In vitro fracture force and marginal adaptation of ceramic crowns fixed onnatural and artificial teeth

Purpose: Artificial teeth made of acrylic resin or alloy are considered sub stitutes for rare caries-free human teeth in in vitro examinations. The pur pose of this study was to compare the fracture strength and marginal adapta tion of all-ceramic single crowns fixed to natural teeth with crowns fixed to artificial teeth after artificial aging. Materials and Methods: The frac ture force and marginal adaptation were investigated in 28 adhesively luted all-ceramic crowns on human molars of different sizes, as well as on alloy and liquid crystal polymer (LCP) artificial teeth. The fracture force was determined using a universal testing machine, and the semiquantitative marg inal adaptation was examined using a scanning electron microscope, in both instances after simulating 5 years of clinical service. Results: Fracture f orce was found to be significantly higher for crowns fixed on substitute ma terials (alloy = 1,838 N; LCP = 1,392 N) than for crowns on human teeth (88 8 N). No significant differences in marginal quality could be determined be tween the groups. All crowns showed marginal gaps of about 10% and perfect margins at about 90%. Conclusion: The high in vitro fracture values of all- ceramic crowns on artificial materials may lead to a misinterpretation of t he tested restorative materials, overvaluing the material properties in a f irst preclinical estimation. Human teeth or materials with a comparable mod ulus of elasticity are therefore preferred in in vitro fracture tests.