Comparative Evaluation of Effect of herbal antioxidants on the shear bond strength of composite resin to enamel following vital teeth bleaching: An In Vitro Study

Introduction

People with discolored teeth make a deliberate effort to avoid smiling. Correction of this dental problem can result in significant improvements in appearance, resulting in increased confidence, charisma, and social life. Advancements in aesthetic dentistry are more gratifying for dentists and provide a new level of dental care to the patients.¹

Extra-coronal bleaching is a popular, conservative, and well-accepted treatment option for discolored teeth that are deemed safe.² To obtain esthetic outcomes in a short period, different concentrations of whitening agents are available in the market.³

Despite their obvious benefits, these bleaching agents have some downsides.⁴ The instant decline in composite resin bond strength to enamel following bleaching is among the most important side effects of bleaching. It has even been proposed that the bond’s weakening is apparent both externally and internally. This could be attributable to the presence of residual peroxide, which limits resin polymerization and the creation of resin tags.5

Antioxidant treatment prior to bonding procedures appears to effectively replace the delay of either restorations or orthodontic bracket cementation following bleaching procedures.⁶ Antioxidant agents such as sodium ascorbate, green tea, aloe vera, tocopherol, or sodium bicarbonate have shown promising results as reversers of these transient side effects caused during whitening and as an alternative to delaying the restorations.⁷

Olive leaves have shown high bioactive compounds content, including phenolic compounds which are attributed to their antioxidant potential. Besides antioxidant potential, it has anti-atherosclerotic, anti-inflammatory, antimicrobial, and anti-allergic properties. It has a broad array of uses in the domains of food, medicine, cosmetics, and pharmaceuticals. In dentistry, however, it is not commonly used.

As there is scant data on the impacts of 2% Olive leaf extract on the shear bond strength of composite resin to bleached enamel, this research was aimed to evaluate and compare the impact of 2% Olive leaf extract and 2% green tea extract on the bond strength of enamel to composite after extra-coronal bleaching with 40% H₂ O₂ .

Materials and methods

Sample preparation

30 extracted intact human maxillary incisors, devoid of defects, were utilized. Using ultrasonic scalers, all teeth were cleared of debris and calculus. Only the facial surfaces were revealed after embedding specimens in blocks of acrylic resin. To acquire a smooth enamel surface for treatment and bonding, the facial surface of all samples was polished using 600-grit silicon carbide paper (Figure 1).

Bleaching procedure

The labial surface of 30 teeth was bleached for 20 minutes with 40 percent Hydrogen Peroxide (Opalescence Boost), as per the manufacturer’s recommendations. The bleaching gel was rinsed with water for 60 seconds before being air-dried (Figure 2).

The specimens were randomly arranged into three groups. (n=10).

Group I -Control- Bleaching with 40% H₂ O₂ followed by an immediate composite build-up.

Group II - Bleaching with 40% H₂ O₂ and application of 2% Olive leaf extract followed by a composite build-up.

Group III-Bleaching with 40% H₂ O₂ and application of 2% green tea extract followed by composite build-up.

Preparation of antioxidant solutions

Following the completion of the whitening procedure, antioxidant solutions namely, 2% olive- leaf extract and 2% green-tea extract were prepared. Dissolving 2g of extract capsules of olive-leaf extract and 2% green tea extract in 100 ml of sterile water yielded 2% solution of each. Using an applicator tip, 2% olive leaf extract was applied to Group II specimens, 2% green tea extract was applied to Group III specimens immediately after the bleaching procedure. It was then rinsed and dried after 10 minutes (Figure 3).

Bonding procedure

All samples were rinsed and air-dried following antioxidant treatment. A 2mm internal diameter and a 2mm height plastic tube was placed on the specimens. The self-adhesive composite (Dyad Flow Self Adhesive Composite, Kerr) was loaded into the tubes and lightcured for 40 seconds, following which the tubes were detached (Figure 4).

Statistical analysis

Version 22.0 of the Statistical Package for Social Sciences [SPSS] for Windows was released in 2013. NY: IBM Corp., Armonk, were utilized to conduct statistical studies. Descriptive analysis included expression of shear bond strength using Mean ± SD. To evaluate the mean shearbond strength among three study groups, a oneway ANOVA test was utilized, followed by a Tukey’s Post-hoc test. The level of significance [P-Value] was set at P<0.05.

Results

Table no.1 illustrates the comparison of mean Shear Bond Strength among 3 groups (Figure 5).

The test results demonstrate that mean Shear Bond Strength for the 2% Olive leaf Extract group was 201.70 ± 52.74, for the 2% Green Tea group was 123.40 ± 57.54 and for the control group, it was 42.20 ± 27.24. This difference in the mean Shear Bond Strength among 3 groups was statistically significant at P<0.001

Table no.2 illustrates the multiple comparisons of mean differences in shear bond strength among the groups. The 2 percent Olive leaf extract group had significantly higher shear bond strength than the 2 percent green tea group and the control group at P=0.006 &amp; P=0.001 respectively. This was followed next by the 2% green tea group showing significantly higher mean shear bond strength as compared to the control group at P=0.003. This infers that the 2% olive-leaf extract group showed significantly highest mean shear bond strength, followed by 2% green tea group and least with the control group.

Discussion

The desire for teeth whitening has increased significantly as a response to the increased attention given to smiles by patients. Bleaching is frequently used to treat discolored teeth. It can eliminate stains and whiten discolored teeth that need aesthetic enhancement.

Currently various agents with varying concentrations are available for in-office vital teeth bleaching. In this study, Opalescence Boost bleaching gel, containing 40% H₂ O₂ and a chemical activator was used. Light activation was not required and it delivers dramatic outcomes after 2 or 3 twenty-minute treatments. Buffers are added to maintain neutral pH levels, assuring optimal patient comfort by closely matching the natural pH of saliva. It has high H₂ O content which helps to maintain the teeth moist during the bleaching process.^8,9

Self-adhering flowable composites reduce the chairside time for both the clinician and the patient by combining etching, bonding, and restorative techniques into a single step.¹⁰ Dyad- Flow is a self-adhering resin composite that combines Optibond Technology in its formulation.

Whitening procedures have various drawbacks which include postoperative sensitivity, pulpal irritation, changes in tooth structure, or microleakage of preexisting restorations.¹¹ It has been shown to weaken the bond between enamel and dentin and dental composite resin. The free radicals and reactive oxygen species (ROS) produced by the bleaching process remain on the tooth’s surface. These can then neutralize free radicals formed during the resin monomer addition polymerization reaction, slowing down the process and interfering with resin phase infiltration during bonding. As a result, bond strength to bleached enamel is inadequate immediately after the treatment.⁷

The gold standard for mitigating the negative impacts of bleaching on composite resin restoration is to postpone any restorative procedure for four days to four weeks post bleaching.^12,13,14 As the peroxide ions disintegrate and the replaced hydroxyl radicals re-enter the hydroxyapatite lattice, the structural alterations produced by their incorporation are resolved after 24 hours to 3 weeks.¹⁵

In this era of instant gratification, products and approaches that deliver the best outcome in a short duration should be employed for treatment. To provide immediate/instant esthetic restoration following bleaching, several approaches have been offered, which include conditioning bleached enamel with alcohol before restoration, removing the enamel surface layer,¹⁶ and using organic solvent-based adhesives.¹⁷ After bleaching, different antioxidant agents have been recommended, including 10% sodium ascorbate, Vitamin E, and herbal antioxidants.¹⁸

Antioxidants have been successfully used in dentistry in recent years due to their positive health effects shown in humans. Its most well-known effect is that it neutralizes the harmful effects of free radicals. It has different uses in restorative dentistry which include pulp capping, remineralization, hypersensitivity, etc.¹⁹ Phytoconstituents have been found to be a good substitute for synthetic and chemical antioxidants.²⁰ In this research, 2% olive leaf extract and 2% green tea extract were used.

Strong bonding with the teeth is crucial for a restoration to survive longer. According to studies, the minimum bond strength required for enamel to withstand the forces on composite resin materials is 17-20 MPa. Different studies showed that this is sufficient for a restoration to last longer. The adhesion between composite and tooth is studied using shear bond strength.²¹

Hence, we studied the effect of antioxidants on the shear bond strength of self-adhesive composite resin to bleached enamel.

When mean shear bond strength of self-adhesive composite to enamel after bleaching were compared among the three groups, application of antioxidants prior to composite restoration increased the shear bond strength significantly compared to the control group. Immediate composite restoration to enamel after vital teeth bleaching showed decreased bond strength (42.20 Mpa). These results were consistent with Borges et al. The delayed O₂ release interferes with the resin polymerization which might result in reduced shear bond strength.²²

The application of 2% Olive-leaf extract for ten minutes increased the shear bond strength significantly compared to 2% green tea extract. Cinnamic acid, Tyrosol, Ferulic acid, Hydroxytyrosol, Gallic acid, Vanillic acid, and Coumaric acid are the active chemicals identified in the olive leaf extract. Its most potent antioxidative substance has been revealed to be phenolic acids.²³ The most prevalent phenolic substance found, hydroxy tyrosol (HT), inhibits ROS, particularly radical superoxide radicals.²⁴ By scavenging peroxyl radicals and halting a peroxidative-chain reaction, the catecholic structure of HT forms a stable resonance structure.²⁵

Green tea extracts contain catechins, which are made up of four different epicatechins (EC) derivatives: EC (6.4%), epigallocatechin (EGC) (19%), EC gallate (ECG) (13.6%), and EGC gallate (EGCG) (59%). Green tea polyphenols have an antioxidant capacity that is directly related to their structure, specifically the hydroxyl groups that promote free radical binding and neutralization.²⁶ Previous research has shown that utilizing 2% green tea extract as an in-office method to repair the lost shear bond strength in bleached enamel is a viable option.²⁷

The molecular weight (MW) of the materials also seems to have played a role. H₂ O₂ is a low MW substance that permeates into the dental hard tissues and breaks down into free radicals, therefore antioxidants should have low MW for efficient scavenging action.¹¹ MW of Hydroxytyrosol was found to be 154.16 g/mol and catechins 290.2 g/mol. ²⁸ This could have enabled the olive-leaf extract to penetrate better than green tea extract.

A study by Lobo et.al., reported that the application of antioxidants such as grape-seed extract, sodium ascorbate, and green tea extract can restore the lost bond strength in bleached enamel.¹²

When compared to 2% green tea extract, using 2% olive leaf extract for 10 minutes boosted shear bond strength substantially, which could be due to the catecholic structure of Hydroxytyrosol in olive leaf extract as well as its molecular weight.

The effect of the whitening agent on the bond-strength of composite resin to the enamel can be reversed after one hour of application of antioxidant, according to a study by Lai et al. ²⁹ Türkün et al., demonstrated that ten minutes of application of antioxidant was sufficient for the reversal.³⁰ Hence, the antioxidant application time frame in this investigation chosen was 10 minutes. More studies should be conducted to see how varying application times, concentrations, and types of antioxidants affect the shear bond strength of bleached enamel surfaces with different bleaching agent concentrations. Conclusion Within the constraints of this research, it can be inferred that 2% Olive leaf extract and green tea extract can be used to reverse the effect of bleaching on the bond strength of composite resin to the enamel.

Conflicts of Interest

None.