ORIGINAL ARTICLE Effect of Resin Cement Mixing Method on the Retention Strength of a CAD/CAM Zirconia Crowns Leyla Sadighpour • Akbar Fazel • Farideh Geramipanah • Mahdi Allahdadi Received: 3 December 2013 / Accepted: 27 February 2014 / Published online: 20 March 2014 Ó Indian Prosthodontic Society 2014 Abstract Several treatments have been suggested to improve the retention of zirconia-based restorations luted with different cements. Resin cements are believed to improve crown retention under certain circumstances. The aim of the present study was to examine the effect of three cements with different mixing methods on the retention of CAD/CAM zirconia crowns. Thirty extracted human molars were randomly divided into three groups and pre- pared for all-ceramic crowns (6° taper, 4-mm height and a 1.2 mm rounded shoulder finish line). A zirconia crown (Tizian CAD/CAM) was fabricated for each tooth. The crowns were air-abraded using airborne particles, adjusted, and cemented to the corresponding tooth with one of the following cements: Panavia F2 (PAN group), RelyX Uni- cem (UNH group) or RelyX Unicem Aplicap (UNA group). After 3,000 rounds of thermal cycling, retention was measured using a specific retentive jig and a universal testing machine. The retention strength was measured by dividing the retention force by the surface area of each tooth. The means of the pull-out test results for each group were compared using analysis of variance and Tukey’s HSD test (a = 0.05). The mode of failure was examined using a stereomicroscope. The mean retention value was 6.45 (0.34) MPa for the UNA group, 4.99 MPa (0.47) for the UNH group, and 4.45 (0.39) for the PAN group; the differences among the three test groups were significant. A mixed failure was observed in 83.3 % of specimens, while no cohesive failure occurred in the crowns. Within the limitations of the present study, of the three tested cements, Relyx Unicem Aplicap cement was associated with the highest retention force for Tizian zirconia crowns. Keywords Zirconia crowns Á Resin cements Á Mixing method Á Retention strength Introduction The use of all-ceramic restorations with improved mechanical properties and a natural appearance has become a common practice in dental offices [1]. Of the most recently developed all-ceramic systems, zirconia- based materials are particularly attractive due to their high strength and durability, as well as their esthetic appeal. Several studies have investigated the longevity of zirconia- based fixed partial dentures (FPDs); in one study, the sur- vival of the zirconia fixed partial dentures (FPDs) was reported as 94 % over 4 years, 92 % over 5 years, and even 100 % over 3 years, which was equal to metal cera- mic FPDs [2–4]. However, the cumulative 5-year survival of single crowns was found to be 88.8 % in another study [5]. In clinical trials, the most frequent complications associated with zirconia-based restorations were chipping of the veneering ceramic, fracture of the framework, and loss of retention [6]. Several strategies have been proposed to increase the retention of all-ceramic restorations, L. Sadighpour Á A. Fazel Á M. Allahdadi Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Kargar Shomali, Hakim Hwy, 143995991 Tehran, Iran e-mail: sedighle@tums.ac.ir; lsedigh@yahoo.com A. Fazel e-mail: dabirdandan@yahoo.com M. Allahdadi e-mail: mahdi.allahdadi@yahoo.com F. Geramipanah (&) Dental Implant Research Center, Tehran University of Medical Sciences, Kargar Shomali, Hakim Hwy, 143995991 Tehran, Iran e-mail: geramipa@tums.ac.ir 123 J Indian Prosthodont Soc (December 2014) 14(Suppl. 1):S31–S36 DOI 10.1007/s13191-014-0355-1