Comparative Evaluation of Retention and Vertical Marginal Accuracy of Co-Cr Copings Fabricated Using Three Different Techniques: An In Vitro Study.

AIM: This study was conducted to comparatively assess the retention and vertical marginal fit of cobalt-chromium copings fabricated by the conventional casting technique, 3D-printed resin pattern, and with direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS: Out of the total 60 test samples, 20 copings were obtained from inlay-casting wax and 20 from casting of 3D-printed resin patterns. In total, 20 copings were obtained from the laser sintering technique. All 60 test samples were then cemented serially on the prepared maxillary-extracted premolars and were evaluated for vertical marginal gap in 8 pre-established reference areas. Retention was evaluated using a universal testing machine. RESULTS: Results obtained for both marginal gap and retention were statistically analyzed, and the values fall within the clinically acceptable range. The DMLS technique proved precedence over the other two techniques used, as it exhibited maximum retention and marginal accuracy, which is an area of prime concern. CONCLUSION: The results from this study encourage further research with different pattern-forming materials and techniques and the need to identify the factors that facilitate better marginal fit and retention of cast restorations. CLINICAL SIGNIFICANCE: This study has myriad of applications in clinical dentistry mainly in decision-making for casting procedure to provide better retention and marginal accuracy for fabrication of Co-Cr crowns. It also aims to aid the clinician to minimize errors by using different techniques for fabrication of wax pattern as well as the coping, keeping abreast with the recent technology to evaluate the accuracy of 3D-printed resin pattern over conventional wax pattern.

In Vitro Comparative Evaluation of Bond Strength of CAD/CAM Monolithic Zirconia Copings Influenced by Luting Agents and Finish Line Design.

AIM: The aim of the in vitro study was to comparatively evaluate the bond strength of CAD/CAM monolithic zirconia copings using three luting agents and two different finish lines. MATERIALS AND METHODS: For the evaluation of bond strength, 60 extracted human maxillary first premolars were prepared to receive CAD/CAM monolithic zirconia copings. They were randomly divided into six groups of 10 samples each to receive CAD/CAM monolithic zirconia copings to bond with three different luting agents on two different finish lines. The luting agents used were RelyX U200, RMGIC, and Maxcem Elite with finish lines which were incorporated were 90° shoulder and radial shoulder finish lines. The tensile bond strength for all 60 samples was tested using the universal testing machine. RESULTS: Between and within the group differences in tensile bond strength were analyzed using one-way ANOVA test of significance with Tukey's post-hoc analysis. The statistical analysis revealed that the CAD/CAM zirconia copings used a combination of 90° shoulder and RelyX U200 as the luting agent (Group II) which offered the maximum bond strength. CONCLUSION: Within the constraints of this study, it could be concluded that CAD/CAM monolithic zirconia copings luted with RelyX U200 cement on a 90° shoulder finish line is the preferred method, taking the bond strength into consideration. CLINICAL SIGNIFICANCE: The results of this study can be extrapolated into a clinical scenario to help the clinician decide the most apt combination of finish line design and the luting agent to achieve superior bond strengths in CAD/CAM zirconia crowns and fixed dental prosthesis.

Hypersensitivity to titanium: a less explored area of research.

Titanium is considered as an excellent biocompatible metal and it is used in implant dentistry. Literature suggests that Ti can induce clinically relevant hypersensitivity and other immune dysfunctions in certain patients chronically exposed to this reactive metal. At the same time, no standard patch test for Ti has so far been developed, and positive reactions to Ti have therefore only rarely been demonstrated with skin testing. This article reports about the corrosion of dental implants, their significance when hypersensitivity is present, and the literature available till date regarding hypersensitivity of titanium.