Methods: A total of 47 subjects were randomly assigned to receive either a three-unit posterior metal-ceramic FDP (Au-Pd-Ag alloy and InLine POM, Ivoclar, Vivadent) or a ceramic-ceramic FDP (ZirCAD and ZirPress, Ivoclar, Vivadent) or both. The two groups were further randomized into three different groups with occlusal veneer thicknesses of 0.5, 1.0, or 1.5 mm; connector heights of 3, 4, or 5 mm; and a radius of curvature at the gingival embrasure of 0.5, 0.75, or 1.5 mm. Patients were enrolled after eligibility criteria were met and two endosseous implants (Osseospeed, Astra) were placed. Custom abutments (Atlantis, Astra) were placed to receive either a computer-designed, machine-milled zirconia FDP or a metal-ceramic FDP with two crown retainers and a pontic. Patients were recalled at 6 months, 1 year and 2 years.
Results: A total of 64 FDPs in 47 patients (19 males, 28 females) were placed with 32 ceramic-ceramic and 32 metal-ceramic prostheses. Nine FDPs exhibited chipping fracture of the veneer during the two-year observation period, representing 14% of the population. Six of the nine FDPs that chipped were ceramic-ceramic, five of these had a 1.5-mm occlusal veneer thickness, and one had a 0.5-mm veneer thickness. Of the three metal-ceramic fractures, each had a 0.5 mm-thick veneer.
Conclusion: Although no statistically significant differences will be reported until the study is completed, preliminary data indicate that metal-ceramic restorations with increased veneer thicknesses exhibited a greater resistance to fracture. Ceramic-ceramic restorations exhibited twice the fracture rate as metal-ceramic FDPs and are susceptible to chipping fractures in veneer ceramics of increased thickness. Supported by NIH-NIDCR Grants K23DE018414 and DE06672, Ivoclar Vivadent, and Astra Tech.
Keywords: Ceramics, Clinical trials and Prosthodontics