The Effect of Energy Densities on the Shear Bond Strength of Self-Adhering Flowable Composite to Er:YAG Pretreated Dentin

Abstract

Objective. To investigate the shear bond strength of self-adhering flowable resin composite, to dentin, after exposing it to Er:YAG laser radiation, at different energy densities. Materials and Methods. Sixty freshly extracted human third molars were randomly divided into five groups (n = 12). In the control group, dentin was left unirradiated, whereas, in the other four groups, dentin was irradiated with Er:YAG laser in noncontact mode (MSP mode = 100 µs; 10 Hz; beam diameter: 1.3 mm; speed of 1 mm/second; air 6 mL/min; and water 4 mL/min), and respectively, with the following level of energy (50 mJ, 60 mJ, 80 mJ, and 100 mJ). Then, self-adhering flowable resin composite was bonded to all prepared dentin surfaces. Shear bond strength (SBS) was applied and fractured surfaces were examined using scanning electron microscopy. Results. SBS values showed significant differences in 60 mJ (P < 0.05) compared to other groups. Morphological evaluation revealed tags or plugs in dentinal tubules, especially when 60 mJ and 80 mJ were used. All four groups tended to leave more residues on the dentin surface, than the control group. Conclusion. Er:YAG dentin irradiation may enhance SBS of the self-adhering flowable resin composite when it is used at the appropriate low level of energy density.

Figure 1

Impact of laser on dentin using a computer driven robot.

Figure 2

Almost half of the irradiated dentin received self-adhering flowable resin composite with the 2.38 × 2 mm cylindrical build-up. The rest of the dentin was left unbounded for SEM observation. D: dentin irradiated without self-adhering flowable resin composite over irradiated dentin; C: cylindrical build-up.

Figure 3

Bar graph showing the mean values with the standard deviations.

Figure 4

SEM observation after irradiation with Er:YAG and before bonding self-adhering flowable resin composite, respectively, with (a) 50 mJ, (b) 60 mJ, (c) 80 mJ, and (d) 100 mJ.

Figure 5

SEM observation after SBS done on dentin surfaces bonded with self-adhering flowable resin composite. (a) shows cohesive fracture with resin composite remnants; some tubules are open without any visible tags or plugs inside. (b) shows adhesive fracture; dentin tubules are visible. Most of them are filled with resin tags or plugs; fracture occurred between tags and composite; peritubular collagen fibrils are visible. (c) shows typical adhesive fracture; dentin is totally visible; tubules are open with less resin composite tags or plugs inside, signifying less infiltration of self-adhering flowable resin composite inside dentin tubules; and peritubular collagen fibrils are visible. (d) shows a large amount of dentin tubules with smaller opening and typical adhesive fracture; and fewer tags or plugs infiltrated dentin tubules. R: resin composite; T: tags or plugs; Tb: dentin tubules.