|Year : 2022 | Volume
| Issue : 1 | Page : 17-21
A comparative evaluation of different saliva cleaning regimens on the shear bond strength of two different ceramics with resin cement: An in vitro study
Tanuj Kumar, Natarajan Kalavathy, Mitha Shetty, P Roshan Kumar, Archana K Sanketh, M Roopa
Department of Prosthodontics, D A Pandu Memorial R V Dental College, Bengaluru, Karnataka, India
|Date of Submission||18-Oct-2021|
|Date of Decision||06-Feb-2022|
|Date of Acceptance||07-Feb-2022|
|Date of Web Publication||14-Mar-2022|
Dr. Tanuj Kumar
Department of Prosthodontics, D A Pandu Memorial R V Dental College, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Contamination of all-ceramic restorations with oral fluids during clinical try-in can have a detrimental effect on their clinical performance. Objective: The aim of this study was to compare the efficiency of four different saliva cleaning regimens on the shear bond strength (SBS) of lithium disilicate and zirconia with resin cement. Materials and Methods: Ten cubic samples of lithium disilicate pressable ceramic (Group A) and monolithic zirconia (Group B) were fabricated. Four surfaces from each sample were coated with saliva, washed with water, and dried. These surfaces were subsequently treated with four different cleaning protocols (water [A1, B1], isopropyl alcohol [A2, B2], sodium hypochlorite [A3, B3], and Ivoclean™ [A4, B4]) and bonded to composite cylinders using dual-cure resin cement. The specimens were then tested for SBS. Results: Group A, subgroup A4 had a significantly higher mean SBS compared to other groups, and for Group B, subgroup B4 had a significantly higher mean SBS compared to other groups. The mean difference in the SBS for subgroup A1 and B1 was −3.862 at P = 0.01; for subgroup A2 and B2, it was −4.164 at P = 0.03; for A3 and B3, it was −4.845 at P < 0.001; and for subgroup A4 and B4, it was −24.990 at P < 0.001. Conclusion: Monolithic zirconia specimens showed significantly more SBS compared to lithium disilicate specimens in all subgroups. The mean SBS was highest for surfaces cleaned using Ivoclean in both groups.
Keywords: Lithium disilicate, monolithic zirconia, saliva contamination, shear bond strength
|How to cite this article:|
Kumar T, Kalavathy N, Shetty M, Kumar P R, Sanketh AK, Roopa M. A comparative evaluation of different saliva cleaning regimens on the shear bond strength of two different ceramics with resin cement: An in vitro study. SRM J Res Dent Sci 2022;13:17-21
|How to cite this URL:|
Kumar T, Kalavathy N, Shetty M, Kumar P R, Sanketh AK, Roopa M. A comparative evaluation of different saliva cleaning regimens on the shear bond strength of two different ceramics with resin cement: An in vitro study. SRM J Res Dent Sci [serial online] 2022 [cited 2022 May 27];13:17-21. Available from: https://www.srmjrds.in/text.asp?2022/13/1/17/339632
| Introduction|| |
The clinical performance and durability of all-ceramic restorations are closely dependent on how they are cemented. Although resin-based adhesive systems are the most popular and versatile means of bonding these restorations, obtaining a sturdy bond between the cement and the ceramic is quite challenging.
Some of the methods of achieving a strong resin bond include chemical adhesion and/or micromechanical interlocking, which can be carried out either by roughening the surfaces or surface conditioning. However, a factor that is often overlooked is the potential contamination of these indirect restorations with saliva and other oral fluids while bonding. It has been observed that the strong affinity of zirconium toward the phosphate groups found in saliva can adversely affect the bonding process. The literature, through the years, has suggested various techniques such as particle abrasion, conditioning with varying amounts of chemicals such as acetone, phosphoric acid, isopropanol, ethanol, chlorhexidine, 0.5% sodium hypochlorite application, and water spray (WS). A new cleaning agent, Ivoclean® (Ivoclar Vivadent, Liechtenstein) has also been introduced to the market recently to clean zirconia surfaces contaminated by blood or saliva and improve the bonding. Although the contamination of lithium disilicate surfaces may not be as lethal as zirconia, studies have shown a significant influence on the bond strength of these restorations following contamination with saliva and/or other oral fluids.
The purpose of this study was to compare and evaluate the efficiency of four different saliva cleaning regimens, including the new cleaning agent Ivoclean, on the shear bond strength (SBS) of two commercially available ceramics (i.e. monolithic zirconia and lithium disilicate) with resin cement.
| Materials and methods|| |
The present study was carried out after obtaining ethical clearance (IRB No. 260/VOL2/2017) from the institutional review board at Rajiv Gandhi University of Health Sciences, Bengaluru, Karnataka. The sample size had been estimated using the software GPower version 220.127.116.11. (Released in March 2014 Heinrich Heine University Dusseldorf; North Rhine-Westphalia; Germany) Considering the effect size to be measured at 64%, the power of the study at 80%, and the margin of the error at 5%, the total sample size needed was 80. Forty samples were further subdivided into four subgroups of 10 each.
A total of 20 cubes, 10 each of two different ceramics (zirconia and lithium disilicate) measuring 8 mm × 8 mm × 8 mm were fabricated. The samples were grouped as Group A and Group B. Group A specimens were made from lithium disilicate (IPS e.max Press, Ivoclar Vivadent) press ingots through lost-wax technique. Wax patterns of the required dimensions (8 mm × 8 mm × 8 mm) were milled with a computer-aided design/computer-aided manufacturing (CAD/CAM) system. The milled patterns were then spruced and invested in a suitable investment material (PressVEST, Ivoclar Vivadent) as per the manufacturer's instructions. Following this, the wax was eliminated and the ingots were pressed at 840°C as directed by the manufacturer. The wax elimination and pressing were carried out by a single operator to avoid any discrepancy.
Group B samples were prepared from presintered CAD discs of zirconium oxide (KATANA, Kuraray Noritake Dental Inc.) which were milled into cubes measuring 8 mm × 8 mm × 8 mm with the CAM machine. Following the milling procedure, the specimens were cut with a diamond disc; the cutting waste/dust was discarded with gentle air. The cut specimens were then placed in a refractory tray and subjected to sintering by placing them in a sintering furnace (HT Speed, MIHM-VOGT, Stutensee, Germany) at 1500°C, as per the manufacturer's instructions. The bonding surfaces of the specimens were abraded with 50 μm alumina particles for 15 s at 2.5 bar pressure at a distance of approximately 10 mm. They were subsequently cleaned with water for 20 s, and air-dried with a three-way syringe. The specimens were measured with a digital caliper to confirm appropriate dimensions.
Saliva was collected from a human donor who refrained from consuming any food or drinks for 1½ h prior to the collection process after obtaining consent. The donor was asked to chew on a sugarless gum without swallowing the saliva for 5 min, following which the saliva was collected into a sterile container. The collected saliva was applied on selected four surfaces of each ceramic sample and left for 10 min [Figure 1]. Then, samples were then washed in running water, air dried, and labeled.
Selected four surfaces of lithium disilicate specimens (Group A) were labeled as A1, A2, A3, and A4, and monolithic zirconia (Group B) were labeled as B1, B2, B3, and B4, respectively, for the application of the four different cleaning protocols.
Saliva cleaning protocols
Each of the four saliva contaminated surfaces were isolated using a rubber dam and cleaned using WS (side A1 and B1), alcohol (side A2 and B2), 0.5% sodium hypochlorite (side A3 and B3), and Ivoclean solution (side A4 and B4). All conditioning, cleaning, and bonding procedures were carried out by the same operator, as per the manufacturer's instructions. The protocols were as follows:
- WS: The saliva-contaminated surface was washed with water for 20 s, and then air-dried for 20 s
- Alcohol: The saliva-contaminated surface was cleaned with 70% isopropanol for 2 min, rinsed with water for 15 s, and then air dried
- Sodium hypochlorite solution: The saliva contaminated surface was treated with 0.5% sodium hypochlorite solution for 20 s, rinsed with water for 10 s, and air dried
- Cleaning solution: A cleaning solution (Ivoclean; Ivoclar Vivadent) was placed for 20 s using a microbrush, then rinsed, and dried thoroughly.
Bonding with resin cement
For testing the SBS, composite cylinders were prepared by fabricating a cylinder of inlay wax with a diameter of 3 mm and height of 4 mm and a mold was prepared using additional polysilicon putty impression material. Once the mold was set, the inlay wax was removed and light-cure composite resin was filled in the mold and photopolymerized for 20 s [Figure 2]. The composite cylinder was then removed from the mold and photopolymerized from all the sides for 40 s.
Dual-cure resin luting cement was dispensed (base and catalyst pastes-3M ESPE RelyX) and mixed according to manufacturer's instructions, and applied to the treated ceramic surfaces and composite specimens. The excess cement was removed and the surfaces were photopolymerized for 40 s [Figure 3]. This sequence of bonding with the resin cement was repeated for all the other surfaces.
|Figure 3: Bonding of treated ceramic surface and composite cylinder with dual-cure resin|
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Testing of shear bond strength
The SBS of the specimens was tested in a universal testing machine. All the specimens were mounted over a customized fixture and subjected to shear loading until failure, at a crosshead speed of 1 mm/min [Figure 4]. The force at which debonding took place was tabulated.
The statistical analysis was performed with the Statistical Package for Social Sciences [SPSS] for Windows, Version 22.0. Released in 2013. Armonk, NY: IBM Corp. Descriptive analyses included expression of SBS using mean and standard deviation. Kruskal–Wallis test, followed by Mann–Whitney post hoc analysis was used to compare the mean SBS for the different cleaning solutions on lithium disilicate and zirconia groups. Mann–Whitney test was used to compare the mean SBS between both the groups under each cleaning treatment protocol. The level of significance (P value) was set at P < 0.05.
| Results|| |
After the specimens were tested for SBS in a universal testing machine, the force at which debonding took place was tabulated. The test results demonstrated different mean SBS with different surface treatment protocols. The difference in the mean SBS between the decontaminating solutions in Group A showed a statistically significant difference at P < 0.001 [Table 1]. The multiple comparisons result showed subgroup A4 having a significantly higher mean SBS compared to water at P = 0.008, isopropyl alcohol at P = 0.02, and 0.5% sodium hypochlorite at P = 0.03 [Table 2]. The difference in the mean SBS with the different decontaminating solutions for Group B showed a statistically significant difference at P < 0.001 [Table 3]. The multiple comparison of mean difference showed subgroup B4 having a significantly higher mean SBS than B1, B2, and B3 at P < 0.001 [Table 4]. In all the subgroups decontaminated with different cleaning agents, Group B specimens showed significantly more SBS compared to Group A specimens. The mean difference in the SBS for subgroup A1 and B1 was −3.862 at P = 0.01; for subgroup A2 and B2, it was −4.164 at P = 0.03; for A3 and B3. it was −4.845 at P < 0.001; and for subgroup A4 and B4, it was −24.990 at P < 0.001 [Table 5].
|Table 1: Comparison of mean shear bond strength (Mpa) between Group “A” specimens|
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|Table 2: Multiple comparison of mean difference in shear bond strength between Group “A”|
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|Table 3: Comparison of mean shear bond strength (Mpa) between Group “B” specimen|
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|Table 4: Multiple comparison of mean difference in shear bond strength between Group “B” specimen|
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|Table 5: Comparison of mean shear bond strength (Mpa) between Group “A” and Group “B” specimens|
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| Discussion|| |
The long-term success of resin-bonded restorations, as documented in multiple clinical studies, has been excellent due to their adhesive bonding to the tooth structures., However, the contamination of these restorations with saliva can compromise the resin bonding due to the remnant organic deposits that form. The exposure of the restorative surfaces to saliva leads to the formation of a thin film, mainly composed of organic proteins, which cannot be washed out with water. This leads to the weakening of the bond strength and hampers its ability to achieve the same bond strength as that of an uncontaminated restoration.,
Ivoclean, a new cleaning agent, has been introduced in the market recently. It comprises an alkaline suspension of zirconium oxide. According to the manufacturer, the contents of Ivoclean include zirconia, polyethylene glycol, water, sodium hydroxide, and a few other additives. Moreover, notably, it has been recommended for use in both zirconia and lithium disilicate restorations for decontaminating the surfaces prior to cementation.
In the present study, the surfaces of the lithium disilicate group cleaned using Ivoclean paste showed significantly more mean SBS (9.323 ± 3.490 MPa) compared to water (5.325 ± 1.251 MPa), isopropanol (5.473 ± 1.635 MPa), and sodium hypochlorite (6.246 ± 2.356 MPa). A possible explanation for this could be the failure to remove the organic residual film, which might have obstructed the penetration and seeping of the silane and luting cement into the microporosities. A study by Alnassar et al. used 96% isopropanol, 34% orthophosphoric acid, 5% hydrofluoric (HF) acid, and Ivoclean to decontaminate the lithium disilicate glass-ceramic (LDGC) surfaces from saliva mixed with silicone disclosing medium. The results showed significantly lesser bond strength, when compared to ceramics that were not contaminated. However, Ivoclean and 5% HF acid were found to be the most effective in cleansing of LDGCs.
Zirconia is known to have a high affinity toward phosphate groups. The phosphate groups in saliva actively bond to the bonding surface of the zirconia restorations, which makes it particularly difficult to achieve a good bond strength with resin cement on contamination. In the current study, a significantly higher SBS was seen in the surfaces cleaned using Ivoclean cleaning paste (34.313 ± 4.7530 MPa) compared to water (9.187 ± 4.083 Mpa), isopropyl alcohol (9.637 ± 5.409 MPa), and 0.5% sodium hypochlorite (11.091 ± 2.081). Due to the high concentration of zirconia particles in Ivoclean, the phosphate groups in saliva are likely to form a bond with the particles in the medium compared to the ceramic surfaces, hence leaving a clean bonding surface behind. This explains the higher bond strength values. A similar observation was noted in a study by Takahashi et al. which compared the efficacy of various cleaning agents on the bond strength of resin cement to zirconia surfaces. The specimens treated with Ivoclean showed a significantly higher bond strength than the groups that were decontaminated with tap water and multi etchant. Another study that evaluated the effect of salivary-contaminant removal methods on the bond strength of resin cement to ceramic specimens found similar bond strengths on using Ivoclean.
One limitation of this study, apart from the experiment being conducted in vitro, is that only the initial bond strength of the specimens was calculated. Further studies would be required to determine the efficacy of the cleaning regimens on the bond strength after thermal cycling to simulate long-term use. Within the limitations of this study, the following conclusions were drawn:
- In the lithium disilicate group, the mean SBS was highest for surfaces cleaned using Ivoclean
- Similarly, higher mean SBS was seen on the surfaces cleaned using Ivoclean in the monolithic zirconia group
- In both lithium disilicate and monolithic zirconia specimens, there were no statistically significant differences in the mean SBSs after cleaning with water, isopropyl alcohol, and sodium hypochlorite.
| Conclusion|| |
It can be concluded that Ivoclean might be an effective and safe choice for removing saliva from ceramic restorations after clinical try-in procedures to enhance the bond strength with resin cement. However, due to certain limitations in this study, it is suggested that further studies need to be conducted to get a clearer idea.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]