Clinical evaluation of marginal fit of uncemented CAD-CAM monolithic zirconia three-unit restorations in anterior areas, using scannable and conventional polyvinyl siloxane impression materials.

BACKGROUND: The accuracy of impression techniques determines the marginal fit of fixed prostheses. Marginal accuracy plays a main role in the success and failure of treatments. This in-vivo study evaluated the marginal fit of anterior three-unit monolithic zirconia fixed partial dentures (FPDs) using conventional and scannable polyvinyl siloxane impression materials. METHODS: Ten patients were selected to replace the lateral teeth with a three-unit monolithic zirconia bridge. For each patient, in the first group, an impression was made with a two-step putty-wash technique using scannable polyvinyl siloxane material (BONASCAN; DMP, Greece). In the identical session, as the second group, an impression of conventional putty-wash polyvinyl siloxane was taken (BONASIL A+ Putty; DMP, Greece). The marginal discrepancy was measured through the replicas, which were cut perpendicularly within the buccolingual and mesiodistal directions. An Independent t-test was employed for data analyses (P < 0.05). RESULTS: The marginal discrepancy in a conventional method for central abutment in mid-buccal, mid-lingual, mid-mesial, and mid-distal was higher than in the scannable method but it was not significant (P > 0.05). Also, the marginal discrepancy for canine abutment in the conventional method was higher than in the scannable method, but it was not significant, either (P > 0.05). CONCLUSIONS: FPDs fabricated from both scannable and conventional impression materials were not superior to each other in marginal fit for both central and canine abutments by evaluation using the replica technique.

The effects of provisional resin cements on the color and retentive strength of all-ceramic restorations cemented on customized zirconia abutments.

This study aimed to evaluate the effects of two types of provisional resin cements on the color and retentive strength of two different all-ceramic restorations cemented onto customized zirconia abutments. Forty-two crowns were made of monolithic zirconia and lithium disilicate ceramics (n = 21 per group) and cemented on customized zirconia abutments by using two provisional resin cements of TempBond Clear and Implantlink Semi, and TempBond serving as the control (n = 7 per cement subgroup). The specimens' color was measured before and after cementation and after thermocycling. The color difference was calculated by using CIEDE2000 formula (ΔE00). The tensile force was applied to assess the retentive strength. Kruskal-Wallis, Dunn's post-hoc, and Mann-Whitney non-parametric tests were used to compare ΔE00(1) and ΔE00(2) and two-way ANOVA followed by one-way ANOVA and Tukey's HSD post hoc test and T-test were used to compare retentive strength between subgroups. In the lithium disilicate group, ΔE00 of the control subgroup (TempBond) was significantly higher than that of Implantlink Semi cements subgroup (P = 0.001). But, in the monolithic zirconia group, ΔE00 of the control subgroup (TempBond) was significantly higher than that of Implantlink Semi (P = 0.020) and TempBond Clear cements (P = 0.007). In the monolithic zirconia group, the control subgroup (TempBond) was significantly more retentive than TempBond Clear (P = 0.003) and Implantlink Semi cement (P = 0.001). However, in the lithium disilicate group, Implantlink Semi cement was significantly more retentive than TempBond Clear (P = 0.019) and TempBond (control) (P = 0.001). The final color of both restorations was significantly affected by the provisional resin cement type. The retentive strength was influenced by both the type of cement and ceramic.

Thermal Transport in 2D Materials.

In recent decades, two-dimensional materials (2D) such as graphene, black and blue phosphorenes, transition metal dichalcogenides (e.g., WS2 and MoS2), and h-BN have received illustrious consideration due to their promising properties. Increasingly, nanomaterial thermal properties have become a topic of research. Since nanodevices have to constantly be further miniaturized, thermal dissipation at the nanoscale has become one of the key issues in the nanotechnology field. Different techniques have been developed to measure the thermal conductivity of nanomaterials. A brief review of 2D material developments, thermal conductivity concepts, simulation methods, and recent research in heat conduction measurements is presented. Finally, recent research progress is summarized in this article.

Effect of Core Materials on the Dimensional Accuracy of Casts Made of Two Different Silicone Impression Materials: An Experimental Study.

BACKGROUND AND AIM: Dimensional accuracy of impressions is crucial to the quality of fixed restorations. This accuracy can be highly affected by the type of core and impression materials. This study aimed to assess the effect of different core materials on dimensional accuracy of two silicone impression materials. MATERIALS AND METHODS: In this in vitro study, three master core models were fabricated of amalgam, composite resin, and nickel-chromium. Of each model, 30 impressions were taken; 15 with additional and 15 with condensational silicone impression material. The accuracy of impressions of the three core materials was assessed by measuring two linear dimensions and one vertical dimension on the stone casts. STATISTICAL ANALYSIS: Data were analyzed with two-way analysis of variance and Scheffe post hoc test (α = 0.05). RESULTS: Accuracy of the three measured dimensions was significantly affected by both the impression and core materials (P < 0.05). Additional silicone was significantly more accurate in linear dimensions, and impressions of the amalgam core were significantly more accurate than other cores in linear dimensions. CONCLUSION: Additional silicone impression material had more detail reproduction, and the impressions of amalgam core were more accurate than the composite and nickel-chromium core materials.

Effects of number of firings and veneer thickness on the color and translucency of 2 different zirconia-based ceramic systems.

STATEMENT OF PROBLEM: Color matching between a zirconia-based ceramic restoration and a natural tooth is a common clinical challenge. PURPOSE: The purpose of this in vitro study was to investigate the effects of the number of firings, veneer thickness, and zirconia core translucency on the final color and translucency of zirconia-based ceramic restorations. MATERIAL AND METHODS: Sixty disk-shaped zirconia specimens (10×1 mm) were prepared in high and low translucencies (n=30 per translucency group). Each zirconia group was subdivided into 3 subgroups (n=10) veneered with ceramic layers of 0.5-, 1-, and 1.5-mm thicknesses. The specimens were then subjected to 1, 3, 5, and 7 firing times. Color and translucency parameters were measured by using a spectrophotometer. Data were analyzed by using multifactorial repeated measures ANOVA and subgroup analysis (α=.05). RESULTS: The number of firings affected the L*, a*, and b* values and translucency parameter in both zirconia-based systems with different veneer thicknesses (P<.05). Increasing the veneer thickness decreased the translucency parameter and increased the L*, a*, and b* values in both zirconia-based systems (P<.05). The color difference values (ΔE) were the highest between 1 and 3, 1 and 5, and 1 and 7 firings, and the lowest between 5 and 7 firings in both zirconia systems. CONCLUSIONS: Repeated firings and porcelain veneer thickness affected the final color and translucency of both zirconia systems and, consequently, adversely influenced the esthetic outcomes. Thus, these factors should be considered in the tooth preparation and laboratory phase.

Evaluation of accuracy of shade selection using two spectrophotometer systems: Vita Easyshade and Degudent Shadepilot.

OBJECTIVE: The aim of this in vitro study was to evaluate the accuracy of shade matching using two spectrophotometric devices. MATERIALS AND METHODS: Thirteen patients who require a full coverage restoration for one of their maxillary central incisors were selected while the adjacent central incisor was intact. 3 same frameworks were constructed for each tooth using computer-aided design and computer-aided manufacturing technology. Shade matching was performed using Vita Easyshade spectrophotometer, Shadepilot spectrophotometer, and Vitapan classical shade guide for the first, second, and third crown subsequently. After application, firing, and glazing of the porcelain, the color was evaluated and scored by five inspectors. RESULTS: Both spectrophotometric systems showed significantly better results than visual method (P < 0.05) while there were no significant differences between Vita Easyshade and Shadepilot spectrophotometers (P < 0.05). CONCLUSION: Spectrophotometers are a good substitute for visual color selection methods.

In Vitro Evaluation of Bacterial Leakage at Implant-Abutment Connection: An 11-Degree Morse Taper Compared to a Butt Joint Connection.

Background and Aim. The geometry of implant-abutment interface (IAI) affects the risk of bacterial leakage and invasion into the internal parts of the implant. The aim of this study was to compare the bacterial leakage of an 11-degree Morse taper IAI with that of a butt joint connection. Materials and Methods. Two implants systems were tested (n = 10 per group): CSM (submerged) and TBR (connect). The deepest inner parts of the implants were inoculated with 2 µL of Streptococcus mutans suspension with a concentration of 108 CFU/mL. The abutments were tightened on the implants. The specimens were stored in the incubator at a temperature of 37°C for 14 days and the penetration of the bacterium in the surrounding area was determined by the observation of the solution turbidity and comparison with control specimens. Kaplan-Meier survival curve was traced for the estimation of bacterial leakage and the results between two groups of implants were statistically analyzed by chi-square test. Results. No case of the implant system with the internal conical connection design revealed bacterial leakage in 14 days and no turbidity of the solution was reported for it. In the system with butt joint implant-abutment connection, 1 case showed leakage on the third day, 1 case on the eighth day, and 5 cases on the 13th day. In total, 7 (70%) cases showed bacterial leakage in this system. Significant differences were found between the two groups of implants based on the incidence of bacterial leakage (p < 0.05). Conclusion. The 11-degree Morse taper demonstrated better resistance to microbial leakage than butt joint connection.