Mechanical Properties of Translucent Zirconia: An In Vitro Study

Round 1

Reviewer 1 Report

Present research is focused on translucent zirconia for dental implants. The mechanical properties are investigated and correlated with microstructural aspects. Therefore the manuscript fits the journal scope. Experimental setup is well established and most of the results are relevant. Unfortunately the manuscript is drafted in a sloppy manner and requires certain improvements and completions. These are presented in the comments below which are mandatory:

Comment 1) Figure 1 is useless for a scientific article intended for specialized readers. They already know how a Vickers indenter looks like and how to measure the indentation mark. So, Figure 1 must be removed.

Comment 2) Figure 2 is useless as it is presented. It must be reorganized as follows: Figure 2a must be removed; SEM images of indentation marks for groups A, B, and C must be presented. Do not forget about images scale bar, it is mandatory. The reorganized Figure 2 must be moved at Results subsection 3.2.

Comment 3) You affirm that SEM image in Figure 4 is for ,,Y-TZP Group” but which one of A, B, and C ? It is mandatory to present high magnification and resolution SEM images for all groups A, B, and C to observe their grains. The similitude or differences among them must be discussed (discussion section must be updated with the observed aspects). The graphical representation of grain size distribution is not proper. It is mandatory to present a proper grain size distribution histogram such as ,,Counts vs. Grain Diameter” or ,,Frequency vs. Grain Diameter” for each group A, B, and C.

Comment 4) Images presented in Figures 5 and 6 are good (they have a high quality) but are wrong presented. You must present in Figure 5 the most representative SEM images at low magnification for groups A, B, and C; and in Figure 6 the most representative SEM images at high magnification for groups A, B, and C.

Comment 5) References 12, 13, 24, 25, 33, 34, 35 and 36 are very old and must to be replaces with newest references published in 2019 – 2022.

Comment 6) Measuring unit ,, MPa√m” is wrong typed. It must be corrected as MPa/m

Comment 7) Line 130: You must explain the meaning of θ presented in equation (1).

Comment 8) Line 64: ,,zircon which is the synthetic diamond” it is totally erroneous affirmation. Synthetic diamond is made of carbon like natural diamond, by a complex industrial process which uses high purity graphite. Therefore, the expression must be corrected as ,,zircon which is the synthetic substitute for diamond”.

Comment 9) Equations are not numbered and are displayed as figures copied with ,,snap-shoot copy – paste” from a pdf source. Therefore, all equations must be numbered and edited with a professional formula editor such as Ms Word built in formula editor or Math Type.

Author Response

We sincerely thank all reviewers for the constructive evaluations made on our study. We apologize for the inaccuracies highlighted, which we have tried to remedy by providing exhaustive answers (we hope) and making changes both on the iconography and on the data reported. Many thanks also for the ideas provided to deepen and develop the topic.

Below are all the answers to the questions posed by the five reviewers.

REVIWER 1

Comments and Suggestions for Authors

Present research is focused on translucent zirconia for dental implants. The mechanical properties are investigated and correlated with microstructural aspects. Therefore the manuscript fits the journal scope. Experimental setup is well established and most of the results are relevant. Unfortunately the manuscript is drafted in a sloppy manner and requires certain improvements and completions. These are presented in the comments below which are mandatory:

R: Thank you very much for the comments

Comment 1) Figure 1 is useless for a scientific article intended for specialized readers. They already know how a Vickers indenter looks like and how to measure the indentation mark. So, Figure 1 must be removed.

R: Fig 1 was removed

Comment 2) Figure 2 is useless as it is presented. It must be reorganized as follows: Figure 2a must be removed; SEM images of indentation marks for groups A, B, and C must be presented. Do not forget about images scale bar, it is mandatory. The reorganized Figure 2 must be moved at Results subsection 3.2.

R: Fig 2 was adjusted following the indications and moved to the more appropriate section

Comment 3) You affirm that SEM image in Figure 4 is for ,,Y-TZP Group” but which one of A, B, and C ? It is mandatory to present high magnification and resolution SEM images for all groups A, B, and C to observe their grains. The similitude or differences among them must be discussed (discussion section must be updated with the observed aspects). The graphical representation of grain size distribution is not proper. It is mandatory to present a proper grain size distribution histogram such as ,,Counts vs. Grain Diameter” or ,,Frequency vs. Grain Diameter” for each group A, B, and C.

R: All the figures were reorganized and described better

Comment 4) Images presented in Figures 5 and 6 are good (they have a high quality) but are wrong presented. You must present in Figure 5 the most representative SEM images at low magnification for groups A, B, and C; and in Figure 6 the most representative SEM images at high magnification for groups A, B, and C.

R: All the figures were reorganized and described better

Comment 5) References 12, 13, 24, 25, 33, 34, 35 and 36 are very old and must to be replaces with newest references published in 2019 – 2022.

R: the references were not changed. It is opinion of the authors that doing so do not give more credit to the study, on the opposite, it would take away credit and respect to researchers who first introduced and discussed the issues. It is useless to cite recent works that for the same statements refer to the same authors.

Comment 6) Measuring unit ,, MPa√m” is wrong typed. It must be corrected as MPa/m 

R: The unit of measure is correct since it is MPa on root square of m and not simply on m. I changed into m^1/2

Comment 7) Line 130: You must explain the meaning of θ presented in equation (1).

R: explanation was reported

Comment 8) Line 64: ,,zircon which is the synthetic diamond” it is totally erroneous affirmation. Synthetic diamond is made of carbon like natural diamond, by a complex industrial process which uses high purity graphite. Therefore, the expression must be corrected as ,,zircon which is the synthetic substitute for diamond”.

R: The correction was made as indicated. Thank you.

Comment 9) Equations are not numbered and are displayed as figures copied with ,,snap-shoot copy – paste” from a pdf source. Therefore, all equations must be numbered and edited with a professional formula editor such as Ms Word built in formula editor or Math Type.

R: The correction was made as indicated. Thank you.

Reviewer 2 Report

Dear Authors,

thank you for the opportunity to discover your work. The topic is interesting for both the research domain and also for the clinical prosthodontics. A larger number of samples would have produced more valuable results, but this could be an idea to extend the study.

These are my suggestions: 

-        Lines 36,37: please rephrase adding a coma after chemically and it before is defined

-        Line 39: zirconium dioxide

-        Line 60: improvements

-        Line 82: please change at with to

-        Line 84-85: ..of high translucent zirconia may sound better

-        Line 89: please rephrase

-        Line 102 please rephrase

-        Line 202: grain size in mm?

-        Lines 205-206: please change Mpa with MPa

-        Line 227: please use capital letter

-        Line 267: please use the article for literature

-        Line 278: please use past tense

-        Line 295: please use the article: for the ceramic material

-        Line 299: ceramic veneer/component instead of veneering

-        Line 308: shows the lowest wear capacity

-        Line 310-311 please rephrase properly

-        Line 312: addressed to this topic / conducted / performed on this topic

-        Line 314: translucent instead of translucency 

Author Response

We sincerely thank all reviewers for the constructive evaluations made on our study. We apologize for the inaccuracies highlighted, which we have tried to remedy by providing exhaustive answers (we hope) and making changes both on the iconography and on the data reported. Many thanks also for the ideas provided to deepen and develop the topic.

Below are all the answers to the questions posed by the five reviewers.

REVIEWER 2

Comments and Suggestions for Authors

Dear Authors,

thank you for the opportunity to discover your work. The topic is interesting for both the research domain and also for the clinical prosthodontics. A larger number of samples would have produced more valuable results, but this could be an idea to extend the study.

R: Thank you very much for the comments

These are my suggestions: 

-        Lines 36,37: please rephrase adding a coma after chemically and it before is defined

R: The correction was made. Thank you.

-        Line 39: zirconium dioxide

R: The correction was made. Thank you.

-        Line 60: improvements

R: The correction was made. Thank you.

-        Line 82: please change at with to

R: The correction was made. Thank you.

-        Line 84-85: ..of high translucent zirconia may sound better

R: The correction was made. Thank you.

-        Line 89: please rephrase

R: The sentence was changed

-        Line 102 please rephrase

R: The sentence was changed

-        Line 202: grain size in mm? 

R: The correction was made. Thank you.

-        Lines 205-206: please change Mpa with MPa 

R: The correction was made. Thank you.

-        Line 227: please use capital letter

R: The correction was made. Thank you.

-        Line 267: please use the article for literature

R: The correction was made. Thank you.

-        Line 278: please use past tense

R: The correction was made. Thank you.

-        Line 295: please use the article: for the ceramic material

R: The correction was made. Thank you.

-        Line 299: ceramic veneer/component instead of veneering

R: The correction was made. Thank you.

-        Line 308: shows the lowest wear capacity

R: The correction was made. Thank you.

-        Line 310-311 please rephrase properly

R: The sentence was changed.

-        Line 312: addressed to this topic / conducted / performed on this topic

R: The correction was made. Thank you.

-        Line 314: translucent instead of translucency 

R: The correction was made. Thank you.

Reviewer 3 Report

1.  In the research design, experiments are conducted in three groups: transparent zirconia, traditional zirconia, and aged transparent zirconia. Isn’t it necessary to include aged traditional zirconia?

2. Grain size measurements were performed on transparent zirconia and the results are shown, but it seems necessary to perform measurements on the other two groups and compare them.

3. It seems necessary to compare the chemical properties of each group using XPS．

4. Isn't it also necessary to examine the crystal state by XRD in the same way?

5. In the discussion, wear with the opposing tooth is mentioned, but it was not evaluated in the experimental content. If it does, it should be incorporated into the study design.

6. It has been concluded that the mechanical properties of transparent zirconia are higher than loads in the oral cavity. Is there a discussion of loads in the oral cavity in the article?

7. Bridging of microcracks is mentioned in Result3.5, and the SEM image is shown in Figure.6. However, if we discuss the brittleness of each zirconia, it is necessary to compare the SEM images among groups A, B, and C.

8, If you are suggesting an in vitro study, you should investigate the stability and toxicity of tissue cells.

9. No comparison has been made with natural teeth in terms of wear resistance.  The comparison should be considered.

10. The figure of average particle size distribution only shows high permeability zirconia (experimental group), but have you compared the average particle size distribution of conventional zirconia? If so, it would be easier to compare with a similar figure.

11. In examining the microstructural properties, surface roughness (Ra) and crystal structure running pavilion (XRD) of high permeability zirconia should be considered.

12. It would be good to distinguish the difference between the two if we also consider the aged conventional zirconia.

Author Response

We sincerely thank all reviewers for the constructive evaluations made on our study. We apologize for the inaccuracies highlighted, which we have tried to remedy by providing exhaustive answers (we hope) and making changes both on the iconography and on the data reported. Many thanks also for the ideas provided to deepen and develop the topic.

Below are all the answers to the questions posed by the five reviewers.

REVIEWER 3

Comments and Suggestions for Authors

R: Thank you very much for the Suggestions

1. In the research design, experiments are conducted in three groups: transparent zirconia, traditional zirconia, and aged transparent zirconia. Isn’t it necessary to include aged traditional zirconia?

R: The aim of the study was to investigate the relatively new high translucent zirconia. The aging of traditional zirconia was already investigated and published by the author (Traini T et al Clin Oral Investig. 2014, 18, 707-14.). Is the opinion of the authors that this aspect is not of interest for the aim of the present study.

2. Grain size measurements were performed on transparent zirconia and the results are shown, but it seems necessary to perform measurements on the other two groups and compare them.

R: The data were reported to complete the comparison

3. It seems necessary to compare the chemical properties of each group using XPS．

R: The X-ray photoelectron spectroscopy (XPS) determines the elemental composition of a material’s surface, It is also applied to determine the chemical or electronic state of these elements. This aspect is not of interest for the topic of the study, that is related to the mechanical behavior of the anterior Prettau usually used for dental crowns and bridges without ceramic veneer.

4. Isn't it also necessary to examine the crystal state by XRD in the same way?

R: This aspect could be of interest (even if widely investigated in dental literature n=33) could be the aim of a further investigation.

5. In the discussion, wear with the opposing tooth is mentioned, but it was not evaluated in the experimental content. If it does, it should be incorporated into the study design.

R: This is another aspect that should be investigate in a separate study and for which many studies are present in dental literature n=63

6. It has been concluded that the mechanical properties of transparent zirconia are higher than loads in the oral cavity. Is there a discussion of loads in the oral cavity in the article?

R: We considered pleonastic this aspect since, it is an information widely known by the dentists.

7. Bridging of microcracks is mentioned in Result3.5, and the SEM image is shown in Figure.6. However, if we discuss the brittleness of each zirconia, it is necessary to compare the SEM images among groups A, B, and C.

R: All data were integrated and images for different groups were added

8, If you are suggesting an in vitro study, you should investigate the stability and toxicity of tissue cells.

R: The material is present on the market with CE mark since it is considered ( and demonstrated) safety for human use.

9. No comparison has been made with natural teeth in terms of wear resistance.  The comparison should be considered.

R: Is the opinion of the authors that this aspect is not appropriate in this study. Should be investigate in a separate study. Since, the all zirconia restorations are always glazed (harvested by glasure) or micro veneered with glass ceramic.

10. The figure of average particle size distribution only shows high permeability zirconia (experimental group), but have you compared the average particle size distribution of conventional zirconia? If so, it would be easier to compare with a similar figure.

R: All data were integrated and images for different groups were added

11. In examining the microstructural properties, surface roughness (Ra) and crystal structure running pavilion (XRD) of high permeability zirconia should be considered.

R: Should be investigate in a separate study.

12. It would be good to distinguish the difference between the two if we also consider the aged conventional zirconia.

R: The aging of traditional zirconia was already investigated and published by the author (Traini T et al Clin Oral Investig. 2014, 18, 707-14.).

Reviewer 4 Report

Reviewer’s Comments:

The manuscript “Investigations on the complex band diagram of flexural wave through the fluid-loaded phononic plate” is very interesting work. The study aim was to investigate the mechanical characteristics of a high-translucent zirconia used for monolithic restorations before and after aging process compared to a low-translucent zirconia. Methods: A total of 23 specimens were used in the present study. Group A (n=10) made of high translucency Y-TZP; Group B (n=7) made of low-translucency Y-TZP and finally the Group C (n=6) was aged high-translucency Y-TZP. Flexural strength, fracture toughness, brittleness, microcrack’s propagation and the grain size were analyzed. Results: The Vickers hardness was: 1483± 187 MPa (group C), 1102 ± 392 MPa (group A) and 1284±32 MPa (group B). The flexural strength was: 440 (96.2) MPa (group C) , 427(59.5) MPa (group A) and 805 (198.4) MPa (group B). However, the following issues should be carefully treated before publication.

1. In abstract, the author should add more scientific findings.

2. Keywords: the synthesized system is missing in the keywords. So, modify the keywords.

3. In the introduction part, the introduction part is not well organized and cited references should cite recently published articles.  

4. Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate the scientific issues in the flexural wave research.

5. Statistical analysis …, The author should provide reason about this statement “The data were analyzed with descriptive statistics (Kolmogorov-Smirnov test) to evaluate whether they had a normal distribution. An ANOVA test was performed. A p-value <0.05 was considered statistically significant”.

6. The authors should explain regarding the recent literature why “The Hv (mean ± SD) values for different groups were: 1102 ± 392 Mpa for group A, 1284±32 Mpa for groupB, and 1483± 187 for group C”.

7. Brittleness (Br). The author should explain the latest literature “The group A was the one with the values immediately below, although significantly superior to the group B”.

8. The author should provide reason about this statement, “Probably the LTD process appears to increase the brittleness of high translucency zirconia”.

9. Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.

10. The conclusion part is very week. Improve by adding the results of your studies.

Author Response

We sincerely thank all reviewers for the constructive evaluations made on our study. We apologize for the inaccuracies highlighted, which we have tried to remedy by providing exhaustive answers (we hope) and making changes both on the iconography and on the data reported. Many thanks also for the ideas provided to deepen and develop the topic.

Below are all the answers to the questions posed by the five reviewers.

REVIEWER 4

Comments and Suggestions for Authors

Reviewer’s Comments:

The manuscript “Investigations on the complex band diagram of flexural wave through the fluid-loaded phononic plate” is very interesting work. The study aim was to investigate the mechanical characteristics of a high-translucent zirconia used for monolithic restorations before and after aging process compared to a low-translucent zirconia. Methods: A total of 23 specimens were used in the present study. Group A (n=10) made of high translucency Y-TZP; Group B (n=7) made of low-translucency Y-TZP and finally the Group C (n=6) was aged high-translucency Y-TZP. Flexural strength, fracture toughness, brittleness, microcrack’s propagation and the grain size were analyzed. Results: The Vickers hardness was: 1483± 187 MPa (group C), 1102 ± 392 MPa (group A) and 1284±32 MPa (group B). The flexural strength was: 440 (96.2) MPa (group C) , 427(59.5) MPa (group A) and 805 (198.4) MPa (group B). However, the following issues should be carefully treated before publication.

R: Thank you very much for the comments

1. In abstract, the author should add more scientific findings. 

R: The abstract was little bit implemented following the limits imposed by the journal (maximum 200 words)

2. Keywords: the synthesized system is missing in the keywords. So, modify the keywords.

R: The suggested keyword was added.

3. In the introduction part, the introduction part is not well organized and cited references should cite recently published articles.

R: The introduction was revised according to the other 4 reviewer, it  was  little bit changed, but substantially conserved in order to introduce the topic to the clinicians readers

4. Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate the scientific issues in the flexural wave research. 

R: The introduction was revised according to the other 4 reviewer, it  was  little bit changed, but substantially conserved in order to introduce the topic to the clinicians readers

5. Statistical analysis …, The author should provide reason about this statement “The data were analyzed with descriptive statistics (Kolmogorov-Smirnov test) to evaluate whether they had a normal distribution. An ANOVA test was performed. A p-value <0.05 was considered statistically significant”.

R: The Kolmogorov-Smirnov test was used to evaluate, as reported, the normal distribution of the data since a parametric test was used, otherwise, a non-parametric test it would have been necessary.

6. The authors should explain regarding the recent literature why “The Hv (mean ± SD) values for different groups were: 1102 ± 392 Mpa for group A, 1284±32 Mpa for groupB, and 1483± 187 for group C”.

R:  the study was improved and much more data was included in order to explain better the results

7. Brittleness (Br).The author should explain the latest literature “The group A was the one with the values immediately below, although significantly superior to the group B”. 

R: the study was improved addressing also this topic

8. The author should provide reason about this statement, “Probably the LTD process appears to increase the brittleness of high translucency zirconia”.

R:  the topic was addressed introducing statements in the discussion section and images.

9. Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.

R: the discussion section was improved

10. The conclusion part is very week. Improve by adding the results of your studies.

 R: the conclusion was adjusted

Reviewer 5 Report

Dear authors,

the topic is original and relevant in the field. It does address a specific gap in the field especially because monolithic materials are gaining popularity.

The manuscript is well written and the research is well performed.

SEM images are really very nice.

Nevertheless, here are some suggestions to improve your manuscript.

Line 5-6:

There are 2 authors in the paper, but in the affiliation, there are five email addresses.

Please correct:

• Department of Innovative Technologies in Medicine & Dentistry, University “G. d’Annunzio” of Chieti- 5 Pescara, Chieti, 66100, Italy; [email protected] (F.V.); [email protected] (B.S.); oriania.trubi- 6 [email protected] (O.T.); [email protected] (S.C.)

Line 202:

The authors wrote about the grain size:

was 165 (+-15) mm.

Please correct from millimeters to nanometers.

Line 286:

Please correct: the SEM images ad high magnification 

Lines 298-9:

The authors should also outline that monolithic zirconia, rather than fractures or chipping, may have failures related to marginal adaptation after cyclic fatigue.

The authors could add a sentence/paragraph on this concept to include this type of failure analysis in the future, as several in-vitro papers/research have outlined different marginal gap progression depending on the type of material. The authors could cite, for example the following paper that compared translucent monolithic zirconia to lithium silicate showing higher external gap progression for zirconia:

Baldi A, Comba A, Ferrero G, Italia E, Michelotto Tempesta R, Paolone G, Mazzoni A, Breschi L, Scotti N. External gap progression after cyclic fatigue of adhesive overlays and crowns made with high translucency zirconia or lithium silicate. J Esthet Restor Dent. 2022 Apr;34(3):557-564. doi: 10.1111/jerd.12837. Epub 2021 Nov 16. PMID: 34783440; PMCID: PMC9298883.

Cyclic fatigue tests could be added in future studies.

Author Response

We sincerely thank all reviewers for the constructive evaluations made on our study. We apologize for the inaccuracies highlighted, which we have tried to remedy by providing exhaustive answers (we hope) and making changes both on the iconography and on the data reported. Many thanks also for the ideas provided to deepen and develop the topic.

Below are all the answers to the questions posed by the five reviewers.

REVIEWER 5

Dear authors,

the topic is original and relevant in the field. It does address a specific gap in the field especially because monolithic materials are gaining popularity.

The manuscript is well written and the research is well performed.

SEM images are really very nice.

Nevertheless, here are some suggestions to improve your manuscript.

R: Thank you very much for the comments

Line 5-6:

There are 2 authors in the paper, but in the affiliation, there are five email addresses.

Please correct:

• Department of Innovative Technologies in Medicine & Dentistry, University “G. d’Annunzio” of Chieti- 5 Pescara, Chieti, 66100, Italy; [email protected] (F.V.); [email protected] (B.S.); oriania.trubi- 6 [email protected] (O.T.); [email protected] (S.C.)

R: Correction was done. 

Line 202:

The authors wrote about the grain size:

was 165 (+-15) mm.

Please correct from millimeters to nanometers.

R: The correction was done

Line 286:

Please correct: the SEM images ad high magnification

R: Correction was done 

Lines 298-9:

The authors should also outline that monolithic zirconia, rather than fractures or chipping, may have failures related to marginal adaptation after cyclic fatigue.

The authors could add a sentence/paragraph on this concept to include this type of failure analysis in the future, as several in-vitro papers/research have outlined different marginal gap progression depending on the type of material. The authors could cite, for example the following paper that compared translucent monolithic zirconia to lithium silicate showing higher external gap progression for zirconia:

Baldi A, Comba A, Ferrero G, Italia E, Michelotto Tempesta R, Paolone G, Mazzoni A, Breschi L, Scotti N. External gap progression after cyclic fatigue of adhesive overlays and crowns made with high translucency zirconia or lithium silicate. J Esthet Restor Dent. 2022 Apr;34(3):557-564. doi: 10.1111/jerd.12837. Epub 2021 Nov 16. PMID: 34783440; PMCID: PMC9298883.

Cyclic fatigue tests could be added in future studies.

R: Thank you for suggesting me to deepen this aspect which, however, is not part of the objectives of this work that analyzes only the mechanical characteristics of the translucent zirconia, even after aging, compared to conventional zirconia. The marginal loss, in the opinion of the authors, is more related to the mechanical characteristics of the cement used rather than to the microstructural variations of the material.

Round 2

Reviewer 1 Report

Dear authors,

The manuscript was well improved according to the requests. SEM images are good, well presented and properly discussed. I observe that you give the grain size as the grain area expressed in μm², this is a common approach of images analysis soft and it is adequate for your manuscript. The particle size statistical analysis plot in Figure 3 is proper. However, there are some aspects that require your attention:

1) Fracture toughness measuring unit as you presented MPa/m^1/2 is still incorrect. Please look carefully at the math implied by your own explanation:

 MPa√m = MPa‧m^1/2 = MPa/m

Therefore you must choose one of two correct variants MPa‧m^1/2 or the other one MPa/m.

2) I respect your decision to keep older references 12, 13, 24, 25, 33, 34, 35 and 36 and agree your explanation regarding this decision. It is all right to keep them. But, another important problem occur: the percent of the newest article (2019 – 2022) cited is only 6.77 % so the current state of art of your manuscript is very poor and the novelty elements are not sustained by proper citations.

The readers expect to read a critical discussion of your obtained results compared with the other results obtained during 2019 – 2022. Comparing of yours results with the one obtained in 1929; 1930; 1981; 1989 and so forth gives to the reader the impression of obsolete and outdated research.

You must increase the newest articles citation number by adding proper references at the discussion. I give you some examples of newest articles that should be cited. Consider the following DOIs:

https://doi.org/10.3390/jcm11174982

https://doi.org/10.3390/polym14122325

https://doi.org/10.3390/jfb13040281

https://doi.org/10.3390/ma15207324

https://doi.org/10.3390/ma15103606

Author Response

REVIEWER 1 (ROUND 2)

R: thank you once again for your help

Comments and Suggestions for Authors

Dear authors,

The manuscript was well improved according to the requests. SEM images are good, well presented and properly discussed. I observe that you give the grain size as the grain area expressed in μm², this is a common approach of images analysis soft and it is adequate for your manuscript. The particle size statistical analysis plot in Figure 3 is proper. However, there are some aspects that require your attention:

1) Fracture toughness measuring unit as you presented MPa/m^1/2 is still incorrect. Please look carefully at the math implied by your own explanation:

 MPa√m = MPa‧m^1/2 = MPa/m

Therefore you must choose one of two correct variants MPa‧m^1/2 or the other one MPa/m.

R the correction was done

2) I respect your decision to keep older references 12, 13, 24, 25, 33, 34, 35 and 36 and agree your explanation regarding this decision. It is all right to keep them. But, another important problem occur: the percent of the newest article (2019 – 2022) cited is only 6.77 % so the current state of art of your manuscript is very poor and the novelty elements are not sustained by proper citations.

The readers expect to read a critical discussion of your obtained results compared with the other results obtained during 2019 – 2022. Comparing of yours results with the one obtained in 1929; 1930; 1981; 1989 and so forth gives to the reader the impression of obsolete and outdated research. 

You must increase the newest articles citation number by adding proper references at the discussion. I give you some examples of newest articles that should be cited. Consider the following DOIs:

https://doi.org/10.3390/jcm11174982

R: not considered appropriate for the present study   (in this study, to the opinion of the authors, there are some bias such as:

1 making bridges which has complex shape that can affect the crack initiation, instead to standardized bars could be useful to test some clinical aspects less to define mechanical properties of the material itself.

2 placing the bridges to be tested for a fracture load over a resin holder with some silicon to mimic the periodontal ligament (not described but visible clearly in the pictures )is inappropriate since the cell load of the testing machine, to determine the load of fracture, takes into the consideration also the displacements that belongs to the resin of the holder and the silicone. The data reported must be considered relatively true.

https://doi.org/10.3390/polym14122325

R: not considered appropriate for the present study   (Evaluating the Effect of Different Polymer and Composite Abutments on the Colour Accuracy of…)

https://doi.org/10.3390/jfb13040281

R: Reported

https://doi.org/10.3390/ma15207324

R: reported

https://doi.org/10.3390/ma15103606

R: not considered appropriate for the present study   (Surface Characteristics of High Translucent Multilayered Dental Zirconia Related to Aging)

the following studies were also reported:

1. Liu, C.; Eser, A.; Albrecht, T.; Stournari, V.; Felder, M.; Heintze, S.; Broeckmann, C. Strength characterization and lifetime prediction of dental ceramic materials. Mater. 2021, 37, 94–105.
2. Kongkiatkamon, S.; Peampring, C. Effect of speed sintering on low temperature degradation and biaxial flexural strength of 5y-tzp zirconia.Molecules 2022, 27, 5272.
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Reviewer 3 Report

This version is very good in current form.

Author Response

REVIWER3 (ROUND2)

Comments and Suggestions for Authors

This version is very good in current form.

R: thank you very much for your help