Evaluation of fracture resistance in simulated immature teeth using Resilon and Ribbond as root reinforcements--an in vitro study. 
To compare the reinforcement and strengthening ability of resilon, gutta-percha, and ribbond in endodontically treated roots of immature teeth.  Sixty five freshly extracted human maxillary anterior teeth were prepared with a Peeso no.  6 to simulate immature teeth (Cvek's stage 3 root development).  After instrumentation, each root was irrigated with sodium hypochlorite and with ethylene diamino tetra acetic acid to remove the smear layer.  To simulate single visit apexification technique a 4-5 mm white Pro Root mineral trioxide aggregate plug was placed apically using schilder carrier.  The teeth were divided into three experimental groups and one control group.  Group I--control group (root canals instrumented but not filled); Group II--backfilled with thermoplastisized gutta-percha using AH plus sealer; Group III--reinforced with Resilon using epiphany sealer; Group IV--reinforced with Ribbond fibers using Panavia F luting cement.  A Universal Testing Machine was used to apply a load, at the level of the lingual cementoenamel junction with a chisel-shaped tip The peak load to fracture was recorded and statistical analysis was completed using student's t-test.  Values of peak load to fracture were 1320.8, 1604.88, 1620, and 1851 newtons for Group I to Group IV respectively.  The results of student's t-test, revealed no significant difference (P > 0.05,) between Group II and Group III.  Comparison between Group IV and Group III and between Group IV and Group II revealed highly significant difference (P > 0.001).  Teeth reinforced with Ribbond fibers using Panavia F luting cement showed the highest resistance to fracture.  Resilon could not strengthen the roots and showed no statistically significant difference when compared with thermoplastisized gutta-percha in reinforcing immature tooth when tested with universal testing machine in an experimental model of immature tooth.