Effect of alcoholic beverages on shear bond strength of composites to enamel.

BACKGROUND: Longevity of composite restoration in the oral cavity is dependent on various factors. One such factor is exposure to various foods and beverages which could alter the properties of the material. AIM: The aim of this in vitro study was to evaluate the effect of most widely consumed alcoholic beverages on shear bond strength of composites to enamel.
MATERIAL AND METHODS: A total of seventy human premolars were embedded in acrylic resin blocks. Labial enamel surfaces was flattened, etched, bonded, and restored with composite resin (Tetric N Ceram - Ivoclar Vivadent AG, Schaan, Liechtenstein). The specimens were randomly divided into four groups: Group I: beer; Group II: wine; Group III: whiskey, and Group IV: artificial saliva. Group I to Group III were again divided into moderate (Group IA, IIA, and IIIA) and heavy (Group IB, IIB, and IIIB) consumption subgroups. The specimens were soaked in their respective groups for 90 min daily in Group IA, IIA, and IIIA and for 30 min every alternate day in Group IB, IIB, and IIIB until 30 days. Universal testing machine was used to determine the shear bond strength of composite with enamel. STATISTICAL ANALYSIS USED: The values obtained were statistically analyzed using two-way analysis of variance followed by post hoc test with the significant level set at P < 0.05, using GraphPad prism software version 6.01.
RESULTS: Group IIB showed the highest reduction in shear bond strength, with a mean value of 6.6 ± 1.2 Mpa in comparison to control with a mean value of 21.8 ± 1.6 Mpa.
CONCLUSION: As the content of alcohol and time of exposure increased along with a decrease in the pH of alcoholic beverages, shear bond strength between composite and enamel decreased.

INTRODUCTION

Resin-based dental restorative materials have come out as one of the most promising materials. Increasing demand for a material which could provide esthetics, ease of handling, and ability to bond to tooth structure leads to the introduction of composite resins.[1]

The long-term clinical performance of composites depends on the type of material used and degradation process over time.[12] Restorations are continuously exposed to saliva, foods, and other beverages that may affect their mechanical properties such as wear resistance, bond strength, integrity between tooth-restoration interface, esthetics, hardness, and roughness.[3]

Alcoholic beverages have become a fashion of life. People drink them to socialize, rejoice, celebrate, and relax. Due to low pH and ethanol content, alcoholic beverages can produce erosion and modify the properties of composites.[4] Alcohol is also thought to have a negative effect on the wear resistance of resin composites and acts as a plasticizer of the polymer matrix.[5] The impact of any beverage on restorative material may be directly related to the amount and frequency of its intake.[6]

Various studies have been done to study the effect of alcoholic beverages on color stability,[7] surface roughness, and microhardness of dental composites.[8] However, to the best of our knowledge, there are no studies done to evaluate the effect of alcoholic beverages on the shear bond strength of composites. Hence, this study tested the null hypothesis that the alcoholic beverages such as beer, whiskey, and wine do not affect the shear bond strength of composite with enamel.

MATERIALS AND METHODS

Seventy freshly extracted human premolars for orthodontic reasons were collected. Teeth with cracks, restorations, and surface defects were excluded from the study. Approval from the Institutional Ethical Committee was taken for the use of the extracted teeth.

Teeth were embedded in acrylic resin blocks with their roots till cementoenamel junction. An abrasive disc was used to flatten the labial enamel surfaces. Stereomicroscope (SZX7 Olympus America Inc., Center Valley, Pennsylvania, U.S.A.) was used to check dentin exposure. Then, enamel was etched with 35% phosphoric acid (N Etch, Ivoclar Vivadent, Schaan, Liechtenstein) for 30 s, rinsed for 15 s, and gently air-dried for 10 s. Followed by application of bonding agent Tetric® N-Bond (Ivoclar Vivadent AG, Schaan, Liechtenstein), the enamel was gently air-dried for 10 s and light cured for 10 s with a visible light-curing unit (Hilux, Ledmax-550, Benlioglu, Turkey). Finally, nanohybrid composite (Tetric N Ceram–Ivoclar Vivadent AG, Schaan, Liechtenstein) was incrementally placed using a silicon mold of 2-mm diameter and 3-mm length and light cured for 40 s.

The pH of alcoholic beverages used in the study was determined using a pH meter (Digital pH meter 335, Systronics Ltd, India). All the specimens were randomly divided into four groups as follows: beer, wine, whiskey, and artificial saliva (control). The first three groups were divided into two subgroups depending on the type of alcoholic consumption, i.e., moderate (Beer-IA, Wine-IIA, and Whiskey-IIIA) and heavy (Beer-IB, Wine-IIB, and Whiskey-IIIB). Each subgroup and control consisted of ten teeth each. Composition of the alcoholic beverages used in this study is described in Table 1.

Table 1

Distribution of specimens and study groups

Group IV specimens were soaked in artificial saliva for 30 days, which was taken as control group. Groups IA, IIA, and IIIA were soaked in their respective alcoholic beverages for 30 min on every alternate day for 30 days. Groups IB, IIB, and IIIB were similarly soaked in their respective alcoholic beverages for 90 min/day for 30 days. Between the soaking periods, the specimens were incubated in artificial saliva at 37°C. Before subjecting the specimens for testing shear bond strength, they were incubated at 37°C for 5 days in artificial saliva.

All specimens were transferred to a universal testing machine (Autograph AG-X, Shimadzu, Japan) individually. They were subjected to shear bond strength analysis at a crosshead speed of 0.5 mm/min, until fracture occurred.

Data were analyzed by GraphPad prism software version 6.01 (Graph Pad Software Inc., La Jolla, CA, USA) and summarized by mean ± standard deviation for continuous data. The comparison between groups was done by one-way analysis of variance test followed by post hoc Turkey test, with the significant level set at P < 0.05.

RESULTS

It was found that the highest reduction in shear bond strength was obtained with Group IIIB (6.6 ± 1.2 Mpa) followed by Group IIIA, Group IIB, Group IIA, Group IB, and Group IA. The maximum shear bond strength value was obtained with Group IV (21.8 ± 1.6 Mpa) [Table 2].

Table 2

Comparison of shear bond strength values in Mpa obtained with different study groups included in the study

DISCUSSION

Despite the enormous advances made in adhesive technology during the past 50 years, the bonded interface itself remains the Achilles heel of an adhesive filling.[910] The strength and longevity of the bond to the two dental hard tissues, i.e., enamel and dentin, is dependent on several factors.[111213] These include the heterogeneity of tooth structure and composition, the features of the dental surface exposed after cavity preparation, and the characteristics of the adhesive itself.[914]

Apart from all these, adhesive restorations in the oral environment are constantly subjected to various interactions between food and drinks consumed, which have different pH and solubility levels. Inevitably, these interactions can cause changes in the mechanical and chemical properties of resin composites.

Methacrylate-based nanohybrid composites (Tetric N Ceram–Ivoclar Vivadent AG, Schaan, Liechtenstein) were used in this study. These composites were selected as these are ideal for anterior and posterior restorations. Nanofillers present in them improve their properties by providing reduction in shrinkage and related stresses. High radiopacity, wear resistance, and excellent polishability with high gloss are other added advantages. Nanocolor pigments aid in imparting chameleon effect to achieve esthetic results.[15]

A fifth-generation bonding system, Tetric® N-Bond (Ivoclar Vivadent AG, Schaan, Liechtenstein), was utilized to bond composite to enamel. It provides high bond strength to enamel and dentin. Nanofillers present in them improve adhesion properties.[15]

Alcoholic drinks have been consumed since ancient times which play an important social role in many cultures. These beverages are available as three main classes: beer, wine, and spirit. The oldest and most widely consumed alcoholic beverage in the world is beer. It only stands third to the popular drinks water and tea.[16] Beer and wine are produced by fermentation process, while whiskey, a form of spirit, is produced by distillation.[17]

The present study was performed to determine the effect of these three main classes of alcoholic beverages, i.e., beer, wine, and whiskey on shear bond strength of composite to enamel. The effect of exposure to alcohol by moderate and heavy consumers was also taken into consideration separately. Artificial saliva was used as “control” to imitate the oral cavity environment.

The United States Dietary Guidelines define moderate alcohol drinking for women as up to 1 drink/day and for men up to 2 drinks/day,[18] while heavy drinking is defined as consuming eight or more drinks/week for women and 15 or more drinks/week for men.[18] The peak level of blood alcohol is achieved in 30–90 min after consumption of alcoholic beverage.[19] One drink is considered as 12 ounces of beer, 5 ounces of wine, and 1.5 ounces of distilled spirits as per these guidelines. Hence, soaking time of 30 min every alternate day for moderate consumption group and 90 min daily for heavy consumption group was chosen.

Based on 30 days' experimental period, all the groups showed significantly decreased bond strength irrespective of their exposure when compared with the control. The highest reduction in shear bond strength was obtained with Group IIB followed by Group IIA of whiskey. Therefore, the hypothesis was rejected based on the fact that the alcoholic beverages reduced the shear bond strength of composite to enamel at the end of the experimental period.

The reduction in shear bond strength could be attributed to the higher alcohol content of whiskey, which is about 41.1% in comparison to beer 4.5% and wine 12.9%.[20]

Various studies have shown the effect of alcohol in reducing the properties of composite resins. According to Sarret et al.,[21] alcohol increases the ductility of composites by acting as a plasticizer of the polymeric matrix. Ethanol can be attributed for reducing the bond between resin matrix and inorganic fillers, which could decrease the erosion resistance and lead to staining of the resin matrix.[22]

Chemical analysis has shown that beer contains caffeic acid, ferulic acid, p-coumaric acid, phenolic acids, 4-hydroxyphenylacetic acid, sinapic acid, syringic acid, and vanillic acid.[23] Presence of these acids attributes to acidic pH of beer being around 4.9.[24] Whiskey contains alcohols, carbonyl compounds, carboxylic acids, and their esters, tannins, polyphenolic compounds, terpenes, pyridines, picolines, pyrazines, thiophenes, polysulfides, and esters of fatty acids.[25] This makes whiskey more acidic (3.5 pH) in comparison to wine (4.4 pH) and beer (4.9) and artificial saliva (7.0). Toodehzaeim et al.[26] reported that decrease in pH resulted in bond failure between composite and enamel.

As the present study was performed in vitro, the beneficial cleaning property of saliva is lacking. To add on, oral habits such as toothbrushing may enhance the forces acting on teeth and restorations. Further studies are required to investigate the effects of alcoholic beverages on shear bond strength of various composites to enamel and dentine using different bonding agents.

CONCLUSION

Within the limitations of this study, it can be concluded that the shear bond strength of composite resin to enamel surface reduced, with the consumption of alcoholic beverages having low pH and higher frequency of intake.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.