Colour and translucency of tooth-coloured orthodontic brackets
Department of Dental Biomaterial Science and Dental Research Institute, School of Dentistry, Seoul National University, Korea
Address for correspondence Dr Yong-Keun Lee, Department of Dental Biomaterial Science, School of Dentistry, Seoul National University, 28 Yeongeon-dong, Jongro-gu, Seoul, Korea, E-mail: ykleedm{at}snu.ac.kr
 |
Summary |
|---|
 Top Summary IntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
The objective of this study was to determine the reflected and transmitted colours and the diffuse light transmittance of tooth-coloured brackets. Four ceramic and four plastic brands were evaluated and five brackets of each brand were tested. Reflected colour and spectral reflectance of the labial surface of the brackets were measured according to the Commission Internationale de l’Eclairage (CIE) colour scale and transmitted colour and diffuse spectral transmittance measured with a spectrophotometer. One-way analyses of variance were performed for the reflected and transmitted colour co-ordinates (CIE L*, a*, and b*) and for light transmittance according to bracket brand.
The range for CIE L* (lightness) was 36.2–50.3, for a* (red–green parameter) –1.3–3.8 and for b* (yellow–blue parameter) –2.9–11.2. All these colour co-ordinates were influenced by bracket brand (P < 0.05). Diffuse light transmittance was also influenced by bracket brand and ranged from 44.9 to 75.9 per cent (P < 0.05).
Colour and transmittance varied by bracket brand. Variations in optical properties influenced the aesthetic performance of the brackets and the degree of cure of the adhesive that is possible through the brackets. Further studies on the clinical implications of colour matching of tooth-coloured brackets with teeth should now be performed.
|
Introduction |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
Three types of orthodontic brackets are currently available: metal, ceramic, and plastic based. As the number of adults seeking orthodontic treatment increased (Khan and Horrocks, 1991
), ceramic brackets were introduced to meet the increasing demand for more aesthetic appliances (Birnie, 1990). In the mid 1980s, the first ceramic brackets made of monocrystalline and polycrystalline ceramic materials became widely available (Winchester, 1991; Harris et al., 1992); the most apparent difference between the two types of brackets being their optical clarity (Swartz, 1988; Liu et al., 2005). Subsequently, the perceived need for more appealing appliances led manufacturers to develop various types of ceramic brackets (Theodorakopoulou et al., 2004).
Plastic brackets have been used for more than 30 years (Kusy and Whitley, 2005). The early brackets were made of polycarbonate, which absorbed water and changed colour during orthodontic treatment (Reynolds, 1975). Newer types of reinforced plastic brackets were subsequently introduced (Bishara and Fehr, 1997) but, whether they are filled or unfilled, polymers are too weak to act as a satisfactory bracket material (Brantley and Eliades, 2001). The manufacture of composite brackets is different in that it is based on the controlled addition of fillers to a synthetic resin matrix, which is then subjected to injection moulding (Powers et al., 1997).
The optical properties of tooth-coloured brackets have a number of clinical implications: firstly, colour matching with the underlying tooth, and, secondly, light transmittance through the bracket which influences the degree of cure of adhesive through the bracket. Although it is generally claimed that tooth-coloured brackets provide high aesthetics (Faltermeier et al., 2006), there have been few studies on the colour matching of these brackets with the dentition. This lack of previous research may be related to the technical difficulties involved in the colour measurement of brackets, the geometry of which hinders accurate colour measurement with a spectrophotometer or a colourimeter.
When a light-cured orthodontic adhesive is used with a metal bracket, it is usually cured at the incisal and cervical edges (indirect irradiation). When the adhesive is irradiated directly through a translucent bracket, the degree of cure of the adhesive is influenced by the translucency of the bracket. The correlation between the diffuse light transmittance of ceramic brackets and the degree of cure of adhesives and direct light transmittance through ceramic brackets have been evaluated (Eliades et al., 1995a,b).
Although various properties of tooth-coloured brackets have been investigated (Reynolds, 1975; Powers et al., 1997; Faltermeier et al., 2006), there are few studies determining optical properties such as colour and translucency. The current study aimed to evaluate the reflected and transmitted colours of tooth-coloured brackets and to determine their diffuse light transmittance. The null hypotheses were as follows: (1) there are no significant differences in the reflected and transmitted colour co-ordinates of tooth-coloured brackets according to bracket brand and (2) there is no significant difference in the light transmittance of these brackets.
|
Materials and methods |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
Materials
Four ceramic and four plastic commercial brands were investigated (Table 1). All brackets were 0.018 inch, Roth prescription for the maxillary central incisor. Five brackets of each brand were tested.
|
Methods
Reflected colour and spectral reflectance measurement
Reflected colour was calculated according to the Commission Internationale de l'Eclairage (CIE) LAB colour scale (2004) by measuring the ratio of the reflected light to the incident light (spectral reflectance) under specified geometric conditions. Reflected colour and spectral reflectance of the labial surface of the brackets were measured according to the CIELAB colour scale relative to the standard illuminant D65 using a reflection spectrophotometer (CM-3500d, Minolta, Osaka, Japan) equipped with an integrating sphere, with external light excluded using a zero calibration cylinder (CIE L* = 0.09, a* = 0.01, and b* = 0.01, average reflectance = 0.01%, zero calibration box, CM-A124, Minolta; CIE, 2004). These conditions eliminated the influence of background variations (Lee et al., 2005). The ultraviolet (UV) component of the illumination and the specular component of reflection were included [specular component included (SCI) mode]. The measuring aperture diameter size was 3 mm, and the illuminating and viewing configuration was CIE diffuse/10 degrees geometry. The measurements were repeated three times for each bracket.
According to the manufacturers of the spectrophotometer (Minolta), the photometric range is 0–175 per cent and the resolution 0.01 per cent. The repeatability in spectral reflectance is within 0.20 per cent standard deviation (SD) and that in chromaticity within 
E
0.05 SD when a white calibration plate is measured 30 times at 10 second intervals.
In the CIELAB colour space, L* is a measure of the lightness of an object and is quantified on a scale such that perfect black has an L* value of zero and a perfect reflecting diffuser an L* value of 100. The CIE a* value is a measure of redness or greenness, and b* is a measure of yellowness or blueness. a* and b* co-ordinates approach zero for neutral colours. Chroma was calculated as C =(a*2 +b*2)1/2 (CIE, 2004).
Transmitted colour and spectral transmittance measurement
Generally, transmitted colour is calculated according to the CIELAB colour scale, by measuring the ratio of the transmitted light to incident light (spectral transmittance) under specified geometric conditions. Transmitted colour and diffuse spectral transmittance of the brackets were measured according to the CIELAB colour scale relative to the standard illuminant D65 using a spectrophotometer (Color-Eye 7000A, GretagMacbeth Instruments Corp., New Windsor, New York, USA), equipped with an integrating sphere. Illuminating and viewing configurations complied with CIE diffuse/8 degrees geometry (CIE, 2004). The UV component of illumination and the specular component of reflection were included (SCI mode).
Opaque cardboard specimen fixing plates, with central windows the same size as those of the brackets, were fabricated. Light transmittance of the specimen fixing plate was zero when there was no window, and for the window-opened plate, 3.62 ± 0.20 per cent compared with the full diameter (20 mm) opening. The measurements were repeated three times for each specimen.
According to the manufacturer of the spectrophotometer (GretagMacbeth), the photometric range of this spectrophotometer is 0–200 per cent and the resolution 0.001 per cent. The repeatability of a white tile is 0.01 E, the wavelength accuracy 0.1 nm, and wavelength precision 0.05nm, within a 400- to 700-nm range.
Statistical analysis
To determine the difference in colour co-ordinates and light transmittance, one-way analysis of variance was performed according to bracket brand. The difference by bracket type (i.e. ceramic or plastic) was not considered because, based on the results of the present study, significant variations were found between bracket types. The means were compared with Scheffe's multiple comparison test (
= 0.05).
|
Results |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
The reflected colour co-ordinates of the brackets are shown in Table 2. The range for CIE L* was 36.2–50.3, for a* –1.3 to 3.8, and for b* –2.9 to 11.2. The distribution of chroma was similar to that of the CIE b* value. All colour co-ordinates were influenced by bracket brand (P < 0.05). Among the eight brands of brackets, Inspire Ice was the lightest in reflected colour and Luxi II was the most chromatic and yellow tinted.
|
Spectral reflectance curves for the ceramic and plastic brackets are presented in Figure 1a,b, respectively. The Luxi II bracket showed an obvious increase in reflectance as the wavelength increased, which resulted in a high CIE b* value. The Spirit MB bracket showed higher reflectance, which resulted in a high CIE L* value, compared with the other plastic brackets.
|
The transmitted colour co-ordinates of the brackets are shown in Table 3. The range for CIE L* was 12.6–18.8, for a* –1.0 to 0.7, and for b* 0.0–2.8. The distribution of chroma was similar to that of the CIE b* value. All colour co-ordinates were influenced by bracket brand (P < 0.05). Among the eight brands, Esther II was the lightest in transmitted colour and Silkon Plus the most chromatic and yellow tinted.
|
Spectral transmittance curves for the ceramic and plastic brackets are shown in Figure 2a,b, respectively. The Inspire Ice bracket showed the highest transmittance and the Crystalline V an obvious change with wavelength. Among the plastic brackets, Esther II demonstrated the highest transmittance and Silkon Plus and Spirit MB showed lower transmittance. Transmittance varied by wavelength.
|
The mean diffuse light transmittance (percentage ratio to the window-opened plate) of the brackets in the wavelength range 360–750 nm is presented in Figure 3. Regardless of bracket type, varied light transmittance was observed in the range of 44.9–75.9 per cent. These light transmittance values were influenced by bracket brand (P < 0.05).
|
|
Discussion |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
The null hypotheses of the present study were rejected as there were significant differences, both in reflected and transmitted colour, by bracket brand and a significant difference in the light transmittance of these brackets. The thickness and geometry of the tested brackets, which varied according to the brand, had a significant influence on the translucency and colour of the brackets. In addition to the colour difference by bracket brand, colour stability of tooth-coloured brackets during orthodontic treatment is also clinically important. Based on the current study, colour stability of these brackets could be reliably evaluated.
The colour of aesthetic brackets should ideally match those of natural teeth. However, the colour co-ordinates of natural teeth vary according to the colour measurement protocols used and also by race, gender, and age (Bolt et al., 1994; Li, 2003). Since the colour co-ordinates of natural teeth vary, shade guides may be used as substitutes (Lee et al., 2001, 2002). Based on the same measurement protocols used in the present study (Lee et al., 2001, 2002), the reflected colour co-ordinates (CIE L*, a*, and b*) for the Vita Lumin vacuum shade guide (Vita Zahnfabrik, Bad Sackingen, Germany) were 40.8–52.8, –1.2 to 1.4, and 3.9–13.5, respectively, and those for the Chromascop shade guide (Ivoclar Vivadent, Schaan, Liechtenstein) 49.4–62.5, –1.1 to 4.5, and 6.8–20.9, respectively. The range for the CIE L* values of the eight tooth-coloured brackets assessed in the present study was 36.2–50.3. However, before considering a comparison of the colour co-ordinates of the shade guides with those of the brackets, one factor that should be borne in mind is that the colour of the brackets was measured over a zero calibration cylinder, which will decrease the CIE L* value because the light reflectance of this box was nearly zero (0.01%). In contrast, the enamel portion of a shade guide tab is backed by a dentine-shaded opaque backing; hence, the measured CIE L* values of shade guide tabs are likely to be higher than those of the brackets. In view of this limitation, direct comparison of colour co-ordinates of brackets with those of shade guide tabs has limited practical applications. Production of a ceramic dental restoration that matches a target shade is dependent on porcelain thickness, and up to 70 per cent colour differences have been reported between restorations and the shade tab due to a high CIE L* in the restoration (Douglas and Przybylska, 1999). Therefore, in addition to background conditions, the influence of other factors on colour matching, such as the thickness and geometry of brackets, should be studied further.
The range for the CIE a* values of the two shade guides has been reported to be –1.2 to 4.5 and for b* values 3.9–20.9 (Lee et al., 2001, 2002). As the range for the CIE a* values of the tooth-coloured brackets measured in the present study was –1.3 to 3.8, the ranges for the CIE a* values of the brackets and shade guides appeared similar. While for CIE b*, the values were –2.9 to 11.2, indicating a discrepancy between the brackets and the shade guides. While the CIE a* and b* values of tooth-coloured brackets were in a similar hue range in the CIE colour space (CIE, 2004), the background conditions and aperture sizes for the colour measurements of the shade guide tabs and brackets were different, which may have influenced the measured colour and these factors should be considered. The individual composition and morphological features of the tested brackets may have influenced the measured colour and translucency. However at this stage, it is difficult to establish the influence of these factors and further studies are required.
Although dental shade guides have been used for many years, the range of shades is not consistent with natural teeth (O’Brien et al., 1991). This inconsistency makes the colour matching of tooth-coloured brackets with natural teeth even more complicated. In addition, colour measured with a shade guide tab is variable for several reasons: the tabs are not a uniform colour, the shade guides vary between batches, the standard illuminant varies, and there are inherent difficulties with colour measurements for tooth-shaped objects (Schwabacher and Goodkind, 1990; O’Brien et al., 1991). There are also disadvantages in using a colourimeter for measuring tooth colour, including the fact that the instruments are designed to measure flat surfaces and small aperture colourimeters are prone to significant edge-loss effects (van der Burgt et al., 1990; Bolt et al., 1994; ten Bosch and Coops, 1995). These problems could also have influenced bracket colour measurement, as the shape and dimensions are more complex and smaller than those of natural teeth. Therefore, this study utilized reliable colour measurement of brackets using a spectrophotometer. The results indicate that the coefficient of variation (CV: SD/mean) for the reflected colour co-ordinates was in the range 1.4–6.8 (mean: 3.8) per cent for CIE L*, –323.5 to 166.2 (mean: –63.3) per cent for a*, and –208.8 to 123.7 (mean: –3.3) per cent for b*. This indicates that the CV values for CIE a* and b* were high but for L* they were low, which confirmed the reliability of the measurement protocol used in the present study. Similar results were obtained for the transmitted colour.
Transmitted colour is important when a bracket is viewed over transmitted light and, as brackets are sometimes viewed clinically from the side, this might influence the colour match of brackets with teeth. However, studies are recommended to investigate this further.
Optical properties of ceramic brackets have previously been evaluated using diffuse light transmittance spectroscopy. The results showed that monocrystalline alumina brackets had the highest diffuse transmittance values at 468 nm, followed by polycrystalline alumina and polycarbonate-base alumina types (Eliades et al., 1995a). In the present study, the monocrystalline bracket, Inspire Ice, showed higher transmittance than the other ceramic brackets, but similar light transmittance values to those of plastic brackets (Esther II and Image). Light transmittance alone should not be a criterion for the selection of a bracket; it should be considered together with clinical performance.
Eliades et al. (1995a) evaluated the extent of direct light transmittance of aesthetic brackets and the correlations between the transmittance, the structure, morphological factors, and composition were determined. The results showed that all three factors significantly affected light transmission. Absolute values obtained by Eliades et al. (1995a) were based on direct transmittance; therefore, direct comparison with the present study is not possible.
Camphoroquinone, which is generally used as a photoinitiator in light-cured resin-based materials, absorbs light between 350 and 550 nm, peaking at 468 nm (Wendl et al., 2004). The results of the present study showed varied light transmittance depending on wavelength (Figure 2a,b). Light transmittance generally increased as the wavelength increased; therefore, the average value in the wavelength range was calculated (Figure 3).
|
Conclusions |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
Within the limitations of the present study, the ranges for the reflected colour co-ordinates were wide: 36.2–50.3 for CIE L*, –1.3 to 3.8 for a*, and –2.9 to 11.2 for b*, and diffuse light transmittance was 44.9–75.9 per cent. These variations would influence the aesthetic performance of tooth-coloured brackets and the degree of adhesive cure through the brackets. Further studies on colour matching with teeth should be performed and more clinically orientated, simulated models for the evaluation of the degree of adhesive cure through the brackets should also be developed.
|
Funding |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
The Korean Government (Ministry of Education, Human Resources Department), Korea Research Foundation Grant (KRF-2006-311-E00091).
|
References |
|---|
|
TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionsFundingReferences |
|---|
-
Birnie D. Ceramic brackets. British Journal of Orthodontics (1990) 17:71–75.[Abstract]
Bishara SE, Fehr DE. Ceramic brackets: something old, something new—a review. Seminars in Orthodontics (1997) 3:178–188.[CrossRef][Medline]
Bolt RA, ten Bosch JJ, Coops JC. Influence of window size in small-window color measurements, particularly of teeth. Physics in Medicine and Biology (1994) 39:1133–1142.[CrossRef][Web of Science][Medline]
Brantley WA, Eliades T, eds. Orthodontic materials: scientific and clinical aspects. In: Thieme, Stuttgart (2001) 77–82.
Commission Internationale de l'Eclairage. Colorimetry—technical report (2004) 3rd edn. Vienna, Austria: Bureau Central de la CIE. CIE Pub. No. 15.
Douglas RD, Przybylska M. Predicting porcelain thickness required for dental shade matches. Journal of Prosthetic Dentistry (1999) 82:143–149.[CrossRef][Web of Science][Medline]
Eliades T, Johnston WM, Eliades G. Direct light transmittance through ceramic brackets. American Journal of Orthodontics and Dentofacial Orthopedics (1995a) 107:11–19.[CrossRef][Web of Science][Medline]
Eliades T, Eliades G, Brantley WA, Johnston WM. Polymerization efficiency of chemically cured and visible light-cured orthodontic adhesives: degree of cure. American Journal of Orthodontics and Dentofacial Orthopedics (1995b) 108:294–301.[CrossRef][Web of Science][Medline]
Faltermeier A, Rosentritt M, Reicheneder C, Müssig D. Experimental composite brackets: influence of filler level on the mechanical properties. American Journal of Orthodontics and Dentofacial Orthopedics (2006) 130(699):e9–14.
Harris A, Joseph V, Rossouw P. Shear peel bond strengths of esthetic orthodontic brackets. American Journal of Orthodontics and Dentofacial Orthopedics (1992) 102:215–219.[CrossRef][Web of Science][Medline]
Khan RS, Horrocks EN. A study of adult orthodontic patients and their treatment. British Journal of Orthodontics (1991) 8:183–194.
Kusy RP, Whitley JQ. Degradation of plastic polyoxymethylene brackets and the subsequent release of toxic formaldehyde. American Journal of Orthodontics and Dentofacial Orthopedics (2005) 127:420–427.[CrossRef][Web of Science][Medline]
Lee YK, Lim BS, Kim CW. Difference in the color and color change of dental resin composites by the background. Journal of Oral Rehabilitation (2005) 32:227–233.[CrossRef][Web of Science][Medline]
Lee YK, Lim BS, Kim CW, Powers JM. Comparison of color of resin composites of white and translucent shades with two shade guides. Journal of Esthetic and Restorative Dentistry (2001) 13:179–186.[CrossRef]
Lee YK, Yoon TH, Lim BS, Kim CW, Powers JM. Effects of color measuring mode and light source on the color of shade guides. Journal of Oral Rehabilitation (2002) 29:1099–1107.[CrossRef][Web of Science][Medline]
Li Y. Tooth color measurement using chroma meter: techniques, advantages, and disadvantages. Journal of Esthetic and Restorative Dentistry (2003) 15:S33–S41.[CrossRef]
Liu JK, Chung CH, Chang CY, Shieh DB. Bond strength and debonding characteristics of a new ceramic bracket. American Journal of Orthodontics and Dentofacial Orthopedics (2005) 128:761–765.[CrossRef][Web of Science][Medline]
O'Brien WJ, Boenke KM, Groh CL. Coverage errors of two shade guides. International Journal of Prosthodontics (1991) 4:45–50.[Medline]
Powers JM, Kim HB, Turner DS. Orthodontic adhesives and bond strength testing. Seminars in Orthodontics (1997) 3:147–156.[CrossRef][Medline]
Reynolds IR. A review of direct orthodontic bonding. British Journal of Orthodontics (1975) 2:171–175.
Schwabacher WB, Goodkind RJ. Three-dimensional color coordinates of natural teeth compared with three shade guides. Journal of Prosthetic Dentistry (1990) 64:425–431.[CrossRef][Web of Science][Medline]
Swartz ML. Ceramic brackets. Journal of Clinical Orthodontics (1988) 22:82–88.[Medline]
ten Bosch JJ, Coops JC. Tooth color and reflectance as related to light scattering and enamel hardness. Journal of Dental Research (1995) 74:374–380.
Theodorakopoulou LP, Sadowsky PL, Jacobson A, Lacefield W Jr. Evaluation of the debonding characteristics of 2 ceramic brackets: an in vitro study. American Journal of Orthodontics and Dentofacial Orthopedics (2004) 125:329–336.[CrossRef][Web of Science][Medline]
van der Burgt TP, ten Bosch JJ, Borsboom PCF, Kortsmit WJPM. A comparison of new and conventional methods for quantification of tooth color. Journal of Prosthetic Dentistry (1990) 63:155–162.[CrossRef][Web of Science][Medline]
Wendl B, Droschl H, Kern W. A comparative study of polymerization lamps to determine the degree of cure of composites using infrared spectroscopy. European Journal of Orthodontics (2004) 26:545–551.
Winchester L. Bond strengths of five different ceramic brackets: an in vitro study. European Journal of Orthodontics (1991) 13:293–305.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||