Effects of sports beverages and polishing systems on color stability of different resin composites.

BACKGROUND: Consumption of certain acidic beverages may alter the physical and esthetic properties of resin composites. AIM: The aim of this study was to evaluate the effects of two sports beverages on color stability of two different types of resin composites polished with different composite polishing systems.
MATERIALS AND METHODS: A total of 96 disk-shaped specimens (diameter: 8-mm and thickness: 2-mm) were made from two different resin composites (Cavex Quadrant Universal-LC, and Clearfil-APX). All of the specimens were stored in distilled water for 24 h at 37°C. Color measurements of each specimen were performed using a colorimeter according to the CIEL*a*b* color scale at baseline and after seven days of immersion in two different sports beverages (Powerade and Buzzer). STATISTICAL ANALYSIS USED: The data were evaluated using Kruskal Wallis and Mann-Whitney U tests.
RESULTS: Significant differences were found between the mean ΔE values of the groups after seven days of immersion (P < 0.05). The highest level of the mean color change was observed in the Clearfil APX specimens immersed in Powerade (ΔE = 3.5 ± 0.9). Control groups stored in distilled water for both composites exhibited small color changes (ΔE-Cavex-bur = 2.1 ± 1; ΔE-Clearfil APX-bur = 2.1 ± 0.4).
CONCLUSION: Sport beverages caused discoloration in the resin composites after seven days.

INTRODUCTION

The clinical use of resin composite as a restorative material has substantially increased in the recent years both for anterior and posterior teeth. However, the major problem associated with the resin composites is the discoloration of the materials because of several factors including bad oral hygiene, tobacco use, certain dietary patterns, inadequate polishing technique, surface texture, and surface integrity.[12]

Dental composites are commercially classified according to their particle size such as microhybrid (10-100 μm), nanofill (5-10 μm), and nanohybrid (15-50 μm) resin composites.[34] It has been reported that structure of the resin matrix and characteristics of the filler particles have an effect on discoloration of the resin composites.[5]

A smooth surface is clinically crucial for any of the resin restorations since it determines the esthetic quality and the long-term success of restorations, whereas a rough surface is the major reason for the external discoloration, mainly because of plaque accumulation.[678] Characteristics of the filler particles of a composite material can determine the surface roughness of a restoration.[9] Therefore, the susceptibility of the restoration to external discoloration can be changed by the filler particle size of the resin composites.[101112] Discoloration of resin restorations is an esthetic failure, which is one of the most frequently encountered clinical problems.[13] Consumption of certain acidic beverages has been reported to alter the physical and esthetic properties of resin composites and thus may affect the clinical success of the restorations.[14] Sports beverages are acidic drinks and, therefore, can affect the clinical outcome of the resin restorations.[15] The effect of different beverages on the color stability of resin composites has been reported in many investigations. However, researchers have focused on the influence of tea, coffee, and cola in most of these studies.[16] Therefore, the aim of this study was to evaluate the color stability of a nanofilled and a microhybrid resin composites polished with different techniques after immersing in two different sport beverages for a seven-day period.

MATERIALS AND METHODS

Two different resin composites of shade A2: A nano-hybrid (Cavex Quadrant Universal LC, Cavex, Haarlem, The Netherlands) and a micro-hybrid (Clearfil AP-X, Kuraray, Osaka, Japan) were selected for this study. Eight specimens per study group yielded a total of 96 disk-shaped specimens of 8 mm in diameter and 2 mm in thickness.

The composite was placed into a Teflon mould and covered with a Mylar strip. A glass plate was applied on top of the Mylar strip in order to remove excess material, to obtain a flat surface, and to protect the resin composite from oxygen inhibition. The composite was cured through the glass plate and Mylar strip for 40 seconds with a LED light-curing unit (3M ESPE Elipar S10). The Teflon mould was reversed and the Mylar strip was placed on to it to cure the resin composite from the other side of the mould for another 40 seconds.

Ninety-six specimens were randomly divided into two subgroups and were polished using two different polishing systems; a series of aluminum-oxide multi-step polishing discs (Optidisc, Kerr, CA, USA) for 15 s for each disc (extra-coarse, coarse, fine, extra-fine) and a two-step diamond impregnated rubber polishers (KerrHawe HiLuster Plus, Kerr, CA, USA) for 15 s for each bur (fine, extra-fine) using a low-speed hand piece without water cooling.

Specimen preparation, finishing, and polishing procedures were carried out by the same operator. The specimens were polished immediately after curing. The finishing and polishing procedures were applied to both sides of the specimens in a single direction according to the manufacturers’ instructions. Each specimen was numbered on the side using a small round bur to determine the measurement surface on top.

The specimens were stored in distilled water for 24 hours at 37°C before the baseline color evaluation. Baseline colors of the resin composites was measured with a VITA Easyshade colorimeter (Vident, Brea, CA, USA), using the CIELAB scale and the L*, a*, b*. ΔE* was determined using the following equation: ΔE*=[(ΔL*)2+(Δa*)2+(Δb*)2]½. The measurements were performed over a neutral background under the same room in daylight without any artificial lighting.[17]

Following the baseline measurements, subgroups of the resin composite specimens were randomly chosen for the sport drinks. The first subgroups of each resin composite were stored in distilled water to serve as control. The other subgroups of each composite resin were individually immersed (n = 8) in vials containing 5 ml of Buzzer (Altanea Icecek A.S., Istanbul, Turkey) and Powerade (The Coca-Cola Co., Istanbul, Turkey). Immersions were carried out three times a day for five minutes at room temperature. After each immersion process, the specimens were washed with distilled water and also stored in distilled water at room temperature during the seven-day cycle. The vials were sealed to prevent the evaporation of the beverages and were renewed after every application.

The color measurements were performed after seven days. All the measurements were obtained by the same investigator. All the specimens were wiped dry using tissue paper. Baseline and seven-day measurements were performed on the same surface of the specimens according to the number signs on the sides. Before each measurement, the colorimeter was calibrated according to the manufacturer's recommendations using the supplied white calibration standard. Color changes (ΔE values) of the specimens were recorded.

Kruskal Wallis and Mann-Whitney U tests were used to evaluate the data from the colorimetric experiments using statistical software (SPSS for Windows, version 18.0; SPSS Inc., Chicago, IL, USA) (α = 0.05).

RESULTS

Descriptive statistics including mean, minimum, maximum, and median values with standard deviation and interquartile range for color stability (ΔE value) of two different composite polished with discs are presented in Table 1. Significant differences were found between the mean ΔE values of the groups after seven days of immersion (P < 0.05). The highest level of the mean color change was observed in the Clearfil APX specimens immersed in Powerade (ΔE = 3.5 ± 0.9) (P < 0.05). The lowest mean color change values were from the Clearfil APX specimens stored in distilled water during the experiment (ΔE = 2 ± 0.4) (P > 0.05). Both of the studied composites polished with discs exhibited significant differences after immersing in the beverages compared with the baseline color measurements (P < 0.05).

Table 1

Descriptive statistics of two different composite polished with a series of discs at baseline and after immersing in the tested sport beverages for a period of 7-days

Table 2 shows descriptive statistics for color stability (ΔE value) of two different composites polished with rubber cups. Significant differences were found between the mean ΔE values of the groups after seven days of immersion (P < 0.05). The greatest color changes were observed in the Cavex specimens immersed in Buzzer (ΔE = 3.3 ± 1.2) (P < 0.05), whereas control groups stored in distilled water for both composites exhibited smaller color changes.

Table 2

Descriptive statistics of two different composite polished with a series of diamond rubber cups at baseline and after immersing in the tested sport beverages for a period of 7-days

Figures 1 and 2 present the mean ΔE values of the two different composites polished with two different polishing procedures at baseline and after immersing in Powerade, Buzzer, and distilled water (P < 0.05). The selected sport beverages caused color changes after seven days of immersion period for both composite (P < 0.05).

Figure 1

Mean ΔE values of Clearfil-APX polished with either discs or rubber cups at baseline and after immersing in Powerade, Buzzer, and distilled water (P < 0.05)

Figure 2

Mean ΔE values of Cavex polished with either discs or rubber cups at baseline and after immersing in Powerade, Buzzer, and distilled water (P < 0.05)

DISCUSSION

The present study analyzed the colorimetric behavior of a microhybrid vs. a nanohybrid composite to evaluate whether different compositions influence the color stability of composite restorations by considering the effect of different sport beverages and polishing systems. These effects were expressed in terms of ΔE measured on the composite disks. Discoloration of composite resin remains a major cause for the esthetic failure of materials and this can be a reason for the replacement of restorations in esthetic areas. This process concerns both patients and dentists, and consumes time and money.[18] Color stability can be evaluated both visually and specific devices. The methodology used in the present study is according to previous studies that used colorimetry and the CIE L*, a*, b* coordinates system. This system was chosen to evaluate color variation (ΔE) because it is appropriate for small color changes determination and have advantages such as repeatability, sensitivity, and objectivity.[19] Discoloration of composite resins by colored soft and/or alcoholic beverages such as coffee, lemonade, and whisky had been reported in many previous studies.[320] In the present study, two different sport beverages were used as the staining solutions because of their frequent consumption, especially by the young generation. It has been declared that these substances can lead to discolorations in teeth as well as in the resin composite restorations.[21] Furthermore, low period of immersions like seven days was reported to be sufficient to evaluate color changes in the resin composites.[22] The finishing and polishing procedures as well as chemical properties of the materials can influence discoloration of the resin composites.[23] The multiple-step systems were reported to provide increased resistance for discoloration of both the nanofill and the microhybrid resin composites.[24] Therefore, two different polishing systems including a series of aluminum-oxide multi-step polishing discs and a two-step diamond polishing burs were selected for this study. However, discoloration was observed on the resin composites polished with both systems after seven days.

It has been reported that the color difference values (ΔE) ranging from 1 to 3 are perceptible to the naked eye and ΔE values greater than three are clinically unacceptable.[325] The nano-hybrid composite polished with polishing rubber burs showed unacceptable color changes when immersed in buzzer and powerade after seven days (ΔECavex-Buzzer = 3.3; ΔECavex-Powerade = 3). However, this composite exhibited clinically acceptable color changes in the sport beverages when polished with the multi-step polishing discs. Therefore, multi-step aluminum-oxide discs can be a better polishing option than diamond rubber burs to provide appropriate surfaces when polishing the nano-hybrid composites.

The micro-hybrid composite polished either with discs (ΔEAPX-Buzzer = 3.3; ΔEAPX-Powerade = 3.5) or burs (ΔEAPX-Buzzer = 3.2) showed clinically unacceptable color changes after seven days of immersion. The color changes of resin composites were reported to be material-dependent. The staining of the composite resins is a result of the absorption of the water and other fluids with color pigments by the resin matrix[26] and the resin's affinity to extrinsic discolorations due to the inappropriate finishing and polishing procedures.[20] The filler particles do not absorb into the bulk of the material. Therefore, the greater the resin matrix is, the greater the water absorption occurs.[3] Furthermore, nano-hybrid fillers were reported to be less color-resistant than the micro-hybrid fillers due to the former's relatively high water sorption character.[21]

Inokoshi, et al.[27] reported that the resin component of resin composites caused discoloration and higher volume fractions of the resin matrix resulted in a great appearance of discoloration. Additionally, the characteristics of the inorganic fillers were declared to have an influence on resin surface roughness and susceptibility to extrinsic discoloration.[328] Clearfil APX is a micro-hybrid composite with the filler particle sizes of 0.02-17 μm and filler loading of 71% by volume. Cavex is a nano-hybrid composite and has filler loading 60% by volume containing nanofillers with the particle sizes of 0.02-2 μm. In the present study, both of the composite resins exhibited color changes after a seven-day period of immersion. However, the nano-hybrid composite seems to show better resistance to discoloration when compared to the micro-hybrid composite. This result may be related to the better polishing capacity and, therefore, less susceptibility to the external staining of nano fillers compared to the micro fillers.

The present study demonstrates that frequently consumed sport beverages have an effect on discoloration of the composites resins. However, the present study is limited by including two different resin composites in only one shade of A2 and two sports beverages. Furthermore, no long-term measurements were performed. Therefore, further researches are needed to investigate other possible factors affecting the discoloration of the resin composites.

CONCLUSIONS

Within the limitations of this study, following conclusions can be addressed:

Sport beverages can cause discoloration in the resin composites when they are consumed frequently.

To avoid external discoloration, multi-step aluminum-oxide discs are better than diamond burs for polishing of the nano-hybrid composites.

Micro-hybrid composites are more susceptible to external discoloration than nano-hybrid composites due to the insufficient polishing capacity of the micro fillers.