Fixture Length and Primary Stability: An In Vitro Study on Polyurethane Foam

Round 1

Reviewer 1 Report

The manuscript describes a study that compared the primary stability of short and long implants with multi-scale surface roughness on polyurethane blocks that mimic bone.

The topic is not novel and the scope is rather limited. A quick search has found at least 4 other publications by the same authors on the same topic, using exactly the same limited methods (torch and resonance frequency), to study the influences of macro geometry, diameter and length (current manuscript) on the same single parameter of primary stability. Each study is rather small and lacks comprehensiveness. This kind of publishing practice dilutes the novelty, significance and impact of the science, renders it incremental at best, with no apparent advantage, except for boosting the authors’ publishing record.

This current manuscript lacks explanation of key terminologies, like “multi-scale surface roughness” and so on. The key for validating the series of studies, why polyrethane foam can “mimic” bone structure, has not been explained up to before Discussion. And the simple statement of “…have been measured Misch’s bone D3 and D2, respectively.” Does not suffice. The name of the student’s t-test was even written wrong, and without the defined threshold value.

The manuscript was not well-prepared: besides the low level of English usage, with many grammatical errors, nearly in every sentence, figure captions do not correspond well with the content of the figures, and 2 figures of the same content of 2 charts were unprofessionally presented with diverse styles. Abstract Background section does not introduce any background. The Discussion was short and in one long paragraph lacks logic and is hard to follow. The Conclusion is weak and not convincing.

Extensive English editing is necessary, and the manuscript needs to be rewritten not only to improve the presentation, interpretation but also the scientific content and soundness.

Overall, the manuscript lacks scientific robustness and rigorousness and more so justification of claims, as a stand-alone manuscript. Thus this reviewer do not recommend further consideration in Applied Sciences.

Some suggestions:

L18 “Background” is missing. The content of “Background” should be under “Aim or Objectives”

“The aim of this study was to compare the primary stability of shorts vs. longs implants with a multi-scale surface roughness on polyurethane blocks mimicking bone.” Needs to be rewritten.

L21 “between” should be paired with and, rather than “or”

L22 what is the geometry of the implants?

L27 should use significantly; the 2 “that” should be replaced with which; what are D2 and D3 bone density?

L30 Both “multi-scale surface roughness” and “multiscale roughness surface” have been used. The terminology does not appear to be consistent.

L100 How was “a multi-scale roughness in 4 different portions,” realized? And by who? What are the scales? Which length range does each scale cover? This terminology must be explained in details before it can be used.

L103, Fig. caption does not correspond well with the fig.

Author Response

REV 1

• The manuscript describes a study that compared the primary stability of short and long implants with multi-scale surface roughness on polyurethane blocks that mimic bone.

The topic is not novel and the scope is rather limited. A quick search has found at least 4 other publications by the same authors on the same topic, using exactly the same limited methods (torch and resonance frequency), to study the influences of macro geometry, diameter and length (current manuscript) on the same single parameter of primary stability. Each study is rather small and lacks comprehensiveness. This kind of publishing practice dilutes the novelty, significance and impact of the science, renders it incremental at best, with no apparent advantage, except for boosting the authors’ publishing record.

AUTHOR’S ANSWER: Dear reviewer we are very sorry that you are not interested on this topic. As you have written, we are very expert about the use of polyurethan foam as a bone substitute that permit to evaluate in an objective way the fixture ‘features that influence on the primary stability. As you know the in vitro studies permit to evaluate the effects of single parameters, contrarily to what happen on clinical and pre-clinical studies, where the effects of parameters are evaluated all together.

As you also said our previous works were characterized by similar methods, but the effects of other parameters were evaluated. We tried to meet all your suggestions and we hope that you could reconsider your opinion

• This current manuscript lacks explanation of key terminologies, like “multi-scale surface roughness” and so on.

AUTHOR’S ANSWER: Dear Reviewer, thank you very much for your comment. Additional information about the implant surfaces of the tested implant have been added, together with the definition of multiscale roughness:

“Is has been shown that the process of double-etching treatment on titanium surfaces (DAE) is able to confer to the samples a multiscale roughness: that is the presence of a concomitant nano- and micro-topografy [16]. Moreover, novel post-processing techniques of the titanium implant, permit production fixtures with a surface treatment that is locally differentiated. Moreover these implants were characterized by a surface treatment locally-differentiated:  a different surface micro-roughness (Ra) characterize the distinct portions of the fixture[24]. So, with the advent of these novel implant surfaces, does still make the difference in increasing the primary stability of the fixtures?

“The cervical portion was characterized by a smooth machined surface and a nano-rough surface with Ra < 1 µ. The rest of the body of the fixture was characterized by a dual acid-etched (DAE) surface, in which the median  had a mean Ra: 3/7 µ, and the apical portion by a mean Ra: 8/12 µ”.

Tumedei M, Petrini M, Cipollina A, Di Carmine M, Piattelli A, Cucurullo A, et al. Comparative Evaluation of Primary Stability between Different Diameters Multi-Scale Roughness Dental Implant by Solid Rigid Polyurethane Simulation. Osteol 2021, Vol 1, Pages 62-72

• The key for validating the series of studies, why polyrethane foam can “mimic” bone structure, has not been explained up to before Discussion. And the simple statement of “…have been measured Misch’s bone D3 and D2, respectively.” Does not suffice.

AUTHOR’S ANSWER: Dear Reviewer, thank you very much for your comment. The following sentence has been added to the text:

In order to evaluate the impact of the length of dental implants on the primary stability, the measurements of short vs. long implants on RFA, ITV and RTV have been measured on polyurethane blocks of 20 and 30 PCF, that mimic the bone density of the Misch’s classes D3 and D2, respectively of 0.32 g/cm³ and 0.48 g/cm³ [12,14,25]. Moreover, also the compressive strength range (MPa) of the 20 and 30 PCF polyurethane block are very similar to the cortical bone strength that ranged between 130-200 MPa, while lower values are reported for the trabecular bone that range between 0.1 and 16 MPa.

“The use of polyurethan foam as a bone substitute for perform orthopedic tests has been validated since 2001 by the ASTM F1839-01 Standard Specification. Since then, many studies have been published on this materials, especially in orthopedics. As shown by Calvert et al. the use of polyurethane as a bone substitute for in vitro studies, permit the use of a material characterized by similar mechanical properties to trabecular bone, like the stress-strain curve, but at the same time the availability of a material that is always the same from lot to lot. In this way is possible the repeatability of the tests, without the risk of bias, is connected with the use of a substrate that changes properties from one sample to another, like natural bone”.

1. ASTM F1839-01 Standard Specification for Rigid Polyurethane Foam for Use as a Standard Material for Testing Orthopaedic Devices and Instruments. Pennsylvania: American Society for Testing and Materials. 2001
2. Patel, P.S., Shepherd, D.E. & Hukins, D.W. Compressive properties of commercially available polyurethane foams as mechanical models for osteoporotic human cancellous bone. BMC Musculoskelet Disord9, 137 (2008). https://doi.org/10.1186/1471-2474-9-137
3. Calvert KL, Trumble KP, Webster TJ, Kirkpatrick LA. Characterization of commercial rigid polyurethane foams used as bone analogs for implant testing. J Mater Sci Mater Med. 2010 May;21(5):1453-61. doi: 10.1007/s10856-010-4024-6. Epub 2010 Feb 17. PMID: 20162325.
4. Palissery V, Taylor M, Browne M. Fatigue characterization of a polymer foam to use as a cancellous bone analog material in the assessment of orthopaedic devices. J Mater Sci: Mater Med. 2004;15:61–7. doi:10.1023/B:JMSM.0000010098.65572.3b.

• The name of the student’s t-test was even written wrong, and without the defined threshold value.

AUTHOR’S ANSWER: thank you very much for your comment.

We have changed “T-test of student test “ with T Test (Student's T-Test). The threshold was set at p = 0.05.

The manuscript was not well-prepared: besides the low level of English usage, with many grammatical errors, nearly in every sentence, figure captions do not correspond well with the content of the figures, and 2 figures of the same content of 2 charts were unprofessionally presented with diverse styles. Abstract Background section does not introduce any background. The Discussion was short and in one long paragraph lacks logic and is hard to follow. The Conclusion is weak and not convincing.

Extensive English editing is necessary, and the manuscript needs to be rewritten not only to improve the presentation, interpretation but also the scientific content and soundness.

Overall, the manuscript lacks scientific robustness and rigorousness and more so justification of claims, as a stand-alone manuscript. Thus this reviewer do not recommend further consideration in Applied Sciences.

AUTHOR’S ANSWER: thank you very much for your comments. The discussion and the abstract have been improved, following your suggestions, the English has been revised and the figure legends have been corrected.

Some suggestions:

L18 “Background” is missing. The content of “Background” should be under “Aim or Objectives”

AUTHOR’S ANSWER: thank you very much for your comments. The following sentence has been added to the abstract:

“Recently, novel dental implants, characterized by different surface roughness, in the distinct parts of the fixture’s body, have been introduced in the market. These surface characteristics could affect the primary stability of the implants”.

“The aim of this study was to compare the primary stability of shorts vs. longs implants with a multi-scale surface roughness on polyurethane blocks mimicking bone.” Needs to be rewritten.

AUTHOR’S ANSWER: thank you very much for your comments. The sentence has been rewritten:

“The aim of this in vitro study was to compare the primary stability of short and long implants, characterized by multi-scale surface roughness, inserted on polyurethane blocks”.

L21 “between” should be paired with and, rather than “or”

AUTHOR’S ANSWER: thank you very much for your comments. The sentence has been rewritten:

“The secondary aim was to understand if the implant length could be a crucial factor in the decision making in immediate or rather than delayed loading protocol, in the different bone densities".

L22 what is the geometry of the implants?

AUTHOR’S ANSWER: thank you very much for your comments. The term “cylindric” has been inserted in the abstract. In the materials and methods, it was already specified.

L27 should use significantly; the 2 “that” should be replaced with which; what are D2 and D3 bone density?

AUTHOR’S ANSWER: thank you very much for your comments. The sentence has been modified as suggested: “Long implant showed a significantly higher primary stability on 30 PCF blocks, that for mechanical properties mimics the high-density bone. On the contrary, no clinically relevant differences were found on 20 PCF blocks, which mimics trabecular bone density".

L30 Both “multi-scale surface roughness” and “multiscale roughness surface” have been used. The terminology does not appear to be consistent.

AUTHOR’S ANSWER: thank you very much for your comments. The term “multiscale roughness surface” has been substituted by “multi-scale surface roughness” through the whole manuscript.

L100 How was “a multi-scale roughness in 4 different portions,” realized? And by who? What are the scales? Which length range does each scale cover? This terminology must be explained in details before it can be used.

AUTHOR’S ANSWER: thank you very much for your comments. The multi-scale roughness and the surface characterized by a locally differentiated roughness are produced directly by the Manufacturer, Resista (Omegna, Italy). The process that permit the production of this surface is a double-etching treatment. The scale of the roughness are comprised between (Ra) of 28.957 (nano-roughness measured at Atomic force microscopy) and 8/12 µ.

L103, Fig. caption does not correspond well with the fig.

AUTHOR’S ANSWER: thank you very much for your comment. Fig. 1 and the relative caption, have been removed, accordingly to REV. 2 suggestions.

Reviewer 2 Report

The authors in their manuscript entitled “Fixture length and primary stability: an in vitro study on polyrethane foam”  compare the primary stability of shorts vs. longs implants with DAE surfaces on polyurethane blocks of different densities, mimicking D2 and D3 bone. Further their  secondary objective was to understand what is the implant length that permit to 
achieve the higher primary stability with different bone densities. In my opinion this is an interesting paper but some minor revisions are needed before its publication.

ntroduction

• the last part  needs to be improved to make the purpose of the work clearer.

Materials and Methods need to be better detailed

Statistical analysis

• I suggest to use ANOVA test for multiple comparison

Figures:

• Figure 1a can be removed, it is not necessary

• The image quality where possible should be improved.

Author Response

The authors in their manuscript entitled “Fixture length and primary stability: an in vitro study on polyrethane foam”  compare the primary stability of shorts vs. longs implants with DAE surfaces on polyurethane blocks of different densities, mimicking D2 and D3 bone. Further their  secondary objective was to understand what is the implant length that permit to 
achieve the higher primary stability with different bone densities. In my opinion this is an interesting paper but some minor revisions are needed before its publication.

Introduction

• the last part  needs to be improved to make the purpose of the work clearer.

Materials and Methods need to be better detailed

Statistical analysis

• I suggest to use ANOVA test for multiple comparison

AUTHOR’S ANSWER: thank you very much for your comment. Here we always had 2 groups:

-Long vs. short implants in 20 PCF

-Long vs. short implants in 30 PCF

-Long implants in 20 PCF vs. 30 PCF

-Short implants in 20 PCF vs. 30 PCF

 For this reason we cannot perform the requested Test.

Figures:

• Figure 1a can be removed, it is not necessary

• AUTHOR’S ANSWER: thank you very much for your comment. Fig. 1 has been removed, accordingly to your suggestion.

• The image quality where possible should be improved.

AUTHORS ANSWER: Thank you very much for your comment, but the included pictures are the original photographs, so we are not able to further increase the image quality.

Reviewer 3 Report

Dear Authors,

The present study has been conducted in vitro to assess Fixture length and primary stability in polyurethane blocks. Kindly address the few concerns

Abstract: 1. In the result section, since it’s an in vitro study, kindly refrain from using the term clinically.

2. The conclusion should be rephrased considering it an in-vitro study. How it can be concluded that fixture length has an impact on bone density when it was an in-vitro study? Rather it should be mentioned in terms of polyurethane block mimicking respective bone density.
3. keywords: Delete the unnecessary sentence in the keyword section

Introduction:

1. “On the contrary, a fibrous tissue of reparation is produced, affecting the implant stability”: cite the reference.
2. Line 46, 47: kindly elaborate on the range of minimum torque values in different bone densities to achieve primary stability. The authors can refer 2147/CCIDE.S174895 , 10.1097/ID.0000000000000479
3. The authors have not mentioned any relationship of fixture length with the systemic diseases. It is suggested to incorporate in the introduction the factors which affect the primary stability and eventually the implant failure. Diabetic patients with high HBA1C levels can have an impact on implant failures. The authors can refer 3390/ijerph17145253

4. “So, in the case we want to plan an implant surgery with immediate loading, which implant length, short or standard, we should prefer in order to obtain the higher primary stability? With the advent of novel implant surfaces, like multi-scale rough double etched treatment (DAE) the use of long implants, does still make the difference in increasing the primary stability of the fixtures?”: I would suggest the authors write/rephrase these sentences in a more scientific manner

Results:

1. Figure 4 : Kindly Keep the same abbreviation though out the text “PCF or pcf ”

Discussion:

1. From Line 224, it should be written as a new paragraph as the authors are discussing another aspect of the study.
2. The authors are suggested to discuss and compare more about the Double etched implant with multi-surface roughness in terms of primary stability.
3. The authors are suggested to discuss the probable impact of short length implants in the natural bone and regenerated bone.
4. The authors can add future directions.

Conclusion: kindly rephrase the sentence by omitting word “clinical” as it’s an in-vitro study.

Regards

Author Response

Dear Authors,

The present study has been conducted in vitro to assess Fixture length and primary stability in polyurethane blocks. Kindly address the few concerns

Abstract: 1. In the result section, since it’s an in vitro study, kindly refrain from using the term clinically.

AUTHOR’S ANSWER: Thank you very much for your suggestion, we have removed clinical terms from this section.

1. The conclusion should be rephrased considering it an in-vitro study. How it can be concluded that fixture length has an impact on bone density when it was an in-vitro study? Rather it should be mentioned in terms of polyurethane block mimicking respective bone density.

AUTHOR’S ANSWER: Thank you very much for your suggestion, the sentences have been corrected in :

“Results: The values of ITV, RTV, and RFA, showed the same trend in all measurements. Long implants showed a significantly higher primary stability on 30 PCF blocks, that present mechanical properties similar to high-density bone. On the contrary, no relevant differences were found on 20 PCF blocks, which mimics trabecular bone density.

(4) Conclusions: The impact of fixture length on primary stability of implants with multi-scale surface roughness, is significant in higher polyurethane densities, but not in lower ones.”

1. keywords: Delete the unnecessary sentence in the keyword section

AUTHOR’S ANSWER: Thank you very much for your suggestion, we have deleted the unnecessary sentence in the keyword section

Introduction:

1. “On the contrary, a fibrous tissue of reparation is produced, affecting the implant stability”: cite the reference.

AUTHOR’S ANSWER: Thank you very much for your suggestion, the following reference has been added:

Wazen RM, Currey JA, Guo H, Brunski JB, Helms JA, Nanci A. Micromotion-induced strain fields influence early stages of repair at bone-implant interfaces. Acta Biomater. 2013 May;9(5):6663-74. doi: 10.1016/j.actbio.2013.01.014. Epub 2013 Jan 19. PMID: 23337705; PMCID: PMC3622828.

1. Line 46, 47: kindly elaborate on the range of minimum torque values in different bone densities to achieve primary stability. The authors can refer 2147/CCIDE.S174895 , 10.1097/ID.0000000000000479

AUTHOR’S ANSWER: Thank you very much for your suggestion, the following reference has been added:

In particular, literature suggests that for ILP, the achievement of Insertion torque value (ITV) > 32 Ncm are necessary, in order to avoid early failures. However, with the advent of novel implant surfaces, this value can further be reduced.

Aldahlawi S, Demeter A, Irinakis T. The effect of implant placement torque on crestal bone remodeling after 1 year of loading. Clin Cosmet Investig Dent. 2018 Oct 9;10:203-209. doi: 10.2147/CCIDE.S174895. PMID: 30349398; PMCID: PMC6183656.

Sierra-Rebolledo A, Allais-Leon M, Maurette-OʼBrien P, Gay-Escoda C. Primary Apical Stability of Tapered Implants Through Reduction of Final Drilling Dimensions in Different Bone Density Models: A Biomechanical Study. Implant Dent. 2016 Dec;25(6):775-782. doi: 10.1097/ID.0000000000000479. PMID: 27540846.

1. The authors have not mentioned any relationship of fixture length with the systemic diseases. It is suggested to incorporate in the introduction the factors which affect the primary stability and eventually the implant failure. Diabetic patients with high HBA1C levels can have an impact on implant failures. The authors can refer 3390/ijerph17145253

 AUTHOR’S ANSWER: Thank you very much for your suggestion, the following reference has been added:

“Also a good glycemic control is fundamental to reduce implants failures in the first stages of healing".

1. “So, in the case we want to plan an implant surgery with immediate loading, which implant length, short or standard, we should prefer in order to obtain the higher primary stability? With the advent of novel implant surfaces, like multi-scale rough double etched treatment (DAE) the use of long implants, does still make the difference in increasing the primary stability of the fixtures?”: I would suggest the authors write/rephrase these sentences in a more scientific manner

AUTHOR’S ANSWER: Thank you very much for your suggestion , the following sentence has been added to the manuscript:

“Our hypothesis is that with the advent of multi-scale roughness surfaces, like the DAE ones, the parameter of length could have a minor influence on primary stability, respect machined implants. If this hypothesis would be confirmed, it could be possible to proceed with an immediate loading protocol (ILP), also in the case of reduced bone height, without the necessity of regenerative procedures.”

Results:

1. Figure 4 : Kindly Keep the same abbreviation though out the text “PCF or pcf ”

AUTHOR’S ANSWER: Thank you very much for your suggestion. We have corrected the mistake in the figures

Discussion:

1. From Line 224, it should be written as a new paragraph as the authors are discussing another aspect of the study.

AUTHOR’S ANSWER: Thank you very much for your suggestion. I have corrected it.

1. The authors are suggested to discuss and compare more about the Double etched implant with multi-surface roughness in terms of primary stability.

AUTHOR’S ANSWER: Thank you very much for your suggestion, these implants are Double etched.

1. The authors are suggested to discuss the probable impact of short length implants in the natural bone and regenerated bone.

AUTHOR’S ANSWER: Thank you very much for your suggestion , the following sentence has been added to the manuscript:

“Our hypothesis is that with the advent of multi-scale roughness surfaces, like the DAE ones, the parameter of length could have a minor influence on primary stability, respect machined implants. If this hypothesis would be confirmed, it could be possible to proceed with an immediate loading protocol (ILP), also in the case of reduced bone height, without the necessity of regenerative procedures”.

1. The authors can add future directions.

AUTHOR’S ANSWER: Thank you very much for your suggestion , the following sentence has been added to the manuscript:

“Future directions of this study are the comparison between this in vitro model and preclinical and clinical results”.

Conclusion: kindly rephrase the sentence by omitting word “clinical” as it’s an in-vitro study.

Regards

Reviewer 4 Report

The article represents an interesting approach on: Fixture length and primary stability: an in vitro study on polyrethane foam. 

The aim of this study comparing 2 lengths is interesting on polyurethane blocks mimicking bone. 

The methodology is clear, the only aspects is that conclusions are limited to some minor aspects. 

This study is interesting to be compared in future with clinical studies. 

Author Response

REV 4

The article represents an interesting approach on: Fixture length and primary stability: an in vitro study on polyrethane foam. 

The aim of this study comparing 2 lengths is interesting on polyurethane blocks mimicking bone. 

The methodology is clear, the only aspects is that conclusions are limited to some minor aspects. 

This study is interesting to be compared in future with clinical studies. 

AUTHOR’S ANSWER: Thank you very much for your appreciation of our work.

Round 2

Reviewer 3 Report

Dear Authors,

The authors have done the modifications in the manuscript . However ,the abstract need modification/ explanation as mentioned below

1. Abstract :

Kindly remove the numbering for IMRD.

2. Conclusion can be modified as : “The impact of fixture length on primary stability of implants with multi-scale sur face roughness, is significant in higher polyurethane densities corresponding to ...............bone density , but not in lower ones.

Regards

Author Response

Please see file attached.

Author Response File: Author Response.pdf