Critical Evaluation of the Push-out Test for Root Canal Filling Materials

Introduction: The push-out test has been widely used in experimental endodontics but has been criticized on technical grounds particularly because the soft-core material undergoes plastic deformation under load. This study systematically evaluated the technique by comparing push-out strength and load profiles in relation to core material stiffness, canal diameter, punch diameter, sample orientation, and mode of failure. Methods: Straight palatal roots of 90 maxillary molars were obturated with an epoxy resin based sealer alone (10 roots) or gutta-percha (70) or epoxy resin (10) cores with a thin layer of sealer cement. Roots were embedded in mounting resin vertically or at an angle of 5 or 10 to the long axis of the root. One-millimeter sections were tested using a universal testing machine with a punch diameter corresponding to 50%, 75%, or 90% of the canal diameter. Bond strengths (MPa) were calculated, and data were analyzed using analysis of variance with post hoc Tukey multiple comparisons (P < .05). After push out, core. materials and canal walls were examined using scanning electron microscopy. Results: Push-out strength was affected by core material stiffness. Angulation up to 10 degrees from vertical had little effect on push-out strength, but load profiles were strongly influenced by orientation. No effect of the punch diameter was observed when the diameter was 90% of the canal diameter, but push-out strength was lower when the punch diameter was 50%-60% of the canal size. Conclusions: Despite limitations, the push-out test may still be suitable for ranking the bonding of root filling materials.