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. 2023 Oct 25;18(10):e0287108. doi: 10.1371/journal.pone.0287108

Retention of zirconia crown to oxidized titanium base abutment: Experimental research

Rawikorn Krongvanitchayakul 1, Chatchai Kunavisarut 1,*
Editor: Sompop Bencharit2
PMCID: PMC10599539  PMID: 37878631

Abstract

Statement of problem

To separate the crown from the titanium base abutment, by using heat, caused oxidization of the titanium base abutment. The effect of this procedure on the retention of a crown is unclear.

Purpose

To compare the resin bond strength and failure type between zirconia crowns and titanium base abutments utilizing four different surface treatments. Surface roughness and morphology of each surface treatment were also investigated.

Material and methods

Forty titanium base abutments (Variobase®) were divided into four groups, 1. Control, 2. Air abraded, 3. Oxidized, and 4. Oxidized-air abraded. Oxidized and oxidized-air abraded groups were debonded from zirconia crowns using constant dry heat at 500 ˚C. For air abraded and oxidized-air abraded groups (after oxidization), the titanium base abutments were air abraded with Al3O2. After cleaning, one specimen of each group was investigated under a non-contact profilometer (50x), then the same samples were investigated under SEM at 25,300,500,1000 magnification and EDS at 30kV of accelerated voltage. All specimens were then cemented (RelyX Ultimate). After aging, with thermocycling under 5C° to 55C°,120 seconds dwell time for 5,000 cycles, bond strength was tested and statistical differences were calculated with One-way ANOVA (p-value <0.05) follow by Tukey test. All separated crowns and titanium base abutments were investigated under a light microscope (20x), using fisher’s exact test for correlation of the failure types.

Results

There was a significant difference in the mean value of tensile bond strength among the control and test groups. Comparisons between control(237.6±46.3N) and oxidized(241.7±46.3N) showed statistically different values from air abraded(372.9±113.2N) when assembled using different surface treatments of the titanium-based abutments. (p-value<0.005) As for failure type, there were statistically significant differences between control versus air abraded, control versus oxidized-air abraded, oxidized versus air abraded, and oxidized versus oxidized-air abraded. (p-value<0.001) The titanium surface morphology shown from the profilometer and SEM was coordinated. Control (Ra 333.8nm) and oxidized (Ra 321.0nm) groups surfaces showed smooth, corrugated surfaces, meanwhile air abraded (Ra 476.0nm) and oxidized-air abraded (Ra 423.8nm) groups showed rough, rugged surfaces.

Conclusion

Heat oxidization of titanium-based abutments did not adversely affect tensile bond strength or the failure mode and surface roughness between titanium base abutments and zirconia crowns. However, air abrasion of the titanium surface increased surface roughness and retentive strength.

Clinical implications

The titanium base abutments that were oxidized under heat treatment did not have an effect on crown retention. Thoroughly air abraded the titanium abutment prior to cementation can increase cement bond strength.

Introduction

Nowadays, a cemented crown on a titanium base abutment is widely used for implant restoration. This method has several distinct advantages that are passive fit, esthetic, stability, biocompatibility, and retrievability of being used for both cement and screw retained restorations [1–3].

After years of usage, restorations on implants may need to be repaired. Studies have reported that more than 10 percent of restorations on single dental implants were broken or chipped after one year [4, 5]. Additionally, an interproximal space occurred up to 66 percent of the time if the dental implant was placed next to a natural tooth [6]. These cases necessitate either reparation or a new restoration, depending on the severity of the damaged restoration [7]. With a screw retained restoration on a titanium base abutment, a dentist can easily remove and replace the restoration.

Dental laboratories can separate the crown from the titanium abutment using constant dry heat to break cement retention. A crown can be remade, then the separated abutment can be cleaned and recemented resulting in the desired restoration [8].

However, debonding the crown with a constant dry heat will cause oxidation on the abutment surface [9]. A study showed the oxidation kinetic of commercially pure titanium after dry heat and found that the titanium oxide layer (TiO2) was altered [10]. The titanium oxide layer became thicker and rougher as the temperature increased [9]. When the temperature reached 276 ˚C crystalline phase began to occur and the abutment was crystallized entirely at 718 ˚C, creating a defect free surface [11]. The chemical bond between the phosphate group in resin cement and the titanium dioxide layer may be affected [10]. A study have shown that heating commercially pure titanium disk over 400 ˚C can decrease resin bond strength due to the thickening of the oxide layer [10]. However, a contrary study on the effects of debonding and rebonding different crown materials on Ti6Al4V disks, found that heating titanium to 320 ˚C for 2 minutes did not affect the zirconia bond using resin cement but did result in an increased bond strength of lithium disilicate [8].

Previous studies on the effect of heat oxidation titanium are focused on shear bond strength, which may not represent actual clinical situations. Crown retention depends on multiple factors such as abutment morphology [12], cement type [13], cement gap [14], and surface treatment [15–17]. There has been no study for crown retention in heat oxidized titanium abutments that simulated clinical situations.

The purpose of this study was to compare the retention of zirconia crowns between the use of new titanium abutments and reusing heat debonded titanium abutments, with both air abraded and non-air abraded. The null hypothesis was that heat oxidation and air abrasion of titanium abutment would not affect the bond strength of zirconia crown using resin cement. The second null hypothesis was there is no correlation between failure patterns and abutment surface treatments.

Material and methods

To estimate the sample size for this study calculation for 4 independent means will be used. The sample size was calculated with G-power 3.1.9.4 program with Alpha 0.05 and Power at 90 using mean and standard deviation from the previous study [14]. The sample size calculated is 10 pieces per group.

Implant analogs were embodied with epoxy resin into PVC blocks with diameters of 15 mm and 30 mm in height. A vertical distance of 3 mm was left from the implant shoulder to simulate vertical bone loss [15]. Titanium based abutments with a gingival height 1 mm, diameter 3.5 mm, and height of 5.5 mm in height (variobase®) were torqued to the analog at 35 Ncm. The scan body of the abutment was scanned by an intraoral scanner (3shape Trios®). Zirconia crowns were designed using a 3shape Dental system® software for the pull-off test by using a Universal testing machine (Instron® model 5566) as shown in the Fig 1. Luting space was set to 50 μm according to manufacturer’s recommendation. Sixty zirconia crowns were milled from monolithic zirconia disk, then they were sintered and air abraded with Al2O3 50 μm, 1 bar pressure, at 2 cm. distance.

Fig 1. Zirconia crown design for pull-out test using a Universal testing machine.

Fig 1

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Forty titanium base abutments were divided into 4 groups.

Group1: Unconditioned titanium base abutment, as a control group

Group2: Air abraded titanium base abutment. All specimens were air abraded with Al2O3 50 μm with a pressure of 1 bar for 10 seconds. Abutments were fixed with customized rotation grip (Fig 2) which placed the abutment at 10mm distance and 45 degrees from air abrasion tip. The motor rotated at 12 rpm to ensure complete air abrasion of the abutment’s surface area [15].

Fig 2. Customized rotation grip for air abrasion protocol.

Fig 2

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Abutment was place at 10mm. distance and 45 degrees from air abrasion tip. The motor rotation set at 12 rpm.

Group3: Oxidized titanium base abutments. The titanium base abutments were bonded with zirconia crowns using RelyxTM Ultimate and left on a bench for 24 hours, then the crowns were debonded with constant dry heat at 500 ˚C for 5 minutes. This was achieved by increasing the heat rate in increments of 45 ˚C using a porcelain furnace.

Group4: Oxidized and air abraded titanium abutment. The same bonding and debonding procedures as group 3 were used, in addition the specimens were air abraded under the same air abrasion protocol as group 2.

After the abutment’s surface was treated and cleaned, one abutment from each of the four groups was selected at random to examine the surface roughness using a non-contact profilometer. An average surface roughness (Ra), mean height of the profile (Rc) and maximum height of the profile (Rz) were extracted from a single profile (2x2 mm2) of the random abutment under 50x magnification. Then abutment samples were covered with a thin layer of gold (SC7620 Mini Sputter Coater; Quorum technologies, Ashford, UK) to investigate surface changes under scanning electron microscope (SEM)(JSM-6610LV; JEOL, Tokyo, Japan) at 300, 500 and 1000 magnification. Simultaneously, the same abutments were investigated composition under energy dispersion X-ray (EDS)(X-Max, Oxford, UK) at 30 kV of accelerated voltage [17].

Prior to bonding, all titanium base abutments and zirconia crowns in each of the four groups were cleaned using an ultrasonic bath and soaked in 99.5 percent acetone for 5 minutes and then dried with an air blower. Then a phosphate bonding (ScotchbondTM Universal) was applied for 20 seconds, and air blasted to remove the excess bonding before cementation. The specimens were cemented by one operator using firm finger pressure for 5 seconds then carefully cleaned of any excess cement. An additional 10 kg of pressure was applied for 6 minutes until the cement was fully set.

All specimens were left at room temperature for 24 hours before stimulating the aging process by using thermocycling at 5 ˚C to 55 ˚C total of 5,000 thermal cycles and dwell time of 120 seconds [17]. A retention test was performed using a Universal testing machine INSTRON 5566, under 1-kN load cell, with a pullout speed of 1mm/min [4].After completion of the retention force test, the unbound crowns and abutments were inspected under 20x magnification light microscope for residual resin cement in order to accurately categorized the failure mode. Failure modes are categorized into 3 types:Type 1: Cement remain on the abutment surface > 90 percent;

Type 2: Cement remain on both side between 10–90 percent;

Type 3: Cement remain on crown > 90 percent (Fig 3).

Fig 3. Failure mode type.

Fig 3

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a) Titanium base abutment show failure mode Type1, cement remained on the abutment surface >90%, b) Titanium base abutment show failure mode Type2, cement remain on the abutment between 10–90%; c) Titanium base abutment show failure mode Type3, cement remain on the abutment <10%.

For mean tensile bond strength and failure mode, statistic estimation of data distribution and comparison was performed using Windows-compatible SPSSTM Statistics version 20, IBM® Corporation, USA. The normal distribution and the variances of the data were tested. Tensile bond strength has normal distribution and variances of the data were equal, One-way ANOVA was used to calculate the possibility. And the significant differences between groups and multiple comparisons was tested with the Tukey test. Mean, SD, and 95% confidential interval were presented. As for failure mode, the non-parametric fisher exact test is performed. Surface roughness was shown as Median(Min,Max) along with a descriptive analysis.

Results

There was a significant difference in the mean value of tensile bond strength among the control, air abraded, oxidized, and oxidized-air abraded groups. The mean tensile bond strength of the control group was 237.6 ± 46.3 N, the oxidized group was 241.7 ± 74.6 N, the air abraded group was 372.9 ± 113.2 N and the oxidized-air abraded group was 297.0 ± 76.3 N (Table 1, Fig 4). Control and oxidized groups appeared to be statistically and significantly different from the air abraded group (p < 0.005). However, there was no significant difference between the oxidized-air abraded group and the air abraded group.

Table 1. Tensile bond strength(N) and failure mode of the control, air abraded, oxidized, and oxidized-air abraded titanium base abutment groups to zirconia crown using resin cement.

Failure mode investigated under light microscope(x20) (Type1, cement remained on the abutment surface >90%; Type2, cement remain on both side between 10–90%; Type3, cement remain on abutment <10%).

Groups p-value
Control (n = 10) Air abraded (n = 10) Oxidized (n = 10) Oxidized-air abraded (n = 10)
Bond strength(N) 237.6 ± 46.3 372.9 ± 113.2 241.7 ± 74.6 297.0 ± 76.3 <0.005a
Failure mode n (%) <0.001b
Type 1 0 10(100) 0 7(70)
Type 2 0 0 1(10) 3(30)
Type 3 10 (100) 0 9 (90) 0
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a Statistically significant differences from bond strength (One way-ANOVA)

b Statistically significant differences from failure mode (fisher’s exact test, Chi-square)

Fig 4. Tensile bond strength(N) of control, air abraded, oxidized and oxidized-air abraded titanium base abutment to zirconia crown using resin cement.

Fig 4

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* P-value <0.005(One way-ANOVA,Tukey test).

As for the surface morphology, despite the color, the control and oxidized groups had a uniform corrugated surface, while the air abraded and oxidized-air abraded groups showed a rough, rugged surface (Fig 5). Air abraded group have the highest surface roughness(Ra 476nm) follow by oxidized air abraded group(Ra 423.8nm),control group(Ra 333.8nm) and oxidized group(Ra 321nm), respectively (Table 2).

Fig 5. Surface of titanium base abutment investigated under non-contact profilometer Alicona (x50).

Fig 5

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a) Control-normal titanium base b) Air abraded titanium base c) Oxidized titanium base d) Oxidized-air abraded titanium base.

Table 2. Median(Min, Max) value of titanium base abutment surface roughness investigated under non-contact profilometer Alicona (x50), extracted 3 times from a single profile photo.

Groups
Control Air abraded Oxidized Oxidized-air abraded
Ra(nm) 333.8 (333.7, 379.7) 476.0 (470.6, 579.3) 321.0 (314.6, 363.7) 423.8 (408.3, 440.8)
Rc(nm) 419.6 (403.6, 488.5) 607.9 (577.2, 995.1) 402.7 (395.4, 484.9) 555.9 (546.1, 605.9)
Rz(μ) 2.23 (1.78, 2.54) 3.21 (2.70,4,76) 1.99 (1.89, 3.35) 2.95(2.93,3.14)
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Similarly to the investigation from SEM, both control (Fig 6) and oxidized (Fig 7) groups showed a uniform corrugated surface, while the air abraded (Fig 8) and oxidized-air abraded (Fig 9) groups showed a rugged surface. But the oxidized abutment surface showed multiple white dirt. EDS investigation reviewed only the oxidized group that presented calcium element on the surface, this reaffirmed the possibility that the white dirt was residual cement (Fig 10). There were differences in element both weight and atomic percent between control VS oxidized and control VS air abraded, oxidized-air abraded (Table 3). In addition, at 25 magnification, a cracked line was presented on the abutment surface of both air abraded and oxidized-air abraded groups (Figs 11–13).

Fig 6.

Fig 6

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Surface of non treated titanium base abutment(control) investigated under Scanning electron microscope(SEM). a) 25 magnification b) 300 magnification c) 500 magnification d) 1000 magnification.

Fig 7. Surface of oxidized titanium base abutment investigated under Scanning electron microscope (SEM).

Fig 7

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a) 25 magnification b) 300 magnification c) 500 magnification d) 1000 magnification.

Fig 8. Surface of air abraded titanium base abutment investigated under Scanning electron microscope (SEM).

Fig 8

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a) 25 magnification b) 300 magnification c) 500 magnification d) 1000 magnification.

Fig 9. Surface of oxidized-air abraded titanium base abutment investigated under Scanning electron microscope (SEM).

Fig 9

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a) 25 magnification b) 300 magnification c) 500 magnification d) 1000 magnification.

Fig 10. Energy dispersion Xray (EDS) graph (X-Max,Oxford,UK) of a control-normal titanium base.

Fig 10

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Table 3. Element composition of titanium base abutment surface investigated under energy dispersion Xray (EDS) (X-Max, Oxford, UK) at 30 kV of accelerated voltage.

Element Control Air abraded Oxidized Oxidized- air abraded
C Weight% 12.88 8.09 9.13 8.09
Atomic% 31.65 20.16 23.56 20.16
O Weight% 11.59 17.24 13.16 17.24
Atomic% 21.38 32.24 25.51 32.24
Al Weight% 4.43 6.56 4.6 6.56
Atomic% 4.85 7.27 5.28 7.27
Ca Weight% - - 0.34 -
Atomic% - - 0.27 -
Ti Weight% 65.48 60.79 67.29 60.79
Atomic% 40.34 37.97 43.56 37.97
Nb Weight% 5.62 7.32 5.48 7.32
Atomic% 1.78 2.36 1.83 2.36
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Fig 11. Energy dispersion Xray (EDS) graph (X-Max,Oxford,UK) of an air abraded titanium base.

Fig 11

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Fig 13. Energy dispersion Xray (EDS) graph (X-Max,Oxford,UK) of an oxidized-air abraded titanium base.

Fig 13

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Fig 12. Energy dispersion Xray (EDS) graph (X-Max,Oxford,UK) of an oxidized titanium base.

Fig 12

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The separate titanium base abutment and zirconia crowns were inspected under a 20x light microscope to determine the failure type. Control and oxidized groups presented only type 3 failure mode. While air abraded and oxidized-air abraded groups presented primarily type 1 failure mode. Test results showed significant statistical differences between the four groups. (p<0.001). Therefore, the second null hypothesis was denied. There were statistically significant differences between (control vs. air abraded), (control vs. oxidized-air abraded), (oxidized vs. air abraded), and (oxidized vs. oxidized-air abraded) groups. (p-value<0.001) (Table 1).

Discussion

This study focused on the effect on the resin bond strength of heat oxidized titanium abutments under a strict debonding protocol using zirconia crowns. The results showed that heat oxidation of titanium base abutments did not have a statistically significant effect on resin bond strength. However, a notable difference in resin bond strength(p-value<0.005) and failure mode(p-value<0.001) was observed in the air abraded titanium group. Consequently, both hypotheses were rejected.

No measurable statistical differences in bond strength were found between the oxidized-air abraded group and the oxidized group, but a significant difference in the failure modes(p-value<0.001) was detected. The cement remained primarily on the “crown” in the oxidized group, whereas the opposite occurred for the oxidized-air abraded group, with the majority of the cement remaining on the “abutment.” Air abrasion titanium abutments considerably increased the resin bond strength between the cement and abutment.

Resin cement is known to be bonded with titanium between the phosphate group and titanium oxide layer. The bonding depends on both micromechanical interlocking and physicochemical state [18, 19]. The oxidization of titanium by using heat can change the physical and chemical properties of the oxide layer, which may affect resin bond strength.

This study found that heat oxidation of titanium at 500 ˚C for 5 minutes does not affect resin cement bond strength to zirconia, which is consistent with the previous study [8]. However, a study found that heating a cp titanium disk over 400˚C can decrease resin bond strength according to the thickening of the oxide layer [9]. This study attempts to imitate real clinical situations. As a result, the morphology of abutment [12], type of cement [13], and cement gap [14] can also be contributing factors for crown retention. There were no discernable differences observed in crown retention between the control and oxidized group in this study.

Air abrasion the titanium abutments with Al3O2 50 μm 2 bar pressure at a 10 mm distance for 10 seconds can increase crown retention and titanium surface roughness. Consistent to previous studies that air abrasion titanium greatly increases zirconia crown retention [15–17]. However, air abraded an oxidized titanium did not increase bond strength significantly when compared with both the controlled and oxidized groups. It was known that heat oxidation changes the oxide layer morphology and titanium’s physical properties [10, 20]. From investigation under SEM and EDS, found no difference between air abraded and oxidized-air abraded in terms of surface morphology and elemental component. However, the titanium surface could be hardened when heating titanium due to titanium grain growth [21]. Supported by a study found that the low oxidation temperature of 450 ˚C followed by a high temperature of 850 ˚C for vacuum heat treatment caused a hard and defect-free surface of the titanium [22]. This study also found increasing of aluminum and oxygen elements after air abrasion. Al2O3 particles could be embedded in the metal surface effect to element component shift and increase resin bond strength [23].

This study was conducted in a laboratory setting, which tries to imitate the clinical environment but may only partially reflect the conditions in a clinical setting, therefore, there should be clinical study to confirm this finding.

Based on results of this study, the oxidized titanium abutment can be used to bond with zirconia crown without compromising the retention between resin cement and restoration. However, air abrasion the titanium abutment did increase the bond strength. Therefore, air abrade the abutment is recommended before bonding restorations.

Conclusions

The debonding protocol using heat to break resin bond did not affect zirconia crown retention using resin cement. Air abrade the titanium base abutment has an influence on both surface roughness and bond strength between abutment and zirconia restoration.

Supporting information

S1 Data

(XLSX)

Click here for additional data file. (9.6KB, xlsx)
S2 Data

(XLSX)

Click here for additional data file. (11.9KB, xlsx)

Data Availability

All relevant data are within the paper and its Supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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Decision Letter 0

Sompop Bencharit

14 Feb 2023

PONE-D-22-35369Retention of zirconia crown to oxidized titanium base abutment: Experimental researchPLOS ONE

Dear Dr. Kunavisarut,

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We look forward to receiving your revised manuscript.

Kind regards,

Sompop Bencharit, DDS, MS, PhD, FACP

Academic Editor

PLOS ONE

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Additional Editor Comments:

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: No

Reviewer #2: Partly

Reviewer #3: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: After reviewing the article, I point out the following topics for the authors to evaluate:

1. On page 11, in the last paragraph of the introduction, the authors point out a single null hypothesis. However, on page 17, they state that the second null hypothesis was confirmed.

2. On page 13, the authors state that a 2X2mm2 area of a single specimen from each group was used to assess roughness. However, on page 16, in table 1, they state that roughness was measured in 3 different specimens (n=3).

3. On page 14, figure 3, the authors describe 6 different situations to characterize 3 types of failures. The descriptions of the situations in the letters D, E, F, are difficult to visualize and do not add relevant information to the situations described in the letters A, B, C. Therefore, I suggest keeping only the characterizations of the letters A, B, C to describe the 3 types of failure.

4. The main limitations of the article presented are the absence of a sample calculation, or the calculation of the power of the sample used, and also the lack of description of the statistical analysis performed.

5. In the results, on page 15, I also suggest reviewing the mean and standard deviation values of one of the roughness parameters (Rc). Did the sandblasted and oxidized sandblasted groups show exactly the same values?

6. On page 15, in Graph 1, I suggest adding indicators whether or not there was a statistically significant difference between the groups.

7. On page 16, table 1, a single p value is presented for two different comparisons of the Ra parameter, described in the legend (control vs. sandblasted) and (sandblasted vs. oxidized).

8. On page 16, still in Table 1, a single p value is presented for four different comparisons of the Rc parameter, described in the legend (control vs. sandblasted), (control vs. oxidized-sandblasted), (Oxidized vs. sandblasted) and (oxidized vs. oxidized-sandblasted).

9. On page 16, in the presentation of the groups, I suggest keeping the sandblasted group as letter b, to correspond to group 2, which was always presented as sandblasted.

10. On page 17, in table 2, it is described that the evaluation of the type of failure was performed with a magnification of X10. In other locations, this described magnification was X20.

11. Still on page 17, in table 2, I suggest reviewing the data from the sandblasted, control and oxidized-sandblasted groups. As the sandblasted group had the highest roughness, wouldn't it be expected that the sandblasted groups would have more type 1 failures? On the other hand, the control and oxidized-sandblasted groups, with less roughness compared to the sandblasted group, wouldn't more type 3 failures be expected?

12. Still on page 17, in the caption of table 2, I suggest repeating the description of the types of failures to facilitate the reading and understanding of the text.

13. In the discussion, on page 18, line 8, wouldn't the comparison described be between oxidized sandblasted group and sandblasted group rather than oxidized sandblasted group and oxidized group?

14. Still on page 18, the authors state: “The majority of the cement remaining on “crown” in oxidized group while the opposite occurred for the oxidized sandblasted group, with the majority of the cement remaining on the “abutment”. Table 2 does not demonstrate this. Note that in the oxidized group, most failures were type 1, which 90% of the cement remained retained in the abutment. As described in item 11, I suggest reviewing the data presented in table 2.

15. On page 19, lines 12 and 13, the authors state: “Sandblasting protocol in this study may not cause enough roughness to increase bond strength significantly.” In the results presented, blasting resulted in increased retention when compared to the control group, which contradicts this statement.

16. It would be important for the authors to point out the possible limitations of their work. As an example, the lack of physicochemical characterization of Ti surfaces before and after oxidation. Furthermore, the method used to characterize the abutment surface in the 4 different groups seems very limited. Perhaps it would be interesting to use other resources such as SEM.

Reviewer #2: Main concern:

The present study has a small impact on the dental field. Most of the cited studies on the subject are old, reinforcing the small impact of the subject in the current context. In addition, several points in the writing of the manuscript must be revised and reformulated to be in Plos One standards. The study did not adequately characterize the problem in the introduction, did not present statistical analysis methods, and did not discuss limitations. In addition, several references presented in the text are not in the references cited at the end of the text.

Abstracts.

- The first sentence of the abstract is strange. Please, review it.

- Explain briefly the method of specimen aging.

- In the results, the authors reported the statistical difference between the groups. However, it is important to present the directions of the effects, i.g., which group was better?

- Please, present the mean and SD of the tests results.

Introduction

- Please, avoid direct citations in the text.

- The sentence “debonding the crown with a constant dry heat will cause oxidation on the

- abutment surface.” needs to be referenced.

- The affirmation of the sentence “These cases provide the need for a new restoration.” Including chipped restoration can lead to an overtreatmnent. Restoration repair should be the first option in these cases. So, I suggest to the authors the reading of below paper:

Anusavice KJ. Standardizing failure, success, and survival decisions in clinical studies of ceramic and metal-ceramic fixed dental prostheses. Dent Mater. 2012;28:102-111

- The authors report the study of Gamelli E et al. However, this study is not in the reference

- The reference cited in the introduction Sailor et al is not cited in the reference

- The sentence “The chemical bond between the phosphate group in resin cement and the titanium dioxide layer may be affected.” need to be referenced. Also, explain how the layer may be affected.

- The authors need to improve the introduction to better characterize the problem of the study. How the oxide affect the cementation? In which clinical situations the dry heat debondation is indicated?

Materials and methods

- The authors report “Sixty zirconia crowns were milled from monolithic zirconia disk”. However, seems that there are ten “n” for the group. Please, clarify this in the study.

- The authors did not report how the statistic was performed in the study.

Results

- Show where the statistical differences are in graph 1. Also, why the authors used a bo plot graph? Box plot should be used for nonparametric distribution. Did the authors check the data distribution? what test was used?

- Table 1. Please, provide similar letters for groups that were similar in the analyzes and different letters for different groups. This is the conventional way of reporting statistical differences in this type of study.

- Present each statistical test performed in the footnote of the table/figure.

- Avoid rewriting all the data (already presented in the tables) in the text. Draw attention to what really matters in the text.

Discussion

- Authors need to discuss the limitations of the present study and the directions for further studies.

- Avoid direct citations.

References:

- Please, avoid the citations of books and old references

- Some references are not under the journal style

Reviewer #3: The study aimed to evaluate potential surface treatments for debonded crown on titanium base abutment. The results are interesting and justified by the methods used. It would be interesting to add in the discussion the explanation of how the debonded method used in the paper can relate to clinical condition, and also the clinical application of sandblasting, as if it is safe to perfome it clinically.

**********

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Reviewer #1: No

Reviewer #2: Yes: Luiz Alexandre Chisini

Reviewer #3: No

**********

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While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Oct 25;18(10):e0287108. doi: 10.1371/journal.pone.0287108.r002

Author response to Decision Letter 0

30 Mar 2023

Thank you for taking the time to review my manuscript. I appreciate your feedback; they were accommodating. I have incorporated all of your suggestions in my revisitation as described in this letter.

Reviewer #1:

1. On page 11, in the last paragraph of the introduction, the authors point out a single null hypothesis. However, on page 17, they state that the second null hypothesis was confirmed.

Answer: The second hypothesis was added to the introduction.

2. On page 13, the authors state that a 2X2mm2 area of a single specimen from each group was used to assess roughness. However, on page 16, in table 1, they state that roughness was measured in 3 different specimens (n=3).

Answer: The roughness was only measured in a single specimen from each group. Table1 has been corrected accordingly.

3. On page 14, figure 3, the authors describe 6 different situations to characterize 3 types of failures. The descriptions of the situations in the letters D, E, F, are difficult to visualize and do not add relevant information to the situations described in the letters A, B, C. Therefore, I suggest keeping only the characterizations of the letters A, B, C to describe the 3 types of failure.

Answer: Figure3 was corrected to remain only cement retained on titanium base abutment as letter A,B,C. Letter D,E,F as figure of cement retained on crown has been removed.

4. The main limitations of the article presented are the absence of a sample calculation, or the calculation of the power of the sample used, and also the lack of description of the statistical analysis performed.

Answer: As for sample size calculation, I add the explanation in the first paragraph of the material and method(page4line238-332). And for description of the statistical analysis, I have explained the statistical analysis in the last paragraph of material and method (page 9, lines 444-453)

5. In the results, on page 15, I also suggest reviewing the mean and standard deviation values of one of the roughness parameters (Rc). Did the sandblasted and oxidized sandblasted groups show exactly the same values?

Answer: The surface roughness description in the paragraph has been removed and rephrased for better focus. And for better understanding Table2 has been modified to Median(Min,Max), according to the data type.

6. On page 15, in Graph 1, I suggest adding indicators whether or not there was a statistically significant difference between the groups.

Answer: The indicators was added to the graph.

7. On page 16, table 1, a single p value is presented for two different comparisons of the Ra parameter, described in the legend (control vs. sandblasted) and (sandblasted vs. oxidized).

Answer: The statistic analysis of Ra has been removed, according its data type, which is a descriptive data extracted from one sample. Therefore, Table1 and 2 was modified accordingly and p-value of surface roughness was removed.

8. On page 16, still in Table 1, a single p value is presented for four different comparisons of the Rc parameter, described in the legend (control vs. sandblasted), (control vs. oxidized-sandblasted), (Oxidized vs. sandblasted) and (oxidized vs. oxidized-sandblasted).

Answer: The statistic analysis of Rc has been removed, according its data type, which is a descriptive data extracted from one sample. Therefore, Table1 and 2 was modified accordingly and p-value of surface roughness was removed.

9. On page 16, in the presentation of the groups, I suggest keeping the sandblasted group as letter b, to correspond to group 2, which was always presented as sandblasted.

Answer: The letter b in Figures legend and Tables was corrected to always presented as sandblasted.

10. On page 17, in table 2, it is described that the evaluation of the type of failure was performed with a magnification of X10. In other locations, this described magnification was X20.

Answer: The table’s legend was corrected to x20 magnification.

11. Still on page 17, in table 2, I suggest reviewing the data from the sandblasted, control and oxidized-sandblasted groups. As the sandblasted group had the highest roughness, wouldn't it be expected that the sandblasted groups would have more type 1 failures? On the other hand, the control and oxidized-sandblasted groups, with less roughness compared to the sandblasted group, wouldn't more type 3 failures be expected?

Answer: The data in table was reviewed and corrected to be in the right order.

12. Still on page 17, in the caption of table 2, I suggest repeating the description of the types of failures to facilitate the reading and understanding of the text.

Answer: The failure type has been added to table 1, therefore caption of table1 has been added the types of failures mode description for more understanding.

13. In the discussion, on page 18, line 8, wouldn't the comparison described be between oxidized sandblasted group and sandblasted group rather than oxidized sandblasted group and oxidized group?

Answer: I intend to emphasize the differences found between two oxidized groups. I have rephrase the sentence to “However, a notable difference in resin bond strength(p-value<0.005) and failure mode(p-value<0.001) was observed in the sandblasted titanium group. Consequently, both hypotheses were rejected. It is worth mentioning that no measurable statistical differences in bond strength were found between the oxidized-sandblasted group and the oxidized group, but a significant difference in the failure modes(p-value<0.001) was detected.”(page14line777-779)

14. Still on page 18, the authors state: “The majority of the cement remaining on “crown” in oxidized group while the opposite occurred for the oxidized sandblasted group, with the majority of the cement remaining on the “abutment”. Table 2 does not demonstrate this. Note that in the oxidized group, most failures were type 1, which 90% of the cement remained retained in the abutment. As described in item 11, I suggest reviewing the data presented in table 2.

Answer: The failure type has been added to table 1. Though, the data of failure mode has been revised and corrected.

15. On page 19, lines 12 and 13, the authors state: “Sandblasting protocol in this study may not cause enough roughness to increase bond strength significantly.” In the results presented, blasting resulted in increased retention when compared to the control group, which contradicts this statement.

Answer: The phrase has been removed. The discussion was focusing on limitation and further investigation instead.

16. It would be important for the authors to point out the possible limitations of their work. As an example, the lack of physicochemical characterization of Ti surfaces before and after oxidation. Furthermore, the method used to characterize the abutment surface in the 4 different groups seems very limited. Perhaps it would be interesting to use other resources such as SEM.

Answer: The SEM along with EDS investigation was performed and added to this study. Moreover, I have discussed more point on limitations and suggestion for further investigation.

Reviewer #2:

Main concern:

The present study has a small impact on the dental field. Most of the cited studies on the subject are old, reinforcing the small impact of the subject in the current context. In addition, several points in the writing of the manuscript must be revised and reformulated to be in Plos One standards. The study did not adequately characterize the problem in the introduction, did not present statistical analysis methods, and did not discuss limitations. In addition, several references presented in the text are not in the references cited at the end of the text.

Answer: This study was performed for more understanding on whether we can reuse a titanium base abutment or not? Reusing the old abutment will save cost to the treatment. In fact, many clinicians are currently using the old abutments with the new restorations without knowing the consequences of oxidation on the abutments.

While revising, I reformulated manuscript to Plos-one pattern, added the sample size calculation, statistical analysis, perform a SEM/EDS examination and discuss more on study limitation and further investigation. Moreover, I revised and avoid cite old references as possible. But some of my concerns, mostly on the study of metal metallurgy, are old, and there are no newer direct references on the issue. Such as “Assefpour-Dezfuly M, Vlachos C, Andrews E. Oxide morphology and adhesive bonding on titanium surfaces. Journal of materials science. 1984;19(11):3626-39.” And “Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Influence of surface oxidation of titanium on adhesion. Journal of dentistry. 1998;26(1):69-73.”.

Abstracts.

- The first sentence of the abstract is strange. Please, review it.

Answer: The first sentence was modified.

- Explain briefly the method of specimen aging.

Answer: The method of specimen aging has been added.

- In the results, the authors reported the statistical difference between the groups. However, it is important to present the directions of the effects, i.g., which group was better?

Answer: The mean and SD was presented to imply the direction of effects.

- Please, present the mean and SD of the tests results.

Answer: The mean and SD has been presented.

Introduction

- Please, avoid direct citations in the text.

Answer: The direct citation has been removed.

- The sentence “debonding the crown with a constant dry heat will cause oxidation on the

abutment surface.” needs to be referenced.

Answer: The phrase has been referenced.

- The affirmation of the sentence “These cases provide the need for a new restoration.” Including chipped restoration can lead to an overtreatmnent. Restoration repair should be the first option in these cases. So, I suggest to the authors the reading of below paper:

Anusavice KJ. Standardizing failure, success, and survival decisions in clinical studies of ceramic and metal-ceramic fixed dental prostheses. Dent Mater. 2012;28:102-111

Answer: I appreciated your suggestion, I have reviewed the journal and used it as reference.

- The authors report the study of Gamelli E et al. However, this study is not in the reference

Answer: The cited article has been added in the manuscript.

- The reference cited in the introduction Sailor et al is not cited in the reference

Answer: The cited article has been added in the manuscript.

- The sentence “The chemical bond between the phosphate group in resin cement and the titanium dioxide layer may be affected.” need to be referenced. Also, explain how the layer may be affected.

Answer: The reference for this statement has been added.

- The authors need to improve the introduction to better characterize the problem of the study. How the oxide affect the cementation? In which clinical situations the dry heat debondation is indicated?

Answer: I have rewrite my introduction for better understanding, and also indicated clinical situation which debonding is necessary. There is no previous study on the problem and there are only few related studies.

Materials and methods

- The authors report “Sixty zirconia crowns were milled from monolithic zirconia disk”. However, seems that there are ten “n” for the group. Please, clarify this in the study.

Answer: To clarify the number of zirconia crowns used in this research, I phrase “Sixty zirconia crowns were milled from monolithic zirconia disk, then they were sintered and sandblasted with Al2O3 50 µm, 1 bar pressure, at 2 cm. distance. Twenty zirconia crowns were used to simulate debonding process on the test titanium-based abutments. The other forty zirconia crowns were used on the experiment.” in material and method (page 5, lines 336-339).

- The authors did not report how the statistic was performed in the study.

Answer: The statistical analysis has been added in the last paragraph of material and method (page 9, lines 444-453)

Results

- Show where the statistical differences are in graph 1. Also, why the authors used a bo plot graph? Box plot should be used for nonparametric distribution. Did the authors check the data distribution? what test was used?

Answer: The indicator of statistical differences was presented in graph1. The box-plot graph is presented for a better exhibition of both distribution of the data and the significant differences in groups, analyzed from the tukey test.

- Table 1. Please, provide similar letters for groups that were similar in the analyzes and different letters for different groups. This is the conventional way of reporting statistical differences in this type of study.

Answer: Table1 and 2 have been modified for better understanding and explicated the data type.

- Present each statistical test performed in the footnote of the table/figure.

Answer: The each statistical test performed in the footnote of the table/figure.

- Avoid rewriting all the data (already presented in the tables) in the text. Draw attention to what really matters in the text.

Answer: The description of all data has been rewritten. Most of data which already presented in table was removed.

Discussion

- Authors need to discuss the limitations of the present study and the directions for further studies.

Answer: Limitation and direction for further studies have been discussed.

- Avoid direct citations.

Answer: The direct citation has been removed.

References:

- Please, avoid the citations of books and old references

Answer: Old references have been revised and some are remained. As the study of metal metallurgy, are old, and there are no newer direct references on the issue. Such as “Assefpour-Dezfuly M, Vlachos C, Andrews E. Oxide morphology and adhesive bonding on titanium surfaces. Journal of materials science. 1984;19(11):3626-39.” And “Taira Y, Matsumura H, Yoshida K, Tanaka T, Atsuta M. Influence of surface oxidation of titanium on adhesion. Journal of dentistry. 1998;26(1):69-73.”.

- Some references are not under the journal style

Answer: The references are revised and rewritten.

Reviewer #3: The study aimed to evaluate potential surface treatments for debonded crown on titanium base abutment. The results are interesting and justified by the methods used. It would be interesting to add in the discussion the explanation of how the debonded method used in the paper can relate to clinical condition, and also the clinical application of sandblasting, as if it is safe to perfome it clinically.

Answer: The discussion has been rewritten and discuss more on limitation of the study, clinical application and direction for further studies.

Finally, I appreciate all your feedbacks. Thank you for your time and consideration.

Attachment

Submitted filename: Response to reviewer.docx

Click here for additional data file. (22.7KB, docx)

Decision Letter 1

Sompop Bencharit

14 Apr 2023

PONE-D-22-35369R1Retention of zirconia crown to oxidized titanium base abutment: Experimental researchPLOS ONE

Dear Dr. Kunavisarut,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by May 29 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Sompop Bencharit, DDS, MS, PhD, FACP

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Additional Editor Comments:

Thank you for addressing the comments from the reviewers. I think the manuscript is significantly improved. There are a few additional requests I would like to add.

1) Please add SEM method in the Methods section.

2) Since you compared the SEM analyses among different groups, I think we need to take it one step further to see if there is damages or changes in material elemental composition. Can you add EDX experiments into this? If not please provide justification and rationale. My thought is that air abrasion may alter the composition of the abutment surface.

3) Please change "sand blasting" to "air abrasion".

4) Can you discuss the depth of the air abrasion and the anodization layer? I assume that air abrasion would not go beyond the anodization layer. If we will recommend this clinically, would this be an issue if someone air abrade the implant abutment too much?

[Note: HTML markup is below. Please do not edit.]

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Oct 25;18(10):e0287108. doi: 10.1371/journal.pone.0287108.r004

Author response to Decision Letter 1

17 May 2023

To the Editor and reviewers of the PLOS ONE journal

Dear Editor and reviewers,

Thank you for taking the time to review my manuscript. I appreciate your feedback; they were accommodating. I have incorporated all of your suggestions in my revisitation as described in this letter.

1) Please add SEM method in the Methods section.

Answer: I have add SEM and EDS method in the Method section(page5 line 141-146)

2) Since you compared the SEM analyses among different groups, I think we need to take it one step further to see if there is damages or changes in material elemental composition. Can you add EDX experiments into this? If not please provide justification and rationale. My thought is that air abrasion may alter the composition of the abutment surface.

Answer: I have add the EDS analysis and add the result graph demonstrate material composition along with a table demonstrate element composition in weight% and atomic%.

I also discuss finding from EDS on increasing of aluminum and oxygen after air abrasion. As reference “23. Ohkubo C, Watanabe I, Hosoi T, Okabe T. Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers. The Journal of prosthetic dentistry. 2000 Jan 1;83(1):50-7.” After air abrasion, Al2O3 particles embedded into metal surface which increase resin bond strength.

3) Please change "sand blasting" to "air abrasion".

Answer: I have change all “sandblasting” to “air abrasion” including the name of groups “sandblasted group” to “air abraded group” and “Oxidized-sandblasted group” to “oxidized-air abraded group” for consistency of the manuscript.

4) Can you discuss the depth of the air abrasion and the anodization layer? I assume that air abrasion would not go beyond the anodization layer. If we will recommend this clinically, would this be an issue if someone air abrade the implant abutment too much?

Answer: Since this study did not investigate on the anodized abutment, we couldn’t make any assumption of this matter. Further research should be conducted to investigate the effect of air-abraded on anodized abutment.

Finally, I appreciate all your feedbacks. Thank you for your time and consideration.

Sincerely,

Assistant Professor Chatchai Kunavisarut

Business address: Department of Advanced General Dentistry, Mahidol University,

No.6 Yothi Road, Ratchathewi District, Bangkok 10400 Hospital (Phayathai Campas)

Tel:+662-200-7777

Email: Chatchai.kun@mahidol.ac.th Mobile:+66890737030

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Decision Letter 2

Sompop Bencharit

30 May 2023

Retention of zirconia crown to oxidized titanium base abutment: Experimental research

PONE-D-22-35369R2

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