Retention of two esthetic crown systems

Purpose: This in vitro study investigated the effect of intaglio surface conditioning and luting cements on retention of monolithic zirconia and metal-ceramic crowns.
Methods: First mandibular molars (n=96), periodontally compromised and indicated for extraction were collected from oral surgery department, faculty of dentistry, Mansoura University and prepared to receive metal-ceramic and zirconia crowns. Forty-eight zirconia copings (Z) with 0.5 mm thickness were fabricated from monolithic zirconia using CAD/CAM machine (Ceramill motion 2). While Forty-eight cast metal copings (C) with 0.5 mm thickness were laboratory fabricated from Ni-Cr alloy and veneered with ceramic (VITA VM9). Intaglio surfaces of zirconia and metal-ceramic crowns were airborne-particle abraded. Zirconia and metal-ceramic copings were divided into 2 groups (n=24). Universal primer (P) (Monobond N) was applied to subgroup (n=24) while the other 24 copings were left without primer application (NP). Each 24 copings were divided into 3 divisions (n=8) according to luting cements: Metacem (M), G-CEM (G) and Ketac Cem Plus (K). A total of 12 groups were tested: M-P-C, G-P-C, K-P-C, M-NP-C, G-NP-C, K-NP-C, M-P-Z, G-P-Z, K-P-Z, M-NP-Z, RG-NP-Z and K-NP-Z. Specimens were stored in water for 3 months interrupted with thermal cycling for 10000 cycles/month. Retentive strength in (N) was measured for each specimen. Statistical analyses were conducted using 3, 2 and 1-way (ANOVA) s and Tukey’s HSD test.
Results: Means±SD retentive strength (N) of test groups were; Metacem (M): P -C, 756.8±96.3 > P-Z, 592.8±82.7 > NP-C, 582.7±79.9 > NP-Z, 499.7±58.6. G-CEM (G): P-C, 659.5±48.1> P-Z, 595.6±67.9 > NP-C, 543.5±56.5 > NP- Z, 467.3±68.5. Ketac Cem Plus (k): P-C, 539.9±76 > NP-C, 461.6±69.8 > P-Z, 455.9±66.7> NP-Z, 452.6±73. Primer application significantly (P<0.05) increased retention of all test groups. Luting cements increased retention of test groups as follow, M > G > K.
Conclusions: Primer application increased retention of both monolithic zirconia and metal-ceramic crowns. Multistep adhesive rein cement and self adhesive resin cement are the luting cements of choice for bonding monolithic zirconia and metal-ceramic compared to resin modified glass ionomer luting cement.