Laboratory Versus CLiniCaL speCtrophotometriC anaLysis in...

1775E.D.J. Vol. 54. No. 3 Laboratory VErsus CLiNiCaL spECtrophotomEtriC Egyptian Dental Journal, 54, 1775:1791, July, 2008

Laboratory Versus CLiniCaL speCtrophotometriC anaLysis in shade seLeCtion of esthetiC restorations ConstruCted from heat pressed aLL-CeramiC and sr-

adoro resin Composite

Heba Hamza*, Mona A. El-Agroudi**, M. Adel E. Kaisy*** and Randa N. El Salawy****

*Assistant Professor of Operative Dentistry, Faculty of Oral and Dental Medicine, Cairo University.** Lecturer of Fixed Prosthodontics, Faculty of Oral and Dental Medicine, Cairo University.*** Assistant Professor of Operative Dentistry, Faculty of Oral and Dental Medicine, Cairo University.**** Assistant Professor of Dental Biomatentials, Faculty of Oral and Dental Medicine, Cairo University

ABSTRACT

The purpose of this study was to compare between clinical and laboratory spectrophotometer for

two materials: Heat pressed all-ceramic and SR-Adoro resin composite. Materials and methods:

A total of eighty discs of 5mm diameter and 0.5 mm thickness were constructed from IPS Empress

and SR Adoro resin composite, forty for each material. Laboratory and clinical spectrophotometer

[easy shade] were used to measure the color changes ∆ E, and parameters L*,a*, b* of all the discs

[A1, A3, B1, B3, C1, C3, D2, D4].All the discs were cemented to enamel discs of shade A3, of same

dimensions using translucent Variolink II resin cement. Color was measured after cementation with

same technique after cementation and color differences were calculated [∆ E]. Data were collected,

tabulated and statistically analyzed. Results: There was significant decrease in mean L* after

cementation at all the level of the study. Meanwhile mean of a* parameter showed no significant

change after the cementation at all the level ∆ of the study. For the laboratory spectrophotometric

analysis of b* parameter, in composite discs for the shades 1M2, 1M1, 3M1, and 2M3 there was

no significant change after cementation, whereas there was significant increase in mean b* for the

shades 2M2, 3M3, 4R1.5and 3L2.5. With the laboratory spectrophotometer analysis there was no

significant change for the mean b* parameter. Meanwhile in ceramics, there was significant increase

in the mean b* using both techniques the laboratory and the clinical spectrophotometer. For the color

changes ∆E there was positive correlation between the clinical and laboratory spectrophotometers.

Conclusions: Within the limitations of this study the following could be concluded: After

cementation of the tested esthetic materials, the lightness decreased, no change at the red-green

level of the shades, with increase toward the yellow except for the shades 1M2, 2M3, 3M1, and

1M1showed no change. The color measurements obtained with digital analysis method were in

accordance with those of the spectrophotometric evaluations, with respect to L*, a*, b*, and ∆E.

As regard the color change ∆E, no detectable color change was recorded in the present study after

cementation of the tested esthetic materials with the translucent cement at all the levels of the study

as the values of ∆E fell within the clinically acceptable range [2.6-3.7].

E.D.J. Vol. 54. No. 31776 heba hamza, et al.

statement of the probLem

Traditionally; shade selection is made by visual comparison of a target (adjacent tooth) to shade guides. The available shade guides, in addition to minor differences in light conditions, have been found to dramatically affect the outcome of restoration color and the production of an acceptable color match. The final color match of restoration to adjacent natural dentition, however, remains problematic. Optical electronics and computer technology not only have provided objective and rapid color determination but also presented the ability to detect the subtle changes in color.

introduCtion

With the advances in dental materials and new techniques in restorative dentistry, the demand for esthetic restorations has increased tremendously. A smile has been said to be one of the most important interactive communication skills of a person. The ultimate objective of esthetics in dentistry is to create a beautiful smile, with teeth of pleasing inherent proportions to one another, and a pleasing tooth arrangement in harmony with the gingiva, lips and face of the patient. In addition, the esthetics of any restoration needs to consider the parameters of surface form, translucency and color (1).

However patient satisfaction of an esthetic restoration is primarily associated with surface and outline form, translucency and color of artificial teeth. Whereas meticulous preparation and laboratory techniques help to achieve the form of the restoration, the color matching remains a dilemma for the dentist. The reflected components of incident white light determine the color of an object. Surface characteristics, such as gloss, curvature and texture affect the degree of light diffusion when striking the particular object (2).

The laminate veneers are becoming increasingly popular for the esthetics of anterior teeth. Their

conservative, reversible, ease of placement and excellent esthetics make them a viable alternative when one is selecting anterior restoration. These restorations are mechanically bonded to tooth structure with an enamel acid etching technique and one of the low viscosity composite resin luting agents. So the whole complex [Laminate-Cement-Enamel] plays a major role in both light perception and shade selection. (3) Laminates may be fabricated from either ceramics or composites. Many types are available for the two categories, but in this research we are much more concerned about one type representative from each material; the heat pressed (IPS Empress) and the fiber reinforced (SR Adoro).

The IPS Empress glass-ceramic has been successfully used as a metal-free dental restorative material in clinical situations for more than 6 years. Numerous studies confirm that this material fulfills the high esthetic standards demanded from restorations such as inlays, onlays, crowns and Laminate veneers (4). The special material properties (good translucency, flexural strength 120 MPa, and chemical and abrasion resistance) required for dental applications as well as the viscous flow process were achieved in the development of leucite-based IPS Empress glass ceramic. This material is derived from the SiO

2-

Al2O

3-K

2O chemical system (5-7). All-ceramic

restorations, having no metal substructure, allow superior translucency and can be used in areas of high esthetic demand. A challenge in the success of these restorations is color assessment and reproducibility. (8)

Several brands of filled polymers are available; the SR Adoro is one of the most recent brands. It is a composite veneering system that offers several advantages over hybrid composite materials as regards wear, handling, plaque resistance and surface finish. The advantageous properties of SR Adoro can be attributed to the high proportion of

1777E.D.J. Vol. 54. No. 3 Laboratory VErsus CLiNiCaL spECtrophotomEtriC

inorganic fillers in the nanoscale range as when they are combined with the newly developed matrix, they impart a homogeneous structure to the material. The ratio between these two components has been carefully adjusted, endowing the material with excellent physical properties and a high resistance to discoloration, plaque and wear (9). Furthermore, the matrix is based on a Urethane Dimethacrylate (UDMA), which has also been newly developed and which is characterized by its toughness, which is higher than that of its predecessors or the frequently used Bis- GMA. In order to achieve a non-sticky, homogeneous consistency and a low-shrinkage system a special prepolymer has been developed, which is also based on the newly developed UDMA and nanoscale fillers. Promoting restorations resistant to discoloration and plaque formation. The result is a virtually homogeneous material, which may well be called a ”Microcomposite”. This nanofilled, light/heat –curing veneering composite is indicated for full coverage veneers and partial veneers, laminate veneers, inlays and onlays and three unit anterior bridges(9).

Highly aesthetic results can be achieved even if a straightforward, basic layering procedure is used thanks to the excellent esthetic properties of the material. Even the basic material of SR Adoro exhibits opalescent characteristics, which are equal to those of the natural tooth in every way. Watchwords, such as brightness, chroma, or opacity and translucency, have been taken into account in the coloration of SR Adoro. These characteristics are apparent in the individual components of SR Adoro and endow the material with its highly esthetic properties (9). When compared to ceramic materials, these composite resins had the lowest material wear rate, the lowest enamel wear rate, and the lowest total wear rate. The material structure of SR Adoro contributes to the excellent grinding and polishing properties providing a restoration with an enamel-like gloss (9).

“The Color does not exist if there is no one to perceive it.” Color matching can be performed using visual and/or instrumental methods. Visual color matching methods are subjective, but omnipresent, while instrumental methods are objective, but still not widespread in dental practice. Precise and objective answers to most of the questions mentioned could be obtained only by using instrumental color matching techniques, because they allow numerical expression of results. A need to overcome subjectivity, as the major disadvantage of the visual shade matching method, induced the evolution of color science. Color science is multidisciplinary and it encompasses elements of physics, chemistry, physiology and psychology. In order to understand the science of color, one should be aware of some physical aspects of light, as well as of both physiological and psychological processes that enable color perception (10).

The entire process starts with the light source, which justifies the saying: “Color is light” as reported by Saleski (10). The structure of the object (type of material, texture) influences its optical properties, i.e. the ratio among absorbed, reflected and transmitted parts of light (11).

Color assessment in dentistry is considered a complex psychophysiologic process that is subject to numerous variables: Dentin is considered the primary source of color, which is modified by the thickness and translucency of overlying enamel. The perceived color of natural teeth is a result of reflected light from the enamel surface, in addition to the scattered light effect within enamel and dentin before being finally reflected back. The final color match of laminate veneers to adjacent natural dentition, however, remains problematic (12, 13).

Traditionally, shade selection is made by visual comparison of a target (adjacent tooth) to shade guides. Among the different types of ceramic –made shade guides The Vitapan classical shade guide (Vident, Brea, Calif) was a gold standard in


dentistry for decades and, to a large extent, still is. This shade guide tabs are divided into four groups, with primary group division based on hue (A, reddish brown) (B, reddish yellow) (C, Gray) (D, reddish gray) and within the groups tab arrangement is based on increasing chroma. It consists of 26 tabs divided into five groups according to the lightness. Within the group tabs are arranged according to the chroma (Vertically) and hue (Horizontally) (14). The Vitapan 3D master color guide is designed identically to the corresponding shade guide (i.e., 26 shades), except that its tabs include only the dentin shade, with no cervical or incisal shades. Several important characteristics have been improved with Vitapan 3D master as compared with the Vitapan classical shade guide: the lightness range is wider; more chromatic tabs are included, the hue range is extended toward reddish spectra part; the shade tabs are more uniformly spaced; group division is better; and, although certain disharmony still exists, the overall tab arrangement is much better (14).

Concerning the resin made shade guides, although some manufacturers claim that shades of their resin composites or acrylics match the shades of ceramic shade guides, it is always beneficial to use a shade guide made of corresponding restorative material. The conception and tab arrangement of resin shade guides are basically similar to the ceramic shade guides. The shade of a composite needed for a tooth-colored restoration is usually determined clinically by use of a shade guide, which may or may not be made of the actual composite. Standard shade guides are based on various arrangement criteria, and sometimes the do not match tooth color or composite shades well. Composites are classified by uses, fillers, and shades: universal shades that are most commonly keyed to Vitapan Classical shades (14).

The tabs in the shade guides are arranged in a similar way; basically there are lighter and darker tabs (except in Vitapan 3D master), in which the tabs are arranged following color differences values

in relation to the lightest tab (with the greatest ∆E) value in relation to other tabs (14).

Reich and Homberger (15) reported that, currently, it was not possible to determine tooth shade accurately in clinical situations with instrumental measurements. Shades of natural teeth were greatly affected by specific characteristics such as fluorescence, metamerism, translucency, nonuniformity across the surface, and irregular shape. Clinical perceptibility of color differences has been the subject of numerous investigations.

Seghi et al (16) reported that in any organized shade selection procedure there should be a color standard to which an object may be compared to or matched. However in dentistry, there is no such match, but rather an individual range of acceptability. The color standard used in the selection of teeth color has been the shade guide.

In a spectrophotometric study, Rosenstiel and Johnston (17) found that corresponding shades of porcelain of different brands produced perceivably different colors.

Similarly, Pizzamiglio (18) concluded that matching the color of ceramic restorations to the color of natural teeth was considered more of an art than a science. It was implied that lack of understanding of the color system, in addition to lack of a precise methodology to quantify color, made this problem difficult.

In order to eliminate the uncontrolled variables during the color matching process, instrumental methods have been developed. Optical electronics and computer technology not only have provided objective and rapid color determination but also presented the ability to detect subtle changes in color. A general industrial demand for color control applications, coupled with rapid advances in optical electronic sensors and computer technology over the past 20 years, has made instrument color matching techniques more accurate, affordable and user friendly (19-22)


By definition the spectrophotometer is a sophisticated instrument, designed to measure an observed object by reflection or transmission, giving the entire spectral curve as a result, limiting color measurement to a visible frequencies range (usually 350-800 nm). The possibility to measure a color numerically with a reliable digital instrument and to have a close correspondence with this number and the restorative material marks a new development in dentistry and spectrophotometers could become part of the routinely used office devices (23). The Laboratory Spectrophotometer is a device-independent color space required for measuring and quantifying color that is independent of the measuring device. Several such systems have been developed to be true representations of colors as perceived by the human eye. The most commonly used color space is based upon the three colors red, green and blue (also referred to as X, Y and Z) (24). The Commission Internationale d’Eclairage (CIE) is an international standards organization with respect to the measurement and reporting of color. The CIE L*a*b* color space has a vertical axis that indicates relative lightness or darkness. The two horizontal axes represent the amounts of red/green and yellow/blue. In the L*a*b* color space: .L. is a measure of the Lightness of an object, ranging from 0 (Black) to 100 (White), a. is a measure of redness (a > 0) or greenness (a < 0), b is a measure of yellowness (b > 0) or blueness (b < 0).

The total color difference determination is a much more important datum in practice than absolute color coordinate values and it is expressed in ∆E units; as E (after the German word Empfindung, meaning sensation) and represents the total color difference from the ideal black.. The total color difference, according to L*, a*, b* coordinates, is calculated as shown in the Following equation (24).

∆E= (∆L2+∆a2+∆b2)½

The Commission Internationale de l’Eclairage (CIE) recommended calculating color difference

(∆E) based on CIELAB color parameters. Several studies reported that perceivable color differences ranged from [1 to 2], whereas acceptable color differences for dental professionals ranged from [2.6 to 3.7] (32). More recently, in order to minimize potential error in color matching by personal estimation, research has endeavored to use the science and theory of color to devise a standard that will allow colors to be classified numerically, for an easier and more precise transfer and communication of color in restorative dentistry. This has been a significant step in the development of Clinical spectrophotometers Easyshade.

The Vita Easyshade (Vident) clinical spectrophotometer is a handled spectrophotometer for tooth shade matching. The instrument consists of a hand piece and a base unit, which are connected by a monocil fiberoptic cable assembly. The hand piece uses multiple spectrophotometers in the measurement process. One spectrophotometer is used to monitor the light source, and two others to measure internally scattered light at two different distances from the point at which the light enters the tooth. These two readings are combined in a proprietary manner that takes into account the scattering, translucency, and thickness of the material to form what is referred to as the principal spectrum representative of the material (24).

Optical electronics and computer technology not only have provided objective and rapid color determination but also presented the ability to detect the subtle changes in color. Developments in optical electronics and computer technology are making the techniques of electronic shade matching more appropriate for everyday use. Advanced electronic shade matching devices are precise, repeatable, and easily assessed in terms that are visually meaningful. They also though have certain challenges to overcome (25). Spectrophotometric color measurements are capable of reliably quantifying Color of both extracted teeth and dental Porcelain/Composite.


The manufacturer claims it responds to light in

a way similar to the human eye. The VITA Easy

shade is a digital device for measuring color in terms

of 3D- master or a classical shade, its idea based on

the spectrophotometer device. It is a self contained,

easy to use, portable, dental shade matching

Colorimeters and spectrophotometers have

demonstrated usefulness in dental research and

consistency in matching opaque objects and some

translucent objects. However for the most part, such

instruments have not performed well with more

complex, multilayered, translucent objects (24).

Therefore the aim of this in vitro study is to

compare between the two techniques; Laboratory

Spectrophotometer and Clinical Spectrophotometer

Vita Easyshade for color measurements of esthetic

restorations constructed from two different systems

[IPS Empress1 (Ceramic)-SR Adoro (Composite)]

and to check the efficacy and reliability of the Vita

Easyshade system, and to evaluate the influence of

cementation of different shaded discs of both systems

to enamel using the Variolink II resin cement on the

final color of the restoration.

The research hypothesis was that the Easyshade

(clinical spectrophotometer) is not a reliable device

and the shade of the restorations would be affected

by the cementation to enamel.

materiaLs and methods

One all- ceramic system [Empress 1]* and one

resin composite system [SR Adoro]** were used in

this study. Resin cement [Variolink II]*** was also

selected.

selection of teeth:

Sound anterior teeth caries, stains free, of shade A3 were selected.

preparation of enamel discs:

The anterior teeth were milled to form discs of enamel from the middle part of labial surface of anterior teeth of 5mm in diameter and 0.5 mm in thickness.

mold construction:

For purpose of standardization of the samples; a specially designed split copper mold was constructed, the mold is supplied with 5 holes each of 5 mm diameter and 0.5mm thickness.

all ceramic system [empress 1] discs construction:

Waxed disc**** samples were constructed in the 0.5 mm mold, sprued, invested, and wax was then eliminated in a burnout furnace*****. IPS Empress ingots of all the tested shades (1M2)-(2M3)- (1M1)-(3L2.5)-(2M2)-(4R1.5)-(3M1)-(3M3) were heated and pressed in the EP 600 furnace******

following manufacturer’s instructions forming the full thickness disc. Samples were ultrasonically cleaned in an ultrasonic bath for five minutes then examined carefully for any crack or defect. The desired shade of the disc samples was achieved by the staining technique using the IPS Empress shading kit.

Composite system [sr adoro]:

Filling the mold incrementally each time with the desired tested shades in this study 1M2)- (2M3)-(1M1)-(3L2.5)-(2M2)-(4R1.5)-(3M1)-(3M3) each increment was cured for 20 seconds

* Ivoclar, Vivadent ,Amherst NY ** Ivoclar-vivadent.Schaan-Liechtenstein.*** Ivoclar-vivadent.Schaan-Liechtenstein.**** voclar, Vivadent ,Amherst NY***** Neytech-Vulcan 3-130. Dentsply.****** EP600 Combi: Ivoclar-vivadent.Schaan-Liechtenstein.


using Optilux 500, turbo light tip. Recurring took place for the whole layers after complete filling the mold. Then the discs were covered on top with SR gel, and then the discs were mounted on an object holder and placed in the Lumamat 100 for 25 minutes. After completion of the polymerization/tempering procedure, SR gel was completely removed. Finishing and polishing were carried out according to the manufacturer instructions.

Cementation of the sample discs:

For purpose of standardization discs of (Empress and SR Adoro) were cemented to enamel discs using the translucent Variolink II (Ivoclar Vivadent) under specially designed loading device of constant load of 500gr. Then excess was removed after complete setting.

Laboratory spectrophotometer analysis:

Color measurements were taken before cementation of the sample discs to enamel discs as control and later after cementation. A positioning jig was used to position the measuring port of the instrument to the same location on the specimen for repeated measures. Quantitative color analysis was performed with a small area colorimeter, which was also used to study color parameters in dental porcelains in previous studies*. All the colorimetric measurements were carried out according to the CIE L*a*b*- color system with a scanning spectrophotometer (Shimatzu UV- 3101PC. Analytical instrume nt division, Koyoto, Japan). It is a double beam direct ratio measuring system. It consists of the photometer unit and a pc computer. Color differences (∆E) of specimens were calculated between the control (before cementation) and (after cementation) using the equation**:

∆e = [(∆L *) 2 + (∆a *) 2+ (∆b *) 2] ½

Clinical spectrophotometer analysis [easyshade system]:

Color measurements were taken before cementation of the sample discs to enamel discs as control and later after cementation.

Description of the device: The Vita Easyshade intraoral dental spectrophotometer is a device consisting of a base unit (Lamp assembly) and hand piece with a fiberoptic cable assembly connecting the hand piece and base unit. The hand piece contains a fiberoptic probe assembly for illuminating and receiving light from a tooth, multiple spectrometers and a microprocessor for communications with the base unit. Easyshade utilizes a 20 Watt halogen stabilized tungsten filament lamp. It has a color temperature of 3350K and is a continuous light source over the full visible and near infrared spectrums. It requires 15 seconds to warm and stabilize.

Methodology of the device: The spectrometers in Easyshade are very linear, thus only one sample is required for calibration. A ceramic/composite block of known color is utilized for calibration and is located over a switch which is used to detect when the instrument is in the calibration mode. Following calibration, Easyshade is ready to measure the discs. The type of material to be measured is selected from a menu on the display via the touch screen. A measurement proceeds by placing the probe on the disc and pressing the probe switch. The probe has additional sensors utilized to measure angle and motion. If the probe is moving during a measurement the white measurement is delayed until the probe is stabilized. Additionally, if the probe is held at an outward angle or is too near an edge of the tooth the measurement may be adjusted for the angle or rejected. It is a simple process to re-measure the tooth.

* Rosenstiel SF, Porter SS, Johnston WM.: Color measurements of all ceramic crown systems. J Oral Rehabil;16:491-501 1989** Wyszecki G, Stiles WS, Wyszecki GN. Color science: concepts and methods, quantitative data a nd formulae. 2nd ed. New York:

John Wiley; p. 166-9, 1982.


resuLts

statistical analysis

Descriptive statistics for numerical data included means and standard deviation (SD) values. Paired t-test was used to compare between means before and after cementation. Pearson’s correlation coefficient was used to determine significant correlation between Spectrophotometric and EZ shade measurements.

Statistical analysis was performed with SPSS

14.0® (Statistical Package for Scientific Studies) for

Windows. The significance level was set at P≤0.05.

I- ΔE

ii-Comparison between color parameters before and after cementation.

tabLe (1): Descriptive statistics of ΔE:

Measurement Material Shade Shade Mean SD

EZ

sha

de

Mean SD

Spec

trop

hoto

met

er

Composite

1M2 A1 3.05 0.1 3.21 0.11M1 B1 2.91 0.2 2.79 0.22M2 C1 2.1 0.1 2.35 0.022M3 A3 2.24 0 2.11 0.13L2.5 B3 1.35 0.2 1.3 0.044R1.5 C3 1.48 0.03 1.45 0.23M1 D2 2.31 0.08 2.27 0.43M3 D4 1.36 0.05 1.48 0.1

Ceramic

1M2 A1 3.46 0.01 3.16 01M1 B1 3.22 0.4 3.18 0.42M2 C1 2.24 0.05 2.29 02M3 A3 2.39 0.05 2.4 0.043L2.5 B3 1.42 0.2 1.48 0.34R1.5 C3 1.55 0.03 1.63 03M1 D2 2.17 0.04 2.24 03M3 D4 1.6 0.1 1.67 0

tabLe (2): The means, standard deviation values and results of paired t-test of Composite:

ShadeCementation

Parameter

Before After P-value

Eas

yshd

e

Before After P-valueMean SD Mean SD


• Spectrophotometric analysis:

• 1M2, 1M1, 3M1 and 2M3:

There was a statistically significant decrease

in mean (L) after cementation. There was no

statistically significant change in mean (a) and (b)

after cementation.

• 2m2, 3m3, 4r1.5 and 3L2.5:



statistically significant change in mean (a) after

cementation. There was a statistically significant

increase in mean (b) after cementation

• EZ shade analysis:

• All shades:



statistically significant change in mean (a) after

cementation. There was a statistically significant

increase in mean (b) after cementation

• Spectrophotometric analysis:

• All shades:

There was a statistically significant decrease in mean (L) after cementation. There was no statistically significant change in mean (a) after cementation. There was a statistically significant increase in mean (b) after cementation

• EZ shade analysis:

• All shades:

There was a statistically significant decrease in mean (L) after cementation. There was no statistically significant change in mean (a) after cementation. There was a statistically significant increase in mean (b) after cementation

iii- Correlation between spectrophotometric and eZ shade measurements

1. Composite

• 1M2:

There was a statistically significant positive correlation between (L) measurements with Spectrophotometer and EZ shade after cementation.

tabLe (3): The means, standard deviation values and results of paired t-test of ceramics:

ShadeCementation

Parameter

Before After P-value Before After P-value

Mean SD Mean SD


There was a statistically significant positive correlation between (a) measurements with Spectrophotometer and EZ shade before and after cementation.

There was none statistically significant positive correlation between (b) and (∆E) measurements with Spectrophotometer and EZ shade before and after cementation.

• 1m1 and 3m1:

There was a statistically significant positive correlation between (L) measurements with Spectrophotometer and EZ shade after cementation.

There was none statistically significant positive correlation between (a), (b) and (∆E) measurements with Spectrophotometer and EZ shade before and after cementation.

• 2M2, 3M3, 4R1.5 and 3L2.5:

There was none statistically significant positive correlation between (L), (a), (b) and (∆E) measurements with Spectrophotometer and EZ shade before and after cementation.

• 2M3:

There was a statistically significant positive correlation between (L) measurements with Spectrophotometer and EZ shade before cementation.

There was a statistically significant positive correlation between (b) measurements with Spectrophotometer and EZ shade before and after cementation.

There was none statistically significant positive correlation between (a) and (∆E) measurements with Spectrophotometer and EZ shade before and after cementation.

2. Ceramic

• 1M2:

There was a statistically significant positive correlation between (L) measurements with Spectrophotometer and EZ shade before and after cementation.

There was none statistically significant positive

correlation between (a) and (b) measurements with

Spectrophotometer and EZ shade before and after

cementation.

• 1M1:

There was none statistically significant

positive correlation between (L), (a), (b) and (∆E)

measurements with Spectrophotometer and EZ

shade before and after cementation.

• 2M2 and 4R1.5:

There was a statistically significant positive

correlation between (a) measurements with


cementation.


correlation between (L) and (b) measurements with


cementation.

• 3M1:


correlation between (L) and (a) measurements with


cementation.


correlation between (b) measurements with


cementation.

• 2M3:


correlation between (b) measurements with


cementation.


correlation between (L), (a) and (∆E) measurements

with Spectrophotometer and EZ shade before and

after cementation.


• 3M3:

There was a statistically significant positive correlation between (b) measurements with Spectrophotometer and EZ shade before cementation.

There was none statistically significant positive correlation between (L) and (a) measurements with Spectrophotometer and EZ shade before and after cementation.

• 3L2.5:

There was a statistically significant positive correlation between (∆E) measurements with Spectrophotometer and EZ shade.

There was none statistically significant positive correlation between (L), (a) and (b) measurements with Spectrophotometer and EZ shade before and after cementation.

disCussion

The research hypothesis in this study was rejected as there was a positive correlation between the clinical and the laboratory spectrophotometer, and the color change ∆E values at all the levels of the study were within the clinically acceptable range.

The aim of an esthetic restoration is to replicate the natural tooth and achieve morphologic, optical and biological acceptance. However patient satisfaction of an esthetic restoration is primarily associated with surface and outline form, translucency and color of the artificial teeth. Where as meticulous preparation and laboratory techniques help to achieve the form of the restoration, the color matching remains a dilemma for the dentist (2). Esthetically acceptable restorations have become more achievable as a result of the improved material properties of composites and porcelains, to mimic the color of natural teeth as closely as possible (26).

The reflected components of incident white light determine the color of an object. Transparent

materials allow for the passage of light with little change. Translucent materials scatter, transmit and absorb light. Opaque materials reflect and absorb; however they do not transmit. Most of the color found in natural tooth is established within the tooth. The semi-translucent structure of tooth makes color matching procedure more complex when compared with an opaque object. Surface characteristics such as gloss, curvature and texture affect the degree of light diffusion when striking the particular object. Therefore it may be challenging for the dentist to match the color of a restoration using shade guides, which are shade matching tools provided by the manufacturer of the restorative materials (2).

Many components of the color matching process contribute to the difficulty of achieving a perfect color match between a restoration and the surrounding dentition. Some of these factors originate from the subjective nature of human color observation. Additionally fatigue, ageing, and emotional status of the clinician, lighting conditions and metamerism add to the complexity of the color matching task.

Traditionally, shade selection is made by visual comparison of a target (adjacent tooth) to shade guides have been reported (1, 3, 4, 10). However some important limitations of shade guides have been reported. These shortcomings include the inability to exactly match the color of the definitive esthetic restoration to those of the natural teeth; (10) discrepancies in the color of like nominal shades of different manufacturers; the lack of proper control of various batches of one shade guide from the same manufacturer (1); presence of different reflection curves and surface textures because of the gloss with regard to natural teeth (3); the uneven distribution and the incapability of obtaining an adequate range of shades to represent the varying color of natural teeth (coverage errors) (10) .

In order to eliminate the uncontrolled variables during the color matching process, instrumental


methods have been developed (8). Optical electronics and computer technology not only have provided objective and rapid color determination (8,10) but also presented the ability to detect subtle changes in color. Colorimeters and spectrophotometers have demonstrated usefulness in dental research and consistency in matching opaque objects (27). However for the most part, such instruments have not performed well with more complex, multilayered translucent objects (10,28)

Therefore in the present in vitro study the aim was to investigate the subtle changes in color of the esthetic restorations of different materials after their cementation to tooth structures and to check applicability of clinical spectrophotometer [easyshade] in dentistry in a way to find out a linear relationship between the performances of both techniques [laboratory and clinical spectrophotometer] and as each method has its own algorithm to determine the color

No gold standard was used in the tests, as the purpose was not to determine which method led to the most accurate results; rather investigation of the linear relationship between the performances of spectrophotometer and digital analysis was of interest. Also as each method has its own algorithm to determine the color, correlation analysis between the shade tabs was used to search the presence of any linear relationship between each of L*, a*, b* values obtained with both methods (2). Also it was preferred to present the raw data in the present research as L*, a*, b* measurements in order to investigate the linearity of the results of laboratory and clinical spectrophotometer [easyshade]. However, in the literature, color changes have been presented as ∆E values, and raw L*, a*, b* values are not shown. Therefore any disparities in the L*, a*, and b* values would not thoroughly discussed in those papers.

Concerning the use of 0.5mm disc thickness: The thickness chosen in the present study was

0.5mm which simulates the minimum thickness for the laminate veneers.

Concerning the shade of the teeth A3: The shade selected teeth was 1M2 which is equivalent to A3 as a mean of standardization, in addition the M is neutral which will not make any impact or shift on the final color, and it is in the group in high lightness.

Concerning the color changes ∆E: No detectable color change was recorded in the present study after cementation of the esthetic restorations of both materials with the translucent cement at all the levels of the study as the values of ∆E fell within the clinically acceptable range as ∆E [2.6-3.7] is considered as clinically acceptable color difference (35).

Thresholds for perceptibility are lower than thresholds for acceptability(20,30). A clinical acceptability threshold, ∆E*=3.3(31), and a perceptibility threshold, ∆E*=3.7(20), for color differences have been reported in the dental literature. These published ∆E* values were established differently from the present study. Ruyter et al (31) performed their study in a controlled laboratory setting with a simulated extended time period using a computer- controlled spectrophotometer, and established a ∆E* of less than 3.3 to be acceptable for color differences. Johnston and Kao ( 20) used the United States Public Health Service system and an expanded visual rating scale for appearance match to assess color match for 42 restorations with a colorimeter within a 12-month period. The authors reported that a color difference of 6.8 ∆E* or greater was a mismatch, and 3.7∆E* or less, clinically imperceptible. The current study showed the mean ∆E* value to be within the clinically acceptable range that also the same as proposed by Johnston and Kao (20). Although these values have been frequently referenced in the dental literature, their current clinical application requires further corroboration. Further research is necessary


to validate these thresholds. Mean while in another study carried out by Kuehni and Marcus(32), they reported color difference ∆E > 2.72 as being unacceptable.

In the present study the results of color changes ∆E recorded for the shades 1M2 and 1M1 respectively [spectrophotometer: composites: 3.05-2.91 and ceramics: 3.46-3.22; easyshade: composites: 3.21-2.79 and ceramics: 3.16-3.18]. These results are considered slight high when compared to different study (29) that could be explained by many factors such as; two different techniques were used such as the laboratory spectrophotometer which measures a circular area with 1.0 mm in diameter which is small enough to tell the true colour of a tooth and esthetic restoration, and minimizes the ‘edge loss’ by measuring the reflection with a detector located at a certain distance which would not interfere with the illumination. In clinical practice in the Easyshade technique, the colour replication process for dental esthetic restorations comprises a shade-selection phase followed by a shade-duplication phase in which errors may exist in both phases.

Concerning the mean L* Values parameter after cementation, and their correlation between both techniques [Laboratory and clinical spectrophotometer]: At all the levels of this in vitro study, there was significant decrease in the lightness (brightness) of all the tested shades of the composite and ceramic discs after cementation which is represented by the significant decrease in the L* mean values when tested by both methods the laboratory and clinical spectrophotometer [Easyshade]. This might be attributed to increase in the thickness of the whole unit [tooth-cement-restoration] lead to light attenuation, as the greater the thickness, the less the translucency of the material. In addition the decrease in the mean L* values, can be explained by the increase of absorption of incident light with thicker specimens that reflect reduced quantity of light and, thus, lower L* values (attenuation of the light) (33-35).

Also it is obvious that the lightness of the shades at all the levels of the study is arranged in a descending order as follow: [1M2, 1M1, 2M2, 3M1, 2M3, 3M3, 4R1.5, 3L2.5] which is coinciding with the literature (36) also this finding is consistent with the material information provided by the respective manufacturers (4,9). This is explained that in the Vitapan 3D master

shade guide tabs there is expanded range of value

between the groups (36 tabs); also the manufacturer

adds the pigments to differentiate between the

shades that have the same opacifying role leading

to gradual decrease in the brightness of the shades

by the scattering effect.

The scattering effect: Also may be related to either internal structure of the assembly. These is

in accordance in a study carried out by Vaarkamp

et al. (37) in which it was found that the hydroxyl apatite crystals contribute significantly to light

scattering when the enamel receiving laminates.

Or in case of chemical composition for

restorations. Stable pigments that may be

incorporated to finalize the color and translucency

of the material, and surface finish that may be

adjusted to provide the desired gloss. Also pigments

may be used to well regulate lightness, chroma, and

hue, but pigments also have the general effect of

decreasing translucency, emphasizing the need for

the basic material to be more translucent than the

most translucent natural tooth structure (36). As well

known that pigments [oxides] act as Opacifiers.

Although additions of Opacifiers to the basic

ceramic material can otherwise affect the resultant

physical properties, a major effect of Opacifiers

is to increase scattering causing the opalescence

property as opalescence is an optical property of a material, in which there is a scattering of the shorter wavelengths of the visible spectrum of

light. This light scattering is caused by particles

dispersed throughout the translucent material that


are smaller than the wave length of the visible light

and have a much higher refractive index than the

matrix material (36-38).

In addition the manipulation of the materials

may result in human errors as voids; the large

discrepancy between the refractive index; for the

crystals or fibers corresponding to the ceramics and

composites; and that for the air or vacuum gives

microscopic voids their significant scattering (38).

These results were not in accordance with those

obtained by Yaman P. et al. 1997. (39) and other

literature. (36) who reported increase in the lightness

rather than decrease.

The present study demonstrated that the

application of clinical spectrophotometer [easyshade]

for color determination of ceramics/composites

yielded results in the L* measurements that

were positively correlated with those obtained

with spectrophotometer. These results were in

accordance with those obtained by Maher 2007 (40) Corciolani and Vichi, 2006 (41); Braun et al,

2007(42) and Dozic’et al. (26) who reported in their

studies a direct positive relation between laboratory

and clinical spectrophotometer. But they are not in

accordance with those obtained by E Cal et al. (2) as

regard the L* value.

Concerning the change in a* parameter [red-

green axis] after cementation: The results revealed

no significant changing in the a* parameter mean

values after cementation for all the shades in both

systems when tested by both methods laboratory

and clinical spectrophotometer [Easyshade]. So the

cementation of the discs to enamel did not influence

the red- green axis. The influence on the a* parameter

in this study would be the esthetic restorations

not the whole complex. This may be attributed to

that only leucite or nano filled composite which

are less complicated structures used in very thin

sections cemented to enamel not dentin which is

mainly affects the color dramatically. When the a*

parameter was positive, this meant that the shade

was shifted toward the red color which meant that

all the light was absorbed and only the red was

reflected which has the longer wave length after

scattering and attenuation and absorption of others

but of no statistical significance, this in accordance

to other studies who reported no change in the a*

parameter (33-35).

The [clinical spectrophotometer-easyshade]

for color determination yielded results in the a*

measurements that positively correlated with those obtained with the spectrophotometer. These

findings were in accordance with those obtained

with Maher 2007(40) Corciolani and Vichi(41),

2006; and Braun et al, 2007(42) , E cal et al.(2)

and Dozic’et al. (26) indicating the reliability of the

Easyshade clinical color measuring device.

Concerning the change in b* parameter [yellow-blue axis] after cementation: In the shades 1M2, 1M1, 3M1and 2M3, there was no significant change of the b* mean values after cementation for the two systems [ceramics and composites] using both testing methods

[laboratory and clinical spectrophotometer], which

means that after cementation of the ceramic/

composite discs to tooth enamel discs, no change

in color was observed with such shades; where M is neutral and the shades are represented by two groups according to literature (14). Neutral colors such as white, grey, and black are, by definition,

colors that have no hue. The same as for the a*,

the influence on the b* would come from the

esthetic restorations. Where as for all the other

shades, there was a significant increase in the b* values after cementation, shifted more toward the yellow i.e. more yellowish, which may be due to

the translucency of the restoration; where as The

translucency of a material or tissue describes the

ability of its pigments and colorants to permit


the underlying background to be expressed.

Concentration of the pigments from one group to

another made by the manufacturer has significant

effect on the b* value in order to give the expanded

range of the shades. When the b*parameter was

increased, this meant that the shade was directed

toward the yellow color which meant that all the

light was absorbed and only the yellow was reflected

which has the longer wave length after scattering

and attenuation and absorption of others (36) . These

findings were in agreement with other studies.(33-

35) The clinical spectrophotometer [easyshade]

for color determination yielded results in the b*

measurements that positively correlated with those

obtained with the laboratory spectrophotometer.

These findings were in accordance with those

obtained with Maher 2007 (40), Corciolani and

Vichi, 2006(41); and Braun et al, 2007 (42) E cal et

al (2) and Dozic’et al. (26) reporting the reliability of

the easyshade clinical color measuring device.

ConCLusions

Within the limitations of this study the following

could be concluded:

After cementation of the discs the lightness

was decreased, no change at the red-green level

of the shades, with increase toward the yellow

except for the shades 1M2, 2M3, 3M1, and

1M1showed no change. The color measurements

obtained with clinical spectrophotometer method

were in accordance with those of the laboratory

spectrophotometric evaluations, with respect to L*,

a*, b*, and ∆E. As regard the color change ∆E, no

detectable color change was recorded in the present

study after cementation of the esthetic restorations

with the translucent cement at all the levels of the

study as the values of ∆E fell within the clinically

acceptable range[2.6-3.7].

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