Altered adhesion of dental sealant to tooth enamel microscopically modified by Er:YAG laser irradiation: An in vitro study

Abstract

Background and aims: Er:YAG laser has become optional for enamel and dentin preparation for a decade. However, it is unclear if Er:YAG laser is acceptable for enamel conditioning prior to an application of a pit-and-fissure sealant. This in vitro study thus aimed to investigate shear bond strength of a sealant to enamel etched with Er:YAG laser, as well as to demonstrate an alteration of enamel surface after the laser was applied.

Materials and methods: One hundred and twenty extracted human premolars were divided into 4 groups (N = 30 per group) in which the enamel surfaces were treated with 1) 37% phosphoric acid, 2) Er:YAG laser 80 mJ/pulse, 2 Hz, 3) Er:YAG laser 120 mJ/pulse, 10 Hz, and 4) Er:YAG laser 140 mJ/pulse, 2 Hz. Prior to sealant application. Shear bond strength was determined by using a universal testing machine. Statistical analysis was performed using One-way ANOVA. Modification of enamel surface after laser ablation was also investigated using scanning electron microscope.

Results: Phosphoric acid-etched enamel yielded the highest shear bond strength when bonded with a sealant. Ablation of enamel with Er:YAG laser did not significantly improve sealant bonding since it demonstrated lower shear bond strength, compared to acid-etched enamel. Despite the presence of cracks after Er:YAG laser application, dissolution of enamel substances was limited.

Conclusion: Our study has shown a reduced shear bond strength of dental sealant to an Er:YAG laser-irradiated enamel, compared with phosphoric acid-etched enamel.

Keywords: Er:YAG laser; enamel conditioning; laser etching; pit and fissure sealant; shear bond strength.

Figure 1:

Sample preparation prior to sealant application. (A) Flaky enamel surface was achieved after Er:YAG laser ablation. (B) A light-cured dental sealant was applied into an orthodontic elastic placed on etched enamel surface.

Figure 2:

SEM evaluation of 37% phosphoric acid-etched enamel. (A) 100X magnification level. (B) 1000X magnification level showed enamel projections caused by the dissolution of enamel rods and peripheries.

Figure 3:

SEM evaluation of 80 mJ/pulse, 10 Hz. Er:YAG laser-irradiated enamel. (A) 100X magnification level. (B) 1000X magnification level showed partial removal of surface enamel.

Figure 4:

SEM evaluation of 120 mJ/pulse, 2 Hz. Er:YAG laser-irradiated enamel. (A) 100X magnification level demonstrated craters and cracks present on enamel surface. (B) 1000X magnification level revealed superficial enamel fusion and surface cracks.

Figure 5:

SEM evaluation of 140 mJ/pulse, 10 Hz. Er:YAG laser-irradiated enamel. (A) 100X magnification level showed enamel cracks, similar to Figure 4A. (B) 1000X magnification level demonstrated limited enamel dissolution and the presence of surface cracking.