Effect of Adhesive System on Bond Strength of Polyetheretherketone (PEEK) and Polyetherketoneketone (PEKK)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper submitted by Goncalves et al. is a comparison between two adhesive systems in terms of shear bond strength. The manuscript is clear, well written and the conclusions are supported by the results. However, I have some comments which will enhance the quality of the manuscript:

1. the authors used distilled water for their analyses but it's mandatory to carry out this type of tests in artificial saliva at different pH values.
2.  electronic microscopy images (SEM or AFM) are also mandatory in order to have an image about the roughness of the surface.
3. FTIR analyses must also be carried out in order to investigate the chemical interactions between the surface and adhesive system.

Author Response

Dear reviewer,

We sincerely appreciate the constructive feedback and the insightful suggestions provided. We acknowledge the importance of conducting the experiments in artificial saliva at different pH values, incorporating electronic microscopy images (SEM or AFM) for surface roughness evaluation, and performing FTIR analyses to assess chemical interactions.

However, due to practical constraints, we are unable to conduct additional experiments at this stage. One reason to submit this manuscript as communication instead of a full article. However, we fully recognize the value of these methodologies and will include a discussion in the limitations section of our manuscript, highlighting these aspects as potential areas for future research.

Reviewer 2 Report

Comments and Suggestions for Authors This article discusses the effect of adhesive systems containing different functional monomers (PETIA, MMA, UDMA) on SBS of PEEK and PEKK. The two adhesive systems (visiolink & PEKKbond) selected by the authors are highly appropriate, as they are among the most widely used and studied products. However, the novelty of the experiment is insufficient, and the manuscript requires revisions.   1. Subheadings are not necessary in the abstract. Please refer to the author guidelines or review recently published articles in J. Compos. Sci. 2. The authors used gingival composite to bond with PEEK and PEKK—what is the rationale behind this choice? Or what is the intended application? This should be addressed in the main text of the manuscript. 3. The surface roughness of all samples was 0.2 μm. Why was this standard chosen? What criteria were used to determine this value? 4. The authors used a sandblasting pressure of 5 bar, which seems relatively high. Some studies have reported that such high pressure could damage the PEEK surface, exposing the TiO₂ fillers (10.3390/polym15092114; 10.1016/j.dental.2024.05.025). The authors should address this issue. 5. Under the same surface treatment conditions, the groups with the highest SBS values (PEEK-none-Visiolink, PEEK-Al₂O₃-Visiolink, PEKK-none-PEKKbond, PEKK-Al₂O₃-PEKKbond) exhibited large standard deviations, some approaching half of the measured values (e.g., PEEK-none-Visiolink; SBS value = 58.74, SD = 27.90). What could be the reason for this variation? 6. PEKKbond contains UDMA (urethane dimethacrylate), but the authors did not discuss its effects on the PEEK and PEKK surfaces. Additionally, the differences in ketone structures between PEEK and PEKK may influence their wettability, potentially affecting the interaction of primers with these materials. This thing should be discussed (10.1016/j.dental.2023.10.001). 7. Although the authors mentioned in the limitations section that the study did not include aging (thermocycling), they should also discuss in the discussion section how different functional monomers, such as PETIA, UDMA, and MMA, may form chemical bonds on PEEK and PEKK surfaces and how these bonds may degrade after aging (10.2186/jpr.JPR_D_23_00063). 8. The conclusion section lacks precision. It is recommended to summarize key research findings and conclusions in a bullet-point format for clarity.

Author Response

1. We appreciated your feedback and have revised the abstract accordingly by removing the subheadings.

2. The use of gingival composite was chosen to simulate a common clinical application where PEEK and PEKK serve as frameworks in dental prostheses. We have clarified this rationale in the main text.

3. The selected surface roughness value was based on previous literature establishing the threshold for polished dental materials. This choice also ensured consistency across all samples.

4. We acknowledged that 5 bar is a relatively high sandblasting pressure and appreciate the references provided. However, we note that in our study, the sandblasting distance was 10 cm, whereas the referenced studies using 2 bar maintained a 1 cm distance from the surface. We have discussed the potential effects of this pressure on PEEK, including possible exposure of TiO₂ fillers, and addressed its implications in the discussion section.

5. The observed variations in shear bond strength (SBS) could be attributed to differences in surface chemistry, primer interaction, or inherent material inconsistencies. We have expanded the discussion to explore these factors in greater depth.

6. We have further elaborated on UDMA’s role in PEKKbond and its impact on adhesion. Additionally, we discussed how structural differences between PEEK and PEKK influence wettability and primer interactions, incorporating relevant literature suggested by the reviewer.

7. While our study did not include aging tests, we recognize the importance of evaluating the long-term stability of chemical bonds formed by PETIA, UDMA, and MMA. We have added this as a study limitation and discussed its potential implications.

8. We have revised the conclusion section to enhance clarity and precision, summarizing key findings in a bullet-point format for improved readability.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The results presented by the authors are enough for a communication.

Reviewer 2 Report

Comments and Suggestions for Authors

The author address all the issues. It can be accepted in current version.