Nowadays, implant screw-retained prosthesis becomes a popular mode of implant supra-structure restoration. Cement retained implant restoration has issues including irretrievability and difficulty of controlling the cement excess beyond the abutment joint. The cement excess can be a major cause of peri-implantitis [13,14,15]. Screw-retained implant restoration has also some disadvantages including the difficulty to get a right positioning of the access-hole compatible with a suitable aesthetic appearance and the aesthetic result of the access-hole restoration [16]. Inclined abutment or angling the screw channel can be an option to ameliorate the aesthetical outcomes [17, 18]. Moving the access hole to an occlusal or palatal/lingual zone would increase the indication of screw retained implant restoration. The development of the computer-assisted implant surgery increases the use of the screw-retained prosthesis compared to the cement retained method [19, 20]. Nevertheless, the integrity of the filling of the access hole is necessary to preserve to occlusal function and the aesthetic outcomes. Moreover, the access hole filling contributes to reinforce the surrounding ceramic [9].

In this context, access-hole filling is a common clinical procedure, but studies are quite limited in the literature. Photo-polymerizing resin composites have been widely used to fill the ceramic access holes, but unfortunately, the prognoses were less favorable [21,22,23]. The use of an efficient ceramic primer (CP) containing phosphoric acid monomer is mandatory to ensure durable adhesion to the feldspathic ceramic surface [24, 25]. In the previous in vitro study [12], ceramic access-hole specimens filled without ceramic pre-treatment showed no bond strength regardless of the use of the bonding agent. For this reason, in this in vivo study, the CP was used for groups CR and M4M.

Ceramic surfaces can be modified by silicate blasting or acid etching procedures to achieve a reliable adhesion [26, 27]. Hydrofluoric acid treatment has also been recommended but demands considerable precautions [28]. Clinically, decontamination by ultrasonic device during these procedures cannot be done easily [29]. It is also important to reduce clinical steps for access-hole filling.