Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors state that “no study has been conducted in Germany using CBCT to investigate the prevalence of unfilled canals and their association with apical periodontitis.” This statement is inaccurate. The authors should review and cite Bürklein et al. (2020, Clinical Oral Investigations), which used CBCT to assess the quality of root canal fillings and the prevalence of apical radiolucencies in a German population.




Since the manuscript already describes the link between missed canals and treatment failure as “overwhelming,” the authors need to clarify what new information this study provides. In particular, how does the selected population or methodology differ from or improve on previous research.

A critical weakness of this retrospective cross sectional design is the missing temporal baseline.

Apical periodontitis needs time to develop after a treatment failure, while existing lesions also need some time to heal after succesfull therapy. How did the authors account for the time passed between the original endodontic treatment and the CBCT evaluation. Without this information, a radiolucency may represent a healing lesion rather then a failing one. Although the authors mention that causality cannot be claimed, even the association remains questionable for this and other reasons outlined bellow.




The authors report that MB1 canals were unfilled in 8% of the cases and distal canals in 9.3%. When a periapical lesion was noticed, how was it confirmed that the pathology was actually linked to the MB2 canal and not other unfilled canals.

The manuscript notes that CBCT may lead to over diagnosis of AP. How was this risk controlled during examiner calibration, especially in differenciating healing lesions from active one.

In the Results section, the predictive variable is reported as the MB2 of the second molar. This discrepancy should be corrected to maintain credibility.

The stated null hypothesis “adequate treatment of all canals results in apical health” is a clinical expectation not a statistical null and should be revised.

The text cites Estrela et al. (2008b), yet the reference list includes only one 2008 entry ( #39). Please clarify this citation or add the missing referrence.

The manuscript notes an inter observer agreement of 100%. While impressive, intra observer reliability should also be reported to confirm internal consistency.

The exclusion criteria are listed but the exact number of excluded scans is not presented. Please specify how many were removed to obtain the final sample.

Include the full version or developer information for Excel

Keywords: Consider revising the keywords to follow MeSH terminology.

Lack of sample size calculation and power analysis:

The study included 75 patients from a single practice but no power analysis or statistical justification is given to show if this sample size supports the conclusions or the reported odds ratio of 0.095.

Author Response

Please see also the attachment (pdf file)

 

Manuscript ID: diagnostics-4158369

Response to Reviewer 1 Comments

Dear Reviewer 1, thank you for your review and all the helpful comments. We will be happy to comply with your request and revise the manuscript according to your instructions and recommendations. Regarding your recommendations the manuscript was revised and changes within the file also include recommendations from other reviewers. All points raised during review round one could be addressed. Thank you again for your time and review.

Point 1: The authors state that “no study has been conducted in Germany using CBCT to investigate the prevalence of unfilled canals and their association with apical periodontitis.” This statement is inaccurate. The authors should review and cite Bürklein et al. (2020, Clinical Oral Investigations), which used CBCT to assess the quality of root canal fillings and the prevalence of apical radiolucencies in a German population.

Response 1:

We thank the reviewer for this important comment. We agree that the statement was inaccurate. The study by Bürklein et al. (2020) has now been reviewed and appropriately cited in the revised manuscript. The text has been modified to acknowledge previous CBCT-based investigations conducted in a German population assessing root canal treatment quality and apical radiolucencies. However, to our knowledge, no study has specifically focused on the prevalence of untreated MB2 canals and their direct association with apical periodontitis in maxillary first molars. The manuscript has been revised within the abstract and the introduction section following your recommendations. The recommended reference was included.

Abstract: Please see lines 14-19.

New text within the abstract:

Background/Objectives: The presence of untreated second mesio-buccal canals (MB2) in maxillary first molars is usually associated with endodontic treatment failure. Previous CBCT-based investigations have evaluated the quality of root canal fillings and the prevalence of apical lesions in endodontically treated teeth. However, evidence specifically addressing untreated MB2 canals and their association with apical periodontitis remains limited. Therefore, the aim of this cross-sectional study was to evaluate the prevalence of unfilled MB2 canals in endodontically treated maxillary first molars and their association with apical periodontitis.

Introduction section Please see lines 57-62 and following.

New text within the revised Introduction section:

Previous CBCT-based investigations conducted in German populations have evaluated the overall quality of root canal fillings and the prevalence of apical radiolucencies following endodontic treatment [12]. However, these studies did not specifically assess untreated MB2 canals or their dedicated association with apical periodontitis in max-illary first molars. Therefore, evidence focusing specifically on untreated MB2 canals and their clinical impact remains limited.

Following reference (number 12) and citation was added: Bürklein, S.; Schäfer, E.; Jöhren, H.P.; Donnermeyer, D. Quality of Root Canal Fillings and Prevalence of Apical Radiolucencies in a German Population: A CBCT Analysis. Clin Oral Investig 2020, 24, 1217–1227. doi:10.1007/s00784-019-02985-y.

Point 2: Since the manuscript already describes the link between missed canals and treatment failure as “overwhelming,” the authors need to clarify what new information this study provides. In particular, how does the selected population or methodology differ from or improve on previous research.

Response 2:

Thank you for this comment. We agree that the association between missed canals and endodontic treatment failure has been widely reported in the literature. However previous studies and meta-analyses have demonstrated a general association between missed canals and apical periodontitis, most investigations evaluated heterogeneous tooth groups or overall treatment quality rather than focusing on a single anatomically complex canal configuration. Moreover, CBCT-based data specifically analysing untreated MB2 canals in maxillary first molars within a German population are currently lacking. The manuscript has been revised accordingly to clarify this aspect.

Please see lines 79-83.

The revised and added text:

Contrary to previous studies evaluating overall endodontic treatment quality, the present study applies a canal specific and tooth specific CBCT approach to investigate unfilled MB2 canals in maxillary first molars within a German population, thereby providing clinically focused results on a key factor potentially influencing post treat-ment apical periodontitis.

Point 3: A critical weakness of this retrospective cross sectional design is the missing temporal baseline.

Response 3:

We agree that the retrospective cross-sectional design does not allow the establishment of a temporal baseline. This limitation is inherent to observational cross sectional CBCT studies, as pre-treatment or immediate post-treatment baseline scans are typically unavailable due to ethical considerations related to radiation exposure. We have addressed this limitation in the discussion section of the revised manuscript.

Please see discussion section. Lines 396-406.

The most important limitation of our cross-sectional study, apart from the sample size, is the type of study, in which the teeth were examined at a specific point in time and thus the information about the course of apical periodontitis is not precisely known, meaning that no cause-and-effect relationship can be established. Regarding the retro-spective cross-sectional design of the study, it was not possible to establish a temporal baseline. However, this limitation is inherent to observational cross sectional CBCT stud-ies, as pre-treatment or immediate post-treatment baseline scans are typically unavailable due to ethical considerations related to radiation exposure.

Point 4: Apical periodontitis needs time to develop after a treatment failure, while existing lesions also need some time to heal after successful therapy. How did the authors account for the time passed between the original endodontic treatment and the CBCT evaluation. Without this information, a radiolucency may represent a healing lesion rather then a failing one. Although the authors mention that causality cannot be claimed, even the association remains questionable for this and other reasons outlined bellow.

Response 4:

Reliable information regarding the exact timing of the original endodontic treatment was not consistently available for all included cases. Consequently, it was not possible to standardize or stratify the analysis according to the elapsed time between treatment and CBCT acquisition. From a technical and endodontic perspective, the absence of filling material in an existing MB2 canal indicates incomplete instrumentation and obturation of the root canal system and may therefore be interpreted as a marker of insufficient treatment quality. Accordingly, the observed association should be understood within the context of treatment adequacy rather than as direct evidence of treatment failure or disease progression. The discussion section was revised accordingly.

Please see lines 358-363.

Following text was added to the discussion section:

Furthermore, the absence of root filling material within an identifiable MB2 canal might indicate incomplete instrumentation, disinfection and obturation of the root canal system and may therefore be interpreted as a radiographic marker of insufficient treatment quality rather than definitive evidence of treatment failure. Accordingly, the observed relationship should be interpreted as an association between treatment adequacy and periapical status at the time of evaluation, without implying causality.

Point 5: The authors report that MB1 canals were unfilled in 8% of the cases and distal canals in 9.3%. When a periapical lesion was noticed, how was it confirmed that the pathology was actually linked to the MB2 canal and not other unfilled canals.

Response 5:

We thank the reviewer for this important comment. To avoid misinterpretation, the manuscript has been revised to clarify that the detected periapical lesions were evaluated in relation to the presence of untreated MB2 canals, without assuming that the pathology originated exclusively from the MB2 canal when additional untreated canals were present.

Please see lines 363-368.

Following text was added to the discussion section:

However, in multirooted teeth periapical radiolucencies cannot be definitively at-tributed to a single untreated canal based solely on cross-sectional CBCT assessment. Therefore, MB2 canals were considered the primary analytical variable of interest, and the observed findings describe an association between the presence of untreated MB2 canals and periapical status without implying that the MB2 canal alone represents the source of the lesion.

Point 6: The manuscript notes that CBCT may lead to over diagnosis of AP. How was this risk controlled during examiner calibration, especially in differenciating healing lesions from active one.

Response 6:

Because of the cross-sectional design of the present study, differentiation between healing and non-healing lesions was not possible, as no longitudinal follow-up examinations were available. All lesions identified in this study corresponded to Estrela class 2 or higher. Therefore, the recorded findings represented clearly detectable periapical radiolucencies.

An additional text was included to address this point.

Please see lines 180-182.

The included text:

Due to the cross-sectional nature of the study, differentiation between healing and ac-tive lesions was not feasible.

Point 7: In the Results section, the predictive variable is reported as the MB2 of the second molar. This discrepancy should be corrected to maintain credibility.

Response 7:

Thank you for this correction. We apologize for this mistake. We checked the entire manuscript. Corrections were made.

Please see lines 14, 19, 21, 61, 81, 151, 172, 226, 281 and 287.

Point 8: The stated null hypothesis “adequate treatment of all canals results in apical health” is a clinical expectation not a statistical null and should be revised.

Response 8:

Thank you for this helpful comment. The stated phrase has been revised accordingly.

Please see lines 111-113.

The revised statement: Accordingly, the null hypothesis stated that the filling status of the MB2 canal has no statistically significant association with the presence of apical periodontitis.

Point 9: The text cites Estrela et al. (2008b), yet the reference list includes only one 2008 entry ( #39). Please clarify this citation or add the missing referrence.

Response 9:

Thank you. We revised the citation accordingly.

Please see line 176.

Point 10: The manuscript notes an inter observer agreement of 100%. While impressive, intra observer reliability should also be reported to confirm internal consistency.

Response 10:

A randomly selected 20 CBCT scans was re-evaluated after a 4 weeks interval of the first evaluation under identical conditions, blinded to the initial assessments. Agreement between the first and second evaluations was analysed using Cohen’s kappa statistics. Excellent intra-observer agreement (Cohen’s κ ≈ 0.90), indicating a high level of consistency in repeated image interpretation. This information has now been added to the Materials and Methods and Results sections of the manuscript.

An additional text was included in the Materials and Methods section to address this point.

Please see lines 203-207.

Prior the first evaluation of CBCT cases, intra-observer reliability was assessed. A randomly selected subset of 20 CBCT scans were re-evaluated after a four weeks interval of the first evaluation under identical viewing conditions, with the examiner blinded to the initial assessments. Agreement between evaluations was calculated using Cohen’s kappa statistics.

An additional text was included in the Results section to address this point.

Please see lines 220-223.

3.1. Intra-Observer reliability

Regarding both calibrated examiners the evaluation showed an excellent in-tra-observer agreement (Cohen’s κ ≈ 0.90). Inter-observer agreement across all parameters reached 100%, eliminating the need for consensus discussion.

Point 11: The exclusion criteria are listed but the exact number of excluded scans is not presented. Please specify how many were removed to obtain the final sample.

Response 11:

Thank you for this important comment. The Sample number of the CBCT scans was 503, 428 were excluded. This information was added to the manuscript.

An additional text was included in the restructured Materials and Methods section to address this point.

Please see lines 160-163.

All CBCT scans available in practice between 2015 and 2023 were analysed regarding the inclusion and exclusion criteria. Therefore, a total of 503 CBCT scans were initially screened. After application of the exclusion criteria, 428 scans were excluded, resulting in the final study sample of 75 CBCT datasets from 75 patients  included in the analysis.

Point 12: Include the full version or developer information for Excel

Response 12:

Thank you. The corrected developer information has been added to the text in the manuscript.

Please see lines 193-194.

Following information was added: (Microsoft Corporation, Redmond, WA, USA)

Point 13: Keywords: Consider revising the keywords to follow MeSH terminology.

Response 13:

Thank you, the keywords have been revised.

Please see lines 38-40.

Following information was added:

Keywords: endodontics, molar, maxilla, second mesio-buccal canal, root canal therapy, periapical periodontitis, cross-sectional studies, dental pulp cavity, spiral cone-beam computed tomography, treatment outcome

Point 14: Lack of sample size calculation and power analysis: The study included 75 patients from a single practice but no power analysis or statistical justification is given to show if this sample size supports the conclusions or the reported odds ratio of 0.095.

Response 14:

As this study was designed as a retrospective observational investigation based on available CBCT datasets, an a priori sample size calculation was not possible. Therefore, a post-hoc power analysis was performed based on the observed association between MB2 filling status and apical periodontitis.

Based on the effect size obtained from the contingency table analysis (chi-square test), the statistical power exceeded the commonly accepted threshold of 80%, indicating that the sample size was sufficient to detect the observed association. This information has been added to the Statistical Analysis section of the manuscript.

An additional text was included in the Materials and Methods section to address this point.

Please see 2.3 Statistical analysis: lines 195-200.

Regarding the study design, this study based on retrospectively available CBCT datasets. Therefore, an a priori sample size calculation was not possible. However, a post-hoc power analysis was conducted based on the observed effect size of the association between MB2 filling status and apical periodontitis. The calculated statistical power exceeded 80%, indicating that the used sample size of 75 CBCT scans was sufficient to detect the observed association.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

  

 

1. The manuscript is well written. The introductory part should be reduced/rewrite. Some limitations should be included.
2. Lines 62-72 are more suitable for the discussion part, they present the results of studies  and are not relevant for  an introductory part.
3. If the main objective was to evaluate the MB2 presence and treatment, why would you consider to evaluate the other canals? Is there a relevance or correlation between those and MB2?
4. Line 68 ” A dentist's lack of knowledge about the root canal system and the complexity of the root canal system, especially in second upper molars, can lead to canals being overlooked during root canal treatment” is this an evidence based information, if yes, please include citation. If not, please explain how did you conclude it.
5. Line 142: The beginning of the sentence is repeated.
6. Regarding methodology, the voxel size stated in line 145 is less than 150 μm, in the table the voxel size was less than 125. Which one is correct?
7. The parameter evaluating the presence or absence of filling in the roots has 2 options. What happens with the partially filled root canals?
8. I would recommend to present data in fig 1 and 2 differently, the images are way to big for the relevance of the information.
9. There is no information about the treatment method applied (what was the disinfection protocol for the canals, what material was used for filling)? These is one of the limitations of the study.

Author Response

Manuscript ID: diagnostics-4158369

Response to Reviewer 2 Comments

Dear Reviewer 2, thank you for your review and all the helpful comments. We will be happy to comply with your request and revise the manuscript according to your instructions and recommendations.

 

Point 1: The manuscript is well written. The introductory part should be reduced/rewrite. Some limitations should be included.

Response 1:

Thank you for the appreciation of our work and the positive comments. We will be happy to comply with your request and revise the manuscript according to your instructions and recommendations. Regarding your recommendations the introduction section was revised and reduced if possible. Changes within the introduction section also include recommendations from other reviewers. Furthermore, we have expanded the limitations in the discussion section.

Please see the changes within the introduction section. Thank you.

Point 2: Lines 62-72 are more suitable for the discussion part.  They present the results of studies and are not relevant for an introductory part.

Response 2:

Thank you for this recommendation. This is right. Therefore, we removed the lines from introduction and integrated them in the discussion section. The citations were adjusted.

Please see lines 324-339.

Moved and adjusted text within the discussion section:

The root canal system exhibits considerable anatomical variation, which poses challenges not only for canal detection but also for adequate cleaning and obturation [50]. Apical periodontitis was observed in 98% of teeth with untreated or insufficiently treated canals, which was shown to be of significantly higher frequency compared to teeth with all canals completely treated [8] . In a recent CBCT-based study from Chile, 70% of maxillary molars with apical periodontitis had missed MB2 canals, demonstrating a statistically significant association (p<0.0001) [51]. A dentist's lack of clinical experience regarding the anatomy and complexity of the root canal system, especially in first upper molars, can lead to canals being overlooked during root canal treatment [52]. These canals serve as a pool for microorganisms, which are the main cause of the development or persistence of apical periodontitis [53] and can have a negative impact on the prognosis [54,55]. Several studies have already impressive-ly demonstrated a connection between root-filled teeth and apical periodontitis [21,42,48]. A recent Saudi Arabian CBCT study reported that apical periodontitis was highly associated with missed canals, with an overall prevalence of 90% among teeth with missed canals, reaching 100% in mandibular teeth [56].

Point 3: If the main objective was to evaluate the MB2 presence and treatment, why would you consider to evaluate the other canals? Is there a relevance or correlation between those and MB2?

Response 3:

Thank you for this important point. Additional canals served as reference parameters in the context to describe general treatment completeness and to avoid misinterpretation of MB2 findings and apical lesions in multirooted teeth. No direct causal relationship or correlation between MB2 canals and the other canals was assumed. Therefore, this interpretation was added in the methods section and as well in the discussion section.

Following section was added to the Materials and Methods section. Please see lines 169-171.

“Although the primary variable of interest was the MB2 canal, the remaining canals were also evaluated to provide a comprehensive assessment of treatment completeness within multirooted teeth and to allow contextual interpretation of MB2-related findings.”

Following correction was added to the Discussion section. Please see lines 351-353.

“The assessment of additional canals was intended to characterize overall treatment status rather than to establish a direct relationship between these canals and MB2 findings.”

Point 4: Line 68 ” A dentist's lack of knowledge about the root canal system and the complexity of the root canal system, especially in second upper molars, can lead to canals being overlooked during root canal treatment” is this an evidence based information, if yes, please include citation. If not, please explain how did you conclude it.

Response 4:

The statement has been revised to reflect evidence-based information by replacing “lack of knowledge” with “lack of clinical experience,” and an appropriate supporting reference (Reference XX) has been added.

Please see improved text in the discussion section: lines 330-337.

This new reference (number 52) was added: Farrash, H.S.; Alsofi, L.; Balto, K. Impact of Visual Magnification on MB2 Canal Detection in a Laboratory-Based Study Using Standardized 3D-Printed Maxillary Molars. Appl. Sci. 2026, 16, 493. https://doi.org/10.3390/app16010493

Point 5: Line 142: The beginning of the sentence is repeated.

Response 5:

Thank you, this is right and was a mistake. We have removed the repetition.

Please see the revised section.

Point 6: Regarding methodology, the voxel size stated in line 145 is less than 150 μm, in the table the voxel size was less than 125. Which one is correct?

Response 6:

Thank you. Sorry for this mistake, it should be 150 in the table and in the text. We revised the table.

Please see the correction within table 1.

Point 7: The parameter evaluating the presence or absence of filling in the roots has 2 options. What happens with the partially filled root canals?

Response 7:

The partially filled canals were excluded from the study to avoid detectional misinterpretation. This statement will be added to the extrusion criteria.

Following sentence was added. Please see line 153-155.

“Furthermore, scans with partially filled canals or overfilled canals were excluded from the study.”

Point 8: I would recommend to present data in fig 1 and 2 differently, the images are way to big for the relevance of the information.

Response 8:

Thank you for this helpful advice. This is completely right. We decided to remove Figure 1 and 2 and clarified the text. Legends and numbering was adjusted.

Please see Results section of the revised manuscript.

Point 9: There is no information about the treatment method applied (what was the disinfection protocol for the canals, what material was used for filling)? These is one of the limitations of the study.

Response 9:

This point is right. Thank you. According to the nature of this cross sectional retrospective cbct study, informations about the treatment methodology and clinical procedures were unavailable. We added this to the limitations in the discussion section.

Please see lines 403-406.

The existing sentence was corrected and further clinical considerations were added.

“In addition, many factors can influence the treatment outcome, including applied techniques, used materials and instruments, the asepsis, the used disinfection protocol, the obturation protocol used,  the preoperative status of the tooth and the expertise of the clinicians [53].”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

the author has addressed my comments. no additional comment

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript was modified according to the recommendations.  It can be published in the present form.