dental applications. CLINICAL SIGNIFICANCE: The addition of AgNPs can improve the antimicrobial properties and suitability of the materials.

In vitro Comparison of the Accuracy (Precision and Trueness) of Seven Dental Scanners.

STATEMENT OF THE PROBLEM: The mechanisms of operation of dental scanners are based on different technologies. Considering these differences, there are many types of scanners available in the market. PURPOSE: This in vitro study aimed to compare the accuracy (precision and trueness) of seven commonly used dental scanners. MATERIALS AND METHOD: In this in vitro experimental study, the accuracy of 7 common extra oral scanners (Sirona ineos inLab, Sirona X5, Dentium, Imes Icore 350I, Amann Girrbach, 3shape D700, and 3Shape E3) were evaluated. Each of scanners performed 7 scans of implant abutment of SIC (SIC MAX.GH1). Data from each scanner were then compared to data received from 3Shape Trios intra oral scanner as a reference. For evaluating the accuracy of each scanner, trueness and precision was evaluated. Collected data were analyzed using Kruskal Wallis and Bonferroni tests via SPSS version 22. RESULTS: Descriptive statistics showed the best trueness was for 3Shape E3 scanner with the average of 35.37µm and the worst trueness belonged to Sirona x5 scanner with the average of 51.75µm. Furthermore, the best precision was achieved for 3Shape E3 scanner with the average of 35.34, while the lowest precision was detected in 3Shape D700. The scanners had statistically significant differences with each other in terms of trueness and precision (p<0.05). CONCLUSION: Based on the results of this study, the extra oral scanner, 3shape E3, had the best trueness and precision. The lowest amount of trueness among the studied scanners was for the extra oral scanner, Sirona x5, and the lowest precision was for scanner 3shape D700.

Marginal Fit of Temporary Restorations Fabricated by the Conventional Chairside Method, 3D Printing, and Milling.

Objectives: This study aimed to compare the marginal fit of temporary restorations fabricated by the conventional chairside method, 3D printing, and milling. Materials and Methods: In this in vitro, experimental study, 14 temporary restorations were conventionally fabricated over an implant abutment and analog that had been mounted in a phantom model at the site of canine tooth, using auto-polymerizing acrylic resin and putty index. In digital manufacturing, the original model was scanned, and the final restoration was designed. Fourteen temporary restorations were milled out of polymethyl methacrylate (PMMA) blocks, and 14 others were printed by a 3D printer. Temporary crowns were placed on the abutment, and images were obtained from specific areas under a stereomicroscope at x100 magnification to measure the amount of marginal gap. Data were analyzed using one-way ANOVA and Tukey's test (α=0.05). Results: The mean marginal gap values for the temporary crowns in the 3D printing, milling, and chairside groups were 91.40, 75.28 and 51.23 µm, respectively. The crowns that were conventionally fabricated chairside exhibited the lowest marginal gap, and the difference in this respect was significant among the three groups (P<0.05). Conclusion: Temporary crowns fabricated by the chairside method showed significantly smaller marginal gap; however, the marginal gap of all three groups was within the clinically acceptable range.

Fit of cobalt-chromium copings fabricated by the selective laser melting technology and casting method: A comparative evaluation using a profilometer.

BACKGROUND: This study aimed to assess the marginal adaptation and internal fit of cobalt-chromium copings fabricated by the selective laser melting (SLM) and conventional techniques using a profilometer. MATERIALS AND METHODS: In this in vitro study sample size was calculated to be a total of 10 in two groups (n = 5). A brass model was used that had a circular cross-section with a round shoulder margin with 0.5 mm thickness and axial walls with 10 mm length and 6° taper. The copings fabricated with both techniques (SLM and casting method) were placed on the model, and vertical marginal gap was measured using a profilometer. The internal fit of copings was assessed by weighing the light-body addition silicone applied inside them, which simulated the cement. Data were analyzed through parametric (Independent t-test) and nonparametric (Mann-Whitney U-test, Bootstrap, Spearman, and Pearson Correlation) analysis. All analyses were performed at a significant level (α = 0.05) using SPSS. RESULTS: The mean marginal gap in the casting group (132.93 ± ) was significantly higher than that in the SLM group (67.14 ± 15.67 µm) (P < 0.05). The mean weight of light-body silicone was 9.60 ± in the SLM and 8.70 ± 1.21 mg in the casting group. No significant difference was noted between the two groups regarding the internal fit (P > 0.05). CONCLUSION: The copings fabricated by the SLM technique showed a smaller vertical marginal gap compared to the casting group. However, the two groups were not significantly different in terms of internal fit.

Effect of Three Commonly Consumed Beverages on Surface Roughness of Polished and Glazed Zirconia-Reinforced Lithium Silicate Glass Ceramics.

OBJECTIVES: This study aimed to assess the effect of three commonly consumed beverages on surface roughness of polished and glazed zirconia-reinforced lithium silicate (ZLS) glass ceramics. MATERIALS AND METHODS: In this experimental study, 104 rectangular specimens were cut from Vita Suprinity blocks with 2 mm thickness. After ultrasonic cleaning and firing of the specimens, they were finished and polished in two groups. Specimens in the first group were polished using a 2-step polishing kit while the second group specimens were glazed and heated in a porcelain firing oven according to the manufacturer's instructions. Baseline surface roughness was measured using a profilometer. Specimens in each group were then randomly divided into 4 subgroups (n=13) for immersion in artificial saliva (control group), cola, orange juice and black tea. Surface roughness was measured again and data were analyzed using two-way ANOVA. RESULTS: The highest and the lowest mean Ra were found in orange juice and saliva subgroups, respectively in both glazed and polished groups. The Ra values of both polished and glazed groups significantly increased after immersion in orange juice and cola (P<0.05). The polished surfaces showed insignificantly higher surface roughness compared with glazed surfaces (P>0.05). CONCLUSION: Orange juice and cola significantly increased the surface roughness of both polished and glazed ZLS ceramics. Type of surface finishing (polishing versus glazing) had no significant effect on the surface roughness of specimens following immersion in different beverages.

Fatigue Fracture Strength of Implant-Supported Full Contour Zirconia and Metal Ceramic Fixed Partial Dentures.

OBJECTIVES: Zirconia restorations have been suggested as a more durable and more appealing alternative to metal restorations. However, their mechanical properties may be negatively affected by fatigue due to superficial stresses or low temperature degradation. This study aimed to assess the fatigue fracture strength of three-unit implant-supported full contour zirconia and pre-sintered cobalt-chromium (Co-Cr) alloy posterior fixed partial dentures (FPDs). MATERIALS AND METHODS: In this in-vitro experimental study, 28 posterior three-unit implant-supported FPDs were fabricated of full contour zirconia and pre-sintered Co-Cr alloy, and were cemented on implant abutments. To simulate the oral environment, FPDs were subjected to 10,000 thermal cycles between 5-55°C for 30 seconds, and were then transferred to a chewing simulator (100,000 cycles, 50 N, 0.5 Hz). Afterwards, fatigue fracture strength was measured using a universal testing machine. Data were analyzed by Mann-Whitney U test. RESULTS: The mean and standard deviation of fracture strength were 2108.6±440.1 N in full contour zirconia, and 3499.9±1106.5 N in pre-sintered Co-Cr alloy. According to Mann-Whitney U test, the difference in this respect was statistically significant between the two groups (P=0.007). CONCLUSIONS: Since the fracture strength values obtained in the two groups were significantly higher than the maximum mean masticatory load in the oral environment, both materials can be used for fabrication of posterior three-unit FPDs, depending on the esthetic demands of patients.

Flexural Strength of Cold and Heat Cure Acrylic Resins Reinforced with Different Materials.

OBJECTIVES: Heat-polymerized acrylic resin has been the most commonly used denture base material for over 60 years. However, the mechanical strength of acrylic resin is not adequate for long-term clinical performance of dentures. Consequently, fracture is a common clinical occurrence, which often develops in the midline of the denture base. This study aimed to evaluate the efficacy of cold-cure and heat-cure acrylic resins, reinforced with glass fibers, polyethylene fibers, and metal wire for denture base repair. MATERIALS AND METHODS: Ninety specimens were prepared and allocated to nine groups. Ten specimens were considered as controls, and 80 were divided into 8 experimental groups. In the experimental groups, the specimens were sectioned into two halves from the middle, and were then divided into two main groups: one group was repaired with heat cure acrylic resin, and the other with cold cure acrylic resin. Each group was divided into 4 subgroups: unreinforced, reinforced with glass fibers, polyethylene fibers, and metal wire. All specimens were subjected to a 3-point bending test, and the flexural strength was calculated. RESULTS: The group repaired with heat cure acrylic resin and reinforced with glass fiber showed the highest flexural strength; however, the group repaired with cold cure acrylic resin and reinforced with polyethylene fibers had the lowest flexural strength. There was no significant difference between the groups repaired with heat cure and cold cure acrylic resins without reinforcement. CONCLUSION: Repairing denture base with heat cure acrylic resin, reinforced with glass fibers increases the flexural strength of denture base.