IMPRESSION
MATERIALS
FOR COMPLETE-ARCH
FPDs
1. The polyether and addition-silicone impression materials were significantly more accurate than the reversible hydrocolloid impression material in producing dies for single restorations. However, all of the impression materials tested produced clinically acceptable single crowns. 2. The polyether and addition-silicone impression materials produced accurate casts that would enable the fabrication and assembly of clinically acceptable FPDs. 3. Reversible hydrocolloid impression material produced casts that were not sufficiently accurate to allow for the assembly of clinically acceptable complete arch FPDs.
8. Sawyer HF, Birtles JT, Neiman R, Podshadley AG. Accuracy of casts
produced from seven rubber impression materials. J Am Dent Assoc 1973;87:126-30. 9. Sawyer HF, Dilts WE, Aubrey ME, Neiman R. Accuracy of casts produced from the three classes of elastomer impression materials. J Am Dent Assoc 1974;89:644-8. 10. Vermilyea SG, Powers JM, Craig RG. Polyether, polysulfide and silicone rubber impression materials: part 2: accuracy of silver-plated dies. J Mich Dent Assoc 1975;57:405-10. 11. Stackhouse JA. A comparison of elastic impression materials. J PROSTHET DENT 1975;34:305-13. 12. Munoz C, Goodacre C, Schnell R, Harris R. Laboratory and clinical
study of a visible light polymerized elastomeric impression material. Int J Proathodont
1988;1:59-66. 13. Henry PJ, Harnist DJR. Dimensional stability and accuracy of rubber
impression materials. Aust Dent J 1974;19:162-6.
REFERENCES
14. Lacy AM, Fukui H, Bellman T, Jendresen MD. Time-dependent accu-
1. Brindsden GI, Sorensen S, McClenahan J. Dimensional accuracy of five
impression materials using a copper-shell technique. J Dent Res 1964;43 (Suppl):911. 2. Hembree JH Jr. Comparative accuracy of elastomer impression materials. J Term Dent Assoc 1974;54:164-7. 3. Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J PROSTHET DENT 1979;42:159-62. 4. Ciesco JN, Malone WFP, Sandrik JL, Maxur B. Comparison of elasto-
meric impression materials used in fixed prosthodontics. J PROSTH~ DENT 1981;45:89-94. 5. Mincham W, Thurgate SM, Lewis AJ. Measurement of dimensional
stability of elastomeric impression materials by holographic interferometry. Aust Dent J 1981;26:395-9. 6. Tjan AHL, Whang S, Tjan AH, Sarkissian R. Clinically oriented evaluation of the accuracy of commonly used impression materials. J PROSTHET DENT 1986;56:4-8.
7. Bassett RW, Vander Heide JD, Smith DD. Clinically oriented tests comparing accuracy of elastic impression materials. J South Calif Dent Assoc 1969;37:47-57.
A qualitative Part II
racy of elastomer impression materials, part II: polyethers, polysulfides, and polyvinylsiloxanes. J PROSTHET DENT 1981;45:329-33. 15. Linke B, Nicholls J, Faucher R. Distortion analysis of stone casts made from impression materials. J PROSTHET DENT 1985;54:794-802. 16. Stauffer J, Meyer J, Nally J. Accuracy of six elastic impression materials used for complete-arch fixed partial dentures. J PROSTHET DENT 1976;35:407-15. 17. Lin CC, Ziebert G, Donegan SJ, Dhuru V. Accuracy of impression materials for complete arch fixed partial dentures. J PROSTHET DENT 1988;59:288-91. 18. Christensen G. Marginal fit of gold inlay castings. J PROSTHET DENT 1966;16:297-305. 19. Dedmon H. Disparity in expert opinions on size of acceptable marginal
openings. J Oper Dent 1982;7:97-101. Reprint requests to: DR. GERALD J. ZIFBERT SCHOOL OF DENTISTRY MARQUEITE UNIVERSITY 604 N. 16TH ST. MILWAUKEE, WI 53233
study for the bond and color of ceramometals.
Ihab Adel Hammad, B.D.S., M.S., D.Sc.,* and Robert Sheldon Stein, D.M.D.** Boston University, School of Graduate Dentistry, Boston, Mass. Many dentists, porcelain manufacturers, and dental technicians empirically state that repeated firings tend to bleach out or alter the original shade of porcelain. This investigation used a sophisticated calorimeter to resolve the controversy. The effect of temperature rise and number of firings had varying effects on color relative to brand of porcelain and specific alloy. (J PROSTHET DENT 1991;&169-79.)
T
he dental profession has long been confronted with the problem of matching the color of artificial tooth substances to the natural dentition. The selection or mod*Former graduate student, Department of Prosthodontics. **Research Professor, Department of Prosthodontics, and Assistant Dean for Clinical Affairs. 10/l/14563
THE JOURNAL
OF PROSTHETIC
DENTISTRY
ification of color for a ceramic restoration is complex and requires careful consideration. Selection of the proper color (shade) is dependent upon the ability of the dental ceramist to analyze the nuances found in natural teeth and to recognize the need for subsequent modifications. Modifications are possible since color is a three-dimensional phenomenon. A ceramic restoration or a tab from a shade guide, when compared with a tooth, may appear to be more
169
Fig. Fig. Fig. Fig.
1. 2. 3. 4.
Plexiglass color samples. Plastic graduated syringe. Complete color sample with opaque and body porcelain. Minolta Chroma meter.
red or yellow than the tooth. The color (shade) also may be more or less intense, creating an overall comparison that is lighter or darker. Tylmanr reported that higher or repeated firing cycles changed the color of the porcelain. Conversely, Barghi et al.2-4 and Jorgenson and Goodkind found that repeated firings did not affect the color stability of any shade tested after firing. An understanding of the concepts of color, proper technique, and selection of material can greatly enhance the ceramist’s ability to achieve a natural-looking restoration. Therefore, it is important to minimize the factors that influence the processing of the shade of ceramometal restorations. Part I of this investigation6 discussed the effects of various and repeated firing cycles, type of alloy, and brand of porcelain on bond strength, specifically at the ceramometal interface and the opaque-body porcelain juncture. This study (Part II) further investigated these effects on ’ the color components (Hue-value-Chroma) of ceramometals.
170
MATERIAL
AND METHODS
The samples used in this investigation were in the form of flat disks similar to those used by Barlow.’ Each sample had a flat cylindrical metal base, over which porcelain was baked. A total of 240 samples were machined out of Delrin (Delrin Products, Inc., Minneapolis, Minn.) plastic (Fig. 1). The total number of samples was then divided into two main divisions each consisting of 120 samples. The samples of one division were cast in Olympia alloy (J. F. Jelenko, Armonk, N.Y.) and samples of the other division were cast in Talladium alloy (Talladium, Los Angeles, Calif.). Each main division was subdivided into 12 groups. The 24 groups were coded according to firing temperature, number of firings, alloy type, and porcelain brand (Tables I and II).
Construction
of the samples
Disks with a diameter of 3/8 inch (9.37 mm) and thickness of 2 mm were designed to approximate the surface area of a central incisor. The samples were constructed by sectioning solid Delrin (acetyl) plastic cylindrical rods by use
FEBRUARY
1291
VOLUME
66
NUMBER
2
BOND AND COLOR OF CERAMOMETAL.
Table
PART II
I. Codes of samples used for testing Hue, Value, and Chroma relative to firing temperature Porcelain
type
Group code
N
Metal type
Recommtemp (Tl)
10 10 10 10
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
Tl ov Tl oc Tl tv Tl tc
Recommtemp 35” F (T2)
10 10
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
T2 ov T2 oc T2 tv T2 tc
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
T3 ov T3 oc T3 tv T3 tc
Firing
temp
10 10 Recommtemp 70” F (T3)
10 10 10
10
of a microtome. The microtome was adjusted to use a 600grit extra fine Carborundum disk. The plastic disks were then converted into metal samples by following the same investing, burnout casting, and surface treatment techniques used in the bond test section.
Opaque porcelain
application
The dimensions of the two opaquing materials (Vita VMK 68, Vident, Baldwin Park, Calif.; and Ceramco II, Johnson & Johnson, East Windsor, N.J.) used in this investigation were controlled to eliminate deviations in the color data due to any differences in material thickness. To provide standard uniformity and thickness, a Paasche airbrush (Paasche Air Brush Co., Chicago, Ill.) was used to apply the corresponding opaque porcelains to the prepared disks. The opaque powders were suspended in industrial grade methane and sprayed onto the disks until a uniform layer was obtained. The suspension was selected for its fast volatilization feature. According to the manufacturers’ recommendations, there should be 0.2 mm of opaque porcelain on the metal substructure. To achieve the required thickness, two layers of opaque material were applied. The first layer was measured with a modified micrometer (L. S. Starrett Co., Athol, Mass.) and adjusted with a second opaque application to meet the (0.2 mm) required thickness. A + 0.02 mm factor of error in opaque thickness was recorded,
Body porcelain
application
Porcelain thickness varies from 0.5 to 1.5 mm. A minimum of 0.5 mm is necessary cosmetically, whereas a maximum of 1.5 mm is allowable for strength.8 In this investigation, a thickness of 1 mm was chosen (0.2 opaque + 0.8 body). The body porcelain buildup was performed by use of a modified graduated plastic syringe 9.38 mm in diam-
THE JOURNAL
OF PROSTRETIC
DENTISTRY
eter (Fig. 2). The sample disks were made to fit precisely in the syringe. This procedure produced the desired porcelain thickness and facilitated its condensation. To obtain maximum and uniform density, a Ceramosonic condenser (Shofu Mfg. Co., Kyoto, Japan) was used. Each sample was allowed to dry inside the mold for 3 minutes and was then separated by pushing the piston upward. Excess porcelain was removed from the metal bases with a moistened No. 0 sable brush. Specimens were allowed to air dry a minimum of 5 minutes before firing. Before glazing, each sample was checked with a micrometer for proper thickness. Adjustments were made by placing each sample in the center slot of a steel supporting block mounted on the table of a dental surveyor (J.M. Ney Co., Bloomfield, Conn.). A porcelain grinding wheel was placed in a slow-speed handpiece, which was attached to the vertical post of the surveyor. The superior part of each sample was reduced to the required thickness (0.8 mm) and measured frequently with a micrometer. After glazing, the combined mean thickness of porcelain was 1 mm (0.2 mm opaque + 0.8 mm body) (Fig. 3). The error factor was 50.03 mm. Micrometer readings of the porcelain thickness displayed no change between the high bisque stage and the natural glaze stage.
Analysis
of samples
A Minolta Chroma meter (CR-121, Minolta Corp., Ramsey, N.J.) was used to analyze the color of each sample (Fig. 4). This meter was selected because it provides highly accurate measurements of chromaticity and illuminance, and enables quick, objective comparisons between two samples. In addition its 3 mm diameter measuring area enables precise targeting for spot color readings. The data obtained were expressed in CIE terminology and were converted to Munsell notation for Hue, Value,
171
HAMMAD
AND
STEIN
Table II. Codes of samples used for testing Hue, Value, Chroma relative to number of firings No. of firings
N
5 Firings (N5)
10
Metal
10 10 10
10
10 10
10 10
9 Firings (N9)
10
10
Group code
N6 ov N6 oc N6 tv N6 tc N7 ov N7 oc N7 tv N7 tc
N9 ov N9 oc N9 tv N9tc
Descriptive statistics for Hue relative to firing temperature
Table III.
Minimum
Group
N
Sum
Mean
SD
Tl ov
10
10 10
31.0 36.1 28.1
3.10
Tl oc Tl tv Tl tc
10
41.5
4.15
0.23 0.36 0.22 0.33
2.7 2.7 2.5 3.8
3.5 4.3 3.1 4.5
T2 T2 T2 T2
ov oc
10 10
tv tc
10 10
34.5 43.7 33.5 43.0
3.45 4.37 3.35 4.3
0.15 0.25 0.14 0.22
3.2 4.1 3.1 3.9
3.6 4.8 3.5 4.6
ov oc
10 10
35.8 43.9 32.5 44.8
3.58 4.39 3.25 4.48
0.16 0.17 0.16 0.30
3.3 4.2 3.0 4.0
3.8 4.7 3.5 4.9
T3 T3 T3 T3
tv
10
t.c
10
3.61 2.81
and Chroma by use of a Minolta data processor (DP-100, Minolta Corp.). Statistical evaluation was then performed to analyze the resultant values.
RESULTS Data of the color tests for all groups were recorded three-dimensionally and expressed in Munsell color notation (Hue, Value, and Chroma) and CIEl notation (L a b). Only Munsell colors were statistically analyzed for interpreting the results. The data were assigned codes as shown in Tables I and II. Descriptive statistics for each of the color component (H V C) in all groups are presented in Tables III through VIII.
HUE Firing temperature According to firing temperature and porcelain brand, analysis of variance (ANOVA) indicated statistically significant differences among means of all of the groups 0, < 0.001). Two-way ANOVA showed statistically significant interaction (p < 0.001) between the effects of 172
type
Vita (v) Ceramco(c) Vita (v) Ceramco(c) Vita (v) Cersmco(c) Vita (v) Ceramco(c) Vita (v) Ceramco(c) Vita (v) Ceramco(c)
Olympia (0) Olympia (0) Talladium (t) Talladium (t) Olympia (0) Olympia (0) Talladium (t) Talladium (t) Olympia (0) Olympia (0) Talladium (t) Talladium (t)
10
7 Firings (N7)
Porcelain
type
Maximum
alloys and porcelain brands. This indicates that the effect of changing the alloy type on Hue varies with the porcelain brand used at a given firing temperature. Three-way ANOVA showed significant interaction (p = 0.001) between the effects of temperatures, alloys, and porcelain brands. This interaction indicates that the effect of changing the firing temperature relative to Hue varies with the alloy-porcelain brand combination (Table IX). t-Tests providing individual comparisons among group means are presented in Table X. These tests showed significant increase in Hue by increase in firing temperatures of all alloy-porcelain combinations tested (p < 0.001) except for the combined Talladium and Ceramco II materials. The increase in Hue for the combination of Talladium and Ceramco II materials was not statistically significant. Ceramco II porcelain showed significantly higher Hues than Vita porcelain at all firing temperatures 0, < 0.001). The use of Ceramco II porcelain and Talladium alloy samples showed significantly higher Hues than the Olympia alloy samples 0, < 0.001). Although Vita porcelain
FEBRUARY
1991
VOLUME
65
NUMBER
2
BOND
AND
COLOR
OF CERAMOMETAL.
Table IV. Descrintive
PART
statistics
II
for Hue relative
to number of firings Maximum
N
Sum
Mean
SD
N5 N5 N5 N5 N7 N7 N7 N7 N9 N9
10 10 10 10 10 10 10 10 10 10 10 10
31.0 36.1 28.1 41.5 30.0 35.5 27.8 39.6 30.6 36.2 28.3 40.0
3.10 3.61 2.81 4.15 3.00 3.55 2.78 3.96 3.06 3.62 2.83 4.00
0.23 0.36 0.22 0.33 0.13 0.39 0.21 0.15 0.15 0.30 0.16 0.29
2.1 2.9 2.5 3.8 2.8 3.1 2.4 3.96 2.9 3.2 2.6 3.6
3.5 4.3 3.1 4.5 3.2 4.2 3.0 4.1 3.4 4.0 3.0 4.4
ov oc
tv tc ov oc
tv tc ov oc
N9 tv N9 tc
Table V. Descriptive
statistics
of Value relative
to firing temperature
Group
N
Sum
Mean
SD
Minimum
Maximum
Tl Tl Tl Tl T2 T2 T2 T2 T3 T3 T3 T3
10 10 10 10 10 10 10 10 10 10 10 10
66.9
6.69
58.7 63.4 61.4 65.0 57.9 62.1 57.1 63.7 51.7 60.3 57.1
5.87 6.34 6.14 6.50 5.79 6.21 5.71 6.37 5.77 6.03 5.71
0.057 0.125 0.201 0.107 0.170 0.314 0.032 0.099 0.095 0.263 0.048 0.296
6.6 5.7 6.1 6.0 6.3 5.5 6.2 5.6 6.2 5.5 6.0 5.4
6.8 6.1 6.9 6.3 6.8 6.2 6.3 5.8 6.5 6.1 6.1 6.1
ov oc
tv tc ov oc
tv tc ov oc
tv tc
Table VI.
Descriptive
statistics
for Value relative
to number of firings
Group
N
Sum
Mean
SD
Minimum
Maximum
N5 N5 N5 N5 N7 N7
10 10 10 10 10 10 10 10 10 10 10 10
66.9
6.69
58.1 63.4 61.4 66.4 58.3 63.0 60.2 65.9 57.6 62.4 59.9
5.87 6.34 6.14 6.64 5.83 6.30 6.02 6.59 5.76 6.24 5.99
0.05 0.12 0.20 0.10 0.14 0.20 0.17 0.24 0.18 0.19 0.18 0.21
6.6 5.7 6.1 6.0 6.5 5.5 6.1 5.5 6.4 5.5 6.1 5.5
6.8 6.1 6.6 6.3 6.8 6.1 6.5 6.5 8.8 6.2 6.5 6.4
ov oc
tv tc ov oc
N7 tv N7 tc N9 ov N9 oc N9 tv N9 tc
showed a higher Hue with Olympia alloy than with Talladium alloy, the difference was not statistically signifi-
cant. Scheffe follow-up tests were also performed and showed similar findings (Table XI). It became readily apparent, because of the large number of samples tested and thus the many degrees of freedom in the statistics, that the Scheffe
THE
Minimum
Group
JOURNAL
OF PROSTHETIC
DENTISTRY
test would indicate statistical ically significant.
Number
differences that are not clin-
of firings
ANOVA indicated no significant change in Hue with an increased number of kings of all alloy-porcelain brand combinations used in the study (Table XII).
173
HAMMAD
Table
Table
VII.
Descriptive statistics for Chroma relative to firing temperature
Group
N
Slim
Mean
SD
Tl Tl Tl Tl T2 T2 T2 T2 T3 T3 T3 T3
10 10 10 10 10 10 10 10 10 10 10 10
14.2 9.4 16.3 9.4 14.7 10.0 16.6 9.3 14.1 9.7 17.0 9.4
1.42 0.94 1.63 0.94 1.47 1.00 1.66 0.93 1.41 0.97 1.70 0.94
0.06 0.07 0.05 0.08 0.08 0.05 0.05 0.07 0.09 0.07 0.08 0.05
ov oc tv tc ov oc tv tc ov oc tv tc
VIII. Group
N
Sum
Mean
SD
N5 ov N5 oc N5 tv N5tc N7 ov N7 oc N7 tv N7 tc N9 ov N9 oc N9 tv N9 tc
10 10 10 10 10 10 10 10 10 10 10 10
14.2 9.4 16.3 9.4 14.4 9.5 16.2 9.6 14.4 9.3 16.3 9.7
1.42 .94 1.63 .94 1.44 .95 1.62 .96 1.44 .93 1.63 .97
0.06 0.07 0.05 0.08 0.05 0.07 0.04 0.09 0.08 0.05 0.05 0.14
Source Temp Alloy Temp/alloy Port Temp/porc Alloy/port Temp/alloy/porc Error
Minimum
Maximum
1.3 0.8 1.6 0.9 1.4 0.9 1.6 0.8 1.2 0.8 1.6 0.9
1.5 1.0 1.7 1.1 1.6 1.1 1.7 1.0 1.5 1.0 1.8 1.0
Descriptive statistics for Chroma relative to number of firings
Table IX. Analysis of variance for Hue relative to firing temperature SS
DF
MS
F
P
6.17 0.02 0.35 27.64 0.05 1.36 0.80 6.24
2 1 2 1 2 1 2 108
3.08 0.21 0.17 27.64 0.02 1.36 0.40 0.05
53.25 .36 3.03 476.69 .46 23.53 6.89 -
MATERIALS
FOR COMPLETE-ARCH
FPDs
1. The polyether and addition-silicone impression materials were significantly more accurate than the reversible hydrocolloid impression material in producing dies for single restorations. However, all of the impression materials tested produced clinically acceptable single crowns. 2. The polyether and addition-silicone impression materials produced accurate casts that would enable the fabrication and assembly of clinically acceptable FPDs. 3. Reversible hydrocolloid impression material produced casts that were not sufficiently accurate to allow for the assembly of clinically acceptable complete arch FPDs.
8. Sawyer HF, Birtles JT, Neiman R, Podshadley AG. Accuracy of casts
produced from seven rubber impression materials. J Am Dent Assoc 1973;87:126-30. 9. Sawyer HF, Dilts WE, Aubrey ME, Neiman R. Accuracy of casts produced from the three classes of elastomer impression materials. J Am Dent Assoc 1974;89:644-8. 10. Vermilyea SG, Powers JM, Craig RG. Polyether, polysulfide and silicone rubber impression materials: part 2: accuracy of silver-plated dies. J Mich Dent Assoc 1975;57:405-10. 11. Stackhouse JA. A comparison of elastic impression materials. J PROSTHET DENT 1975;34:305-13. 12. Munoz C, Goodacre C, Schnell R, Harris R. Laboratory and clinical
study of a visible light polymerized elastomeric impression material. Int J Proathodont
1988;1:59-66. 13. Henry PJ, Harnist DJR. Dimensional stability and accuracy of rubber
impression materials. Aust Dent J 1974;19:162-6.
REFERENCES
14. Lacy AM, Fukui H, Bellman T, Jendresen MD. Time-dependent accu-
1. Brindsden GI, Sorensen S, McClenahan J. Dimensional accuracy of five
impression materials using a copper-shell technique. J Dent Res 1964;43 (Suppl):911. 2. Hembree JH Jr. Comparative accuracy of elastomer impression materials. J Term Dent Assoc 1974;54:164-7. 3. Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J PROSTHET DENT 1979;42:159-62. 4. Ciesco JN, Malone WFP, Sandrik JL, Maxur B. Comparison of elasto-
meric impression materials used in fixed prosthodontics. J PROSTH~ DENT 1981;45:89-94. 5. Mincham W, Thurgate SM, Lewis AJ. Measurement of dimensional
stability of elastomeric impression materials by holographic interferometry. Aust Dent J 1981;26:395-9. 6. Tjan AHL, Whang S, Tjan AH, Sarkissian R. Clinically oriented evaluation of the accuracy of commonly used impression materials. J PROSTHET DENT 1986;56:4-8.
7. Bassett RW, Vander Heide JD, Smith DD. Clinically oriented tests comparing accuracy of elastic impression materials. J South Calif Dent Assoc 1969;37:47-57.
A qualitative Part II
racy of elastomer impression materials, part II: polyethers, polysulfides, and polyvinylsiloxanes. J PROSTHET DENT 1981;45:329-33. 15. Linke B, Nicholls J, Faucher R. Distortion analysis of stone casts made from impression materials. J PROSTHET DENT 1985;54:794-802. 16. Stauffer J, Meyer J, Nally J. Accuracy of six elastic impression materials used for complete-arch fixed partial dentures. J PROSTHET DENT 1976;35:407-15. 17. Lin CC, Ziebert G, Donegan SJ, Dhuru V. Accuracy of impression materials for complete arch fixed partial dentures. J PROSTHET DENT 1988;59:288-91. 18. Christensen G. Marginal fit of gold inlay castings. J PROSTHET DENT 1966;16:297-305. 19. Dedmon H. Disparity in expert opinions on size of acceptable marginal
openings. J Oper Dent 1982;7:97-101. Reprint requests to: DR. GERALD J. ZIFBERT SCHOOL OF DENTISTRY MARQUEITE UNIVERSITY 604 N. 16TH ST. MILWAUKEE, WI 53233
study for the bond and color of ceramometals.
Ihab Adel Hammad, B.D.S., M.S., D.Sc.,* and Robert Sheldon Stein, D.M.D.** Boston University, School of Graduate Dentistry, Boston, Mass. Many dentists, porcelain manufacturers, and dental technicians empirically state that repeated firings tend to bleach out or alter the original shade of porcelain. This investigation used a sophisticated calorimeter to resolve the controversy. The effect of temperature rise and number of firings had varying effects on color relative to brand of porcelain and specific alloy. (J PROSTHET DENT 1991;&169-79.)
T
he dental profession has long been confronted with the problem of matching the color of artificial tooth substances to the natural dentition. The selection or mod*Former graduate student, Department of Prosthodontics. **Research Professor, Department of Prosthodontics, and Assistant Dean for Clinical Affairs. 10/l/14563
THE JOURNAL
OF PROSTHETIC
DENTISTRY
ification of color for a ceramic restoration is complex and requires careful consideration. Selection of the proper color (shade) is dependent upon the ability of the dental ceramist to analyze the nuances found in natural teeth and to recognize the need for subsequent modifications. Modifications are possible since color is a three-dimensional phenomenon. A ceramic restoration or a tab from a shade guide, when compared with a tooth, may appear to be more
169
Fig. Fig. Fig. Fig.
1. 2. 3. 4.
Plexiglass color samples. Plastic graduated syringe. Complete color sample with opaque and body porcelain. Minolta Chroma meter.
red or yellow than the tooth. The color (shade) also may be more or less intense, creating an overall comparison that is lighter or darker. Tylmanr reported that higher or repeated firing cycles changed the color of the porcelain. Conversely, Barghi et al.2-4 and Jorgenson and Goodkind found that repeated firings did not affect the color stability of any shade tested after firing. An understanding of the concepts of color, proper technique, and selection of material can greatly enhance the ceramist’s ability to achieve a natural-looking restoration. Therefore, it is important to minimize the factors that influence the processing of the shade of ceramometal restorations. Part I of this investigation6 discussed the effects of various and repeated firing cycles, type of alloy, and brand of porcelain on bond strength, specifically at the ceramometal interface and the opaque-body porcelain juncture. This study (Part II) further investigated these effects on ’ the color components (Hue-value-Chroma) of ceramometals.
170
MATERIAL
AND METHODS
The samples used in this investigation were in the form of flat disks similar to those used by Barlow.’ Each sample had a flat cylindrical metal base, over which porcelain was baked. A total of 240 samples were machined out of Delrin (Delrin Products, Inc., Minneapolis, Minn.) plastic (Fig. 1). The total number of samples was then divided into two main divisions each consisting of 120 samples. The samples of one division were cast in Olympia alloy (J. F. Jelenko, Armonk, N.Y.) and samples of the other division were cast in Talladium alloy (Talladium, Los Angeles, Calif.). Each main division was subdivided into 12 groups. The 24 groups were coded according to firing temperature, number of firings, alloy type, and porcelain brand (Tables I and II).
Construction
of the samples
Disks with a diameter of 3/8 inch (9.37 mm) and thickness of 2 mm were designed to approximate the surface area of a central incisor. The samples were constructed by sectioning solid Delrin (acetyl) plastic cylindrical rods by use
FEBRUARY
1291
VOLUME
66
NUMBER
2
BOND AND COLOR OF CERAMOMETAL.
Table
PART II
I. Codes of samples used for testing Hue, Value, and Chroma relative to firing temperature Porcelain
type
Group code
N
Metal type
Recommtemp (Tl)
10 10 10 10
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
Tl ov Tl oc Tl tv Tl tc
Recommtemp 35” F (T2)
10 10
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
T2 ov T2 oc T2 tv T2 tc
Olympia (0) Olympia (0) Talladium (t) Talladium (t)
Vita (v) Ceramco(c) Vita (v) Ceramco(c)
T3 ov T3 oc T3 tv T3 tc
Firing
temp
10 10 Recommtemp 70” F (T3)
10 10 10
10
of a microtome. The microtome was adjusted to use a 600grit extra fine Carborundum disk. The plastic disks were then converted into metal samples by following the same investing, burnout casting, and surface treatment techniques used in the bond test section.
Opaque porcelain
application
The dimensions of the two opaquing materials (Vita VMK 68, Vident, Baldwin Park, Calif.; and Ceramco II, Johnson & Johnson, East Windsor, N.J.) used in this investigation were controlled to eliminate deviations in the color data due to any differences in material thickness. To provide standard uniformity and thickness, a Paasche airbrush (Paasche Air Brush Co., Chicago, Ill.) was used to apply the corresponding opaque porcelains to the prepared disks. The opaque powders were suspended in industrial grade methane and sprayed onto the disks until a uniform layer was obtained. The suspension was selected for its fast volatilization feature. According to the manufacturers’ recommendations, there should be 0.2 mm of opaque porcelain on the metal substructure. To achieve the required thickness, two layers of opaque material were applied. The first layer was measured with a modified micrometer (L. S. Starrett Co., Athol, Mass.) and adjusted with a second opaque application to meet the (0.2 mm) required thickness. A + 0.02 mm factor of error in opaque thickness was recorded,
Body porcelain
application
Porcelain thickness varies from 0.5 to 1.5 mm. A minimum of 0.5 mm is necessary cosmetically, whereas a maximum of 1.5 mm is allowable for strength.8 In this investigation, a thickness of 1 mm was chosen (0.2 opaque + 0.8 body). The body porcelain buildup was performed by use of a modified graduated plastic syringe 9.38 mm in diam-
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eter (Fig. 2). The sample disks were made to fit precisely in the syringe. This procedure produced the desired porcelain thickness and facilitated its condensation. To obtain maximum and uniform density, a Ceramosonic condenser (Shofu Mfg. Co., Kyoto, Japan) was used. Each sample was allowed to dry inside the mold for 3 minutes and was then separated by pushing the piston upward. Excess porcelain was removed from the metal bases with a moistened No. 0 sable brush. Specimens were allowed to air dry a minimum of 5 minutes before firing. Before glazing, each sample was checked with a micrometer for proper thickness. Adjustments were made by placing each sample in the center slot of a steel supporting block mounted on the table of a dental surveyor (J.M. Ney Co., Bloomfield, Conn.). A porcelain grinding wheel was placed in a slow-speed handpiece, which was attached to the vertical post of the surveyor. The superior part of each sample was reduced to the required thickness (0.8 mm) and measured frequently with a micrometer. After glazing, the combined mean thickness of porcelain was 1 mm (0.2 mm opaque + 0.8 mm body) (Fig. 3). The error factor was 50.03 mm. Micrometer readings of the porcelain thickness displayed no change between the high bisque stage and the natural glaze stage.
Analysis
of samples
A Minolta Chroma meter (CR-121, Minolta Corp., Ramsey, N.J.) was used to analyze the color of each sample (Fig. 4). This meter was selected because it provides highly accurate measurements of chromaticity and illuminance, and enables quick, objective comparisons between two samples. In addition its 3 mm diameter measuring area enables precise targeting for spot color readings. The data obtained were expressed in CIE terminology and were converted to Munsell notation for Hue, Value,
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Table II. Codes of samples used for testing Hue, Value, Chroma relative to number of firings No. of firings
N
5 Firings (N5)
10
Metal
10 10 10
10
10 10
10 10
9 Firings (N9)
10
10
Group code
N6 ov N6 oc N6 tv N6 tc N7 ov N7 oc N7 tv N7 tc
N9 ov N9 oc N9 tv N9tc
Descriptive statistics for Hue relative to firing temperature
Table III.
Minimum
Group
N
Sum
Mean
SD
Tl ov
10
10 10
31.0 36.1 28.1
3.10
Tl oc Tl tv Tl tc
10
41.5
4.15
0.23 0.36 0.22 0.33
2.7 2.7 2.5 3.8
3.5 4.3 3.1 4.5
T2 T2 T2 T2
ov oc
10 10
tv tc
10 10
34.5 43.7 33.5 43.0
3.45 4.37 3.35 4.3
0.15 0.25 0.14 0.22
3.2 4.1 3.1 3.9
3.6 4.8 3.5 4.6
ov oc
10 10
35.8 43.9 32.5 44.8
3.58 4.39 3.25 4.48
0.16 0.17 0.16 0.30
3.3 4.2 3.0 4.0
3.8 4.7 3.5 4.9
T3 T3 T3 T3
tv
10
t.c
10
3.61 2.81
and Chroma by use of a Minolta data processor (DP-100, Minolta Corp.). Statistical evaluation was then performed to analyze the resultant values.
RESULTS Data of the color tests for all groups were recorded three-dimensionally and expressed in Munsell color notation (Hue, Value, and Chroma) and CIEl notation (L a b). Only Munsell colors were statistically analyzed for interpreting the results. The data were assigned codes as shown in Tables I and II. Descriptive statistics for each of the color component (H V C) in all groups are presented in Tables III through VIII.
HUE Firing temperature According to firing temperature and porcelain brand, analysis of variance (ANOVA) indicated statistically significant differences among means of all of the groups 0, < 0.001). Two-way ANOVA showed statistically significant interaction (p < 0.001) between the effects of 172
type
Vita (v) Ceramco(c) Vita (v) Ceramco(c) Vita (v) Cersmco(c) Vita (v) Ceramco(c) Vita (v) Ceramco(c) Vita (v) Ceramco(c)
Olympia (0) Olympia (0) Talladium (t) Talladium (t) Olympia (0) Olympia (0) Talladium (t) Talladium (t) Olympia (0) Olympia (0) Talladium (t) Talladium (t)
10
7 Firings (N7)
Porcelain
type
Maximum
alloys and porcelain brands. This indicates that the effect of changing the alloy type on Hue varies with the porcelain brand used at a given firing temperature. Three-way ANOVA showed significant interaction (p = 0.001) between the effects of temperatures, alloys, and porcelain brands. This interaction indicates that the effect of changing the firing temperature relative to Hue varies with the alloy-porcelain brand combination (Table IX). t-Tests providing individual comparisons among group means are presented in Table X. These tests showed significant increase in Hue by increase in firing temperatures of all alloy-porcelain combinations tested (p < 0.001) except for the combined Talladium and Ceramco II materials. The increase in Hue for the combination of Talladium and Ceramco II materials was not statistically significant. Ceramco II porcelain showed significantly higher Hues than Vita porcelain at all firing temperatures 0, < 0.001). The use of Ceramco II porcelain and Talladium alloy samples showed significantly higher Hues than the Olympia alloy samples 0, < 0.001). Although Vita porcelain
FEBRUARY
1991
VOLUME
65
NUMBER
2
BOND
AND
COLOR
OF CERAMOMETAL.
Table IV. Descrintive
PART
statistics
II
for Hue relative
to number of firings Maximum
N
Sum
Mean
SD
N5 N5 N5 N5 N7 N7 N7 N7 N9 N9
10 10 10 10 10 10 10 10 10 10 10 10
31.0 36.1 28.1 41.5 30.0 35.5 27.8 39.6 30.6 36.2 28.3 40.0
3.10 3.61 2.81 4.15 3.00 3.55 2.78 3.96 3.06 3.62 2.83 4.00
0.23 0.36 0.22 0.33 0.13 0.39 0.21 0.15 0.15 0.30 0.16 0.29
2.1 2.9 2.5 3.8 2.8 3.1 2.4 3.96 2.9 3.2 2.6 3.6
3.5 4.3 3.1 4.5 3.2 4.2 3.0 4.1 3.4 4.0 3.0 4.4
ov oc
tv tc ov oc
tv tc ov oc
N9 tv N9 tc
Table V. Descriptive
statistics
of Value relative
to firing temperature
Group
N
Sum
Mean
SD
Minimum
Maximum
Tl Tl Tl Tl T2 T2 T2 T2 T3 T3 T3 T3
10 10 10 10 10 10 10 10 10 10 10 10
66.9
6.69
58.7 63.4 61.4 65.0 57.9 62.1 57.1 63.7 51.7 60.3 57.1
5.87 6.34 6.14 6.50 5.79 6.21 5.71 6.37 5.77 6.03 5.71
0.057 0.125 0.201 0.107 0.170 0.314 0.032 0.099 0.095 0.263 0.048 0.296
6.6 5.7 6.1 6.0 6.3 5.5 6.2 5.6 6.2 5.5 6.0 5.4
6.8 6.1 6.9 6.3 6.8 6.2 6.3 5.8 6.5 6.1 6.1 6.1
ov oc
tv tc ov oc
tv tc ov oc
tv tc
Table VI.
Descriptive
statistics
for Value relative
to number of firings
Group
N
Sum
Mean
SD
Minimum
Maximum
N5 N5 N5 N5 N7 N7
10 10 10 10 10 10 10 10 10 10 10 10
66.9
6.69
58.1 63.4 61.4 66.4 58.3 63.0 60.2 65.9 57.6 62.4 59.9
5.87 6.34 6.14 6.64 5.83 6.30 6.02 6.59 5.76 6.24 5.99
0.05 0.12 0.20 0.10 0.14 0.20 0.17 0.24 0.18 0.19 0.18 0.21
6.6 5.7 6.1 6.0 6.5 5.5 6.1 5.5 6.4 5.5 6.1 5.5
6.8 6.1 6.6 6.3 6.8 6.1 6.5 6.5 8.8 6.2 6.5 6.4
ov oc
tv tc ov oc
N7 tv N7 tc N9 ov N9 oc N9 tv N9 tc
showed a higher Hue with Olympia alloy than with Talladium alloy, the difference was not statistically signifi-
cant. Scheffe follow-up tests were also performed and showed similar findings (Table XI). It became readily apparent, because of the large number of samples tested and thus the many degrees of freedom in the statistics, that the Scheffe
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test would indicate statistical ically significant.
Number
differences that are not clin-
of firings
ANOVA indicated no significant change in Hue with an increased number of kings of all alloy-porcelain brand combinations used in the study (Table XII).
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HAMMAD
Table
Table
VII.
Descriptive statistics for Chroma relative to firing temperature
Group
N
Slim
Mean
SD
Tl Tl Tl Tl T2 T2 T2 T2 T3 T3 T3 T3
10 10 10 10 10 10 10 10 10 10 10 10
14.2 9.4 16.3 9.4 14.7 10.0 16.6 9.3 14.1 9.7 17.0 9.4
1.42 0.94 1.63 0.94 1.47 1.00 1.66 0.93 1.41 0.97 1.70 0.94
0.06 0.07 0.05 0.08 0.08 0.05 0.05 0.07 0.09 0.07 0.08 0.05
ov oc tv tc ov oc tv tc ov oc tv tc
VIII. Group
N
Sum
Mean
SD
N5 ov N5 oc N5 tv N5tc N7 ov N7 oc N7 tv N7 tc N9 ov N9 oc N9 tv N9 tc
10 10 10 10 10 10 10 10 10 10 10 10
14.2 9.4 16.3 9.4 14.4 9.5 16.2 9.6 14.4 9.3 16.3 9.7
1.42 .94 1.63 .94 1.44 .95 1.62 .96 1.44 .93 1.63 .97
0.06 0.07 0.05 0.08 0.05 0.07 0.04 0.09 0.08 0.05 0.05 0.14
Source Temp Alloy Temp/alloy Port Temp/porc Alloy/port Temp/alloy/porc Error
Minimum
Maximum
1.3 0.8 1.6 0.9 1.4 0.9 1.6 0.8 1.2 0.8 1.6 0.9
1.5 1.0 1.7 1.1 1.6 1.1 1.7 1.0 1.5 1.0 1.8 1.0
Descriptive statistics for Chroma relative to number of firings
Table IX. Analysis of variance for Hue relative to firing temperature SS
DF
MS
F
P
6.17 0.02 0.35 27.64 0.05 1.36 0.80 6.24
2 1 2 1 2 1 2 108
3.08 0.21 0.17 27.64 0.02 1.36 0.40 0.05
53.25 .36 3.03 476.69 .46 23.53 6.89 -
