Marginal discrepancy of collarless metal ceramic restorations

Comparative Study of the Direct-lift and Platinum Foil Techniques in the Marginal Discrepancy of Collarless Metal Ceramic Restorations

Wilson MATSUMOTO1 Ramon Jesus BAEZ2 Heitor PANZERI1 1Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil 2University of Texas, Health Science Center at San Antonio, Texas, USA

Braz Dent J (1996) 7(2): 109-113 ISSN 0103-6440

This study was carried out to evaluate the marginal discrepancy of collarless metal ceramic restorations, using a combination of three different techniques to manufacture the porcelain butt margin with two brands of body porcelain. Statistical analysis showed no significant difference between the techniques or brands of body porcelain used in this study.

Key Words: collarless metal ceramic restorations, marginal discrepancy, shoulder porcelain.

Introduction

Collarless metal ceramic restorations combine the high quality esthetics of porcelain and the strength of a metal structure. Several techniques for manufacturing collarless metal ceramic restorations have been described (Vickery et al., 1969; Goodacre et al., 1977; Toogood and Archibald, 1978; Duncan et al., 1991). The restoration made by the platinum foil technique has shown good marginal adaptation (Cooney et al., 1985). Lately, however, the direct-lift technique has become popular because it is simpler and of lower cost than the platinum foil technique (Prince and Donovan, 1983). Chaffee et al. (1991) stated that the direct-lift technique is highly sensitive and for this reason collarless metal ceramic restorations have shown marginal discrepancies ranging from 0 to 145 µm (Donovan and Prince, 1985; Omar, 1987; Cagidiaco et al., 1991; Lomanto and Weiner, 1992; Belles et al., 1991; Boyle et al., 1993). To overcome this wide variation in marginal discrepancies several types of porcelain have been developed to manufacture collarless metal ceramic restorations. The objective of the present study was to compare the platinum foil and direct-lift techniques using commercially available porcelains to manufacture collarless metal ceramic restorations.

Material and Methods

In order to simulate a clinical situation as closely as possible, sixty extracted human premolars were used. The teeth were prepared using diamond points in a high speed hand piece with water as the refrigerating system, following the standardized approach described by Rosenstiel et al. (1988). The two-step impression technique was applied to all prepared teeth using a polyvinyl siloxane material (EXPRESS, 3M, St. Paul, MN). A type IV dental stone (DIE-KEEN, Columbus Dental., St. Louis, MO) was vacuum mixed with the appropriate amount of water (100/19) and poured into the impression. Four coats of die spacer (TRU-FIT Die Relief, George Taub Products & Fusin Co., Jersey City, NJ) were applied to the die following the long axis of the tooth and stopping at the axio-gingival angle. The wax coping thickness was about 0.4 to 0.5 mm on the facial veneer area and the lingual portion was extended leaving approximately 2.0 mm of the lingual metal collar. The wax copings were invested in vacuum mixed phosphate-bonded investment (HI-TEMP, Whip Mix Corp., Louisville, KY). The patterns were cast in base metal alloy (REXILLIUM III, Jeneric/Pentron Inc., Wallingford, CT). After divestment all copings were cleaned using 50 micron aluminum oxide abrasive (APM, Sterngold, Attleboro, MA) at 60 psi and finished with aluminum oxide stones assuring a uniform metal coping thickness of 0.3 to 0.4 mm. The following brands of porcelains were selected: Ceramco II (Ceramco Inc., Burlington, NJ), Willceram (Williams, Amherst, NY), Spectrum VLC shoulder (Dentisply Int., York, PA), Ceramco II shoulder (Ceramco Inc., Burlington, NJ) and Willshoulder (Williams, Amherst, NY). The restorations were constructed using three techniques to make the porcelain margin (direct-lift with visible light cured (VLC) shoulder porcelain, direct-lift with shoulder porcelain, and platinum foil with body porcelain) and two brands of body porcelain (Ceramco II and Willceram). In the direct-lift technique both VLC shoulder porcelain and shoulder porcelain were fired only two times. The completed crowns were cemented to the teeth using zinc phosphate cement (Fleck’s Cement, Mizzu Inc., Clifton Forge, VA) mixed according to the manufacturer’s recommendations. Twenty-four hours later, the crown-teeth assemblies were embedded in epoxy resin (Buehler, Lake Bluff, IL). After cure the assemblies were sectioned longitudinally at the midpoint faciolingually with an ultrathin diamond disc (Isomet Plus Precision Saw, Buehler, Lake Bluff, IL) using a 300-g load and a speed of 700 rpm. A petroleum distillate (Isomet Fluid, Buehler, Lake Bluff, IL) was used as lubricant. The sectioned specimens were metallographically polished using three differents grits (320, 400, and 600, Buehler, Lake Bluff, IL) with water as a lubricant. Measurements were made 50 µm internally to the finished margin of the preparation at the clearer, more-defined half of each sectioned specimens (Figure 1). The measurements were made under a light microscope (Gaertner Scientific Corp., Chicago, IL).

Results and Discussion

When the marginal discrepancy of collarless metal ceramic restorations prepared by 6 different techniques (Table 1) was compared by analysis of variance (ANOVA) (Table 2) no significant differences between techniques or interactions between them were identified. A precise cervical fitting is a fundamental condition for clinical success and depends on several factors involved in the manipulation of the materials used in the construction of fixed prosthodontic restorations. The quality of restorations can be assessed by marginal discrepancy measurements, defined in this study as the existing space between the cervical porcelain butt of the restoration and the gingival shoulder of the preparation. The major feature of the present study is that all of the preparations followed a technique used by most general dentists. No hand instruments were used in the finishing of the preparations. The grains of the diamond point used during the preparations could be one of the determinant factors in the marginal discrepancy because collarless metal ceramic restorations demand an extremely smooth preparation to permit precise adaptation (Prince and Donovan, 1983). The mean marginal discrepancies were higher in all of the 6 groups when compared to the discrepancies found by Omar (1987), Belles et al. (1991) and Boyle et al. (1993) but similar to the results obtained by Cagidiaco et al. (1992). Several reasons may explain these results: the skill of the technician (Cooney et al., 1985), the deformation or rounding of the porcelain margin (Belles et al., 1991; Boyle et al., 1993), a larger number of corrections (Omar, 1987; Lomanto and Weiner, 1992) and cementing the restorations or not (Cagidiaco et al., 1992; Boyle et al., 1993). Although statistical analysis showed no significant difference among methods, the mean values obtained for Ceramco II shoulder + Ceramco II, Willshoulder + Willceram and Platinum foil + Willceram were higher than clinically acceptable discrepancies, while the mean values obtained for VLC shoulder + Ceramco II, VLC shoulder + Willceram and Platinum foil + Willceram were within clinically acceptable values (Christensen, 1966; McLean and Von Fraunhofer, 1971).

Clinical Implications

With the increase of the importance of esthetics in Dentistry, collarless metal ceramic restorations will be used more frequently, especially in patients with a high smile and/or with a delicate and thin gingival margin. As these restorations do not present a metal collar in the facial margin the preparation finish line could be located at the gingival margin or supragingivally. However, more corrections are necessary during the construction of the porcelain butt margin to obtain better marginal discrepancy.

Conclusions

1. There was no statistical difference in the marginal discrepancy of porcelain margin with the combinations of techniques and brands of body porcelain used.
2. The high marginal discrepancy demonstrated the necessity of additional corrections in the porcelain butt margin.
3. Clinically acceptable marginal discrepancy can be obtained with the techniques and materials used in this study.

References

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Correspondence: Prof. Dr. Wilson Matsumoto, Departamento de Materiais Dentários e Prótese, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, 14040-904 Ribeirão Preto, SP, Brasil. E-mail: wmatsumo@usp.br

Accepted May 31, 1996
Electronic publication: February, 1997

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