Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Article titled "The Effect of the Incorporation of a 3D-Printed Titanium Framework on the Mechanical Properties of CAD/CAM Denture Base Materials" addresses the issue of insufficient mechanical properties of dentures. In the introduction, the authors outline quite generally the material that is most often chosen for this purpose and indicate possible methods of strengthening the structure and improving properties, for example through nanoparticles or nylon or polyamide fibers. At the same time, the authors indicate possible negative effects and problems caused by such modifications. On this basis, they propose their own modification procedures and verify how they affect the mechanical properties of the new, improved material. In the methodology, the authors describe the stages of sample preparation, but they could also show the reader what they look like. I think it is equally important to indicate the dimensions of these samples. There is also no description of how the sample strengthening procedure was carried out. Were the samples conditioned in liquids before testing? If so, which ones and for how long, if not, why? Dental materials work in the environment of saliva, which does not remain indifferent. Many sources and methodological descriptions of research emphasize the importance of this stage of sample preparation - it was missing here. What was the calibration during the fracture test? Fig 1 - the descriptions of the axes are unclear, the charts are illegible, the signature is on the second page, lines are visible from under the charts. The description of the breakthroughs is correct and comprehensive, but photos of this size are not legible. A short and concise discussion and sparse sources indicate that the topic is not important, but from a clinical perspective it is very important.

Author Response

Response to Reviewer 1.

Dear reviewer we would like to thank you for your expertise and time for evaluating our manuscript Entitled "The Effect of the Incorporation of a 3D-Printed Titanium Framework on the Mechanical Properties of CAD/CAM Denture Base Materials"

We agree with your comments and completed point by point the changes and additions that you recommended. We believe that now, the new version is better thanks to your recommendations.

Therefore, following your recommendations, here are all the modifications completed to the manuscript.

Q1. In the methodology, the authors describe the stages of sample preparation, but they could also show the reader what they look like.

Response 1. Many thanks for pointing this out. We added Figure 1a and 1b.  that contains images that illustrate the three experimental groups In addition, we renumbered the consecutive images within the manuscript.

 

Q2. I think it is equally important to indicate the dimensions of these samples.

Response 2. Thanks for pointing this out.

The sample dimensions are registered within the materials and methods section. We highlighted in green within the text the information requested by the reviewer 1.  “A bar design was created using Tinker CAD (Autodesk Inc., San Rafael, CA, USA) (Following ISO standards for fracture test and bending tests). The dimensions of the samples were 60 mm length, 10 mm width, and 4 mm thickness.”

 

Q3. There is also no description of how the sample strengthening procedure was carried out.

Response 3. Many thanks for your comment.

“To fabricate the milled samples (without and with reinforcement), the STL file was sent to the Avadent (AvaDent^®, Scottsdale, AZ, USA), who applied our design to mill the bars using their proprietary technology. A brief description was provided by the manufacturer. A 3D-printed framework was designed to the desired geometry and fabricated by printing of titanium powders. Afterward, the framework was embedded into liquid resin, and the resin processed by heat and pressure which resulted in the incorporation of the framework into the denture base material.  Afterwards the samples were milled to its final dimensions. The printing procedure was described within the text as follows “The printed samples were fabricated on site using a Form3, 3D-printer (Formlabs, Somerville, MA, USA) using OP (Original Pink) denture base material (Ref. PKG-RS-F2-DB) from Formlabs (Formlabs, Somerville, MA, USA). The samples were printed with horizontal orientation of 0° parallel to the printing surface. After printing, the supports were removed, the samples were washed in isopropyl alcohol for 15 minutes (Form Wash; Formlabs, Somerville, MA, USA), and post-cured with UV light at 45°C for 30 minutes (Form Cure; Formlabs, Somerville, MA, USA).”  

Q4. Were the samples conditioned in liquids before testing? If so, which ones and for how long, if not, why?  Dental materials work in the environment of saliva, which does not remain indifferent. Many sources and methodological descriptions of research emphasize the importance of this stage of sample preparation - it was missing here.

Response 4. Many thanks for pointing this out.

The samples were maintained in a controlled environment at 21 Celsius degrees and a relative humidity of 30%. No immersion in water or conditioning was completed before the mechanical tests to preserve the maximum strength that the materials possessed before any ageing or thermocycling occurs.

The information was added to the materials and methods section.

Q5. What was the calibration during the fracture test?

Response 5. Many thanks for your comment. The following sentence was added to the fracture test calibration: “Calibration was needed first, to evaluate the stabilization of the samples in the sample holder, and second to determine that center of the samples was centered with tip of the pendulum point. The center of the samples was identified using a digital caliper and a pen was used to mark the location The calibration allowed to confirm that 30mm was the center of the samples and that point was coincident with the pendulum tip. Finally, the dimensions of the samples: width (10mm), thickness (4mm), and length (60mm) were recorded in the impact tester.”  

Q6. Fig 1 - the descriptions of the axes are unclear, the charts are illegible, the signature is on the second page, lines are visible from under the charts. The description of the breakthroughs is correct and comprehensive, but photos of this size are not legible.

Response 6. Dear reviewer many thanks for your comment.  You were right. When we created the image composition and pasted together the three figures, the resolution decreased. Therefore, now the figures were uploaded as separated figures and now are more legible.

 

Sincerely,

 

The authors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for your manuscript.

In addition to the comments provided in the attached PDF, I have several general concerns.

Abstract needs to be rewritten with removed redundancies and focusing more on dentistry and dentures.

Introduction needs to be revised with inclusion of more references and more precise descriptions of materials and their properties. A figure illustrating typical fracture locations in dentures and the materials used could enhance understanding. For instance, please

·        Specify the type and quantification of the strength mentioned.

·        Provide references for claims about the effectiveness of nanoparticles, fibers, and metal reinforcements.

·        Include more details about the materials used for metal frameworks.

·        Add visual aids to illustrate fracture locations and materials used.

Materials and Methods section also needs more clarity and visual aids. Please:

·        Specify the number of samples more clearly and explain how subgroups were created.

·        Include images of the CAD models and fabricated samples with dimensions and scale.

·        Clarify the process for calculating fracture toughness from the energy required to fracture the samples.

The results section also require more clarification and additional visuals. Please:

·        Provide more details on how fracture toughness was calculated.

·        Include images or graphs of the stress/strain curves and fracture analysis results.

·        Ensure the terminology and descriptions are consistent and clear.

·        High variability in deformation values for printed samples indicates inconsistencies that need to be addressed for reliable application.

The discussion section needs some revision. Please:

·        Emphasize the practical implications of the findings for clinical dentistry.

·        Suggest potential future research directions based on the study's limitations and findings.

Conclusion section is insufficient. Please use bullet points to revise the conclusions.

Thank you.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Response to Reviewer 2.

Dear Reviewer 2, sincere thanks for your time and expertise during your evaluation of our manuscript entitled “The Effect of the Incorporation of a 3D-Printed Titanium Framework on the Mechanical Properties of CAD/CAM Denture Base Materials" We agree with your comments and completed point by point revisions to our manuscript to address your concerns.

The authors believe that this new version is significantly improved thanks to your recommendations.  We did not receive a PDF with comments; we could only see your written comments. We have addressed all your requests to the best of our ability

Q1. Abstract needs to be rewritten with removed redundancies and focusing more on dentistry and dentures.

Response 1. The redundancies in the abstract were removed and we described a little more about dentures:

“Complete dentures should withstand occlusal forces and wear. However, over time, dentures can suffer fatigue and develop cracks, chipping, and fractures. Conventional methods for the fabrication of complete dentures involve injection molding, thermal curing, and the use of microwaves with polymethyl methacrylate (PMMA)-based materials. These methods have served well for many years. More recently, the incorporation of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) to fabricate complete dentures has been shown to enhance the dentures' mechanical properties, including resistance to wear and impact strength. This study aims to investigate the mechanical properties and fracture types of CAD/CAM denture base materials (both milled and printed) compared to a novel proprietary method that embeds a 3D-printed framework within PMMA-milled blocks. The null hypothesis is that incorporating a 3D-printed framework does not affect the mechanical properties of milled PMMA blocks. Methods: Three groups of bars were fabricated using CAD/CAM methods: printed (P), milled (M), and milled with a 3D-printed metallic framework reinforcement (M + F). A three-point bending test evaluated deformation, followed by an impact fracture test for fracture toughness. Descriptive fractographic analysis assessed fracture characteristics. Statistical analysis using a paired t-test com-pared differences between groups. Results: The P group showed more elastic deformation than the M and M + F groups (p<0.05). The M + F group achieved higher fracture toughness compared to the M and P groups (p<0.05). Conclusions: Within the limitations of this experimental study, the null hypothesis can be rejected. Milled samples with an embedded 3D-printed titanium frame-work possesses higher resistance to impact than milled samples without framework and printed samples and milled samples with an embedded 3d-printed titanium framework present in-creased flexural strength and lower elastic deformation compared to milled samples without framework and printed samples.”

Q2. Introduction needs to be revised with inclusion of more references and more precise descriptions of

materials and their properties. A figure illustrating typical fracture locations in dentures and the materials used could enhance understanding.

Response 2. Additional references were added to the introduction section.

Q3.  Provide references for claims about the effectiveness of nanoparticles, fibers, and metal reinforcements.

Response 3. Dear reviewer. Within the section, each statement is supported with references. Please see the attached paragraphs from the introduction section, all using appropriate references.

“To increase the fracture resistance and flexural strength of denture bases, different approaches are used including, impact-resistant polymers (by chemical modification) and reinforcement of the PMMA (nanoparticles/nanotubes, fibers, and metal reinforcements)   [11–18]. The use of nanoparticles aims to improve the mechanical properties of the denture base polymer (specifically resin hardness), however, if the nanoparticles are non-homogeneously distributed and produce nanoparticles agglomerates, the toughness, flexural strength, and tensile strength are impaired given their uneven dispersion within the polymer matrix [12,13]. Furthermore, the properties of nanoparticle-reinforced polymers are influenced by factors such as nanoparticle geometry, form, orientation, surface treatment, and interfacial adhesion with the polymer matrix which are difficult to control [14,15]. Additionally, variations in standardization, polymerization cycles, and manipulation methods can further impair the flexural strength of the nanoparticle reinforced polymer [16].

Another option is reinforcing the PMMA with different fibers, such as nylon, polyethylene, polyamide, and glass fibers which in the laboratory showed enhanced flexural strength, impact strength, and fatigue resistance of the denture bases [17]. However, the literature indicates that this method is technique-sensitive and presents inconsistent values in their reinforcing effects [17].

Metal framework reinforcements can be added to complete or partial dentures offering certain advantages such as light weight (compared with thick denture bases), increased patient comfort (due minimal thickness of the metal framework less invasion of the intraoral spaces), high strength, excellent biocompatibility, and increased fracture toughness [18,19], in addition metal frameworks can be casted or digitally manufactured [20].

 

Q4. Include more details about the materials used for metal frameworks.

Response 4. A paragraph was added including information about metallic frameworks as well as new references.

“Metal framework reinforcements can be added to complete or partial dentures of-fering certain advantages such as light weight (compared with thick denture bases), increased patient comfort (due minimal thickness of the metal framework less invasion of the intraoral spaces), high strength, excellent biocompatibility, and increased fracture toughness [18,19], in addition metal frameworks can be casted or digitally manufactured [20]. In general, frameworks can be fabricated by casting methods using different metallic alloys including Cobalt-Chromium (Co-Cr), Titanium (Ti), and Gold (Au). [21] “

 

Q5. Add visual aids to illustrate fracture locations and materials used.

Response 5. Red arrows and landmarks are included in the composed figure 6.

Q6, Materials and Methods section also needs more clarity and visual aids. Please: Specify the number of samples more clearly and explain how subgroups were created.

Response 6. The sample size analysis was added as subsection 2.1 and the remaining subsections of were renumbered, in addition, a figure 1 showing the sample distribution was also added and the rest of figures renumbered accordingly. In addition, Figure 2a, and 2b shown the samples side to side to help the reader understand the groups.

 

Q7. Include images of the CAD models and fabricated samples with dimensions and scale.

Response 7. The image of the CAD model is only one, exported as an .stl file to the printing or milling units. You can find attached as an appendix the STL model of the bar used to fabricate all the samples.

Q8. Clarify the process for calculating fracture toughness from the energy required to fracture the samples.

Response 8. Thanks for your comment. We completed an impact fracture test which allowed us to register the energy required to fracture the samples.  The subsection 2.3 was renamed from “fracture toughness” to “Impact fracture test” In addition, the description for the impact fracture test was improved as follows “After the bending tests and stress/strain curves were completed. The remaining 33 samples were tested using a Tinius Olsen IT-503/504 impact tester machine (Tinius Olsen Testing Machine Co, Horsham, PA, USA) equipped with a 5.5 J pendulum. Un-notched impact tests were performed on all the samples to evaluate the energy required to fracture them. Initially, calibration was necessary to ensure the stabilization of the samples in the sample holder and to verify that the center of the samples was aligned with the tip of the pendulum. The center was identified using a digital caliper, and the location was marked with a pen. Calibration confirmed that 30 mm was the center of the samples, coinciding with the pendulum tip. Finally, the impact tests were conducted using samples with dimensions: width (10 mm), thickness (4 mm), and length (60 mm). The impact fracture values were recorded in kJ/m² (kilojoules per square meter of cross-section)”

Q9. The results section also require more clarification and additional visuals. Please: Provide more details on how fracture toughness was calculated.                                                        

Response 9.  The following modifications were added to the fracture toughness test.  As mentioned in the previous comment, the following paragraph was added to the method. “After the bending tests and stress/strain curves were completed. The remaining 33 samples were tested in a Tinius Olsen IT-503/504 impact tester machine (Tinius Olsen Testing Machine Co, Horsham, PA, USA) with a 5.5 J pendulum. Unnotched impact tests were completed for all the samples. With this test, we evaluated the energy required to fracture the samples. Calibration was needed first, to evaluate the stabilization of the samples in the sample holder, and second to determine that center of the samples was centered with tip of the pendulum point. The center of the samples was identified using a digital caliper and a pen was used to mark the location The calibration allowed to confirm that 30mm was the center of the samples and that point was coincident with the pendulum tip. Finally, the impact tested was programmed with the dimensions of the samples: width (10mm), thickness (4mm), and length (60mm). The impact fracture values were recorded in kJ/m2 (kilojoules/cross section of the samples).”

Q10.  Include images or graphs of the stress/strai curves and fracture analysis results.                             

Response 10. New Images were included 2a, 2b, and the stress/strain figures are now presented as figures 3a, 3b, and 3c to improve the quality. The remaining figures of the whole manuscript were renumbered

Q11. Ensure the terminology and descriptions are consistent and clear.  

Response 11. We revised descriptions and terminology as recommended by the reviewer.

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Q12. High variability in deformation values for printed samples indicates inconsistencies that need to be addressed for reliable application.                                                                                                             Response 12. Thanks for your comment. The following paragraph was added to the discussion section as well as new supporting references. “The elastic deformations suffered by the 3D-printed samples resulted in higher standard deviations. This was produced by the nature of the 3D-printed material more than produced by inconsistencies in the experiment. Printed materials fabricated by printing of liquid resins, possess inherent defects created during the printing process. These include porosity, line separation, and gaps which certainly possess an impact on the mechanical strength. Meanwhile, the pucks used for milling denture base materials are fabricated under standardized conditions of pressure and temperature, resulting in a denser structure with minimal porosity and improved mechanical properties. [33-35]. “

Q13. The discussion section needs some revision. Please  emphasize the practical implications of the findings for clinical dentistry.                                           

Response 13.  Thanks for your comment the following paragraphs were rewritten:

“4.1 Practical implications

The results of the present experimental study demonstrated that 3D-printed samples experience higher elastic deformation. Thus, 3D-printed complete dentures will expe-rience deformation (flexing), and unstable occlusion under increased axial and non-axial loads (like these produced clenching and bruxism). Furthermore, the lack of rigidity of 3D-printed denture bases can result in inefficient or reduced bite force, thus, reducing the chewing efficiency.  In contrast, milled + reinforced samples and milled samples present lower elastic deformation, which will result in more stable occlusion and higher masticatory efficiency.  The resistance to impact fracture is superior in milled samples with framework, compared to milled samples and printed samples.   Therefore, based on the results of this it is encouraged to add a reinforcement method to any CADCAM denture base materials. This is especially true, in 3D-printed denture base materials. The fracture type of printed samples was shattered and occurred in multiple directions with multiple fracture facets, material chipping, and material loss. The clinical implication is that in case of an impact the 3#-printed denture may broke in multiple pieces which may preclude repair.”

Q14. Suggest potential future research directions based on the study's limitations and findings.                 Response 14. Many thanks for your commendations. The following paragraph was added before the conclusions.

4.2 Opportunities for research

Different aspects require further exploration including: the effect of the CADCAM ma-terial thickness in reinforced versus non-reinforced CADCAM denture bases, inclusion of a control group conventionally fabricated to compare with reinforced and non-reinforced denture base materials, evaluate the effect of ageing (thermocycling) on the mechanical properties of reinforced versus non-reinforced CADCAM materials, and investigate if the reinforcement leaks to the oral environment.  

 

 

 

 

Q15. Conclusion section is insufficient. Please use bullet points to revise the conclusions.                                 

Response 15. The conclusions were rewritten as bullet points following your recommendations as follows:

 “Within the limitations of this experimental study, the null hypothesis is rejected. 

-Milled samples with an embedded 3D-printed titanium framework possesses higher resistance to impact than milled samples without framework and printed samples.

-Milled samples with an embedded 3d-printed titanium framework present increased flexural strength and lower elastic deformation compared to milled samples without framework and printed samples. “

 

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

Dear Reviewer many thanks for your comments. 

Sincerely, 

The authors

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for including my comments and suggestions in your report. However, I have few more concerns. 

1. Figures 2b and 6 require clearly annotated labels and scales.

2. Please revise the conclusions section at your discretion.

3. Here and there the units are written as m2 instead of m².

Thank you.

 

Author Response

Dear Reviewer many thanks for your comments and for pointing out areas of improvement. 

In relation to your concerns here are the point by point answers: 

1. Figures 2b and 6 require clearly annotated labels and scales.                                                  Response: Labels and scales were added to figure 2b. In regards to Figure 6, to improve the quality, the figure was separated in figures 6, 7, and 8.  The labels added and captions added to each of the new figures 6, 7, and 8

2. Please revise the conclusions section at your discretion.                                                                         Response: The conclusions  were rewritten for clarity as follows:

Within the limitations of this experimental study, the null hypothesis can be rejected. The study found that milled denture base material, printed denture base material, and milled denture base material with an embedded metallic framework exhibit different flexural strength and impact fracture toughness.

Thus, the following can be concluded:

First, milled samples with an embedded 3D-printed titanium framework demonstrate higher resistance to impact compared to milled samples without a framework and printed samples.

Second, milled samples with an embedded 3D-printed titanium framework show increased flexural strength and lower elastic deformation compared to milled samples without a framework and printed samples.

Third, printed denture base material exhibits the lowest resistance to impact and the lowest flexural strength compared to milled denture base materials with and without a framework."

3. Here and there the units are written as m2 instead of m².                                                                         Response: We revised the whole text to be sure that the units were consistent and replaced m2 by m²

Sincere thanks for your time and effort.