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. 2025 Jul;19(3):678-687.
doi: 10.1055/s-0044-1791682. Epub 2024 Dec 30.

Effect of Apical Preparation Size and Preparation Taper on Smear Layer Removal Using Two Different Irrigation Needles: A Scanning Electron Microscopy Study

Rania Lebbos  1 , Naji Kharouf  2   3 , Deepak Mehta  4 , Jamal Jabr  5 , Cynthia Kamel  1 , Roula El Hachem  1   6 , Youssef Haikel  2   3   7 , Marc Krikor Kaloustian  1
Affiliations

Effect of Apical Preparation Size and Preparation Taper on Smear Layer Removal Using Two Different Irrigation Needles: A Scanning Electron Microscopy Study

Rania Lebbos et al. Eur J Dent. 2025 Jul.

Abstract

Objectives: The aim of this study was to determine the effect of apical preparation size and preparation taper on smear layer removal using a metallic needle and a new polymer needle (IrriFlex, Produits Dentaires SA "PD," Vevey, Switzerland).

Materials and methods: One hundred and eight single-rooted teeth with one canal were randomly divided into four groups according to the preparation and irrigation needle used: G1-30, 0.04 and IrriFlex (n = 25); G2-25, 0.06 and IrriFlex (n = 25); G3-30, 0.04 and metallic needle (n = 25); and G4-25, 0.06 and metallic needle (n = 25). All groups received the same final irrigation protocol and sonic activation. Each tooth was sectioned and observed under a scanning electron microscope (SEM).

Statistical analysis: Data were statistically analyzed by using one-way and two-way analysis of variance on ranks with a significance level at p = 0.05.

Results: For all groups, there was significantly higher smear layer in the apical third (p < 0.001) compared with the coronal and middle thirds. The 25, 0.06 preparation demonstrated better cleaning efficiency than the 30, 0.04 preparation throughout the canal when irrigated with a metallic needle; however, there were no significant differences in the middle and apical thirds when IrriFlex was used. There were also no differences of smear layer removal between G1 and G3 and G2 and G4 in the coronal part. In the middle and apical parts, G1 showed better elimination of smear layer compared with G3. There were slight differences in the middle third between G2 and G4, while G2 showed less cleaning efficiency compared with G4 in the apical third (p = 0.022).

Conclusion: All groups showed less smear layer in the middle and coronal thirds of the canal compared with the apical third. The 25, 0.06 preparation was more effective in removing smear layer compared with the 30, 0.04 preparation. IrriFlex improved irrigation in the 30, 0.04 preparation, while its efficacy was less evident in the 25, 0.06 preparation.

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Conflict of interest statement

None declared.

Figures

Fig. 1
Fig. 1
Example of an axial cross-section, 5 mm from the apex, to determine whether the canal ( green ) was oval in the buccolingual direction. ( A ) Cone beam computed tomography (CBCT). ( B ) Figure based on CBCT. ( C ) Figure with values.
Fig. 2
Fig. 2
Superimposition of the instrument ( purple ) onto the canal ( green ) ensuring that the canal is encompassed by the instrument along its majority length. ( A ) Distal. ( B ) Buccal. ( C ) Mesial.
Fig. 3
Fig. 3
Representative scanning electron microscopy micrographs (×2,000) of each smear layer score in the coronal, middle, and apical thirds of root canals.
Fig. 4
Fig. 4
Flowchart of the methodology. CBCT, cone beam computed tomography; SEM, scanning electron microscope.
See this image and copyright information in PMC

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