Evaluation of Surface Treatment Methods on Fatigue Resistance and Static Flexural Bond Strength in CAD-CAM Resin Composites

Abstract

This in vitro study aimed to assess the influence of different surface treatments prior to repairing a CAD-CAM resin composite on both fatigue and static flexural bond strength when bonded to a direct resin composite. CAD-CAM resin composite blocks (Tetric CAD) were ground and divided into three treatment groups: (1) aluminum oxide air-abrasion (50-?m particle size) followed by adhesive application (AA + AD group), (2) adhesive application only (AD group), and (3) silane treatment (SIL group). For comparison, both direct (DIR-RC) and indirect resin composites (IND-RC) were tested to determine their cohesive strength. The composite blocks were sectioned into beams (1 × 2 × 12 mm) and subjected to flexural bond strength tests under static loading (n = 10; 1 mm/min) and cyclic fatigue loading (n = 15; initial load = 5 N, frequency = 1.4 Hz, step increment = 5 N, 10,000 cycles per step) using a ball-in-hole testing setup. Finite element analysis was used to analyze the results in megapascals (MPa). Additionally, failure modes and surface topography were evaluated. Under static loading, both the AA + AD and AD groups demonstrated significantly higher bond strength compared to the SIL group. However, after fatigue loading, no statistically significant differences were observed among the surface treatment groups. The IND-RC group exhibited the highest flexural strength under both static and fatigue conditions. Fatigue loading reduced bond strength in all experimental groups, with the SIL group showing the greatest reduction. Importantly, none of the surface treatments fully restored the original strength of the CAD-CAM resin composite. However, surface grinding, with or without air abrasion, followed by adhesive application, provided comparable and favorable results. Thus, adhesive application in combination with surface grinding appears to be an effective strategy for the clinical repair of CAD-CAM resin composites.

Introduction

Technological advances in CAD-CAM systems allow fabrication of indirect dental restorations with fewer defects and improved outcomes, often within a single appointment. Ceramic blocks offer excellent aesthetics and long-term success but are brittle and prone to fracture. Resin-based CAD-CAM materials, with elastic moduli closer to dentin, better distribute stress, are easier to mill, and avoid issues common to direct composites, showing high clinical success rates. However, they can suffer fatigue failure under stress, often repaired conservatively with direct resin composites.

Effective bonding between CAD-CAM resin composites and repair materials is critical but challenging due to differences in polymerization. Surface pretreatment methods—such as air-abrasion, silane application, or adhesive application—significantly enhance bond strength compared to no treatment.

This study evaluated three surface treatments on CAD-CAM resin composite blocks before repair with direct resin composite: air-abrasion plus adhesive (AA+AD), adhesive only (AD), and silane only (SIL), alongside controls of direct and indirect resin composites. Mechanical tests included static flexural strength, bond strength, and fatigue loading. Surface roughness was standardized.

Results showed that indirect CAD-CAM resin composites had superior flexural bond strength and fatigue resistance compared to repaired groups. Among surface treatments, no significant differences were found in bond strength or fatigue performance, though the silane-only group showed greater strength reduction after fatigue. Failure modes were characterized by microscopy.

Overall, surface pretreatment is essential for successful adhesion and repair of CAD-CAM resin composites, with air-abrasion combined with adhesive application providing reliable outcomes.

Conclusion

It is important to recognize that none of the repair techniques evaluated was able to completely restore the original strength of the CAD-CAM restorative material. Surface treatments involving diamond bur grinding, air-abrasion, and/or adhesive application yielded comparable results, regardless of the specific combination used. However, using silane alone is not advised, as it leads to low initial bond strength.

References

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Copyright

Copyright © 2025 Nilesh V. Kalyankar, Shishir R. Rathod, Yusufzai M. Khan, Shivram B. Janjal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.