Comparison of Marginal Fit between Collarless Metal Ceramic and two all Ceramic Restorations

Marginal adaptation of the crown is a crucial factor in determining its clinical acceptability. Crown fit as judged by marginal seal influences the longevity of the cast restorations to a great extent. Metal ceramic restorations have been implicated for the discoloration in area of labio-gingival margin. Attempts to rectify this, by altering the design of metal frame works as eliminating the labial metal collar with substitution with shoulder porcelain may improved the esthetics. Excellent esthetics and superior biocompatibility of all-ceramic restorations making them the best alternative to conventional metal-ceramic restorations. Objectives: This study measured and compared the precision of fit of Collarless metal-ceramic crowns and two types of all ceramic crowns, by measuring the gap dimension between the crowns margin and finishing line of the prepared tooth. Materials and Methods: Thirty samples were prepared for this study. Divided into 3 groups (N=10): Group A, (n=10) metal ceramic with porcelain collar, Group B, (n=10) IPS Empress and Group C, (n=10) IPS Empress CAD. A standardized 2 Stainless Steel dies were machined. The first die for all ceramic samples, and the second for the collarless metal ceramic samples. The Stainless Steel master dies were duplicated with polyether impression material using custom made trays and these were poured with type IV improved stone. For IPS Empress crowns (Group B), wax patterns were made by soft inlay wax over the stone dies. The wax patterns were sprued and invested and casted in special pressing furnace. After pressing, recover the restoration by airborne particle abrasion, remove the sprue, and refit it to the die. For IPS Empress CAD (Group C ), Cerec in lab CAD/CAM system (Sirona, Bensheim, Germany)was used for machining the appropriate ceramic block In order to obtain the final crowns. After that crowns were covered with IPS Empress Universal Glaze and fired in a program at CS Furnace to 770oc. The marginal fit of crowns was evaluated with optical micro scope. Results: The results showed that, IPS Empress CAD group C revealed the poorest marginal integrity with 99. 4 ±0.53 μm. IPS Empress Group B was next in line with 72. 8±0.71 μm. Compared to this first group of allceramic restorations, the result of 32. 5±0.74 μm obtained with conventional metal ceramic collarless restorations was clearly better. Conclusion: Group C metal ceramic collarless crowns had highest marginal fit when compared with Group B and Group A. Use of Metal ceramic crowns with shoulder porcelain has the potential to improve the esthetical of the restoration especially at marginal area without significantly affecting its marginal fit [A. M. Fahmy. Comparison of Marginal Fit between Collarless Metal Ceramic and two all Ceramic Restorations. Journal of American Science. 2012;8(6):528-534]. (ISSN: 1545-1003). http://www.americanscience. org. 68