Assessment of Peri-Implant Bone Density Using Intraoral Periapical Radiographs: A Retrospective Observational Clinical Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors, your manuscript explores a significant and clinically relevant topic: utilising radiographic assessment of peri-implant bone density (PIBD) as a non-invasive method to evaluate osseointegration. It leverages a large retrospective dataset, adheres to a standardised radiographic protocol, and employs transparent statistical methods.

The abstract is well-organised and effectively outlines the study's goals, methods, main results, and conclusions. It appropriately summarises the sample size, analytical approach, and key findings. The identification of three radiographic healing phases is notably emphasised. Suggestions: Briefly include the clinical implications of PIBD assessment, such as monitoring osseointegration or guiding follow-up decisions. Minor stylistic edits could enhance conciseness, but no major revisions are necessary.

The introduction offers a comprehensive overview of osseointegration, bone remodelling, and radiographic assessment, effectively combining biological and clinical perspectives with accurate references. It clearly explains why PIBD evaluation via periapical radiographs is appropriate. To improve, the research gap should be more explicitly articulated near the end of the introduction. Additionally, briefly differentiating this study from CBCT-based or histological approaches could highlight its practical clinical relevance.

Materials and Methods. Study Design and Ethics

The retrospective observational design is suitable and well-defined. Ethical approval and informed consent are properly recorded. Suggestion: Clearly mention the potential selection bias resulting from including only successful implants, either here or in the limitations section.

Radiographic standardisation, equipment specifications, and ROI definitions are outlined in sufficient detail to guarantee reproducibility. Utilising ImageJ and fixed digital masks enhances methodological consistency. Specify whether ROI placement was carried out by a single calibrated examiner or multiple operators, and if intra- or inter-examiner reliability was evaluated. Additionally, briefly explain the clinical significance of grouping the ROIS into the ROI5 variable within this section.

Outcome Measures (PIBD and MBL). Normalising PIBD to the area of maximum radiopacity (ROI_8) is methodologically appropriate and clearly justified. MBL measurement procedures are well described and calibrated. To enhance clarity, include a brief explanation of how PIBD variability might influence potential clinical interpretation, even in retrospective analyses.

The statistical approach is solid and suitable. Implementing Shapiro–Wilk testing followed by non-parametric methods makes sense. Post-hoc corrections are properly used. You might consider adding effect sizes or a brief note on the statistical power limitations for smaller ROI or time subgroups.

Results are clearly presented, systematically organised, and effectively supported by tables and figures. The temporal PIBD pattern is convincingly illustrated, and MBL data are reported transparently. The absence of a correlation between PIBD and MBL is explicitly stated and supported by statistical analysis. When highlighting statistically significant differences, briefly mention their clinical importance or lack thereof. Some later time intervals have smaller sample sizes; noting this limitation in the Results section could enhance transparency.

The discussion is comprehensive and well-balanced. The authors correctly interpret PIBD changes as part of physiological remodelling rather than indicating pathological bone loss. Their comparison with previous animal and clinical studies is relevant and properly referenced. Additionally, a clearly distinguish between physiological and pathological bone changes, providing a logical explanation for the decrease and subsequent increase in PIBD. The discussion thoughtfully addresses the lack of correlation between PIBD and MBL. To improve, reduce some repetitive explanations of the remodelling phases and briefly suggest how PIBD monitoring could be integrated into routine clinical decisions, such as timing of loading or follow-up schedules.

Limitations are appropriately acknowledged, including retrospective design, two-dimensional imaging, and lack of control over confounders. You should explicitly mention that excluding failed implants limits predictive conclusions regarding PIBD and implant failure. The issue of small subgroup sizes for certain ROIs could be emphasised more clearly.

The conclusions accurately represent the findings without exaggeration. The identification of three radiographic healing phases is convincingly supported. The importance of low-dose radiographic monitoring is well highlighted. To enhance clarity, eliminate slight repetition of phrases from the Discussion, and include a brief concluding sentence about future clinical applications to strengthen the section.

The reference list is thorough, up-to-date, and relevant, citing important classical and modern studies appropriately. Citation formatting aligns consistently with MDPI guidelines.

Overall, the paper is well-organised, clearly articulated, and methodologically solid. Its results contribute to the current literature by supporting the concept of various radiographic healing stages post-implantation and pointing out the weak link between PIBD and marginal bone level (MBL). With minor clarifications and some methodological enhancements, the manuscript would be ready for publication.

Author Response

Dear Reviewers,

we greatly appreciate the time and effort you devoted to reviewing our manuscript and to helping improve its quality. We hope that this revised version adequately addresses your comments and suggestions. To facilitate the evaluation of the changes made, we have provided a PDF version of the manuscript in which all modifications are clearly highlighted. Please note that the line numbers referred to in our responses correspond to this PDF file.

 

Thank you again for your valuable work.

Kind regards,

 

The Authors

 

 

REVIEWER 1

 

Dear authors, your manuscript explores a significant and clinically relevant topic: utilising radiographic assessment of peri-implant bone density (PIBD) as a non-invasive method to evaluate osseointegration. It leverages a large retrospective dataset, adheres to a standardised radiographic protocol, and employs transparent statistical methods.

The abstract is well-organised and effectively outlines the study's goals, methods, main results, and conclusions. It appropriately summarises the sample size, analytical approach, and key findings. The identification of three radiographic healing phases is notably emphasised. Suggestions: Briefly include the clinical implications of PIBD assessment, such as monitoring osseointegration or guiding follow-up decisions. Minor stylistic edits could enhance conciseness, but no major revisions are necessary.

 

Reply: We would like to warmly thank you for the positive and constructive feedback on the clinical relevance and clarity of Abstract. In line with your suggestion, we have revised the manuscript by adding a brief statement on the potential clinical implications of peri-implant radiographic bone density (PIBD) assessment (lines 35-38). We also added minor stylistic edits to improve conciseness. (lines 30-31).

 

The introduction offers a comprehensive overview of osseointegration, bone remodelling, and radiographic assessment, effectively combining biological and clinical perspectives with accurate references. It clearly explains why PIBD evaluation via periapical radiographs is appropriate. To improve, the research gap should be more explicitly articulated near the end of the introduction. Additionally, briefly differentiating this study from CBCT-based or histological approaches could highlight its practical clinical relevance.

 

Reply: We appreciate your insightful suggestion. We have revised the final part of Introduction to more explicitly articulate the research gap. In addition, we briefly differentiated our approach from histological and CBCT-based assessments, highlighting why these are not suitable for follow-up in daily clinical practice (lines 76-89).

 

Materials and Methods. Study Design and Ethics

The retrospective observational design is suitable and well-defined. Ethical approval and informed consent are properly recorded. Suggestion: Clearly mention the potential selection bias resulting from including only successful implants, either here or in the limitations section.

 

Reply: We acknowledged this important point, so we clearly mentioned the potential selection bias resulting from including only successful implants (lines 311-314).  

 

Radiographic standardisation, equipment specifications, and ROI definitions are outlined in sufficient detail to guarantee reproducibility. Utilising ImageJ and fixed digital masks enhances methodological consistency. Specify whether ROI placement was carried out by a single calibrated examiner or multiple operators, and if intra- or inter-examiner reliability was evaluated. Additionally, briefly explain the clinical significance of grouping the ROIS into the ROI5 variable within this section.

 

Reply: In line with the reviewer’s comment, we added that the AOIs placement was carried out by a single examiner (line 136).  Intra or inter-examiner reliability were not evaluated. We also explained the clinical significance of grouping the AOIs into the ROI5 variable (line 153).

 

Outcome Measures (PIBD and MBL). Normalising PIBD to the area of maximum radiopacity (ROI_8) is methodologically appropriate and clearly justified. MBL measurement procedures are well described and calibrated. To enhance clarity, include a brief explanation of how PIBD variability might influence potential clinical interpretation, even in retrospective analyses.

 

Reply: We appreciated the reviewer’s valuable suggestion; therefore we clarified how PIBD variability might influence potential clinical interpretation (lines 159-161).

 

The statistical approach is solid and suitable. Implementing Shapiro–Wilk testing followed by non-parametric methods makes sense. Post-hoc corrections are properly used. You might consider adding effect sizes or a brief note on the statistical power limitations for smaller ROI or time subgroups.

 

Reply: Thank you for this comment. We have added a sentence in the Discussion section acknowledging potential power limitations and suggesting that effect size analysis could be addressed in future prospective studies. (lines 310-311)

 

Results are clearly presented, systematically organised, and effectively supported by tables and figures. The temporal PIBD pattern is convincingly illustrated, and MBL data are reported transparently. The absence of a correlation between PIBD and MBL is explicitly stated and supported by statistical analysis. When highlighting statistically significant differences, briefly mention their clinical importance or lack thereof. Some later time intervals have smaller sample sizes; noting this limitation in the Results section could enhance transparency.

 

Reply: Thank you for this comment. The text has been modified according to the reviewer’s requests. (lines 258-259 and 211-212)

 

The discussion is comprehensive and well-balanced. The authors correctly interpret PIBD changes as part of physiological remodelling rather than indicating pathological bone loss. Their comparison with previous animal and clinical studies is relevant and properly referenced. Additionally, a clearly distinguish between physiological and pathological bone changes, providing a logical explanation for the decrease and subsequent increase in PIBD. The discussion thoughtfully addresses the lack of correlation between PIBD and MBL. To improve, reduce some repetitive explanations of the remodelling phases and briefly suggest how PIBD monitoring could be integrated into routine clinical decisions, such as timing of loading or follow-up schedules.

 

Reply: We appreciate your supportive and valuable comments. Following your suggestions, the Discussion has been streamlined by reducing repetitive descriptions (lines 240-243), and a brief explanatory sentence has been added in order to clarify how PIBD changes may be considered in routine clinical decision-making (lines 236-240).

 

Limitations are appropriately acknowledged, including retrospective design, two-dimensional imaging, and lack of control over confounders. You should explicitly mention that excluding failed implants limits predictive conclusions regarding PIBD and implant failure. The issue of small subgroup sizes for certain ROIs could be emphasised more clearly.

 

Reply: Thank you for this point. As suggested, an explicit statement has been added to the limitations section to clarify that excluding failed implants limits predictive conclusions regarding PIBD and implant failure (lines 311-314). Furthermore, the limitations section has been revised to clarify that some ROI5 subgroups included a limited number of observations, which may affect the interpretation of the results (lines 307-311).

 

The conclusions accurately represent the findings without exaggeration. The identification of three radiographic healing phases is convincingly supported. The importance of low-dose radiographic monitoring is well highlighted. To enhance clarity, eliminate slight repetition of phrases from the Discussion, and include a brief concluding sentence about future clinical applications to strengthen the section.

 

Reply: Thank you for noting this point. The conclusion section has been revised to reduce minor repetition (lines 340-344) and to include a brief statement highlighting potential future clinical applications (lines 349-351).   Finally, we would like to thank the reviewer for the careful evaluation and valuable suggestions. We are confident that the revisions made have enhanced the quality and readability of the manuscript.

 

The reference list is thorough, up-to-date, and relevant, citing important classical and modern studies appropriately. Citation formatting aligns consistently with MDPI guidelines.

 

Overall, the paper is well-organised, clearly articulated, and methodologically solid. Its results contribute to the current literature by supporting the concept of various radiographic healing stages post-implantation and pointing out the weak link between PIBD and marginal bone level (MBL). With minor clarifications and some methodological enhancements, the manuscript would be ready for publication.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study focuses on peri-implant radiographic bone density (PIBD) as an indicator of osseointegration in patients who have undergone successful implant-prosthetic rehabilitation. Normalized bone density values were computed for predefined regions of interest (ROIs), and changes in Marginal Bone Level (MBL) were also evaluated. Employing a retrospective design, this study analyzed 88 implants in 64 patients (198 radiographs; 1,299 measurements). The grouping was clearly defined, the application of statistical methods was generally standardized, and the data presentation was relatively comprehensive. The observed temporal pattern confirms three radiographic healing phases following implant placement. Nevertheless, this article exhibits several limitations that require targeted refinement

 

This study focuses on peri-implant radiographic bone density (PIBD) as an indicator of osseointegration in patients who have undergone successful implant-prosthetic rehabilitation. Normalized bone density values were computed for predefined regions of interest (ROIs), and changes in Marginal Bone Level (MBL) were also evaluated. Employing a retrospective design, this study analyzed 88 implants in 64 patients (198 radiographs; 1,299 measurements). The grouping was clearly defined, the application of statistical methods was generally standardized, and the data presentation was relatively comprehensive. The observed temporal pattern confirms three radiographic healing phases following implant placement. Nevertheless, this article exhibits several limitations that require targeted refinement, which are specified as follows:

1. References 21and 23 pertain to the same article. Furthermore, the citation of reference 30 appears to be somewhat contrived. It is recommended that a thorough revision and verification of the references and the article's content be conducted to emphasize the novelty and practicality of the article.
2. Prior to commencing the project design, it is imperative to carry out comprehensive literature searches. For instance, refer to the research article by Chen's team in 2023 with the DOI: 10.1186/s12903-023-03014-x, the research article by Nurcan Yurtoglu's team in 2025 with the DOI: 10.3390/jcm14113820, and the research article by Itt Assoratgoon's team in 2025 with the DOI: 10.1016/j.prosdent.2025.01.015. These recent papers encompass the author's research content and employ advanced research techniques. It is advised that the author conduct an in - depth search in the discussion section and elucidate the innovation of this study.
3. In the "Materials and Methods" section, the sentence "one during follow-up, regardless of the time interval between acquisitions." does not align with the subsequent experimental content and result descriptions. Table 3. Study time intervals, T0/T1/T2/T3/T4/T5. The description in "Materials and Methods" should be precise.
4. The maximum follow - up period T5 in this study is 2 years. In the context of observing bone resorption around the implants, a 2 - year follow - up period is evidently inadequate. It is recommended that the follow - up period be extended to 5 years. Alternatively, in the discussion section of the paper, the reasons for selecting a 2 - year follow - up period should be comprehensively described.
5. Table 2 - Definition of Regions of Interest (ROI). ROI_8 represents the area with the maximum density. What is the basis for this selection? In the discussion section of the paper, it is essential to provide a comprehensive explanation and cite the most recent literature to support it, thereby enhancing the article's persuasiveness.
6. In the Discussion section, "(iii) Some implants may have been placed early after tooth extraction, before complete socket healing." Early implant placement after tooth extraction and immediate implant placement are not conventional procedures. There will be significant differences in bone resorption after 2 years. This part should be fully explained and classified in the Inclusion criteria, and statistical and analytical classifications should be conducted to increase the objectivity and authenticity of the article's data analysis.
7. It is recommended to provide detailed explanations and classifications for the implants in different areas, and conduct classification statistics and analysis to enhance the objectivity and authenticity of the data analysis in the article.

8，Reference 12: Hasan, I. et al. carried out a similar study in 2015. Reference 26: Dias, D.R. et al. also carried out a similar study in 2016. Reference 27: Eskandarloo, A. et al. also carried out a similar study in 2019. After the citation, please emphasize the innovation and practicality of the design of this paper through comparison and contrast with these studies.

It is recommended that the author meticulously address each of the aforementioned issues individually. Following these revisions and enhancements, the article may be considered for publication.  

Comments on the Quality of English Language

average

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

See in the attached file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors, I appreciate your careful effort in responding to the main concerns from the previous review. The revised manuscript demonstrates clear progress in methodological clarity, clinical context, and discussion of limitations. Notably, clearer AOI placement, an improved Introduction, and a broader Discussion significantly boost the scientific rigor and readability. Overall, the revision has improved the manuscript, with only a few minor editorial adjustments still recommended.

The abstract has been revised to highlight the clinical importance of PIBD monitoring and its influence on postoperative choices. It now uses AOIs instead of ROIs, and the explanation of temporal patterns is clearer.

I recommend slightly simplifying the Methods section for improved readability, and some minor stylistic adjustments could make the text more concise.

The Introduction has been notably enhanced, clearly outlining the research gap regarding longitudinal PIBD assessment using standardised periapical radiographs and its relationship with MBL. The clinical rationale for low-dose imaging is explained more clearly. The strengths encompass a clear biological and clinical background, a direct acknowledgement of the limitations of CBCT and histology, and a strengthened statement of aims.

I suggest adding a sentence that highlights what makes this study unique compared to earlier research.

The study design is explicitly detailed, with the inclusion of implant characteristics (surface, diameter, protocol) serving as a noteworthy enhancement. Ethical approval and patient consent are appropriately documented.

Radiographic Protocol and AOI Definition. This subsection has been notably enhanced. Explicitly stating that a single examiner placed all AOIs improves methodological transparency. The detailed description of image alignment and standardisation makes the process clear and reproducible. Key strengths involve well-defined AOIs, a standardised acquisition protocol, and consistent examiner reporting.

I recommend considering whether intra-examiner reliability was evaluated, even retrospectively.

The explanation of the normalisation process and the MBL measurement method is clear. Furthermore, the clinical interpretation of PIBD variability has been more effectively contextualized.

The statistical methods remain appropriate and thoroughly documented. The authors correctly employ non-parametric tests along with post hoc corrections. The recognition of diminished robustness at subsequent time points constitutes a valuable contribution.

 It is recommended to include a brief discussion on effect size considerations within the main text, as presently it is confined solely to the limitations section.

The results are clearly organized and align with the methodology. Tables and figures are effectively integrated. The authors appropriately report the decreasing sample sizes at later intervals and their implications for interpretation. The strengths include transparent reporting, good correspondence between text and tables, and a clear presentation of temporal trends.

 

The Discussion has been significantly enhanced. The authors now better incorporate clinical implications, methodological limitations, and comparisons with recent studies. The explanation of PIBD and MBL as complementary indicators is clear. The strengths include balanced interpretation, enhanced clinical context, updated references, and a clear clarification of the absence of correlation between PIBD and MBL.

The Limitations section is now thorough and transparent. The authors openly address selection bias, AOI representativeness, normalisation constraints, limited follow-up, and lack of stratification. Their strengths include an honest recognition of weaknesses, methodological self-criticism, and a forward-looking outlook.

The Conclusions are consistent with the results and help prevent overinterpretation. The revised version more clearly emphasises the study's descriptive and confirmatory features and its potential for personalised follow-up.

The Reference list has been expanded and updated, incorporating recent relevant studies appropriately. Citation formatting now aligns with MDPI standards.

Overall, you have thoroughly responded to the reviewers’ comments, greatly improving the clarity, transparency of methods, and clinical significance of the manuscript. The updated version presents a clearly organised and scientifically solid contribution to implant dentistry. With just a few minor editorial tweaks, it is ready for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf