Laser-texturing and traditional surface modification to improve the adhesion of glass fiber-reinforced composite posts to resin cements

Objectives: The aim of this study was to perform an experimental evaluation of the synergistic effects of lasertexturing and different traditional surface modification approaches to improve the adhesion of glass fiberreinforced composite (GFRC) posts to resin-matrix cements used in endodontically treated teeth rehabilitation. Methods: One hundred and ten freshly extracted mandibular single-rooted premolars were endodontically treated and groups of specimens were divided according to the GFRC cementation after different surface treatment, as follow (n = 10): silane-based conditioning (SIL); 9.7 % HF acid-etching (HF); 35 % H2O2 etching (H2O2); gritblasting (GB); HF plus H2O2 etching (HFH2O2); 6 W Nd:YAG laser-texturing (L6W); 4.5 W Nd:YAG lasertexturing (L4.5W); 3 W Nd:YAG laser-texturing (L3W); 3 W Nd:YAG plus 35 % H2O2 (L3WH2O2); 3 W Nd: YAG plus SIL (L3WSIL); and untreated (C). GFRC posts were cemented into the tooth root canals using a dualcured resin cement. Then, specimens were cross-sectioned and mechanically assessed by push -out bond strength tests. Specimens were inspected by optical microscopy and scanning electron microscopy (SEM) at magnification from x 30 up to x 2000. The failure mode was recorded by microscopic analyses after the bond strenght tests. Results: Surface analyses of the GFRC posts showed a rough and retentive morphological aspect with a removal of the outer epoxy matrix layer and exposure of glass fibers after laser-texturing, grit-blasting, or etching under 35 % H2O2. The highest bond strength values at 21.8 MPa was recorded for GFRC posts after laser-texturing on 3W plus silane-based conditioning followed by the group etched with 35 % H2O2 (20.5 MPa). The failure mode was microscopically characterized as cohesive and mixed pathways. The lowest bond strength values around 5 and 9 MPa and adhesive failure were recorded for the untreated GFRC group or specimens etched with HF. Conclusions: The combination of acidic etching and silane conditioning with laser-texturing at moderate intensity promoted an adequate surface modification of GFRC posts and increased adhesion to a resin-matrix cement. Such combination of physicochemical approaches can enhance the long-term mechanical behavior of the restorative interface at endodontically treated teeth. Clinical relevance: Combining traditional and novel physicochemical approaches can provide promising adhesion pathways for glass fiber-reinforced composite posts to resin-matrix cements. A high mechanical interlocking of the resin-matrix cements and the stable retention of the teeth root intracanal posts can decrease the risks of clinical failures by fracture and detachment of the intraradicular interface.