Fracture strength and bending of inlay-retained fixed partial dentures

Objectives: The aim of this in-vitro study was to compare the fracture strength and the amount of bending in all-ceramic with fiber-reinforced composite, inlay-retained fixed partial dentures. Methods: Forty mandibular premolars and 40 mandibular molars were collected. The roots of the teeth were covered with a 0.2 mm thick layer of polyether material to simulate the periodontium. The teeth were embedded in polimetilmetacrylate resin at a mesiodistal separation of 11 mm to represent a mandibular molar gap. The specimens were randomly divided into 4 groups of 10 teeth each with box-shaped proximal preparations. Two different all-ceramic systems (IPS e.max Press, ICE Zirkon) and two different fiber-reinforced composite systems (EverStick, Vectris) with a connector size of 16 mm2 were used to restore prepared abutment teeth. After thermal cycling (5-55°C x 5000), a vertical force was loaded (N) to the center of the inlay-retained fixed partial dentures at a crosshead speed of 0.5 mm/min. The specimens were examined for failure types with a stereomicroscope and radiography. Statistical analysis was performed using the Kruskal-Wallis test and the Mann-Whitney U test (p <0.05). Results: The fracture strengths were significantly higher in the ICE Zirkon specimens (1540 N) and the EverStick specimens (1057 N) than in the Vectris specimens (794 N) and the IPS e.max Press specimens (606 N); in addition, the fracture strength was significantly higher in the ICE Zirkon specimens than in the EverStick specimens (p<0.05). The amount of bending was significantly greater in the EverStick (1.94 mm) and Vectris (1.87 mm) specimens than in the ICE Zirkon specimens (1.07 mm) and the IPS e.max Press specimens (1.18 mm) (p<0.05). Conclusions: Yttrium-oxide partially stabilized zirconia-based ceramic inlay-retained fixed partial dentures demonstrated the highest fracture strength. The fiber-reinforced composite inlay-retained fixed partial dentures demonstrated higher bending values than the all-ceramic inlay-retained fixed partial dentures.