Our aim was to evaluate the effects of staining solutions on the discoloration of orthodontic adhesives.
Six orthodontic adhesives were investigated (Transbond XT [3M Unitek, Monrovia, Calif, USA], Heliosit Orthodontic [Ivoclar Vivadent, Liectenstein], Light Bond [Reliance Orthodontic Products, Itasca, IL, USA], Bisco Ortho [Bisco, Schamburg, IL, USA], Quick Cure [Reliance Orthodontic Products, Itasca, IL, USA], and Filtek Supreme XT [3M ESPE, St Paul, Minn, USA]), and 5 beverages (tea, cola, coffee, red wine, and yogurt). Sixty specimens were prepared. Five specimens from each group were stored in each of the 5 staining solutions. The 5 remaining specimens from each group served as the controls and were stored in distilled water. The specimens were immersed in staining solutions and water at 37°C ± 1°C for 5 days. The test period was 25 days. Before and after the test period, color measurements were carried out with a spectrophotometer, and color changes (ΔE∗) were calculated. Statistical differences were evaluated by using analysis of variance (ANOVA) and the Tukey HSD tests.
Adhesive materials, staining agents, and their interactions were found to play statistically significant roles ( P <0.001) in color changes. Among the adhesive materials, the Light Bond water control group consistently showed the lowest ΔE∗ value for all materials, and the Filtek Supreme XT group showed the highest ΔE∗ value for all materials. After the in-vitro experimental process for staining solutions and water, unsatisfactory color stability was observed for the conventional adhesive systems except for Light Bond, Transbond XT, and Bisco Ortho water control group (ΔE∗ >3.7), respectively.
In esthetically critical areas, discoloration of adhesive materials for fixed orthodontics can cause patient dissatisfaction. Orthodontic composites will discolor from staining beverages during their lifespan.
For over 60 years, resin-based adhesive composites have been used for direct or indirect bonding of orthodontic attachments to teeth for orthodontic purposes. Most orthodontic adhesives are variations on adhesive and direct-restorative formulations produced for use in restorative dentistry.
Direct bonding of orthodontic brackets to teeth has been an important subject in orthodontic research, because of the significance of a stable bond between a tooth etched with phosphoric acid and its bracket. Most studies in the orthodontic literature have focused on evaluation of the physical and mechanical properties of adhesives resins. However, discolorations of resin-based adhesive composites have been investigated in only a few studies. A study showed that orthodontic bracket bonding and debonding can cause changes in the appearance of tooth enamel. In addition to the formation of structural and surface defects, some variables—eg, enamel loss caused by etching—can affect the enamel color, inducing various alterations on the enamel surface, including white spots. Although there are many findings about enamel white spot formation associated with orthodontic treatment, the incidence of enamel color changes caused by orthodontic bonding and debonding protocols has interested only a few investigators. There is some evidence that adhesive resin tags could reach a depth of 50 μm in the enamel. As a result of these parameters, debonding and cleaning protocols cannot reverse adhesive resin impregnation into the enamel. Enamel discolorations can occur by direct absorption of food colorants and products from the corrosion of orthodontic appliances. The long-term presence of these resin residues in the enamel tags that extend over the middle third of the buccal surface makes the color stability of these materials critical for tooth color.
The color stability of resin-based adhesive composites might be affected by external and internal factors. External influences are colored mouth rinses and staining foods (such as coffee and red wine), matrix (hydrophobic or hydrophilic), and type of filler particles (organic, inorganic, silica gel, silane coupling agent, and size). The material’s superficial roughness has an important role in the color changes of adhesive composites influenced by the different materials. A number of factors influence the extent of discoloration of photo-curing materials, such as the adsorption of dyes or plaques, water sorption, incomplete polymerization, photo-initiator components (eg, camphorquinone), resin matrix composition, light-curing devices, and irradiation times. The proof for internal color change of adhesive materials can be found in the aging under various physical and chemical conditions, such as humidity, ultraviolet irradiation, and thermal changes. The system of photo-initiators used in adhesive composite as well as on the applied form and the time span of curing have a certain effect on the discoloration of the material. They are induced by chemical changes in the materials’ matrices and hence affect all layers of the material; they cause irreversible discolorations in the polymer. There are 2 investigations about the influence of the ultraviolet light exposure on discoloration of orthodontic adhesives and its effect on the change of tooth color.
In esthetically critical areas, resin-based adhesive materials must maintain not only the attachment of orthodontic appliance but also an esthetic appearance over the period of service. Discoloration of adhesive materials for fixed orthodontics can cause patient dissatisfaction; this is especially problematic when orthodontic adhesives are subjected to prolonged exposure to staining materials during lengthy treatment. Hence, the color change might be an important criterion in the selection of a particular orthodontic adhesive material for use in an esthetically critical area. Therefore, the aim of the study was to evaluate the combined effect of 5 staining beverages on the discoloration of orthodontic adhesives.
Material and methods
The resin-based adhesive composites investigated were Bisco Ortho (Bisco, Schaumburg, Ill), Heliosit Orthodontic (Ivoclar Vivadent, Liechtenstein), Light Bond (Reliance Orthodontic Products, Itasca, Ill), Quick Cure (Reliance Orthodontic Products), Transbond XT (3M Unitek, Monrovia, Calif), and Filtek Supreme (3M ESPE, St Paul, Minn) to test for color changes ( Table I ). An Elipar FreeLight 2 (3M ESPE) was the light-curing device for preparing the light-polymerizing specimens. The specimens were stored in common colored beverages; for the control group, distilled water was used. The drinks were black tea, black coffee, yogurt, red wine, and a soft drink based on cola ( Table II ).
|Bisco Ortho||Bis-GMA (15%-40%), TEG-DMA (5%-15%), fused silica (30%-60%)||Bisco, Schaumburg, Ill
Lot no: 0600004598
|Heliosit Orthodontic||UDMA, Bis-GMA and decandiol-DMA (85%), dispersed silicon dioxide (14%), catalysts and stabilizers (1%)||Ivoclar Vivadent, Liechtenstein
Lot no: G21064
|Light Bond||UDMA, TEG-DMA (22%), fused silica, sodium fluoride (78%)||Reliance Orthodontic Products, Itasca, Ill
Lot no: 0609234
|Quick Cure||Silica-crystalline, silica-fused (50%-90%), Bis-GMA (1%-10%),
TEG-DMA (5%-10%), sodium fluoride (0.1%-2.0%)
|Reliance Orthodontic Products, Itasca, Ill
Lot no: 0604936
|Transbond XT||Bis-GMA (5%-10%), Bis-EMA (10%-20%), TEG-DMA (5%-10%),
silane-treated quartz (70%-80%), silane-treated silica (2%)
|3M Unitek, Monrovia, Calif
Lot no: 6CX6WM0088
|Filtek Supreme||Bis-GMA, TEG-DMA, and Bis-EMA (35%), zirconia-silica (65%)||3M ESPE, St Paul, Minn
Lot no: 6BY3910A1E
|Cola Turka||Cola||Ulker Food, İstanbul, Turkey|
|Altnbas||Black tea||Caykur, Rize, Turkey|
|Nescafe Classic||Coffee||Nestle, Vevey, Switzerland|
|Seker Sut||Natural yogurt||Seker Sut, Konya, Turkey|
|Dikmen||Red wine||Kavakldere, Ankara Turkey|
Sixty cylindrical specimens (10 for each adhesive group) were manufactured in polytetrafluoroethylene molds at room temperature. Each disk had a diameter of 6 mm and a depth of 1 mm. The manufacturers’ instructions were used for preparing, handling, and polymerizing the materials. The mold was filled with material, and the upper and lower surfaces of the mold were covered by 2 glass slides (3 mm). These slides were gently pressed together for removing excess test material. The specimens were cured with the light-emitting diode device having a tip of 8 mm with light intensity of 1200 mW per square centimeter. Standardization of the distance between the light source and the specimen was provided by the thickness of glass slide, which also provided a smooth surface for testing. The specimens were then immersed in distilled water at 37°C ± 1°C for 24 hours for complete polymerization.
Sixty specimens of each adhesive composite resin were divided into 6 groups (n = 10) for staining. Five randomly selected specimens from each group were stored in each of the 5 staining solutions. The 5 remaining specimens from each group were the controls and were stored in distilled water. The specimens were immersed in the staining solutions and water at 37°C ± 1°C for 5 days. The test period was 25 days. The solutions and water were changed daily. The black tea and coffee were prepared with boiled distilled water according to the manufacturer’s suggested concentrations. The yogurt, red wine, and cola came from the market ready to drink. The solutions (50 mL for each) and the specimens were placed in small receptacles. After 1 day in the solutions, the specimens were gently rinsed with distilled water for 5 minutes and dried with tissue paper.
The baseline color of all specimens was measured with a colorimeter (Vita Easyshade, Vita Zahnfabrik H. Rauter, Bad Sackingen, Germany) against a white background according to the system of the Commission Internationale de l’Eclairage (CIE) —L∗, a∗, b∗—after 24 hours of storage in distilled water. All measurements were repeated 3 times, and averages for the values of L∗, a∗, and b∗ were evaluated. After all discoloration processes, final color measurements was carried out.
The CIE system uses the 3-dimensional colorimetric measurements: L∗ values correspond to the brightness of a color, a∗ values to the red-green content, and b∗ values to the yellow-blue content. The color changes (ΔE∗) were calculated from the L∗, a∗, and b∗ values for each specimen according to the following formula, which determines the 3-dimensional color space:
Δ E ∗ = [ ( L 1 ∗ − L 2 ∗ ) 2 + ( a 1 ∗ − a 2 ∗ ) 2 + ( b 1 ∗ − b 2 ∗ ) 2 ] 1 / 2