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

doi:10.1016/j.joen.2012.12.032

Journal of Endodontics

Volume 39, Issue 5, May 2013, Pages 669-673

https://doi.org/10.1016/j.joen.2012.12.032 Get rights and content

Abstract

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° 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.

Section snippets

Material Properties

The elastic modulus and yield stress were determined for gutta-percha, the epoxy resin–based sealer cement (AH Plus; Dentsply DeTrey, Konstanz, Germany), and an unfilled epoxy resin used to fabricate master cones (EpoFix; Struers, Ballerup, Denmark) using triplicate cylindrical specimens (4-mm diameter × 7 mm long) subjected to compressive loading in a universal testing machine (MTS Model 810; MTS Corp, Eden Prairie, MN). Yield stress was calculated as the stress at which the stress-strain

Material Properties

The elastic modulus and yield stress of gutta-percha (elastic modulus 0.37 ± 0.09 GPa, yield stress 7.07 ± 0.55 MPa) were much lower than for the epoxy core (2.13 ± 0.05 GPa, 54.39 ± 4.46 MPa) and sealer alone (AH Plus) (3.28 ± 0.07 GPa, 37.83 ± 1.82 MPa).

Effect of Core Stiffness

The push-out bond strength was affected by core materials of different stiffness (Fig. 1A). The push-out strength with gutta-percha as the core material was much lower than with epoxy resin cores or filling the entire canal with sealer cement.

Discussion

Although bond strength testing may not be a completely reliable predictor of the clinical behavior of sealer cements (18), bond strength testing is the best measure of adhesion currently available 19, 20 and has become widely used as a surrogate for sealing ability. The push-out test has been used to compare bond strengths of different types of root canal sealers with or without different core materials and with different root dentin pretreatment procedures 12, 15, 17, 21, 22, 23, 24, 25. The

Acknowledgments

The authors deny any conflicts of interest related to this study.

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: Supported by the Postgraduate Research Fund of Melbourne Dental School, University of Melbourne, Melbourne, Australia.

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

Abstract

Introduction

Methods

Results

Conclusions

Section snippets

Material Properties

Material Properties

Effect of Core Stiffness

Discussion

Acknowledgments

Composites Part A Appl Sci Manuf

J Endod

Dent Mater

J Endod

J Endod

J Endod

J Endod

J Endod

J Endod

J Endod

J Endod

Dent Mater

J Endod

Biomechanical evaluation of bone-porous material interfaces

J Biomed Mater Res

An extrusion test for determination of bond strength to dentin

J Dent Res

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