The effect of different surface treatment methods on the pull-out bond strength of PEEK endocrowns

Polyetheretherketone (PEEK) has gained increasing attention as a restorative material for endocrown fabrication because of its favorable biomechanical properties and dentin-like elastic modulus. However, its low surface energy and chemically inert structure may compromise adhesive bonding to resin cements. This study aimed to evaluate the effect of different surface treatment protocols on the pull-out bond strength of PEEK endocrowns.

Sixty extracted sound human molars were used in this study. Standard endodontic access cavities were prepared for all teeth and root canal treatment was completed following a uniform clinical protocol. After endodontic therapy, the required occlusal preparations for endocrown restorations were performed. The prepared teeth were scanned using an intraoral scanner and PEEK endocrowns were fabricated for each specimen using a computer-aided design/computer-aided manufacturing system. The endocrowns were then randomly allocated to four groups according to the surface treatment protocol: Group C (Control), no surface treatment was applied; Group T, tribochemical silica coating followed by silanization; Group S, sandblasting followed by the application of a methyl methacrylate (MMA)-based primer (Visio.link^®, Bredent GmbH, Germany); and Group L, Er: YAG laser treatment. All endocrowns were cemented to the prepared teeth using dual-cure resin cement according to the manufacturer's instructions. After cementation, the specimens were subjected to thermal aging. Subsequently, the samples were mounted on a universal testing machine, and pull-out tests were performed to determine their bond strengths. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey's post-hoc test (α = 0.05). The significance level was set at p < 0.05.

Surface treatment protocols significantly affected pull-out bond strength (p < 0.001). The highest bond strength was observed in the tribochemical silica coating + silane group, followed by the sandblasting + MMA primer group, with no significant difference between them (p > 0.05). The laser-treated group showed significantly higher values than the control group but significantly lower values than both chemically treated groups (p < 0.05). The untreated control group exhibited the lowest bond strength.

Surface treatment significantly improves the bonding performance of PEEK endocrowns. Protocols combining micromechanical roughening with chemical priming provided the most favorable bond strength values and may represent more reliable options for adhesive cementation of PEEK restorations.