Assessment of surface treatment with atmospheric cold plasma on the bond strength of fiber post

One of the important factors that affecting the long-term success of endodontically treated teeth is adequate restorative treatment performed afterwards. Post-and-core systems have been frequently used in cases with excessive loss of healthy coronal dental tissue. Recently, fiber reinforced posts have been suggested very often due to the similarity in elastic modulus with dentine and aesthetic properties. However, the most common cause of failure for these posts is post debonding. One of the possible reasons of this loss of retention is the bonding failure between resin composite cement and fiber post. To improve the adhesion, various surface treatments on fiber posts have been performed. Cold atmospheric plasma (CAP) is a novel technology and there are some studies showing that this technology provides several types of surface treatments on dental structures or materials when the surfaces need special modifications or adhesion improvement. The purpose of this in vitro study was to evaluate the effect of surface treatment with CAP on the bond strength of glass fiber posts luted with resin cement to the extracted teeth and to compare it with the conventional surface treatments. Sixty extracted human maxillary central anterior teeth due to periodontal or prosthetic reasons were selected. The coronal portion of each tooth was removed to obtain 13-mm-long roots and the root canals were instrumented to the working length of 1 mm from the apex. After complete endodontic treatment, all samples were kept in the incubator at 37°C and 100% humidity. One week later, all roots were randomly divided into four groups (n=15) according to the type of treatment performed to the post surface: Group 1 (plasma), Group 2 (silane), Group 3 (hydrofluoric acid-HF) and Group 4 (control-no surface treatment). Before post space preparation, the roots were vertically embedded into a plastic holder with autopolymerizing acrylic resin. After 8-mm-deep post space preparation, all glass fiber posts (Angelus Exacto No: 2) with the different surface treatments (plasma, silane and HF) and without surface treatment (control) were cemented using a self-adhesive resin cement (Panavia SA Cement Automix) and polymerized with a light source. Surface treatments of fiber posts in the plasma group were performed using a non-thermal atmospheric pressure dielectric barrier discharge (DBD) air plasma. The roots were sectioned transversally into 1 mm thick slices and the samples were obtained from three different regions of the root (cervical, middle and apical). For measuring bond strength, the push-out test was performed to all samples by a universal test machine. Moreover in order to evaluate the effect of surface treatments better, treated post surfaces were examined by SEM and their contact angles were measured. Push-out test results showed that the highest bond strength values were obtained in the plasma group with a statistically significance compared to other groups (P ˂ 0,05). In addition the lowest bond strength values were found in the control group. The contact angle measurements showed that the most hydrophilic surface was observed in the plasma treatment group (~0°) and the most hydrophobic surface was found in the control group. SEM analysis revealed that a significant increase in the surface roughness was observed on the surface treated by plasma. In conclusion, the surface treatment of posts with plasma application significantly enhances the interfacial bond strength between fiber posts and resin cements. It is also evident that the plasma treatment is a more effective method compared to other conventional surface treatments.