Effectiveness of Various Cleaning Protocols in Enhancing Resin–Zirconia Bond Strength After Saliva Contamination

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript investigates the effect of different cleansing protocols on the micro-shear bond strength between resin cement and high-translucency zirconia after saliva contamination. However, the author focus on saliva contamination, but they did not include a control group without contamination. This is unprofessional and weakens the study.XPS only shows the surface elements, which can easily be contaminated by air (C, N, O). Using the N signal from XPS to judge the cleaning effect is not reliable. 

This study aims to evaluate different cleaning protocols on the micro-shear bond strength between resin cement and high-translucency zirconia after saliva contamination. The topic is clinically relevant, but the experiment has a fundamental flaw: there is no control group without contamination. By omitting a clean baseline, the study cannot distinguish whether the results are due to the cleaning protocols or simply the presence of saliva. This disconnects the work from its own research question.

Because of this issue, the study does not fill any meaningful gap in the field and provides no solid new insight compared with existing literature. The conclusions are built on an incomplete experimental design and therefore do not truly answer the main question.

Author Response

Reviewer 1

 

Dear Reviewer,

We would like to thank you for your constructive and thoughtful comments regarding our manuscript titled:“[Effectiveness of Various Cleaning Protocols in Enhancing Resin-Zirconia Bond Strength After Saliva Contamination] ” (Manuscript ID: [prosthesis-3881120]).

We have carefully considered all suggestions and revised the manuscript accordingly. Below, we provide a point-by-point response to each comment.

Comment 1:

Response: We thank the reviewer for the detailed evaluation. We respectfully address the three main concerns raised:

The study design has been revised to explicitly include a clean, non-contaminated zirconia group, which is now defined as the (Control Group). This group did not undergo saliva contamination or any cleaning procedure and serves as the baseline for comparison with all other experimental groups.

The inclusion of this control group provides a clear reference condition and allows a more accurate assessment of the effect of each cleaning protocol on micro-shear bond strength. We also clarify that uncontaminated specimens were already used as a reference in the experimental workflow, but in the original version they were not explicitly labeled and presented as a standalone “Control Group.” In the revised manuscript, this baseline group is now fully defined, described in the Materials and Methods, and statistically reported in the Results and Tables.

We appreciate the reviewer’s comment, which helped improve the clarity and completeness of the study.

Modification to Manuscript:

1. This revision can be found on page 1, between lines 27 and 30

Among the tested groups, the control group exhibited the highest µSBS value (59.5 ± 4.2 MPa), followed by Ivoclean (56.7 ± 4.8 MPa), phosphoric acid + ethanol (46.8 ± 4.7 MPa), and sodium hypochlorite (41.1 ± 5.7 MPa), with the lowest value observed with water (33.5 ± 6.3 MPa).

 

2. This revision can be found on page 4, between lines 139 and 159

 

 To assess the effectiveness of different surface decontamination methods on the μSBS between resin cement and saliva-contaminated zirconia, four different cleaning protocols were tested. A total of 50 zirconia specimens were divided randomly into five groups (n = 10 per group). The first group served as an uncontaminated control, while the remaining groups were contaminated with saliva and cleaned using different protocols. The experimental groups are summarised below.

 

1. Control group: specimens were not contaminated and did not undergo any cleaning.
2. Distilled Water: contaminated specimens were rinsed with distilled water for 30 seconds and air-dried for 10 seconds.
3. Sodium Hypochlorite (5.25%): After air-drying, contaminated specimens were treated with 5.25% NaOCl (Promida, Istanbul, Turkey) for 30 seconds using gentle agitation, then rinsed with tap water and air-dried [16].
4. Phosphoric Acid (37%) + Ethanol (96%): Contaminated surfaces were cleaned with 37% phosphoric acid (Ivoclar Vivadent, Schaan, Liechtenstein) for 30 seconds, rinsed thoroughly, air-dried, then immersed in 96% ethanol (Aljoud, Baghdad, Iraq) for 2 minutes, before final air-drying.
5. Ivoclean: Contaminated specimens were treated with Ivoclean (Ivoclar Vivadent, Liechtenstein) for 20 seconds, rinsed with tap water, and air-dried.

 

3. This revision can be found on page 7-8, between lines 236 and 254

 

Results

            Descriptive Statistics

A total of 50 µSBS values were recorded from the five groups with different surface decontamination protocols. The minimum, maximum, standard deviation, and mean of each group are given in Table 1. The group treated with water demonstrated the lowest mean µSBS (33.5 ± 6.3 MPa). The control group demonstrated the highest bond (59.5 ± 4.2 MPa), followed by Ivoclean (56.7±4.8 MPa). Normality testing confirmed a normal distribution for all groups (p > 0.05). One-way ANOVA indicated significant differences in µSBS between the five groups (p < 0.009), as presented in Table 2. Post hoc Tukey's HSD test, presented in Table 3, revealed significant differences among most group pairs, except between control and Ivoclean, and NaOCl and H₃PO₄ + ethanol (p > 0.05).

 

 Table 1. Descriptive statistics of µSBS (MPa).

Groups	N	Minimum	Maximum	Mean	SD	SE
Control Group	10	52.0	66.0	59.5	4.2	1.5
H2O	10	25.0	43.0	33.5	6.3	1.9
NaOCl	10	30.0	46.0	41.1	5.7	1.8
H3PO4+Ethanol	10	40.0	51.0	46.8	4.7	1.5
Ivoclean	10	50.0	63.0	56.7	4.8	1.5

 

 

Table 2.One-way ANOVA results between groups (Control,H2O, NaOCl, H3PO4 + Ethanol, Ivoclean)

 

Microshear
Groups	N	Mean	SD	Statistics	df	P-Value
Control	10	59.5	4.2	42.4	4	< 0.009
H2O	10	33.5	6.3
NaOCl	10	41.1	5.7
H3PO4+Ethanol	10	46.8	4.7
Ivoclean	10	56.7	4.8

 

 

Table 3. Tukey HSD Test Results Among Different Groups.

 

Post hoc Pairwise differentiation (Tukey HSD)
(I) Group	(J) Group	Mean difference (I-J)	Std. Error	P-Value
Control	H2O	26.0	4.3	<0.001
	NaOCl	18.4	4.3	<0.001
	H3PO4+Ethanol	13.3	4.3	<0.001
	Ivoclean	3.2	4.3	0.5
H2O	NaOCl	-7.6	2.4	0.02
	H3PO4+Ethanol	-13.3	4.0	<0.001
	Ivoclean	-23.2	4.0	<0.001
NaOCl	H3PO4+Ethanol	-5.7	4.0	0.1
	Ivoclean	-15.6	4.0	<0.001
H3PO4+Ethanol	Ivoclean	-9.9	4.0	0.002

 

 

4. This revision can be found on page 11, between lines 315 and 325

 

The results of this study indicate that a clean, non-contaminated zirconia surface has the highest µSBS, consistent with its surface characteristics. Elemental analysis showed that this surface was dominated by zirconium and exhibited only minor carbon and oxygen signals, indicating minimal organic deposition. XPS further supported this observation: no nitrogen (N1s) was detected on the clean surface, consistent with the absence of adsorbed salivary protein. In addition, the clean zirconia showed the lowest contact angle value among all groups, reflecting a more wettable surface. Together, these findings indicate that an uncontaminated zirconia surface remains chemically available for interaction with functional phosphate monomers, which is essential for durable bonding to resin cement. These observations are consistent with previous reports that emphasise preserving a clean zirconia surface as critical for achieving predictable adhesion in restorative dentistry [25,26].

 

Comment 2: XPS only shows the surface elements, which can easily be contaminated by air (C, N, O). Using the N signal from XPS to judge the cleaning effect is not reliable.

Response: We thank the reviewer for this comment. We agree that XPS is intrinsically surface-sensitive and that adventitious carbon and oxygen may originate from ambient exposure. For this reason, we did not interpret the XPS data using a single element in isolation. Instead, we evaluated the full surface chemistry pattern, including N1s, C1s, O1s, and Zr3d.

In our study, nitrogen (N1s) was not detected on the uncontaminated zirconia surface, but it appeared after saliva exposure and decreased again following decontamination. This behavior is consistent with the presence and subsequent removal of salivary proteinaceous residues, because nitrogen is a characteristic component of adsorbed salivary proteins. Importantly, this nitrogen signal did not occur randomly; it co-occurred with an increase in surface carbon and a marked reduction in the Zr3d signal after contamination, indicating that the zirconia was covered by an organic overlayer rather than cleanly exposed.

After cleaning, XPS showed a partial recovery of the Zr3d contribution together with a reduction in carbon and, in most protocols, a reduction or disappearance of nitrogen. These trends were in agreement with our FTIR and SEM findings, which also confirmed the presence of saliva-derived organic films on contaminated samples and their progressive removal after cleaning.

Taken together, these correlated observations indicate that the cleaning protocols – particularly the more effective ones – helped re-expose bonding-relevant zirconia surfaces, rather than relying on the N1s signal alone as a surrogate for cleanliness.

 

 

Comment 3: Clinical relevance and contribution

Response : We agree that clinical relevance is essential. The present study specifically investigates high-translucency 5Y-TZP zirconia, which differs from conventional 3Y-TZP in yttria content, optical behavior, and transformation toughening. This newer class of zirconia is increasingly used in anterior and aesthetic regions, but—unlike silica-based ceramics—it cannot be predictably etched and silanized. As a result, long-term success becomes highly dependent on reliable chemical bonding to resin cements after intraoral try-in and saliva exposure.

In this context, decontamination is not a purely laboratory detail; it is a clinical step that directly determines whether an MDP-containing resin cement can re-establish an effective interaction with the zirconia surface. By directly comparing common chairside cleaning approaches (water rinsing, sodium hypochlorite, phosphoric acid + ethanol) with a dedicated zirconia cleaner (Ivoclean) on saliva-contaminated 5Y-TZP, and by correlating surface chemistry (XPS/FTIR/SEM) with micro-shear bond strength, our results indicate which decontamination strategy most effectively restores a bonding-ready zirconia surface.

Therefore, the revised manuscript does not only describe contamination, but provides clinically applicable guidance for bonding high-translucency 5Y-TZP after saliva exposure — a scenario that occurs routinely during try-in.

Once again, thank you for your valuable feedback. We believe these revisions have strengthened our manuscript and clarified several key aspects.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The topic is of clinical interest. The study is well designed with many research methods in order to combine results to extract robust conclusions. The results are clear and well presented

I have only minors comments

At the beginning of the discussion, the text in the lines #294-312 are not needed, they have already been mentioned earlier, they are redundant.

Some spelling errors

#11  to evaluated the influence of various decontamination protocols on the 11

#62 «Unlike»

#149 «These»

#343  «These»

#353  «Lümkemann etal» instead of «[42] observed»

Author Response

Reviewer 2

 

Dear Reviewer,

We would like to thank you for your constructive and thoughtful comments regarding our manuscript titled:“[Effectiveness of Various Cleaning Protocols in Enhancing Resin-Zirconia Bond Strength After Saliva Contamination] ” (Manuscript ID: [prosthesis-3881120]).

We have carefully considered all suggestions and revised the manuscript accordingly. Below, we provide a point-by-point response to each comment.

Comment 1: At the beginning of the discussion, the text in the lines #294-312 are not needed, they have already been mentioned earlier, they are redundant..

Response: We thank the reviewer for the careful reading and constructive feedback. As suggested, the text between lines 294–312 at the beginning of the discussion has been removed in the revised manuscript. The Discussion now begins with a more focused and concise introduction to the interpretation of the findings.

Modification to Manuscript: This study evaluated the effect of different cleaning protocols on saliva-contaminated zirconia to identify which provides the most effective durable bond strength after simulated ageing. The cleaning method had a significant influence on bond strength, leading to the rejection of the null hypothesis that zirconia cleaning procedures would not affect its bonding to resin cement.

This revision can be found on page 11, between lines 310and 314

 

Comment 2: Some spelling errors

Response: We appreciate this suggestion; all spelling corrections have been made throughout the manuscript. We truly appreciate your time and insightful comments.

 

Thank you again for your time and guidance and valuable feedback. We believe these revisions have strengthened our manuscript and clarified several key aspects.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The current manuscript (prosthesis-3881120) investigates the influence of different decontamination protocols on the micro-shear bond strength (µSBS) between high-translucency zirconia and resin cement after salivary contamination. The study is methodologically well-structured and addresses a clinically relevant problem. The inclusion of multiple surface characterization techniques (SEM, XPS, FTIR, and contact angle) provides a comprehensive understanding of surface changes, which enhances the scientific value of the work. However, while the experimental execution is solid, the novelty is moderate, as similar comparative studies on cleaning methods have been widely reported. Before acceptance, the following points should be addressed.

1. In Discussion section, FTIR results indicate that phosphoric acid + ethanol and even water could effectively remove phospholipids, while Ivoclean still left residues. However, the µSBS results showed the highest bond strength for Ivoclean. Please expand the discussion to reconcile this inconsistency, possibly considering surface energy and the role of residual ZrO₂ particles in promoting MDP–zirconia interaction.
2. In Introduction section, although similar studies exist, this work focuses on high-translucency 5Y-TZP. Please highlight more explicitly in the Introduction why this material system requires re-evaluation of cleaning protocols compared with conventional 3Y-TZP.
3. Some grammatical errors and inconsistent units (MPa, °C) should be corrected; a light professional English editing is recommended.
   
   

    

Comments on the Quality of English Language

The English is generally understandable, but several sentences are lengthy or contain grammatical inconsistencies. Minor editing is needed to improve clarity, sentence structure, and scientific tone. A light professional language revision is recommended to enhance readability and consistency.

Author Response

Reviewer 3

Dear Reviewer,

We would like to thank you for your constructive and thoughtful comments regarding our manuscript titled:“[Effectiveness of Various Cleaning Protocols in Enhancing Resin-Zirconia Bond Strength After Saliva Contamination]”(Manuscript ID: [prosthesis-3881120]).

We have carefully considered all suggestions and revised the manuscript accordingly. Below, we provide a point-by-point response to each comment.

Comment 1: In Discussion section, FTIR results indicate that phosphoric acid + ethanol and even water could effectively remove phospholipids, while Ivoclean still left residues. However, the µSBS results showed the highest bond strength for Ivoclean. Please expand the discussion to reconcile this inconsistency, possibly considering surface energy and the role of residual ZrO₂ particles in promoting MDP–zirconia interaction

Response: We thank the reviewer for this valuable comment. FTIR in our study was primarily used to monitor phospholipid-related CH₂ bands as an indicator of salivary lipid contamination. After cleaning with water or phosphoric acid + ethanol, these bands were markedly reduced, whereas Ivoclean still showed detectable residual signal.

However, FTIR alone does not indicate whether the zirconia surface is functionally available for chemical bonding. XPS showed that after water rinsing, surface carbon and nitrogen remained high and the Zr3d signal was very low (1.04%), indicating that a thin saliva-derived organic film was still masking the zirconia surface. This explains the lowest µSBS in the water group (33.5 ± 6.3 MPa), despite the apparently “clean” FTIR response.

The phosphoric acid + ethanol protocol exposed more zirconia (Zr3d = 10.59%) and reduced surface carbon, which improved bonding strength (46.8 ± 4.7 MPa), but did not achieve the highest values.

Ivoclean behaved differently. SEM revealed zirconia-rich (ZrO₂) particles remaining on the surface. These particles act as a scavenger layer: they preferentially bind salivary phosphates and lipids and, at the same time, re-deposit zirconia-like material onto the surface. This process re-exposes chemically active zirconia/oxide sites that can interact with MDP in the primer and cement and also provides additional micromechanical retention.

As a result, Ivoclean achieved µSBS values (56.7 ± 4.8 MPa) that were comparable to the uncontaminated control (59.5 ± 4.2 MPa), even though FTIR still detected some residue. In summary, FTIR reflects phospholipid removal, but durable bonding depends on restoring MDP-reactive zirconia and creating micromechanical interlocking — which Ivoclean achieved most effectively.

 This revision can be found on page 11, between lines 371 and 383

Modification to Manuscript: FTIR of the Ivoclean-treated specimens still showed some detectable organic signal, indicating that traces of salivary residue were not completely eliminated. Taken alone, this finding could suggest incomplete decontamination. However, complementary surface analyses clarify how this group nevertheless achieved the highest bond strength values. XPS revealed a reduction in surface carbon and re-exposure of zirconium, while FESEM showed agglomerated ZrO₂ particles remaining on the surface after treatment. These ZrO₂-rich particles originate from the alkaline zirconia-based suspension and act as a scavenger layer: they preferentially bind salivary phosphate- and lipid-containing contaminants and, at the same time, re-deposit zirconia-like material on the restoration surface [29]. In practical terms, this process re-establishes chemically active zirconia/oxide sites that can interact with phosphate MDP groups in the primer and resin cement, even if small amounts of organic residue are still present [37]. In addition, ZrO₂ deposits increase the local surface texture and provide micromechanical retention sites.

Comment 2: In Introduction section, although similar studies exist, this work focuses on high-translucency 5Y-TZP. Please highlight more explicitly in the Introduction why this material system requires re-evaluation of cleaning protocols compared with conventional 3Y-TZP

Response: We agree with the reviewer and have clarified this point in the Introduction. High-translucency 5Y-TZP differs from conventional 3Y-TZP in composition and clinically relevant behavior. The higher yttria content (approximately 5 mol% vs. approximately 3 mol%) increases the cubic phase fraction, which enhances optical translucency for anterior and other highly aesthetic restorations, but at the same time reduces transformation toughening and overall flexural strength compared with traditional 3Y-TZP. As a result, long-term clinical performance becomes more dependent on reliable resin bonding rather than solely on bulk fracture resistance.

Importantly, bonding to 5Y-TZP still relies on chemical coupling (e.g., MDP–zirconia interaction) because, like 3Y-TZP, it does not contain a glassy phase and cannot be predictably etched in the same way as silica-based ceramics. This makes salivary contamination clinically critical: adsorbed phospholipids and proteins can block access to zirconia oxide sites that are required for durable chemical bonding. For this reason, we consider that cleaning protocols validated on conventional 3Y-TZP cannot simply be assumed to perform identically on high-translucency 5Y-TZP, which is now widely used in aesthetic zones. The current study directly addresses this need by evaluating different decontamination strategies on 5Y-TZP after saliva exposure.

This revision can be found on page 2, line 44-56.

Modification to Manuscript: High-translucency zirconia (5Y-TZP) is a recent generation of materials designed for highly aesthetic fixed dental restorations. Due to its higher yttria content, 5Y-TZP exhibits an increased fraction of the cubic phase and therefore greater optical translucency, better mimicking natural dentition, particularly in the anterior region [1]. This improvement in appearance, however, is accompanied by reduced transformation toughening and a moderate decrease in flexural strength compared with conventional 3Y-TZP. As a result, long-term clinical performance becomes more dependent on reliable bonding to resin cement, rather than solely on bulk fracture resistance.

Despite this, high-translucency zirconia still exhibits clinically acceptable mechanical behaviour, with reported flexural strength values in the range of approximately 800–1200 MPa, along with favourable fracture toughness. In addition, 5Y-TZP maintains key advantages associated with zirconia ceramics, including high biocompatibility, chemical stability, and resistance to intraoral degradation [2].

 

Comment 3: Some grammatical errors and inconsistent units (MPa, °C) should be corrected; a light professional English editing is recommended.

Response: We thank the reviewer for this observation. The manuscript has been revised to correct grammatical issues (e.g., sentence structure, capitalization, and spacing) and to improve clarity in the Materials and Methods, Results, Discussion, and Conclusion sections. We also standardized all units and notation throughout the text. Temperatures are now consistently reported in °C (e.g., 37 °C, 5 ± 2 °C, 55 ± 2 °C), bond strength values are expressed in MPa, and thermocycling parameters and test conditions are described using consistent wording. Also the manuscript has been edited by a professional English-language institute to improve grammar, clarity, and scientific tone. A language editing certificate can be provided if needed. We believe these edits improve the readability and technical accuracy of the manuscript.

We thank the reviewer again for the time, guidance, and constructive feedback. We believe that the revisions have strengthened the manuscript and clarified several key aspects.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript and included suitable control groups, satisfactorily addressing my previous comments. I recommend the paper for publication in its present form.