In Vitro Evaluation of the Effect of Different Surface Treatments on Shear Bond Strength of New to Old Composite Restorations

Ebrahim Yarmohammadi; Maryam Farshchian

doi:10.4103/denthyp.denthyp_20_20

Official publication of the American Biodontics Society and the Center for Research and Education in Technology

ORIGINAL RESEARCH

Year : 2020 | Volume : 11 | Issue : 4 | Page : 108-111

In Vitro Evaluation of the Effect of Different Surface Treatments on Shear Bond Strength of New to Old Composite Restorations

Ebrahim Yarmohammadi, Maryam Farshchian
Department of Restorative Dentistry, Dental School, Hamadan University of Medical Sciences, Hamadan, Islamic Republic of Iran

Date of Submission	20-Feb-2020
Date of Decision	30-May-2020
Date of Acceptance	09-Jul-2020
Date of Web Publication	18-Nov-2020

Correspondence Address:
Maryam Farshchian
Department of Restorative Dentistry, Dental School, Hamadan University of Medical Sciences, Hamadan
Islamic Republic of Iran

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/denthyp.denthyp_20_20

Abstract

Introduction: Composite resins have developed in past years, however, failures may occur which needs whole restoration repairing. this study aimed to evaluate the effect of different surface treatments on shear bond strength of new to old composite restorations. Materials and Methods: A total of 60 blocks of Z250 composite resin were divided to four groups 1) no surface preparation (control group), 2) abrasion through aerosols using 50-micron aluminum oxide particles, 3) abrasion through diamond milling with 125-micrometer particles, 4) surface preparation using hydrofluoric acid. Shear bond strength in different methods such as etching with hydrofluoric acids (with and without silanization), air abrasion, and diamond milling was compared with the control group. All data were analyzed using the Kolmogorov-Smirnov test and one-way analyses of variance (ANOVA) and Tukey’s post hoc test. Results: In comparing the groups with each other, it was found that shear bond strength in Hydrofluoric acid and silanization group was significantly higher than control (P = 0.017). Conclusion: The effects of etching with hydrofluoric acid and silanization in increasing shear bond strength between aged and new composite resins are superior to control, which could be a suitable repair protocol to obtain optimal repair bond strength.

Keywords: Air abrasion, composite resins, hydrofluoric acid, shear strength

How to cite this article:
Yarmohammadi E, Farshchian M. In Vitro Evaluation of the Effect of Different Surface Treatments on Shear Bond Strength of New to Old Composite Restorations. Dent Hypotheses 2020;11:108-11

How to cite this URL:
Yarmohammadi E, Farshchian M. In Vitro Evaluation of the Effect of Different Surface Treatments on Shear Bond Strength of New to Old Composite Restorations. Dent Hypotheses [serial online] 2020 [cited 2023 Jun 2];11:108-11. Available from: http://www.dentalhypotheses.com/text.asp?2020/11/4/108/300864

Introduction

Composite resins have significantly improved in past years; however, failures may occur simply as a result of fractures, secondary caries, discoloration, marginal ditching.^{[1],[2],[3],[4]} The choice for treatment is restoration or replacing.^{[5],[6],[7],[8],[9]} Based on several clinical trials, repairing the pre-existing restoration is a more conservative alternative that can reduce operative trauma, preserve the sound tooth structure, and increase the longevity of the restoration.^{[4],[5],[10],[11],[12]}

Bonding between two composite layers is accomplished by the presence of an oxygen-enriched surface layer (containing unreacted C═C bonds) which remains unpolymerized^{[3],[5],[7],[13]} and allows the new composite resin to bond to it.^{[7],[13],[14]} The adhesion between an old composite resin and a new one is reduced by 25% to 80% due to a diminished amount of unreacted double bonds.^{[1],[12],[15]} The success in this adhesion depends on the chemical composition of the surface, surface conditioning methods applied, wetting, and roughness.^{[7],[12],[13]} Therefore, different surface treatment modalities have been introduced to increase the composite resins repair bond strength,^{[1],[2],[4],[7],[8],[9]} such as etching with hydrofluoric or phosphoric acids, bur roughening, air abrasion, silica coating and silanization.^{[4],[6],[7],[8],[9]} As to best of our knowledge, there isn’t enough prospective study about the efficacy of different mechanical and chemical surface treatment procedures on bond strength between aged and new composite resin, therefore, this study was designed to evaluate and compare the effect of different surface treatments on shear bond strength of new to old composite restorations.

Materials and Methods

Study design and target group

This in vitro study was conducted in the Dental Research Center of Hamedan University of Medical Science, from November 2018 to May 2019. The effect of etching with hydrofluoric acid, diamond milling, air abrasion on shear bond strength of new to old composite restorations (intervention groups) was compared to samples without receiving any surface treatment (control group). This in vitro study was approved by Kermanshah University Of Medical Sciences (No, 9802241560).

A total of 60 specimens were constructed by a cylindrical mold of stainless steel using shade A2 of micro-hybrid composite Z250 (3M ESPE, ST Paul, MN, USA) in 5 mm diameter and 3 mm high. The specimens were placed in self-hardening acrylic resin (Acropars 200, Marlic Medical Industries Co., Iran) and they were polished with 800/600/320/ grit silicon carbide paper (Leco) under cooling water flow as a lubricant.

All samples have passed thermodynamic cycles (1000 heat cycles between 5°C and 55°C) by thermocycling Machin (THE-1100, SD Mechatronik, Feldkirchen-Westerham, Germany) before applying the new resin composite. Then, they were divided into five groups of 12 samples:

The first group received no surface Surface treatment and only the G-Premio Universal Adhesive (GC; japan, Tokyo) was applied to the surface of the samples (control group). G-Premio Universal Adhesive placed on the surface as a single layer, after 10 seconds it was dried for 5 seconds, it was then light-cured for 20 seconds by the LED curing unit (1200 mW/cm², Bluephase 20i, Ivoclar Vivadent, Schaan, Liechtenstein).
The second group received abrasion through aerosols using 50-micron aluminum oxide particles (Bisco, USA) at 4 bar pressure for 10 seconds from 10 mm sample distance and perpendicular to the surface of the sample by micro blaster machine (Dento-prep TM/Denmark/dental micro Blaster) and after washing and air drying, the samples received G-Premio Universal Adhesive (GC; japan, Tokyo) with the same protocol previously mentioned.
The third group received abrasion through diamond milling (Switzerland) with 125-micrometer particles and a very delicate layer was removed from their surface and after washing and air-drying, G-Premio Universal Adhesive was applied.
The fourth group received surface preparation using hydrofluoric acid. The 9% hydrofluoric acid (Ultradent) (product Inc, Utah, USA) was applied for 60 seconds and then rinsed with water for 30 seconds and air-dried, and after that G-Premio Universal Adhesive was applied.
The fifth group was treated with 9% hydrofluoric acid (Ultradent, Inc, Utah, USA) for 120 seconds and then ultrasonic silicification (product Inc, Utah, USA) for 60 seconds after which G-Premio Universal Adhesive was applied.

After surface treatment, the specimens were placed in another mold with a height of 6 mm and a diameter of 5 mm, and the new composite with color A3.5 was packed with a 6 mm diameter (in two 1.5 mm layers) and each layer was cured for 20 seconds. The reason for using the color A3.5 was the visual observation of the fracture line and facilitated failure detection with the help of two different colors. Afterwards, the mold was removed and all samples were kept in distilled water at 37° C for 24 h to give time to post-curing polymerization to take place. Shear bond strength was measured using a universal testing machine (Dartec, HC.10, England). The samples were fixed on a stand and the block band location was pressurized with a transversally oriented composite cylinder at a crosshead speed of 0.5 mm/min. The maximum pressure which led to the separation of the composite cylinder from the blocks was measured and the shear bond strength was calculated using the following formula:

SBS(in MPa) = P × 9.8/r² × π (SBS: Shear Bond Strenght, Mpa: Mega Pascal, P: Pressure applied by the universal test machine in Kg, r: radius of the surface contact circle, π: the numerical value of pi).

Data analysis

Statistical analysis of data was performed using SPSS version 22 software (SPSS Inc., Chicago, IL, USA). Kolmogorov-Smirnov test was conducted to evaluate the normal distribution of all quantitative studied parameters. one-way analyses of variance (ANOVA) and Tukey’s post hoc test was used. The two-tailed p-values less than 0.05 were considered significant.

Results

Results revealed that shear bond strength in Hydrofluoric acid and silanization group was significantly higher than control (P = 0.017) [Table 1]. On the other hand, there was a significant difference in shear bond strength between air abrasion (15±5.27) and Hydrofluoric acid and silanization (20.95±7.38) groups (P = 0.044). However, no significant difference was found between other groups (P > 0.05) [Table 1] and [Figure 1].

Table 1 Shear bond strength in different studied groups

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Figure 1 Shear bond strength in different studied groups (HF+Sil: Hydrofluoric acid and silanization, HF: Hydrofluoric acid, DM: Diamond milling, AA: Air abrasion).

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Discussion

According to results, etching with hydrofluoric acid and silanization presented higher shear bond strength between aged and new composite resins as compared to control samples. Moreover, it was observed that shear bond strength in this group was higher than the specimens treated with airborne-particle abrasion, however other groups did not significantly differ with the control group.

In the study performed by Zaghloul et al.^[17] it was shown that additional silanization step cannot be eliminated if the repair protocol comprises either etching with hydrofluoric acid or coating with silica. Similar to the results of the other studies, we found that etching with hydrofluoric acid in combination with silanization had better effects on shear bond strength which was better than applying hydrofluoric acid alone (however, we did not observe significant differences between hydrofluoric acid with and without silanization). The literature review article performed by Barghi N showed that silanization provides a more reliable bond than etching with hydrofluoric acid alone, although the combinations of both are recommended.^[18]

Silanes are adhesion promoters containing two different reactive functional groups that can react and couple with different inorganic and organic materials, which are used to increase the union of dissimilar materials. The hydrolyzable functional groups bond to the surface hydroxyl groups of inorganic layers creating a siloxane bond (Si-O-Si). On the other hand, the organic non-hydrolyzable functional group with a carbon-carbon double bond can react with resin composite substrates containing double bonds.^[19],[20] It could be concluded that there should be a balance between the hydroxyl groups of inorganic substrates and the hydrolyzable functional groups present in the silane. Thus, the concentration of the silane solution formed the quality of the siloxane bond^[19] and the surface pre-treatment protocol that determines the number of hydroxyl groups exposed.

The composite includes organic resin matrix, mineral filler, coupling agent and initiator system. Hydrofluoric acid can help to enhance the bond strength of composite to composite restoration by dissolving the filler materials through the composite component leaves microporouses on old restoration surface which increases mechanical retention.^[21]

In an experimental study, researchers investigated the effect of short-term exposure to 1% hydrofluoric acid to improve the strength of the dental restoration bond. The results of this study, performed on microhybrid and nanofilled composites, showed that short-term) 1 second (exposure to 1% hydrofluoric acid on the nanofilled composites could improve bond strength, whereas, for microhybrid material, this time should be at least 30 seconds.^[22] Another study looked at the effect of different chemical surface treatment methods on the composite-composite bond strength. In this research, which was performed on 40 composite blocks, 37% phosphoric acid, 10% hydrofluoric acid, 30% citric acid and 7% maleic acid were used for etching and surface treatment of composites. The findings revealed that compared to 37% phosphoric acid which is commonly used, 10% hydrofluoric acid could be a viable alternative for surface treatment of composite resin restoration.^[23] In 2018, a study was conducted in Iran which evaluated the micro-shear bond strength of the old and new composite restoration via binding and using different composite systems. It was reported that the use of acid etching did not have a significant effect on the micro-shear bond strength between methacrylate- and silorane-based composites, but the application of P90 silorane binding caused a greater micro-shear bond strength in the silorane-based composite.^[24]

Given the conflicting results of various studies, it is clear that more studies are needed for enhancing shear bond strength between aged and new composite resins. Furthermore, it is recommended to consider different preparation methods, the use of different bondings, different composites and different methods of measuring composite shear bond strength in subsequent studies.

Conclusion

Within the limitations of this study, it was shown that etching with hydrofluoric acid and silanization could have superior effects in increasing shear bond strength between aged and new composite resins, which could be a suitable repair protocol to obtain optimal repair bond strength. However many randomized double-blinded clinical trials are needed to compare different methods on shear bond strength between aged and new composite resins especially in vivo studies.

Financial support and sponsorship

This study was financially supported by the Kermanshah University of Medical Sciences Grant No, 9802241560.

Conflicts of interest

The authors have indicated that they have no conflicts of interest regarding the content of this article.

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Figures

[Figure 1]

Tables

[Table 1]

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