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 ).

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.

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.