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

IntroductionThe 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.MethodsStraight 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.ResultsPush-out strength was affected by core material stiffness. Angulation up to 10° 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.ConclusionsDespite limitations, the push-out test may still be suitable for ranking the bonding of root filling materials.