The experimental composite resin (FC) was prepared by mixing 22.5 wt. % of short E-glass fibers (3 mm in length) and 22.5 wt. % of semi-interpenetrating polymer network (IPN) resin with 55 wt. % of silane treated silica fillers. The clinical crowns of 30 human extracted maxillary incisors were sectioned at the cemento-enamel junction. Five groups of direct complete crowns were fabricated (n = 6); Group A: made from particulate filler composite resin (PFC) (Grandio Caps, VOCO, control), Group B: PFC with fiber post (everStick, StickTeck), Group C: made from PFC with everStick fiber post and FRC-substructure, Group D: made from FC, Group E: made from FC with FRC-substructure. The root canals were prepared and posts were cemented with resin cement (ParaCem Universal). All restored teeth were stored in water at room temperature for 24 h before they were statically loaded with speed of 1.0 mm/min until fracture. Data were analyzed using ANOVA (p = 0.05). Failure modes were visually examined.
ANOVA revealed that restorations made from experimental fiber composite resin had higher load-bearing capacity (349 N) (p < 0.05) than the control restorations (173 N). No significant difference was found in load-bearing capacity between restorations reinforced with FRC-substructure and those without (p > 0.05).
Restorations made from short glass fiber containing composite resin with IPN–polymer matrix showed better load-bearing capacity than those made with either plain PFC or PFC reinforced with fiber post.