From polyetheretherketone to 3D‑printed composites: hydrothermal stability and cement‑dependent resin bonding of...

This study evaluated the water sorption/solubility, surface characteristics, and bonding performance of different high‑performance polymers intended for restorations and appliances used in pediatric dentistry, emphasizing their hydrothermal stability and cementation protocols for durable bonding.

Disc‑shaped specimens of milled polyetheretherketone (PEEK), ceramic‑filled 3D‑printed composite resin, and milled polymethylmethacrylate (PMMA)‑based acrylic polymer were prepared. Water sorption and solubility were determined according to ISO 4049 after storage in distilled water and artificial saliva. Surface treatments included no treatment, airborne‑particle abrasion, and abrasion followed by application of a dimethacrylate/methyl methacrylate‑based primer. Surface microstructure, roughness, and wettability were evaluated. Shear bond strength was tested using either resin cement or glass ionomer cement under three aging conditions (24‑h water storage, thermocycling, and highly accelerated aging), and failure modes were classified.

All materials showed very low water sorption (W_sp) and solubility (W_sl) below ISO 4049 limits (W_sp < 5 µg/mm³ and W_sl ~ 1 and 2 µg/mm³), with minor medium‑ and time‑dependent changes, indicating similar hydrolytic stability among the polymers. Airborne‑particle abrasion markedly increased surface roughness (from ~ 0.65 μm to 2.75-5.35 μm), whereas primer application reduced roughness while maintaining microroughness and significantly improved wettability; however, final roughness and contact angles remained material‑dependent. With resin cement, shear bond strength ranged from 17.07 to 23.26 MPa after 24‑h storage, decreased to 10.18-14.28 MPa after thermocycling, and increased up to 25.72 MPa after highly accelerated aging for the 3D‑printed and milled composites, with predominantly mixed or cohesive failures. Glass ionomer cement produced substantially lower bond strengths (0-8.70 MPa) and predominantly adhesive failures under all conditions.

High‑performance polymers exhibited excellent resistance to water sorption and solubility and maintained favorable surface characteristics after clinically relevant pretreatments. Under the present in vitro conditions, resin cement combined with airborne‑particle abrasion and primer achieved more durable bonding than glass ionomer cement and may help guide material selection for pediatric‑oriented restorations and appliances.