Antibacterial Effect of Er:YAG Laser Irradiation Applied by a New Side-Firing Spiral Tip on Enterococcus faecalis Biofilm in the Tooth Root Canal—An Ex Vivo Study
, Adi Farber 1,2 and Sharonit Sahar-Helft 2,3Round 1
Reviewer 1 Report
In the "Introduction" part, there is insufficient information about the Er:YAG laser interactions with the irrigants and the physical background behind this modality. In the "Discussion" part, there are some sentences like: "The irrigation solution (289) is absorbed by the laser beam and creates large elliptical vapor bubbles that expand and (290) then implode." This statement is not entirely correct because the chromophore of 2940 nm is the water, and it must be explained clearly that all water-based irrigants can be activated by Er:YAG laser. Additionally, there are no detailed explanations for why NaOCl antibacterial actions become stronger during laser-assisted irrigation (mechanical agitation due to photoacoustic effects or increasing of chemical properties due to slightly increased temperature, or both?). This is very important for a proper understanding of the presented new modality.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
We want to thank the reviewer for critically reviewing our manuscript and providing us with comments that have helped us to improve the manuscript.
Point 1: In the "Introduction" part, there is insufficient information about the Er:YAG laser interactions with the irrigants and the physical background behind this modality.
Response 1: We have now added an explanation about the Er:YAG laser interactions with the irrigants and the physical background behind this modality in the introduction.
The following text has been added: “The treatment is based on the delivery of Er:YAG laser light which is highly absorptive in water at approximately 1–3 μm penetration depth [19]. The laser energy causes a cavitation bubbles effect which results in a movement much deeper in the main root canal than the traditional methods of a syringe or ultrasonic waves [20]. The irrigation absorbed by the Er:YAG laser energy has not only an effect on the lateral canals and other outlying structures, but also on the apical part of the root canal [19]. Laser-activated irrigation permits a major cleaning mechanism by liquid velocity resulting from the laser-induced cavitation bubble effect [21].×´
Point 2: In the "Discussion" part, there are some sentences like: "The irrigation solution (289) is absorbed by the laser beam and creates large elliptical vapor bubbles that expand and (290) then implode." This statement is not entirely correct because the chromophore of 2940 nm is the water, and it must be explained clearly that all water-based irrigants can be activated by Er:YAG laser.
Response 2: The sentence has now been modified, in the discussion section.
The following text has been modified: “The wavelength of the Er:YAG laser (2940 nm) is close to the absorption peak of water (3000 nm) [43], such that the energy of Er:YAG laser is maximally absorbed by the water-based irrigation solutions upon irradiation. This leads to explosive boiling irrigation, induction of cavitation bubbles in close proximity to canal walls during their collapses, generation of shear flows that are able to remove particles from the surface.”
Point 3: Additionally, there are no detailed explanations for why NaOCl antibacterial actions become stronger during laser-assisted irrigation (mechanical agitation due to photoacoustic effects or increasing of chemical properties due to slightly increased temperature, or both?). This is very important for a proper understanding of the presented new modality.
Response 3: We added an explanation for why NaOCl antibacterial actions become stronger during laser-assisted irrigation in the discussion section.
The following text has been added: “The influence of Er:YAG laser light absorbed by NaOCl is very effective. The effect is likely caused by a physical mechanism. The Er:YAG laser light generates violent shock waves with greater liquid displacement. The most intense fluid motions are located near the fiber tip [51]. According to Sahar-Helft et al. [17], irradiating at closer proximity to the biofilm was found to significantly reduce bacterial viability within the biofilm (p < 0.05). This observation explains the reason of using the novel Endo-tip in our research. Using fiber tip deeper inside the root canal resulted in better biofilm removal. The energy provided by the fiber tip is near the walls and along the entire root canal, generating shock waves that contribute to the efficacy of debridement and removal of the biofilm [52].”
Author Response File: 
Author Response.docx
Reviewer 2 Report
In the manuscript entitled “Antibacterial effect of Er:YAG laser irradiation applied by a new side-firing spiral tip on Enterococcus faecalis biofilm in the tooth root canal – An ex vivo study”, the authors described the evaluation of the antibacterial and anti-biofilm effect of Er:YAG laser treatment on a tooth root model infected with Enterococcus faecalis. The subject is really interesting and fascinating for publication, but there are some comments regarding the manuscript. Authors may find useful to consider following comments and suggestions in preparation of the manuscript. Nevertheless, I believe the paper can be accepted for publication after major revision.
Some comments and corrections for authors:
1. Overally, the manuscript has some punctuation errors and needs to be corrected.
2. In introduction section, there should be a figure that clearly showing the importance of the main subject.
3. The results are good, but what about the cytotoxicity or negative effect of the used chemicals?
4. There can be obtained two main conclusions from the results. Can’t be obtained another one or merged in a one conclusion?
5. Thoroughly check the consistency of references.
Author Response
Response to Reviewer 2 Comments
We want to thank the reviewer for critically reviewing our manuscript and providing us with comments that have helped us to improve the manuscript.
Point 1: Overally, the manuscript has some punctuation errors and needs to be corrected.
Response 1: We read carefully the manuscript again and recorrected punctuation errors.
Point 2: In introduction section, there should be a figure that clearly showing the importance of the main subject.
Response 2: An image the tooth root canal has been added to the introduction, with explanation in the text.
The following text has been added: “Endodontic therapy includes removal of the microflora and irritants from the canal and the periapical tissues, and thorough debridement is essential for the treatment to be successful [22]. Success of root canal treatment depends on complete eradication of biofilms and their byproducts from the root canal system [23]. Endodontic treatments include various irrigants as an adjunct along with mechanical preparation for the disinfection of the root canals. Their major goal is to remove the bacterial layer that has penetrated inside the root canal and to prevent reinfection.
Figure 1. The image illustrates the novel Endo tip (in dark brown color) inside a root canal, where the propagation of the laser energy is all along the canal, including the lateral walls. The image was kindly obtained by Prof. Adam Stabholz at our Faculty.
Point 3: The results are good, but what about the cytotoxicity or negative effect of the used chemicals?
Response 3: We have now added text to the discussion section stating the low cytotoxicity of the chemicals at the applied concentrations for short-term treatment. In a separate manuscript that is under preparation, we have studied other parameters showing that laser activation has no significant side effects on the chemical composition of the treated teeth.
The following text has been added: " All agents used in this study are in clinical use for endodontic treatments. Long term use of NaOCl in the root canal can lead to adverse effects. However, in our study it was used for only 60 sec, which doesn’t cause any damage to the tooth [32]. EDTA may also be cytotoxic if applied for long periods, while its short application for 60 sec as done in our study, doesn’t have any significant side effects on the tooth [33].”
Point 4: There can be obtained two main conclusions from the results. Can’t be obtained another one or merged in a one conclusion?
Response 4: The conclusion section has now been modified into three major points.
Point 5: Thoroughly check the consistency of references.
Response 5: We have now checked carefully the consistency of the references, and corrected them accordingly.
Author Response File: Author Response.docx
