The effect of smear layer on the push-out bond strength of root canal calcium silicate cements.

INTRODUCTION: The aim of this study was to evaluate the effect of smear layer removal on the push-out bond strength between radicular dentin and three calcium silicate cements (CSC) in comparison with gutta percha and sealer.

METHODS: Eighty human anterior extracted teeth were decoronated, cleaned and shaped to size 50/0.05 apically and randomly divided into 2 major groups: (A) smear layer preserved, and (B) smear layer removed using irrigation with 17% EDTA. Roots within each major group were further divided into 4 subgroups according to the obturation material used: (1) ProRoot MTA, (2) Biodentine, (3) Harvard MTA, (4) Gutta percha and AH-plus sealer. Obturated roots were stored in synthetic tissue fluid for 7 days to allow maximum setting of the root filling materials. Three 2-mm-thick slices were obtained from each root at different section levels (coronal, middle, apical). The canal diameters and slice thickness were measured, and the adhesion surface area for each slice was calculated. Push-out bond strength test was carried out using a universal testing machine. The bond failure mode was assessed under an optical microscope at 40×.

RESULTS: The mean push-out bond strength in groups 1A, 2A and 3A were 7.54 (±1.11), 7.64 (±1.08) and 8.79 (±1.55)MPa respectively, while those for groups 1B, 2B and 3B were 6.58 (±1.13), 6.47 (±1.08), 7.71 (±1.81)MPa, respectively. In the gutta percha and sealer groups the push-out bond strength means were: 1.98 (±0.48) and 2.09 (±0.51)MPa in the preserved and removed smear layer groups respectively. The push-out strength values were significantly reduced when the smear layer was removed in the CSC groups (P<0.05) while no significant difference was detected in the gutta percha and sealer groups.

CONCLUSIONS: Based on the conditions of this ex vivo study, it can be concluded that smear layer removal is detrimental to the bond strength between calcium silicate cements and dentin.