Effect of Orthophosphoric Acid and Er:YAG Laser Etching on Micro-shear Bond Strength to Enamel: An In Vitro Pilot Study

Ludovica Zanigni1, Vittorio Checchi2, *, Bruno Davide Pugliese2, Uros Josic1, Claudia Mazzitelli1, Luca Giannetti2, Lorenzo Breschi1, Cesare Nucci1
1 Department of Biomedical and Neuromotor Sciences, Dental School, University of Bologna, Bologna, Italy
2 Department of Surgery, Medicine, Dentistry and Morphological Sciences, Unit of Dentistry and Oral-Maxillo-Facial Surgery, University of Modena and Reggio Emilia, Modena, Italy

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© 2022 Zanigni et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the University of Modena & Reggio Emilia, Via dal Pozzo 71, 41100 Modena, Italy; Tel: +390594224763; E-mail:



Dental conditioning is one of the most important phases during enamel bonding procedures to obtain clean surfaces, smear layer removal with collagen active sites and hydroxyapatite exposure.


The aim of this study was to compare the micro-shear bond strength (µSBS) of different adhesive systems after two different etching techniques: 37% orthophosphoric acid (H3PO4) and Er:YAG laser.


Ninety permanent extracted molars were embedded into epoxy resin blocks and sectioned longitudinally. Specimens were randomly assigned to one of the following groups (n=30), depending on the etching protocol: 37% H3PO4 for 30 s (Group 1), Er:YAG laser 100mJ-10Hz (Group 2), and Er:YAG laser 100mJ-10Hz followed by 37% H3PO4 for 30 s (Group 3). Each group was further divided into two subgroups depending on the bonding agent used on enamel (n=15): A) EE-Bond (Tokuyama) and B) Peak universal (Ultradent). A two-way analysis of variance (two-way ANOVA) was conducted and the level of significance was set to p=0.05.


The etching procedure was a significant factor influencing the results (p=0.006), while no differences were observed for the two adhesive systems tested (p>0.05). Group 3 recorded the highest bond strength values, according to the following sequel: Group 3 < Group 2 < Group 1 < 0.05.


The combination of phosphoric acid etching with Er:YAG laser provided the most favourable bond strength to enamel. Further morphological studies are currently ongoing.

Keywords: Enamel etching, Er:YAG laser, 37% orthophosphoric acid, Micro-shear test, Bond strength, in vitro study.