IOSR Journal of Dental and Medical Sciences (IOSR-JDMS) e-ISSN: 2279-0853, p-ISSN: 2279-0861.Volume 19, Issue 6 Ser.4 (June. 2020), PP 13-17 www.iosrjournals.org DOI: 10.9790/0853-1906041317 www.iosrjournal.org 13 | Page An In–Vitro Comparative Study on the Marginal Adaptation of Metal Ceramic Crowns and Zirconium Dioxide Crowns with Rounded Shoulder Finish Line Preparation Shivani Parmar Corresponding Author: Shivani Parmar Abstract Statement of Problem.Although metal ceramic and zirconium dioxide restorations are widely used, there is a lack of information about how the fit is affected by fabrication procedures. The adequacy of the fit of all- ceramic restorations hasbeen questioned. Purpose. This study examined the effect of porcelain and glaze firing cycles on the fit of metal ceramic and zirconium dioxidecrowns. Material and methods.Fifteen standardized metal ceramic copings, zirconia copings and further crowns were fabricated on a metal die.A device was used to apply a uniform load on specimens during measurement and to reposition thespecimens on the measurement device after each manufacturing process. The specimens were not cemented andwere measured on the metal die using a stereomicroscope. Measurements were recorded at 18 points selectedalong horizontal and vertical planes. The crown systems were compared by use of the Student t test and 1-wayanalysis of variance (ANOVA). Analysis of Variance (ANOVA) and independent t-test were used for intra- and inter-group comparisons of marginal gap of metal copings, zirconia copings, porcelain fused to metal crowns and zirconia crowns. Results.In this study mean marginal openings for conventionally fabricated metal copings was 18μm, for CAD/CAM fabricated zirconia copings was 10μm, for metal ceramic crowns was 20μm and for zirconia crowns it was 14μm respectively.The meanwise comparison of marginal gap of metal copings, zirconia copings and metal ceramic crowns, zirconia dioxide crowns were measured on all the surfaces. The mean difference obtained wasmaximum on mesial surface and minimum on the labial surface which was statistically significant as p value was< 0.05. No statistical difference was observed in zirconia copings and zirconia crowns. Conclusion.Within the limitations of this study, it was concluded thatdistortion does occur in fixed prostheses during the porcelain firing cycle. Zirconia system showed significantly less distortion as compared to metal ceramic system. After veneering of zirconia copings marginal discrepancy was increased. Higher mean marginal gap was recorded in metal (Ni–Cr) copings and porcelain fused to metal crowns compared to zirconia copings and crowns. The difference in mean marginal gap between them was found to be statistically significant (p value <0.05). -------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 22-05-2020 Date of Acceptance: 09-06-2020 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction In the last decades, since the development of porcelain fused to metal procedures in the early sixties, metal ceramic restorations have represented the “gold standard” for years in prosthetic dentistry 1 . The following requirements should be fulfilled for successful porcelain fused to metal restorations there should be accurate abutment castings and ease of casting, accurate soldering, rigidity of the metal frame, ability of the porcelain to fuse to metal, adequate strength of final restoration, esthetic tolerance, tissue tolerance and ease of repair 2 . Nevertheless, the investing procedures of wax patterns and casting procedures for metal alloys involve many technical variables and considerable number of operative steps and firing cycles, making the final quality of the restorations highly technique sensitive. Moreover, the metal framework and layer of opaque porcelain needed for masking underlying metal grayish shade lead to significant limitation for the esthetics 1. All these limitations of porcelain fused to metal restorations has forefront to the development of new all ceramic materials with superior mechanical properties such as high fracture toughness flexural strength, and promising esthetic results. Besides, this lack of glass and dense polycrystalline microstructure provides resistance to hydrofatigue 3 . Inspite of type of material being used for the full crown restorations, one of the most important factor for their success is the marginal adaptation, which can be influenced by finish line design repeated ceramic firing cycles, and cementation materials 4 . Lack of adequate fit in crowns might affect fracture strength and thus reduces longevity, in addition to other known adverse effects of poor fit such as damage to the adjacent soft