Investigation of microleakage at the interface between a Co-Cr based alloy and four polymeric veneering materials

. Marginal adaptation and resistance to microleakage are important factors for clinical success in fixed prosthodontics. Alloy corrosion that sometimes occurs under a veneer in the cervical area may result in cervical staining, a metallic taste, or even failure of the interface.

This study investigated cervical microleakage between a Co-Cr alloy and 4 indirect polymeric veneering materials used with different conditioning systems.

Sixteen metallic frameworks (copings) were obtained by fabricating 0.6-mm calibrated wax patterns on a master cast abutment. The wax patterns were provided with 0.4-mm beaded retention on the veneering surfaces and cast in a Co-Cr based alloy (Biosil F) used for fixed partial dentures. The Co-Cr copings were divided equally into 4 groups and veneered with 4 polymeric materials (Signum, Solidex, Superpont C+B, and Targis). Three chemical conditioning systems (Siloc, Targis-Link, and Silicoater MD) were used with the respective veneering system recommended by the manufacturer; Conolar opaque was used for Superpont C+B. No control group was created. After 2 weeks of storage in distilled water at 37 degrees C, 2000 cycles at 5-55 degrees C, and 24 hours of storage in 0.5% basic fuchsine, specimens were embedded in clear liquid casting resin and sectioned along a perpendicular cervical-incisal plane through the middle of the cervical collar. The surfaces of the resulting sections were examined in the cervical area with a metallurgical microscope to detect dye penetration. Leakage was quantitatively evaluated with the use of a scoring system (established by the authors) that indicated the presence/absence of dye in 3 regions of the cervical interface from the collar to the incisal margin. Scores were compared and analyzed with the use of 1-way analysis of variance followed by post-hoc Tukey's honestly significant difference test (P=.05).

Superpont C+B was associated with the highest microleakage scores (3.75 +/- 0.5). The least microleakage at the interface was produced by Targis (1 +/- 0.816), followed by Solidex (2.5 +/- 1.0) and Signum (2.25 +/- 0.975). Only the difference between Targis and Superpont C+B was significant (P<.05).

Within the limitations of this in vitro study, the extent of cervical microleakage between the coping and veneer depended on the particular polymeric material used for veneering. The extremes of the study were Targis/Targis-Link (lowest leakage scores) and Superpont C+B (highest leakage scores). Differences among the chemical retention systems tested were not significant.