Chroma Meter

Tooth Color Measurement LJsiiig Cliroina Meter: Techniques A ({vantages a i d Disa dvaiit ages

ABSTRACT Tooth whitening has become a popular and routine dental procedure, and its efficacy and safety have been well documented. However, the measurement of tooth color, particularly in the evaluation of the efficacy of a system intended to enhance tooth whiteness, remains a challenge. One of the instruments used for assessing tooth color in clinical whitening studies is the Minolta Chroma Meter CR-32 1 (Minolta Corporation USA, Ramsey, NJ, USA). This article describes the instrument and discusses various measuring procedures and the Chroma Meter's advantages, limitations, and disadvantages. The available information indicates that, although Minolta Chroma Meter CR-321 provides quantitative and objective measurements of tooth color, it can be tedious to use with a custom alignment device. The Chroma Meter data are inconsistent with the commonly used visual instruments such as Vitapan Classical Shade Guide (Vita Zahnfabrik, Bad Sickingen, Germany), although in many cases the general trends are similar. It is also questionable whether the small area measured adequately represents the color of the whole tooth. A more critical challenge is the lack of methods for interpreting the Chroma Meter data regarding tooth color change in studies evaluating the efficacy of whitening systems. Consequently, at present the Chroma Meter data alone do not appear to be adequate for determining tooth color change in whitening research, although the quantitative measurements may be useful as supplemental or supportive data. Research is needed to develop and improve the instrument and technique for quantitative measurement of tooth color and interpretation of the data for evaluating tooth color change.

CLINICAL. SIGNIFICANCE This paper will help readers to understand the advantages and limitations of the Minolta Chroma Meter used for evaluating the efficacy of tooth-whitening systems so that proper judgment can be made in the interpretation of the results of clinical studies.

(1 Esthet Restor Dent 15: S33-S41, 2003)

oath whitening has been a den- demonstrated the efficacy of perox- T tal procedure for more than ide-based whiteners, and their

research efforts had been made sidered adequate on the basis of until 1989 when Haywood and comprehensive laboratory and clini- Heymann published their paper cal investigations.14 However, tha t first introduced at-home tooth research on tooth color measure- whitening. I The accumulated data ment, particularly the color change from clinical studies has or shade reduction that occurs dur- the instruments commonly used ini-

ing the course of whitening treatment, remains limited.

The chromatometer (or chromo- meter), particularly the Minolta Chroma Meter (Models CR-221 or CR-32 1, Minolta Corporation USA, Ramsey, NJ, USA), is one of

100 years; liowever, few scientific safety, when used properly, is con-

T O O T H C O L O R M E A S U R E M E N T U S I N G CHROMA M E T E R : T E C H N I Q U E S . A D V A N T A G E S . AND D I S A D V A N T A G E S

tially (and until recently) for objective measurement of tooth color and evaluation of whitening efficacy in clinical s t ~ d i e s . ~ ? ~ This article reviews the working mechanisms of the Minolta Chroma Meter CR-321, clinical measurement procedures, advantages, limitations, and disadvantages, and its proper use for evaluating the efficacy of tooth- whitening systems.

T H E I N S T R U M E N T : C H R O M A METER A N D COLORZMETER

The Chroma Meter is a colorimeter. There are two types of colorimeters: those that measure concentra- tion of a colored solution with reference to standards, and those that measure colors of a surface by comparison with standards. The later type of colorimeter has been used for measuring tooth color.

In the literature the term Chroma Meter, which is used by Minolta, is interchangeable with chromatometer. Although several specialized colorimeters, such as ShadeEye@ (Shofu Dental Co., San Marcos, CA, USA), Shadescan@ (Cynovad Inc., Montreal, Quebec, Canada), and Shadevision@ (X-Rite Inc., Grandville, MI, USA), have become available during recent years, they are designed mainly for dental prac- titioners and thus have rarely been used for research purposes. So far the majority of published studies have involved the use of the Minolta

and discussion to the Minolta Chroma Meter CR-321.

As shown in Figure 1, the Minolta Chroma Meter CR-321 consists of a measuring head and an instrument panel. It is designed to measure small areas of glossy surfaces. The aperture provides a measuring area of 3 mm in diameter, with 45" circumferential illumination by 30 optical fibers and 0" viewing geometry (Figure 2) .'

The Minolta Chroma Meter CR-321 uses the tristimulus color-sensing

method, which is based on the three-component theory of color vision by human eyes, as its working mechanism (Figure 3). Accord- ing to this theory, color receptors of human eyes sense three primary colors: red, green, and blue, and all colors are perceived as mixtures of these three primary colors. The Commission Internationale de I'Eclairage (CIE) defined the standard observer in 1931 to have the color-matching functions of x(h), y(h), and z(h). The XYZ tristimulus values are calculated with the standard observer color-matching func-

Figure 1. Minofta Chroma Meter Model CR-321.

Chroma Meter, either CR-221 or CR-321, which has essentially the same working mechanisms. There- fore, this article limits the review

Figure 2. Diagram of the longitudinal section of the measuring head of Minolta Chroma Meter CR-321 showing the aperture (3 mm in diameter) with 45" circumferential illumination and 0" viewing geometry. Reproduced and modified with per- mission from Konica Minolta Photo Imaging USA, Inc.

s34 I O U R N A L O F E S T H E T I C A N D R E S T O R A T I V E D E N T I S T R Y

L I

Figure 3. Schematic illustration of the tristimulus color- sensing method used for Minolta Chroma Meter CR-321 (lower) compared with the color-perception process of human eyes (upper). Reproduced and modified with per- mission from Konica Minolta Photo Imaging USA, Inc.

tions. For better visualization of the color defined by the XYZ tristimulus values, the CIE also developed in 1931 a Yxy color space, in which Y is the lightness and x and y are

the numeric definition of a color as well as the difference between two colors, as illustrated in Figure 4. The color difference is calculated using the following formula:

the chromaticity coordinates determined from the XYZ tristimulus values. The XYZ tristimulus values

AE*& = [(AL*)2+(Aa")2+(Ab")2]1'2

and yxY color space are the faun- dation of the currently used CIE color spaces, including the L"a".b'" color space, or CIELAB.' Details on color theories and various color spaces are discussed elsewhere in this publication.'

M E A S U R E M E N T O F T O O T H C O L O R USING M I N O L T A C H R O M A M E T E R

There have been two methods reported for measuring tooth color using the Minolta Chroma Meter

The Minolta Chroma Meter CR-321 is capable of expressing a color in various parameters, but the L"a'"b" values have been used exclusively in tooth-whitening research, probably owing to their popularity in virtu- ally all fields of color measurement. The L" value ranges from 0 to 100 and increases with the lightness of the color. The +a'" and -a" indicate the red and green directions, respectively, and the +b" and -b" point to the directions of yellow and blue colors, respectively. With the coordinates, the L''a"b" system allows

CR-221 or CR-321-either with or without a custom alignment device. The purpose of using a custom alignment device is to ensure accuracy and precision by measuring the same surface area of each tooth at each appointment.

Various types of alignment devices have been used. Figure 5 shows a typical custom alignment device that consists of a jig and a shield. Owing to smaller sizes of mandibu- lar teeth, it is common to measure the labial surfaces of the six maxillary anterior teeth (nos. 6, 7, 8, 9, 10, and 11). Using a study model prepared from an alginate impres- sion, the custom alignment jig with full palatal coverage is fabricated. The jig is constructed of a visible light-polymerized material, in which are embedded individually aligned female dual-pin sleeves corresponding to each tooth to be measured. To fabricate the cus-

Figure 4. Coordinates of two colors (A and B) in the CIELAB color space and the formula for determining their difference (AE *nb). Reproduced and modified with permis- sion from Konica Minofta Photo Imaging USA, Inc.

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TOOTH COLOR MEASUREMENT USING CHROMA METER: T E C H N I Q U E S . ADVANTAGES. AND DISADVANTAGES

ing of the Chroma Meter aperture, its fabrication and clinical measuring processes are tedious and time consuming. The disinfection and storage of the alignment device between appointments also present a challenge. Consequently, attempts have been made to conduct the measurements of tooth color using the Chroma Meter without a custom alignment device, by the hand- held method.1° The aperture of the Chroma Meter head is directly placed at the middle of the tooth to take the measurement.

Figure 5. A custom alignment device for use with the Minolta Chroma Meter CR-322. A, An acrylic shield for head aperture with a male dual-pin and an alignment jig with six dual- pin female sleeves and the model. B, An assembled custom alignment device illustrating clinical measurement with the Chroma Meter.

tomized acrylic shield that fits on the head of the Chroma Meter, a male dual-pin that matches the female sleeve is embedded in the shield. The pin-sleeve sets are posi- tioned such so that the aperture of the measurement head of the Chroma Meter is in direct contact with the middle third of the labial surface of the tooth and centered mesiodistally. This provides repeatable alignments of the position of the Chroma Meter head aperture to the tooth during each measurement.

It is imperative that each custom alignment device be examined before its use to check the clinical fitting between the parts of the

device, the device and the surface of each tooth, the device and the Chroma Meter aperture head, and the aperture and tooth surface. An ill-fitted alignment device, if unde- tected, provides a false sense of repositioning and adversely affects the accuracy of the measurements. In addition, the measurement taking needs to follow the recommended procedures such as repositioning the aperture for each of the three measurements for each tooth. Com- plete fitting of the aperture to the shield and tooth surface must be ensured for each measurement.

Although a custom alignment device provides repeatable position-

The hand-held method is simple to use, but little information is available regarding the accuracy and precision of the data. As the color of a tooth is not uniform, it is important to determine the effect of any deviations on the L"a"b" measurements and, consequently, the calculated AEOab value. A study conducted in this laboratory found that the vertical deviations are more critical than are the horizontal ones.'l Ten extracted human maxillary central incisors with no caries, stain, or restoration were selected. The root of each tooth was embedded in den- ture resin. Seven positioning devices were fabricated so that the aperture of the Minolta Chroma Meter CR- 321 would be placed at seven defined labial surface areas of the tooth, including the center, 1 mm deviations to the apical, incisal, left and right, as well as 2 mm to the apical and incisal. In addition, measurements were performed at the center of each tooth with the hand- held positioning method. Three

S36 J O U R N A L O F E S T H E T I C A N D R E S T O R A T I V E D E N T I S T R Y

measurements were made for each position on each tooth by repositioning the aperture for each measurement. All measurements were made with a black background, and care was taken to avoid dehydra- tion of the teeth during the measurements. The results showed that

a , and Ab" values were t h e ~ L : : . A ::. , , higher for vertical deviations than for horizontal ones (Table 1). The variations for the hand-held group were similar to those for the 1 mm apical deviation, except for Ab". The AE"-.l~, values were 1.20 for right and left horizontal deviations, 1.72 and 2.01 for I mm apical and incisal vertical changes, respectively, 3.04 and 2.99 for 2 mm apical and incisal vertical changes, respectively, and 1.41 for the hand- held group. Significant differences ( p c .05) were detected in L" values in all deviations compared with the center, except for the 1 mm right deviation. The data are generally in agreement with a study using a spectrophotometer in which the AE:'.3~, error caused by a vertical deviation of 2 mm was 3.67 times that induced by a 5 mm horizontal deviation. I'

Because the deviations of tooth area measured by the Chroma Meter, particularly for vertical deviations, can significantly affect the reliabil- ity of the data, the use of a custom alignment device is preferred. When the Chroma Meter measurements are obtained using the hand-held method, it is important to recognize the potential errors associated with the method, and it is advisable to

take particular precautions in interpreting the data.

A D V A N T A G E S A N D L I M 1 T A T I O N S O t USIN(; M I N O I . T A C H R O M A Mt.TER F O R T O O T H C O I O R ASSESSMENT

Minolta Chroma Meters, including the CR-321, have been used in various industries, such as ceramic, food, paint, plastic, printing, and textile, for color measurement. The major advantage of using the Minolta CR-321 Chroma Meter is the production of objective and quantitative data. When used properly, the Chroma Meter provides standardized measuring conditions and thus eliminates a number of factors, such as variations in light- ing and human color perception, that can significantly affect the accuracy of the color assessnient.i.3 However, the Minolta Chroma Meter CR-321 was not designed for assessing tooth color, particularly in a clinical setting. The measuring device, which is bulky and heavy, is difficult to hold by hand, particu-

l a - ly when i t IS necess'iry to cissess a large number of participants. In addition, the cone-shaped measuring head prevents proper contact of the aperture to the surface of inis- aligned teeth. Proper contact of the aperture to the surface o f cuspids may also be difficult to achieve because of their position and curva- ture of the labial tooth surface. In dddition, only the color of a small area (7.07 mml) , which is c 10% of the labial surface area for '1 typical inaxillary central incisor, IS

measured; thus, the measurements hardly represent the color of a wr h o 1 e tooth .

The major limitation or disadvan- tage of using the Chroma Meter for tooth-whitening assessment is the lack of an established standard method to correlate the L"., a;'., and b:'. values, particularly the AL", ha::., ~ b : > , a nd AEBal,, to tooth color change, making interpretation of data difficult. There are inconsis- tencies in color ranking between

TABLE 1. EFFECT OF DEVIATIONS OF APERTURE FROM THE MIDDLE OF EXTRACTED HUMAN CENTRAL INCISORS O N AL*, Aa*. Ab* , AND 4E*.b.

Deviation from Cente2 AL* Aa* Ab* A E . . ~

1 mm left 0.32 i 0.76 0.03 * 0.22 -0.38 i 0.96 1.20 * 0.48 1 mm right 0.02 i 1.18 0.03 i 0.10 -0.44 i 0.96 1.20 i 0.96 Hand-held -0.73 2 0.96 -0.05 i 0.11 -0.13 i 1.03 1.41 i 0.62 1 mm apical 0.70 i 0.88 0.05 2 0.22 1.39 i 0.68 1.72 i 0.84 1 mm incisal -1.03 * 1.20 0.12 2 0.21 -1.12 i 1.19 2.01 = 0.99 2 mm incisal -1.91 2 1.59 0.17 * 0.37 -1.50 * 1.72 2.99 2 1.51 2 mm apical 0.97 1.99 0.07 i 0.24 2.29 i 0.75 3.04 1.10

Adapted from Ma J et al." 'Measured using the Minolta Chroma Meter CR-321. tN = 10; three measurements were made for each tooth at each location, with reposirioning for each measurement. SMeans and SDs were calculated from the t i E * a h values obtained from each of the 10 teeth.

V O I IIMt 1 7 . \ L I P P L E M E N T I , 2 0 0 1 S37

T O O T H C O L O R M E A S U R E M E N T U S I N G CHROMA M E T E R : T E C H N I Q U E S . A D V A N T A G E S . AND D I S A D V A N T A G E S

Minolta Chroma Meter measurements and shade guides. The most commonly used shade guide in clinical tooth-whitening research is the Vitapan Classical (Vita Zahnfabrik, Bad Sickingen, Germany), which consists of 16 shades and may be arranged by value from lightest ( B l ) to darkest (C4) as per manu- facturer’s instructions (Table 2). However, this value-based ranking is not parallel to the L’> measurements, which represent the value in the CIELAB color space, determined using the Minolta Chroma ihleter CR-321 (see Table 2).14 Only two (D3 and C4) of the 16 shades have a matching ranking. The devi- ‘ition between the two rankings can

Nevertheless, the results obtained from human panelists appear more clinically relevant because the major outcome of tooth-whitening treatment is the reduction of tooth shade (ie, the increasing whiteness) as perceived by human eyes.

Another problem that further exac- erbates the difficulties in interpreting the Minolta Chroma Meter data regarding clinical efficacy of tooth whiteners is that the AE“,i, values, which are intended to quan- tify the difference of two colors and are calculated using the three- dimensional L”., a” , and b” measurements, vary significantly

among shade tabs of equal difference in numeric value. Whereas the 16 Vitapan Classical shade tabs are known not to be spaced evenly when arranged on basis of their lightness or value, they have custom- arily been assigned to consecutive numeric values for data compilation and analysis (see Table 2). As is illustrated in Figure 6, for one shade difference in Vitapan Classi- cal, AE“;,i, can vary from 1.97 (C2 vs D4) to 4.88 (D2 vs A2); for two- shade differences, the variation of the AE“,,i, ranges from 0.92 (B2 vs A2) to 6.65 (A1 vs D2). Clearly, the numeric Vitapan Classical shade changes are not parallel to the

be as large as seven shades: D4 has the eighth ranking on the value- hased Vitapan Classical Shade Guide, whereas it is the fifteenth ranking according to the L” values. I t is of interest that, compared with the ranking by the L“. values, per- sonal color perception matches better with the value-based ranking of Vitapan Classical shade tabs.’” The arrangements of the randomized 16 Vita shade tabs by 402 panelists on the basis of their perception of “whiteness” had 8 shades matching the recommended value-based ranking, including the “whitest” ( B l ) and the “darkest” (C4) extremes; the greatest deviation was three shades (Table 3). The value-based ranking of 26 Vitapan Classical shades is known to be nonlinear in terms of the “whiteness” of their tabs; it thus does not represent a true incremental increase in whiteness or darkness of the tooth color.

TABLE 2. C O M P A R I S O N OF V A L U E - B A S E D S H A D E R A N K I N G TO T H A T D E T E R M I N E D BY L’ M E A S U R E M E N T S O B T A I N E D F R O M C H R O M A M E T E R .

Value-Based V i p a n Minoha Chroma Classical Shade Ranking Meter L* hhSUrem8nt

Shade Tab Numeric Numeric L*

B1 A1 B2 D2 A2 c1

1 4 55.18 2 1 58.58 3 2 55.44 4 9 51.99 5 3 55.30 6 5 53.43

c 2 7 12 50.78 D4 8 15 49.45 A3 9 6 53.37 D3 10 10 51.38 B3 11 7 53.10 A3.5 12 11 51.29 I34 13 8 52.41 c 3 14 13 49.89 A4 1s 14 49.86 c4 16 16 47.28 +As measured with a Minolta Chroma Meter CR-321; data from Li Y et aL’4

TABLE 3. C O M P A R I S O N OF V A L U E - B A S E D S H A D E R A N K I N G T O T H A T PREFERRED BY A G R O U P OF S T U D Y P A N E L I S T S .

Value-Based Vitapan Ranking by Classical Shade Ranking 402 Panelists'

Shade Tab Numeric Numeric Shade l a b

B1 A1 B2 D2 A2 c1 c2 D4 A3 D3 B3 A3.5 B4 c 3 A4 c4

I 2 3 4 5 6 7

8 9

10 11 12 13 14 15 16

1 2 6 3 4 5 9

10 7 8

11 12 13 14 15 16

B1 A1 c1 B2 D2 A2 A3 D3 c2 D4 B3 A3.5 B4 c3 A4 c4

tData from Buisson JC et al.Is

the shade guide, a visual instrument, and the Minolta Chroma Meter, an electronic instrument, is not unex- pected. As stated by Carsten, "The complexity of the visual system pre- cludes complete dependence on electronic shade matching in the near future." Carsten believes that "until this equipment can produce a result that rivals the abilities of the eye and visual cortex to interpret light, learning to accurately shade match with eyes will remain an important task for discriminating dentists and patients."13

Interpretation of statistical differences detected in the L", a", and b'* measurements to clinical significance of whitening efficacy is a challenge, particularly when the shade data are not available. Owing to the nature of the data, the quantitative L", a", and b" measurements tend to provide a

AE"ab values. This discrepancy may have contributed to the divergent relationship between the numeric Vitapan shade reduction and the AE:'ah values observed in some tooth-whitening studies. A recent article reported a reduction of 6.49 Vitapan Classical shades and a AE:i value of 13.82 at the 7-day evaluation; a shade reduction of 7.72 was detected at 14 days, but the AE"ah became 7.23, which is only 52.3% of the AE"ab value at 7 days.Ib Another study showed a generally similar trend between the Vitapan Classical shade reductions and the AE::-,~ data; however; rever- sals were also observed (Figure 7).b The inconsistency in results between

Figwe 6. Vitapan Classical Shade Guide arranged according to the value of the tabs and examples of AE;'*b values for one (upper) and two (lower) shade differences calculated from L *, a *, and b * measurements obtained from the Minolta Chroma Meter CR-321. Data from Lr Y e t aL6

V O L U M E 1 5 , S U P P L E M E N T 1 , 2 0 0 3 S 3 9

TOOTH COLOR MEASUREMENT USING CHROMA METER: T E C H N I Q U E S . ADVANTAGES. AND DISADVANTAGES

Figtire 7. Com- parison of Vita- pail Classical shade reduc-tioii (see F i p r e h for numeric conver- sion) to AE"%,i, viilues ohtairicd from the same groicp of s t ~ d y panelists. Data f r o m Li Y rt 01."

greater statistical power to detect the significance at relatively smaller differences. However, the clinical relevance of these statistically significant differences is unclear. The cer- tainty of the statistical significance is further discounted by the clinical discrepancies in the color ranking as well as the color spacing within and hetween the Vitapan Classical and Minolta Chroma Meter measurements. Clearly, the interpretation of statistics of Chroma Meter results without shade data needs to be done extremely cautiously, especially when the clinical efficacy of two tooth- whitening systems is compared.

It is of interest that there appear to be marked differences in the

surements obtained from the Minolta Chroma Meter CR-321 compared with other systems, such as other colorimeters (eg, ShadeEye and Shadevision), spectrophotometers (eg, Easyshade@, Vident, Brea, CA, USA; and SpectroShade System@, M H T International, Zurich, Switzerland), and digital imaging system (Procter & Gamble, Mason, OH, USA), that are also

values of tooth mea- L ::. a ::. alld b :t 3 ,

capable of generating the same parameters. In general, the L"., a;', and b" values of tooth measurements obtained from the Minolta Chroma Meter CR-321 tend to be lower than those obtained with other systems (Table 4). Theoreti- cally, the measurements should be the same for the same color as they are all based on the three-dimensional coordinates of the CIELAB color space. One of the piausible factors that may contribute to this difference is the small ( 3 mni in diameter) measurement aperture of the Minolta Chroma Meter CR- 321. A study using a spectrophotometer and a spectroradiometer found that the L"., a':., and b" values obtained from extracted human

teeth decreased with smaller-size measuring windows." The LA':. measurements were 54.32, 49.41, and 47.61 for windows diameters of 5 , 4, and 3 mm, respectively. The trend for a:' and b:" measurements was similar, indicating that tooth color measurements using a small window tend to shift toward green and blue color coordinates in the CIELAB color space. The authors suggested that these shifts are caused by the wavelength-dependent edge loss. Although the applic- ability of these spectrophotometric data to the Minolta Chroma Meter is unclear, it appears that a larger measuring aperture is desirable not only because of the possible influence of wavelength-dependent edge loss on the shift of measurement in color coordinates but also because, clinically, the whole labial surface o f the tooth is perceived for its color.

Consequently, the limitations or disadvantages of using Minolta Chroma Meter CR-32 1 for evaluating tooth-whitening efficacy are caused by a combination of complex and unique factors. Quantitative assessment of the efficacy o f whiten-

TABLE 4 . C O M P A R I S O N O F R A N G E S O F L'. a ' , A N D b' M E A S U R E M E N T S OF H U M A N TEETH 1

Minolta CR-321 Other Instruments' Parameter Low High Low High

L* 40 60 65 75 a* -1.5 0.5 -1.5 10 b' 2 12 12 23

+Measured using Minolta Chroma Meter CR-321 and compared with the same parameters determined with other instruments. *Examples indude other colorimeters (eg, ShadeEye and ShadeVi- sion), spectrophotometers ( Easyshade and Specaoshade), and digital imaging system (see text% details).

540 I O U R N A I O F E S T H E T I C A N D R E 5 T O R A T I V E D F N T I S T R Y

ing systems requires not only accuracy and precision of the color measurements but also standardized methods to correlate the quantitative data to tooth color changes that are linear, evenly spaced, and perceiv- able by human eyes. The ultiinate challenge to achieve this goal may be not only the color measurement of tooth but also the method to determine tooth color change or shade reduction mainly in the direc- tion from darkness to whiteness after a whitening treatment.

CON C. 1. IJSI 0 N

The Minolta Chroma Meter CR-32 1 provides objective and quantitative data for color measurements. However, its use for tooth color measurement is techni- cally sensitive and can be tedious when used with a custom alignment device; also, the data are inconsistent with that of the Vitapan Classical Shade Guide and other electronic instruments. A more critical challenge is the lack of methods for interpreting the Chroma Meter data to tooth color change in studies evaluating the efficacy of whitening systems. Research efforts are needed to develop and improve instruments suitable for tooth color measurement as well as to define the clinical relevance of Chroma Meter measurements. Although the use of the Minolta Chroma Meter without an alignment device offers several advantages, limited data are available to support its validity. Additional research is necessary to determine whether

the accuracy and precision of the method is acceptable.

In conclusion, with current instruments and techniques, the Minolta Chroma Meter CR-321 alone does not appear to be adequate for determining tooth color change in whitening studies, although the quantitative measurements may be useful as supplemental or supportive data. Research is needed to develop and improve the instrument and technique for quantitative measurement of tooth color and interpretation of the data for evaluating tooth color change.

DISC1 O S U R F , A N D A C K N 0 W 1.E D G M E N T S

I would like to thank the faculty and staff of the Clinical Research Program and Biocompatibility and Toxicology Research Laboratory, Loma Linda University School of Dentistry, for their contributions to the data used in this paper, and Robin Lavengood, BS, of Konica Minolta Photo Imaging USA Inc. for the information on the Chroma Meter CR-321.

The author has no financial interest in any of the companies with prod- ucts mentioned in this article.

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