effects of opaque and porcelain surface texture on the color of ceramometal restorations

RESEARCH AND EDUCATION SEC-l-ION EDITOR

JOHN J. SHARRYt

Effects of opaque and porcelain surface texture on the color of ceramometal restorations

Alejandro Obregon, D. D. S., M.S.,* Richard J. Goodkind, D.M.D., M.S.,** and William B. Schwabacher, B.Chem., Ph.D.*+* University of Minnesota, School of Dentistry and General College, Minneapolis, Minn.

A n understanding of color concepts can greatly enhance the dentist’s ability to achieve a natural looking restoration. The color of a porcelain crown is influenced by three factors: (1) the characteristics of the light source, (2) the modification of the light by the porcelain crown, and (3) the observer’s interpretation of these effects.

Individually and collectively these three factors can have a profound influence upon the perceived color of any artificially fabricated restoration. The light from any source can be described in terms of the relative energy emitted at each wavelength. Visible light has a wavelength between 380 and 750 nm. Wavelengths below 480 nm are recognized as the color blue. Green has a wavelength between 480 and 560 nm: yellow between 560 and 590 nm, and orange between 590 and 630 nm. Red has a wavelength longer than 630 nm.’

Northern daylight shows high relative energy in the blue region, with substantially less in the red and yellow ranges. Standardization of natural light is difficult.’ The color quality of a light source can be expressed in the Kelvin temperature scale assuming a black body distribution. Some light sources have energy distribution which approximate the ideal illuminants C or D.3

Several factors can modify the color of a porcelain restoration when the light strikes its surface. The restoration can affect the light beam by various physical phenomena like scatter, transmission, absorption, reflection, and refraction. In addition,

Received third place, American College of Prosthodontists Research Competition Award, San Antonio, Tex.

*Graduate Student, Division of Prosthodontics. **Professor and Director of Graduate Prosthodontics, University

of Minnesota, School of Dentistry. ***Professor and Head, Division of Science, Business and Math-

ematics, General College, University of Minnesota. iDeceased.

surface gloss and fluorescence can also modify tooth color.

If only part of the light passing through a porcelain tooth is scattered, the porcelain exhibits translu- cency,G and if the scattering is so intense that no light passes through, the tooth appears opaque. The color of the tooth also depends on the amount and kind of absorption present. If there is no light absorption, the object appears white. If the light is transmitted unchanged through the porcelain material, the restoration will have a transparent appearance.’

The change of direction of a light beam caused by the change in the speed of light through different materials is called refiuction. The amount of change in direction of light depends upon the wavelength of the light. Light with shorter wavelengths bends the most.’ About 4% of the incident light is reflected back from the outer surface of a porcelain material without being modified except for direction. If the angle of incidence equals the angle of reflection, the phenomenon is called specular reflection (gloss).

Burke6 states that the surface texture of any object is a considerably important part of the appearance of the object. If the object has a smooth surface, the light is reflected in a narrow cone centered about the angle of reflectance. An increasingly roughened surface would reflect the individual segments of the specular beam at slightly different angles. The reflected light from a roughened surface subtends a greater solid angle. When the surface is flat, the

roughness is more pronounced in all directions. If the surface configuration has a matte finish, there is an excessive amount of light reflected at the surface level and a reduction of light transmission through the porcelain material (Fig. 1). The texture, curva- ture, and gloss of porcelain restorations vary a great deal and as a result modify the light striking these surfaces.

Lemire and Burke4 stated that surface #texture

330 SEPTEMB1.R 1981 VOLUME 46 NUMBER 3 OOZZ-3913/81/090330 + 11$01.10/00 1981 The ‘2. V. Moshy Co.

OPAQUE AND PORCELAIN SURFACE TEXTURE-EFFECTS

Fig. 1. Reflected light from various surfaces. Effect of three different surfaces on incident light.

Fig. 3. Topographic analysis of glossy opaque surface.

Fig. 2. Topographic analysis of dull opaque sample surface.

controls the degree of scattering or reflection of the light striking the natural tooth or the porcelain restoration. There is no difference in the total scattering between high gloss and low gloss surfaces of a restoration. They also assumed that the texture or surface characterization of the restoration can dra- matically change the hue of the restoration.

Burke” also stated that with a highly glazed surface, the restoration became more translucent and the color hue changed toward yellow-orange. For some samples the color value decreased.

Pincus7 stated that jacket crowns should be fabricated so that the surface texture of the restoration be composed of convexities and concavities matching the enamel surface of the adjacent teeth to reproduce the characteristics of the light reflection to reproduce natural looking crowns.

EissmanX has reported that the texture of the surface form of a tooth is its most important feature. Rough or irregular texture surface will reflect an irregular and diffuse pattern of light, which will

Fig. 4. Silicone mold used to fabricaie the porcelain samples.

effects of various opaque and porcelain surface textures on two different shades of porcelain. The light source and observer were kept constant to eliminate these variables as possible sources of exper- imental error. A spectrophotometer was used to measure the color of the porcelain samples when the porcelain and opaque surface textures of the sample restorations were modified.

MATERIAL AND METHODS

modify the color of the crown. Horizontal or vertical The samples used in this study were 100 fiat gold incremental lines in the texturing procedure will give disks over which porcelain was baked. The diameter an illusion of width or length to the porcelain of these samples was similar to that of a natural tooth. central incisor or to the size of the tabs used in dental

The purpose of this study was to compare the shade guides.

THE JOURNAL OF PROSTHETIC DENTISTRY 331

OBRECON, GOODKIND, AND SCHWABACHER

Fig. 5. Porcelain sample buildup prior to oven firing.

Samples were divided into two broad categories, representing a light and dark shade of porcelain. Each major division was divided into four subdivi- sions composed of the following categories of samples: (1) 10 samples had a natural, glazed (glossy) opaque and smooth porcelain surface texture, (2) 10 samples had a regular (dull) opaque with smooth porcelain surface texture, (3) 10 samples had a regular (dull) opaque with rough porcelain surface texture, and (4) 10 samples had a glossy opaque and rough surface texture. A total of 100 samples were fabricated: 80 with a porcelain thickness of 2 mm, 10 with a porcelain surface of 1 mm, 5 with a glossy opaque surface only, and 5 with dull opaque only.

Fabrication of the metal base

A solid delrin acetyl plastic rod (Almac Plastics, Minneapolis, Minn.) with a diameter of 3/8 inch was sliced with a microtome (custom made by Biomateri- al Dept., University of Minnesota) containing a 600 extra-fine carborundum disk. A 0.02 mm amount of space was provided between each cut to allow for the thickness of the disk between each sample. After the disks were fab.ricated, measurements were made and disks were examined for accuracy of the cut.

Each pattern was sprued on its side with sticky wax using 1.5 mm length 12-gauge sprue (Kerr Mfg. Co., Romulus, Mich.). Five patterns were luted at equal distances to an 18 mm long 8-gauge wax sprue and placed on a sprue former (Whip Mix Corp., Louisville, KY.).

The patterns were invested utilizing a phosphate bonded investment (Ceramigold, Whip Mix Corp.,

Fig. 6. Two millimeter porcelain samples prepared for analysis by spectrophotometer with an integrating sphere.

Louisville, Ky.) with a liquid to powder ratio of 9.5 cc for 60 gm of powder. One hour was allowed for the investment to harden. The alloy used for the fabrication of the samples was a precious alloy containing 52.5% gold, 27% palladium, and other trace elements (Cameo, J. F. Jelenko Co., New Rochelle, N.Y.). Alloys were cast following the manufacturer’s directions. After the metal samples were cast and separated from their sprues, the thickness of the metal disks was measured using a micrometer (L. S. Starrett Co., Athal, Mass.).

Porcelain buildup

The porcelain selected for this study was Ceramco G, vacuum-fired shades A3 (darker) and Bl (lighter) with their corresponding paint-opaques (Ceramco Inc., East Windsor, N.J.). The furnace utilized was a Ney Barkmeyer vacuum porcelain furnace (Mark II, J. M. Ney Co., Hartford, Conn.). The furnace was calibrated using a pyrometer kit (J. M. Ney Co.) to assure accuracy of firing temperatures during the investigation.

Opaque application. To provide standard uniformity and thickness, the opaque layer was sprayed on the sample disks using a Paasche Air Brush (Paasche Air Brush Co., Chicago, Ill.).

The corresponding opaques were mixed with industrial grade methane as a suspending medium. Two thin layers of opaque were sprayed on each of the metal disks. The first layer was fired according to the manufacturer’s directions. The application of the

332 SEPTEMBER 1981 VOLUME 46 NUMBER 3


Fig. 7. Topographic analysis of rough porcelain surface Fig. 8. Topographic analysis of glossy porcelain surface of sample. of sample.

Table I. Hue with specular reflectance

Shade Opaque Porcelain Mean SD Standard

error Minimum Maximum

A3 Glossy Smooth 1.587Y 0.1401 0.0443 1.35 1.76 A3 Glossy Rough 1.588Y 0.3012 0.0953 1.22 2.09 A3 Dull Smooth 2.317Y 0.4149 0.1312 1.74 2.96 A3 Dull Rough 2.284Y 0.3987 0.1261 1.71 3.02 81 Glossy Smooth 4.086Y Cl258 0.0816 3.62 4.58 81 Glossy Rough 4.249Y 0.3322 0.1051 3.82 4.94 Bl Dull Smooth 3.634Y 0.27 0.0854 3.2 4 Bl Dull Rough 3.426Y 0.325 0.1028 3.06 4.16

Table II. Chroma with specular reflectance

Shade Opaque Porcelain Mean SD Standard

error Minimum Maximum

A3 A3 A3 A3 BI 81 Bl BI

Glossy Glossy Dull Dull Glossy Glossy Dull Dull

Smooth 2.879 0.0846 0.0268 2.79 3.04 Rough 2.826 0.0797 0.0252 2.67 2.94 Smooth 2.706 0.0657 0.0208 2.61 2.81 Rough 2.855 0.0486 0.0154 2.8 2.96 Smooth 1.8 0.1095 0.0346 1.6 1.97 Rough 1.87 0.0622 0.0197 1.78 1.98 Smooth 2.028 0.1644 0.052 1.61 2.23 Rough 2.09 0.1037 0.0328 1.94 2.24

second layer of opaque followed the initial procedure; however, the oven temperature was increased 10” F to produce a glossy opaque surface. After the two opaque layers were baked, they were measured with a micrometer, and their opaque thickness was recorded. The opaque samples ranged from 0.26 to 0.30 mm in thickness. Four randomly selected samples, two with dull opaque and two with glossy opaque, were topographically analyzed with a modified Material Test System Machine Model 812 (M. T. S. System Corp., Minneapolis, Minn.) to

record differences in the surface texture of the opaque layer. The differences observed visually in opaque textures were confirmed in this manner (Figs. 2 and 3).

Fabrication of silicone molds

Molds were fabricated according to the methods used by Barlow* and Jorgenson and Goodkind.s

Blocks of aluminum were turned in a lathe to

*Barlow, F. L.: Personal communication, 1976.


OBREGON, GOODKIND, AND SCHWABACHER

SPECULAR REFLECTANCE INCLUDED

n SPECULAR REFLECTANCE EXCLUDED I--~

=, 4.OY

4

s

Y P 3.OY

3

2

+G ?..OY 2 c" m

I .o Y

0 9 I2 3 4 5 6 7 8 MEAN HUE WITH SPECTRAL REFLECTANCE INCLUDED

GROUPS OF SAMPLES

KEY

Shade Opaque Porcelain Shade opaque Porcelain l.- A 3 Glossy Smoth 5.- B 1 Glossy Smooth 2.- A 3 6.- Bl Glossy Rough 3.- A3

~~~;'y Rough Swath ?.- Bl Dull

4.- A 3 DUll Rough B.- 81 Dull

V-3 Shade OPaquc POlX~l~i~ Shada Opaque PDlX~l~lfl

I.- A 3 Glossy Smwth Glossy Swath 2.- A 3 3.- A 3

Gbt'y Myh: ::: ;1 both 81 xy bugh Smmth

4.- A 3 Dull Rough i:: 6 1 Dull Rough

Figs. 9 and 10. Comparison of data with specular reflectance included and excluded for Hue. The data were highl; correlated. -

fabricate a mold former. Xantopren Blue impression material (Unitek Corp., Monrovia, Calif.) was used for the fabrication of molds.

For easy separation during porcelain fabrication, each mold was sectioned into three pieces. Each of the sections had a tongue and a groove to key the three pieces for marginal integrity (Fig. 4). The purpose of this mold was to ensure uniformity in porcelain sample size.

Gingival porcelain buildup to high bisque bake

Ceramco C: vacuum-fired porcelain, shades A3 and Bl, were mixed with deionized water using an agate spatula until they formed a creamy mix. Water was periodically added to the original mix to pre- serve its uniform consistency during the porcelain buildup of each sample.

opaque layer and the gingival porcelain. The porcelain was gently tapped with the edge of the spatula to provide for better condensation. After each addition, the porcelain was dried with tissue paper. The sample was allowed to dry inside the mold for 5 minutes and was then separated from the mold. Excess porcelain was removed from the metal bases with a moistened No. 0 Dixon Brush (Dedeco, Brooklyn, N.Y.). Each sample was fired according to the manufacturer’s recommended instructions (Figs. 5 and 6.)

Grinding procedure

The metal sample was placed over a glass slab within the three sections of the silicone mold. The silicone mold was sprayed with a thin coat of cooking lubricant to provide easy separation of the con- densed porcelain from the mold. The three sections of the mold were held together with finger pressure during the porcelain buildup. The porcelain was placed into the silicone mold with an agate spatula. Care was used to avoid trapping air between the

The sides of the porcelain samples were trimmed flush with the sides of the metal base using a green universal stone (Dedeco) in a slow-speed handpiece. Following this procedure, each sample was placed into the center slot of a heat-treated steel supporting block which was mounted in the table of a dental surveyor (‘J. M. Ney and Co.). A C-2 sintered diamond (Ceramco, Inc.) was placed into the slow- speed handpiece which was attached to the vertical post of the surveyor.

The superior part of the sample was reduced to within 0.03 mm of the required thickness. To produce samples with smooth surface texture, the porce-



3.0

2.5

2.0

1.5

0 11

CHROMA

n SPECULAR REFLECTANCE INCLUDED

n

q SPECULAR REFLECTANCE EXCLUDED

I2 3 4 5 6 7 6

GROUPS OF SAMPLES

CHROMA

il ’ I / / I 15 2.0 25 3.0 3.5

MEAN CHROMA WITH SPECTRAL REFLECTANCE INCLUDED

KEY Shade Opaque Porcelain Shade Opaque Porcelain

l.- A3 Glossy booth Y (h' z"d,:: E$"

$J Shade OPPWC P.WCe1.l"

2.- A": %"

Rough I.- A3 Shade cv.wc Porccl*ln

tloslY mstk 5.- 81 GIOSI), YDw,h 3.- booth ?- 81 Dull 2.- 13 6.. 81

4.- A3 Dull Rough 8:- 81 Dull El:: 3.- A3

uy;sy Rough smooth

1.- A, DYI 1 Roqh ::: ::

M;w Rwrh

Pull Y icy

Figs. 11 and 12. Comparison of data with specular reflectance included and excluded fol Chroma. The data were highly correlated.

lain was rubbed against a sheet of wet or dry 400 grit textured sandpaper. The samples to be analyzed with rough surface texture were fabricated as fol- lows. A Minikor air abrasive blasting unit (Williams Cold Refining Co., Buffalo, N.Y.) which contained 280 pm aluminum oxide particles (size was deter- mined by sedimentation analysis) was used to pre- pare the roughened surface.

After the texture was applied, measurements of the samples were made. Reduction of the thickness of the porcelain surface due to the blasting procedure ranged between 0.02 to 0.03 mm.

Glazing procedure

Each sample was cleaned with steam heat. The manufacturer’s recommended schedules were used for each sample. Micrometer readings were made and recorded, and measurements ranged from 1.96 to 2.03 mm with a mean of 2 mm for the 2 mm samples.

The range for 1 mm samples was 0.97 to 1.03 mm with a mean of 1.01 mm.

After all the samples were measured, six samples randomly selected were analyzed with a topographic testing machine (MTS System Corp.) to examine the


differences between the two different surface textures (Figs. 7 and 8).

Analysis of samples

A General Electric Recording Spectrophotometer was used to measure reflection spectra of the samples. This method gave this investigation the advan- tage of accuracy and allowed the measurement of changes impossible to discern with the human eye. A standard observer and standard illuminants could then be used in calculation. The reflection intensities were measured in 10 nm steps and converted to CIE tristimulus values using CIE observer 1931 and illuminant C and D 6500.“’ These measurements were made with and without specular component. An approximate Munsell color notation for Hue, Chroma, and Value was calculated using an ASTM-D-1535 (Hunter Laboratory Associates, Fairfax, Va.).

RESULTS

Separate statistical analyses were calculated for Hue, Chroma, and Value. An analysis was per- formed using the Student Newman-Keuls method for individual comparisons among the means. This

OBRECON, GOODKIND, AND SCHWABACHER

5 6 7 8

GROUPS Of SAMPLES

“u f E

7.6 -

i: z 2 E

7.4 -

w w E 5 7.2 - g s

VALUE

’ ’ ’ ’ ’ ’ 1 I I I I 7.0 1.2 7.4 1.6 7.0 6.0

MEAN VALUE WITH SPECTRAL REFLECTANCE INCLUDED

El%‘” Sh,& opwut POrcclaln

Dlolsy Smooth 2.- A3 Rough

A3 ::: A 3

$;'Y smcatll 7.-

Lhll Rwgh 8.- i1

Figs. 13 and 14. Comparison of data with specular reflectance included and excluded for ‘r’alue. The data were highly correlated.

Table III. Value with specular reflectance

Standard Shade Opaque Porcelain Mean SD error Minimum Maximum

A3 Glossy Smooth 7.319 0.0396 0.0125 7.23 7.36 A3 Glossy Rough 7.403 0.0287 0.0091 7.33 7.43 A3 Dull Smoolh 7.218 0.0569 0.018 7.11 7.3 A3 Dull Rough 7.251 0.0463 0.0146 7.18 7.33 Bl Glossy Smooth 7.815 0.0597 0.0189 7.74 7.95 Bl Glossy Rough 7.786 0.0624 0.0197 7.63 7.87 Bl Dull Smooth 7.749 0.0771 0.0244 7.67 7.94 Bl Dull Rough 7.729 0.0526 0.0166 7.65 7.51

statistical test is a series of t-like tests which are calculated by dividing the difference between the means by the standard error of the mean.

Hue

The Hue re.sults for 2 mm samples are shown in Table I. The analysis showed statistically significant interaction between Bl and A3 shades and opaque surface textures. The glossy opaque samples with shade A3 were shifted in Hue toward the yellow-red scale as compared to the dull opaque samples. The

samples of shade Bl with glossy opaque surface demonstrated a Hue shift toward a purest yellow Hue.

For Hue, the surface texture of the body porcelain did not produce significant differences at the 95% confidence interval. The data with specular reflectance included and excluded were submitted to a correlation test. The results of this test proved that the two sets of data were highly correlated (Figs. 9 and 10). The results for Hue in the 1 mm samples showed that the rough porcelain surface texture was



5 5 5 43 2 I ‘9876 4321 ‘9876

GY ’ I I I I I I I I I I I I I I I I

Y YR

Fig. 15. Munsell’s Hue scale.

STUDENT-NEWMAN - KEULS

HUE

Rough & Dull ,,,,,,,,a,,,,,,,,

Smooth & Glossy -

STUDENT-NEYYAN-KEULS

3.4260 3.6340 4.0860 4.2490

SHADE Bl

Fig. 16. Diagrammatic interpretation of results for Hue samples.

toward yellow-red compared to the smooth porcelain surfaces when the opaque was dull. Examination of opaque samples only demonstrated that the glossy opaque had a yellow-red Hue and the dull opaque had a yellow Hue.

Chroma

The results for Chroma are shown in Table II. The 2 mm Chroma samples with dull opaque and smooth surface texture were significantly lower in Chroma than the rest of the samples with shade A3, which were not significantly different from one another.

The samples with shade B 1 showed that the glossy opaque layer decreased the Chroma of the Bl samples, and the porcelain surface texture did not produce statistically significant differences in Chroma.

STUDENT-NEWMAN-KEULS

CHROMA

2.7060 2.8260 2.8550 2.8790

SHADE A3

STUDENT-NEWMAN - KEULS

CHRDNA

I .8000 I .8700 2.0280 2.0900

SHADE Bl

Rough & Dull ,ma,,,s,,,,,,st,,

Smooth a Glossy -

Fig. 17. Diagrammatic interpretation of results for Chro- ma samples.

The results for Chroma with specular reflectance excluded were also submitted to a correlation test, and the samples proved to be highly correlated (Figs. 11 and 12).

The results for Chroma in the 1 mm samples showed that the rough porcelain surface texture increased the saturation of the samples.

Value

The results for Value are shown in Table III. For the samples with shade A3, the dull opaque surface texture had a lower Value than the glossy opaque samples. However, the porcelain surface texture on the samples with dull opaque was :not significantly different in Value. The A3 samples with glossy opaque and rough porcelain surface texture proved to have significantly higher Values than the samples



VALUE

7.2160 7.2516

IT, F”““s”“‘l

7.3190 7.4030

SHADE A3


VALUE

7.7290 7.7490 7.7060 7.6150

SHADE 61

Fig. 18. Diagrammatic interpretation of results for Value samples.

with glossy opaque and smooth surface texture. For the samples with shade Bl, the difference in

the opaque layer seemed to produce significant differences in Value. The Bl samples with glossy opaque tended to have higher Values. The porcelain surface texture did not produce significant differences m Value for the samples with shade Bl.

The A3 samples of 1 mm porcelain thickness behaved in the same manner as the 2 mm samples for Value. The two sets of data with specular reflectance included and excluded were also highly correlated (Figs. 13 and 14).

DISCUSSION

Porcelain thicknesses of 1 and 2 mm were selected for this study. These amounts of porcelain are commonly used on many ceramometal restorations. The spectrophotometer was used to record the data since it provided the accuracy, sensitivity, and repro- ducibility needed for this investigation.

It became evident from the results obtained in this study that surface texture, whether present in the opaque layer or in the porcelain itself, can affect the color of the restoration. This study partially confirms



the assumptions made by Burke6 that surface texture of the porcelain can affect the appearance of the restoration in all three dimensions of color-Hue, Value, and Chroma.

Hue

The results of this study showed that surface texture in the opaque layer of the samples produced significant differences in Hue. Samples with shade A3 and glossy opaque demonstrated a shift in Hue toward the yellow-red Hue scale. The samples with shade Bl with a high gloss in the opaque layer showed a shift in Hue away from the yellow-red scale.

This phenomenon may have been caused by a chemical breakdown of the opaque at elevated temperatures which occurred when the highly glazed opaque surface was produced. When opaque samples of shade A3 were evaluated, the glossy opaque surface texture registered 9.8 yellow-red Hue, as opposed to dull opaque which registered 1.06 yellow Hue (Fig. 15).

The differences in behavior from the two shades in the opaque layer can be explained in the following manner. Shade Bl contained a greater amount of whiter colorants which were used in the opaque to produce the lighter shade. One explanation might be that the different colorants added to the two shades of opaque in this study broke down in different ways creating these Hue differences.

This investigation also proved that for the 2 mm samples the two different porcelain surface textures did not produce significant changes in Hue (Fig. 16). However, for the 1 mm samples with shade A3, the samples with a smooth porcelain surface texture shifted away from the yellow-red range.

Chroma

The results of this investigation showed that for shade Bl the porcelain surface texture did not produce any significant changes in the saturation of the 2 mm samples. However, the dull opaque layer produced a significant increase in Chroma over the glossy opaque (Fig. 17).

The Bl porcelain sample data showed a slight enhancement in reflection around 580 nm when compared to the more featureless A3 spectra. Supposing the glossy opaque surface shows more specular reflection than the dull opaque does, it is not unreasonable that this specular reflection should turn out to be less wave length dependent than the more diffuse reflections of the dull opaque surface.


This might explain how the Bl porcelain over glossy opaque would have less peak measured reflection around the yellow region and thus a lower saturation.”

The results for Chroma for the four groups of A3 samples are different. Statistically, the A3 groups with glossy porcelain and rough opaque had the lowest Chroma determination and they were different from the other three groups which were not significantly different from each other. The ambigu- ity in these results may have been caused by complex interactions between the opaque and porcelain textures which are difficult to identify.

Results obtained in this study for 1 mm samples with shade A3 did not produce any significant difference in behavior from the 2 mm samples.

Value

Value seemed to show the most significant changes when surface textures were modified. The results of this investigation showed that for shade A3, the reflection of the light from a highly glazed opaque layer tended to increase the Value making the ceramometal sample appear lighter. However, porcelain surface texture seemed to alter the Value in the opposite way than did the opaque layer. This meant that for the samples with shade A3, the smooth porcelain surface texture tended to decrease the Value. Thus, the results of this study showed an additive effect.

The effect that the different opaque textures had on the various samples was the most significant. Perhaps the dull A3 opaque samples had lower Values because as the light beam struck the rough interface, the light was deflected within the valleys and peaks created by the textured surface. As a result, more reflected light may have been absorbed, creating a lower Value reading. On the other hand, glossy opaques increased the light reflectance which enhanced or increased the Value of the samples. The effects of porcelain surface texture in this study are difficult to explain.

The samples of shade Bl behaved similarly to A3 samples for Value (Fig. 18). The samples with glossy opaque layer and smooth porcelain surface texture were not significantly different from the samples with glossy opaque and rough porcelain surface texture. However, the samples with glossy opaque and smooth porcelain surface texture were significantly different from the samples with dull opaque and both porcelain surface textures. This meant that the opaque layer had a greater effect on Value than

did the texture of the porcelain surface. For shade Bl, the smooth porcelain surface had a. higher Value than the rough porcelain surface with glossy opaques.

The results of this investigation confirmed the statement made by Lemire and Burke’ that the opaque layer by itself has a higher Value than the combination of opaque and body porcelain. Lemire and Burke also stated that with the more saturated shades the Value will be lower as the thickness of porcelain is increased. This study confirmed this statement in only one instance.

The Value of a ceramometal restoration can be raised or lowered depending on the surface characteristics of the opaque layer and, to a lesser extent, the porcelain surface. The halo-like effect of observ- able opaque, creating a bright spot in the center of a porcelain-fused-to-metal restoration, can make it difficult to obtain the correct shade.

In light of this study, practical !suggestions to eliminate this effect would be to (1) retain a dull texture to the opaque and (2) maintain as thick a layer of body porcelain as possible.” Value can be increased in restorations by providmg a smooth porcelain surface and achieving a glossy surface to the opaque layer.

Color changes due to different porcelain and opaque textures are difficult to discern by the human eye. Some of the differences in color observed by the spectrophotometer in this study were not clinically observed by five highly trained prosthodontists in the ambient light.

SUMMARY

A total of 80 ceramometal samples were constructed with two different types of surface texture in the opaque layer (glossy and dull). Porcelain was applied to these samples with two different surface textures (smooth and rough). Samples were made in 2 mm thick porcelain shades B 1 and A.3. In addition, 10 1 mm samples were constructed with shade A3 having dull opaque, smooth, and rough porcelain surface textures. Ten samples of opaque only were constructed with two different surface textures (glossy and dull).

Each sample was analyzed in the recording spectrophotometer, and CIE color notations were calculated. These data were translated to the Munsell Scales (Hue, Chroma, and Value). Two randomly selected samples of each group were then reevaluated in the spectrophotometer using a device which excluded the specular reflectance factor.


The three dim.ensions of color-Hue, Chroma, and Value-were statistically analyzed and compared by the Student-Newman Keuls procedure. Each set was submitted to a correlation test to determine significant differences.

CONCLUSIONS

This study demonstrated the difference between Hue, Chroma, and Value between Ceramco shades A3 and Bl when the porcelain and opaque textures were modified.

Porcelain surface texture, whether rough or smooth, did not make a difference in Hue. However, the glossy type surface in the opaque layer shifted for shade A3 from yellow toward yellow-red, and toward yellow for shade B 1.

This study demonstrated that Chroma is greater for dull opaque than for glossy opaque with shade Bl, but for shade A3 the statistical interaction between dull opaque and smooth porcelain texture decreased the Chroma.

Value had essentially an additive effect of opaque and porcelain textures for shade A3. The smooth surface porcelain texture increased the Value of shade Bl compared to the rough porcelain surface.

The interactions that occur between the texture of porcelain and opaque affecting color are complex phenomena. They may be related to the modification of light by transmission, absorption, refraction, scattering, and reflection.

We would like to express our appreciation to Kathleen Keenan,

Ph.D., Professor, Department of Human and Oral Genetics,

University of Minnesota, School of Dentistry, for her assistance in

the statistical interpretation of the data.


REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

Billmeyer, Jr., F., and Saltzman, M.: Principles of Color

Technology. New York, 1966, Wiley and Sons. Preston, J. D.: Dental Porcelain: The State of the

Art-1977-Color and Esthetics. University of Southern California, Los Angeles, 1977.

The Science of Color. Committee on Calorimetry, Optical

Society of America, 1963, pp 128 and 255.

Lemire, P., and Burke, B.: Color in Dentistry. J. M. Ney Co.,

1975.

Evans, R. M.: An Introduction to Color. New York, 1948,

Wiley and Sons. Burke, B.: Dental Pomelain: The State of the

Art-1977-Color and Esthetics. University of Southern

California, Los Angeles, 1977, pp 293-295.

Pincus, C.: Porcelain: The State of the Art-1977-Color and

Esthetics. University of Southern California, Los Angeles,

1977.

Eissman, H.: Dental Porcelain: The State of the

Art--1977-Visual Perception and Tooth Contour. Universi-

ty of Southern California, Los Angeles, 1977.

Jorgenson, M. W., and Coodkind, R. J.: Spectrophotometric

study of five porcelain shades relative to the dimensions of

color, porcelain thickness, and repeated firings. J PROSTHET

DENT 42:96, 1979.

Hemmendinger, H.: Color Measurement Laboratory. Belvi-

dere, NJ., 1980. McLean, J. W.: The Science and Art of Dental Ceramics, vol

1. Chicago, 1979, Quintessence Publishing Co., Inc.,

p 129.

Reprint requesfs to: DR. ALEJANDRO OBRECON

UNIVERSITY OF MINNESOTA SCHOOL OF DENTISTRY

9-176 HEALTH SCIENCES UNIT A

MINNEAPOLIS, MN 55455


effects of opaque and porcelain surface texture on the color of ceramometal restorations

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