Standardized Protocol to Evaluate the Effect of Surface Treatments, Luting Cements, and Thermocycling on PEEK–Composite Bond Strength

Summary

This protocol aims to evaluate the effects of surface treatment protocols, luting cement selection, and thermocycling on the shear bond strength between PEEK and an indirect composite resin.

Abstract

Polyetheretherketone (PEEK) has gained increasing attention as a biomaterial in prosthodontics; however, achieving durable adhesion to veneering composite materials remains a major challenge due to its chemically inert structure. This study presents and validates a standardized, reproducible protocol for evaluating shear bond strength (SBS) between PEEK and an indirect composite resin under different surface treatments, luting cements, and thermocycling conditions. A total of 240 PEEK discs were divided into four groups according to surface treatment: no surface treatment, sandblasting, sulfuric acid etching, and laser irradiation. Surface morphology was analyzed using atomic force microscopy. Each group was then subdivided according to the luting cement used (zinc oxide non-eugenol cement or self-adhesive resin cement; n = 30), and further subdivided into thermocycled and non-thermocycled groups (n = 15). SBS was measured using a universal testing machine, and failure modes were analyzed under a stereomicroscope. Among all experimental groups, specimens luted with self-adhesive resin cement and not subjected to thermocycling demonstrated the highest SBS values (25.134 ± 1.665 MPa), whereas specimens luted with zinc oxide non-eugenol cement and subjected to thermocycling exhibited the lowest SBS values (1.958 ± 0.345 MPa). For all surface treatment protocols, SBS values were significantly higher in specimens luted with self-adhesive resin cement compared with zinc oxide non-eugenol cement (p < 0.001). Thermocycling significantly reduced SBS values across all groups (p < 0.001). This protocol highlights critical procedural steps, including surface treatment selection and cement type, that significantly influence bonding outcomes. The standardized workflow and visual demonstration of key steps provide a reproducible framework for evaluating PEEK–composite bonding.

Introduction

Polyetheretherketone (PEEK) has emerged as a promising high-performance polymer in prosthodontics due to its favorable mechanical properties, chemical stability, low density, and tooth-colored appearance^1,2,3. Compared with conventional materials such as titanium, PEEK offers advantages including ease of chairside modification and reduced esthetic compromise⁴. However, despite these advantages, its clinical application is limited by its chemically inert structure and low surface energy, which result in poor adhesion to resin-based materials

Protocol

This in vitro. protocol follows institutional guidelines for laboratory-based dental research. Ethical approval was not required because no human participants or animal tissues were involved. All the materials used in this study are described in the Table of Materials.

1. Preparation of PEEK specimens

1. Fabricate 240 disc-shaped polyetheretherketone (PEEK) specimens with a diameter of 8 mm and a thickness of 3 mm from commercially available PEEK rods using a precision cutting device under standardized laboratory conditions (Figure 1A–C....

Results

This protocol enables reproducible assessment of the effects of surface treatment, luting cement type, and thermocycling on the bonding performance between polyetheretherketone (PEEK) and an indirect composite resin. AFM revealed distinct surface topographies depending on the applied surface treatment (Table 1). Untreated PEEK specimens exhibited relatively smooth and homogeneous surfaces with minimal irregularities. Sandblasted specimens showed increased surface roughness with irregular peaks and valley.......

Discussion

The present study introduced a standardized in vitro. protocol for evaluating the combined effects of surface treatment protocols, luting cement selection, and thermocycling on the shear bond strength between polyetheretherketone (PEEK) and an indirect composite material. The results demonstrated that these variables significantly influenced bonding outcomes, thereby rejecting the null hypothesis. Surface treatment constitutes a critical component of the protocol. Consistent with previous investigations, sandbla.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Polyetheretherketone (PEEK) rods	Mitsubishi Chemical Group (MCAM)	KETRON® CLASSIX LSG PEEK (white)	Used to fabricate disc-shaped specimens
Precision cutting device	Buehler	IsoMet 1000	Used for sectioning PEEK rods into standardized discs
Polishing device	Buehler	Phoenix Beta	Used for standardized surface polishing
Silicon carbide abrasive paper (600-grit)	3M	01993 (Wetordry™ Sandpaper Sheet, 600 grit)	Used under water cooling for surface polishing
Ultrasonic cleaner	Tecno-Gaz	Astra S	Used for cleaning specimens
Aluminum oxide particles (110 µm)	—	—	Used for airborne particle abrasion
Sandblasting unit	Danville Engineering	MicroEtcher ERC	Used for surface roughening
Sulfuric acid (98%)	Sigma-Aldrich (Merck)	258105	CAUTION: Corrosive; handle with appropriate protective equipment
Er:YAG laser system	Hoya ConBio	—	Used for laser surface treatment of PEEK
Atomic force microscope	Quesant Instrument Corporation, USA	—	Used for surface topography analysis
Indirect composite resin	GC Corporation	Gradia Indirect	Used for fabrication of composite discs
Zinc oxide non-eugenol cement	Kerr	TempBond NE	Temporary luting cement
Self-adhesive resin cement	3M ESPE	RelyX U200 Automix	Resin luting cement
Light-curing unit	Kerr	Optilux	Used for polymerization of resin cement
Thermocycler	Salubris Technica	Dentester	Used for artificial aging
Self-curing acrylic resin	Bayer Dental Ltd.	Meliodent	Used for specimen embedding
Universal testing machine	Instron	3345	Used for shear bond strength testing
Stereomicroscope	Nikon	SMZ 800	Used for failure mode analysis