The Antimicrobial Effect of the Incorporation of Inorganic Substances into Heat-Cured Denture Base Resins—A Systematic Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The aim of this study is to provide readers with a overview of the current state of the antimicrobial effects of inorganic antimicrobial substances on heat-cured denture base resins. The influence of the concentration and element of antimicrobial agents on different microorganisms were summarized and discussed. The topic is interesting and will be useful for interested parties. The writing is good and I am enjoy reading it. While the topic fits within the scope of the journal, I only have a few minor comments. Please consider revising the manuscript based on the following comments:

1. Line 199, Figure 1(b): I suggest to add the name and unit of y axis in the figure, not just describe in figure caption.

2. In the discussion section, Authors mentioned most of the tests were done by CFU, and there exists some inconsistent results among different studies. Authors could add a bit discussing that different testing methods may influence the results, for example, CFU only measures live microorganisms, while SEM, RT-PCR measures both live and dead microorganisms.

3. Line 348: Authors mentioned in vivo tests are necessary. Here, I'd like to suggest authors stressing the addition of antimicrobial elements may cause allergies to the surrounding tissues even with limited exposure. So biocompatibility is another concern here.

Thank you for considering these comments. I believe that addressing these concerns will strengthen the scientific quality of this manuscript.

Author Response

First of all, we would like to thank you for the comments. All the modifications stated are highlighted in the newly submitted revised manuscript.

Comment 1: Line 199, Figure 1(b): I suggest to add the name and unit of y axis in the figure, not just describe in figure caption.
Response 1: We agree and, after making all the modifications suggested by the other reviewers (including correcting the caption to Figure 2), we have added the name and measurement unit "Particle size (nm)" to the y axis in Figure 2(b) Page 7. 

Comment 2: In the discussion section, Authors mentioned most of the tests were done by CFU, and there exists some inconsistent results among different studies. Authors could add a bit discussing that different testing methods may influence the results, for example, CFU only measures live microorganisms, while SEM, RT-PCR measures both live and dead microorganisms.
Response 2: We have expanded the topic on CFU assay limitations to state what the limitations are. This modification can be found in Page 10 lines 297 to 298 - "However, CFU assays do not detect dead, culturable or inactive cells, only measuring culturable live cells^[31]"

Comment 3: Line 348: Authors mentioned in vivo tests are necessary. Here, I'd like to suggest authors stressing the addition of antimicrobial elements may cause allergies to the surrounding tissues even with limited exposure. So biocompatibility is another concern here.
Response 3: Following this comment, we have specified the importance of biocompatibility and cytotoxicity tests. This addition can be found in Page 11 lines 378 to 380 - "Likewise, biocompatibility tests are needed to evaluate the possibility of contact allergies and toxicity resulting from the incorporation of metallic particles into denture bases."

Reviewer 2 Report

Comments and Suggestions for Authors

This review provides an overview regarding the use of antimicobial inorganic particles in denture base materials (heat cured). The reduction of the biofilm formation on denture bases is an important topic. This review will therefore be interesting for the readers. The objective was also to identify the most promising antimicrobials for denture bases. Unfortunately, due to the use of different experimental conditions in the selected publications, this objective could not be reached.

Overall, I found that his article was well written and I would recommend it for publication.

I would have additionally the following questions/comments:

1) Why did the authors choose to only considerer articles published starting from 2019? 2019-2024 seems to be quite a short period for a review.

2) I think it would be great to mention alternative technologies (other than based on inorganic particles)to improve the antimicrobial properties in the introduction. It would give a better overview. The expected advantages of antimicrobial substances could be described.

3)  I would expect that the addition of particles such as silver would be problematic for the coloration of the material. Is there any data concerning the addition of the mentionned particles on the estethic properties of the cured denture bases?

4) Why did the authors only select heat cure denture bases? AM technologies are increasingly used in dentistry. It would have been interesting to include articles regarding the addition of antimicrobial substances to 3D printed denture bases.

5) There are 2 'Figure 1' in the document

Author Response

First of all, we would like to thank you for the comments. All the modifications stated are highlighted in the newly submitted revised manuscript.

Comment 1: Why did the authors choose to only considerer articles published starting from 2019? 2019-2024 seems to be quite a short period for a review.
Response 1: During initial research we found that this is a topic with a growth tendency in the number of studies, having observed a publication peak following 2019 (specifically 2021). Therefore, we decided to focus on the newest studies of the last five years.

Comment 2: I think it would be great to mention alternative technologies (other than based on inorganic particles)to improve the antimicrobial properties in the introduction. It would give a better overview. The expected advantages of antimicrobial substances could be described.
Response 2: Following this comment, we have added a summary of other types of antimicrobials used to modify PMMA for their antimicrobial properties. This can be found in Page 2, lines 44 to 47 - "Natural products, specifically chitosan, chemical compounds, such as nystatin and chlorhexidine, organic extracts, namely tea tree oil and thymoquinone, and inorganic particles present promising antimicrobial properties by causing cell death in the microorganisms and preventing the adherence of bacteria and fungi^[4,8,9]."

Comment 3: I would expect that the addition of particles such as silver would be problematic for the coloration of the material. Is there any data concerning the addition of the mentionned particles on the estethic properties of the cured denture bases?
Response 3: In fact there were references to colour alterations related to the modifications, thus we have included this information in Page 11, lines 358 to 361 - "Besides, as observed in the article by De Matteis et al.^[15], colour changes may occur. Therefore, it is necessary to evaluate the effect of the incorporation of particles such as silver in the physical properties and aesthetics."

Comment 4: Why did the authors only select heat cure denture bases? AM technologies are increasingly used in dentistry. It would have been interesting to include articles regarding the addition of antimicrobial substances to 3D printed denture bases.
Response 4: Heat-cured PMMA is the resin most commonly used in denture bases. In an attempt to decrease the heterogeneity of the samples, and since other resins are newer and there are fewer studies on them, we decided to focus on heat-cured PMMA.

Comment 5: There are 2 'Figure 1' in the document
Response 5: Thank you, we have corrected this mistake in the caption and the references in the text in Page 7.

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript summarizes and presents the results of a systematic review on anti-microbial properties of Heat-cured PMMA materials.

The search algorithm is well described. I have no doubts in the relevance of the conclusion drawn on the bases of this systemic review.

The main conclusion is that experiments are done and published in the literature. As the tests in different studies are done at different conditions, it is difficult to draw a general relation between the applied materials (nano particles) and the anti-bacterial action of the PMMA. Very important is the summary presented in the Fig. 1 in the manuscript which relates the type and size of the particles with their action.

Even though the manuscript presents already known results I believe that it will be interesting for the readership of the journal as it clearly defines the systematic tests which are missing to draw the full picture of the processes.

I suggest publication of the manuscript with the following minor remarks:

- in section 3.1 the authors classified 14 publications as bias risk free and one which might be related to some bias. It would be useful to present the analyses done to define the risk of bias.

- Fig. 1b – please properly define the y-axes of the graph (axes title and measurement units).

Author Response

First of all, we would like to thank you for the comments. All the modifications stated are highlighted in the newly submitted revised manuscript.

Comment 1: in section 3.1 the authors classified 14 publications as bias risk free and one which might be related to some bias. It would be useful to present the analyses done to define the risk of bias.
Response 1: Following this comment, we have included the nine questions from the JBI checklist to the Materials and Methods in Page 3 line 117 and lines 119 to 132. We have also added to the Results section a summary of the answers given to the questions in Page 4 lines 177 to 182 - "While most questions received affirmative responses, the question “Was follow up complete and if not, were differences between groups in terms of their follow up adequately described and analysed?” was deemed not applicable for all the included studies. On the other hand, the questions “Were there multiple measurements of the outcome both pre and post the intervention/exposure?” and “Was appropriate statistical analysis used?” were marked as unclear in three and one article, respectively."

Comment 2: Fig. 1b – please properly define the y-axes of the graph (axes title and measurement units).
Response 2: We agree and, after making all the modifications suggested by the other reviewers (including correcting the legend to Figure 2), we have added the name and measurement unit "Particle size (nm)" to the y axis in Figure 2(b) Page 7. 

Reviewer 4 Report

Comments and Suggestions for Authors

The title of the article does not reflect its content. It should be changed because it misleads the reader. The content is the effect of inorganic antimicrobial substances on the development of bacteria and fungi. In my opinion, so that the reader can better familiarize themselves with the results, they should be discussed separately for Candida albicans and separately for bacteria. In some places they have such sentences as "that lower concentrations of silver presented better antimicrobial effects, while the higher concentrations were less effective." what does greater concentration mean and what does lower concentration mean? - please rephrase this

Author Response

First of all, we would like to thank you for the comments. All the modifications stated are highlighted in the newly submitted revised manuscript.

Comment 1: The title of the article does not reflect its content. It should be changed because it misleads the reader. The content is the effect of inorganic antimicrobial substances on the development of bacteria and fungi.
Response 1: We agree and have modified the title to "Antimicrobial Effect Of The Incorporation Of Inorganic Substances Into Heat-Cured Denture Base Resins - A Systematic Review" so that it matches the focus of this review.

Comment 2: In my opinion, so that the reader can better familiarize themselves with the results, they should be discussed separately for Candida albicans and separately for bacteria.
Response 2: Following this comment, we have added subheadings to the Results to better separate Fungi results from Bacteria results, in Page 7 line 235, and Page 8 line 253.

Comment 3: In some places they have such sentences as "that lower concentrations of silver presented better antimicrobial effects, while the higher concentrations were less effective." what does greater concentration mean and what does lower concentration mean? - please rephrase this
Response 3: We have rephrased that section in Pages 7 e 8 lines 247 to 250 - "... found that PMMA modified with lower concentrations of silver presented better antimicrobial effects, while using higher concentrations of silver to modify the resin proved to be less effective at preventing cell growth and biofilm formation."

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Author

Still I dont know what mean found that PMMA modified with lower concentrations ( how many %??? of silver presented better antimicrobial effects, while using higher concentrations how many %??? of silver to modify the resin proved to be less effective at preventing cell growth and biofilm formation."

Author Response

First of all, we would like to thank you for the comment. All the modifications stated are highlighted in green in the newly submitted revised manuscript.

Comment 1: Still I dont know what mean found that PMMA modified with lower concentrations ( how many %??? of silver presented better antimicrobial effects, while using higher concentrations how many %??? of silver to modify the resin proved to be less effective at preventing cell growth and biofilm formation."
Response 1: We rewrote the paragraph to include the specific concentrations that presented the best and worst effects in the study by Souza Neto et al.
This modification can be found in Pages 7-8, lines 246 to 251: "For Candida glabrata, Souza Neto et al.^[16] found that although there were no statistically relevant differences in the results in the CFU results across the three concentrations, PMMA modified with lower concentrations of silver, specifically 0.5% in the micrographs of biofilm and 0.05% in the three assays, presented better antimicrobial effects. In contrast, using higher concentrations of silver, particularly 0.5% in the CV assay and 5% in the other tests, to modify the resin proved to be less effective at preventing cell growth and biofilm formation."