In the metal-free copings tested, zirconia showed the best adaptation. The retention of copings was not influenced by internal fit or material type.

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Purpose. This study aimed to compare marginal and internal adaptation in endocrowns made from translucent zirconia and zirconium lithium silicate using CAD-CAM technology. Materials and Methods. Twenty-eight freshly extracted upper molars were mounted in acrylic resin and underwent root canal therapy and endocrown preparation up to 2 mm above the cementoenamel junction. Endocrowns were CAD-CAM milled from zirconium lithium silicate (ZLS) and translucent zirconia (Zr). Internal and marginal adaptation was assessed by the replica technique before cementation. Marginal adaptation was evaluated by a stereomicroscope (×32) before and after cementation and also after thermomechanical aging. Results. The ZLS group showed significantly higher internal adaptation compared to the Zr group ( P  = 0.028), while the marginal adaptation differences, at different times with different methods, were not statistically significant ( P  > 0.05). Axiomarginal angle had the highest and axiopulpal angle showed the lowest adaptation in both groups. The cementation process and thermomechanical aging increased the marginal gap in both groups significantly ( P  < 0.001). The marginal gap assessed by the replica technique before cementation was 7.11 µm higher than direct view under a stereomicroscope with intraclass correlation coefficient of 0.797. Conclusion. Zirconia seems to be an acceptable material for endocrown with comparable internal and marginal adaptation to ZLS. Cementation and thermomechanical aging had significantly negative effects on marginal gap. The marginal gap assessed by the replica technique was higher than direct view under the stereomicroscope technique.

BackgroundVinyl Polyether Siloxane is a newly introduced impression material and studies on that is scarce. Implant insertion in posterior mandible might be angulated due to anatomical considerations. The purpose of this study was to compare the dimensional and angular accuracy of impressions using full-arch versus sectional tray and Vinyl Polysiloxane versus Vinyl Polyether Siloxane in angulated implants.Material and MethodsFour implants were placed in dental areas #19, #21, #28 and #30 of a Kennedy class I mandibular acrylic model with 30° lingual angulation. Twenty sectional and 20 full-arch open trays were made on the primary cast. Impressions were taken using Vinyl Polysiloxane and Vinyl Polyether Siloxane (n=10 in 4 groups); and were poured with type IV dental stone. The coordinate measuring machine was used to measure displacements in the X, Y and Z axes and rotational discrepancies of implants. The data were analyzed using SPSS 22 and two-way ANOVA.ResultsType of tray had no significant effect on the dimensional and angular accuracy of impressions (p >0.05). Type of impression material significantly affected linear displacement (∆r) (P <0.05); but it did not significantly affect the rotational displacement (P >0.05).ConclusionsVinyl Polysiloxane yielded more accurate impressions of angulated implants. Key words:Dental implant, impression material, impression tray, vinyl polysiloxane, vinyl polyether silicone, coordinate measuring machine.

Zirconia has been used for rehabilitation of edentulous spaces approximately for a decade, and there have been several reports regarding the clinical performance and retention of zirconia crowns. Outstanding mechanical properties, biocompatibility, and excellent aesthetics make zirconia-based crowns as a popular crown among the current all-ceramic crowns in restorative dentistry. However, restoration with a zirconia crown is a challenging treatment. The goal of this study was to assess the current literature to summarize the studies reporting the effective risk factors on retention of zirconia crowns to provide clinicians with a useful point of view in the decision-making process for use of these restorations. Literature based-search was performed to find related articles until August 2020 using EMBASE, Google Scholar, and MEDLINE. Search terms used were “zirconia restorations properties,” “zirconia crowns clinical performance,” “zirconia crown survival,” “biological complications,” and “zirconia crown retention.” Results were limited to papers available in English. The references of all related literature were also searched for further citations. Overall, although clinical long-term and follow-up studies are a vital requirement to conclude that zirconia has great reliability, it seems that zirconia crown restorations are both well tolerated and sufficiently resistant.