Impact of Diamond-like Carbon Films on Reverse Torque: Superior Performance in Implant Abutments with Internal Conical Connections

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article titled "The effects of diamond-like carbon films on the reverse torque of implant abutments with internal conical connections" provides a prosthetic abutments with Diamond-Like-Carbon (DLC) nano-films to evaluate their effect on the reverse torque after masticatory cycling.

 

 

Major Comments:

1.     Despite mentioning "reverse torque," the title doesn't explain what this statistic means or where it fits in. Could it be made more clear by include a sentence explaining the significance of reverse torque in relation to implant abutments?

2.     Consider revising the title to reflect the key findings or specific focus on Diamond-Like Carbon (DLC) films.

3.     Abstarct: A general reader may find the mention of "seventy-eight sets" and the specific angles overwhelming; think of a more concise way to summarize this.

4.     Although the introduction gives a decent summary of the issue, it may be improved by going into further detail on the present shortcomings of the coatings that are now in use and how DLC fills in these gaps.

5.     The null hypotheses are spelled out in detail, however the reasoning for the selection of these particular hypotheses is not provided. To give the study a better base, think about developing on this.

6.     While intriguing, the selection of 8º and 11º taper sizes is not entirely sound. Could the writers elaborate on the selection process for these specific angles? Is there proof that these angles matter in a therapeutic setting?

7.     The samples have been grouped clearly, but may more control groups—such as those with various coatings or untreated groups under various circumstances—have been taken into account?

8.     There is no explanation for the sample size of 13, which was utilized for each group. Was a power analysis performed to evaluate the suitability of this sample size for identifying meaningful differences?

9.     It is explained how to install abutments using a digital torque meter, but to guarantee consistency, further information on the process of measuring and verifying torque values has to be provided.

10.  Although they employed the Kruskal-Wallis and Dunn's tests, the authors ought to elaborate on their selection of non-parametric tests. Was the normalcy of the data checked?

11.  Although the authors discovered notable variations in torque loss throughout groups, they do not address the clinical significance of these variations. In what ways might these variations affect possible clinical results?

 

12.  The possible consequences of various clinical circumstances (such as differing bone densities and patient behaviours) that were not replicated in this study ought to be discussed.

Author Response

Major Comments:

 

1. Despite mentioning "reverse torque," the title doesn't explain what this statistic means or where it fits in. Could it be made more clear by include a sentence explaining the significance of reverse torque in relation to implant abutments?

It was included in Introduction:

Reverse torque, the force required to remove an implant abutment, is crucial for assessing the mechanical stability of implant-abutment connections. Studies have shown that both indexed and non-indexed abutments experience significant torque loss after insertion[1,2]. However, non-indexed abutments generally demonstrate better torque retention compared to indexed ones[3]. The implant material also influences reverse torque values, with hydroxyapatite-coated implants exhibiting significantly higher torque removal values than titanium implants[4]. Additionally, mandibular implants tend to show greater torque resistance than maxillary implants. These findings suggest that factors such as abutment design, implant material, and placement location play important roles in maintaining implant stability. Understanding reverse torque values is essential for determining appropriate torque levels for abutment fastening and ensuring the long-term success of implant-supported restorations[1].

 

 

2. Consider revising the title to reflect the key findings or specific focus on Diamond-Like Carbon (DLC) films.

Title was changed to: Impact of Diamond-Like Carbon Films on Reverse Torque: Superior Performance in Implant Abutments with Internal Conical Connections

 

3. Abstract: A general reader may find the mention of "seventy-eight sets" and the specific angles overwhelming; think of a more concise way to summarize this.

The abstract was changed to: The loosening or fracture of the prosthetic abutment screw is the most frequently reported complication of implant dentistry. Thin diamond-type carbon (DLC) films offer a low friction coefficient and high wear resistance, functioning as a solid lubricant to prevent the weakening of the implant-abutment system. This study evaluated the effects of DLC nanofilms on the reverse torque of prosthetic abutments after simulated chewing. Abutments with 8º and 11º taper connections, with and without DLC or silver-doped DLC coatings, were tested. The films were deposited through the Plasma Enhanced Chemical Vapor Deposition process. After 2 million cycles of mechanical loading, reverse torque was measured. Analyses with Scanning Electron Microscopy were conducted on three samples of each group before and after mechanical cycling to verify the adaptation of the abutments. Tribology, Raman and Energy-dispersive spectroscopy analyses were performed. All groups showed a reduction in insertion torque, except the DLC-coated 8º abutments, which demonstrated increased reverse torque. The 11º taper groups experienced the most torque loss. The nanofilm had no significant effect on maintaining insertion torque, except for the DLC8 group, which showed improved performance.

 

4. Although the introduction gives a decent summary of the issue, it may be improved by going into further detail on the present shortcomings of the coatings that are now in use and how DLC fills in these gaps.

It was added

When searching the literature, the coatings used in implant dentistry are intended for the prior preparation of the implant and consider their advantages in the osseointegration process. For example, common coating materials include carbon, bisphosphonates, bioactive glass, fluoride, hydroxyapatite (HA), and titanium nitride (TiN)[5]. HA remains the most biocompatible, while bioglass shows promise. TiN coatings may reduce bacterial colonization, enhance fibroblast proliferation, and improve mechanical properties [6]. The use of DLC film on screws shows another perspective on the use of coatings, as a solid lubricant in the fixation of prostheses, aiming at the perfect coupling of prosthetic components on implants.

 

 

5. The null hypotheses are spelled out in detail, however the reasoning for the selection of these particular hypotheses is not provided. To give the study a better base, think about developing on this.

Null hypotheses were rewritten: There is no influence of the presence of films on the reverse torque after mechanical cycling. Reverse torque is a critical parameter in assessing the long-term stability of dental implants, as it reflects the ability of the abutment to resist loosening under functional loads. By testing this null hypothesis, the study aimed to determine whether the application of nanofilms introduces any beneficial or detrimental effects on the reverse torque, which could influence clinical outcomes.

• DLC coating does not present different mechanical behavior comparing to silver nanoparticles doped DLC coating. This hypothesis was formulated to compare the mechanical performance of two different types of coatings: pure DLC and silver-doped DLC. Silver doping is known for its antimicrobial properties, but it is important to evaluate whether adding silver nanoparticles affects the mechanical integrity of the coating, particularly in terms of reverse torque after mechanical cycling. By examining this hypothesis, the study sought to clarify whether silver doping compromises the mechanical benefits of DLC or enhances it without negatively impacting reverse torque stability.
• The DLC films do not interfere in the reverse torque independently of abutment walls angulations (8º and 11º). The angulation of the abutment walls can influence the mechanical interaction between the abutment and the implant, potentially affecting the distribution of stresses and the overall stability of the connection. This hypothesis was crucial to determine whether the mechanical benefits or potential drawbacks of DLC films are consistent across different abutment designs, or if they are dependent on specific geometric factors.

 

6. While intriguing, the selection of 8º and 11º taper sizes is not entirely sound. Could the writers elaborate on the selection process for these specific angles? Is there proof that these angles matter in a therapeutic setting?

It was added: Implants with conical connections are generally manufactured with a difference in the angles of the conicities between the implant and the abutment. This fact directly influences the behavior of the implant system in general, the size of the microgap, the tension generated in the bone tissue, the loss of preload of the screw and, in particular, the removal torque[7]. Tapered implants showing advantages in low-density bone and immediate loading scenarios, increasing primary stability and minimize stability loss at compression sites[8]. Research on dental implant taper angles suggests that increasing the abutment taper angle can significantly improve fracture resistance, with 8° and 10° angles showing higher fracture forces compared to 6°[9]. When comparing internal conical connections with different taper angles (5.4°, 12°, 45°, and 60°), no significant differences were found in bacterial leakage under dynamic loading conditions. [10].

 

 

7. The samples have been grouped clearly, but may more control groups—such as those with various coatings or untreated groups under various circumstances—have been taken into account?

The groups tested and considered were those presented in the research. We appreciate the suggestion that will be taken into consideration for future studies.

 

8. There is no explanation for the sample size of 13, which was utilized for each group. Was a power analysis performed to evaluate the suitability of this sample size for identifying meaningful differences?

It was added: The sample size was based on the previous study from Figueiredo et al. that adopt a significance level of 5%, a beta power of 80%, using the Bonding test data, determining a total of 8 samples.

 

 

9. It is explained how to install abutments using a digital torque meter, but to guarantee consistency, further information on the process of measuring and verifying torque values has to be provided.

It was added: Briefly, the implants were positioned such that the platform was precisely located at a height of 3.0 ± 0.5 mm above the surface of the fixation block. The installation process employed specialized wrenches tailored for the specific implants used (codes CMSWA and 612.305, Titaniumfix, São José dos Campos, Brazil), in conjunction with a calibrated torque wrench. A digital caliper (Digimess, Nikeypar) was utilized to accurately verify the installation height. Subsequently, the abutments were affixed using a torque wrench explicitly designed for the installation and removal of the prosthetic abutments in use (code CMDTAC, Titaniumfix, São José dos Campos, Brazil), with the tightening torque applied via a digital torque wrench (TQ-680, Instrutherm, São Paulo, Brazil) featuring a precision of 0.01 Ncm. The tightening torque was administered following the manufacturer's specifications, applying 32 Ncm for the Solid abutment and 20 Ncm for the Direct abutment. Ten minutes after the initial tightening, the same torque value was reapplied. Upon achieving the desired tightening torque, the hemispherical loading devices were meticulously positioned on the abutments.

 

10. Although they employed the Kruskal-Wallis and Dunn's tests, the authors ought to elaborate on their selection of non-parametric tests. Was the normalcy of the data checked?

It was added The data were tested for normality by the Kolmogorov-Smirnov Normality Test.

11. Although the authors discovered notable variations in torque loss throughout groups, they do not address the clinical significance of these variations. In what ways might these variations affect possible clinical results?

It was added:

The results of the present study, particularly the differences in coating types (DLC vs. silver-doped DLC) and abutment angulations (8º vs. 11º), can have several potential impacts on clinical outcomes. DLC8 group showed superior reverse torque compared to other groups, including those with silver-doped DLC. This suggests that the DLC coating might provide better mechanical stability, reducing the risk of abutment loosening. In clinical practice, this could translate to longer-lasting implant stability, less frequent need for adjustments or re-tightening, and a lower risk of complications related to screw loosening, reducing overall healthcare costs and improving patient satisfaction.

DLC coatings are known for their hardness and wear resistance[11], which can reduce material wear over time. In contrast, the addition of silver nanoparticles, that could offer antimicrobial properties[12] reducing the risk of peri-implantitis, altered the mechanical properties of the coating. The silver-doped DLC demonstrates lower mechanical stability, fasting the wear, potentially shortening the lifespan of the abutment and increasing the need for earlier intervention or replacement. The study showed that 11º abutments experienced higher torque loss than 8º abutments. Clinically, this could mean that implants with a steeper taper (11º) might be more prone to loosening over time, especially if not coupled with an optimal coating. This could lead to a higher likelihood of abutment failure, necessitating more frequent follow-ups, retightening, or even implant replacement. [13]

12. The possible consequences of various clinical circumstances (such as differing bone densities and patient behaviors’) that were not replicated in this study ought to be discussed.

It was added:

Bone density is a critical factor in the success of dental implants and the planning of treatment. Various preoperative methods exist for assessing jawbone density, many of which show strong correlations with clinical outcomes [14]. Computed tomography provides valuable insights into bone quality before implant placement, highlighting significant variations in density across different oral regions [13]. The anterior mandible typically exhibits the highest bone density, followed by the anterior maxilla, posterior mandible, and posterior maxilla [13]. Additionally, bone density varies significantly between individuals and even within different areas of the same jaw [15]. Factors such as bone quality, bone quantity, and overall patient health are critical to implant success [16]. While it is generally observed that women have lower bone density than men, no significant correlation has been established between bone density and patient age [15]. These findings underscore the importance of carefully selecting the abutment angulation and conducting a patient-specific assessment to customize implant treatment according to each patient’s unique anatomical and functional needs. For example, a patient with higher occlusal forces might benefit more from an 8º abutment with a diamond-like carbon (DLC) coating, which can minimize the risk of abutment loosening and enhance long-term stability.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1. The abstract is poorly structured and redundant, and authors should carefully revise the abstract to be informative and concise, highlighting the main research questions, the data and methods used, the main findings, and the significance of the study.

2. In the introduction section, the background on the use of DLC coatings in other medical fields is slightly brief, and it is suggested that this section be expanded to more fully demonstrate the versatility and potential applications of DLC coatings..

3. Discuss how this study expands on or differs from existing research, pointing out gaps in the existing literature and the contributions of this thesis.

4. Literature 8 in the manuscript is incorrectly formatted and should be changed to "[8]".

5. There is an error in formatting between lines 212 and 213 in the manuscript, is line 212 a bullet point or is it the same sentence as below?

6. The explanation for the higher torque exhibited by the DLC8 group is insufficient, and it is suggested that possible reasons, such as the effect of coating thickness or material properties, be further explored.

7. For the physical and chemical properties of the DLC coatings, more detailed characterization data, such as coating thickness, hardness, roughness, etc., could be provided to enhance the completeness of the technical details.

8. Overly broad statements should be avoided in the conclusion section, and a more specific description of the significance of the research findings and their limitations is recommended.

9. A discussion of the limitations of this study could have been added at the appropriate place in the paper, and the authors also acknowledge sources of error and uncertainty and discuss potential applications and extensions of the study.

10. Kruskal-Wallis and Mann-Whitney tests were used to analyze the data, and the final result stated that the data did not present a normal distribution. Here you can add some visualizations instead of simple descriptions.

11. Although the thickness of DLC and silver-doped DLC coatings is mentioned, the potential effect of thickness on mechanical properties is not discussed. It is suggested to add some discussion on the influence of different thickness DLC coatings on the experimental results, or provide relevant literature support.

12. The current experiment only focuses on the short-term mechanical cycling effect. Although the author proposes to increase the number of cycles in a short period of time to simulate the long-term cycling effect, it is suggested to add some data support related to the number of long-term cycles to ensure the effectiveness of multiple cycles in the short term.

13. In this paper, the effect of DLC coating on torque loss is discussed only from the data results, but the mechanism of action is not discussed. It is recommended to add a section that properly explains the mechanism by which DLC coatings can affect torque loss by reducing the coefficient of friction or other means.

14. It is recommended that the discussion address in more detail the practical implications of the experimental results in clinical practice, especially the potential of DLC coatings to improve the long-term stability of implants and reduce complications.

Author Response

Comments and Suggestions for Authors

1. The abstract is poorly structured and redundant, and authors should carefully revise the abstract to be informative and concise, highlighting the main research questions, the data and methods used, the main findings, and the significance of the study.

The abstract was changed to: The loosening or fracture of the prosthetic abutment screw is the most frequently reported complication of implant dentistry. Thin diamond-type carbon (DLC) films offer a low friction coefficient and high wear resistance, functioning as a solid lubricant to prevent the weakening of the implant-abutment system. This study evaluated the effects of DLC nanofilms on the reverse torque of prosthetic abutments after simulated chewing. Abutments with 8º and 11º taper connections, with and without DLC or silver-doped DLC coatings, were tested. The films were deposited through the Plasma Enhanced Chemical Vapor Deposition process. After 2 million cycles of mechanical loading, reverse torque was measured. Analyses with Scanning Electron Microscopy were conducted on three samples of each group before and after mechanical cycling to verify the adaptation of the abutments. Tribology, Raman and Energy-dispersive spectroscopy analyses were performed. All groups showed a reduction in insertion torque, except the DLC-coated 8º abutments, which demonstrated increased reverse torque. The 11º taper groups experienced the most torque loss. The nanofilm had no significant effect on maintaining insertion torque, except for the DLC8 group, which showed improved performance.

 

 

2. In the introduction section, the background on the use of DLC coatings in other medical fields is slightly brief, and it is suggested that this section be expanded to more fully demonstrate the versatility and potential applications of DLC coatings.

It was added: The unique properties of DLC coatings depend on the ratio of sp3/sp2 phases, which can be tailored for specific applications[18]. These coatings are widely used in orthopedic, cardiovascular, and dental applications, for various biomedical devices such as vascular stents, prosthetic heart valves, and surgical instruments[19]. Known for their hemocompatibility, they are applied to artificial heart surfaces in contact with blood and are effective in pressure sensors, chemical electrodes, and biochemical sensors. They promote rapid endothelization of implants, minimize platelet activation, and reduce thrombus formation. DLC coatings are considered highly promising for biomedical applications, with growing potential in automotive and adhesive uses as well[18,19].

 

3. Discuss how this study expands on or differs from existing research, pointing out gaps in the existing literature and the contributions of this thesis.

It was added clinical significance: The results of the present study, particularly the differences in coating types (DLC vs. silver-doped DLC) and abutment angulations (8º vs. 11º), can have several potential impacts on clinical outcomes. DLC8 group showed superior reverse torque compared to other groups, including those with silver-doped DLC. This suggests that the DLC coating might provide better mechanical stability, reducing the risk of abutment loosening. In clinical practice, this could translate to longer-lasting implant stability, less frequent need for adjustments or re-tightening, and a lower risk of complications related to screw loosening, reducing overall healthcare costs and improving patient satisfaction.

DLC coatings are known for their hardness and wear resistance[11], which can reduce material wear over time. In contrast, the addition of silver nanoparticles, that could offer antimicrobial properties[12] reducing the risk of peri-implantitis, altered the mechanical properties of the coating. The silver-doped DLC demonstrates lower mechanical stability, fasting the wear, potentially shortening the lifespan of the abutment and increasing the need for earlier intervention or replacement. The study showed that 11º abutments experienced higher torque loss than 8º abutments. Clinically, this could mean that implants with a steeper taper (11º) might be more prone to loosening over time, especially if not coupled with an optimal coating. This could lead to a higher likelihood of abutment failure, necessitating more frequent follow-ups, retightening, or even implant replacement. [13]

It was added existing research, pointing out gaps:

 Some studies have evaluated the performance of coated dental prosthetic abutments under simulated masticatory loads and torque tests. Diamond-like carbon (DLC) coatings on abutments showed mixed results. One study found that DLC coating reduced screw loosening after mechanical cycling[43]. However, another study reported no improvement in torque maintenance for DLC-coated screws with or without diamond nanoparticles[44]. Bacchi et al. (2015)[45] observed that conventional titanium screws maintained higher loosening torque values than DLC-coated screws after cyclic loading. For zirconia abutments, a study found that ceramic coating did not significantly affect their mechanical behavior under static and dynamic loading conditions[46]. These studies demonstrate that while various coatings have been investigated for dental prosthetic abutments, their effectiveness in maintaining torque and mechanical stability varies, highlighting the need for further research in this area.

 

4. Literature 8 in the manuscript is incorrectly formatted and should be changed to "[8]".

The formatting of citations and references has been revised. Sorry for the error.

5. There is an error in formatting between lines 212 and 213 in the manuscript, is line 212 a bullet point or is it the same sentence as below?

It was a type error. We apologize for our mistake.

6. The explanation for the higher torque exhibited by the DLC8 group is insufficient, and it is suggested that possible reasons, such as the effect of coating thickness or material properties, be further explored.

Screw joint failure begins with external functional loading, which gradually reduces the pre-load in the joint. The DLC layer's lower friction coefficient and greater hardness compared to pure titanium may help prevent implant abrasion, erosion, and deformation[48]. The superior torque results in DLC8 coated groups can also be explained by this. Dziedzic et al.[49] reported that the carbon coating on screw threads reduced interface friction and enhanced preload values, thereby increasing the clamping force between the abutment and implant platform. The DLC’s low friction coefficient enables greater preload with the same torque, improving joint stability.

7. For the physical and chemical properties of the DLC coatings, more detailed characterization data, such as coating thickness, hardness, roughness, etc., could be provided to enhance the completeness of the technical details.

It was added:

The thickness of the DLC nanofilm was 1.58 μm and the thickness of the DLC-Ag nanofilm was 2.91 μm. Since the deposition time was the same for both films, this difference in thickness is probably explained by the fact that each molecule of methane, the precursor gas for the DLC film, has only one carbon atom, while hexane, the precursor gas for the AgDLC film, has six carbon atoms.

Regarding the coefficient of friction (COF) performed using a spherical steel tip (4 mmᴓ) with a progressive load of 2 Ncm, the control group presented the higher COF (0.46 ±0.14), followed by DLC (0.15 ±0.2) and DLC-Ag (0.12 ±0.2). The low coefficient of friction and high hardness of the DLC layer  offered some benefits in preventing deformation of the implant top.

The average surface roughness, carried out through a digital optical profilometer, measurement’s (Ra - mm) were 0.4 ± 0.02 (C), 0.4 ± 0.07 (DLC) and 0.3 ± 0.01 (DLC-Ag). Ra represents the average between the values ​​of the peaks and valleys present in the tested area.

 

8. Overly broad statements should be avoided in the conclusion section, and a more specific description of the significance of the research findings and their limitations is recommended.

It was changed to: Based on the findings of this in vitro study, it can be concluded that the use of diamond-like carbon (DLC) coatings, particularly with an 8º abutment angulation, significantly enhances the mechanical stability of abutment screws by minimizing torque loss after load cycling. The DLC coating proved more effective than silver-doped DLC, which exhibited reduced mechanical stability. These results suggest that DLC-coated abutments may offer greater implant longevity and fewer complications related to screw loosening in clinical settings. However, the study's limitations include the specific conditions under which the tests were conducted, which may not fully replicate the complexities of the oral environment. Further in vivo research is necessary to validate these findings and assess the long-term clinical performance of DLC coatings in various implant scenarios.

 

9. A discussion of the limitations of this study could have been added at the appropriate place in the paper, and the authors also acknowledge sources of error and uncertainty and discuss potential applications and extensions of the study.

This study presents certain methodological limitations that could be addressed in future research. Regarding the selection of implants, to standardize the clinical scenario, implants with the same external diameter (4.0 mm) were chosen. However, these implant models exhibit specific design characteristics that influence this standardization. The implant with an 8° taper (c-fix; Titaniumfix, Brazil) features an M2.0 internal thread (2 mm diameter) and an octagonal indexing system. In contrast, the implant with an 11° taper (b-fix; Titaniumfix, Brazil) has an M1.6 internal thread (1.6 mm diameter) and a dual hexagonal indexing system. The indexing systems impact the area occupied by the taper, which may affect the active area of each implant model. Consequently, the load distribution across each thread differs, given the variation in threaded area and active taper area in each model. Future studies should consider standardizing the internal thread diameter, selecting implants with different diameters, to determine if the active taper area associated with thread diameter influences reverse torque values after mechanical cycling. The tribological analyses conducted were qualitative only. The results for the coefficient of friction, average roughness, and scratch hardness were not subjected to statistical analysis. More detailed studies are necessary to investigate whether there is a correlation between tribological results and reverse torque values. Another analysis that was not statistically tested involved scanning electron microscopy images. The assessment of taper adaptation and thread wear was purely visual, and quantitative evaluations are required for more significant and conclusive results. Additionally, regarding the adaptation of the abutments, the application of DLC and AgDLC films was carried out across the entire active area of the abutments (taper and threads), but the effect of the film on abutment adaptation was only evaluated after fatigue testing. The differences in reverse torque values between coated and uncoated abutments may not have been as apparent due to potential misadaptation in the taper area of the abutments with DLC and AgDLC films, which could have influenced the reverse torque values. Future studies should examine the thickness of the films and their influence on taper adaptation before fatigue testing to achieve film thicknesses that do not affect adaptation.

 

10. Kruskal-Wallis and Mann-Whitney tests were used to analyze the data, and the final result stated that the data did not present a normal distribution. Here you can add some visualizations instead of simple descriptions.

A new figure was added. Figure 1. Boxplot of the relative difference (%) of the torque values ​​obtained (A). Column graph of the average relative difference (%) of the torque values ​​obtained (B).

 

11. Although the thickness of DLC and silver-doped DLC coatings is mentioned, the potential effect of thickness on mechanical properties is not discussed. It is suggested to add some discussion on the influence of different thickness DLC coatings on the experimental results, or provide relevant literature support.

It was added The thickness of DLC coatings plays a significant role in their performance, with thicker coatings providing better friction reduction in elastohydrodynamic lubrication conditions[37]. Additionally, DLC coatings can serve as an effective galvanic corrosion barrier between titanium abutments and nickel-chromium superstructures without compromising the fit and integrity of prosthetic assemblies[38]. While DLC coatings have shown potential to enhance the reliability of dental implant-supported restorations, their effectiveness may vary depending on the coating method and thickness[37,39].

 

 

12. The current experiment only focuses on the short-term mechanical cycling effect. Although the author proposes to increase the number of cycles in a short period of time to simulate the long-term cycling effect, it is suggested to add some data support related to the number of long-term cycles to ensure the effectiveness of multiple cycles in the short term.

It was added: Research on mechanical cycling of implant-abutment connections reveals significant effects on their stability and performance. Short-term cycling (36x10⁴ cycles) leads to improved adaptation and sealing ability, with decreased microgap size in Morse taper connections[44]. Some studies employed long term cyclic loading using 5 million cycles as the upper limit[44–46]. Fatigue limits varied across designs, ranging from 210-240 N for different connectionsto 300-800 N in another study [45]. Internal connections generally showed higher fatigue strength than external ones, while external hex designs exhibited higher static strength[46]. Zirconia abutments demonstrated higher fatigue strength than titanium in external hex configurations[46].

 

 

13. In this paper, the effect of DLC coating on torque loss is discussed only from the data results, but the mechanism of action is not discussed. It is recommended to add a section that properly explains the mechanism by which DLC coatings can affect torque loss by reducing the coefficient of friction or other means.

It was added: Screw joint failure begins with external functional loading, which gradually reduces the pre-load in the joint. The DLC layer's lower friction coefficient and greater hardness compared to pure titanium may help prevent implant abrasion, erosion, and deformation[48]. The superior torque results in DLC8 coated groups can also be explained by this. Dziedzic et al.[49] reported that the carbon coating on screw threads reduced interface friction and enhanced preload values, thereby increasing the clamping force between the abutment and implant platform. The DLC’s low friction coefficient enables greater preload with the same torque, improving joint stability.

 

14. It is recommended that the discussion address in more detail the practical implications of the experimental results in clinical practice, especially the potential of DLC coatings to improve the long-term stability of implants and reduce complications.

It was added

The results of the present study, particularly the differences in coating types (DLC vs. silver-doped DLC) and abutment angulations (8º vs. 11º), can have several potential impacts on clinical outcomes. DLC8 group showed superior reverse torque compared to other groups, including those with silver-doped DLC. This suggests that the DLC coating might provide better mechanical stability, reducing the risk of abutment loosening. In clinical practice, this could translate to longer-lasting implant stability, less frequent need for adjustments or re-tightening, and a lower risk of complications related to screw loosening, reducing overall healthcare costs and improving patient satisfaction.

DLC coatings are known for their hardness and wear resistance[11], which can reduce material wear over time. In contrast, the addition of silver nanoparticles, that could offer antimicrobial properties[12] reducing the risk of peri-implantitis, altered the mechanical properties of the coating. The silver-doped DLC demonstrates lower mechanical stability, fasting the wear, potentially shortening the lifespan of the abutment and increasing the need for earlier intervention or replacement. The study showed that 11º abutments experienced higher torque loss than 8º abutments. Clinically, this could mean that implants with a steeper taper (11º) might be more prone to loosening over time, especially if not coupled with an optimal coating. This could lead to a higher likelihood of abutment failure, necessitating more frequent follow-ups, retightening, or even implant replacement. [13]

Bone density is a critical factor in the success of dental implants and the planning of treatment. Various preoperative methods exist for assessing jawbone density, many of which show strong correlations with clinical outcomes [14]. Computed tomography provides valuable insights into bone quality before implant placement, highlighting significant variations in density across different oral regions [13]. The anterior mandible typically exhibits the highest bone density, followed by the anterior maxilla, posterior mandible, and posterior maxilla [13]. Additionally, bone density varies significantly between individuals and even within different areas of the same jaw [15]. Factors such as bone quality, bone quantity, and overall patient health are critical to implant success [16]. While it is generally observed that women have lower bone density than men, no significant correlation has been established between bone density and patient age [15]. These findings underscore the importance of carefully selecting the abutment angulation and conducting a patient-specific assessment to customize implant treatment according to each patient’s unique anatomical and functional needs. For example, a patient with higher occlusal forces might benefit more from an 8º abutment with a diamond-like carbon (DLC) coating, which can minimize the risk of abutment loosening and enhance long-term stability.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I am satisfied with the author's reply.