Bonding property of resin cement to composite resin crown

Purpose:Direct Crownsmade of a composite resinmaterial recently developed by 3M ESPE. These crowns maintain the coronal morphology even in an uncured state. The advantage is that the entire process of crown fabrication until cementing and delivery can be completed chairside on the same day. There has not been a detailed study on how adhesion with resin cement is affected by bonding performed immediately after polymerization of composite resin. Thus, this study examined the effects of time period after crown fabrication on the bonding property. Methods and materials: This study used a combination of composite resin and resin cement from the same manufacturer. The following items were used: 3M ESPE Direct Crowns with RelyX Unicem 2 Automix self-adhesive resin cement and Kuraray Noritake Dental Estenia C&B with Panavia F 2.0. Discs of Estenia C&B and Direct Crowns were fabricated (10mm diameter and 3mm thickness). They were divided into groups with bonding performed immediately after fabrication of discs (0h-Direct Crown group and 0h-Estenia C&B group) and groups with bonding performed 48h later (48h-Direct Crown group and 48h-Estenia C&B group). Amicrotensile bond strength test was performed after bonding. Subsequently, fracture surface morphology of samples was examined by scanning electronmicroscopy. ATR-FTIR (Attenuated total reflection-Fourier transform infrared spectroscopy) analysis was performed on Direct Crowns. Results: The adhesive strength was significantly higher in the 0h-Direct Crown group (76.6± 13.4MPa) compared with the 0h-Estenia C&B group (60.9± 14.8MPa), the 48h-Direct Crown group (45.8± 9.7MPa), and the 48h-Estenia C&B group (53.7± 12.5MPa). When fracture surfaces were examined after the microtensile bond strength test, the 0h-Direct Crown group had many mixed fractures but no fracture at the interface between composite resin and resin cement. The other three groups had mainly mixed fractures and fractures at the interface between composite resin and resin cement. The results of ATR-FTIR analysis suggest that the degree of surface polymerization was low for Direct Crowns immediately after fabrication compared with Direct Crowns 24h later. Conclusion: The results of this study suggest that Direct Crowns are effective in clinical use with their high adhesion due to bonding immediately after fabrication.