An 18-month clinical evaluation of semiprecious and nonprecious alloy restorations

An I&month clinical evaluation nonprecious alloy restorations

of semiprecious and

H. M. Landesman, D.D.S., M.Ed.,* G. G. de Gennaro, D.D.S., M.S. Ed.,** and J. T. Martinoff, M. A., M. Ed., Ph.D. *** University

of Southern California,

School of Dentistry, Los Angeles, Calif.

T An the past 5 years, the dental profession has become increasingly interested in alternatives to gold alloys, primarily as a result of the increased cost of gold. Many alternatives have been introduced, often of different composition, which frequently require different methods of manipulation. Although many laboratory investigations have evaluated the physical properties of these casting alloys, there has been little clinical evaluation. The purpose of this study was to evaluate the clinical performance of two semiprecious and one nonprecious dental casting alloys. Type III gold was used as a control for comparison.

LITERATURE

REVIEW

In 1907, Haynes’ obtained a patent on the chromium-cobalt alloys. In 1929, Erdle and Prange’ perfected the materials and techniques so that the alloy could be used for dental applications and received several patents on their processes and materials. Until recently, these alloys have been used principally for frameworks for removable partial dentures. In 1943, Paffenberger et a1.3 reviewed several unsuccessful commercial attempts to introduce gold alloy substitutes. The major problem was of corrosion. In 1966, Teteruck and Mumford’ used different dies, including a Bureau of Standards die, and found that a silver-palladium alloy was unacceptable for general use because of different degrees of surface roughness. They compared the fit of certain dental casting alloys, investments, and techniques. In 1973, Moffa et al5 evaluated two nonprecious alloys for use with porcelain veneers and found that

*Associate Professor and Associate Restorative Dentistry. **Assistant Professor and Chairman, try. ***Director,

Office

0022-3913/81/080161

of Dental

Chairman,

Department

hardness, rigidity, resistance to permanent deformation, sag resistance, and bond strength to porcelain, were significantly greater than with a control goldbased alloy. In 1976, Moon and ModjeskiG reported on the burnishability of low-content gold alloys, goldsilver-platinum (palladium) alloys, silver palladium alloys, and nonprecious alloys as compared to the American Dental Association (ADA) gold alloys. They showed that the ADA gold alloys are easily burnishable, while the alloys tested were either difficult or impossible to burnish in the as-cast state. In 1976, Nitkin and Asgar? evaluated the fit of precious, semiprecious, and nonprecious alloy castings and found that castings made with nonprecious metal were inferior in fit to castings made from precious and semiprecious alloys. In 1977, Dale and MoserS performed an in vitro study of five semiprecious metals that could be cast by a technique similar to that used with dental gold alloys. Parameters such as accuracy of fit, marginal adaptation, ease of polishing, and corrosion were tested. Their findings favor silver-palladmm compositions as a substitute for types III and IV gold alloys. Also in 1977, Valega” did a summary of much of the research being performed with gold alloy alternatives which was published after a conference held at the National Institute of Health.

MATERIAL

AND METHODS

The alloys evaluated in this study, the manufacturers’ specifications, and the recommended techniques are listed in Table I.

of

Laboratory investigation Section

of Operative

Dentis-

Education.

+ 06$00.60/0 0 1981 The C. V. Mmby Co.

Before making restorations for patients, procedures were tested in the laboratory to verify the

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Table 1. Manufacturers’

specifications

Name Control alloy (Harmony Line Hard) Minigold

WLW

Litecast (Not to be confused with Will-Ceram Litecast)

and recommended

reliability of the materials and techniques. To test castability, three different preparations were used. An inlay, an onlay, and a complete crown were prepared on lava test dies. Reversible-hydrocolloid* impressions were then made. Each impression was poured in die stonet within 5 minutes after separation. Eight stone dies were made for each preparation. Strict adherence to the recommended water/ powder ratio was observed. For each of the three preparations, two dies were used for each of the four metals to be tested. Each die was coated with a separating mediumz to protect the surface. The dies were allowed to set for 24 hours, at which time they were trimmed. A lubricants was applied, and the wax patterns were made in inlay wax)l, except for the margins which were carved in soft wax.1 Subsequently, the patterns were invested using either a gypsum# or phosphate investment** as indicated for each metal. Vacuum mixing with a static-pour technique WAS used without hygroscopic expansion. All heating was started from a cold oven. The gypsum investment was heated to 1,100” F for 1 hour; the phosphate investment was heated to 1,300 “F for 1% hours. A horizontal broken-arm centrifu-

*Heavy Bodied Hydrocolloid, Van R Dental Products, Inc., Los Angeles, CA. jDie Keen, Modern Materials, Sad Fernando, CA. $Super-Sep, Kerr Mfg. Co., a Division of Sybron Corp., Romulus, MI. OSlikdie, Slaycris, Portland, OR. [INo. 2 Inlay Wax, Maves, Cleveland, OH. TWaxup Wax, Kerr Mfg. Co., a Division of Sybron Corp., Romulus, MI. *Luster Cast, Kerr Mfg. Co., a Division of Sybron Corp., Romulus, MI. **Ceramigold, Whip Mix Corp., Louisville, KY. 162

AND

MARTINOFF

techniques

Composition (three primary components) Gold Silver Copper Gold Silver Copper Palladium Silver Indium Nickel Chromium Cobalt

DE GENNARO,

Melting range

(74%) (12%) (9%) (40%) (47%) (741%) (25%)

1,665-1,765’F

Gypsum

Air-Gas

1,590-1,702'F

Gypsum

Air-Gas

1,915-2,070’F

Phosphate

2,435-2,.559’F

Phosphate

(71%) (4%) (62x%)

Casting technique

Investment

Induction Oxygen-Acetylene Oxygen-Gas Oxygen-Gas

(191h%) (141h%)

gal casting machine* was used with an air-gas torch for the gypsum investment and an oxygen-gas torch for the phosphate investment. The castings were cleaned manually and either pickled or sandblasted as indicated. All nodules were removed using a 25-power binocular microscope. The castings were subsequently seated on the appropriate stone die using finger pressure. Abraded areas on the die were noted, and the corresponding discrepancy in the casting was relieved. Next, each casting was fitted to the appropriate

lava

die.

Since

the Mohs

hardness

of lava

is

about seven, it was assumed that the castings would not abrade the lava test die. The castings were evaluated by visual and tactile examination using a sharp explorer. Of the 24 castings, 19 were considered acceptable as to fit. Of those castings deemed unacceptable, none were of the control alloy Harmony Line Hard,? none were of Minigold,? two were of WLW,t and three were Litecast.? The test dies were vapor coated with an approximately 100 A layer of gold-platinum for scanning electron microscope (SEM) study. Micrographs were made of the marginal area according to the following plan. (1) The inlays and onlays were examined at the gingival margin. (2) The complete crown was examined at the labial margin which had an accentuated chamber and the proximal margin(s) which had a feather margin. There were 32 measurements of different geometric configurations at the margins. Fig. 1 illustrates typical SEM micrographs of the various metals. *Broken Arm Centrifugal Casting Machine, Kerr Mfg. Co., a Division of Sybron Corp., Romulus, MI. ?Williams Gold Refining Co., Inc., Buffalo, NY.

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Fig. 1. Tog left, Control alloy, gingival bevel of inlay. Top right, Minigold, gingival bevel of onlay. Botfom left, WLW, proximal of full crown. Bottom right, Litecast, gingival bevel of onlay. (Magnification, X 60.) -IHE JOURNAL

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Table II. f analysis nonprecious

comparing clinical performance of control restorative materials (percentage of occurrence)

Control (Harmony (n = 37)

Line Hard)

I8

Minigold (n = 18) WLW (n = 22)

Litecast (n = 7)

alloy with other semiprecious Absence of abrasion (No. and % of restorations)

Absence of abnormal patient sensitivity (No. and % of restorations)

Absence of gingival irritation (No. and W of restorations)

DE GENNARO,

AND

MARTINOFF

and

Absence of tarnish and corrosion (No. and 46 of restorations)

37 (937P3%) 18 100

48.6 6 33.3

100 18 100

WS)

WS)

11

20

(72894%) 12 66.7

PW 20

WI 6 27.5

FW

90.9

2 28.6

W) 6 85.7

(r&i; 6 85.7

(P < .ow 1 14.3

PW

W)

WI

(P < .w

NS = not significant.

Table III. Rank-order

analysis

of alloys tested

Gingival irritation

Control (Harmony Line Hard)

Patient sensitivity

Abrasion

Tarnish and corrosion

Mixed rank

2

1

2

1

1.5

Minigold

3

I

1

2

1.75

(n = 18) WLW (n = 22)

1

3

3

3

2.5

4

4

4

4

4

(n = 37)

Litecast (n = 7)

The laboratory studies indicated that no one metal was superior to another as far as marginal integrity was concerned, as long as appropriate techniques for each metal were used. Variables such as type of investment, water/powder ratio, burnout temperature, casting temperature, and perhaps type of casting apparatus, all appear to play a major role in the final fit of these technique-sensitive metals.

Clinical

investigations

All teeth were prepared using conservative cavity or crown preparations. A high-speed handpiece with water spray was used for tooth preparations, and burs were replaced as often as necessary to reduce cutting trauma and thermogenesis. Impressions were made with either silicone, mercaptan rubber, or reversible-hydrocolloid impression materials. Accurate temporary restorations were made with ethyl and/or methyl methacrylate autopolymerizing resins. The control restorations were 164

permanently cemented;* the test restorations were cemented with a temporary cement.7 The test alloys and location in the mouth were randomly assigned to avoid any bias in results from preferred location in the mouth. For every test alloy used in a patient’s mouth, at least one control restoration was inserted. The patients received 37 control restorations and 47 test restorations. Of the test restorations, 18 were of Minigold, 22 were of WLW, and seven were of Litecast. Of the test restorations, 13 were MOD onlays, 15 were partial veneer crowns, 17 were complete crowns, and two were three-unit fixed partial dentures. The clinical tests of the nonprecious or semiprecious alloys were evaluated for a period of 18 *Zinc Phosphate Cement, Mizzy Inc., Clifton Forge, VA. tTemp-Bond, Kerr Romulus, MI.

Mfg.

Co., a Division

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months: at 3-month, l-year, and l%-year intervals. At the end of 18 months, the satisfactory test alloy restorations were permanently cemented. Although the evaluation of castings in terms of laboratory and clinical performance is subjective, rating scales were developed to provide analytic evaluations. To minimize differences in applying the rating scales, each of the castings was independently judged by two evaluators. The following evaluations were made for all restorations: Gingival imitation. The gingiva at each test and control restoration and at two adjacent teeth were recorded using the following scale: 0 = no inflammation, healthy tissues, 1 to 2 mm sulcular depth 1 = slight inflammation, slight edema, light bleeding on probing, and 1 to 3 mm sulcular depth 2 = moderate inflammation, moderate edema, bleeding on probing, substantial periodontal pocket formations, and tooth mobility of 1 mm 3 = severe inflammation, edema, bleeding, deep periodontal pocket formations, and excessive tooth mobility Tooth sensitivity. This involved pulpal sensitivity to hot or cold temperatures, as well as electrical sensitivity when a restoration came into contact with another restoration, certain food materials, or eating instruments. Although one would not expect pulpal irritation reactions to the differences in chemical composition of these alloys, since each alloy was isolated from the pulp by a cement layer, there may be differences in coefficients of thermal and electrical conductivity in the alloys. Ratings of patient awareness of, or sensitivity to, the restorations were recorded using the following scale: 0 = no abnormal patient sensitivity I = a slight awareness, but no discomfort 2 = moderate sensitivity 3 = a severe response Abrasion. Occlusal abrasion was measured visually and was, at best, on an arbitrary scale as substantial differences in extent of wear was observed. Abrasion depends upon chewing patterns, chemical composition of saliva, and dietary preference of the individual patients. Rating of abrasion was according to the following scale: 0 = no abrasion observed 1 = slight abrasion 2 = moderate abrasion Tarnish and/or corrosion. Rating of tarnish and/ or corrosion was according to the following scale:

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0 = no surface tarnish or evidence of corrosion; surface similar to original 1 = a dulled surface appearance; no major discoloration or pitting 2 = surface discoloration and/or pit,ring RESULTS

AND

DISCUSSION

The findings indicated that no significant statistical differences I’$ < .05) existed betwseen the control alloy and the three test alloys in relation to three of the four clinical criteria. While there were slight differences in the percentage of gingivae without inflammation, pulpal sensitivity, and abrasion of the alloys, these differences were not large enough to reject the null hypothesis (Table II). There were, however, statistically significant differences between the control alloy and WLW (p < ,001) and Litecast (p < .OOl) in relation to tarnish and corrosion. The control alloy produced significantly fewer restorations with tarnish and corrosion. There was no significant difference between the control alloy and Minigold in terms of tarnish and corrosion. Closer examination of the slight (differences that did exist revealed that in relation to gingival injuv, WLW restorations presented the most favorable findings with the least inflammation and the highest percentage of normal gingiva adjacent to the metal. In terms of rank ordering, WLW presented the most positive results; the control alloy was second; Minigold was third; and Litecast was fourth. Regarding tooth sensitivity, 100% of the subjects with both the control alloy and the Minigold restorations indicated no abnormal sensitivity or discomfort associated with the casting alloy; 91% of the patients with WLW restorations and 86% of the patients with Litecast restorations presented similar findings. No occlusal abrasion was found i,n the Minigold restorations. Of the control alloy restorations, only one of the 37 restorations presented slight abrasion. Similar findings were recorded with the Litecast restorations, as only one of the seven restorations exhibited slight abrasion. Two of the 22 WLW restorations showed similar results. In relation to tarnish and corroa.ion, the control presented the most favorable findings; 78% of the restorations showed no surface tarnish or evidence of corrosion. The Minigold restorations demonstrated the second-best rating, with WLW and Litecast showing significantly more surface discoloration and evidence of pitting (p < .OOl). A final rank ordering, comparing each of the four

LANDESMAN, DEGENNARO, AND MARTINOFF

casting alloys on all of the clinical criteria that were evaluated, indicated that the control alloy had the highest rank and presented the most favorable result. Minigold ranked second; WLW ranked third; and Litecast ranked fourth (Table III). However, in making these comparisons, the data are based on differences so slight in three of the four clinical areas that they are statistically insignificant. SUMMARY SEM studies indicate that the control alloy, Minigold, WLW, and Litecast metals presented similar results in relation to marginal fit when proper techniques are followed. Clinical evaluation based on the criteria of gingival irritation, patient sensitivity, and abrasion demonstrated no statistically significant differences between the casting alloys tested and the control. The control alloy had significantly fewer restorations with tarnish and corrosion than either WLW or Litecast. There was no significant difference between the control alloy and Minigold in terms of tarnish and corrosion. We would like to thank Drs. Duane McKay, Stephen Sanders, Daniel S&van, Robert Tupac, and Lloyd Vakay, for performing the clinical procedures on the patients.

R. W. and Prange, C. H.: U.S. Patent 1,956,278, April 24, 1934; Prange, C. H.: U.S. Patent 1,958,466, May 15, 1934. 3. Pafl’enbarger, G. C., Caul, H. J., and Dickson, G.: Base metal alloy for oral restorations. J Am Dent Assoc 30:852, 1943. 4. Teteruck, W. R., and Mumford, G.: The Ft of certain dental casting alloys using different investing materials and techniques. J PROSTHET DENT 16:5, 1966. 5. Moffa, J. P., Lugassy, A., Guckes, A., and Gettleman, L.: An evaluation of nonprecious alloys for use with porcelain veneers. Part I. Physical properties. J PROSTHETDENT 30:4, 1973.

6.

Modjeski, P. J., and Moon, P. C.: The burnishability of dental casting alloys. J PROSTHETDENT 36:4, 1976. 7. Nitkin, D. A., and Asgar K.: Evaluation of alternative alloys to type III gold for use in fixed prosthodontics. J Am Dent Assoc 93:622, 1976. 8. Dale, J. W., and Moser, J. B.: Semiprecious alloys for cast restorations: A preliminary report. J PROSTHETDENT 38:6, 1977. 9. Valega, T. M.: Alternatives to gold alloys in dentistry. Conference proceedings at the National Institute of Health, Bethesda, 1977, U.S. Department of Heaith, Education, and Welfare. Reprint requeststo: DR. HOWARD M. ~NDESMAN UNIVERSITYOF SOUTHERNCALIFORNIA SCHOOLOF DENTISTRY P.O. Box 77951 Los ANGELES. CA 90007

REFERENCES 1. Haynes, E.: U.S. Patent 873, 745, December 17, 1907. 2. Prange, C. H.: U.S. Patent 1,909,008, May 16, 1933; Erdle,

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