Evaluation of the Effect of Different Herbal Tea on Discoloration of Different Kinds of Composite

Document Type: Original Article

Authors

1 Assistant professor, Dental Materials Research Centre, Department of Restorative and Esthetic Dentistry, Faculty of Dentistry, Babol University of Medical Sciences, Babol, Iran

2 Dental student, Student research committee, Babol University of Medical Sciences, Babol, Iran

3 MSc in Statistics, Health Research Institute, Babol University of Medical Sciences, Babol, Iran

Abstract


Objectives: The aim of this study was to evaluate the effect of six herbal teas on the color stability of two types of nanohybrid and one microhybrid resin composite.  Materials and Methods: 70 disc-shaped specimens, 210 in total (7*2mm), were fabricated from each of the following materials in metal mould : Tetric N ceram, Grandio, Gradia Direct Anterior. Specimens were stored in distilled water at 37°C for 24 hours in an incubator for completion of polymerization. After baseline evaluation (L*, a*, b*CIELAB scale), the specimens were divided into seven subgroups, according to the test and control storage solutions (n=10). Randomly selected specimens from each material were immersed in 20 ml of the test solutions (Borago, Green, Hibiscus, Thyme, Black and Lemon Verbena teas) at 37˚c for 24 hours and 48 hours. Solutions were refreshed every 24 hours. All samples were polished using Soflex discs with Medium, Fine, Superfine grit after storage in herbal teas. Specimens color was measured in 24, 48 hours and after polishing. The collected data was statistically analyzed using two-way analysis of variance with repeated measure and Tukey’s HSD at a significance level of 0.05. Results: All samples displayed color changes after immersion in the herbal teas. Hibiscus tea induced the highest level of discoloration after 24 hours immersion in all three composites. Black tea induced highest level of discoloration in (Grandio ΔE=7.44). Hibiscus tea and Thyme tea induced highest level of discoloration in (Tetric N ceram ΔE=11.) and (Gradia Direct ΔE=14.11), respectively, after 48 hours immersion. The least discoloration was found with Borage tea in 24 and 48 hours. After re-polishing the color change was reduced. Grandio showed the greatest color reduction in Black tea. Color improvement of Tetric N ceram was better than Gradia Direct.
Conclusion: All tested restorative materials showed a color shift after immersion in herbal teas, which Tetric N ceram displayed the highest color change in Hibiscus tea and Borago tea induced lowest discoloration on Grandio after 24 h immersion. Thyme tea induced the highest level of discoloration on Gradia Direct and least discoloration was found in Borago tea on Grandio after 48 hours immersion.

Keywords

Main Subjects


Introduction

The resin composites are among the most popular cosmetic restorative materials in dentistry for esthetic supply and their use have increased in recent years. Despite the progress in their manufacturing, color stability over time is still a major problem (1,2)and leads to patient dissatisfaction and the need for composite restorations replacement and spending more cost and time(3,4).

Composite discoloration is caused by internal and external factors. Internal factors for color change include resin matrix changes, interface of matrix and fillers over time (5), type of photoinitiator, size and distribution of the filler particles and the degree of matrix  hydrophilicity(3,6). External discoloration occurs through the surface and deep adsorption of pigments from an external source. The discoloration is influenced by oral hygiene, smoking, foods and drinks (7, 8). Recently, the role of drinks and herbal juices in teeth discoloration and tooth-colored direct and indirect restorative materials has received special attention.

Hot drinks like tea and coffee are among the most commonly consumed drinks in the world. Herbal tea and fruit tea are favored to a great deal for medical reasons (9).

In terms of medicinal value of plant species, it can be referred to antioxidant potentiality, reduction of the risk of cancer and cardiovascular disease, reduction of the risk of diabetes and Alzheimer’s (9,10). In fact, most antioxidants are supplied by fruits and plants. Tea, which is one of the causes of discoloration in resin restorations, has been commonly used by people around the world owing to its beneficial properties for health (9, 10, 11, 12).

Resin composites are classified based on several characteristics including size, composition, type of filler and physical and mechanical properties (13).  In recent years, nanotechnology has advanced in the field of dental composites. Nanocomposites consist of nanohybrid composites with particles of 40 to 50 nanometers size and nano-filled composites containing nanoparticles and nanoclusters (14, 15).

It is claimed that nanocomposites show higher surface quality, polishability, and mechanical properties. Color stability of these composites subjected to environmental factors seems to be better than microhybrid composites (14, 15, 16).

In addition to the material composition, particle characteristics and methods of finishing and polishing have a direct effect on the surface roughness and color stability. Inadequate polishing leads to increased plaque germs, gingivitis and discoloration in composite restorations (17, 18).

Many studies have already been conducted on composites discoloration in color-induced environments (tea, coffee, juice, soda). Due to increased consumption of herbal tea (11), the aim of this study was to investigate the effects of several different herbal teas on the color stability of two different types of resin composites.

The null hypothesis tested in present study was that the daily drink of herbal teas does not significantly affect color stability of tested restorative materials.

 

Materials and Methods

This in-vitro experimental study was conducted on two nanohybrid composite resins (Tetric N ceram, Grandio) and a microhybrid composite resin (Gradia Direct Anterior). The characteristics and composition of these materials are presented in Table 1. Seventy specimens measuring 7 mm in diameter and 2 mm in height were fabricated (to match with the tip of VITA Easyshade Advance® (VITA Zahnfabrik) )  with A2 shade of the mentioned composites. The composites were placed into the molds and pressed by placement of one mm thick glass slabs beneath and above the metal mould(18). Samples were cured for 20 s from each side using the overlapping technique with VALO broadband LED light cure device (VALO, Ultradent, South Jordan, UT, USA), (light intensity710- 840 mW/cm2). Intensity of the device was assessed with a radiometer (Kerr, Demetron, Orange, CA, USA) after every ten curing. Upper surfaces of each specimen were polished with 400, 800 and 1200-grit silicon carbide papers successively, under running water.  Specimens were then stored in distilled water at 37°C for 24 hours to allow completion of polymerization. Primary color assessment (L*, a*, b*) of specimens was done using spectrophotometer (VITA Easyshade Advance®) against a white background. In the next step, each group was randomly divided into 7 subgroups of 10 for storage in water and herbal teas solution for 2 days. (n=10)

To prepare the tea solution, a tea bag was placed in 200 ml boiling water for 2 minutes. Distilled water was used for the control groups. The (pH) of each solution was measured by pH meter (OAKTON, LABRTON PHT-110, Vernon Hills, Il USA). The pH of herbal tea solutions are shown in Table-2. Randomly selected specimens from each material were immersed in 20 ml of the treatment solutions. Samples were kept in closed containers to prevent evaporation of solutions and stored for 2 days in an incubator at 37°C. Selection of 2 days time period was due to the fact that if a person averagely drinks 4 cups of tea every day with the mean duration of drinking a cup of tea being one minute, every 24-hour immersion in tea solution would correspond to one year consumption of tea (19). Treatment solutions were refreshed every 24 hours and the specimens, color were measured at 24 and 48 hour. Specimens were removed from the solutions, placed in distilled water container and were shaken 10 times, rinsed with distilled water for 5 seconds and cleaned with a soft toothbrush to remove any debris or contamination. All samples underwent color assessment with (VITA Easyshade Advance®) spectrophotometer. After 48 hours immersion, Specimen surface  was polished by the use of low-speed hand piece and Soflex polishing discs (3M ESPE) starting from medium, fine to superfine coarse to achieve smooth surfaces.

The amount of color shift was recorded in CIELAB system, which is a three-dimensional color space: color luminosity that varies from white to black (L*), and the chromaticity of the color as a* and b*, red-green (a*), and blue-yellow (b*). Color change of specimens (∆E) was calculated according to the following formula: ∆E= [(∆L) 2+ (∆a) 2+ (∆b) 2]1/2 .Two-way analysis of variance with repeated measure (ANOVA) was applied to assess and compare the effects of the material type and herbal tea on color changes, and Tukey’s HSD (Honestly Significant Differences) was used to evaluate data before and after color change in each group (P<0.05).

 

 

Table 1. Compositions, type, and manufacturers’ of the resin composites tested in this study

 

Brand name

Composite type

Compositions

Manufacturer

Tetric N Ceram

Nano-hybrid

Matrix: phosponic acid acrylate, HEMA, Bis-GMA, UDMA, ethanol,

catalyst, and stabilizers

Filler: (55–57 vol %), (79wt %) Barium glass, ytterbium trifluoride, mixed

oxide, and copolymers (between 40–3000 nm)

 

Ivoclar Vivadent,

Schaan, Liechtenstein

 

 

 

Grandio

 

 

Nano-hybrid

Matrix: BisGMA, TEGDMA

Filler:Silica: 20–60 nm; barium-alumia

borosilicate: 0.1–2.5µm

(87.0wt. %)  (71.4 vol %)

 

 

Voco (Cuxhaven,

Germany)

 

 

Gradia direct anterior

 

MicroHybrid

Matrix : UDMA,DMA

Filler:Silicon dioxide, prepolymers

(850 nm, 64%vol/73%wt)

GC, Tokyo, Japan

 

 

Table 2. Type, (pH) and manufacturers’ of the Tea(Immersion media) tested in this study

Immersion Media

Brand

Ph

Manufacturer

Borago Tea

Golestan

5.93

Tehran,Iran

Green Tea

Dilshah

6.62

Tehran,Iran

Hibiscus Tea

Shahsavand

2.75

Mashhad,Iran

Thyme Tea

Pers Tea

7.26

Fars,Iran

Black Tea

Golestan

6.5

Tehran,Iran

Lemon Verbena Tea

Pers Tea

7.6

Fars,Iran

Distilled Water

-----------

7

 

 

 

 

 

Result

Table 3 presents the means and standard deviations (SD) of the color change values (ΔE*) of each material (24 hours, 48 hours and after polishing respectively) after immersion in the test and control solutions. All samples displayed color changes after immersion in the herbal teas. Amongst specimens immersed in distilled water as the control group, all materials showed color changes less than ΔE*=3.3, which were considered visually imperceptible. Hibiscus tea induced the highest level of discoloration among the six solutions after 24h in three tested composite; however, after 48h the highest discoloration was observed in Thymus vulgaris (ΔE*= 14.11±3.30 for Gradia Direct). Least discoloration was found in Borago tea after 24h and 48h. (ΔE*= 1.32±0.86 and 1.77(0.84), respectively, for Grandio). Two-way Repeated Measures ANOVA showed that color change (ΔE*) was significantly increased overtime (p<0.001) in all groups. Since the interaction of composite and solution was significant (p<0.001), the analysis was performed for each composite, separately.

Repeated Measures ANOVA analysis for each composite showed that in all three composite groups, the effect of storage media was significant on the ΔE* (p<0.001). Tukey’s multi comparison test revealed that in comparison with the control group (DDW), Borago did not cause statistically significant discoloration in any of composite groups (p>0.05). Also, amongst specimens immersed in distilled water and Borago tea, all material (except for Tetric N Ceram after 48h) showed color change less than 3.3, which was considered visually imperceptible. Tables 4 and 5 show the multiple comparison tests of different composite types or storage media on color shift in different groups.  The results of Tukey’s multi comparison test for different composite types and storage media are presented.

 

Table 3.  Mean value and standard deviation for ΔE* in different groups after 24 and 48 hours and after polishing.

Solution

Time

Color difference (ΔE*)

Tetric N Ceram

Gradia Direct

Grandio

Mean(SD)

Mean(SD)

Mean(SD)

Borago

After 24h

2.83(1.20)

2.50(0.68)

1.32(0.86)

After 48h

3.55(1.40)

3.14(1.33)

1.77(0.84)

After Polishing

3.32(1.07)

2.75(0.97)

2.21(1.07)

Green Tea

After 24h

4.84(0.66)

2.78(0.51)

2.41(1.31)

After 48h

6.80(1.67)

5.30(1.74)

3.59(1.12)

After Polishing

4.80(1.20)

2.89(1.23)

2.04(0.63)

Hibiscus Sabdariffa

After 24h

9.26(3.95)

7.42(2.89)

4.14(3.01)

After 48h

11.41(3.57)

7.53(1.34)

5.21(2.83)

After Polishing

8.59(4.10)

5.53(1.27)

3.75(2.28)

Thymus vulgaris

After 24h

5.92(1.51)

5.88(1.54)

2.75(0.91)

After 48h

9.22(1.93)

14.11(3.30)

5.39(1.38)

After Polishing

6.92(3.07)

12.50(3.74)

3.00(1.85)

Black Tea

After 24h

7.23(1.87)

5.35(0.97)

3.82(0.78)

After 48h

11.05(2.04)

9.31(1.87)

7.44(1.29)

After Polishing

7.15(2.97)

4.80(3.49)

4.16(1.86)

Lemon verbena

After 24h

3.70(0.96)

2.04(1.30)

1.69(0.70)

After 48h

3.90(1.24)

2.35(1.72)

2.32(1.28)

After Polishing

4.41(1.70)

2.67(1.45)

1.72(0.96)

Distilled Water

After 24h

0.88(0.40)

2.92(3.64)

0.76(0.53)

After 48h

0.89(0.29)

1.22(0.59)

1.34(1.30)

After Polishing

2.42(0.71)

2.57(0.93)

2.40(1.21)

           

 

 

 

Table 4.  Multiple comparison results (p-value) for the effect of composite type on the ΔE* in different storage media. (Tukey’s test, p

 

Composite

Storage Media

p-value

Tetric  N Ceram

Gradia Direct

Grandio

Tetric N Ceram

Borago

 

0.7

0.003

Green Tea

 

0.004

<0.001

Hibiscus Sabdariffa

 

0.1

0.001

Thymus vulgaris

 

0.01

<0.001

Black Tea

 

0.02

<0.001

Lemon verbena

 

0.01

0.004

Distilled Water

 

0.09

0.95

Gradia Direct

Borago

0.7

 

0.02

Green Tea

0.004

 

0.11

Hibiscus Sabdariffa

0.1

 

0.11

Thymus vulgaris

0.01

 

<0.001

Black Tea

0.02

 

0.04

Lemon verbena

0.01

 

0.92

Distilled Water

0.09

 

0.16

Grandio

Borago

0.003

0.02

 

Green Tea

<0.001

0.11

 

Hibiscus Sabdariffa

0.001

0.11

 

Thymus vulgaris

<0.001

<0.001

 

Black Tea

<0.001

0.04

 

Lemon verbena

0.004

0.92

 

Distilled Water

0.95

0.16

 

Table 5: Multiple comparison for the effect of storage media on the ΔE* in different composites. (Tukey’s test, p

 

Storage Media

 

Composite

p-value

Borago

Green Tea

Hibiscus Sabdariffa

Thymus vulgaris

Black Tea

Lemon verbena

distilled water

Borago

Tetric N Ceram

 

0.04

<0.001

<0.001

<0.001

0.98

0.1

Gradia Direct

 

0.62

<0.001

<0.001

<0.001

0.97

0.94

Grandio

 

0.25

<0.001

0.003

<0.001

0.99

0.98

Green Tea

Tetric N Ceram

0.04

 

<0.001

0.36

0.003

0.20

<0.001

Gradia Direct

0.624

 

     <0.001

<0.001

<0.001

0.16

0.11

Grandio

0.25

 

0.12

0.61

0.002

0.69

0.04

Hibiscus Sabdariffa

Tetric N Ceram

<0.001

<0.001

 

0.02

0.78

<0.001

<0.001

Gradia Direct

<0.001

<0.001

 

0.01

1.00

<0.001

<0.001

Grandio

<0.001

0.12

 

0.96

0.73

0.001

<0.001

Thymus vulgaris

Tetric N Ceram

<0.001

0.36

0.02

 

0.5

0.001

<0.001

Gradia Direct

<0.001

<0.001

0.01

 

0.008

<0.001

<0.001

Grandio

0.003

0.61

0.96

 

0.18

0.03

<0.001

Black Tea

Tetric N Ceram

<0.001

0.003

0.78

0.5

 

<0.001

<0.001

Gradia Direct

<0.001

<0.001

1.00

0.008

 

<0.001

<0.001

Grandio

<0.001

0.002

0.73

0.18

 

<0.001

<0.001

Lemon verbena

Tetric N Ceram

0.98

0.20

<0.001

0.001

<0.001

 

0.01

Gradia Direct

0.97

0.16

<0.001

<0.001

<0.001

 

1.00

Grandio

0.99

0.69

0.001

0.03

<0.001

 

0.73

Distilled water

Tetric N Ceram

0.1

<0.001

<0.001

<0.001

<0.001

0.01

 

Gradia Direct

0.94

0.11

<0.001

<0.001

<0.001

1.00

 

Grandio

0.98

0.04

<0.001

<0.001

<0.001

0.73

 

 

 

 

After polishing

The results of the present study showed that the overall ΔE of Tetric N ceram is higher (ΔE*=5.15) than that of Gradia Direct (ΔE* = 4.81) and Grandio (ΔE* = 2.75) after polishing.

All samples displayed color shift after polishing. The results show that the color shift of the specimens was reduced. As shown in table 3, all three materials in Borago tea, Gradia direct and Grandio in Green tea and Lemon verbena tea, Grandio in Thyme tea reduced to acceptable range (ΔE* <3.3)

Post polishing ΔE* values in distilled water were not significantly different between restorative materials (P>0.05).

Grandio samples immersed in Lemon V. showed lowest discoloration after polishing.

 

 

Discussion

In this study, we examined the effect of 6 kinds of herbal tea on color stability of nanohybrid composite and microhybrid composite. The results of this study suggest that herbal tea causes color change in these materials.

 ,the average of tested restorative materials, were 1.32 (Grandio in borage) to 9.26 (hibiscus tea inTetric N-ceram) in 24 hours and 1.77 (Grandio in borage) to 14.11 (Gradia in thyme) in 48. In dentistry, the dental discoloration less than understandable range is called acceptable discoloration, which is ΔE 3.3. Thus, ΔE 3.3 is considered as clinically imperceptible discoloration.

Composite discoloration over time has a multifactorial mechanism. Internal factors cause chemical changes in resin matrix and external factors (e.g. deep absorption, and patients’ nutrition) cause discoloration in restorations over surface, . In addition, surface characteristics, filler quantity and size and matrix properties (water absorption and hydrophilic characteristics)are effective in composites discoloration (19, 20, 21).

All three substances showed the greatest discoloration in hibiscus tea solution in 24 hours. Black tea had the most discoloration after that. However, it was not statistically significant. Both solutions are dark and have a high volume of pigments.

Another possible reason for color formation of hibiscus teas can be the pH of the solution. pH changes (acidic or basic solution) seem to be harmful for composites. Neamat et al. in 2000 suggested that low pH in color-induced solutions has a negative impact on the integrity of the restoration surface through softening the resin matrix (22, 23). That study found that color-induced materials with low pH lead to chemical erosion in compomer causing the ions exit from its matrix. This brings about more water absorption and thus more discoloration (6, 22, 23).  This result is in line with our results. In our study, the highest color formation in all samples was related to hibiscus tea with minimum pH Also as the color shift was affected by the time in this study, it can be concluded, the color change might be attributed by water and color pigment sorption over the time after 48 hours immersion.

Another influential factor in the color properties of composite is the filler size. According to a study by Thakib et al. and Han et al. in 2008, the volume of filler is linearly associated with erosion resistance (26, 27). Composite can be damaged and discolored by erosional properties and discoloring agents of different fluids. By increasing the volume of filler, resistance to erosion and matrix softening increases, which lead to better resistance to discoloration. Less filler volume leads to more water absorption at the interface of the filler and matrix and filler and matrix disruption (21).  Results of the present study also show that Tetric N-ceram has the greatest discoloration with the least amount of filler (55-57%) compared to Grandio composite with 71.4% volume of filler and Gradia Direct with the volume of filler of 64%.

Also Teric N-ceram contains barium glass particles. Studies conducted by Hubbezoglu et al. in 2008 and Hirata et al. in 2000 stated that composites with barium glass particles tend to absorb more water. These particles can thin light and thus reduce the luminosity (28, 29).  The presence of these particles in Tetric N-ceram composite is probably another reason for its significant discoloration.

External surface and colorability features are also affected by the size of fillers (6).  The size range of fillers is 40-3000 nm in Tetric N-ceram, 20-250 nm in Grandio and 850 nm in Gradia Direct (Table-1). Tetric N-ceram is a nanohybrid composite that despite having nanoparticles showed significant discoloration. It can be due to the wide range of fillers in Tetric N-ceram (large filler particles of 3000 nm). Moreover, Gradia Direct showed more discoloration than Grandio due to its larger filler particles. Grandio composite with smaller filler particles has a smoother surface and this leads to less colorability than the other two composites.

Monomers with UDMA base compared to other monomers with methacrylate base are less willing to change their color due to low water absorption and low viscosity. Resin composites that have more TEGDMA monomer are more susceptible to discoloration than composites containing UDMA monomer. These monomers make resin matrix hydrophilic, which enhances water and fluid absorption, causing discoloration of the material (30), but it was not observed in discoloration of Grandio and Gradia Direct. Despite having UDMA, Gradia Direct revealed more changes than Grandio that contains TEGDMA. This can be due to the dominant role of filler in comparison with the matrix in the composite properties. The HEMA monomer available in Tetric N-ceram that makes matrix hydrophilic can perhaps be a reason for more discoloration in Tetric N-ceram because of more water absorption (8, 21, 30).

. Color of samples has increased at 48 hours compared with 24 hours due to increased confrontation with the solution as well as greater penetration of color-induced materials into the resin.

As mentioned before, in the first 24 hours, black tea showed the second most color induction - which was not statistically significant to hibiscus tea. Discoloration caused by black tea has been proven previously and is due to the presence of yellow pigments (22).

Borage and lemon solutions which are brightly colored have the least amount of pigment, and in the present study also showed the lowest color induction so that the discoloration was not clinically significant (ΔE < 3.3).

Discoloration of all samples decreased after polishing but did not reach the clinically acceptable range.

The improved color samples immersed in Black tea after polishing can be influenced by surface adsorption of yellow pigments in black tea on samples surface (21, 31). Most discoloration reduction after polishing belonged to the samples immersed in a solution of black tea and the color of all the samples was significantly better. This was clearer in Grandio than the other two composites. It is generally accepted that the polishability of resin composites greatly depends on size, shape, and quantity of filler particles (32). Improved color of Grandio can be because of the higher filler particles and smaller filler particles in this composite compared to the other two composites (Table-1).  That showed more polishability of this material, but it did not fall within clinically acceptable range.

In clinical situations, there might be different factors affecting color stability of restorative material such as presence of saliva, effect of different foods and beverages and oral hygiene which are difficult to be replicated. Since exposure to different substances in the oral environment is cyclic, another critical factor would be the method of exposure to staining solutions. Further experiments are therefore needed to resemble in vivo conditions.

 

Conclusion

Composite colorability depends on composite type and type of herbal tea consumed. All composites show discoloration in all herbal tea solutions. This discoloration is somewhat improved by polishing composite surface.

Tetric N ceram was the material with the highest discoloration in Hibiscus Tea and Grandio was the material with the lowest discoloration in Borago tea after 24 hours immersion.

Thyme tea induced the highest level of discoloration on Gradia Direct and least discoloration was found in Borago tea on Grandio after 48 hours immersion.

Amongst specimens immersed in distilled water and Borago tea, all three materials showed color changes less than 3.3, which were considered visually imperceptible

In the present study and with regard to the limitations of the study, Grandio samples showed the least discoloration in borage and lemon solutions.

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