in vitro evaluation of color replication of metal ceramic specimens using visual and instrumental...

Yilmaz and Karaagaclioglu

Clinical ImplicationsClinicians may make more accurate shade determinations using visu-al assessment rather than the colorimeter evaluated. The colorimeter software, which provides results in a porcelain mode for the porce-lain brand evaluated, should be reevaluated by the manufacturer.

Statement of problem. It remains unclear whether or not the performance of intraoral colorimetric devices is accurate.

Purpose. The purpose of this study was to evaluate the color replication of metal ceramics using an intraoral colorim-eter and visual shade determination.

Material and methods. Twenty-five metal ceramic specimens were prepared to match 5 different shades (A1, B1, C3, D3, A3.5) of the Vitapan Classical shade guide. Five clinicians determined the shades of the specimens using the same shade guide. The shade determination was based on the agreement of at least 3 of the 5 observers. Instrumen-tal shade determinations were made with an intraoral colorimeter (ShadeEye NCC) to obtain results in terms of the Vitapan Classical shade guide. Based on these shade determinations, 50 additional metal ceramic specimens (25 visually determined and 25 instrumentally determined) were prepared. The master (initial) and definitive (additional) specimens were analyzed with a spectrophotometer. L*, a*, b* values of each specimen were measured, and the color difference between the master and definitive specimens was calculated. The Wilcoxon signed rank test was used to analyze the color difference (ΔE) values (α=.05).

Results. Visual shade determination produced lower ΔE values than instrumental shade determination. The differenc-es between ΔE values of different shade determination methods were significant for master specimens of the shades B1 and A3.5 (P=.02). The ΔE value calculated from the result of instrumental determination of shade B1 (ΔE=2.97) was within the clinically acceptable limit (ΔE=3.5), whereas the ΔE value for A3.5 (4.03) exceeded the limit for clinical acceptability. The ΔE values for C3 exceeded the acceptable limit for both shade determination methods (ΔE>3.5).

Conclusions. Color replication of metal ceramic specimens using visual shade determination was more accurate compared to instrumental shade determination. The replication of the high-value shades (A1-B1) was observed to be reliable with both shade determination methods. (J Prosthet Dent 2010;105: 21-27)

In vitro evaluation of color replication of metal ceramic specimens using visual and instrumental color determinations

Burak Yilmaz, DDS, PhD,a and Lale Karaagaclioglu, DDS, PhDb

College of Dentistry, The Ohio State University, Columbus, Ohio; Faculty of Dentistry, Ankara University, Ankara, Turkey

aAssistant Professor, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University.bProfessor, Department of Prosthodontics, Faculty of Dentistry, Ankara University.

Understanding of the process by which color and translucency of fixed restora-tions are determined and achieved to replicate the color and appearance of adjacent teeth is important for achiev-ing an esthetic restoration. Errors, especially in the color replication pro-cess, have been a challenge for dentists and technicians and may result in pa-

tient dissatisfaction.1 The goal in many clinical situations

is to provide a metal ceramic or ce-ramic restoration that accurately rep-licates the color of adjacent teeth. For fixed restorations, this process con-sists of a shade matching phase fol-lowed by a shade duplication phase. Shade matching can be accomplished

through either a visual shade match-ing method or through instrumental analysis. The shade duplication pro-cess occurs in the dental laboratory, where the restoration is fabricated using porcelain corresponding to the shade selected in the shade matching phase.2

Visual assessment of shade and

22 Volume 105 Issue 1

The Journal of Prosthetic Dentistry Yilmaz and Karaagaclioglu

translucency is the method most fre-quently used in contemporary den-tal practice.3 Previous studies have shown that visual shade determina-tion is difficult to achieve accurately and yields unreliable and inconsistent results.4-6 The most commonly used method for selecting a shade is com-parison of a tooth’s color to that of a commercially available porcelain shade guide.3,7

Instrumental shade determination can be accomplished with the use of colorimeters. Colorimeters provide direct color coordinate specifications without mathematical manipulation. This is achieved by sampling light re-flected from an object through 3 col-or filters that simulate the response of the color receptors in the eye.8 Vari-ous clinical color-measuring devices are available. ShadeEye NCC (Shade-Eye NCC; Shofu Inc, Kyoto, Japan) is an instrument that provides intraoral readings in terms of shade guides of 4 different porcelain systems (Vita 3D- Master and Vitapan Classical; VITA Zahnfabrik, Bad Säckingen, Germany, and Vintage Halo; Biodent, Toron-to, Canada) for clinical use and CIE L*a*b* coordinates. The CIE L*a*b* color system is frequently used for dental color research and it defines color space by 3 coordinates: L*, a*, and b*. L* describes the achromatic character of the color which is light-ness. The coordinates a* and b* de-scribe the chromatic characteristics of the color. The a* coordinate rep-resents the redness-greenness and b* coordinate represents the yellowness-blueness of the object evaluated. The strength of this system is in its ability to be clinically interpreted, as equal differences across the CIE L*a*b* color space (color differences, or ΔE) represent approximately uniform steps in human color perception, im-proving the interpretation of color measurements. Thus, the magnitude of perceptible and/or acceptable col-or difference can be defined between, for example, a ceramic crown and the adjacent natural dentition.8,9

This magnitude of color differ-

ence is based on human perception of color; color differences greater than 1 ΔE unit are visually detectable by 50% of human observers under ideal lighting conditions.10 However, under normal clinical conditions, such small color differences would go undetect-ed because average color differences below 3.7 ΔE units have been rated as a match in the oral environment.11 Douglas et al12 reported that the pre-dicted color difference at which 50% of dentist observers could perceive a color difference (50/50 perceptibil-ity) was 2.6 ΔE units. However, the predicted color difference at which 50% of subjects would request that the restoration be remade due to color mismatch (clinically unaccept-able color match) was 5.5 ΔE units. O’Brien13 rated ΔE values in terms of clinical acceptance and displayed the thresholds in a table, which allows for clinical interpretation (perfect, excel-lent, good, clinically acceptable, mis-match) in relation to ΔE values that serve as approximate tolerances.

Visual and instrumental shade determination methods have been extensively evaluated.1,5,6,10,14-28 How-ever, few studies have compared the color replication performance of an intraoral dental colorimeter with vi-sual shade determination.6,19

The purpose of this study was to evaluate the color difference of the total color replication process with 2 different porcelain shade matching systems: visual shade matching using the Vitapan Classical shade guide and an intraoral dental colorimeter using the VITA VMK 95 porcelain system (VITA Zahnfabrik). The null hypothesis was that there would be no differences between the color replication perfor-mance of an intraoral dental colorim-eter and visual shade determination.

MATERIAL AND METHODS

Color differences between metal ceramic specimens fabricated accord-ing to visual and instrumental tech-niques were compared with master specimens. Twenty-five metal ceramic

specimens were prepared to match 5 different shades (A1, B1, C3, D3, A3.5) of the Vitapan Classical shade guide. The sample size of 5 per shade was estimated by a power analy-sis calculation (power=0.97, effect size=2.92). Circular plastic patterns (Essix A+, .040; Raintree Essix, Inc, Los Angeles, Calif ) were used for the fabrication of metal specimens (10-mm diameter, 1-mm thickness). The specimens were sprued and invested using a phosphate-bonded invest-ment (Alphacast Vario; Schütz Dental Group, Rosbach, Germany) and cast with a base metal alloy (Heraenium NA; Heraeus Kulzer GmbH, Hanau, Germany) using a gas-oxygen torch and a centrifugal casting machine according to the manufacturer’s in-structions. The specimens were air-borne-particle abraded with 250-µm aluminum oxide (Korox 250; BEGO, Bremen, Germany) to remove the in-vestment material. The sprues were sectioned and the specimens adjusted with tungsten carbide rotary cutting instruments (Komet/Gebr Brasseler GmbH, Lemgo, Germany), airborne-particle abraded with 110-µm alu-minum oxide (Basic Classic; Renfert GmbH, Hilzingen, Germany), and steam cleaned (VAP 6A; Zhermack SpA, Badia Polesine, Italy).

The thickness of each specimen was verified with a micrometer ac-curate to 0.01 mm (Praecimeter S; Renfert GmbH) at 4 different points, and specimens that did not meet the dimensional criteria were replaced with appropriately sized new speci-mens. The specimens were oxidized according to the manufacturers’ rec-ommendations. All specimens were airborne-particle abraded with 110-µm aluminum oxide (Basic Classic; Renfert GmbH) after the oxidation cycle. Opaque porcelain (VITA VMK 95; VITA Zahnfabrik) of each selected shade was applied to all specimens with a brush-on application tech-nique. The average opaque thickness for the specimens was measured to be 0.1 mm (±0.05 mm) with the mi-crometer. A 1-mm layer of dentin por-

23January 2011


celain was applied and fired. Addi-tional porcelain was added after each application stage to compensate for firing shrinkage and to obtain appro-priate thickness. The thicknesses of the disks were verified with the digital micrometer and adjusted as neces-sary with porcelain contouring stones (703.104.120; Komet/Gebr Brasseler GmbH). Subsequently, all specimens were sequentially finished with 600-, 800-, and 1000-grit silicon carbide paper (3M ESPE, St. Paul, Minn). All specimens were airborne-particle abraded after grinding to produce a uniform surface texture for accurate colorimetric measurements. Each speci-men was ultrasonically cleaned in dis-tilled water so that residual alumina particles would not affect the color.

Five clinicians (3 men and 2 wom-en, age range of 26-53 years) from the Department of Prosthodontics, Anka-ra University School of Dentistry, with a negative history of visual color deficien-cy as confirmed by the Farnsworth Mun-sell 100 Hue test (GretagMacbeth, New Windsor, NY), determined the shade of the specimens visually using shade guides (Vitapan Classical; VITA Zahn-fabrik). The sessions were performed in a custom-made viewing booth29 with 65K illumination (Sylvania, Danvers, Mass). The sessions were repeated 3 times at 1-month intervals,29 and the results were recorded. Each observer performed a total of 75 visual shade determinations. The observers were blinded from their own previous data and those of other observers. The shade of each specimen for one ob-server was determined if there was

agreement between at least 2 of the 3 selections of that observer. The de-finitive shade was determined if there was agreement between at least 3 of the 5 selections of all observers. If an agreement was not achieved, addi-tional shade determinations were per-formed until agreement was reached. The results were collected and record-ed by an investigator. Institutional re-view board approval for the study was received from the Ankara University Faculty of Dentistry.

Instrumental shade determina-tions were performed in the same booth with the custom immobilizing device of the colorimeter (ShadeEye NCC; Shofu Inc). The instrument was calibrated with the white working standard of the manufacturer. One experienced observer made all mea-surements. The probe was placed in the middle of each specimen, and 3 consecutive determinations at 1-min-ute intervals were made in the porce-lain mode using the Vitapan Classical guide mode. If the same shade was determined by the instrument for at least 2 of the 3 measurements, this was accepted as the instrument-de-termined shade.

Twenty-five additional specimens were prepared from the visual shade determination results, and 25 speci-mens were prepared from the instru-mental shade determination results using the previously described stan-dardized conditions. The master and definitive specimens were ana-lyzed with the use of a spectropho-tometer (Avaspec-2048; Avantes BV, Eerbeek, the Netherlands). L*,

a*, and b* values of each specimen were measured, and the color differ-ence between the master and defini-tive specimens was calculated with the use of the following equation, which is the Euclidean distance30-32:ΔE(L,a,b)= [(L1

*-L2*)2+( a1

*-a2*)2+ (b1

*-b2*)2]1/2

The ΔE values were evaluated ac-cording to the clinical color matching tolerance13 defined in Table I. This ta-ble provides clinicians the ability to in-terpret color differences with detailed descriptions (perfect, excellent, good, clinically acceptable, mismatch). The Wilcoxon signed rank test was used to analyze the color difference (ΔE) values (α=.05).

RESULTS

The color differences between master and definitive specimens were compared, and the results are dis-played in Table II. Visual shade deter-mination produced lower ΔE values than instrumental shade determina-tion. Delta E differences were statisti-cally significant for master specimens in the shades of B1 and A3.5 (P=.02). The ΔE value calculated from the re-sult of instrumental determination of shade B1 (ΔE=2.97) was within the clinically acceptable limit (ΔE=3.5), which means that the color difference between master and definitive speci-mens was not clinically perceivable, whereas the color difference result for A3.5 was over the limit, meaning the difference was perceivable (ΔE=4.03). The ΔE values for C3 were over the acceptable limit for both methods (ΔE>3.5), and the results (minimum-maximum) showed variation only for C3 for instrumental technique (Table II). The percentage results of visual and instrumental determinations by means of the Vitapan Classical shade guide are displayed in Table III and IV, respectively.

The observers agreed with one an-other on the correct shade 64% of the time for A1, and 94%, 35%, 31%, and 63% of the time for B1, D3, C3, and A3.5, respectively. The colorimeter agreed with its own data as to the

Table I. Clinical color-matching tolerance13

0

0.5-1

1-2

2-3.5

>3.5

Reprinted with permission from Quintessence Publishing Co Inc, Chicago.

Perfect

Excellent

Good

Clinically acceptable

Mismatch

MatchClinical ColorColor Difference

(ΔE)



Table II. Color differences between master and definitive specimens. The significant differences were determined with Wilcoxon signed ranks test

Table III. Percentages (%) of visual shade determinations

Table IV. Percentages (%) of instrumental shade determinations

A1

B1

D3

C3

A3.5

Results are significantly different at level α=.05

0.60

0.78

0.13

2.97

2.94

3.90

4.66

5.15

0.15

4.03

Mean

Color Difference (ΔE)

0 (0-2.97)

0.78 (0.78-0.78)

0.11 (0.11-0.23)

2.97 (2.97-2.97)

4.47 (0-5.12)

3.90 (3.90-3.90)

2.44 (0-11.53)

3.56 (3.56-7.53)

0.13 (0.13-0.36)

4.03 (4.03-4.03)

Excellent

Excellent

Perfect



Mismatch

Mismatch

Mismatch

Perfect

Mismatch

Maximum) Tolerance(Minimum- Matching

Median Clinical Color

Color

Visual shade determination

Instrumental shade determination









.48

.02

.68

.49

.02

P

A1

B1

C3

D3

A3.5

64

5

1

4

–

A1

10

1

–

–

–

A2

1

–

–

1

2

A3

–

–

–

–

63

A3.5

11

94

–

1

–

B1

–

–

–

–

16

A4

9

–

–

1

–

B2

–

–

–

–

–

B3

–

–

–

–

–

B4

1

–

1

4

–

C1

1

–

16

20

1

C2

3

–

31

5

7

C3

–

–

16

–

4

C4

–

–

9

29

–

D2

–

–

23

35

7

D3

–

–

3

–

–

D4

Selected ShadesMasterSpecimenShades

A1

B1

C3

D3

A3.5

26

100

–

A1

74

–

–

–

–

A2

–

–

–

100

–

A3

–

–

47

–

–

A3.5

–

–

–

–

–

B1

–

–

53

–

100

A4

–

–

–

–

–

B2

–

–

–

–

–

B3

–

–

–

–

–

B4

–

–

–

–

–

C1

–

–

–

–

–

C2

–

–

–

–

–

C3

–

–

–

–

–

C4

–

–

–

–

–

D2

–

–

–

–

–

D3

–

–

–

–

–

D4

Selected ShadesMasterSpecimenShades

25January 2011


correct shade for A1 26% of the time. The instrument provided no correct results for the other 4 shades (B1, D3, C3, and A3.5).

DISCUSSION

The results of this study support the rejection of the null hypothesis, as significant differences were not-ed between the results of visual and instrumental shade determination methods in terms of color replication. This study focused on comparing dif-ferent shade determination methods to each other. The master specimens fabricated according to the 2 meth-ods were not compared to a gold standard, which would have allowed interpretation of the accuracy of the methods used.

In the current study, the shades of the master specimens were select-ed from widely different colors. The values of the specimens were differ-ent: B1 and A1 were considered to be high-value shades, D3 was con-sidered to be a medium value, and C3 and A3.5 were considered to be low-value shades.20 The colors of the definitive specimens were close to those of the master specimens, and differences were clinically not perceivable for the high-value colors using either technique. The color dif-ference between the definitive and master specimens exceeded the clini-cally acceptable limit, which means it was perceivable for both techniques for shade C3 (ΔE>3.5), with C3 be-ing the least accurately reproduced shade among the specimens. The color difference between definitive and master specimens using the in-strumental technique for medium- and low-value colors was perceivable (ΔE>3.5). However, all ΔE values were less than 3.5 units, which means that, except for C3, the difference was not perceivable in visual determination. High-value specimens were of a better quality than medium- and low-value specimens using both techniques. In general, as the value decreased and the chroma increased, success of the

reproduction decreased for both the visual and instrumental techniques. There was one exception: the visual method was successful with the A3.5 shade. This result may be attributed to the frequent existence of shade A in the population.

The examiners performed better than the colorimeter in matching the correct shade for the metal ceramic specimens. B1 was the most accu-rately matched shade, whereas C3 was the least accurate when visual shade determination was used. The colorimeter correctly determined only shade A1. The high-value shades were identified accurately, especially when visual determination was used. Lath et al3 also reported decreased visual color matching success for low-value colors. In visual shade determination, D2 and C3 were the most recorded results when the observers evaluated shade D3, B2 and A2 shades were se-lected for A1, D3 was mostly recorded during the tests of C3, and A4 was re-corded for A3.5. The colorimeter only recorded A shades for each master specimen.

Visual shade determination pro-duced lower ΔE values than instru-mental shade determination. The color difference results between visual shade determination and instrumental shade determination were significantly differ-ent for shades B1 and A3.5 (P=.02). The clinical color matching tolerance is shown in Table I. The greater color difference obtained with the color-imeter might be due to the fact that the manufacturers of the instrument and the porcelain powder were differ-ent. Nevertheless, the manufacturer of the colorimeter stated that the in-strument could be used with differ-ent porcelain brands, and with the popular brand of porcelain tested in the current study. This study did not test the instrument’s accuracy using the manufacturer’s own brand of por-celain. Previous studies have shown that variables such as number of fir-ings,16,30 layering and staining tech-niques, and the type of dental alloys17 are important factors that affect the

definitive color of porcelain restora-tions. The thickness of the porcelain layers has also been shown to have a significant influence on the shade.33 Therefore, the metal ceramic speci-mens were prepared to a specified thickness under standardized condi-tions. Moreover, it was stated that environmental and lighting condi-tions have an important role in shade selection.20,23 Therefore, a viewing booth was used during both evalua-tion sessions to minimize the errors that could occur due to environmen-tal variables.

Paul et al6 compared visual and in-strumental shade determination tech-niques in an in vivo study that used a design similar to that of the current study. The color of a maxillary central incisor restoration was determined by means of visual and instrumental techniques, and 2 definitive restora-tions were fabricated according to the shades determined with both meth-ods. The definitive restorations were placed, and the color difference be-tween the ceramic restoration and the adjacent natural central incisor was determined using data obtained with a spectrophotometer. It was observed that the colorimeter achieved better results than the visual technique in 9 of 10 specimens.

Wee et al19 performed shade deter-mination on 11 VITA porcelain speci-mens with 2 different shade guides (VITA 3D-Master and the Vitapan Classical; VITA Zahnfabrik) and a col-orimeter (ShadeEye EX; Shofu Inc). Definitive specimens were fabricated according to each method. Porcelain powder made by the manufacturer of the colorimeter was used for speci-men fabrication, and then the shades of the specimens were determined with the colorimeter. Additional specimens were fabricated using VITA porcelain powder, and the shades of these speci-mens were determined visually with the help of the shade guides. The color of the definitive specimens was compared to the master specimens with a color-imeter. The authors concluded that all color differences between the defini-



tive and master specimens were per-ceivable, and, therefore, both tech-niques were found to be unsuccessful. They also stated that the porcelain powder produced by the manufactur-er of the shade guide or colorimeter should be used for the fabrication of the restorations.

Results from a colorimeter can be changed because the standardized illuminating light emitted from the device can be scattered, absorbed, transmitted, reflected, and even dis-placed in a sideways direction due to the translucent optical properties of teeth and porcelain.22 When using an instrument with a small aperture for both illumination and collection of light, the amount of reflected light is reduced, causing an inadequate reading of lightness.15 The relatively opaque metal ceramic specimens used in the current study were pre-pared to have a wider diameter than the aperture of the instrument to minimize measurement errors; how-ever, the translucent character of natu-ral teeth should be considered during clinical measurements.

This study does not allow for con-clusions to be made regarding the clinical performance of the tested de-vice, as no measurements were made on natural teeth. There are several factors that may influence the clini-cal accuracy of this device. Unlike the metal ceramic specimens used in this study, natural teeth have variable sur-face texture and anatomic variations that may influence shade measure-ment. The disadvantages of using a colorimeter to measure tooth color are that the instruments are designed to measure flat surfaces, and small aperture colorimeters are prone to significant edge-loss effects.21-23 In ad-dition, the curved surface of a tooth may negatively impact upon the uni-form reflectance of light to the color-imeter.18 As metal ceramic specimens with flat surfaces were used in the cur-rent study, additional in vivo studies are needed before a recommendation for clinical performance can be made.

Only a single instrument was eval-

uated in this study. Further clinical in-vestigation with different instruments is planned to observe the efficacy of the instruments when used to deter-mine shades of natural teeth with curved surfaces.

In the current study, the visual method was observed to produce better color replication results than the instrumental method. This result, within the limitations of this study, may be attributed to the colorimeter software, which calculated the read-ings in terms of the Vitapan Classical shade guide. The use of the porcelain powder produced by the manufactur-er of the colorimeter, along with that manufacturer’s porcelain prescrip-tion, may achieve improved results, and should be evaluated in future studies. Moreover, Vitapan Classical is a commonly used shade guide for clinical shade matching. The prosth-odontists in this study were experi-enced with the use of this guide, an advantage that should not be ignored with respect to the visual shade deter-mination technique.

CONCLUSIONS

Visual shade determination yield-ed better color replication of metal ceramic specimens than instrumental shade determination. The replication of the high-value shades (A1 and B1) was observed to be reliable with both shade determination methods.

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Corresponding author:Dr Burak YilmazThe Ohio State University College of Dentistry, Division of Restorative and Prosthetic Dentistry 305W 12th Ave, Postle Hall, Rm 3005GColumbus, OH 43212Fax: 614-294-9422E-mail: [email protected]

Copyright © 2010 by the Editorial Council for The Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature

Effect of immediate dentin sealing on preventive treatment for postcementation hypersensitivity

Hu J, Zhu Q. Int J Prosthodont 2010;23:49-52.

Purpose. The aim of this study was to investigate the effect of Prime & Bond adhesive on preventing postcementation hypersensitivity of vital abutment teeth restored with a full-coverage restoration using the immediate dentin sealing (IDS) technique.

Materials and Methods. Twenty-five male patients received 25 three-unit fixed partial dentures. A split-mouth design was used and two vital abutment teeth in each patient were allocated randomly into Groups A or B. Teeth in Group A were treated with Prime & Bond using the IDS technique while teeth in Group B were used as a control and left un-treated. The discomfort interval scale, ranging from 0 to 4, was adopted to evaluate hypersensitivity. The double-blind method was applied during the operation so that neither the patient nor the clinician knew which abutment had been treated. The sensitivity assessment was performed 1 week, and 1, 6, 12, and 24 months after cementation. Results were analyzed using the sign test.

Results. Scores for teeth in Group A were statistically significantly lower than those in Group B at 1 week and 1 month postcementation (P < .05), whereas there was no significant difference between Groups A and B at the end of 6, 12, and 24 months (P > .05).

Conclusion. Preventive treatment with Prime & Bond using the IDS technique can significantly reduce postcementa-tion hypersensitivity.

Reprinted with permission of Quintessence Publishing.

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