Comparison of three types of fiber-reinforced composite molar crowns on their fracture resistance and marginal adaptation

Three types of fiber-reinforced composite (FRC) molar crowns were tested on their fracture resistance and marginal adaptation under simulated oral str ess conditions. Two glass fiber systems, one processed with a vacuum/pressu re system, the other by manual fiber adaptation, and a polyethylene fiber s ystem were evaluated. Every group consisted of 12 crowns. All crowns were luted adhesively on human molars and exposed to thermal cyc ling and mechanical loading (TCML: 6000 x 5 degreesC/55 degreesC; 1.2 x 10( 6) x 50 N; 1.66 Hz). The marginal adaptation was evaluated through dye-pene tration and analyzed semi-quantitatively with a scanning electron microscop e. The fracture resistance was measured using a Zwick universal testing mac hine. The highest fracture resistance was observed on the glass-fiber systems (Fi breKor/Sculpture 1875 N +/- 596; Vectris/Targis 1726 +/- 542), though stati stically, the polyethylene system (belleGlass/Connect 1388 +/- 620) was not significantly weaker. All systems exceeded the fracture resistance require d to withstand the maximum masticatory forces expected in the molar region. The marginal adaptation generally had a tendency towards larger gaps after TCML. The crown/composite-cement bond deteriorated significantly after TCM L with the manual fiber adaptation and the polyethylene fiber system. The c ement/tooth bond strength depended on which composite-cement/dentin-adhesiv e system was used. Conclusion: The fracture resistance of molar crowns made of glass-fiber rei nforced composite was higher than those of polyethylene fiber-reinforced co mposite crowns. However, there was no statistically significant difference. The marginal adaptation seems to depend on the fiber systems and composite -cement/dentin adhesive system used. (C) 2001 Elsevier Science Ltd. All rig hts reserved.