A total of 60 access-holes in 14 patients (5 male and 9 female) aging from 34 to 69 were restored and observed during 12 months. All subjects were informed about the study, and their written consent to participate in the study was taken.

The materials used in this study are presented in Table 1. They include a phosphoric acid monomer ceramic primer (CP): UCP (Super-Bond Universal Ceramic Primer, Sun Medical, Moriyama, Japan), a photo-polymerizing nanohybrid composite (FS): (Fantasista, shade A2, Sun Medical) and its accompanying photo-polymerizing bonding agent (BA):(Hybrid Bond, Sun Medical) and a modified 4-META/TBB-MMA resin (M4M) :(Bondfill SB, Sun Medical).

Access-hole fillings were divided into CR and M4M groups.

Prior to the filling, the bottom of the access holes was filled with a PTFE (polytetrafluoroethylene) film (GEB SAS, Roissy CDG, France) to protect the screw. The thickness of this protective layer was approximately 2 mm.

CP was applied and immediately air blown. BA was applied for 20 s, air blown for 5 s and then photo-polymerized using a polymerizing unit (Kerr Demi™plus, KavoKerr Group, Washington DC, USA) for 3–5 s. FS was placed by an incremental technique with less than 1 mm thickness for each layer until covering the top of the access hole. Each layer was photo-polymerized for 20 s. The occlusal adjustment was carried out with a diamond bur (Komet 368EF.204.023, Gebr. Brasseler GmbH & Co. KG, Lemgo, Germany), and the polishing was performed using a series of silicone polishers (Komet 9400, 9401, and 9402) with a 5000-rpm speed under water irrigation.

CP was applied and air blown. Then, the base liquid of M4M was activated by adding the TBB initiator (3:1 ratio), and a powder/liquid mixture was applied, using a brush-dip technique until the filling of the access hole was completed (Fig. 1). The resin was left for 10 min to complete auto-polymerization. The occlusal adjustment was carried out with the same manner, and the polishing was performed using silicone polishers (Komet 9557, 9553) under the same condition.