Tooth Discoloration after Bracket De-bonding: An in Vitro Study

Dental News Volume XVIII, Number III, September, 2011

by Dr. Yousef Tashkandi, Pr. Jan Huggare, Pr. Fadi El-Homsi

Abstract

The purpose of this study: to assess the changes in color and brightness of dental enamel after bracket de-bonding following 10 days exposure to discoloring solutions of tea and coffee.

Materials and Methods: Twenty premolars were divided into two groups of 10 teeth each. Buccal surfaces of these teeth were divided vertically into two sites, control and test sites. Test sites were subjected to bracket bonding and de-bonding procedures. Enamel changes in color and brightness were evaluated twice, after brackets de-bonding as a base line reading, and after 10 days of incubation in tea and coffee.

Vita Easy-Shade spectrophotometer was used for recording the changes in classical shade guide and L* values (lightness).

Results: The mean Classical and L* value changes in both groups, tea and coffee, showed a significant discoloration and an increased darkness in both control and test sites (p < 0.001). These changes were significantly higher in test sites for both the classical shade guide (p < 0.003) and for L* values (p < 0.001), even though these sites were significantly brighter at baseline readings (p < 0.002 for classical and p < 0.001 for L*). Tea and coffee showed similar degree of staining potential of the enamel surfaces.

Conclusion: There is significant change in enamel discoloration after brackets de-bonding which affects the stability of enamel color and brightness.

Key words: De-bonding, Classical shade, Easyshade guide, Enamel discoloration, Spectrophotometer, Tea and Coffee stain.

Introduction

Multiple irreversible adverse effects and changes to enamel surfaces during orthodontic treatment can occur during etching, bracket bonding and de-bonding procedures. These changes include; enamel loss, decalcification and formation of white spots, an increased risk of caries development, formation of enamel micro-cracks and scratches, and abrasions induced by enamel smoothing procedures 1, 2, 3, 4.

Different acid etching techniques showed different levels of enamel loss with formation of enamel pores that varied in sizes (5-6 μm in diameter and 30-60 μm in depth), giving a honeycomb appearance 5, 6, 7. During the bonding procedures the adhesive resins fill these pores and form retentive resin tags or projections 8.

After bracket de-bonding, several methods have been used to eliminate the remaining composite resins such as high or low speed rotary instruments with spiral 12-fluted tungsten carbide burs or ultrasonic scalers. Regardless of the method used, loss of enamel surface and presence of remaining resin tags have been reported 7.

The color of enamel surfaces is usually defined by the combined effects of intrinsic and extrinsic discoloring agents 9, 10. Long-term exposure of resin tags to extrinsic discoloring agents (from diet, tea, coffee, chlorhexidine, or iron salts) increases the risk of enamel staining.

Light and chemically cured adhesives were changed in color when they were subjected to artificial photo-aging 11. Faltermeier et al. recently reported unsatisfactory color stability of orthodontic adhesive resins when the teeth were exposed to food colorants, as for instance tea 12. Several studies reported color changes of composite resins after tea and coffee exposure, with more pronounced discoloration in coffee than tea 13, 14. Similar degree of discoloration of composite resins from tea and coffee exposure was found in other studies 15, 16.

The phenomenon of color appearance is complex and encompasses both subjective and objective phenomena. It consists of three direction entities, which were described first by Sigried Forsius in 1611 17. Usually, it is described according to the Munsell colour space in terms of value (L*), chroma (C*), and hue (h*), in which L* represents the brightness of the color with a zero value of pure black and 100 of pure white. The C* denotes the degree of saturation of a color in an object and h* represents the pure colors.

Professional visual color assessment depends on several factors such as: type of light sources, teeth surface textures, effect of the surrounding structures and other biological aspects and finally color decision in the observers brain 18.

Color matching in dentistry is routinely performed visually with the traditional methods of shade selection using prefabricated shade guide tabs and color duplication 19. Several shade guides are available on the market and one that well matches Munsell´s description is the Vita Classical shade guide. In this guide the tabs are divided into four groups with a primary group division based on hue. Group A represents the reddish brown color, group B the reddish yellow, group C the gray, and group D the reddish gray. In each group the shade guide tabs are arranged using chroma as a base 20.

Although this is the most popular and traditionally used method, it gives subjective and inconsistent results. This is because of variable viewer interpretation and environmental influences such as age and emotion of the viewer, fatigue of the human eye, level of experience, lighting conditions and also physiological variables such as color blindness 21.

In 1998, color analysis instruments were used to provide more reproducible, faster and accurate results than visual shade matching 22, 23, 24.

 Spectrophotometer and colorimeter devices are now used to assess teeth color through classical shade guides, and through generating mathematical comparable L*, C* and h* values that allows quantifying the color 21, 24, 25.

The aim of this in vitro study was to assess the changes in enamel color and brightness after bracket de-bonding and after 10 days exposure to coffee and tea.

Materials and Methods

An ethical approval of this study was obtained from the Regional Board of Ethical Vetting in Stockholm to use human teeth extracted due to orthodontic reasons.

Teeth selection

Twenty upper and lower premolars, freshly extracted for orthodontic reasons, were selected from patients 14-18 years of age. All teeth had visually intact occlusal, buccal and lingual enamel surfaces, without any visual discoloration. They were stored in physiological saline solution at 8° C until the experiment started. They were randomly divided into two groups of 10 teeth each, one group for immersion in tea and the other in coffee.

Buccal surfaces of all teeth were vertically divided into two halves; one was used as a test site and the other as a control. Two orthodontic brackets (Victory, Monrovia, USA) were bonded to each test site, while control sites were left untouched (Fig 1).

Fig 1: Brackets bonded on test sites. (T) = Test site. (C) = Control site.

Fixation of teeth for spectrophotometer measurements

To enable the spectrophotometer probe (Fig 2) to assess the same area on each site during repeated measurements, both teeth and spectrophotometer tip were fastened at a fixed distance. Two changeable moulds of silicon putty material (President, Coltene, USA) were constructed for each tooth, one to assess test site and the second to assess the control site. Both moulds were constructed to allow the tip of the spectrophotometer probe to be placed at right angle to the control and test sites (Fig 3).

Fig 2: Easy-Shade Spectrophotometer.

Fig 3A: Position and assessment of Control site. 

Fig 3B: Position and assessment of Test site.

Preparation of test surfaces

Enamel surfaces were first cleaned with a low speed rotating rubber-cup with pumice and water, and then dried thoroughly using a 3-in-1 syringe and air-drying with oil free compressed air before starting bonding procedures. Test sites were etched with 35% phosphoric acid gel (Ultra-Etch®, South Jordan, USA) according to the manufacturer instructions. Then, teeth were thoroughly washed with running water and air-dried for 20 seconds until the enamel surfaces became frosty white in appearance. A thin uniform coat of resin primer Transbond XT (3M Unitek®, Monrovia, USA) was applied to test sites and cured with a light curing device (Orthodux, LED, 3M Unitek®, Seefeld, Germany) for 10 seconds.

Since the size of the bracket base was smaller than the diameter of the spectrophotometer probe, two orthodontic premolar brackets were bonded vertically in test sites using adhesive composites (Transbond XT, 3M Uniteck®, Light Cured Orthodontic Adhesive Monrovia, USA) according to the manufacturer instructions. The distance between the two brackets was less than 1mm and it was covered completely with adhesive resin. The excess composite materials were removed from the remaining bracket margins using a dental probe (Fig 1).

After brackets bonding, the teeth were kept in isotonic solution (Natriumklorid 9 mg/ml, Fresenius Kabi AB, Uppsala, Sweden) at 37° C for 24 hours, and then the brackets were removed with a de-bonding pliers. The remaining adhesive composites were removed by a 30- fluted carbide flat fissure burr (Morrisburgy, Canada) rotating at 20,000-30,000 rev/min. A dental probe was run over enamel test surfaces to ensure complete removal of excessive adhesive composite material.

Baseline measurements for color and brightness were registered after de-bonding, on both test and control sites. The final measurements were made after 10 days of incubation in the discoloring solutions.

To protect the roots from absorbing staining solution, all roots were covered with an impression compound (Thermoplastics Impression material, Salerno, Italy), up to 1 mm above the cemento-enamel junction. The impression compound was removed and changed after five days in the staining solution.

Staining solutions

To induce staining and discoloration of enamel surfaces, 10 teeth were immersed in tea and 10 in coffee media without any additives. A stock solution of tea was prepared by immersing a prefabricated (2 x 2 g) tea bag (Yellow Lipton, United Kingdom) into 200 ml of 65 degrees Celsius (°C) hot water. The coffee solution was prepared also by pouring 5 g of instant coffee (Nescafe, Sweden) into 200 ml of 65°C hot water. The prepared teeth were separately put in test-tubes with 3ml of each solution at 37° C in a dark environment for 10 days. Both solutions were changed every two days. Then, teeth were brushed with a medium-bristle toothbrush, rinsed with tap-water and dried with oil free compressed air for 5 seconds before each measurement.

Spectrophotometer analysis

Enamel discoloration and brightness were assessed using the Vita Easy-shade spectrophotometer (Fig 2 & 3). It uses D65 illumination for shade matching and this represents a phase of daylight with a correlated colour temperature of about 6500 K. “Normal Mode” and “Tooth single” settings were selected. The device was calibrated with a calibration block (supplied with the device) each time when the device was switched on.

Both classical shades and L* values (expressing lightness) were utilized in this study. The classical shade tabs were arranged in value order, where each shade was given a number between 1 and 16. Number 1 represents the lightest value and 16 represents the darkest (Table I).

A baseline assessment was registered twice for both the control and test sites in classical

shades and L* values after bracket de-bonding and cleaning of enamel surfaces. The mean of classical shades and L* was calculated for each surface. The final assessment was also registered twice after 10 days of incubation period in coffee and tea and the differences between the baselines were calculated. Fig. 4 summarizes the methods and measurement sequence.

Table I: Vita Classical shade guide tabs ranked in commonly known ranking from the lightest (1) to the darkest (16)

Fig 4: Methods and measurement sequence.

Statistics

The data was analyzed by three-way ANOVA with repeated measures on two factors: between-group factor (which was the media: tea and coffee respectively), and the within groups factor (sites and time). The interaction between time and site was of special interest, implying to the statistical test of whether there was a significant difference between test and control sites after 10 days. Mean differences for the control and test sites after 10 days in tea and coffee were estimated from the ANOVA-model with 95% confidence intervals (CI).

Results

Regardless of media, the site and time interaction was significant in both classical shade and L* values (p < 0.001).

Assessments at 10 days showed that the test sites were significantly darker than control sites in both groups for both classical shades and L* values (p = 0.003 and p < 0.001 respectively).

·   - Test sites were lighter than control sites at baseline in both classical and L* values (p = 0.002 and p < 0.001 respectively).

The mean classical shade of test sites was changed from A3.5 to A4, in both groups. Therefore the mean difference in changing the color of test sites was three shade tabs (Table II).

Table II: Mean Tea and Coffee Classical shade values for Control and Test sites and the difference between baseline and at 10 days

·   - Control sites were significantly changed to darker color after 10 days in both classical shade and L* values (p < 0.001), for both tea and coffee groups.

The mean classical shade of control sites was changed from B4 to C3, in both groups. Therefore the mean difference in changing the color of control sites was one shade tab.

So the mean difference in color change between the control and test sites was two shade tabs, for both groups, which was statistically significant (p < 0.001) (Fig. 5).

Fig 5: Mean Classical shade change from baseline to 10 days in Control and Test sites for Coffee and Tea.

The mean L* values for both groups at baseline and after 10 days, and the mean difference between control and test sites are illustrated in Table III.

Table III: Mean Tea and Coffee L* values for Control and Test sites and the difference between baseline and at 10 days

It showed that after 10 days in media, teeth in the tea group became darker (lower L* values) than those in the coffee group (p = 0.002). Regardless of media, the mean difference in L* values between control and test sites were different and the test sites became darker (lower L* values). This also was statistically significant (p < 0.001) (Fig. 6).

Fig 6: Mean L* value changes from baseline to 10 days in Control and Test sites for Coffee and Tea

Since all 20 teeth and both media exhibited changes in color and increased the darkness of control and test surfaces with a statistically significant differences, the mean changes for all teeth in classical shades and L* values from baseline to 10 days are presented in Fig. 7 and 8.

Fig 7: Mean Classical value changes from baseline to 10 days for Control and Test sites of 20 teeth.

Fig 8: Mean L* value changes from baseline to 10 days for Control and Test sites of 20 teeth.

Discussion

Three-way ANOVA was used to determine the repeated measures on media, sites and time respectively. As the three factor interactions were not significant, the time and media interaction was independent of sites and the site and time interaction was independent of media. Therefore the results were presented as the mean of all 20 teeth for each site.

This study disclosed a great effect of tea and coffee in changing the color and brightness of de-bonded enamel surfaces. Few studies have been conducted to reveal discoloration effects of residual resin projections after orthodontic bracket de-bonding.

Since several in-vitro studies on discoloration after tooth bleaching have used coffee and tea as discoloring agents 15, 16, 26, it seemed reasonable to use these agents in this study.

However, long continuous exposure time of media on enamel surfaces is not representing the actual consumption of coffee and tea by the individuals. But due to the need of accelerating the effects of these media in this study, the effect of long time use of these beverages could give similar results.

The effect of tea and coffee in this study showed marked changes in color and brightness of teeth in both control and test enamel surfaces. Whereas, some studies showed a more pronounced effect on composite resins with coffee 13, 14.

The Easy-shade spectrophotometer was used to provide objective and more reproducible measurements of the change in Vita classical shade and L* values 23, 24. In addition, L* values were chosen to define the brightness and darkness effect mathematically and to support the classical shade measurements which has a more clinical significance. It has been shown that the major parameter causing color changes was in L* values rather than in chroma 27. Since baseline measurement were obtained after de-bonding and cleaning enamel surfaces from gross adhesive composites, the significant differences between control and test sites in baseline reading might be due to the effect of surface etching and the presence of remaining resin projections. These resin infiltrates also might alter the light reflection and influence the color parameters.

In a study Hintz et al. examined the bleaching effect of 10% carbamide peroxide on both control and test (bonded and de-bonded) surfaces for 4 hours every day for 30 days. They found that the control sites had significant color changes at the beginning of the experiment. By the end of 30 days, these changes became insignificant and both surfaces were affected equally. It partially supports the results of the present study, in which both control and test sites were subjected to color changes 28.

 Another study assessed the discoloration and staining of enamel surfaces in four media which supports the susceptibility of control sites to be stained as well as the prepared tests sites 26.

Unsatisfactory color stability and potential discoloration were found with the use of a conventional orthodontic adhesive resin; Transbond XT, which is the same kind of adhesive resin that has been used in this study 12. The discoloration of test sites in this study was probably due to the degree of water absorption of the hydrophilic resin 29.

Several enamel changes occur throughout life, such as decreasing in facial enamel thickness above cemento-enamel junction 30. In addition to that, enamel surfaces of elderly people are darker and have more cracks than teeth of young people 31. These changes might alter the response of enamel surfaces to discoloration if adult teeth have been used.

Conclusion

The exposure of de-bonded enamel surfaces to tea and coffee, for 10 days, changed the color and brightness of these surfaces. The discoloration was more obvious in enamel surfaces that had been subjected to bracket bonding and de-bonding. Further studies should be done to evaluate the extent of these stains in bonded and de-bonded surfaces in order to avoid the destructive effect of bonding and de-bonding procedures, and subsequently having a bonding material with high color stability.

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Acknowledgements

I would like to express my sincere thanks to Professor Lars-Åke Linden and for his supervision.

I also would like to thank Ms. Elisabeth Berg and Dr. Abeer Sofrata, for their help in statistics and data analysis.