Veterans Administration Cooperative Studies Project 147. A precementation comparison of metal ceramic restorations made with a gold-containing alloy or alternative alloys Participants
of CSP No. 147,* and Harold F. Morris, Medical Center, Ann Arbor, Mich.
No.
D.D.S., MS.**
Veterans Administration
This analysis compared the precementation quality of metal ceramic restorations made from different alternative alloys after they had been returned from the central dental research laboratory. Ticon, Micro-Bond N/P2, Ceramalloy II, and W-l materials were evaluated by use of 11 well-defined criteria and for overall performance. The evaluations were compared with those of Olympia, a goldcontaining alloy, which served as the control. The results showed statistically sign&ant differences between Olympia alloy and some of the alternative alloys for six of the 11 criteria. These differences, however, were not sufficient to be considered clinically significant (clinically detectable). In the comparison of their overall performances no statistically significant differences were found. (J PROSTHET DENT 1991;65:196-206.)
N
umerous investigators have reported on the advantages and disadvantages of the alternative alloys for metal ceramic restorations.‘-l7 However, with the exception of Moffa et al’s &year investigation,18 limited data are available based on comprehensive, long-term clinical studies. It is imperative that alloys used in dentistry be capable of producing quality restorations that will function for a reasonable period of time while maintaining the health of natural teeth and their supporting tissues. The main purpose of CSP No. 147 was to compare the clinical behavior of several alternative alloys with Olympia (J. F. Jelenko & Co., Armonk, N.Y.), an alloy containing 51.5% gold, for metal ceramic restoration during 10 years of clinical function. This analysis compared approximately 1200 metal ceramic restorations
(crowns and fixed partial
dentures) on dies, before cementation by use of welldefined, clinically
METHOD
relevant
criteria.
AND MATERIAL
In this study two restorations were made for each of the 600 patients, one from Olympia alloy (control) and the other from an alternative alloy (Ticon, Micro-Bond N/P2, Ceramalloy II, or W-l) (Table I) according to a randomized, paired-comparison experimental design.lg Six Veter-
Supported by the Veterans Administration Medical Research Service/Cooperative Studies Program and the National Institute of Dental Research, Interagency contract No. lYOl-DE50004-00, and conducted by the Veterans Administration CSP Nos. 147/242 Dental Research Group. *Complete authorship appears on last page of article. **Study Chairman; Director, Clinical Research Center for Restorative Materials; and Clinical Assoicate Professor, University of Michigan, School of Dentistry, Ann Arbor, Mich. 10/l/22257
196
ans Administration Medical Centers (Allen Park and Ann Arbor, Mich.; Buffalo, N.Y.; Pittsburgh, Pa.; and San Diego and San Francisco, Calif.) participated in the study. Each center had two investigators, designated as Principal Investigator One (PI-l) and Principal Investigator Two (PI-2). PI-1 provided all restorative dental treatment and PI-2 completed all periodontal treatment. The investigators were standardized in all criteria at a l-week training session, at the beginning of the study. Training was repeated at semiannual meetings. The wax patterns were cast in a phosphate-bonded investment (Ceramigold, Whip-Mix Corp., Louisville, Ky.) following manufacturer’s instructions. Ceramco porcelain was used for all alloys except W-l, which required WillCeram porcelain (Table I). Appropriate solders (Table I) were used to join units for fixed partial dentures. The restorations were returned to the participating VA Medical Centers for evaluation on dies by clinical investigators using study criteria (Table II). The restorations were independently evaluated by each investigator and conflicts were resolved by consensus. To avoid bias, the identity of the alloys was not disclosed.lg The restorations were evaluated based on a rating process that considered certain criteria more important than others.20 R, S, M ratings were satisfactory whereas T and V ratings were unsatisfactory and were considered clinically significant. The results of the evaluations were statistically compared using Dunnett’s test.21 This test simultaneously controls for type 1 errors in comparing a control to different treatment groups. Analysis of ordinal ratings often resulted in statistically significant differences between the means. However, this does not necessarily indicate that the differences were large enough to be clinically significant. Criteria were established to facilitate the transfer of the statistical results into
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COMPARISON
Table
I.
OF METAL
CERAMIC
RESTORATIONS
Alloys, presolders, and porcelains
Olympia (control alloy) J. F. Jelenko & Co. Armonk, N.Y. Ticon Ticonium, Co. Albany, N.Y. Ceramalloy II Johnson & Johnson Dental Products co. East Windsor, N.J. Micro-Bond N/P2 Austenal Dental, Inc., A Nobelpharma co. Chicago, Ill. W-l Williams Dental Co., Inc. Buffalo, N.Y.
Olympia, Presolder J. F. Jelenko & Co. Will-Ceram Super White Williams Dental Co., Inc. Buffalo, N.Y. Ceramalloy High Fusing Solder Johnson & Johnson Dental Products co.
OF PROSTHETIC
DENTISTRY
Ceramco Johnson & Johnson Dental Products Co.
Ceramco Johnson & Johnson Dental Products Co.
Williams Ceramic Solder (special high fusing white) Williams Dental Co., Inc.
Will-Ceram Williams Dental Co. Inc.
*One unit is equal to one level on the ordinal rating scale used in this study for all evaluations except “overall score” where two units approximate one level in the ordinal rating scale.
JOURNAL
Ceramco Johnson & Johnson Dental Products co. Ceramco Johnson & Johnson Dental Products Co.
Micro-Bond N/P2 Presolder Austenal Dental, Inc., A Nobelpharma co.
clinically relevant information (Table III). These criteria provided for three levels of clinical significance. 1. No clinical difference (NCD). No statistically significant difference exists and the means differ by less than 1 unit. * 2. Clinical interest (CI). A statistically significant difference exists and the means differ by less than 1 unit.* (Although these clinical interest differences may not be clinically significant at this time, the dentist should be aware that they exist and that a trend has been established that may be expected to increase with continued clinical use.) 3. Clinically significant difference (CSD). A statistically significant difference exists and the means differ by more than 1 unit,* which is believed to be large enough to be clinically significant and can be expected to increase with time. In addition to evaluating the restorations on individual criteria, an overall or total performance score reflected the behavior of an alloy for all criteria. This total performance score was divided into an “overall rating” and an “overall score.“2o In general, the overall rating was based on a fivepoint scale and the overall score was based upon an expanded lo-point scale to permit the distinction of finer differences. It should be noted that when evaluations for a criterion were somehow omitted, not legible, or their accuracy questioned, they were not included in the analysis. This procedure was necessary to prevent the introduction of bias during the attempt to recover these evaluations.
THE
Porcelains
Presolder
Alloy
RESULTS AND DISCUSSION I. Comparison of the individual
criteria
The frequency distribution of the evaluations for each alloy and criterion is provided in Table IV. Only limited information can be obtained from this table. For example, it appears that Olympia alloy had more unsatisfactory evaluations (T, V) than did any of the alternative alloys. This was because a larger number of restorations were made from Olympia alloy (n = 556). It represented only 1.3% of the total Olympia alloy restorations compared with 2.1% for the Ceramalloy II alloy restorations. Meaningful conclusions cannot be formulated without information as to (1) which alloy means are statistically different, (2) which criteria are statistically different, (3) how the alloys compare in their overall evaluations, and (4) when statistically significant, which differences are large enough to be considered clinically relevant (Tables III and V). Statistically significant differences were found when the means of the alternative alloys were compared with Olympia alloy by use of Dunnett’s test for the following criteria: retention on die, marginal integrity, pitting of surface, polish/tarnish of surface, polish/tarnish of connector/solder joint, and veneer-to-metal integrity (Table III). These statistical differences represented six out of 11 criteria evaluated. Results from all 11 criteria are listed. Certain criteria were judged to be of critical importance and were designated critical criteria. 2oThe criteria were as follows. A. Fit on die (critical criterion). No significant statistical differences were found between Olympia and any of the alternative alloys (Table III). Only 13 (0.01%) of all 1116 restorations received unsatisfactory ratings (Table IV). 197
CSP
Table
II.
Clinical
criteria,
rating scale with definitions
and critical
Rating
1471242
AND
MORRIS
elements
Criteria
v
Fit on die# Casting seats on die with light force and margins coincide with finish lines. Casting seats on die without force so that margins coincide with finish lines. Casting seats on die with moderate force; however there is some interference so that margins coincide with finish lines. Casting fails to seat on die with moderate force or finish lines exposed 0.25 mm or casting is unstable.
R S M T v
Retention Die retained in casting when inverted, can be removed with light force. Die not retained in casting when inverted, but casting stable when seated. Die retained in casting when inverted and can be removed only with moderate force. Die retained in casting when inverted and casting can be removed only with extensive force. Casting rocks or rotates slightly on die, indicating lack of stability.
R S M T v
Marginal integrity# Not detectable or scarcely detectable with explorer Slightly under/over extended or slightly detectable with explorer Moderately under/over extended or moderately detectable with explorer Decidedly under/over extended or decidedly detectable with explorer Margin open, explorer can penetrate into tooth restoration interface.
R S M T v
Pitting of surface# Uniformly smooth, no pits evident Barely detectable local pits removable in finishing and polishing process Moderate local pitting, removable in finishing and polishing process Decidedly local or generalized pitting; removal necessitates alteration of dimensions and contours Deeply pitted; removal necessitates alteration of dimensions and contours
R S M T v
Polish/tarnish of surface Uniformly glossy, highly shined appearance Glossy with local dull areas (scratches) Uniformly dull (scratches) Locally tarnished Generally tarnished
R S M
Sating key: R, 5; S, 4; M, 3; T, 2; V, 1. R, #Critical criteria.
S,
and M, satisfactory;T
and V, unsatisfactory.
Light seating force or no force (passive fit) reflects the investigators’ definition of ideal fit. If a casting fails to seat on a die passively, this could result in abrasion or distortion of the die, which would produce an unacceptable fit on the tooth. Fit on die provides information related to possible sensitivity to laboratory procedures. B. Retention on die. W-l, Ticon, and Micro-Bond N/ P2 alloys were retained on their dies significantly better (alpha level 0.01) than Olympia alloy. However, these differences were only of clinical interest because the difference between their means was less than 1 unit (Table III). Twenty-two (0.02 X) of 1114 restorations received unsatisfactory ratings (Table IV). Ideal retention was defined as a casting that would be retained on the die when inverted and would require a light force for removal. A casting that drops off the die easily may
result in a loose, nonretentive restoration. Alloys with poor retention on dies may be sensitive to laboratory handling of that alloy.
198
NO.
C. Marginal integrity on die (critical criterion). Micro-Bond N/P2 was the only alternative alloy whose marginal integrity was significantly lower in quality than the Olympia alloy restorations. Eighteen (0.02%) of 1114 restorations received unsatisfactory ratings. Ideal marginal integrity was defined as a nondetectable margin on tactile examination with a new explorer. Marginal integrity is a critical criterion because of its generally accepted influence on the longevity of the restoration and the health of the periodontium. Marginal integrity provides information related to inherent alloy characteristics as well as possible sensitivity to laboratory handling. D. Pitting of surface (critical criterion). Ticon and Ceramalloy II alloys were significantly worse than Olympia alloy although W-l and Micro-Bond
N/P2 alloys were not.
These differences, while of clinical interest, were less than 1 unit and therefore not large enough to be clinically significant. Olympia and W-l alloys were generally free of pitting whereas the base-metal restorations generally
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CERAMIC
RESTORATIONS
Table II. Cont’d. Criteria
Rating
R S M T v
Pitting of connector/solder joint surface# Uniformly smooth, no pits evident Barely detectable local pits removable in finishing and polishing process Moderate local pitting removable in finishing and polishing process Decidedly local or generalized pitting; removal necessitates alteration of dimensions and contours Deeply pitted; removal necessitates alteration of dimensions and contours
R S M T V
Polish/tarnish of connector/solder joint surface Uniformly glossy, highly shined appearance Glossy with local dull areas (scratches) Uniformly dull (scratches) Locally tarnished Generally tarnished
R S M T V
Veneer to metal integritya Not detectable or scarcely detectable with explorer Slightly detectable with explorer; porcelain slightly under/over extended, or under/over contoured Moderately detectable with explorer; porcelain moderately under/over extended, or under/over contoured Decidedly detectable with explorer as two-way catch indicating porcelain margin fracture Gross fracture of porcelain at or away from margin Veneer esthetics (porcelain color)# Not detectably different in color from shade guide tab Slightly different in color from shade guide tab Moderately different in color from shade guide tab Decidedly different in color from shade guide tab Definite mismatch
R T V
Crazing No crazing evident Minor crazing evident, but repairable Crazing evident, nonrepairable
R S M T
Glaze Uniformly glazed, smooth surface Glaze missing slightly in local area(s) Glaze missing in large areas(s); slight pitting on surface may be evident. Decided pitting of surface or absence of glazed or polished surface
R S M T V
showed some evidence of slight pitting. Only three restorations received unsatisfactory ratings (Table IV). The ideal surface is defined as having a complete absence of pitting. Slight pitting can increase finishing time and result in a restoration of poor contour. Excessive or deep pitting can result in a nonfunctional restoration. Pitting provides information related to inherent alloy characteristics and possible sensitivity to laboratory handling. E. Polish/tarnish of surface. The polish of the Olympia alloy restorations was significantly better than that of the base-metal alloys. No statistically significant difference was evident between Olympia and W-l alloys, The differences that existed for the base-metal alloys were only of clinical interest. One out of 1183 restorations received an unsatisfactory rating. Ideal surface polish was defined as a uniformly glossy surface. The first three ratings R, S, and M reflect a glossy
THE
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OF PROSTHETIC
DENTISTRY
or dull surface and are satisfactory. The next two ratings (T and V) reflect tarnish and are unsatisfactory. Tarnish is defined, in this study, as a surface discoloration and/or a loss of the surface finish or luster. Because the restorations were evaluated after they were returned from the dental laboratory, tarnish (unsatisfactory ratings) was highly unlikely. All restorations except one were either uniformly glossy or glossy with localized dull areas. The noble alloys Olympia and W-l had a larger percentage of the highest rating (R). A high surface polish can be associated with low to medium alloy hardness that allows ease of finishing and polishing. Highly polished surfaces help in the prevention of plaque accumulation. F. Pitting of connector/solder joint surface (critical criterion). The sample size for this criterion is smaller because it only applies to fixed partial dentures that were presoldered. No statistically significant differences existed
199
C8P
Table
III.
Comparison of Olympia (control alloy) with W-l, Ticon, Ceramalloy
Criteria
N
A Fit on die# Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond B Retention on die Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond C Marginal integrity# Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond
II N/P2
II N/P2
II N/P2
D Pitting of surface#
Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 E Polish/tarnish
of surface
Olympia Versus W-l Versus Ticon
Versus Ceramalloy II Versus Micro-Bond N/P2 F Pitting of connector/solder Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond
joint#
II N/P2
1116 556 141 143 142 134 1114 555 141 143 142 133 1114 555 141 143 142 133 1198 598 152 151 150 147 1183 592 150 147 150 144 326 159 43 35 48 41
NO.
1471242
AND
MORRIS
II, and Micro-bond N/P2 alloys Significant clinical difference
Dunnett’s test
Mean
SD
Diff
4.55 4.68 4.66 4.54 4.64
0.65 0.51 0.60 0.76 0.68
0.13 0.11 -0.01 0.09
4.51 4.71 4.73 4.65 4.77
0.79 0.59 0.63 0.55 0.56
0.20 0.22 0.14 0.26
4.23 4.23 4.11 4.25 4.03
0.74 0.75 0.77 0.76 0.78
0.00 -0.12 0.02 -0.20
4.73 4.72 4.58 4.61 4.63
0.49 0.48 0.62 0.53 0.54
-0.01 -0.15 -0.12 -0.10
** *
NCD CI CI NCD
4.71 4.72 4.59 4.41 4.58
0.47 0.45 0.49 0.60 0.51
0.01 -0.12 -0.30 -0.13
* ** *
NCD CI CI CI
4.79 4.72 4.57 4.60 4.83
0.51 0.63 0.65 0.68 0.38
-0.07 -0.22 -0.19 0.04
NCD NCD NCD NCD
** ** **
CI CI NCD CI
*
NCD NCD NCD CI
NCD NCD NCD NCD
#Critical criteria. Diff, (Alternative alloy mean)-(Olympia mean); *, significant at 0.05 alpha level, Dunn&t’s test; **, significant at 0.01 alpha level, Dunnett’s test; NCD, no clinical difference-no significant statistical difference exists and means differ by less than 1 unit+; CI, clinical interest-significant statistical difference exists and means differ by less than 1 unit +; while these differences may not be clinically significant at this time, clinician should be aware that they exist. CSD, Clinically significant difference-significant statistical difference exists and means differ by more than 1 unit +, which is believed to be large enough to be clinically significant. +One unit is equal to one level on ordinal rating scale used in this study for all evaluations except “overall score” where 2 units approximate one level in ordinal rating scale.
between Olympia and any of the other solder joint connectors for the alternative alloys. Ideal pitting was defined as a complete absence thereof. A pitted connector could cause weakening and possible failure of the fixed prosthesis. For this reason, this was a critical criterion in the overall evaluation. G. Polish/tarnish
of connectors.
The Olympia
alloy
connectors were significantly better than Ceramalloy II alloy. Although statistically significant, the difference was
200
small and of clinical interest only. One of 328 connectors received an unsatisfactory rating. This rating scale was identical to the rating scale for polish/tarnish of the alloy surface. All solder joints except one were uniformly glossy or glossy with localized dull areas. Olympia (presolder) and W-l (Williams Ceramic solder) connectors received the highest percentage of R ratings. Eleven solder joints were evaluated as uniformly dull compared with two evaluations for polish/tarnish of the
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VOLUME
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NUMBER
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COMPARISON
Table
III.
OF METAL
CERAMIC
RESTORATIONS
Cont’d.
N
Criteria
G Polish/tarnish of connector solder joint Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond NiP2 H Veneer-to-metal integrity# Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 I Veneer esthetics (porcelain color)# Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 J Crazing of porcelain Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond NIP2 K Glaze of porcelain Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2
328 159 43 36 49 41 1202 601 152 151 150 148 1202 601 152 151 150 148 1202 601 152 151 150 148 1202
restoration surface. These results may reflect inherent characteristics of the solder system or they may reflect the limited finishing access typical for connector surfaces. H. Veneer-to-metal integrity (critical criterion). The veneer-metal interface of the Olympia alloy restorations was significantly better than Ceramalloy II alloy. This difference was of clinical interest. No statistically significant difference was found when Olympia alloy was compared with the other alternative alloys. Only one of the restorations received an unsatisfactory rating. Ideal porcelain-to-metal integrity was defined as an intact porcelain-to-metal interface. The study protocol required that all restorations have metal occlusal surfaces and facial metal collars. Changes in quality of veneerto-metal integrity could occur at the junction of the porcelain and metal on the occlusal surface or at the junction of the porcelain-to-metal collar. Preparation design for the facial surface was a beveled shoulder or beveled chamfer with a metal margin placed subgingivally to evaluate “local biocompatibility.” Poor quality of the veneer-to-metal
THE
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DENTISTRY
Dunnett’s test
Significant clinical difference
Mean
SD
Diff
4.69 4.72 4.41 4.31 4.61
0.53 0.50 0.56 0.68 0.54
0.03 -0.22 -0.38 -0.08
4.77 4.68 4.73 4.65 4.70
0.48 0.51 0.46 0.54 0.53
4.67 4.68 4.65 4.60 4.61
0.52 0.54 0.52 0.63 0.57
0.01 -0.02 -0.07 -0.06
NCD NCD NCD NCD
4.93 4.95 5.00 4.95 4.88
0.43 0.29 0.00 0.35 0.56
0.02 0.07 0.02 -0.05
NCD NCD NCD NCD
601 152 151 150 148
4.32 4.24 4.31 4.31 4.29
**
NCD NCD CI NCD
*
NCD NCD CI NCD
-0.09
-0.04 -0.12 -0.07
0.94 0.98
-0.08
0.94 0.94 0.95
-0.01 -0.01 -0.03
NCD NCD NCD NCD
interface in this location could adversely affect periodontal health. Fracture of the porcelain-to-metal junction itself could result in failure. Veneer-to-metal integrity reflects the quality of the porcelain-to-metal interface. This quality is dependent on the compatibility of the expansion/ contraction characteristics of the porcelain and metal as well as porcelain-to-metal bond strengths. I. Veneer esthetics (critical criterion). No significant difference existed between Olympia and any of the alternative alloys. Providing the correct porcelain color over base-metal alloys is more difficult when compared with gold-containing alloys. When base-metal alloys oxidize, the oxide layer formed is a dark grey-black that could be difficult to mask with the application of the opaque porcelain. Thus it could be more difficult to match the shade guide when base-metal alloys are used. The frequency distribution shows that although approximately a third of all the restorations did not match the shade guide when returned from the dental laboratory, this finding was not related to the alloy used.
201
CSP NO. 1471242 AND MORRIS
Table IV. Frequency distribution
for each criterion and alloy Satisfactory
Criteria
N
A Fit on die# Olympia Ticon Ceramalloy II Micro-Bond N/P2 B Retention# Olympia
M (%**)
T (%**)
v (%**)
Ticon Ceramalloy II Micro-Bond N/P2 C Marginal integrity Olympia W-l Ticon Ceramalloy II Micro-Bond NiP2 D Pitting of surface# Olympia W-l Ticon Ceramalloy II N/P2 of surface
II
212 39 36 43 33
(38.2) (27.7) (25.2) (30.3) (24.8)
6 3 4 5 3
(1.1) (2.1) (2.8) (3.5) (2.3)
340 107 113 97 109
(61.4) (75.9) (79.1) (68.3) (81.8)
187 29 25 40 20
(33.8) (20.6) (17.5) (28.2) (15.2)
10 4 2 5 3
(1.8) (2.8) (1.4) (3.5) (2.3)
3 0 2 0 0
214 55 44 58 40
(38.5) (39.0) (30.8) (40.9) (30.3)
264 66 76 65 59
(47.7) (46.8) (53.2) (45.8) (44.7)
69 18 20 16 31
(12.5) (12.8) (14.0) (11.3) (23.5)
444 112 96 94 96
(74.2) (73.7) (63.6) (62.7) (65.1)
145 38 47 53 49
(24.3) (25.0) (31.1) (35.3) (33.5)
8 2 7 3 1
425 108 86 79 85
(71.7) (72.0) (58.5) (46.7) (58.7)
165 42 61 71 58
(27.9) (28.0) (41.5) (47.3) (40.6)
131 34 23 34 35
(82.4) (79.1) (65.7) (70.8) (85.0)
23 7 9 9 6
114 32 18 21 27
(72.7) (74.4) (50.0) (42.9) (65.0)
42 10 17 22 13
7 0 1 3 2
(1.3) (0.0) (0.7) (2.1) (1.5)
(0.5) (0.0) (1.4) (0.0) (0.0)
14 1 1 0 1
(2.5) (0.7) (0.7) (0.0) (0.8)
5 1 1 2 2
(0.9) (0.7) (0.7) (1.4) (1.5)
3 1 2 1 0
(0.5) (0.7) (1.4) (0.7) (0.0)
(1.3) (1.3) (4.6) (2.0) (0.7)
1 0 1 0 1
(0.2) (0.0) (0.7) (0.0) (0.7)
-
1 0 0 0 1
(0.2) (0.0) (0.0) (0.0) (0.7)
1 0 0 0 0
(0.2) (0.0) (0.0) (0.0) (0.0)
-
(14.5) (16.3) (25.7) (18.8) (15.0)
4 1 3 5 0
(2.5) (2.3) (8.6) (10.4) (0.0)
1 1 0 0 0
(0.6) (2.3) (0.0) (0.0) (0.0)
-
(26.4) (23.3) (47.2) (44.9) (32.5)
2 1 1 6 1
(1.3) (2.3) (2.8) (12.2) (2.5)
1 0 0 0 0
(0.6) (0.0) (0.0) (0.0) (0.0)
-
-
1198
1183
Ticon
Micro-Bond N/P2
(59.5) (70.2) (71.3) (64.1) (71.4)
1114
Olympia W-l Ceramalloy II Micro-Bond N/P2 F Pitting of connector/solder joint surface# Olympia W-l Ticon Ceramalloy II Micro-Bond N/P2 G Polish/tarnish of connector/solder joint Olympia W-l
-
331 99 102 91 96 1114
W-l
Ticon Ceremslloy
s (%**)
1116
W-l
Micro-Bond E Polish/tarnish
R (%**)
Unsatisfactory
326
328
#Critical criteria. **Percentage of restorations receiving this rating for each alloy.
J. Crazing of porcelain. No statistically significant differences existed between Olympia and any of the alternative alloys. Thirty-four restorations (2.83 % ) showed some crazing. Micro-Bond N/P2 alloy had eight unsatis-
factory ratings. An incompatibility
between the porcelain
and metal could produce stresses in the porcelain that can cause crazing or fracture. This may explain the crazing of the restorations.
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Table IV. Co&d. Unsatisfactory
Satisfactory N
Criteria
H Veneer to metal integrity# Olympia W-l Ticon Ceramalloy II Micro-Bond N/p2 I Veneer esthetics (porcelain color)# Olympia W-l Ticon Ceramalloy II Micro-Bond N/F’2 J Crazing Olympia
JOURNAL
T (%**)
(79.2) (69.7) (73.5) (68.7) (74.2)
115 43 39 42 33
(19.2) (28.3) (25.8) (28.0) (22.5)
9 3 1 5 5
(1.5) (2.0) (0.7) (3.3) (3.4)
1 0 0 0 0
(0.2) (0.0) (0.0) (0.0) (0.0)
v
(%a*)
412 107 100 98 96
(66.5) (70.4) (66.2) (65.3) (64.6)
184 42 50 48 50
(30.7) (27.6) (33.1) (32.0) (34.0)
1 3 0 0 0
(0.2) (1.3) (0.0) (0.0) (0.0)
4 1 1 4 2
(0.7) (0.7) (0.7) (2.7) (1.4)
-
12 1 0 2 5
(2.0) (0.7) (0.0) (1.3) (3.4)
192 (32.0) 52 (34.2) 50 (33.1) 49 (32.7) 48 (32.7)
3 2 0 0 1
(0.5) (1.3) (0.0) (0.0) (0.7)
-
1202 -
1202 583 (97.0) 147 (96.7) 151 (100) 147 (98.0) 140 (94.6)
II N/P2
-
6 4 0 1 3
(1.0) (2.6) (0.0) (0.7) (2.0)
1202 394 92 97 96 93
II N/P2
(65.5) (60.5) (64.2) (64.0) (62.6)
comparison
of alloys
Differences observed among the alloys with regard to individual criteria are important. It is of greater value to compare the total overall performance of the alloys in an effort to obtain more clinically relevant information. This necessitated the development of an entirely different concept in the evaluation of restorations for this study-an overall performance, which was divided into an overall rating (scale 1 to 5) and an overall score (scale 1 to 1O).2oIt combines all the criteria to provide an evaluation of overall performance. Certain criteria were designated as more “critical” and were given greater consideration. These criteria have been identified.2o
THE
M (%**)
476 106 111 103 110
K. Glaze of porcelain. No statistically significant differences existed between Olympia and any of the alternative alloys. Glaze of porcelain may be indirectly related to individual alloys. The frequency distribution table (Table IV) shows a larger number of M ratings (glaze missing in large surfaces). Slight pitting on the surface was also evident. This is the lowest satisfactory rating that can be given and approximately a third of all the restorations received this rating. When polishing is near the metal-to-porcelain interface, the porcelain may be abraded, which may explain the surface lacking glaze. II. Overall
s (%**)
1202
W-l
Ticon Ceramalloy Micro-Bond K Glaze Olympia W-l Ticon Ceramalloy Micro-Bond
R (%**)
OF PROSTHETIC
DENTISTRY
12 6 4 5 6
(2.0) (4.0) (2.7) (3.3) (4.1)
-
The overall ratings and scores were compared by use of Dunnett’s test (Table V). No differences existed between Olympia and any of the alternative alloys when all of the criteria were combined. On overall performance, the alternative alloys were similar in quality to Olympia when evaluated at precementation. Clinical interpretation of the performance of the alloys is difficult because a combination of variables determines clinical performance and alloy selection. The results of this study suggest that while differences of clinical interest exist for many of the criteria, when the alloys were compared for overall performance-an overall rating and score-no statistically or clinically significant differences were evident. Other variables such as mechanical properties, castibility, casting sensitivity, casting accuracy, ease of handling, ease of soldering, sag resistance, potential for greening, porcelain/metal compatibility, tarnish/corrosion resistance, biocompatibility, and unit cost, which are not included in this article, must be considered in selecting an alloy. Furthermore, these evaluations represent precementation findings. It is possible that as a result of clinical function, some of the significantly different but not clinically significant criteria may deteriorate further and ultimately increase to be considered clinically significant. Clinical performance during clinical function will be reported shortly.
203
CSP NO.
1471242
AND
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Table V. Comparison of overall evaluations of Olympia (control alloy) with W-l, Ticon, Ceramalloy II, and Micro-Bond N/P2 alloys Criteria
Overall rating Olympia VersusW-l VersusTicon VersusCeramalloy II VersusMicro-Bond N/P2 Overall scorell Olympia Versus W-l VersusTicon Versus Ceramalloy II Versus Micro-Bond N/P2
N 1084 541 137 137 139 130 1084 541 137 137 139 130
Dunnett’s test
Significant clinical difference
Mean
SD
Diff
3.84 3.87 3.80 3.72 3.68
0.75 0.69 0.68 0.72 0.76
0.03 -0.04 -0.12 -0.16
NCD NCD NCD NCD
9.30 9.39 9.32 9.21 9.19
0.04 0.75 0.90 0.08 0.02
0.09 0.02 -0.09 -0.11
NCD NCD NCD NCD
I, Oveml rating = rating scale of 1 to 5 (worse to better); 11,overall wore = rating scale of 1 to 10 (worse to better). Remainder of key is in footnote to Table III.
Because small differences in the composition of an alloy can produce major differences in its properties, caution must be used in trying to apply the results of this study to other alloys with similar chemical formulations. It is important to note that the recorded differences are the result of well-controlled laboratory conditions that were established and maintained for the duration of this study, and that slightly different conditions in other dental laboratories and studies may produce slightly different results.
CLINICAL
SIGNIFICANCE
This report compares restorations made from alternative alloys with those of Olympia, a gold-containing alloy, as they were received from the dental laboratory. The results show that, for several individual criteria, statistically significant differences between alternative alloys and an AuPd control alloy exist, although at precementation they are not large enough to be considered clinically significant. When the overall performances of the alloys were compared, the differences among the alloys were neither statistically nor clinically significant. Nevertheless, the observed differences are of clinical interest because they may represent weaknesses that could progressively deteriorate with time during prolonged clinical function.
CONCLUSIONS 1. Significant differences were found between Olympia alloy and some of the alternative alloys for the following precementation criteria: retention on the die, marginal integrity, pitting of metal surface, polish/tarnish of metal surface, polish/tarnish of connector/solder joint surface, and veneer-to-metal integrity. 2. No statistically significant differences were found be-
204
tween Olympia alloy and any of the alternative alloys for fit on die, pitting of connector/solder joint surface, veneer esthetics (porcelain color), crazing of porcelain, and glaze of porcelain. 3. Olympia alloy was significantly better than one or more of the base metal alloys for the precementation criterion of marginal integrity, pitting of surface, polishltarnish of surface, polish/tarnish of connector/solder joint surface, and veneer-to-metal integrity. 4. The base metal alloys, Ticon and Micro-Bond N/P2, were significantly better than Olympia alloy for the precementation criterion of retention on die. No other base metal alloy in any of the other criteria performed better than Olympia alloy. 5. Olympia alloy was not significantly better than W-l alloy for any of the precementation criteria. 6. W-l alloy was significantly better than Olympia alloy for the precementation criterion of retention on die. 7. For total overall performance (combining all criteria in the overall rating), Olympia alloy was not significantly better than any of the alternative alloys. 8. The overall score showed no significant differences between Olympia alloy and any of the alternative alloys for the combined criteria evaluated on dies before cementation. 9. All statistically significant differences exhibited were not of sufficient magnitude to be considered clinically significant. They were of clinical interest only, inasmuch as their means did not differ by more than 1 unit. REFERENCES 1.
Valega TM. Alternative to gold alloys in dentistry. U.S. Dept of Health, Education, and Welfare Publication No (NIH) 77-1227, Washington DC: Government Printing Office, 1977.
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2. Eden GT, Franklin OM, Powell JM, et al. Fit on porcelain fused to metal crown and bridge casting. J Dent Res 1979;5832360-8. 3. Duncan JD. The casting accuracy of nickel-chromium alloys for fixed prostheses. J PROSTHET DENT 1982;47:63-8. 4. Espevik S. Corrosion of base metal alloys in vitro. Acta Odontol Stand 1978;36:113-6. 5. Raucher F. The action of trace minerals of concern to dentistry. Part II. NY State Dent ,J 1979:45:273-5. 6. Woody RD, Huget EF, Horton JE. Apparent cytotoxicity of base metal casting alloys. J Dent Res 1977;56:739-43. 7. Bergman M, Berman B, Soremark R. Tissue accumulation of nickel released due to electrochemical corrosion of non-precious dental casting alloys. J Oral Rehabil 1980;7:325-30. 8. Pettersen AH, Jacobsen N. Nickel corrosion of non-precious casting alloys and cytotoxic effect of nickel in vitro. J Biomed Eng 1978;2:419-21. 9. Molfa JP, Guckes AD, Okawa MT, et al. An evaluation of non-precious alloys for use with porcelain veneers. Part II. Industry safety and biocompatibility. J PROSTHET DENT 1973;30:432-41. 10. Adrian JC, Huge& EF. Tissue responses to base-metal dental alloys. Milit Med 1977;142:748-86. 11. Civjan S, Huge& EF, Godfrey GD, et al. Effects of heat treatment on mechanical properties of two nickel-chromium-based casting alloys. J Dent Res 1972;51:1537-45. 12. Moffa JP, Lugassy AA, Guckes AD, et al. An evaluation of nonprecious alloys for use with porcelain veneers. Part I. Physical properties. J PROSTHET DENT 1973;30:424-31. 13. Hesby DA, Kobes P, Garver DC, et al. Physical properties of a repeatedly used nonprecious metal alloy. J PROSTHET DENT 1980;44:291-3. 14. Wight TA, Bauman JC, Pelleu GB. An evaluation of four variables affecting the bond strength of porcelain to nonprecious alloys. d PROSTHET DENT 1977;37:570-7. 15. Vincent PF, Stevens L, Basford KE. A comparison of the casting ability of precious and nonprecious alloys for porcelain veneering. J PROSTHET DENT 1977;37:527-36. 16. Thomas DH. A study of an increased mold temperature on the casting ability of some nonprecious alloys for porcelain veneers. J PROSTHET DENT 1982;48:52-8. 1.7. Moffa JP, Ellison JE, Hamilton JC. Incidence of nickel sensitivity in dental patients. [Abstract]. J Dent Res 1983;62:199. March 1983 (Abstr No. 271) p. 199. 18. Moffa JP, Jenkins WA, Ellison JA, et al. A clinical evaluation of two base-metal alloys and a gold alloy for use in fixed prosthodontics: a five-year study. J PROSTHET DENT 1984;52:491-500. 19. Morris HF, et al. Veterans Administration Cooperative Studies Project No. 147; Part I: A multidisciplinary, multicenter experimental design for the evaluation of alternative metal ceramic alloys. J PROSTHET DENT 1986;56:402-6. 20. Morris I-IF, et al. Veterans Administration Cooperative Studies Project No. 147; Part II: A new assessment system for rating metal ceramic crowns. J PROSTHET DENT 1986;56:546-51. 21. Dunnett CW. New tables for multiple comparisons with a control. Biometrics 1964;20:482-91. Reprint requests to: DR. HAROLD F. MORRIS (154) VA MEDICAL CENTER 2215 FULLER RD. ANN ARBOR, MI 48105
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ADDENDUM Authors: Warren M. Stoffer, D.M.D., Veterans Administration (VA) Medical Center, and Clinical Associate Professor, University of Pittsburgh, School of Dental Medicine, Pittsburgh Pa.; Linda Didenko, M.S. (Study Biostatistician), VA Hospital, Hines Ill.; Adele Gray, D.D.S., VA Medical Center, Ann Arbor, Mich.; James Lockwood, D.D.S., VA Medical Center, Ann Arbor, Mich.; Dennis Weir, D.D.S., M.A., VA Medical Center, and Assistant Clinical Professor, University of California San Francisco, School of Dentistry, San Francisco, Calif.; E. Richard McPhee, D.D.S., M.S., Consultant, VA Medical Center, and Professor of Prosthodontics, University of Michigan, School of Dentistry, Ann Arbor, Mich.; Norman Glasscock, D.D.S., VA Medical Center, Hampton, Va.; Sheldon Winkler, D.D.S., Temple University, School of Dentistry, Philadelphia, Pa.; Alan Helisek, C.D.T., VA Medical Center, Ann Arbor, Mich. Coauthors: John Blankenship, D.D.S., M.S.; James Pikulski, D.D.S.; Thomas Stein, D.M.D., M.S.; Gregory Movsesian, D.D.S.; Frank Lauciello, D.D.S.; John Mozrall, D.D.S.; Roger Cwynar, D.M.D.; Richard Navarro, D.D.S., MS.; Stephen Schlimmer, D.D.S.; Micheal Mackey, D.D.S.; Terry O’Toole, D.D.S.; Raul Caffesse, D.D.S., M.S.; David Irvin, D.D.S.; Alan Cantor, Ph.D. Executive Committee: Harold F. Morris, D.D.S., M.S., Chairman; Linda Didenko, M.S.; Warren M. Stoffer, D.M.D.; Dennis Weir, D.D.S., M.A.; Norman Glasscock, D.D.S.; Alan Helisek, C.D.T.; E. Richard McPhee, D.D.S., M.S.; Raul Caffesse, D.D.S., M.S.; Robert Lorey, D.D.S., M.S. (Ad hoc). Data Monitoring Board: Gunnar Ryge, D.D.S., M.S., Chairman; Marjorie Swartz, B.S., M.S.; Bart Hsi, Ph.D.; William Gillette, D.D.S.; Joseph Moffa, D.D.S., MS. Statistical Coordinating Center: William G. Henderson, Ph.D.; Linda Didenko, M.S.; Roland Mais, M.S.; Barbara Christine; Jean Rowe. Chairman’s Office: Harold F. Morris, D.D.S., M.S.; Patricia M. Zawadzki, R.D.H., M.S.; Peggy A. Piech; Beverly K. Barnes. Clinical Research Assistants: Nancy Bernat; Anne Cade; Greer Collins; Kari Gregerson; Mary Petrie; Mary Ann Steffensmeier; Sandra Reed.
205
of CSP No. 147,* and Harold F. Morris, Medical Center, Ann Arbor, Mich.
No.
D.D.S., MS.**
Veterans Administration
This analysis compared the precementation quality of metal ceramic restorations made from different alternative alloys after they had been returned from the central dental research laboratory. Ticon, Micro-Bond N/P2, Ceramalloy II, and W-l materials were evaluated by use of 11 well-defined criteria and for overall performance. The evaluations were compared with those of Olympia, a goldcontaining alloy, which served as the control. The results showed statistically sign&ant differences between Olympia alloy and some of the alternative alloys for six of the 11 criteria. These differences, however, were not sufficient to be considered clinically significant (clinically detectable). In the comparison of their overall performances no statistically significant differences were found. (J PROSTHET DENT 1991;65:196-206.)
N
umerous investigators have reported on the advantages and disadvantages of the alternative alloys for metal ceramic restorations.‘-l7 However, with the exception of Moffa et al’s &year investigation,18 limited data are available based on comprehensive, long-term clinical studies. It is imperative that alloys used in dentistry be capable of producing quality restorations that will function for a reasonable period of time while maintaining the health of natural teeth and their supporting tissues. The main purpose of CSP No. 147 was to compare the clinical behavior of several alternative alloys with Olympia (J. F. Jelenko & Co., Armonk, N.Y.), an alloy containing 51.5% gold, for metal ceramic restoration during 10 years of clinical function. This analysis compared approximately 1200 metal ceramic restorations
(crowns and fixed partial
dentures) on dies, before cementation by use of welldefined, clinically
METHOD
relevant
criteria.
AND MATERIAL
In this study two restorations were made for each of the 600 patients, one from Olympia alloy (control) and the other from an alternative alloy (Ticon, Micro-Bond N/P2, Ceramalloy II, or W-l) (Table I) according to a randomized, paired-comparison experimental design.lg Six Veter-
Supported by the Veterans Administration Medical Research Service/Cooperative Studies Program and the National Institute of Dental Research, Interagency contract No. lYOl-DE50004-00, and conducted by the Veterans Administration CSP Nos. 147/242 Dental Research Group. *Complete authorship appears on last page of article. **Study Chairman; Director, Clinical Research Center for Restorative Materials; and Clinical Assoicate Professor, University of Michigan, School of Dentistry, Ann Arbor, Mich. 10/l/22257
196
ans Administration Medical Centers (Allen Park and Ann Arbor, Mich.; Buffalo, N.Y.; Pittsburgh, Pa.; and San Diego and San Francisco, Calif.) participated in the study. Each center had two investigators, designated as Principal Investigator One (PI-l) and Principal Investigator Two (PI-2). PI-1 provided all restorative dental treatment and PI-2 completed all periodontal treatment. The investigators were standardized in all criteria at a l-week training session, at the beginning of the study. Training was repeated at semiannual meetings. The wax patterns were cast in a phosphate-bonded investment (Ceramigold, Whip-Mix Corp., Louisville, Ky.) following manufacturer’s instructions. Ceramco porcelain was used for all alloys except W-l, which required WillCeram porcelain (Table I). Appropriate solders (Table I) were used to join units for fixed partial dentures. The restorations were returned to the participating VA Medical Centers for evaluation on dies by clinical investigators using study criteria (Table II). The restorations were independently evaluated by each investigator and conflicts were resolved by consensus. To avoid bias, the identity of the alloys was not disclosed.lg The restorations were evaluated based on a rating process that considered certain criteria more important than others.20 R, S, M ratings were satisfactory whereas T and V ratings were unsatisfactory and were considered clinically significant. The results of the evaluations were statistically compared using Dunnett’s test.21 This test simultaneously controls for type 1 errors in comparing a control to different treatment groups. Analysis of ordinal ratings often resulted in statistically significant differences between the means. However, this does not necessarily indicate that the differences were large enough to be clinically significant. Criteria were established to facilitate the transfer of the statistical results into
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Table
I.
OF METAL
CERAMIC
RESTORATIONS
Alloys, presolders, and porcelains
Olympia (control alloy) J. F. Jelenko & Co. Armonk, N.Y. Ticon Ticonium, Co. Albany, N.Y. Ceramalloy II Johnson & Johnson Dental Products co. East Windsor, N.J. Micro-Bond N/P2 Austenal Dental, Inc., A Nobelpharma co. Chicago, Ill. W-l Williams Dental Co., Inc. Buffalo, N.Y.
Olympia, Presolder J. F. Jelenko & Co. Will-Ceram Super White Williams Dental Co., Inc. Buffalo, N.Y. Ceramalloy High Fusing Solder Johnson & Johnson Dental Products co.
OF PROSTHETIC
DENTISTRY
Ceramco Johnson & Johnson Dental Products Co.
Ceramco Johnson & Johnson Dental Products Co.
Williams Ceramic Solder (special high fusing white) Williams Dental Co., Inc.
Will-Ceram Williams Dental Co. Inc.
*One unit is equal to one level on the ordinal rating scale used in this study for all evaluations except “overall score” where two units approximate one level in the ordinal rating scale.
JOURNAL
Ceramco Johnson & Johnson Dental Products co. Ceramco Johnson & Johnson Dental Products Co.
Micro-Bond N/P2 Presolder Austenal Dental, Inc., A Nobelpharma co.
clinically relevant information (Table III). These criteria provided for three levels of clinical significance. 1. No clinical difference (NCD). No statistically significant difference exists and the means differ by less than 1 unit. * 2. Clinical interest (CI). A statistically significant difference exists and the means differ by less than 1 unit.* (Although these clinical interest differences may not be clinically significant at this time, the dentist should be aware that they exist and that a trend has been established that may be expected to increase with continued clinical use.) 3. Clinically significant difference (CSD). A statistically significant difference exists and the means differ by more than 1 unit,* which is believed to be large enough to be clinically significant and can be expected to increase with time. In addition to evaluating the restorations on individual criteria, an overall or total performance score reflected the behavior of an alloy for all criteria. This total performance score was divided into an “overall rating” and an “overall score.“2o In general, the overall rating was based on a fivepoint scale and the overall score was based upon an expanded lo-point scale to permit the distinction of finer differences. It should be noted that when evaluations for a criterion were somehow omitted, not legible, or their accuracy questioned, they were not included in the analysis. This procedure was necessary to prevent the introduction of bias during the attempt to recover these evaluations.
THE
Porcelains
Presolder
Alloy
RESULTS AND DISCUSSION I. Comparison of the individual
criteria
The frequency distribution of the evaluations for each alloy and criterion is provided in Table IV. Only limited information can be obtained from this table. For example, it appears that Olympia alloy had more unsatisfactory evaluations (T, V) than did any of the alternative alloys. This was because a larger number of restorations were made from Olympia alloy (n = 556). It represented only 1.3% of the total Olympia alloy restorations compared with 2.1% for the Ceramalloy II alloy restorations. Meaningful conclusions cannot be formulated without information as to (1) which alloy means are statistically different, (2) which criteria are statistically different, (3) how the alloys compare in their overall evaluations, and (4) when statistically significant, which differences are large enough to be considered clinically relevant (Tables III and V). Statistically significant differences were found when the means of the alternative alloys were compared with Olympia alloy by use of Dunnett’s test for the following criteria: retention on die, marginal integrity, pitting of surface, polish/tarnish of surface, polish/tarnish of connector/solder joint, and veneer-to-metal integrity (Table III). These statistical differences represented six out of 11 criteria evaluated. Results from all 11 criteria are listed. Certain criteria were judged to be of critical importance and were designated critical criteria. 2oThe criteria were as follows. A. Fit on die (critical criterion). No significant statistical differences were found between Olympia and any of the alternative alloys (Table III). Only 13 (0.01%) of all 1116 restorations received unsatisfactory ratings (Table IV). 197
CSP
Table
II.
Clinical
criteria,
rating scale with definitions
and critical
Rating
1471242
AND
MORRIS
elements
Criteria
v
Fit on die# Casting seats on die with light force and margins coincide with finish lines. Casting seats on die without force so that margins coincide with finish lines. Casting seats on die with moderate force; however there is some interference so that margins coincide with finish lines. Casting fails to seat on die with moderate force or finish lines exposed 0.25 mm or casting is unstable.
R S M T v
Retention Die retained in casting when inverted, can be removed with light force. Die not retained in casting when inverted, but casting stable when seated. Die retained in casting when inverted and can be removed only with moderate force. Die retained in casting when inverted and casting can be removed only with extensive force. Casting rocks or rotates slightly on die, indicating lack of stability.
R S M T v
Marginal integrity# Not detectable or scarcely detectable with explorer Slightly under/over extended or slightly detectable with explorer Moderately under/over extended or moderately detectable with explorer Decidedly under/over extended or decidedly detectable with explorer Margin open, explorer can penetrate into tooth restoration interface.
R S M T v
Pitting of surface# Uniformly smooth, no pits evident Barely detectable local pits removable in finishing and polishing process Moderate local pitting, removable in finishing and polishing process Decidedly local or generalized pitting; removal necessitates alteration of dimensions and contours Deeply pitted; removal necessitates alteration of dimensions and contours
R S M T v
Polish/tarnish of surface Uniformly glossy, highly shined appearance Glossy with local dull areas (scratches) Uniformly dull (scratches) Locally tarnished Generally tarnished
R S M
Sating key: R, 5; S, 4; M, 3; T, 2; V, 1. R, #Critical criteria.
S,
and M, satisfactory;T
and V, unsatisfactory.
Light seating force or no force (passive fit) reflects the investigators’ definition of ideal fit. If a casting fails to seat on a die passively, this could result in abrasion or distortion of the die, which would produce an unacceptable fit on the tooth. Fit on die provides information related to possible sensitivity to laboratory procedures. B. Retention on die. W-l, Ticon, and Micro-Bond N/ P2 alloys were retained on their dies significantly better (alpha level 0.01) than Olympia alloy. However, these differences were only of clinical interest because the difference between their means was less than 1 unit (Table III). Twenty-two (0.02 X) of 1114 restorations received unsatisfactory ratings (Table IV). Ideal retention was defined as a casting that would be retained on the die when inverted and would require a light force for removal. A casting that drops off the die easily may
result in a loose, nonretentive restoration. Alloys with poor retention on dies may be sensitive to laboratory handling of that alloy.
198
NO.
C. Marginal integrity on die (critical criterion). Micro-Bond N/P2 was the only alternative alloy whose marginal integrity was significantly lower in quality than the Olympia alloy restorations. Eighteen (0.02%) of 1114 restorations received unsatisfactory ratings. Ideal marginal integrity was defined as a nondetectable margin on tactile examination with a new explorer. Marginal integrity is a critical criterion because of its generally accepted influence on the longevity of the restoration and the health of the periodontium. Marginal integrity provides information related to inherent alloy characteristics as well as possible sensitivity to laboratory handling. D. Pitting of surface (critical criterion). Ticon and Ceramalloy II alloys were significantly worse than Olympia alloy although W-l and Micro-Bond
N/P2 alloys were not.
These differences, while of clinical interest, were less than 1 unit and therefore not large enough to be clinically significant. Olympia and W-l alloys were generally free of pitting whereas the base-metal restorations generally
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Table II. Cont’d. Criteria
Rating
R S M T v
Pitting of connector/solder joint surface# Uniformly smooth, no pits evident Barely detectable local pits removable in finishing and polishing process Moderate local pitting removable in finishing and polishing process Decidedly local or generalized pitting; removal necessitates alteration of dimensions and contours Deeply pitted; removal necessitates alteration of dimensions and contours
R S M T V
Polish/tarnish of connector/solder joint surface Uniformly glossy, highly shined appearance Glossy with local dull areas (scratches) Uniformly dull (scratches) Locally tarnished Generally tarnished
R S M T V
Veneer to metal integritya Not detectable or scarcely detectable with explorer Slightly detectable with explorer; porcelain slightly under/over extended, or under/over contoured Moderately detectable with explorer; porcelain moderately under/over extended, or under/over contoured Decidedly detectable with explorer as two-way catch indicating porcelain margin fracture Gross fracture of porcelain at or away from margin Veneer esthetics (porcelain color)# Not detectably different in color from shade guide tab Slightly different in color from shade guide tab Moderately different in color from shade guide tab Decidedly different in color from shade guide tab Definite mismatch
R T V
Crazing No crazing evident Minor crazing evident, but repairable Crazing evident, nonrepairable
R S M T
Glaze Uniformly glazed, smooth surface Glaze missing slightly in local area(s) Glaze missing in large areas(s); slight pitting on surface may be evident. Decided pitting of surface or absence of glazed or polished surface
R S M T V
showed some evidence of slight pitting. Only three restorations received unsatisfactory ratings (Table IV). The ideal surface is defined as having a complete absence of pitting. Slight pitting can increase finishing time and result in a restoration of poor contour. Excessive or deep pitting can result in a nonfunctional restoration. Pitting provides information related to inherent alloy characteristics and possible sensitivity to laboratory handling. E. Polish/tarnish of surface. The polish of the Olympia alloy restorations was significantly better than that of the base-metal alloys. No statistically significant difference was evident between Olympia and W-l alloys, The differences that existed for the base-metal alloys were only of clinical interest. One out of 1183 restorations received an unsatisfactory rating. Ideal surface polish was defined as a uniformly glossy surface. The first three ratings R, S, and M reflect a glossy
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or dull surface and are satisfactory. The next two ratings (T and V) reflect tarnish and are unsatisfactory. Tarnish is defined, in this study, as a surface discoloration and/or a loss of the surface finish or luster. Because the restorations were evaluated after they were returned from the dental laboratory, tarnish (unsatisfactory ratings) was highly unlikely. All restorations except one were either uniformly glossy or glossy with localized dull areas. The noble alloys Olympia and W-l had a larger percentage of the highest rating (R). A high surface polish can be associated with low to medium alloy hardness that allows ease of finishing and polishing. Highly polished surfaces help in the prevention of plaque accumulation. F. Pitting of connector/solder joint surface (critical criterion). The sample size for this criterion is smaller because it only applies to fixed partial dentures that were presoldered. No statistically significant differences existed
199
C8P
Table
III.
Comparison of Olympia (control alloy) with W-l, Ticon, Ceramalloy
Criteria
N
A Fit on die# Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond B Retention on die Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond C Marginal integrity# Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond
II N/P2
II N/P2
II N/P2
D Pitting of surface#
Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 E Polish/tarnish
of surface
Olympia Versus W-l Versus Ticon
Versus Ceramalloy II Versus Micro-Bond N/P2 F Pitting of connector/solder Olympia Versus W-l Versus Ticon Versus Ceramalloy Versus Micro-Bond
joint#
II N/P2
1116 556 141 143 142 134 1114 555 141 143 142 133 1114 555 141 143 142 133 1198 598 152 151 150 147 1183 592 150 147 150 144 326 159 43 35 48 41
NO.
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II, and Micro-bond N/P2 alloys Significant clinical difference
Dunnett’s test
Mean
SD
Diff
4.55 4.68 4.66 4.54 4.64
0.65 0.51 0.60 0.76 0.68
0.13 0.11 -0.01 0.09
4.51 4.71 4.73 4.65 4.77
0.79 0.59 0.63 0.55 0.56
0.20 0.22 0.14 0.26
4.23 4.23 4.11 4.25 4.03
0.74 0.75 0.77 0.76 0.78
0.00 -0.12 0.02 -0.20
4.73 4.72 4.58 4.61 4.63
0.49 0.48 0.62 0.53 0.54
-0.01 -0.15 -0.12 -0.10
** *
NCD CI CI NCD
4.71 4.72 4.59 4.41 4.58
0.47 0.45 0.49 0.60 0.51
0.01 -0.12 -0.30 -0.13
* ** *
NCD CI CI CI
4.79 4.72 4.57 4.60 4.83
0.51 0.63 0.65 0.68 0.38
-0.07 -0.22 -0.19 0.04
NCD NCD NCD NCD
** ** **
CI CI NCD CI
*
NCD NCD NCD CI
NCD NCD NCD NCD
#Critical criteria. Diff, (Alternative alloy mean)-(Olympia mean); *, significant at 0.05 alpha level, Dunn&t’s test; **, significant at 0.01 alpha level, Dunnett’s test; NCD, no clinical difference-no significant statistical difference exists and means differ by less than 1 unit+; CI, clinical interest-significant statistical difference exists and means differ by less than 1 unit +; while these differences may not be clinically significant at this time, clinician should be aware that they exist. CSD, Clinically significant difference-significant statistical difference exists and means differ by more than 1 unit +, which is believed to be large enough to be clinically significant. +One unit is equal to one level on ordinal rating scale used in this study for all evaluations except “overall score” where 2 units approximate one level in ordinal rating scale.
between Olympia and any of the other solder joint connectors for the alternative alloys. Ideal pitting was defined as a complete absence thereof. A pitted connector could cause weakening and possible failure of the fixed prosthesis. For this reason, this was a critical criterion in the overall evaluation. G. Polish/tarnish
of connectors.
The Olympia
alloy
connectors were significantly better than Ceramalloy II alloy. Although statistically significant, the difference was
200
small and of clinical interest only. One of 328 connectors received an unsatisfactory rating. This rating scale was identical to the rating scale for polish/tarnish of the alloy surface. All solder joints except one were uniformly glossy or glossy with localized dull areas. Olympia (presolder) and W-l (Williams Ceramic solder) connectors received the highest percentage of R ratings. Eleven solder joints were evaluated as uniformly dull compared with two evaluations for polish/tarnish of the
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Table
III.
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CERAMIC
RESTORATIONS
Cont’d.
N
Criteria
G Polish/tarnish of connector solder joint Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond NiP2 H Veneer-to-metal integrity# Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 I Veneer esthetics (porcelain color)# Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2 J Crazing of porcelain Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond NIP2 K Glaze of porcelain Olympia Versus W-l Versus Ticon Versus Ceramalloy II Versus Micro-Bond N/P2
328 159 43 36 49 41 1202 601 152 151 150 148 1202 601 152 151 150 148 1202 601 152 151 150 148 1202
restoration surface. These results may reflect inherent characteristics of the solder system or they may reflect the limited finishing access typical for connector surfaces. H. Veneer-to-metal integrity (critical criterion). The veneer-metal interface of the Olympia alloy restorations was significantly better than Ceramalloy II alloy. This difference was of clinical interest. No statistically significant difference was found when Olympia alloy was compared with the other alternative alloys. Only one of the restorations received an unsatisfactory rating. Ideal porcelain-to-metal integrity was defined as an intact porcelain-to-metal interface. The study protocol required that all restorations have metal occlusal surfaces and facial metal collars. Changes in quality of veneerto-metal integrity could occur at the junction of the porcelain and metal on the occlusal surface or at the junction of the porcelain-to-metal collar. Preparation design for the facial surface was a beveled shoulder or beveled chamfer with a metal margin placed subgingivally to evaluate “local biocompatibility.” Poor quality of the veneer-to-metal
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Dunnett’s test
Significant clinical difference
Mean
SD
Diff
4.69 4.72 4.41 4.31 4.61
0.53 0.50 0.56 0.68 0.54
0.03 -0.22 -0.38 -0.08
4.77 4.68 4.73 4.65 4.70
0.48 0.51 0.46 0.54 0.53
4.67 4.68 4.65 4.60 4.61
0.52 0.54 0.52 0.63 0.57
0.01 -0.02 -0.07 -0.06
NCD NCD NCD NCD
4.93 4.95 5.00 4.95 4.88
0.43 0.29 0.00 0.35 0.56
0.02 0.07 0.02 -0.05
NCD NCD NCD NCD
601 152 151 150 148
4.32 4.24 4.31 4.31 4.29
**
NCD NCD CI NCD
*
NCD NCD CI NCD
-0.09
-0.04 -0.12 -0.07
0.94 0.98
-0.08
0.94 0.94 0.95
-0.01 -0.01 -0.03
NCD NCD NCD NCD
interface in this location could adversely affect periodontal health. Fracture of the porcelain-to-metal junction itself could result in failure. Veneer-to-metal integrity reflects the quality of the porcelain-to-metal interface. This quality is dependent on the compatibility of the expansion/ contraction characteristics of the porcelain and metal as well as porcelain-to-metal bond strengths. I. Veneer esthetics (critical criterion). No significant difference existed between Olympia and any of the alternative alloys. Providing the correct porcelain color over base-metal alloys is more difficult when compared with gold-containing alloys. When base-metal alloys oxidize, the oxide layer formed is a dark grey-black that could be difficult to mask with the application of the opaque porcelain. Thus it could be more difficult to match the shade guide when base-metal alloys are used. The frequency distribution shows that although approximately a third of all the restorations did not match the shade guide when returned from the dental laboratory, this finding was not related to the alloy used.
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CSP NO. 1471242 AND MORRIS
Table IV. Frequency distribution
for each criterion and alloy Satisfactory
Criteria
N
A Fit on die# Olympia Ticon Ceramalloy II Micro-Bond N/P2 B Retention# Olympia
M (%**)
T (%**)
v (%**)
Ticon Ceramalloy II Micro-Bond N/P2 C Marginal integrity Olympia W-l Ticon Ceramalloy II Micro-Bond NiP2 D Pitting of surface# Olympia W-l Ticon Ceramalloy II N/P2 of surface
II
212 39 36 43 33
(38.2) (27.7) (25.2) (30.3) (24.8)
6 3 4 5 3
(1.1) (2.1) (2.8) (3.5) (2.3)
340 107 113 97 109
(61.4) (75.9) (79.1) (68.3) (81.8)
187 29 25 40 20
(33.8) (20.6) (17.5) (28.2) (15.2)
10 4 2 5 3
(1.8) (2.8) (1.4) (3.5) (2.3)
3 0 2 0 0
214 55 44 58 40
(38.5) (39.0) (30.8) (40.9) (30.3)
264 66 76 65 59
(47.7) (46.8) (53.2) (45.8) (44.7)
69 18 20 16 31
(12.5) (12.8) (14.0) (11.3) (23.5)
444 112 96 94 96
(74.2) (73.7) (63.6) (62.7) (65.1)
145 38 47 53 49
(24.3) (25.0) (31.1) (35.3) (33.5)
8 2 7 3 1
425 108 86 79 85
(71.7) (72.0) (58.5) (46.7) (58.7)
165 42 61 71 58
(27.9) (28.0) (41.5) (47.3) (40.6)
131 34 23 34 35
(82.4) (79.1) (65.7) (70.8) (85.0)
23 7 9 9 6
114 32 18 21 27
(72.7) (74.4) (50.0) (42.9) (65.0)
42 10 17 22 13
7 0 1 3 2
(1.3) (0.0) (0.7) (2.1) (1.5)
(0.5) (0.0) (1.4) (0.0) (0.0)
14 1 1 0 1
(2.5) (0.7) (0.7) (0.0) (0.8)
5 1 1 2 2
(0.9) (0.7) (0.7) (1.4) (1.5)
3 1 2 1 0
(0.5) (0.7) (1.4) (0.7) (0.0)
(1.3) (1.3) (4.6) (2.0) (0.7)
1 0 1 0 1
(0.2) (0.0) (0.7) (0.0) (0.7)
-
1 0 0 0 1
(0.2) (0.0) (0.0) (0.0) (0.7)
1 0 0 0 0
(0.2) (0.0) (0.0) (0.0) (0.0)
-
(14.5) (16.3) (25.7) (18.8) (15.0)
4 1 3 5 0
(2.5) (2.3) (8.6) (10.4) (0.0)
1 1 0 0 0
(0.6) (2.3) (0.0) (0.0) (0.0)
-
(26.4) (23.3) (47.2) (44.9) (32.5)
2 1 1 6 1
(1.3) (2.3) (2.8) (12.2) (2.5)
1 0 0 0 0
(0.6) (0.0) (0.0) (0.0) (0.0)
-
-
1198
1183
Ticon
Micro-Bond N/P2
(59.5) (70.2) (71.3) (64.1) (71.4)
1114
Olympia W-l Ceramalloy II Micro-Bond N/P2 F Pitting of connector/solder joint surface# Olympia W-l Ticon Ceramalloy II Micro-Bond N/P2 G Polish/tarnish of connector/solder joint Olympia W-l
-
331 99 102 91 96 1114
W-l
Ticon Ceremslloy
s (%**)
1116
W-l
Micro-Bond E Polish/tarnish
R (%**)
Unsatisfactory
326
328
#Critical criteria. **Percentage of restorations receiving this rating for each alloy.
J. Crazing of porcelain. No statistically significant differences existed between Olympia and any of the alternative alloys. Thirty-four restorations (2.83 % ) showed some crazing. Micro-Bond N/P2 alloy had eight unsatis-
factory ratings. An incompatibility
between the porcelain
and metal could produce stresses in the porcelain that can cause crazing or fracture. This may explain the crazing of the restorations.
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Table IV. Co&d. Unsatisfactory
Satisfactory N
Criteria
H Veneer to metal integrity# Olympia W-l Ticon Ceramalloy II Micro-Bond N/p2 I Veneer esthetics (porcelain color)# Olympia W-l Ticon Ceramalloy II Micro-Bond N/F’2 J Crazing Olympia
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T (%**)
(79.2) (69.7) (73.5) (68.7) (74.2)
115 43 39 42 33
(19.2) (28.3) (25.8) (28.0) (22.5)
9 3 1 5 5
(1.5) (2.0) (0.7) (3.3) (3.4)
1 0 0 0 0
(0.2) (0.0) (0.0) (0.0) (0.0)
v
(%a*)
412 107 100 98 96
(66.5) (70.4) (66.2) (65.3) (64.6)
184 42 50 48 50
(30.7) (27.6) (33.1) (32.0) (34.0)
1 3 0 0 0
(0.2) (1.3) (0.0) (0.0) (0.0)
4 1 1 4 2
(0.7) (0.7) (0.7) (2.7) (1.4)
-
12 1 0 2 5
(2.0) (0.7) (0.0) (1.3) (3.4)
192 (32.0) 52 (34.2) 50 (33.1) 49 (32.7) 48 (32.7)
3 2 0 0 1
(0.5) (1.3) (0.0) (0.0) (0.7)
-
1202 -
1202 583 (97.0) 147 (96.7) 151 (100) 147 (98.0) 140 (94.6)
II N/P2
-
6 4 0 1 3
(1.0) (2.6) (0.0) (0.7) (2.0)
1202 394 92 97 96 93
II N/P2
(65.5) (60.5) (64.2) (64.0) (62.6)
comparison
of alloys
Differences observed among the alloys with regard to individual criteria are important. It is of greater value to compare the total overall performance of the alloys in an effort to obtain more clinically relevant information. This necessitated the development of an entirely different concept in the evaluation of restorations for this study-an overall performance, which was divided into an overall rating (scale 1 to 5) and an overall score (scale 1 to 1O).2oIt combines all the criteria to provide an evaluation of overall performance. Certain criteria were designated as more “critical” and were given greater consideration. These criteria have been identified.2o
THE
M (%**)
476 106 111 103 110
K. Glaze of porcelain. No statistically significant differences existed between Olympia and any of the alternative alloys. Glaze of porcelain may be indirectly related to individual alloys. The frequency distribution table (Table IV) shows a larger number of M ratings (glaze missing in large surfaces). Slight pitting on the surface was also evident. This is the lowest satisfactory rating that can be given and approximately a third of all the restorations received this rating. When polishing is near the metal-to-porcelain interface, the porcelain may be abraded, which may explain the surface lacking glaze. II. Overall
s (%**)
1202
W-l
Ticon Ceramalloy Micro-Bond K Glaze Olympia W-l Ticon Ceramalloy Micro-Bond
R (%**)
OF PROSTHETIC
DENTISTRY
12 6 4 5 6
(2.0) (4.0) (2.7) (3.3) (4.1)
-
The overall ratings and scores were compared by use of Dunnett’s test (Table V). No differences existed between Olympia and any of the alternative alloys when all of the criteria were combined. On overall performance, the alternative alloys were similar in quality to Olympia when evaluated at precementation. Clinical interpretation of the performance of the alloys is difficult because a combination of variables determines clinical performance and alloy selection. The results of this study suggest that while differences of clinical interest exist for many of the criteria, when the alloys were compared for overall performance-an overall rating and score-no statistically or clinically significant differences were evident. Other variables such as mechanical properties, castibility, casting sensitivity, casting accuracy, ease of handling, ease of soldering, sag resistance, potential for greening, porcelain/metal compatibility, tarnish/corrosion resistance, biocompatibility, and unit cost, which are not included in this article, must be considered in selecting an alloy. Furthermore, these evaluations represent precementation findings. It is possible that as a result of clinical function, some of the significantly different but not clinically significant criteria may deteriorate further and ultimately increase to be considered clinically significant. Clinical performance during clinical function will be reported shortly.
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MORRIS
Table V. Comparison of overall evaluations of Olympia (control alloy) with W-l, Ticon, Ceramalloy II, and Micro-Bond N/P2 alloys Criteria
Overall rating Olympia VersusW-l VersusTicon VersusCeramalloy II VersusMicro-Bond N/P2 Overall scorell Olympia Versus W-l VersusTicon Versus Ceramalloy II Versus Micro-Bond N/P2
N 1084 541 137 137 139 130 1084 541 137 137 139 130
Dunnett’s test
Significant clinical difference
Mean
SD
Diff
3.84 3.87 3.80 3.72 3.68
0.75 0.69 0.68 0.72 0.76
0.03 -0.04 -0.12 -0.16
NCD NCD NCD NCD
9.30 9.39 9.32 9.21 9.19
0.04 0.75 0.90 0.08 0.02
0.09 0.02 -0.09 -0.11
NCD NCD NCD NCD
I, Oveml rating = rating scale of 1 to 5 (worse to better); 11,overall wore = rating scale of 1 to 10 (worse to better). Remainder of key is in footnote to Table III.
Because small differences in the composition of an alloy can produce major differences in its properties, caution must be used in trying to apply the results of this study to other alloys with similar chemical formulations. It is important to note that the recorded differences are the result of well-controlled laboratory conditions that were established and maintained for the duration of this study, and that slightly different conditions in other dental laboratories and studies may produce slightly different results.
CLINICAL
SIGNIFICANCE
This report compares restorations made from alternative alloys with those of Olympia, a gold-containing alloy, as they were received from the dental laboratory. The results show that, for several individual criteria, statistically significant differences between alternative alloys and an AuPd control alloy exist, although at precementation they are not large enough to be considered clinically significant. When the overall performances of the alloys were compared, the differences among the alloys were neither statistically nor clinically significant. Nevertheless, the observed differences are of clinical interest because they may represent weaknesses that could progressively deteriorate with time during prolonged clinical function.
CONCLUSIONS 1. Significant differences were found between Olympia alloy and some of the alternative alloys for the following precementation criteria: retention on the die, marginal integrity, pitting of metal surface, polish/tarnish of metal surface, polish/tarnish of connector/solder joint surface, and veneer-to-metal integrity. 2. No statistically significant differences were found be-
204
tween Olympia alloy and any of the alternative alloys for fit on die, pitting of connector/solder joint surface, veneer esthetics (porcelain color), crazing of porcelain, and glaze of porcelain. 3. Olympia alloy was significantly better than one or more of the base metal alloys for the precementation criterion of marginal integrity, pitting of surface, polishltarnish of surface, polish/tarnish of connector/solder joint surface, and veneer-to-metal integrity. 4. The base metal alloys, Ticon and Micro-Bond N/P2, were significantly better than Olympia alloy for the precementation criterion of retention on die. No other base metal alloy in any of the other criteria performed better than Olympia alloy. 5. Olympia alloy was not significantly better than W-l alloy for any of the precementation criteria. 6. W-l alloy was significantly better than Olympia alloy for the precementation criterion of retention on die. 7. For total overall performance (combining all criteria in the overall rating), Olympia alloy was not significantly better than any of the alternative alloys. 8. The overall score showed no significant differences between Olympia alloy and any of the alternative alloys for the combined criteria evaluated on dies before cementation. 9. All statistically significant differences exhibited were not of sufficient magnitude to be considered clinically significant. They were of clinical interest only, inasmuch as their means did not differ by more than 1 unit. REFERENCES 1.
Valega TM. Alternative to gold alloys in dentistry. U.S. Dept of Health, Education, and Welfare Publication No (NIH) 77-1227, Washington DC: Government Printing Office, 1977.
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2. Eden GT, Franklin OM, Powell JM, et al. Fit on porcelain fused to metal crown and bridge casting. J Dent Res 1979;5832360-8. 3. Duncan JD. The casting accuracy of nickel-chromium alloys for fixed prostheses. J PROSTHET DENT 1982;47:63-8. 4. Espevik S. Corrosion of base metal alloys in vitro. Acta Odontol Stand 1978;36:113-6. 5. Raucher F. The action of trace minerals of concern to dentistry. Part II. NY State Dent ,J 1979:45:273-5. 6. Woody RD, Huget EF, Horton JE. Apparent cytotoxicity of base metal casting alloys. J Dent Res 1977;56:739-43. 7. Bergman M, Berman B, Soremark R. Tissue accumulation of nickel released due to electrochemical corrosion of non-precious dental casting alloys. J Oral Rehabil 1980;7:325-30. 8. Pettersen AH, Jacobsen N. Nickel corrosion of non-precious casting alloys and cytotoxic effect of nickel in vitro. J Biomed Eng 1978;2:419-21. 9. Molfa JP, Guckes AD, Okawa MT, et al. An evaluation of non-precious alloys for use with porcelain veneers. Part II. Industry safety and biocompatibility. J PROSTHET DENT 1973;30:432-41. 10. Adrian JC, Huge& EF. Tissue responses to base-metal dental alloys. Milit Med 1977;142:748-86. 11. Civjan S, Huge& EF, Godfrey GD, et al. Effects of heat treatment on mechanical properties of two nickel-chromium-based casting alloys. J Dent Res 1972;51:1537-45. 12. Moffa JP, Lugassy AA, Guckes AD, et al. An evaluation of nonprecious alloys for use with porcelain veneers. Part I. Physical properties. J PROSTHET DENT 1973;30:424-31. 13. Hesby DA, Kobes P, Garver DC, et al. Physical properties of a repeatedly used nonprecious metal alloy. J PROSTHET DENT 1980;44:291-3. 14. Wight TA, Bauman JC, Pelleu GB. An evaluation of four variables affecting the bond strength of porcelain to nonprecious alloys. d PROSTHET DENT 1977;37:570-7. 15. Vincent PF, Stevens L, Basford KE. A comparison of the casting ability of precious and nonprecious alloys for porcelain veneering. J PROSTHET DENT 1977;37:527-36. 16. Thomas DH. A study of an increased mold temperature on the casting ability of some nonprecious alloys for porcelain veneers. J PROSTHET DENT 1982;48:52-8. 1.7. Moffa JP, Ellison JE, Hamilton JC. Incidence of nickel sensitivity in dental patients. [Abstract]. J Dent Res 1983;62:199. March 1983 (Abstr No. 271) p. 199. 18. Moffa JP, Jenkins WA, Ellison JA, et al. A clinical evaluation of two base-metal alloys and a gold alloy for use in fixed prosthodontics: a five-year study. J PROSTHET DENT 1984;52:491-500. 19. Morris HF, et al. Veterans Administration Cooperative Studies Project No. 147; Part I: A multidisciplinary, multicenter experimental design for the evaluation of alternative metal ceramic alloys. J PROSTHET DENT 1986;56:402-6. 20. Morris I-IF, et al. Veterans Administration Cooperative Studies Project No. 147; Part II: A new assessment system for rating metal ceramic crowns. J PROSTHET DENT 1986;56:546-51. 21. Dunnett CW. New tables for multiple comparisons with a control. Biometrics 1964;20:482-91. Reprint requests to: DR. HAROLD F. MORRIS (154) VA MEDICAL CENTER 2215 FULLER RD. ANN ARBOR, MI 48105
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ADDENDUM Authors: Warren M. Stoffer, D.M.D., Veterans Administration (VA) Medical Center, and Clinical Associate Professor, University of Pittsburgh, School of Dental Medicine, Pittsburgh Pa.; Linda Didenko, M.S. (Study Biostatistician), VA Hospital, Hines Ill.; Adele Gray, D.D.S., VA Medical Center, Ann Arbor, Mich.; James Lockwood, D.D.S., VA Medical Center, Ann Arbor, Mich.; Dennis Weir, D.D.S., M.A., VA Medical Center, and Assistant Clinical Professor, University of California San Francisco, School of Dentistry, San Francisco, Calif.; E. Richard McPhee, D.D.S., M.S., Consultant, VA Medical Center, and Professor of Prosthodontics, University of Michigan, School of Dentistry, Ann Arbor, Mich.; Norman Glasscock, D.D.S., VA Medical Center, Hampton, Va.; Sheldon Winkler, D.D.S., Temple University, School of Dentistry, Philadelphia, Pa.; Alan Helisek, C.D.T., VA Medical Center, Ann Arbor, Mich. Coauthors: John Blankenship, D.D.S., M.S.; James Pikulski, D.D.S.; Thomas Stein, D.M.D., M.S.; Gregory Movsesian, D.D.S.; Frank Lauciello, D.D.S.; John Mozrall, D.D.S.; Roger Cwynar, D.M.D.; Richard Navarro, D.D.S., MS.; Stephen Schlimmer, D.D.S.; Micheal Mackey, D.D.S.; Terry O’Toole, D.D.S.; Raul Caffesse, D.D.S., M.S.; David Irvin, D.D.S.; Alan Cantor, Ph.D. Executive Committee: Harold F. Morris, D.D.S., M.S., Chairman; Linda Didenko, M.S.; Warren M. Stoffer, D.M.D.; Dennis Weir, D.D.S., M.A.; Norman Glasscock, D.D.S.; Alan Helisek, C.D.T.; E. Richard McPhee, D.D.S., M.S.; Raul Caffesse, D.D.S., M.S.; Robert Lorey, D.D.S., M.S. (Ad hoc). Data Monitoring Board: Gunnar Ryge, D.D.S., M.S., Chairman; Marjorie Swartz, B.S., M.S.; Bart Hsi, Ph.D.; William Gillette, D.D.S.; Joseph Moffa, D.D.S., MS. Statistical Coordinating Center: William G. Henderson, Ph.D.; Linda Didenko, M.S.; Roland Mais, M.S.; Barbara Christine; Jean Rowe. Chairman’s Office: Harold F. Morris, D.D.S., M.S.; Patricia M. Zawadzki, R.D.H., M.S.; Peggy A. Piech; Beverly K. Barnes. Clinical Research Assistants: Nancy Bernat; Anne Cade; Greer Collins; Kari Gregerson; Mary Petrie; Mary Ann Steffensmeier; Sandra Reed.
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