Comments on abstract, title, references

Regarding the title, I would add "in-vitro study" to make it more informative. The abstract has false information that needs to be corrected. for example it stated that the posts were cemented with self-adhesive resin cement, but in the materials and methods section the authors stated that metal posts were cemented with glass ionomer cement. Moreover, the authors need to specify the type, shape and manufacturer of the FRC posts used in your study. The results in the abstract should state the statistical significance that the authors reported in the results section and the p-values. The conclusion should also mention any differences between the anterior and posterior regions as per the aim of the study. The entire abstract requires language editing. I would suggest adding key studies to the references mainly those utilizing multi-post techniques, and also those about how the ferrule effect contribute to fracture resistance. The citation style should be consistent when writing the authors names. In the reference list, a few included the first initial of the author’s name, others listed first and middle initial and some included more.

Comments on introduction/background

The research question is clearly outlined. However, it is not clear in the background what we already know about that specific topic. The only 2 studies mentioned in the literature review that utilized the multiple posts technique were not discussed properly (reference number 8 and 9). The authors need to elaborate on them and may be add more studies to justify your research question. A good starting point to find more relevant studies to your research topic would be looking at a systematic review by Silva et al in 2021 by the title " The influence of customization of fiber posts on fracture strength and failure pattern: a systematic review and meta-analysis of ex-vivo studies". Also, since the ferrule effect is the most important factor to enhance the fracture resistance of ETT, I would add the key studies and guidelines established in the literature.

The literature review show many statements that lack a reference. I suggest that you add the missing references, or if they were your own words then they should be in the discussion section.

Kindly proof read the entire section for proper citation, grammar mistakes and typographical errors.

Comments on methodology

Regarding the sample collection, the authors did not mention the storage conditions of the extracted teeth. Any dehydration can affect their fracture resistance. Sample size is relatively small.

The sample preparation was the same whether the tooth was to receive a custom-made cast post or a FRC ready made post using only gates glidden and peaso reamer drills. Drills up to size 5 was used with no regards to the remaining radicular dentin thickness. The post drills corresponding to the FRC post size and shape were not used and the FRC post was not chosen to closely fit the corresponding canal, consequently increasing the cement layer thickness. Unlike the custom-made posts that were fabricated to perfectly fit the corresponding canal.

furthermore, how was the tooth preparation for the metal coping standardized? and how was the thickness of the remaining radicular dentin standardized?

Also, since the ferrule height and width are the most important factors to resist fracture of ETT treated with posts and cores, the ferrule width that remained after the tooth preparation and the post space preparation needs to be taken into account.

The type and shape of the FRC post used in the study must be specified along with the manufacturer. Same applies for the adhesive resin cement used in the cementation of the FRC posts and the type of composite used for the core build-up. Also, the specific dimensions of the full-veneer metal copings was not stated.

Regarding the testing, the authors need to mention the name and model of the testing machine used, along with the ISO-standard number used for the fracture toughness testing. Mode of failure should be recorded, as well as the location of the fracture.

Comments on data and results

Up to my knowledge, the results are well presented. I am not familiar with Kruskal-Wallis analysis, and will need an experts opinion.

Moreover, adding the mode of failure would be valuable from a clinical standpoint. For example, whether the tooth fractured, or the post fractured, or both. Location of the fracture and whether it was catastrophic in nature.

Comments on discussion and conclusions

The first sentence of the discussion states that the most common failure of endodontically treated teeth restored with posts is fracture of the post and the restored tooth. However, according to the literature, the most common failure is post loosening followed by root fracture. Please review Dr. Goodacre’s and Baba’s research in this area. I believe that the first paragraph of the discussion section belongs in the introduction section, since it states the aim of the study along with relevant literature review.

In the second paragraph there is unnecessary repetition of the results section, and 2 of the numbers stated are switched in the text. The following discussion in this paragraph needs to be more concise. The authors are advised to omit statements that are irrelevant to the research. With regards to the assumption that the higher fracture resistance of multiple FRC posts in comparison to the single FRC post was attributed to the luting cement holding multiple posts together therefore adding to the flexibility of the post is confusing. The reason is that the samples of the single FRC posts were not prepared in the standard manner that is done in clinic, in terms of intimacy of fit of the post to the canal, therefore, the amount of cement thickness is unknown. The authors stated that the single post group showed the least fracture resistance, what if the teeth with thinner dentin thickness were the ones restored with single posts?

Other issues that could have affected the stress delivery to the samples is the metal coping fabricated, it should have been standardized and fabricated to simulate a crown. The FRC posts shape was not mentioned, parallel vs tapered-sided, they would have an affect on the results since the parallel-sided post requires removal of additional radicular dentin than tapered-sided posts. Results of the study could have been affected greatly with the fact that the exact amount of remaining radicular dentin was not taken into account.

The static load to failure represents the worst-case scenario that could happen. Adding the mode of failure and weather the fracture location was catastrophic deeming the tooth non-restorable is a valuable point that was addressed in previous research. Including this in your study and looking at how would placing multiple posts affect the restorability after tooth fracture would add good clinical insights.

Recommendations to the authors for future research is to try a larger sample size, examine the roots of the teeth for curvatures and depressions to avoid thinning of radicular dentin, try to simulate the oral conditions; for example, cyclic loading would be more representative, thermocycling of the samples would have a degrading effect on the cement layer and would make the results more realistic.