Stress Distribution in a Mandibular Kennedy Class I with Bilateral Implant-Assisted Removable Partial Denture: A Finite Element Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors studied the stress distribution of a partially implant-supported RPD and a conventional RPD. While this topic seems in principal of interest to the community, the current manuscripts lacks details from a biomechanical point of view that need to be addressed:

1. Details where the forces were applied exactly. I recommend showing a occlusal view with all areas where all areas where forces were applied are marked. Was the total force of 200 N equally distributed? And does the chosen force distribution represent a realistic force distribution as applied during chewing? Or is it rather closer to pressing or similar? This is currently not clear and not well discussed.
2. Provide rigorous details about all boundary conditions used in your FEA. Without them the results are useless! Where were the supports placed? Were all components modelled as bonded or was a contact simulation performed, if yes what were the details?
3. Details about where and how the metal frame connects to the bone are also of interest. Can the stress peaks in the distal region (e.g. red area in 3f)) be explained by details of the specific geometry. And can this be expanded to similar geometries? And what the expected role of the mucosa in this context?
4. What mesh elements were used? Type, sizes, refinements if applicable.
5. Was a mesh convergence analysis performed?
6. “nonlinear FEA”: What was nonlinear in your FEA? Did the authors perform a contact simulation?
7. Details of the prostheses should be shown in a way that clarifies at what areas it is connected (in detail!) to the teeth and bone (mucosa was neglected if I get it right). This is important to understand the biomechanics.
8. I recommend providing a table with all material parameters for clarity (currently only in the text).
9. Figure 3: The legend is unreadable, fix it.
10. For bone I recommend to stick to the principal stresses. Von Mises is for ductile materials, although this not consistently used in the dental FEA community.
11. Was a PDL modelled? If yes what material model and parameters were applied?
12. What were the stresses in the prosthesis?

Author Response

To Reviewer #1

The authors studied the stress distribution of a partially implant-supported RPD and a conventional RPD. While this topic seems in principal of interest to the community, the current manuscripts lacks details from a biomechanical point of view that need to be addressed.

 

Thank you for your kind comments and suggestions. The points of improvement are as follows.

 

1. Details where the forces were applied exactly. I recommend showing a occlusal view with all areas where all areas where forces were applied are marked. Was the total force of 200 N equally distributed? And does the chosen force distribution represent a realistic force distribution as applied during chewing? Or is it rather closer to pressing or similar? This is currently not clear and not well discussed.

We appreciate reviewer’s notion. Each type of force of 200N was equally distributed and forces were applied on the removable partial denture in both CRPD and IARPD. In a real masticatory process, the force applied varies due to different factors from the beginning of crushing to the formation of the food bolus and according to the food consistency. However, a force of 200N was chosen because it is an average force and is described in previous studies for the force applied in chewing simulation. Following reviewer’s notion, we clarified this idea further on Line 139, that reads as follows: “A force of 200 N was selected as an average value to simulate the chewing process [9,17]”, on Line 145, that reads as follows: “Each type of force was applied on the removable partial denture in both CRPD and IARPD, and was equally distributed”, and in the discussion section from Lines 239-242: “A static, uniformly distributed force of 200 N was selected, as it is considered an average value to simulate the forces involved in mastication [9, 17]. Although the force applied during real chewing varies due to factors such as the stage of food processing, from crushing to bolus formation, and food consistency, and from Line 285-287: “Diagonal and combined forces created higher stress in both the teeth and alveolar bone, especially in the distal part of the edentulous space (buccal shelf), where the longer lever arm increased pressure on the residual ridge”. All these additional sentences are highlighted in yellow color.

 

2. Provide rigorous details about all boundary conditions used in your FEA. Without them the results are useless! Where were the supports placed? Were all components modelled as bonded or was a contact simulation performed, if yes what were the details?

We appreciate reviewer’s critical comment. The occlusal rests were placed on the mesial surface of the left lower first premolar and at the level of the cingulum of both canines. We emphasized this point on Line 93, that now reads as follows: “The occlusal rests were placed on the mesial surface of the left lower first premolar and at the level of the cingulum of both present canines”.

For this analysis the mucosa was modeled assuming depreciable values to simulate an extreme scenario. A single geometry was generated where the prosthesis apparently makes contact with the mandibular bone. The areas of greater tension are related to the position of the implant, however in CRPD it would be produced directly in the mucosa and therefore transmitted to the mandibular bone, registering higher values. An additional paragraph containing this information was added from Line 109-114, that reads as follows: “The mucosa was modeled with depreciable values to simulate an extreme scenario. A single geometry was generated where the prosthesis apparently makes contact with the mandibular bone. The digital design for the teeth and bone anatomy was created considering normal dental occlusion, as well as the anatomy of the roots and mandibular bone, assuming a single structure between removable partial denture, teeth and bone. A conventional removable partial denture was also digitally designed (Figure 2b)”. These changes are highlighted in yellow color.

 

3. Details about where and how the metal frame connects to the bone are also of interest. Can the stress peaks in the distal region (e.g. red area in 3f)) be explained by details of the specific geometry. And can this be expanded to similar geometries? And what the expected role of the mucosa in this context?

We appreciate reviewer’s notion. Regarding the connection of the metal frame to the bone, the model assumed a single structure for the analysis. In the case of IARPD, the applied forces are transmitted to the implant, which dissipates the loads along its longitudinal axis, protecting the mucosa and reducing the impact on the alveolar bone. In CPRD, the stresses affect the mucosa, transmitting directly to the alveolar bone, which can cause poor force distribution and increase the risk of mandibular bone resorption. The stress peaks in the distal area of the alveolar bone are explained by the direction and intensity of the applied forces. An implant positioned more distally to the abutment teeth improves stability and force distribution, while a nearby implant generates leverage, especially when forces are applied diagonally, which could harm the supporting tissues and could increase the risk of bone resorption. The results obtained for the analyzed geometry in Kennedy Class I with RPD can be applied, with some limitations, to similar geometries with unilateral or bilateral free ends, both conventional and implant-assisted. However, it is essential to consider the mucosa and periodontal tissue to improve the accuracy of the model. We have, accordingly, revised the explanation of peak values of the bone distal region, emphasizing it from line 347-354, that now reads as follows: “The results of our study also emphasize the critical role of implant positioning in force distribution. Implants placed more distally to the abutment teeth improves stability and force distribution, while a nearby implant generates leverage, especially when forces are applied diagonally, which could harm the supporting tissues and could increase the risk of bone resorption. The results obtained for the analyzed geometry in Kennedy Class I with RPD can be applied, with some limitations, to similar geometries with unilateral or bilateral free ends, both conventional and implant-assisted. However, it is essential to consider the mucosa and periodontal tissue to improve the accuracy of the model”. The paragraph is highlighted in yellow color.

4. What mesh elements were used? Type, sizes, refinements if applicable.

We appreciate reviewer’s question. We added the following sentence in Line 129, that reads as follows: “Tetrahedral mesh generated numerically due to being a complex structure as the RPD, tooth, and bone were considered a unit”. The sentence is highlighted in yellow color.

 

5. Was a mesh convergence analysis performed?

We appreciate reviewer’s question. Yes, we performed mesh convergence analysis. Following reviewer’s valuable comment, additional information on this matter was added from Line 131-133, that now reads as follows: “A mesh convergence analysis was used to reduce the size of the tetrahedral elements in order to improve the accuracy of the analysis, achieving an ideal balance of all the elements generated by the software”. This paragraph is highlighted in yellow color.

6. “nonlinear FEA”: What was nonlinear in your FEA? Did the authors perform a contact simulation?

We appreciate reviewer’s question. Following reviewer’s valuable comment, we added further information from Line 127-131, and now reads as follows: “A 3D simulation was performed to analyze a complex structure. A full adhesion contact between the prosthesis and the hard and soft tissues was assumed in the general contact simulation. Tetrahedral mesh generated numerically due to being a complex structure, as the RPD, tooth, and bone were considered a unit”. The additional paragraph is highlighted in yellow color.

 

7. Details of the prostheses should be shown in a way that clarifies at what areas it is connected (in detail!) to the teeth and bone (mucosa was neglected if I get it right). This is important to understand the biomechanics.

We agree with reviewer’s notion. Further information was added from Line 108-113 that now reads as follows: “The mucosa was modeled with depreciable values to simulate an extreme scenario. A single geometry was generated where the prosthesis apparently makes contact with the mandibular bone. The digital design for the teeth and bone anatomy was created considering normal dental occlusion, as well as the anatomy of the roots and mandibular bone, assuming a single structure between removable partial denture, teeth and bone”. This additional information is highlighted in yellow color.

 

8. I recommend providing a table with all material parameters for clarity (currently only in the text).

We agree with reviewer’s suggestion. We clarified this idea further by adding “Table 1. Mechanical properties of materials” in Material and Methods, section 2.3 Finite elements analysis, from Line 135.

 

9. Figure 3: The legend is unreadable, fix it.

We totally agree with reviewer’s notion. We fixed the legend and the font size in all figures of the manuscript.

 

10. For bone I recommend to stick to the principal stresses. Von Mises is for ductile materials, although this not consistently used in the dental FEA community.

We appreciate reviewer’s important suggestion. Regarding this matter, we added additional information from Line 124-126 that now reads as follows: “Although the mandibular bone is a non-homogeneous, anisotropic, and non-ductile structure, for this study, the mandibular cortical bone was considered, as it is more homogeneous and isotropic”. The additional information is highlighted in yellow color.

 

11. Was a PDL modelled? If yes what material model and parameters were applied?

We appreciate reviewer’s question. The periodontal ligament (PDL) was not modeled due to its complexity and the time it would take to create the model. However, it is important to note that modeling the PDL with real biomechanical parameters could change both the distribution and intensity of the stresses. Thank you for pointing this out. Therefore, we have clarified this idea further from Line 325-329, that now reads as follows: “Also, the periodontal ligament (PDL) was not modeled due to its complexity and the time it would take to create the model. However, it is important to note that modeling the PDL with real biomechanical parameters could change both the distribution and intensity of the stresses”. The change is highlighted in yellow color.

 

12. What were the stresses in the prosthesis?

We appreciate reviewer’s question. In our study, the tension was not evaluated at the prosthesis level, only in the teeth and mandibular bone.

 

Thank you, again, for your criticism.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The study analyzed the stress distribution in the teeth and alveolar bone of a mandibular model considered Kennedy Class I (bilateral edentulous areas in the posterior region). The study compared the restoration with a bilateral implant-assisted removable partial denture and a conventional removable partial denture, using Finite Element Analysis to analyze the mechanical and structural behavior under different loading conditions.

Vertical, diagonal, and combined stresses were analyzed, including teeth from the lower left first premolar and lower right canine.    

The methodology is consistent with the hypothesis, well-presented, and detailed, facilitating the replication of the study. The results are interesting and could benefit from further discussion. I suggest that the authors address the clinical implications of the findings in the discussion section. 

I also suggest the authors strongly address the limitations of the study in the Conclusions, emphasizing the importance of clinical studies where statistical analyses can be conducted.          

Author Response

To Reviewer #2

 

The study analyzed the stress distribution in the teeth and alveolar bone of a mandibular model considered Kennedy Class I (bilateral edentulous areas in the posterior region). The study compared the restoration with a bilateral implant-assisted removable partial denture and a conventional removable partial denture, using Finite Element Analysis to analyze the mechanical and structural behavior under different loading conditions.
Vertical, diagonal, and combined stresses were analyzed, including teeth from the lower left first premolar and lower right canine.

 
The methodology is consistent with the hypothesis, well-presented, and detailed, facilitating the replication of the study. The results are interesting and could benefit from further discussion.

Thank you for your kind comments and suggestions. The points of improvement are as follows.

 

1. I suggest that the authors address the clinical implications of the findings in the discussion section. 

We appreciate the reviewer’s suggestion. From the clinical viewpoint, our predictive simulation model demonstrated that forces transmitted to the bone in a Kennedy Class I with removable partial dentures are more evenly distributed to the teeth and implants in an IARPD, reducing bone stress, and thus leading to the long-term success of IARPDs. Also, the increased load on the lower left central incisor found in our model due to the presence of a fulcrum may cause clinical implications that need to be assessed for individualized patient considerations and precautions. Please find these and other comments in sub-section “4.1 Clinical implications” from Line 331-354, which is highlighted in yellow color.

2. I also suggest the authors strongly address the limitations of the study in the Conclusions, emphasizing the importance of clinical studies where statistical analyses can be conducted.          

We appreciate the reviewer’s suggestion. We would like to keep the limitations at the end of the Discussion section in order to make the conclusion of our study easy to be understood for the reader. However, we reinforced the description of the limitations of our study (Line 320-329), and added an additional sentence regarding the importance of clinical studies, following reviewer’s important suggestion from Line 364 that now reads as follows: “Future research can follow up with users of implant-assisted prostheses designed based on the findings of our study, in order to evaluate clinical aspects and user perception”. The additional sentence is highlighted in yellow color.

Thank you again for your comments and suggestions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 This is a well-designed study where the authors assessed the stress distribution in a mandibular Kennedy Class I restored with a bilateral implant-assisted removable partial denture using Finite Element Analysis (FEA).

I have a few points that need clarification:

1.Can the authors clearly highlight the clinical relevance of this study? I recommend adding a heading titled Clinical Relevance and explicitly stating how these results may help in diagnosis and treatment planning.

2.The authors have acknowledged their limitations well. Some limitations of the study include the selection of the left lower first premolar and the right lower canine as posterior abutment teeth. Additionally, for the FEA analysis, the prostheses, as well as hard and soft tissues, were treated as isotropic, linear, and elastic materials. The study only considered static force application, using material mechanical property values from previous studies. It is important to acknowledge that FEA is useful for understanding biomechanical behavior and functions well in controlled settings. This is a good approach, as it may help readers identify areas to focus on for future research.

3.There are a few typos and punctuation errors. Please check the whole manuscript and address them.

4.Overall, the manuscript is well written, and I believe it meets the requirements for publication after minor revisions.

Author Response

To Reviewer #3

 

This is a well-designed study where the authors assessed the stress distribution in a mandibular Kennedy Class I restored with a bilateral implant-assisted removable partial denture using Finite Element Analysis (FEA).

 

Thank you for your kind comments and suggestions. The points of improvement are as follows.

 

1. Can the authors clearly highlight the clinical relevance of this study? I recommend adding a heading titled Clinical Relevance and explicitly stating how these results may help in diagnosis and treatment planning.

We understand the reviewer’s notion. Following reviewer’s valuable suggestion we added sub-section “4.1 Clinical implications” within the Discussion section. Please find the additional information explaining the clinical relevance of our study from Line 331-354, which is now highlighted in yellow color.

 

2. The authors have acknowledged their limitations well. Some limitations of the study include the selection of the left lower first premolar and the right lower canine as posterior abutment teeth. Additionally, for the FEA analysis, the prostheses, as well as hard and soft tissues, were treated as isotropic, linear, and elastic materials. The study only considered static force application, using material mechanical property values from previous studies. It is important to acknowledge that FEA is useful for understanding biomechanical behavior and functions well in controlled settings. This is a good approach, as it may help readers identify areas to focus on for future research.

We appreciate reviewer’s notion on the limitations of our study. We hope this study can lead to future clinical studies following up with users of implant-assisted prostheses designed based on the findings of our study.

 

3. There are a few typos and punctuation errors. Please check the whole manuscript and address them.

We agree with reviewer’s comment. The manuscript was thoroughly reviewed and typos and punctuation errors were corrected.

4. Overall, the manuscript is well written, and I believe it meets the requirements for publication after minor revisions.

We appreciate reviewer’s encouraging comments to our study. It is our hope that this work may contribute to the dental implant prosthodontic community.

 

Thank you again for your comments and suggestions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All my comments have been adressed, i have no further comments.