Influence of optical properties of esthetic brackets (color, translucence, and fluorescence) on visual perception

Introduction

The aims of this study were to evaluate the optical properties of esthetic brackets and determine their influence on visual perception.

Methods

Eighty esthetic brackets of 16 commercial brands were tested. The color and translucency of the brackets, as well as the color of the maxillary central incisors of 40 subjects, were measured with a spectrophotometer. The fluorescence of the brackets was determined by duly calibrated appraisers. The color differences between the brands of brackets and the teeth were calculated. Data were analyzed by using 1-way analysis of variance; the Scheffé multiple comparison test was used to establish the difference between brands of brackets, (α = 0.05).

Results

The color parameters L ∗ a ∗ b ∗ of nontranslucent brackets ranged from 49.4 to 86.0, –1.6 to 3.0, and 1.9 to 14.6, respectively. The direct transmission of light ranged from 0.0% to 38.8% transmittance. No bracket showed fluorescence. The color and translucency, as well as the color difference, of the brackets were influenced by brand ( P <0.01).

Conclusions

The optical properties of esthetic brackets have a direct influence on visual perception; translucent brackets and the nontranslucent InVu (TP Orthodontics, LaPorte, Ind) brackets were less visually perceptible.

Ceramic brackets appeared in the mid-1980s and were better able meet patients’ functional and esthetic demands; plastic brackets had left much to be desired, particularly regarding color stability, deformation, torque, friction, tie-wing fracture, and debonding. With improvement in the physical and mechanical properties of esthetic brackets by the incorporation of ceramic or glass particles and a metal channel as reinforcement in plastic brackets, in addition to surface preparation of the channel in the ceramic brackets, the demand for esthetics became the main target. Less visual perception, to which the term esthetic is related, was desired.

The lingual brackets and transparent orthodontic aligners (Invisalign; Align Technology, Santa Clara, Calif) are the orthodontic appliances that are the least visually perceptible; however, only esthetic brackets allow a conventional orthodontic procedure to be performed. Their optical properties (color and stability, translucency, and fluorescence) are unquestionable factors for reducing visual perception. Moreover, the knowledge and careful evaluation of the optical properties of patients’ teeth by the orthodontist, especially shade (color), should be considered because they also influence the esthetic performance of brackets.

Esthetic brackets are translucent or nontranslucent, according to their optical properties and availability on the market. The nontranslucent type can be made of plastic or polycrystalline ceramic (machined or injected), and the translucent type is made of plastic or monocrystalline ceramic (popularly called sapphire). For these brackets to have a good esthetic appearance, the nontranslucent type needs to have similar color and fluorescence to the underlying tooth. The translucent type requires a translucency that allows the color and fluorescence of the tooth to appear, and both should have good color stability.

Fluorescence is an optical property inherent to the natural tooth when irradiated by ultraviolet light. This fluorescence, which appears to come from within, makes teeth whiter and lighter in daylight, giving the natural tooth an appearance of vitality. When anterior tooth restorations (composites or porcelain) and esthetic brackets without this property are exposed to ultraviolet light, either daylight or environments with black light, they become dark, causing esthetic disharmony. Although this property has been studied by dentists and prosthetists and included in their materials, in the orthodontic literature, there are still no reports on it.

Although the appearance of orthodontic appliances plays a significant role in the decision of some patients to undergo orthodontic treatment, and this is attributable to the good esthetics of these brackets, few studies have assessed their color and translucence, and none have evaluated fluorescence. The purpose of this study was to evaluate the optical properties of esthetic brackets compared with natural teeth and their influence on visual perception according to the Commission Internationale I’Eclairage color scale and the difference in color.

Material and methods

A total of 80 maxillary right central incisor brackets (slot size, 0.022-in Roth prescription) of 16 commercial brands were obtained. Of these, 12 brackets were ceramic, and 4 were plastic; 5 brackets of each brand were tested ( Table I ).

Table I
Distribution of the groups according to material, type of bracket, code, brand, composition, and manufacturer
Type Code Brand Composition and manufacturer
Ceramic Translucent RAD Radiance Monocrystalline, American Orthodontics, Sheboygan, Wis
Translucent PUR Pure Monocrystalline, Ortho Technology, Tampa, Fla
Nontranslucent CLY Clarity Polycrystalline injected, metal slot, 3M Unitek, Monrovia, Calif
Nontranslucent INV InVu Injected polycrystalline, polymer mesh base, TP Orthodontics, LaPorte, Ind
Nontranslucent SIG Signature Machined polycrystalline, Rocky Mountain Orthodontics, Denver, Colo
Nontranslucent TRL Translux Machined polycrystalline, Aditek lmta, São Paulo, Brazil
Nontranslucent ICR Iceram Machined polycrystalline, Orthometric, São Paulo, Brazil
Nontranslucent ILS Illusion Machined polycrystalline, Ortho Organizers, Carlsbad, Calif
Nontranslucent MYQ Mystique Machined polycrystalline, GAC, Central Islip, NY
Nontranslucent ALR Allure Machined polycrystalline, GAC, Central Islip, NY
Nontranslucent TEC Tecnident Machined polycrystalline, Tecnident, São Carlos, São Paulo, Brazil
Nontranslucent INO In-ovation Self-ligating machined polycrystalline , GAC, Central Islip, NY
Plastic Translucent SPR Spirit MB Polycarbonate reinforced with ceramic Ormco, Glendora, Calif
Translucent ELT Elation Polycarbonate, metal slot, GAC, Central Islip, NY
Nontranslucent SIL Silkon Plus Filler reinforced plastic, American Orthodontics, Sheboygan, Wis
Nontranslucent COM Composite Composite, Morelli, São Paulo, Brazil

After approval from the ethics committee of Federal University of Rio de Janeiro in Brazil, 80 maxillary right and left central incisors in 40 patients who came to the postgraduate orthodontic clinic for the first time were used in the study. There were 16 men and 24 women, aged 20 to 30 years, without distinction as to social and racial groups, with the following characteristics: (1) no previous orthodontic treatment, (2) healthy permanent central incisors (no cavities, fillings, root canal treatments, or patches of decalcification or pigmentation), (3) no smoking habits, and (4) no tooth whitening less than 6 months previously.

The colorimetric readout of the labial surface of the brackets was performed with a digital portable spectrophotometer, Easyshade Compact (model DEASYC220; model DEASYC220; VITA, Bad Säckingen, Germany), positioned perpendicularly to the bracket with a prefabricated positioner ( Fig 1 , A ), by using the same luminosity. The brackets were arranged on a mirrored surface, intraoral mirror (No. 5; Barasch Sylmar, São Paulo, Brazil), because the spectrophotometer did not read that kind of surface, but this surface does not influence the color of the brackets as the black and white surface, thus avoiding the influence of background. To exclude any environmental factors, we used a black opaque cardboard mask with a central window the size of the bracket, and measurements were made without moving the position of the spectrophotometer. The color was evaluated according to the International Commission I’Eclairage color scale relative to the D65 illumination pattern, which uses the mathematical process based on a colorimetric curve to divide the color into 3 fields: L ∗, which represents the brightness or color values (from black to white), the axis a ∗, measuring values from green to red, and axis b ∗, which measures values from yellow to blue.

Fig 1
A, Prefabricated positioner; B, spectrophotometer in the position to read in vivo.

Five measurements were made for each bracket without removing the spectrometer from its position. The value obtained for each specimen (L ∗ a ∗ b ∗) was the mean of these measures.

The spectrophotometer and the measurement system were the same for the teeth as those used for the brackets. All measurements were performed by 1 operator (H.L.F.), under the same light (the same as the brackets), and a standardized protocol had been devised for the subjects for tooth preparation and color evaluation in vivo by using the spectrophotometer. Before the measurements, each subject’s teeth were subjected to prophylaxis with pumice and water. Then the teeth to be evaluated were lightly dried with a paper towel before taking the readouts. Immediately after the cleaning and drying procedure, the color of the teeth was measured by the spectrophotometer ( Fig 1 , B ). The 3 measurements of each tooth were taken in the middle third region of the labial surface, without removing the spectrophotometer from its place, so that there would be no time for drying and a change in color. The calibration process was performed between each tooth to be measured to compensate for any deviation in the amount of light produced by the internal light.

A microprocessed spectrophotometer especially developed for working under ultraviolet and visible light bands (SP-220; Bioespectro, São Paulo, Brazil) was used to evaluate the translucency of the brackets. An opaque black cardboard mask measuring 1 cm 2 with a central window the size of the bracket was fabricated for each bracket. The mask-bracket set, in turn, was placed on the outer surface of the cubette, facing the light beam at a corresponding height, so that this light beam could only pass through the region of the bracket. Before each bracket was measured, the spectrophotometer was calibrated by using only the cubette, corresponding to 100% transmittance, and the cubette with the mask, without a window, corresponding to no transmittance. The analysis of direct transmission of the brackets was performed 3 times at a wavelength of 400 to 700 nm, corresponding to the wavelength of visible light. The value obtained for each specimen was the mean.

After measuring the color of the subject’s teeth and the nontranslucent brackets, the color difference (ΔE) between the means was calculated by using the equation: ΔE=[(ΔL)2+(Δa)2+(Δb)2]1/2
Δ E = [ ( Δ L ) 2 + ( Δ a ) 2 + ( Δ b ) 2 ] 1 / 2
.

To find the difference in color between the teeth and the translucent brackets, a bovine tooth was used for each bracket, and 5 brackets of each brand were tested. The color of the bovine teeth was measured 5 times, and then the bracket was bonded (Transbond XT; 3M Unitek, Monrovia, Calif), and the color of the tooth was measured again 5 times over the bracket. After this, the color difference was calculated by using the same equation as above.

Two properly calibrated examiners (H.L.F. and L.H.M.) qualified the fluorescence of the brackets; in case of disagreement between them, a third examiner qualified the fluorescence, indicating “yes” for those with fluorescence and “no” for those without it, using as the reference the fluorescence of an intact natural tooth (maxillary central incisor) extracted for periodontal reasons. This qualification was performed in a completely dark room, where the samples were exposed to a black light of the Quadriluz black/G-Light, 40 W type (Marschall, Feira de Santana, Brazil), at a distance of 30 cm, perpendicular to the samples.

After bonding the brackets to the bovine teeth, bracket behavior with regard to the visual appearance of tooth fluorescence was observed by an examiner (H.L.F.) to determine whether there was a difference when translucent and nontranslucent brackets had been bonded.

Statistical analysis

Statistical differences were investigated for the parameters of bracket color and translucence by using 1-way analysis of variance (ANOVA) with a level of significance of 0.05. In addition, differences between brands of brackets were investigated with the Scheffé multiple comparison test (post hoc) (α = 0.05). For tabulation and data analysis, we used SPSS software (version 16.0; SPSS, Chicago, Ill).

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Apr 8, 2017 | Posted by in Orthodontics | Comments Off on Influence of optical properties of esthetic brackets (color, translucence, and fluorescence) on visual perception
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