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In agreement with the PLOS ONE style templates the section names were removed from the first page.

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Additional information about company providing the specimen and the informed written consent was included in the online submission form and the manuscript.

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The name and version of the software for statistical analysis was added to the manuscript.

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Several factors and their influence on the results are identified and discussed in this study. The parameters sex and age were taken into account by distributing them evenly among the implant groups. Bone quality is another limiting factor that comes together with individual biological specimen. It is shown that the quality of the bone varied greatly. In addition, it was investigated whether the mechanical stability, in particular the stiffness, of the reconstructions differed between the implant groups. This was highlighted in more detail in an additional section of the manuscript. No relevant difference between the stiffnesses of the reconstructions could be found in the static testing as well as in the dynamic testing. Thus, this parameter can be excluded as a confounding factor. In addition, for the reconstruction of the mandible, an area on the mandible was identified that is easily weakened by the application of screws. Bone fracture in this area is a prominent failure type in this study. It indicates that for further development of the implant, avoiding the fixation in this area could be beneficial for stability in case of low bone quality.

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The phrase referring to these data was removed from the manuscript.

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"This work was supported by the German Research Foundation (DFG) and the Technical University of Munich (TUM) in the framework of the Open Access Publishing Program.

The research project “TOPOS - Development, Manufacturing and Testing of Topology Optimized Osteosynthesis Plates” (AZ-1019-12), in whose context the presented study was conducted, is funded by the Bavarian Research Foundation (BFS).

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."

We note that one or more of the authors are employed by a commercial company: Josefinum, and private practice for Oral and Maxillofacial Surgery at Pferseepark

a) Please provide an amended Funding Statement declaring this commercial affiliation, as well as a statement regarding the Role of Funders in your study. If the funding organization did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors' salaries and/or research materials, please review your statements relating to the author contributions, and ensure you have specifically and accurately indicated the role(s) that these authors had in your study. You can update author roles in the Author Contributions section of the online submission form.

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If your commercial affiliation did play a role in your study, please state and explain this role within your updated Funding Statement.

Updated Funding Statement:

This work was supported by the German Research Foundation (DFG) and the Technical University of Munich (TUM) in the framework of the Open Access Publishing Program.

The research project “TOPOS - Development, Manufacturing and Testing of Topology Optimized Osteosynthesis Plates” (AZ-1019-12), in whose context the presented study was conducted, is funded by the Bavarian Research Foundation (BFS).

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The funder Josefinum, and private practice for Oral and Maxillofacial Surgery at Pferseepark provided support in the form of salaries for authors JW, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.

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Updated Competing Interests Statement:

The authors have declared that no competing interests exist.

The affiliation Josefinum, and private practice for Oral and Maxillofacial Surgery at Pferseepark of JW does not alter our adherence to PLOS ONE policies on sharing data and materials.

Additional Editor Comments:

The authors propose a well-conducted study to compare topology optimized, patient specific osteosynthesis plates (TOPOS-implants) versus 1.0 mm miniplates by biomechanical testing using fibula-reconstructed cadaveric mandibles.

Introduction: To increase the clinical relevance, please include data about the benefits of PSI versus plates, referring to some clinical outcomes: recovery time for patients, shorten surgical and hospital time, etc.

A corresponding paragraph was added to the Introduction.

The aim of the study should be stated

A paragraph stating the aim of the study was added to the end of the Introduction.

The topology optimization of implants, the new technique tested in this manuscript, is defined as “…a powerful mathematical tool which allows creating an optimal structural design within prescribed loading and boundary conditions.”. This definition was supported by just one reference (#10) in page 4 line 76. This is a key point for this manuscript, so please add a more detailed definition and features of this specific technique to lead medical readers.

Thank you very much for pointing this out. More details about topology optimization and the advantages for osteosynthesis plates are added to the introduction.

Conclusions: They should state more precisely the benefits of TOPOS-implants over miniplates rather than “significant superiority”, which is an unprecise and subjective word.

The sentence was changed to:

This study displays a significantly increased cyclic loading capacity of mandible reconstructions with topology optimized and patient specific implants in comparison with miniplates as clinical standard

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

________________________________

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

________________________________

3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: No

Reviewer #2: Yes

________________________________

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Reviewer #1: Yes

Reviewer #2: Yes

________________________________

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Abstract

Line 26: Please mention that “1.0mm” refers to thickness. Define “miniplates” and disclose their titanium grade.

Line 29: Thickness and other dimensions of the TOPOS plates should be mentioned.

Line 30: Titanium alloy? Grade?

The information about the materials of the used plates and the thickness of 1.0 mm was added to the abstract.

In Lines 212-215 you explain that the TOPOS plates fractured under lower static load than the miniplates. Also that the fibula fractured more quickly, but SD probably did not allow to reach statistical significance. Should this not be mentioned?

We agree that the information about the results from static testing would be interesting for the abstract. But due to the limited amount of words and in order to make the abstract more understandable, we reduced it to the sentence: “Static testing was used to confirm mechanical similarity between the reconstruction groups.”

Concerning the results of static testing there must be a misunderstanding, neither TOPOS-implant nor miniplates fractured. The reconstructions were tested in a whole and bone fracture was the main failure type, only once plastic deformation of miniplates occurred. A sentence referencing the result table for the static testing in the supplementary data was added to the manuscript. The differences between the mean values of the groups (elastic limit: 11 N, reconstruction failure: 13 N) are small compared to the SD and the absolute mean value for static testing. This is the reason why we concluded comparable mechanical properties in static testing for the two groups in the abstract.

The shape of the implant seems more important than any other characteristics (line 279). This can be mentioned in the abstract.

In general, the abstract can reflect the findings in a much better and much understandable way.

To further emphasize the importance of the shape of the implants, it was included in the introductory words of the abstract.

M&M

Line 135: is high stiffness (= high brittleness) correctly the goal? Would reduced plasticity and increased elasticity not be a better criterion? Please explain in your text.

Brittleness as a material property often comes together with a high material stiffness. But in this case, the optimization goal was to maintain a high stiffness for the whole implant despite significant material reduction. The Young’s moduli, which are a measure for elasticity and can be seen as the material stiffness, are very similar for titanium grade 4 and grade 5. So, the material properties are not changed and the implant still has a ductile mechanical behavior. The created geometry is optimized to allow as little deformation as possible with the given material. This is criterion is chosen to have a better distribution of internal stress in the implant and to improve fatigue properties. An optimization of the implant to higher elastic deformation would have been possible, but this always comes with a decreased stiffness for the implant. In consequence the reconstruction is not as stable and the risk of interfragmentary motion is higher, which impedes proper bone healing.

Line 164: what do you mean with “surgical procedures”?

Thank you for pointing that out. The sentence can be misleading to the reader, because the in-vitro reconstruction is not comparable with the intraoperative situation. The sentence was changed to: “The fixation of corresponding bone segments was performed with standard surgical equipment. The position of the screws was chosen for every reconstruction individual by surgeon.”

Line 165: why did you choose for the same (small diameter) screws? Luckily none failed. Is the position of the screws not important? The configuration should be explained and the influence of the latter on bone fracture.

The same diameter of screws was chosen to have comparable conditions for both reconstruction techniques. With only two length of screws the variational parameter were kept at a minimum, while maintaining the capability to create stable reconstructions. The position of the screws was chosen by the operating surgeon either at planning for TOPOS-implants or during reconstruction for the miniplates. That the position of the screws plays an important role is part of the results of this paper. This is especially important for the mandible angle, where a weakening effect of the screws becomes obvious.

Line 176-182: this is difficult to understand. Please rephrase. Did you take laterotrusion (= horizontal shear forces at the occlusal level in the molar area) and protrusion (= vertical shear forces at the incisors) into account?

We did a restructuring of the paragraph with additional information added for better understanding. The force direction for the testing setup was derived from the major muscle groups. The in-vivo forces that are resulting from the muscular movement are dependent on the contact situation of the teeth. This includes shear forces at the incisors and the molar area. Due to the fact that we have only a bite point contact at the premolar, which is constraint in vertical direction for the setup, shear forces at the incisors are not present. Horizontal shear forces can occur for the setup at the bite point due to frictional contact. But this was not emphasized for this study. The loading situation was derived from different numerical and experimental models for testing of the mandible. The bearing at the end of the left mandible segment creates the biggest lever arm for the loading, which is like a worst-case scenario for possible chewing loads considering the remaining teeth.

Line 180: name of device, name of company, city, country

Thank you very much for this hint. The test system has already been described as custom made in a previous paragraph. To avoid confusion for the reader, this has been pointed out again in the manuscript.

Lines 212-218 belong to the Results section.

The paragraph was moved to the Result section.

Line 230: could Young modulus not be determined per specimen after static and cyclic loading, to test differences between mandibles, being probably a confounding factor?

The information about the stiffness of the reconstruction (static: stiffness in elastic region, dynamic: actuator displacement) was added to the supplementary information and also mentioned in the Result and Discussion sections. Especially the displacement of the actuators shows that the both reconstruction types show very similar mechanical reaction to the applied load. This eliminates the stiffness of the reconstruction as confounding factor for this study.

Line 236: did you perform a Shapiro-Wilk test to conclude this?

Yes, due to the fact that the specimen number was too small for a D’Agostino & Pearson omnibus test, a Shapiro-Wilk normality test was performed. This indicated that the results of the dynamic testing were not normally distributed. (Shapiro-Wilk normality test: miniplates group p = 0.002; TOPOS-group p = 0.0008). This information was added to the manuscript.

Results

Line 253: I read “No TOPOS-implant failed for the applied cycles” and then I read in Line 254: “Failure is noted in the TOPOS implant group”, which is confusing.

Thank you very much for pointing that out. The second sentence was changed to “…, reconstruction failure (including bone fractures) is noted (…) in the TOPOS implant group…”.

Overall a good paper, but difficult to read for a surgeon. Its impact may increase of you make it more accessible.

Thank you very much for this hint. We hope the revision made it easier accessible for the readers.

Reviewer #2: According to the study design by the authors, the research work it is according to be in the right way by the literature available. Could be interesting in the future to use the same design of study to evaluate the properties of PSI vs reconstruction plates. The only thing that I miss was the blind selection of the groups of miniplates vs PSI.

Thank you very much. A comparison with reconstruction plates does sound like an interesting consecutive project.

The specimen in this study were first separated in two groups with a similar distribution of the parameters sex and age. This was done so that the result could be considered independent of these factors. Otherwise age and sex could have been confounding factors.

Attachments

Attachment

Submitted filename: Response to Reviewers.docx

Dear Mr. Cordova,

dear Mr. Mommaerts,

dear Mr. Carrasco,

thank you very much für the second revision of our manuscript entitled “Improving mandibular reconstruction by using topology optimization, patient specific design and additive manufacturing? – A biomechanical comparison against miniplates on human specimen”. In the following I would like to respond to each point mentioned in your revision.

1. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

The reference list has been checked. All references are accessible and no retractions are present. During the two revision cycles the following references position have been added to the reference list: 10-18, 35-37

2. As a general comment, the revision of the final revised version (PONE-D-20-39788R1) was complex because it doesn't include changes highlighted in red or yellow color. All changes were presented at the end of the compiled PDF file document as raw tracked changes. TO MAKE THE NEXT REVISION EASY, PLEASE, BE SURE TO HIGHLIGHT FINAL MODIFICATIONS IN RED COLOR ONLY IN THE FINAL REVISED VERSION

I am sorry to hear about these inconveniences. I did use the normal Track changes function in Word, which includes a highlighted mark-up, as stated in the requirements for submission of revisions. Somehow, in the transition to the compiled pdf there must have been a problem with these markups. Nevertheless, in my pdf-summary of the upload the mark-up was tracked and highlighted normally. I did upload now tracked changes files as pdf in order to prevent this complication. If there is still a problem with the mark-up, please explain me, how exactly to solve this.

Comments by Reviewer 1

3. Reviewer 1: Line 135: is high stiffness (= high brittleness) correctly the goal? Would reduced plasticity and increased elasticity not be a better criterion? Please explain in your text.

Brittleness as a material property often comes together with a high material stiffness.

But in this case, the optimization goal was to maintain a high stiffness for the whole implant despite significant material reduction. The Young’s moduli, which are a measure for elasticity and can be seen as the material stiffness, are very similar for titanium grade 4 and grade 5. So, the material properties are not changed and the implant still has a ductile mechanical behavior. The created geometry is optimized to allow as little deformation as possible with the given material. This is criterion is chosen to have a better distribution of internal stress in the implant and to improve fatigue properties. An optimization of the implant to higher elastic deformation would have been possible, but this always comes with a decreased stiffness for the implant. In consequence the reconstruction is not as stable and the risk of interfragmentary motion is higher, which impedes proper bone healing.

Reviewer 1: Then please explain the importance of stress shielding, the micro strains involved related to the Utah paradigm..

Thank you very much for pointing this out. To emphasize for the reader, that stress shielding and bone loss due to reduced micro strains is not an issue for these implants, two sections were added to the manuscript. First, the optimization process was rephrased to show that an optimization goal for high stiffness does not result in an extraordinary stiffness for the implant. Secondly it was highlighted that the mechanical similarity of the reconstruction does also mean similar mechanical stresses for the fracture area.

The following sentence was added to the Material&Methods section for clarification:

“… In other words, the optimization is a material reduction process that results in the least possible loss of stiffness for the implant.”

The topic concerning stress shielding and micromotions in the fracture is now addressed with the following paragraph in the discussion section:

“The mechanical similarity also confirms that there is no excessive stiffening caused by the TOPOS implants. If the bone fragments are positioned too rigidly for osteosynthesis, it can result in inhibition of sufficient micromotions in the fracture gap [35,36]. Stress shielding like effects can lead to impaired healing in this context due to low interfragmentary strains at the fracture site [37]. But as already described there is no indication for this found in mechanical testing. “

4. Reviewer 1: Line 180: name of device, name of company, city, country

Thank you very much for this hint. The test system has already been described as custom made in a previous paragraph. To avoid confusion for the reader, this has been pointed out again in the manuscript.

Reviewer 1: Difficult to confirm the results by a re-test by a third party. Please describe the flaw.

The following sentence was added to the manuscript for clarification:

“The biomechanical testing in this study was performed on an in-house developed testing setup. Using a custom-made solution like this comes with the disadvantage of limited reproducibility for third parties. But a commercially available solution does not exist for this testing scenario. And due to the detailed description of the testing and the publication presenting the experimental setup by Foehr et al. [26], distinct transparency, comprehensibility and adaptability of the experiments are ensured.”

We hope the revised version of our article meets all the conditions for publication in your journal.

Attachments

Attachment

Submitted filename: Response to Reviewers.docx