The aim of this research was to evaluate the mechanical impact of utilizing different
fiber-reinforced composite (FRC) systems to reinforce inlay-retained bridges in dissected
lower molars with different levels of periodontal support. A total of 24 lower first
molars and 24 lower second premolars were included in this study. The distal canal
of all molars received endodontic treatment. After root canal treatment, the teeth
were dissected, and only the distal halves were kept. Standardized class II occluso-distal
(OD) (premolars) and mesio-occlusal (MO) (dissected molars) cavities were prepared
in all teeth, and premolar–molar units were created. The units were randomly distributed
among four groups (n = six/group). With the aid of a transparent silicone index, direct
inlay-retained composite bridges were fabricated. In Groups 1 and 2, both discontinuous
(everX Flow) and continuous (everStick C&B) fibers were used for reinforcement, while
in Groups 3 and 4, only discontinuous fibers (everX Flow) were used. The restored
units were embedded in methacrylate resin, simulating either physiological periodontal
conditions or furcation involvement. Subsequently, all units underwent fatigue survival
testing in a cyclic loading machine until fracture, or a total of 40,000 cycles. Kaplan–Meyer
survival analyses were conducted, followed by pairwise log-rank post hoc comparisons.
Fracture patterns were evaluated visually and with scanning electron microscopy. In
terms of survival, Group 2 performed significantly better than Groups 3 and 4 (p <
0.05), while there was no significant difference between the other groups. In the
case of impaired periodontal support, a combination of both continuous and discontinuous
short FRC systems increased the fatigue resistance of direct inlay-retained composite
bridges compared to bridges that only contained short fibers. Such a difference was
not found in the case of sound periodontal support between the two different bridges.
