Review Reports - The Effect of Implant–Abutment Contact Area on the Stress Generation of Bone-Level and Tissue-Level Implants

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

Please see my commens and questions in the attached file.

Best regards,

WS HAN

Comments for author File: Comments.pdf

Author Response

Concerning your construction of geometrical models of implants, why didn’t you ask to the manufacturer the original design plan? Did you have any particular reasons to proceed as you showed it on the paper?

Answer: Thank you for your question. The approach we used in constructing the geometrical models of the implants is a well-known reverse engineering technique in implantology. This method is based on modeling the implant after fitting the abutment with the recommended torque, ensuring that the final representation reflects the clinical scenario accurately.

Additionally, this approach serves as a didactic tool for my master’s students involved in the project, allowing them to gain hands-on experience in 3D modeling and reverse engineering techniques. Moreover, the simplification provided by this method has been previously investigated in the literature and deemed adequate for studying dental implants (https://doi.org/10.1080/10255842.2016.1176156).

There in no size on your structure, even main sizes of each component. It’s very difficult to know whether your results could be comparable with others.

Answer: We acknowledge the importance of providing dimensional details for better comparability with other studies. The dimensions of the components have now been explicitly added in the manuscript, in accordance with ISO 14801 guidelines.

Contact conditions between abutment and screw, between screw and implant and between abutment and implant are very important for mechanical behaviour and lifespan of implants. Could you precise these contact conditions that you applied to FE modelling? What are the friction coefficients that you used?

Answer: The contact conditions applied between the abutment and screw, screw and implant, and abutment and implant have now been detailed in the methods section. We used rough contacts and added it as the study’s limitation.

Did you apply a torque of tightening to the screw? This torque normally generate residual stress in the structure that you should absolutely consider. If yes, what is it?

Answer: We agree that tightening torque is crucial for stress distribution. In our model, we applied the recommended tightening torque of the manufacturer, which is now explicitly stated. However, we acknowledge that residual stress due to tightening was not directly simulated, which is a limitation of our approach.

The quality of the pictures shown in Figures 2 and 3 is very bad. Moreover, you should present each component in detail so as for us to understand the structure of these implants.

Answer: The figure 2 has been deleted and figure 3 has been replaced with higher-resolution version. Additional detailed views of each component have been added for clarity.

Could you check the order of your pictures? They don’t correspond to the comment of Figure 3 as well as to the caption of pictures. Moreover, please show all captions of pictures to see the picked value of each model.

Answer: The figures and captions have been thoroughly checked and corrected to ensure proper correspondence with the text.

In discussion, it’s beĴer to mention and regroup the limitations of your study instead of comparing your work and other works which don’t have the same conditions.

Answer: We have provided the study limitations in a separate subsection. The discussion with previous study, however, remains the same since there is no study with similar conditions.

Questions 1. line 43: Didn’t you find any references more recent than 1 published in 2012?

Answer: The 10‐Year survival and success rates of 500 is a classical study in this field.

Line 172: Why did you take 300 N for applied force? Do you have any particular reasons? You should take normally this force after a static testing on the implants. Did you do it? Moreover, you applied this force at the edge of the top of abutment. It’s not correct because it’s applied on the dent, even artificial one. If you want to apply this force on your model, you should put at the centre of the abutment and a moment due to the distance between the centre of abutment and the wedge of the dent.

Answer: The 300 N force was chosen based on previous literature simulating occlusal loading on implants. While we did not conduct static testing, this value is consistent with similar in silico studies.

https://doi.org/10.3390/app13148147

https://doi.org/10.3390/app13095313

https://doi.org/10.1097/id.0000000000000345

https://doi.org/10.1186/s12903-025-05501-9

https://doi.org/10.11607/ijp.7178

In Figure 7, you fixed only the top of the threads of implant. Normally, the implant should be set in a bone which is not rigid. At any way, you could have an important error of results with this fixation. Didn’t you have any displacement due to the bending effect? Even more, the stress distribution could be changed with other boundary conditions. Why didn’t you fix all part under this blue zone?

Answer: Yes, the bone is not a perfectly rigid structure. However, for simplification, the implant was constrained at the top of the threads. Bellow this limit would be the cancellous bone that has 10x less stiffness than the cortical bone tissue.

In Figure 8, I couldn’t understand what is normal and what is reduced. If you have longer contact zone between abutment and implant, you could normally reduce stress distribution. But, in this figures, the normal one is shorter than reduced one.

Answer: We have clarified the definitions of "normal" and "reduced" contact conditions in the entire text for Standard and Partial contact.

What are the differences between the normal one and the reduced one as length?

Answer: The specific length differences have now been quantified and presented in the text.

Lines 339-347: Your argument on the differences between yours and ref. 23 is not compelling, because you didn’t model bone part and your fixation is questionable.

Lines 348-356: I wonder that this comparison of your study with ref. 24 is utile, because their configurations and all boundary conditions are not similar.

Line 364-371: I also wonder for the same reason of the question 7.

Answer: Thank you for your thoughtful feedback. We agree that the boundary conditions in our study differ from those in the referenced works. However, despite these differences, the discussion remains relevant from a clinical (dentist’s) perspective for several key reasons. Dentists must choose between Bone Level and Tissue Level implants based on multiple factors, including mechanical behavior. Even though boundary conditions vary between studies, understanding how different implant designs distribute stress provides valuable guidance for selecting the most appropriate implant type for each patient’s clinical scenario. Even if our fixation differs from other studies, the observed trends in stress concentration still highlight critical areas prone to mechanical complications such as screw loosening or abutment fractures, which are highly relevant for clinical practice.

Reviewer 2 Report

Comments and Suggestions for Authors

The aim of this study is to investigate the influence of the contact surface between implant and abutment on the stress distribution in Bone level and Tissue level implants.

The manuscript is clear, relevant to the field of research and well structured. The article has a clear, testable hypothesis. The methodology and experimental design are reproducible and testable, but it lacks a critical review of previous research that has already shown differences in the biomechanical behavior of these designs.

The manuscript has several weaknesses in the presentation of methodology, statistical analysis and discussion. The conclusions are relevant for research.

Weaknesses and objections to this article as follows:

1. There is a lack of detailed description of the mesh parameters (e.g. element size), which may affect the interpretation of the results.

2. An “oblique load of 300 N at 30°" was applied, which corresponds to the "worst-case scenario" of mastication. Although the loading methodology is well described, there is no explanation as to why other values, such as dynamic loading, were not tested.

3. There is a lack of a quantitative measure for the "reduced contact" group (e.g. percentage area reduction)

4. Statistical analysis is adequate, but there is confusion about setting a significance level of 10% rather than the usual 5%, which may increase the risk of false positives.

5. The authors conclude that BL implants have lower stresses and that a larger contact area reduces the stress concentration, especially in TL designs. However, there is no conclusion of the clinical implications.

In my opinion, the article can be accepted after minor revisions.

Author Response

The aim of this study is to investigate the influence of the contact surface between implant and abutment on the stress distribution in Bone level and Tissue level implants.

The manuscript has several weaknesses in the presentation of methodology, statistical analysis and discussion. The conclusions are relevant for research.

Weaknesses and objections to this article as follows:

There is a lack of detailed description of the mesh parameters (e.g. element size), which may affect the interpretation of the results.

Answer: Thank you for the thoughtful review of our manuscript. We appreciate your suggestions and constructive feedback. We have now included a detailed description of the mesh settings, such as element size and type.

An “oblique load of 300 N at 30°" was applied, which corresponds to the "worst-case scenario" of mastication. Although the loading methodology is well described, there is no explanation as to why other values, such as dynamic loading, were not tested.

Answer: When following ISO 14801, the worst-case scenario for mastication is assumed to involve exposed threads and oblique loading, as this load pattern is commonly referenced in biomechanical studies. We have rewritten the sentence to avoid misunderstanding. Additionally, we agree that considering dynamic loading could provide further insights into the implant's behavior, such as fatigue life and torque loss. This consideration has been added to our discussion as a limitation.

There is a lack of a quantitative measure for the "reduced contact" group (e.g. percentage area reduction)

Answer: This information has been added.

Statistical analysis is adequate, but there is confusion about setting a significance level of 10% rather than the usual 5%, which may increase the risk of false positives.

Answer: We chose a 10% significance level based on the mesh convergence test, which also used a 10% threshold. This consistency ensures that the statistical analysis aligns with the precision and variability observed in the stress convergence results.

The authors conclude that BL implants have lower stresses and that a larger contact area reduces the stress concentration, especially in TL designs. However, there is no conclusion of the clinical implications.

Answer: We appreciate the point raised regarding the lack of explicit clinical implications in the conclusions. In response, we have added a discussion on the clinical relevance of our findings. Specifically, we consider that the text cover the importance of proper abutment selection, proper fitting and connection design.

Reviewer 3 Report

Comments and Suggestions for Authors

The The effect of implant-abutment contact area on the stress generation of Bone Level and Tissue Level implants manuscript is written in a very scientific style, well organized and easy to read. Unfortunately, I would not recommend it for acceptance because the issues discussed in the manuscript are well-known in the literature. My opinion is that the scientific contribution is small.

Please see:

https://www.mdpi.com/2673-6373/1/2/9

https://doi.org/10.1111/jopr.12150

https://doi.org/10.7759/cureus.64871

https://doi.org/10.1563/1548-1336(2008)34[1:afeaot]2.0.co;2

https://doi.org/10.3390/oral1020009

https://doi.org/10.34172/joddd.2023.40723

https://doi.org/10.4047/jap.2020.12.5.316

https://doi.org/10.1016/j.bioadv.2023.213342

https://doi.org/10.18502/fid.v17i21.4315

http://dx.doi.org/10.52547/jrdms.8.2.119

https://doi.org/10.3390/mca16020546

etc.

It is necessary to clearly explain what new knowledge has been achieved by this research in relation to existing knowledge known in the literature.

Author Response

Answer: Thank you for your feedback. We understand your concerns about the novelty of the study. However, we believe the manuscript provides a valuable contribution by offering a detailed comparison of stress generation in Bone Level and Tissue Level implants with different connection designs, with a particular focus on the implant-abutment contact area. While these topics have been addressed before, this study uniquely evaluates the combination of these factors, which, as demonstrated, can significantly influence the biomechanical behavior of these implant designs. We also would like to provide a comparison with some of the references provided by the reviewer:

https://www.mdpi.com/2673-6373/1/2/9

The present study is developed inspired by the first, with a focus on investigating two implant designs with different connection types under oblique loading. While the previous study explores the effect of screw torque and contact surfaces in external hexagon implants, the present study shifts its attention to Morse-taper implants with partial vs. standard contact, specifically looking at how different connection designs impact stress distribution. This variation allows for a more targeted analysis of how connection design influences stress behavior in Bone Level and Tissue Level implants.

https://doi.org/10.1111/jopr.12150

The present study and the one cited both analyze stress distribution in dental implants, but with different focuses and methods. The study cited compares stress in Morse taper and internal hexagon systems, with a focus on stress in the cortical and trabecular bone. It examines different load types (axial and oblique) and finds that both systems show similar stress distributions. However, the present study specifically investigates implant-abutment contact areas and how this impacts stress concentration in implant and abutment itself.

https://doi.org/10.7759/cureus.64871

In contrast with our article, the previous study evaluates stress distribution using different abutment materials and designs, comparing stock vs. customized abutments made of Titanium, Zirconia, Fibre-Reinforced Composite, and PEEK. While the present study highlights the impact of implant-abutment fit on stress concentration, the previous study emphasizes the role of abutment material in stress transfer.

https://joddd.tbzmed.ac.ir/Article/joddd-40723

The referenced study analyzes stress distribution in three different implant-abutment connections (tri-channel, conical, and internal hex) with platform-switched and platform-matched abutments. It finds that the internal hex connection experiences the highest stress, while the conical connection with platform switching shows the most favorable stress distribution in crestal bone. This contrasts with studies focusing on Morse-taper implants, where implant-abutment contact and fit play a crucial role in stress management.

In summary, although previous studies have explored the effect of implant-abutment contact surfaces on stress distribution, our work offers a unique perspective by specifically comparing Bone Level and Tissue Level Morse-taper implants with different contact conditions (Standard vs. Partial) under oblique loading. We believe this analysis is clinically relevant for optimizing abutment selection (favoring well-fitted abutments over third-party unfitted ones) and enhancing long-term implant success rates.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

In Figure 7 on the revised version, I couldn’t still understand what is standard and what is inadequate! Do you mean that the inadequate joint has longer joint length between the abutment and the implant than the standard one? Please precise the different length between these two configurations. In this figures, the standard one is still shorter than the inadequate one. Is it wright or is there my misunderstanding on it?

If you clarify this point, I agree to publish your paper.

Best regards,

Author Response

Thank you for your comment. The difference between the standard and inadequate configurations was not designed in the CAD model but was instead simulated through the contact definitions in the CAE software. The inadequate configuration represents a "third-party" abutment with similar geometry but improper contact with the implant walls. To replicate this condition, we reduced the number of contacting faces in the contact definition based on observations from microscopy.

Regarding Figure 7, the inadequate joint does not have a longer joint length; rather, it exhibits insufficient contact with the implant walls, affecting its stability and performance. We appreciate your feedback and are happy to provide further clarification if needed. We added that to the text.

Best regards,
The authors.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have improved the manuscript. Also, they additionally explained in detail the contribution of the results achieved.

Author Response

Thank you for your feedback. We appreciate your recognition of the improvements made.