Review Reports - Comparative Study of the Trueness of the Inner Surface of Crowns Fabricated from Three Types of Lithium Disilicate Blocks

Round 1

Reviewer 1 Report

The study is innovative, well-conducted and well-presented.

One comment: from figures it seems that no sintering was performed before scanning, but this aspect is not clarified in Materials section. Please specify that in Materials and discuss the reasons in to Discussion.

P.4, line 146: “corrections were was made prior”: erase “was”

Author Response

We are grateful to the reviewers for their critical comments and useful suggestions that have helped us to greatly improve our paper. As indicated in the following responses, we have reflected all these comments in the revised version of our paper. Furthermore, we have had the manuscript checked by a professional English editing service.

Reviewer #1

1. One comment: from figures it seems that no sintering was performed before scanning, but this aspect is not clarified in Materials section. Please specify that in Materials and discuss the reasons in to Discussion.

Response: Thank you for your suggestion for improving the quality of the manuscript. We have specifically addressed the issue you highlight.

P.4, lines 143-144: “Any residue was removed from the produced crown by washing it in distilled water for 5 min using an ultrasonic cleaner. After drying, it was mounted in a jig, and its inner surface was scanned using a touch probe scanner (DS10, Renishaw plc, Gloucestershire, UK) without a crystallization firing cycle (Figure 2B).”

P.8, lines 259-263: “The inner trueness of a lithium disilicate crown was evaluated without a crystallization firing cycle. The crystallization firing cycle causes some shrinkage [42] and can affect the trueness. The method described herein did not involve a crystallization firing cycle. This was done to exclude any variables that could occur in the firing cycle. However, further studies are needed to evaluate the trueness after the crystallization firing cycle to better approximate actual clinical practice.”

2. P.4, line 146: “corrections were was made prior”: erase “was”

Response: Thank you for your comment. We have deleted “was”.

Author Response File: Author Response.pdf

Reviewer 2 Report

aking into account all the several features, the accuracy, scientific quality, scientific content and the interpretation of the results are interesting.

- The approach is interesting and the topic is appropriate for the journal.

- The work has a very clear structure and all the sections are well written in a way that is easy to read and understand. In addition, the structure of the paper is very good.

- The paper is focused on Comparative Study of the Trueness of Crowns Fabricated from Three Types of Lithium Disilicate Block, reporting interesting results. In the introduction, the author start to state: “The introduction of dental computer-aided design and computer-aided manufacturing (CAD-CAM) technology has led to a decrease in practitioner errors as well as material failures [1,2]. In addition, the production efficiency is greatly superior with CAD-CAM, relative to existing methods [3]. The CAD-CAM process produces prostheses through scanning, CAD, and then CAM processes. An actual model can be produced, to produce a virtual working mode …”. Then they rapidly introduce 3D printing and focus the attention on ceramic materials. For this reason, in the introduction of the work I suggest to BRIEFLY stress the importance of additive manufacturing techniques (i.e., 3D printing), which are based on CAD/CAM methodologies and should be employed for different applications and studies (i.e., Mechanical and Thermal Properties of Dental Composites Cured with CAD/CAM Assisted Solid-State Laser. Materials 2018, 11, 504), as well as to introduce concepts in the field about the potential applications of new hybrid materials based on sol-gel methods (i.e., “Theoretical design of multilayer dental posts using CAD based approach and sol-gel chemistry”. Materials 2018, 11(5), 738 …). Then, the authors should continue to stress their approach and study on Comparative Study of the Trueness of Crowns Fabricated from Three Types of Lithium Disilicate Block .This could improve the quality of their work, giving the possibility to better understand the value of their research.

- The introduction and the list of references should be improved.

- It seems that the paper does not contain repetitions.

- The quality of figures should be improved (especially figure 3).

- The title is adequate and appropriate for the content of the article.

- The abstract contains information of the article.

- Figures and captions are essential and clearly reported.

Author Response

Reviewer #2

1. The introduction and the list of references should be improved.

Response: Thank you for your suggestion for improving the quality of the manuscript. We have added references to improve the Introduction section.

9. Maietta, S.; De Santis, R.; Catauro, M.; Martorelli, M.; Gloria, A. Theoretical design of multilayer dental posts using CAD-based approach and sol-gel chemistry. Materials. 2018, 11, 738. [https://doi.org/10.3390/ma11050738]

10. De Santis, R.; Gloria, A.; Maietta, S.; Martorelli, M.; De Luca, A.; Spagnuolo, G.; Rengo, S. Mechanical and thermal properties of dental composites cured with CAD/CAM assisted solid-state laser. Materials. 2018, 11, 504. [https://doi.org/10.3390/ma11040504]

2. The quality of figures should be improved (especially figure 3).

Response: Thank you for your comment. We have increased the resolution of the figures.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article is well written, the structure of the article is well ordered, and the supporting figures and graphics are appropriate.

The process followed is very well described and the methodology used is well understood.

Therefore, scientific soundness is high, the statistics used are adequate and the results are coherent and meaningful.

The bibliography is abundant, relevant and up-to-date.

After reading the article, the following questions and doubts have arisen:

- I understand that step 1 of digitizing a reference model with unknown accuracy and then obtaining a working model designed with another unknown accuracy is irrelevant in the proposed comparative study.

- The fact that the outer surface of the crowns has not been compared is not irrelevant so I think it should appear in the title of the paper.

- Due to the range of precision and accuracy in which the research has been performed I believe that the number and strategy of digitalization of the points used with the touch probe scanner should be detailed better.

- In figure 4, it can be interpreted that the views given for the comparison of the four regions are top views. On the one hand, I think it would be appropriate to add a figure in perspective where the four regions are specified. On the other hand, I think that the views given in figure 4 should also be at least in the position where the region is seen best which I suppose should not be the same for all regions.

- Some issues or technical data that are mentioned in section 4 discussion are repeated or otherwise should have been mentioned in the Materials and Methods description. In my opinion, this section 4 could be more concise and thus more clarifying.

Author Response

Reviewer #3

1. I understand that step 1 of digitizing a reference model with unknown accuracy and then obtaining a working model designed with another unknown accuracy is irrelevant in the proposed comparative study.

Response: Thank you for your suggestion for improving the quality of the manuscript. We have carefully considered your comments. As the reviewer notes, step 1 of the reference model is irrelevant to the proposed comparative study. Therefore, we have omitted step 1 from the reference model and have revised the contents. Figure 1 has also been revised.

2. The fact that the outer surface of the crowns has not been compared is not irrelevant so I think it should appear in the title of the paper.

Response: Thank you for your comment. We have addressed the issue that you point out.

P.1, lines 2-3: “Comparative Study of the Trueness of Inner Surface of Crowns Fabricated from Three Types of Lithium Disilicate Block”

3. Due to the range of precision and accuracy in which the research has been performed I believe that the number and strategy of digitalization of the points used with the touch probe scanner should be detailed better.

Response: We agree with the reviewer’s suggestion. We have specifically addressed the issue that you point out.

P.4, lines 145-149: “The touch probe was used to scan from the inner end of the crown to the end of the crown margin. The coordinates of about 20,000 points on the inner surface of the crown were recorded by the touch probe. The inner surface of the crown that had been milled by the 1.0-mm milling burr head was precisely scanned using a probe with a diameter of 0.5 mm.”

4. In figure 4, it can be interpreted that the views given for the comparison of the four regions are top views. On the one hand, I think it would be appropriate to add a figure in perspective where the four regions are specified. On the other hand, I think that the views given in figure 4 should also be at least in the position where the region is seen best which I suppose should not be the same for all regions.

Response: We very much appreciate the reviewer’s comment and respect the reviewer’s insight. As the reviewer points out, Figure 4 was compared only in the top views. We thought that detailed comparisons of the four regions would be difficult using only Figure 4. Therefore, we have added Figure 5 so that the four regions can be observed in five directions.

5. Some issues or technical data that are mentioned in section 4 discussion are repeated or otherwise should have been mentioned in the Materials and Methods description. In my opinion, this section 4 could be more concise and thus more clarifying.

Response: We agree with the reviewer’s suggestion. We have shifted the technical data from the Discussion to Materials and Methods.

“…..In addition, Dimitrova [43] measured repeatability/reproducibility, taking pictures of the abutment tooth with an optical scanner and measurements with a touch-probe scanner, with the results obtained with the touch-probe scanner exhibiting excellent repeatability/reproducibility (optical scanner: 8.2 µm; touch-probe scanner: 6.9 µm). The touch probe scanner used in the present study featured a probe with a diameter of 0.5 mm, which softly touched the surface of the ceramic and was capable of rising and falling 200 μm. Since the use of this method did not incur any errors caused by the optical characteristics of the object, it was ideal for scanning the inner surface of a lithium disilicate crown. In addition, the trueness could be analyzed precisely because of the excellent repeatability/reproducibility that was possible with this instrument. However, unlike in some previous studies [26,44], the trueness of the outer surface of the crown was not evaluated in the present study. …..”

Author Response File: Author Response.pdf

Reviewer 4 Report

See the attached file.

Comments for author File: Comments.pdf

Author Response

Reviewer #4

INTRODUCTION

1. Further information about the CAM processes should be added. Milling (= subtractive process) is actually used as CAM process.

Response: We very much appreciate the reviewer’s comment and respect the reviewer’s insight. We have added information so that the CAM processes can be easily understood by a reader.

P.2, lines 53-55: “CAM processes are classified as either subtractive or additive manufacturing [10], but milling (a subtractive process) is actually used as a CAM process. In fact, milling is the most commonly used manufacturing process. For CAM, a 5-axis milling unit can produce prostheses more accurately than a 4-axis machine [9-11]. ….”

2. The lines numbered 41 to 43 seem not to be usefull. Additive manufacturing is not the aim of this paper.

Response: We agree with the reviewer’s suggestion. We have deleted the text in question.

“The introduction of dental computer-aided design and computer-aided manufacturing (CAD-CAM) technology has led to a decrease in practitioner errors as well as material failures [1,2]. In addition, the production efficiency is greatly superior with CAD-CAM, relative to existing methods [3]. The CAD-CAM process produces prostheses through scanning, CAD, and then CAM processes. An actual model can be produced, to produce a virtual working model, using a model or intraoral scanner through 3-dimensional (3D) printing and milling. Otherwise, a prosthesis can be produced through 3D printing and milling after designing it with CAD software without a model.”

3. Line 55. “With a 5-axis milling machine, it is possible to mill pointed angles more accurately, given that a wider range of tools with more diverse diameters can be used.” This sentence is not clear. What is the link between the number of axis and the number of tool?

Response: Thank you for your comment. We thought that the use of a 5-axis milling machine was irrelevant to the number of tools. The use of a 5-axis milling machine increases the number of axes compared to a 4-axis machine. Therefore, we have revised the following text.

P.2, lines 57-58: “With a 5-axis milling machine, it is possible to mill pointed angles more accurately, given that a wider range of milling with a greater number of axes relative to the 4-axis mill can be used [9,12].”

4. Line 55. “With a 5-axis milling machine, it is possible to mill pointed angles more accurately, given that a wider range of tools with more diverse diameters can be used.” Further information can be added: With a 5-axis milling machine, the contact point between the tool and the prosthesis to be milled can be controlled, leading to the control of the milling conditions.

Response: Thank you for your suggestion for improving the quality of the manuscript. We have added information.

P.2, lines 58-59: “…. With a 5-axis milling machine, it is possible to mill pointed angles more accurately, given that a wider range of milling with more the number of axes relative to the 4-axis can be used [9,12]. With a 5-axis milling machine, the contact point between the tool and the prosthesis to be milled can be controlled, thus realizing better control of the milling conditions. However, somewhat more time is required to complete machining when using a 5-axis milling unit [9]. Accordingly, for chairside CAD-CAM, the use of a 4-axis milling unit is preferred to keep the chairside time within a clinically acceptable range. Several studies have evaluated the impact of the use of a chairside 4-axis milling unit on the inner surface of the prosthesis [9,10]. To the best of our knowledge, however, there have been no studies that have evaluated trueness according to region.”

5. Line 61. What is the benefit of evaluating the trueness according to the region? What is the clinical implication?

Response: Thank you for your comment. The benefit of evaluating the trueness by region is to assess which region produces poor trueness, which can provide good data regarding the marginal and internal fit of the prosthesis. We have added a description of the clinical implication.

P.2, lines 93-95: “…. This operation can increase fatigue crack initiation, leading to a shorter crown lifetime. And, a prosthesis with an excellent degree of trueness can reduce the chairside time [11,34]. Many previous studies have evaluated the trueness of the prosthesis [11, 33-36]. The benefit of evaluating the trueness according to the region is to assess which region exhibits poor trueness, which can be used as reference data for the marginal and internal fit of the prosthesis. However, there have been no studies that have evaluated the trueness of the inner surface of the crowns and how that varies with the type of lithium disilicate block.”

6. Lines 71-72. “This can save time compared to visual examinations, and accurate analysis can be conducted with the development of a scanner.” This sentence needs more explanations to be understand.

Response: We agree with the reviewer’s suggestion. We have added information so that the text is more readily comprehensible to a reader.

P.2, lines 76-78: “Three-dimensional evaluation is often applied to determine whether mass-produced products have been accurately produced by manufacturing processes [19-21]. This can save time compared to visual examinations, [19] and accurate analysis can be conducted with the development of a scanner [9]. Visual examinations require more time because human errors can occur and given that the evaluation is done by hand. In addition, due to advances in scanning technology, very precise scanning (< 10 μm) can be obtained and accurate analysis is possible. Likewise, given the take-up of CAD-CAM techniques in dentistry, three-dimensional data have been evaluated in numerous studies [5,22-26]. The distance from a certain reference point or a form was measured [23,27,28], or a 3D analysis was conducted by overlapping a CAD reference model on a CAD test model [5,22-24,26]. This 3D analysis relies on an alignment process whereby the CRM is overlapped using software. In general, the overlap is investigated through best-fit alignment [29-31].”

7. Lines 81-83. “The trueness evaluation is important because an inaccurate inner surface on the prosthesis has the greatest effect on the marginal and internal fit. Thus, a prosthesis with an excellent degree of trueness can reduce the chairside time.” Further information can be added: an inaccurate inner surface on the inner prosthesis leads the dentist to post-process the crown with its dental handpiece. This operation can increase fatigue crack initiation, leading to a shorter crown lifetime.

Response: Thank you for your suggestion for improving the quality of the manuscript. We have added information to the text.

P.2, lines 89-91: “…. The trueness evaluation is important because an inaccurate inner surface on the prosthesis is the one of several factors (dental preparation, preparation’s scan) of effect on the marginal and internal fit. An inaccurate inner surface on the inner prosthesis requires the dentist to post-process the crown with a dental handpiece. This operation can increase the risk of fatigue crack initiation, leading to a shorter crown service life. Furthermore, a prosthesis with an excellent degree of trueness can reduce the chairside time [11,34]. Many previous studies have evaluated the trueness of the prosthesis [11, 33-36]. The benefit of evaluating the trueness according to the region is to assess which region produces poor trueness, which can be reference data for the marginal and internal fit of the prosthesis. However, there have been no studies that have evaluated the trueness of the inner surface of the crowns and how that varies with the type of lithium disilicate block.”

8. Lines 81-83. “The trueness evaluation is important because an inaccurate inner surface on the prosthesis has the greatest effect on the marginal and internal fit.” The inner surface on the prosthesis is not the only shape to be important. The dental preparation made by the dentist and its scan, are also important. The marginal and internal fit are given the both (the inner crown and the dental preparation).

Response: Thank you for your comment. We have addressed the issue that you point out.

P.2, lines 88-89: “The trueness evaluation is important because an inaccurate inner surface on the prosthesis is one of several factors (dental preparation, preparation’s scan) that affect the marginal and internal fit.”

MATERIALS AND METHODS

9. Simple experimental design should be made. Instead of making a reference model to be scanned, it is possible to design the crown model inner surface directly with the wanted geometry. So the “reference model” and the “intraoral scanning” steps can be suppressed.

10. Why the “intraoral scanning” step is not realized with the contact scanner? The trueness of the contact scanner is better than the trueness of the intraoral scanner.

Response: Thank you for your suggestion. As the reviewer points out, the contact scanner is better at measuring trueness than the intraoral scanner. In clinical practice, however, the "intraoral scanning" step involves acquiring a virtual model using an intraoral scanner. In the present study, we acquired a virtual model using an intraoral scanner according to the clinical procedure.

11. Lines 118-119. “Also, the designed virtual crown was extracted as a stereolithography (STL) file (CDM) to enable its use as the base data for the trueness evaluation.” STL files are discretized surfaces. So some errors are introduced by generating a STL file.

Response: Thank you for your accurate comment. As the reviewer points out, we also thought that the generation of the STL file would incur some errors. However, in the present study, the crown milling path according to the STL file was set in the CAM software after the generation of the STL file, and the actual crown was made through the milling process. Therefore, we believe that the error that is incurred by the generation of the STL file is not reflected in the trueness evaluation of this study. We have added some text to the description so that it is more easily comprehensible to a reader.

P.4, lines 123-234: “To produce the STL file for the designed crown, it was moved to a milling unit (EZIS HM; DDS). The EZIS HM is a chairside 4-axis milling unit. A crown milling path based on the STL file was set in the CAM software (EZIS VR; DDS). According to the manufacturer, it offers a processing accuracy of ± 10 µm and a maximum spindle speed of 63,000 rpm and can produce a crown at a rate of 15 min/unit. ….”

12. Line 128. Two points are printed. One of them can be deleted.

Response: Thank you for your comment. We have addressed the issue that you point out.

13. Line 145. The probe ball diameter must be compared to the inner connection radius.

Response: Thank you for your suggestion for improving the quality of the manuscript. As the reviewer points out, the probe ball diameter must fall within the radius of the object being measured for accurate contact scanning. In our experiments, the radius of the inner crown was the radius formed along the milling burr diameter, so we compared the milling burr diameter and the probe ball diameter. We have added a corresponding description.

P.4, lines 147-149: …. The touch probe scanner uses a probe with a diameter of 0.5 mm, which gently touches the surface, and is capable of rising and falling through 200 µm. The touch probe was scanned from the inner end of the crown to the end of the crown margin. The coordinates recorded by the touch probe were about 20000 points and formed into the inner surface of the crown. The inner surface of the crown milled using the 1.0-mm milling burr was precisely scanned using a probe with a diameter of 0.5 mm. Since the use of this method did not incur any errors caused by the optical characteristics of the object, it was ideal for scanning the inner surface of a lithium disilicate crown. In addition, the trueness could be analyzed precisely because of the excellent repeatability/reproducibility that was possible with this instrument [39].….”

14. Line 146. “To ensure precision, corrections were was made prior to each scan.” This sentence must be corrected and explained.

Response: Thank you for your comment. We have addressed the issue that you point out.

P.4, lines 152-153: “To ensure accuracy, the touch probe scanner was calibrated prior to each scan.”

15. Lines 152-153. “The inner surface of the crown was divided into four parts (marginal, axis, angular, and occlusal regions).” This division choice needs to be explained and justify.

Response: We very much appreciate the reviewer’s comment and respect the reviewer’s insight. The trueness of the inner surface of the crown may affect the marginal and internal fit, and many previous studies have evaluated the marginal and internal fit according to the region. We have added a description of this to the text.

P.4, lines 162-165: “The 3D analysis program used in this study was Geomagic Company’s 3D inspection software (Geomagic control X v2018.0.0, 3D Systems Inc, USA), as recommended by ISO-12836 [25]. A CDM file was retrieved to the 3D inspection software, which was set to perform a 3D comparison of the inner surface of the crown. The inner surface of the crown was divided into four parts (marginal, axis, angular, and occlusal regions). The trueness of the inner surface of the crown may affect the marginal and internal fit, and many previous studies have evaluated the marginal and internal fit according to the region [2,13-18]. Therefore, the inner surface of the crown was divided into four parts to evaluate the trueness. The region up to 0.5 mm from the prosthesis margin was defined as the marginal region; the region starting at the end of the marginal region through the axis to the point where the curve starts was the axis region; the region starting from the end of the axis region through the line angle to the point where the curve ends was the angular region; and the remaining region starting from the angular region was the occlusal region.”

16. Lines 161-162. “The dimensional difference between the CDM file and the CSM file was calculated for all the data points of the partitioned inner region.” The direction of measurement must be detailed.

Response: Thank you for your suggestion for improving the quality of the manuscript. The difference between all the data points of the CDM and CSM were calculated from the data points that are closest to each other in every direction. We have added a description to the text so that it is more readily comprehensible to a reader.

P.5, lines 174-175: “The dimensional difference between the CDM file and the CSM file was calculated for all data points of the partitioned inner region. The differences between all the data points of the CDM and CSM were calculated from the closest data points to each other in all directions. At this time, the data points were calculated with the root mean square (RMS) value using the following formula:”

17. Lines 171-175. Further details (or hypothesis) are needed to explain why the tool cannot reach or exceed the target position.

Response: We very much appreciate the reviewer’s comment and appreciate the reviewer’s insight. We have added a description to the text.

P.5, lines 183-185: “The CAM process aims to reproduce a modeled design and produce an accurate product. The tool target position may not be reached or exceeded, however, due to various factors affecting the cutting rate (e.g., the hardness of the material, performance of the milling unit). Therefore, the 3D comparison is shown as a color-difference map, with a range of ± 100 µm (20 color segments) and an allowable tolerance range (green) of ± 10 µm assigned. The red zone (10–100 µm) shows that the CSM data is located above the CDM data, implying that the milling failed to reach the target position. In addition, the blue zone (- 10 to - 100 µm) shows that the CSM data are located below the CDM data, implying that the milling exceeded the target position. The green zone (± 10 µm) corresponds to the areas that were machined very precisely.”

18. The figure 4 color map is too small. It is difficult to read numbers.

Response: Thank you for your comment. We have modified the color map in Figure 4 and have increased the resolution, such that the numbers are now easier to read.

19. Lines 205-209. This paragraph looks like lines 171-175.

Response: Thank you for your suggestion for improving the quality of the manuscript. As the reviewer points out, the same content was repeated. We have deleted the description from the Materials and Methods section.

“Figure 4 and 5 show the color difference map for 3D analysis. In the angular region, the red zone was predominant, meaning that the milling failed to reach the target position. In the marginal region, the green color is most common, indicating that the milling was performed accurately. In the axis and occlusal regions, several color zones appear to equal degrees. The green zone appeared least with e.max. Furthermore, in the angular and occlusal regions, the range of the red zone was greatest.”

DISCUSSION

20. Line 219. See part 7.

21. Line 223. “Kim noted that the number of mill burs affects the accuracy, with the trueness in the angular region being lower with three mill burs than with two mill burs.” This sentence is unclear. Further explanations must be added.

Response: We very much appreciate the reviewer’s comment and appreciate the reviewer’s insight. The true ness when using three burrs is better than that when using two burrs because he use of three burrs leads to a greater range of burr diameters . A smaller-diameter burr can more precisely mill angular regions. We have revised the text to correct the description and have added information to the text.

P.7, lines 242-244: “Kim [26] noted that the number of mill burrs affects the accuracy, with the trueness being better when three burrs were used, relative to when two burrs were used. The use of three burrs produces a better trueness than when only two burrs are used because the use of three burrs leads to a greater range of burr diameters. A smaller-diameter burr can be used to more precisely mill angular regions.”

22. Line 225. “Kirsch found that the trueness was lower with a 5-axis milling machine than with a 4-axis machine.” This sentence is true. For more information, this is due to the milling machine stiffness. The more the machine is equipped with axes, the more the stiffness decreased.

Response: We very much appreciate the reviewer’s comment reviewer and respect the reviewer’s insight. We have addressed the issue that the reviewer points out.

P.7, lines 245-247: “Kirsch [11] found that the trueness was lower with a 5-axis milling machine than with a 4-axis machine. This is because of the stiffness of a milling machine decreases as the number of axes increases.”

23. Line 250.”… as was capable of rising and falling through 200㎛.” This sentence is not clear. It must be explained.

Response: Thank you for your comment. We have deleted the technical data from the Discussion section, given that it also appears in the Materials and Methods.

24. Lines 259-260. The outer surface is as important as the inner surface. Many functions are attached to the outer crown surface. Such as aesthetic, non-dental plaque adhesion, wear, occlusion, proximal contact points, ...

Response: We very much appreciate the reviewer’s comment and respect the reviewer’s insight. We have deleted this sentence because we overlooked the importance of the outer surface of the crown.

“We were unable to do so because the narrow, deep regions and those regions with an undercut could not be scanned using a touch-probe scanner. In addition, those parts connected to the outer surface when the crown is separated from the block may, for additional reasons, affect the trueness. If the outer shape were to be unsatisfactory, however, it could be corrected in the clinic without difficulty, so its importance is less than that of the inner surface. However, further study should be undertaken to analyze the trueness of the outer surface of the crown.”

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The new version of the paper gathers all the suggestions made by the reviewers. The research paper reveals interesting information about the three types of crowns.

Reviewer 4 Report

Lines 225-226 : "The inner surface of the crown milled using the 1.0-mm milling burr was precisely scanned using a probe with a diameter of 0.5 mm." It is similar to the line 222.

Lines 233-234 : "Since errors may occur depending on the operator [27,40], a single skilled operator (K.S.) performed all the scans and analyses." Why didn't you used an automated Coordinate Measuring Machine (CMM) cycle?

Lines 244-246 : How the point is choosen? Is the point depending on where you are looking at on the inner surface?

Line 256 : How the inital alignment was made? best fit?

Line 277 : Maybe the term "accurately" is better than "precisely"?

Lines 357-358 : Yes good idea. Further study should be undertaken to analyze the differences between the tested biomaterials. Are the differences due to the biomaterials themselves or to the milling conditions which were not adapted to the milled biomaterials.

Author Response

Reviewer #4

1. Lines 225-226 : "The inner surface of the crown milled using the 1.0-mm milling burr was precisely scanned using a probe with a diameter of 0.5 mm." It is similar to the line 222.

Response: Thank you for your suggestion for improving the quality of the manuscript. As the reviewer notes, the two sentences were similar. Therefore, we have deleted the duplicated sentence and shifted sentence forward.

“….The touch probe scanner uses a probe with a diameter of 0.5 mm, which gently touches the surface, and is capable of rising and falling through 200 µm. The inner surface of the crown milled using the 1.0-mm milling burr was precisely scanned using a probe with a diameter of 0.5 mm. The touch probe was used to scan from the inner end of the crown to the end of the crown margin…..”

2. Lines 233-234 : "Since errors may occur depending on the operator [27,40], a single skilled operator (K.S.) performed all the scans and analyses." Why didn't you used an automated Coordinate Measuring Machine (CMM) cycle?

Response: We very much appreciate the reviewer’s comment and respect the reviewer’s insight. In our study, the inner surface of crown was scanned by automated Coordinate Measuring Machine (CMM) cycle. We have revised the inappropriate sentence and shifted on to the sentence below.

“….To ensure accuracy, the touch probe scanner was calibrated prior to each scan. All the scanning processes conducted as part of this study were conducted at an ambient temperature of 23 ± 2°C in accordance with ISO-12836. Since errors may occur depending on the operator [27,40], a single skilled operator (K.S.) performed all the scans and analyses. In addition, the scanned virtual crown was extracted as an STL file to enable its use as test data in the trueness evaluation (CSM)…..”

“The 3D analysis program used in this study was Geomagic Company’s 3D inspection software (Geomagic control X v2018.0.0, 3D Systems Inc, USA), as recommended by ISO-12836 [27]. Since errors may occur depending on the operator [27,40], a single skilled operator (K.S.) performed all the analyses. A CDM file was retrieved to the 3D inspection software, which was set to perform a 3D comparison of the inner surface of the crown…..”

3. Line 256 : How the inital alignment was made? best fit?

Response: Thank you for your suggestion for improving the quality of the manuscript. We have revised the issue you highlight.

“After preparing a CDM file, a CSM file was retrieved, and the initial alignment was conducted with the best fit alignment.”

4. Line 277 : Maybe the term "accurately" is better than "precisely"?

Response: Thank you for your suggestion for improving the quality of the manuscript. We have revised the issue you highlight.

“The green zone (± 10 µm) corresponds to the areas that were machined very accurately.”

5. Lines 357-358 : Yes good idea. Further study should be undertaken to analyze the differences between the tested biomaterials. Are the differences due to the biomaterials themselves or to the milling conditions which were not adapted to the milled biomaterials.

Response: We agree with the reviewer’s suggestion. We have carefully considered your comments. There are differences due to the biomaterials themselves or to the milling conditions. We have added a description to the text so that it is more readily comprehensible to a reader.

“Since different types of lithium disilicate block vary in terms of their cutting rates, we could assume that the trueness would differ depending on the type of lithium disilicate block used. Since our study controlled various variables (replacement of the milling burr, the use of a milling machine with high accuracy (± 10 µm), the use of a touch-probe scanning process in which the ceramic material does not scatter the light, and sufficient sample size with an actual power of 98.93%), this assumption is reliable. If the hardness of the material themselves is low, the cutting rate will be greater. And the hardness varies depending on the product. The milling conditions (precision, spindle speed, number of axes) depend on the type of milling unit. Further studies should be conducted to analyze the differences between the biomaterials tested. According to Song [41], the feed rate and depth of cut may differ depending on the type of block, with lithium disilicate ceramic being the most difficult of the ceramic materials to process…..”

Author Response File: Author Response.pdf