The Stress Distribution and Deformation of Maxillary Bilateral Distal-Extension Removable Partial Dentures with U-Shaped Palatal Major Connectors Fabricated from Different Materials: A Finite Element Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Reviewer Questions
The article titled “The stress distribution and deformation of maxillary bilateral distal-extension removable partial denture with U-shaped palatal major connector fabricated from different materials: A finite element analysis” is interesting, well-written, and presents a clear methodology. However, I have a few questions that I believe need further clarification from the authors. If these points were already addressed in the manuscript and I missed them, I kindly ask the authors to clarify.

Methodology & Model Validity

1. Was the applied force of 320 N chosen to simulate normal occlusal load, or does it represent a worst-case scenario? Please justify.
2. Were dynamic loading or fatigue simulations considered, given that RPDs are used over extended periods?

Results Interpretation
3. Although CoCr showed higher stress at the abutment, PEEK demonstrated greater deformation. How might this trade-off affect long-term abutment stability and patient comfort?
4. The abstract states that both CoCr and PEEK are “unlikely to cause severe mechanical damage.” On what basis was this conclusion made? Was there a specific threshold stress value used for comparison?

Clinical Relevance
5. How do the findings translate into real-world clinical practice? Should clinicians prefer PEEK over CoCr in certain patient groups (e.g., with reduced abutment support or compromised periodontal health)?
6. Given that PEEK showed more deformation, what are the implications for retention, stability, and patient comfort?

 

Author Response

Reviewer #1 Comments and Responses

 We sincerely thank the reviewer for the positive comments and thoughtful feedback. We have addressed the questions raised and provided clarifications in the revised manuscript. If any points were previously included and overlooked, we hope the revisions make them clearer.

1. Question 1: Was the applied force of 320 N chosen to simulate normal occlusal load, or does it represent a worst-case scenario? Please justify.

Response: A force of 320 N should be viewed as a worst-case scenario load for RPD patients, not as a normal occlusal force.

Fully dentate individuals exhibit higher maximum bite forces, averaging 464–547 N, while RPD wearers show much lower values, around 297 N or about 35% of natural dentition (for example, one large cross-sectional study found that RPD patients had an average maximum bite force of 297 ± 29 N) [1,2].

Thus, 320 N lies above the typical range for RPD patients but within the lower range of fully dentate individuals. In experimental or simulation contexts, this force is best used to test durability and mechanical limits of RPD frameworks under extreme or accidental loading, rather than to represent normal masticatory conditions.

 

2. Question 2: Were dynamic loading or fatigue simulations considered, given that RPDs are used over extended periods?

Response: In this study, the dynamic loading was not applied. Our study focused on static loading conditions, which involve a single application of force to simulate mastication. This study specifically reports the maximum von Mises stress and displacement under this static masticatory load. Static loading was deliberately chosen because it is simpler, less resource-intensive, and more standardized, although it does not fully replicate the long-term, cyclic forces experienced in the oral environment, as would be captured by dynamic or fatigue simulations.

 

3. Question 3: Although CoCr showed higher stress at the abutment, PEEK demonstrated greater deformation. How might this trade-off affect long-term abutment stability and patient comfort?

Response: Selecting between CoCr and PEEK materials for RPD frameworks involves weighing biomechanical advantages and disadvantages.

The rigidity of CoCr RPD provides superior denture stability and masticatory efficiency but transmits greater stress to abutment teeth, potentially increasing the risk of bone resorption and abutment loss over time, particularly in periodontally compromised patients. In contrast, PEEK RPD generates lower abutment stress and may better preserve periodontal health, yet their increased flexibility can result in greater framework deformation, leading to micro-movements and reduced functional stability. While CoCr RPD provides more stability, PEEK RPD tends to improve comfort and esthetics. The choice between these materials depends on careful patient assessment and individualized treatment planning to ensure both abutment protection and functional performance.

 

4. Question 4: The abstract states that both CoCr and PEEK are “unlikely to cause severe mechanical damage.” On what basis was this conclusion made? Was there a specific threshold stress value used for comparison?

Response: According to our conclusion that "CoCr RPD and PEEK RPD had similar stress on mucosa and PDL, with stress values all within the tissues' physiological limitations. Both PEEK RPD and CoCr RPD were unlikely to cause severe mechanical damage to mucosa and PDL," this can be explained as follows:

Jia et al. reported that 150 kPa (0.15 MPa) represents excessive stress that aggravates periodontal destruction and promotes periodontitis progression [3]. In our study, PDL stress values for PEEK and CoCr (0.002-0.003 MPa) were below this threshold, suggesting both materials are unlikely to cause serious PDL damage.

Ogawa et al. reported the pressure-pain threshold for oral mucosa at approximately 0.63 MPa [4], while another study reported 1 MPa [5]. In our study, mucosal stress values for PEEK and CoCr (0.353-0.442 MPa) remained below these thresholds, indicating both materials are unlikely to cause serious mucosal damage.

 

5. Question 5: How do the findings translate into real-world clinical practice? Should clinicians prefer PEEK over CoCr in certain patient groups (e.g., with reduced abutment support or compromised periodontal health)?

Response: According to our results, PEEK RPD may be the preferred choice for patients with reduced abutment support or compromised periodontal health because PEEK generates lower stress on the abutment and PDL. However, CoCr RPD appears to be a better option for patients with extensive free-end edentulism, such as Kennedy Class I cases with significant posterior tooth loss, since PEEK's increased framework displacement in these situations may compromise prosthetic stability.

While both materials demonstrate clinical suitability, comprehensive long-term data and research in patients remain insufficient.

 

6. Question 6: Given that PEEK showed more deformation, what are the implications for retention, stability, and patient comfort?

Response: Retention: Proper PEEK clasp design helps achieve good retention. However, this flexibility may cause a decrease of retention over time due to material fatigue or deformation from clinical use.

Stability: The greater flexibility of PEEK causes more deformation in the RPD, resulting in reduced stability, particularly in patients with free-end cases. The RPD framework tends to move more during function, which may reduce masticatory efficiency and create pressure on the surrounding mucosa.

Patient Comfort: PEEK's flexibility and lighter weight enhance wearing comfort, leading to high patient satisfaction. However, the pressure on the mucosa during RPD movement might compromise patient comfort or cause patient discomfort.

 

Reference

1. Nitschke, I.; Moede, C.; Koenig, A.; Sobotta, B.A.J.; Hopfenmüller, W.; Jockusch, J. An Evaluation of Reference Bite Force Values: Investigating the Relationship Between Dental Prosthetic Restoration and Bite Force in a Cross-Sectional Study. JCM 2025, 14, 2723, doi:10.3390/jcm14082723.
2. Miyaura, K.; Morita, M.; Matsuka, Y.; Yamashita, A.; Watanabe, T. Rehabilitation of Biting Abilities in Patients with Different Types of Dental Prostheses. J Oral Rehabil 2000, 27, 1073–1076, doi:10.1046/j.1365-2842.2000.00620.x.
3. Jia, R.; Yi, Y.; Liu, J.; Pei, D.; Hu, B.; Hao, H.; Wu, L.; Wang, Z.; Luo, X.; Lu, Y. Cyclic Compression Emerged Dual Effects on the Osteogenic and Osteoclastic Status of LPS-Induced Inflammatory Human Periodontal Ligament Cells According to Loading Force. BMC Oral Health 2020, 20, 7, doi:10.1186/s12903-019-0987-y.
4. Ogawa, T.; Tanaka, M.; Ogimoto, T.; Okushi, N.; Koyano, K.; Takeuchi, K. Mapping, Profiling and Clustering of Pressure Pain Threshold (PPT) in Edentulous Oral Mucosa. Journal of Dentistry 2004, 32, 219–228, doi:10.1016/j.jdent.2003.11.001.
5. Ramakrishnan, A.N.; Röhrle, O.; Ludtka, C.; Varghese, R.; Koehler, J.; Kiesow, A.; Schwan, S. Numerical Study of the Stress State on the Oral Mucosa and Abutment Tooth upon Insertion of Partial Dentures in the Mandible. Numer Methods Biomed Eng 2022, 38, e3604, doi:10.1002/cnm.3604.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript describes the investigation of the stress distribution and deformation of cobalt-chromium (CoCr) and polyetheretherketone (PEEK) maxillary bilateral distal-extension removable partial denture (RPD) on abutment, periodontal ligament (PDL), mucosa and RPD framework using FEA.

The topic and scope fit the journal’s section “Prosthodontics;” the method is limited; the result dissemination is not adequate and some practical implications may be expected.

Overall, the manuscript is not well prepared with poor English usage, limiting the narrative and scientific rigor. Reproducibility is low, as the FEA method was not well described, the three main stages were not introduced. Further, although the title and Abstract indicate stress distribution and deformation were investigated, only stress results have been presented, the deformation results, such as type of deformation (elastic or plastic) and strain, etc. have not been presented.

Major revision is necessary to address these main shortcomings.

Points for consideration:

1. The Objectives are not well introduced. The introduction reviews the literature about dental material science, though some studies applied FEA, this has not been highlighted. Also, the advantage and disadvantage of FEA should be introduced.
2. The CBCT measurement detail has not been introduced.
3. The method section should introduce the 3 main stages of FEA. The boundary conditions have not been defined, nor the full geometry and dimension of the domain.
4. Line 103 section, what is the connector thickness?
5. All figures need scale bars.
6. Table 1, the source of these applied fundamental property parameters has not been referred to. The Young’s modulus of CoCr is overly high, higher than the value range comprehensively determined for dental CoCr alloy in 10.1016/j.dental.2010.04.007. Please cite this here.
7. Please explain “bonded condition” in Line 131 “…denture base were in bonded condition due to computational constraints.”
8. Line 150, please complete this sentence “However, the stress on mucosa and PDL in CoCr RPD and PEEK RPD were not significantly (Table 2).”
9. Please explain “snowshoe effect.”
10. In discussion, the authors compare with other studies and stated the results were in line with these. Please refer to some numerical results to evidence this.
11. In Line 251-255, the authors discussed rigid framework, stress accumulation and deformation and flexible behavior. This is not well formulated. Please reformulate with sound and rational mechanical terms to properly discuss mechanical behavior, young’s modulus, rigid body behavior and stress-strain relation, etc.
12. The same for Line 265-266, “…was nonlinear compressive behavior” was not well formulated.
13. Conclusion 3, without clearly presented deformation behavior results, this conclusion is not well supported.

Author Response

Reviewer #2 Comments and Responses

 

         We sincerely thank the reviewer for the detailed and constructive feedback. We have carefully revised the manuscript to address all the comments and improve clarity, scientific rigor, and reproducibility. Our point-by-point response is as follows:

 

1. Question 1: The Objectives are not well introduced. The introduction reviews the literature about dental material science, though some studies applied FEA, this has not been highlighted. Also, the advantage and disadvantage of FEA should be introduced

Response: We have revised the introduction to clearly present the study objectives and to emphasize the application, advantages, and limitations of finite element analysis (FEA) in dental materials research. Please see Lines 86–104 in the revised manuscript.

 

2. Question 2: The CBCT measurement detail has not been introduced.

Response: Details regarding the CBCT measurement have now been added in Lines 106–109 of the revised manuscript.

 

3. Question 3: The method section should introduce the 3 main stages of FEA. The boundary conditions have not been defined, nor the full geometry and dimension of the domain.

Response: The materials and methods section has been revised to include the three main stages of finite element analysis (FEA), as well as detailed descriptions of the model geometry, dimensions, and boundary conditions.

 

4. Question 4: Line 103 section, what is the connector thickness?

Response: We have reviewed Line 103 in the original manuscript and did not find a detail regarding to the “connector thickness.” However, we assume the reviewer may refer to the major connector thickness, which has already been indicated in Line 133 and 136.

 

5. Question 5: All figures need scale bars.

Response: Thank you for the comment. We are not entirely certain about the specific meaning of “scale bars” in this context. Could the reviewer kindly clarify whether this refers to color measurement scale bars in simulation figures (e.g., for displacement or stress values), or to dimensional scale references in anatomical or geometric illustrations? We will be happy to revise the figures accordingly once clarified.

 

6. Question 6: Table 1, the source of these applied fundamental property parameters has not been referred to. The Young’s modulus of CoCr is overly high, higher than the value range comprehensively determined for dental CoCr alloy in 10.1016/j.dental.2010.04.007. Please cite this here.

Response: Even the Young’s modulus of CoCr is higher than the value range determined in the study by 10.1016/j.dental.2010.04.007., but from the reference that we use, the Young’s modulus of CoCr RPD is indicated as 235 GPa.

Table 1. Mechanical properties of components used in the finite element models.

Structure	Young’s modulus (GPa)	Poisson’s ratio
Enamel [1]	41.1	0.35
Dentin [1]	18.6	0.35
Cementum [2]	15.4	0.31
Periodontal ligament [1]	0.0004	0.49
Residual ridge mucosa [3]	0.03736	0.49
Cortical bone [1]	11.76	0.25
Cancellous bone [1]	1.47	0.3
Resin acrylic and artificial teeth [1]	2.45	0.3
Cobalt-chromium alloys (CoCr) [4]	235	0.33
Polyetheretherketone (PEEK) [4]	4.1	0.4

 

Reference

1. Nakamura, Y.; Kanbara, R.; Ochiai, K.T.; Tanaka, Y. A Finite Element Evaluation of Mechanical Function for 3 Distal Extension Partial Dental Prosthesis Designs with a 3-Dimensional Nonlinear Method for Modeling Soft Tissue. The Journal of Prosthetic Dentistry 2014, 112, 972–980, doi:10.1016/j.prosdent.2014.03.011.
2. Vikram, Nr.; Senthil Kumar, K.; Nagachandran, K.; Hashir, Ym. Apical Stress Distribution on Maxillary Central Incisor during Various Orthodontic Tooth Movements by Varying Cemental and Two Different Periodontal Ligament Thicknesses: A FEM Study. Indian J Dent Res 2012, 23, 213, doi:10.4103/0970-9290.100429.
3. Choi, J.J.E.; Zwirner, J.; Ramani, R.S.; Ma, S.; Hussaini, H.M.; Waddell, J.N.; Hammer, N. Mechanical Properties of Human Oral Mucosa Tissues Are Site Dependent: A Combined Biomechanical, Histological and Ultrastructural Approach. Clin Exp Dent Res 2020, 6, 602–611, doi:10.1002/cre2.305.
4. Chen, X.; Mao, B.; Zhu, Z.; Yu, J.; Lu, Y.; Zhang, Q.; Yue, L.; Yu, H. A Three-Dimensional Finite Element Analysis of Mechanical Function for 4 Removable Partial Denture Designs with 3 Framework Materials: CoCr, Ti-6Al-4V Alloy and PEEK. Sci Rep 2019, 9, 13975, doi:10.1038/s41598-019-50363-1.

 

7. Question 7: Please explain “bonded condition” in Line 131 “…denture base were in bonded condition due to computational constraints.”

Response: The explanation has been added in Lines 167–169:

“‘Bonded contact conditions’ refer to a common modeling simplification in which two contacting surfaces, such as the tooth/framework and denture base/mucosa, are assumed to be perfectly attached without any sliding, separation, or micro-movement at the interface.”

 

8. Question 8: Line 150, please complete this sentence “However, the stress on mucosa and PDL in CoCr RPD and PEEK RPD were not significantly (Table 2).”

Response: The sentence has been revised for clarity in Line 189 as follows:

“However, the stress values on the mucosa and periodontal ligament (PDL) between the CoCr RPD and PEEK RPD models were not significantly different (Table 2).”

 

9. Question 9: Please explain “snowshoe effect.”

Response: The manuscript has been revised (Lines 240–241) to clarify that the “snowshoe effect” in the context of RPDs refers to the principle of maximizing the surface area of contact between the denture base and the underlying oral tissues (residual ridge and supporting mucosa) to evenly distribute occlusal forces.

 

10. Question 10: In discussion, the authors compare with other studies and stated the results were in line with these. Please refer to some numerical results to evidence this.

Response: The manuscript has been revised (Lines 266–267, 283, and 295–296) to include relevant numerical values from previous studies, supporting the comparison and demonstrating that the present results are consistent with those findings.

 

11. Question 11: In Line 251-255, the authors discussed rigid framework, stress accumulation and deformation and flexible behavior. This is not well formulated. Please reformulate with sound and rational mechanical terms to properly discuss mechanical behavior, young’s modulus, rigid body behavior and stress-strain relation, etc.

Response: The section has been revised (Lines 296–307) to improve clarity and mechanical accuracy.

 

12. Question 12: The same for Line 265-266, “…was nonlinear compressive behavior” was not well formulated.

Response: The section has been revised (Lines 332–339) for improving scientific accuracy and readability.

 

13. Question 13: Conclusion 3, without clearly presented deformation behavior results, this conclusion is not well supported.

Response: We respectfully note that Conclusion 3 is directly supported by the results presented in the manuscript. Specifically, the findings indicate that the rigidity of the RPD framework significantly influences both stress distribution and elastic deformation. The CoCr framework, being stiffer, exhibited higher maximum stress (107.99 MPa) concentrated at the proximal plates, retentive framework, and major connector regions, while undergoing minimal elastic deformation (0.0082 mm). In contrast, the more flexible PEEK framework showed lower maximum stress (11.7 MPa) with slightly greater elastic deformation (0.0128 mm), indicating more uniform stress distribution and higher compliance under vertical loading. Based on these results, the recommendation to increase PEEK framework thickness to compensate for its lower stiffness is fully justified.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Interesting finite elements research. However some points should be deeply revised. Please add the relevant and recent literature where necessary.

1) U-shaped major connector is the most fragile design comparing to palatal strap due to minimal extension which forces the technician to fabricate a thicker design. Moreover rigidity and minimum thickness makes palatal strap preferable especially in Kennedy class I and II RPDs.

2) Caution should be taken while using PEEK framework in patients with free end teeth loss.

3) Is 2mm thickness for a major connector in the maxilla accepted by patients? Are there datas for this?

 4) Are there clinical studies for the long term reliability of PEEK RPDs? Clinical studies would reveal patient tolerance, and one main disadvantage of PEEK is that is difficult to repair. 5 year prognosis for RPD is well documented?

5) Are there datas PEEK and acrylic teeth/resin teeth bond? Please add this in discussion part, because tooth debonding is a major problem in most RPDs and CDs

6) Clasp design is the same for CoCr and PEEK frameworks?

Author Response

Reviewer #3 Comments and Responses

 

Thank you for your valuable feedback. We appreciate your suggestions and will carefully revise the identified points. Relevant and recent literature will be added where necessary to strengthen the discussion and support our findings

 

1. Question t 1: U-shaped major connector is the most fragile design comparing to palatal strap due to minimal extension which forces the technician to fabricate a thicker design. Moreover rigidity and minimum thickness makes palatal strap preferable especially in Kennedy class I and II RPDs.

Response: Thank you for your comment. We have addressed it by incorporating relevant content into the Introduction section (Lines 60–66).

 

2. Question 2: Caution should be taken while using PEEK framework in patients with free end teeth loss.

Response: Thank you for your comment. We have addressed it by adding relevant discussion to the Discussion section (Lines 318–324).

 

3. Question 3: Is 2mm thickness for a major connector in the maxilla accepted by patients? Are there data for this?

Response: Yes, clinical evidence supports the use of a 2 mm thick PEEK major connector. A case report documented the application of PEEK major connectors in both maxillary and mandibular RPDs for a patient with Kennedy Class III, modification 1 (Reference: Line 249). The major connector was fabricated with a uniform thickness of 2 mm, demonstrating a good adaptation to the oral tissues. The patient reported a high satisfaction with the lightweight design and the esthetics resulting from the absence of visible metal in the clasp regions. A one-month follow-up indicated that the prostheses functioned comfortably under normal use [1].

 

4. Question 4: Are there clinical studies for the long term reliability of PEEK RPDs? Clinical studies would reveal patient tolerance, and one main disadvantage of PEEK is that is difficult to repair. 5 year prognosis for RPD is well documented?

Response: Clinical studies on PEEK RPDs are available; however, most report only short-term outcomes of up to one year. These studies [1–3]  primarily assess patient satisfaction, framework fit, and periodontal health, generally indicating that PEEK RPDs perform comparably to CoCr frameworks in terms of comfort, patient acceptance, and periodontal indices. Nonetheless, a long-term data beyond one year, including a 5-year prognosis, remain limited, and the material’s limited reparability should be considered for extended clinical use.

 

5. Question 5: Are there data PEEK and acrylic teeth/resin teeth bond? Please add this in discussion part, because tooth debonding is a major problem in most RPDs and CDs

Response: Thank you for your comment. We have addressed this by adding relevant content to the Discussion section (Lines 325-331).

 

6. Question 6: Clasp design is the same for CoCr and PEEK frameworks?

Response: Yes, the clasp design of CoCr and PEEK RPDs is the same.

 

Reference

1. Piemnithikul, N.; Angkasith, P.; Chaijareenont, P. Removable Partial Denture Polyetheretherketone Framework: A Case Report. CM Dent J 2021, 42, 185–198.
2. Harb, I.E.; Abdel‐Khalek, E.A.; Hegazy, S.A. CAD/CAM Constructed Poly(Etheretherketone) (PEEK) Framework of Kennedy Class I Removable Partial Denture: A Clinical Report. Journal of Prosthodontics 2019, 28, doi:10.1111/jopr.12968.
3. Zoidis, P.; Papathanasiou, I.; Polyzois, G. The Use of a Modified Poly‐Ether‐Ether‐Ketone (PEEK) as an Alternative Framework Material for Removable Dental Prostheses. A Clinical Report. Journal of Prosthodontics 2016, 25, 580–584, doi:10.1111/jopr.12325.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

I belive this work contributes meaningful insights into the clinical selection of materials.

A major strength of the paper lies in its use of finite element analysis (FEA), which allows for precise visualization and quantification of stress distribution patterns within both the denture base and supporting oral structures. 

The comparison between different materials—likely including cobalt-chromium, titanium alloys, and polymer-based options—provides a practical framework for clinicians seeking to balance rigidity, comfort, and biological compatibility.

 

The findings highlight how material stiffness and elastic modulus influence both the magnitude and localization of stress. As expected, stiffer alloys demonstrated reduced deformation but transmitted greater stress to abutment teeth and supporting bone, while more flexible materials showed the opposite trend.

 

In conclusion, the study is not without limitations. FEA, while powerful, inevitably relies on assumptions about boundary conditions, material homogeneity, and load application that may not fully replicate intraoral variability. The absence of clinical validation or long-term in vivo correlation reduces the immediate generalizability of the results. It underscores the importance of material selection in removable partial denture design and provides a foundation for future studies that integrate computational modeling with clinical outcomes. For practitioners and researchers alike, it offers a balanced perspective on the trade-offs between rigidity, stress distribution, and deformation in distal-extension cases

Author Response

Reviewer #4 Comments and Responses

 

1. Comments and Suggestions for Authors: I believe this work contributes meaningful insights into the clinical selection of materials.

A major strength of the paper lies in its use of finite element analysis (FEA), which allows for precise visualization and quantification of stress distribution patterns within both the denture base and supporting oral structures.

The comparison between different materials—likely including cobalt-chromium, titanium alloys, and polymer-based options—provides a practical framework for clinicians seeking to balance rigidity, comfort, and biological compatibility.

The findings highlight how material stiffness and elastic modulus influence both the magnitude and localization of stress. As expected, stiffer alloys demonstrated reduced deformation but transmitted greater stress to abutment teeth and supporting bone, while more flexible materials showed the opposite trend.

In conclusion, the study is not without limitations. FEA, while powerful, inevitably relies on assumptions about boundary conditions, material homogeneity, and load application that may not fully replicate intraoral variability. The absence of clinical validation or long-term in vivo correlation reduces the immediate generalizability of the results. It underscores the importance of material selection in removable partial denture design and provides a foundation for future studies that integrate computational modeling with clinical outcomes. For practitioners and researchers alike, it offers a balanced perspective on the trade-offs between rigidity, stress distribution, and deformation in distal-extension cases

 

Response: We sincerely thank the reviewer for these constructive feedback and are pleased that our study offers valuable insights for removable partial denture material selection. The recognition of FEA as a key strength is appreciated, as it allowed precise stress distribution analysis in denture bases and oral structures, with the reviewer's summary of material stiffness and elastic modulus effects confirming our work's clinical relevance. We acknowledge the noted limitations regarding FEA assumptions (boundary conditions, material homogeneity, load application) that may not fully represent actual intraoral conditions, and agree that the absence of clinical validation limits the result generalizability. Future research that integrate computational modeling with clinical follow-up should be considered to improve the practical applicability. The reviewer's comments are invaluable in refining our manuscript discussion.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Some issues raised have been addressed. 

Scale bars refer to dimensional scale references in anatomical or geometric illustrations.

The limitation of the study should be discussed, in general for FEA, many simplifications have been made, and the E value selection should be discussed. The high value, 235 GPa, cited from ref [20] has its own limitation, as E is a fundamental material property, due to the limitation of determination method and thermal mechanical history (refer to 10.1016/j.dental.2010.04.007),  hence the value has a range. And the value choice of [20] has not been justified by those authors and this should not be taken as the absolute authority. And FEA outcome is sensitive to the E value. It is intuitive to discuss this. 

One more point pertinent to the scientific rigor is that the simulation results should be value ranges, like 0.59±0.07 MPa and 375.48±39.31 MPa [20], rather than a single value as presented here. Statistical analysis is also missing. Please address this. 

Author Response

Reviewer #2 Comments and Responses

 

1. Comments and Suggestions for Authors:

Some issues raised have been addressed. 

Scale bars refer to dimensional scale references in anatomical or geometric illustrations.

The limitation of the study should be discussed, in general for FEA, many simplifications have been made, and the E value selection should be discussed. The high value, 235 GPa, cited from ref [20] has its own limitation, as E is a fundamental material property, due to the limitation of determination method and thermal mechanical history (refer to 10.1016/j.dental.2010.04.007),  hence the value has a range. And the value choice of [20] has not been justified by those authors and this should not be taken as the absolute authority. And FEA outcome is sensitive to the E value. It is intuitive to discuss this. 

One more point pertinent to the scientific rigor is that the simulation results should be value ranges, like 0.59±0.07 MPa and 375.48±39.31 MPa [20], rather than a single value as presented here. Statistical analysis is also missing. Please address this.

 

Response: We sincerely thank the reviewer for the valuable and thought-provoking suggestions. 

The scale bars have now been added to all relevant anatomical and geometric illustrations in the figures as suggested.

The point raised regarding the inherent variability of material properties and its effect on simulation outcomes is fundamentally important, and we fully concur with the scientific principle behind reporting value ranges. In the design of this study, our primary objective was to establish a comparative baseline between a conventional material (CoCr) and a novel alternative (PEEK) under identical, highly controlled conditions. By employing a deterministic FEA with a single, representative value for each parameter, including the Young's modulus, we aimed to isolate the effect of the material choice itself on the biomechanical behavior of the RPD. This approach, while simplifying the real-world scenario, allows for a clear and unambiguous comparison of the performance trends between the two materials. We are confident that while a sensitivity analysis varying the Young's modulus would indeed result in a range of output stress values, the fundamental trend and the core conclusion of our study would remain unchanged. Specifically, the significantly lower modulus of PEEK compared to CoCr is the primary driver of the observed differences in stress distribution and deformation. A minor variation (e.g., ±10%) in the E-value of CoCr would not alter the fact that it is orders of magnitude stiffer than PEEK. Consequently, the conclusion that the PEEK RPD induces lower stress on abutment teeth while undergoing greater deformation itself would still hold true. To better address the reviewer's concern and to enhance the clarity of our methodology's scope for future readers, we have revised the manuscript (Lines 341–363) in two key areas. First, we have expanded the Discussion section to include a paragraph acknowledging the deterministic nature of our results and discussing the anticipated stability of our comparative conclusions even with small variations in material properties. Second, we have significantly strengthened the Limitations section to explicitly state that this study provides a comparative, rather than predictive, analysis and that a probabilistic or sensitivity analysis would be a valuable next step for future research aiming to quantify the precise clinical performance range. We believe these revisions properly contextualize our findings and address the spirit of the reviewer's comment, while maintaining the original focus and scope of our investigation.  

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Overall a great effort from authors to advance the manuscript

1)Introduction completely revised by adding 2 paragraphs.

2) Materials and methods were more accurate and descriptive for 3D model, FEA and

3) results with minor corrections.

4) In Discussion more details and analyses were added, especially in the role of rigidity of the framework, the factor of tooth debonding and a thorough analysis of the major limitations of the study.

 Overall, a fair and well-organized research with many clinical outcomes that can be questioned or disputed in future studies.

 

Author Response

Reviewer #3 Comments and Responses

 

1. Comments and Suggestions for Authors:

Overall a great effort from authors to advance the manuscript

1)Introduction completely revised by adding 2 paragraphs.

2) Materials and methods were more accurate and descriptive for 3D model, FEA and

3) results with minor corrections.

4) In Discussion more details and analyses were added, especially in the role of rigidity of the framework, the factor of tooth debonding and a thorough analysis of the major limitations of the study.

Overall, a fair and well-organized research with many clinical outcomes that can be questioned or disputed in future studies.

Response: We sincerely thank the reviewer for the positive and encouraging comments. We truly appreciate the valuable feedback acknowledging our efforts to improve the manuscript. The introduction, materials and methods, results, and discussion sections were thoroughly revised according to the previous suggestions, and we are pleased that the revisions have strengthened the clarity, accuracy, and scientific value of the work.

 

Thank you once again for your constructive review and kind recognition of our efforts.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

The points raised have been addressed.