Hybridization quality and bond strength of adhesive systems according to interaction with dentin

Abstract

Objective: To evaluate the hybridization quality and bond strength of adhesives to dentin.

Materials and methods: Ten human molars were ground to expose the dentin and then sectioned in four tooth-quarters. They were randomly divided into 5 groups according to the adhesive used: Two single-step self-etch adhesives - Adper Prompt (ADP) and Xeno III (XE), two two-step self-etching primer systems - Clearfil SE Bond (SE) and Adhe SE (ADSE), and one one-step etch-and-rinse system - Adper Single Bond (SB). Resin composite (Filtek Z250) crown buildups were made on the bonded surfaces and incrementally light-cured for 20 s. The restored tooth-quarters were stored in water at 37°C for 24 h and then sectioned into beams (0.8 mm(2) in cross-section). Maximal microtensile bond strength (μ-TBS) was recorded (0.5 mm/min in crosshead speed). The results were submitted to one-way ANOVA and Tukey's test (α = 0.05). Thirty additional teeth were used to investigate the hybridization quality by SEM using silver methenamine or ammoniacal silver nitrate dyes.

Results: SE reached significantly higher μ-TBS (P < 0.05); no significance was found between ADSE and XE (P > 0.05), and between SB and ADP (P > 0.05); ADSE and XE were significantly higher than SB and ADP (P < 0.05). The bonding interface of SB showed the most intense silver uptake. SE and ADSE showed more favorable hybridization quality than that observed for ADP and XE.

Conclusions: The bond strength and hybridization quality were affected by the interaction form of the adhesives with dentin. The hybridization quality was essential to improve the immediate μ-TBS to dentin.

Keywords: Adhesive systems; ammoniacal silver nitrate; bond strength; hybrid layer; silver methenamine.

Figure 1

Distribution of the failure pattern (%) of the adhesives evaluated

Figure 2

Representative SEM images of the dentin side of fractured specimens bonded with the adhesives evaluated. (a - a2) Specimens bonded with Adper Single Bond (SB); (b - b2) Specimens bonded with Clearfil SE Bond (SE); (c - c2) Specimens bonded with Adhese SE (ADSE); (d - d2) Specimens bonded with Adper Prompt (ADP); (e - e2) Specimens bonded with Xeno III (XE). (a - e) Low-power magnification of whole area of the fractured specimens. (a1-e1) Higher magnification of the circled area. (a2-e2) Higher magnification of the area limited by a rectangle. (B) Bottom of the hybrid layer; (T) Top of the hybrid layer; (AD) Adhesive resin; (HL) Hybrid layer; (RC) Resin composite; (white arrows) dentinal tubules filled by resin tags; (asterisk) intertubular dentin covered by the adhesive; (pointer) exposed collagen fibrils; (between black arrows) blistering microstructures

Figure 3

Representative SEM images of the resin-dentin interfaces bonded with Adper Single Bond. (a) Secondary electron image of unstained specimen (control). An authentic hybrid layer with 5-6-μm-thick was observed. Funnel-shaped resin tags (TG) with lateral branches (white arrow) were noted. (b) Back-scattering image of silver-methenamine-stained specimen. The silver nitrate uptake was observed at the bottom of the hybrid layer (between white arrows). (c) Back-scattering image of ammoniacal-silver-nitrate-stained specimen. Intense silver penetration occurred throughout the hybrid layer (between black arrows). Water trees were observed in the adhesive layer (pointer). (RC) Resin composite; (AD) Adhesive layer; (HL) Hybrid layer; (D) Dentine

Figure 4

Representative SEM images of the resin-dentin interfaces bonded with Clearfil SE Bond (SE) (a-c) and Adhese SE (ADSE) (d-f). Secondary electron images of unstained specimens (control) bonded with SE (a) and ADSE (d), showing the interaction zone (arrow) with thin hybrid layers (HL) and cylindrical resin tags (TG). Back-scattering images of stained specimens (SE - b and c; ADSE - e and f) showing the hybridization quality. When silver methenamine was used, a spotted nanoleakage pattern was observed for SE (b), which was characterized by silver clusters outlining the bottom of the hybrid layer (between arrows). ADSE (e) exhibited a diffuse nanoleakage pattern at the bottom of the hybrid layer (between arrows). The ammoniacal silver nitrate resulted in a clearer silver impregnation along the bonding interfaces. An intermittent nanoleakage pattern was produced for SE (c) (between arrows), while it was more continuous for ADSE (f) (between arrows). Both SE and ADSE exhibited some extensions of silver deposits toward the adhesive layer (pointer). (RC) Resin composite; (AD) Adhesive layer; (D) Dentine

Figure 5

Representative SEM images of the resin-dentin interfaces bonded with Adper Prompt (ADP) (a-c) and Xeno III (XE) (d-f). Secondary electron images of unstained specimens (control) showing a hybrid layer about 3-4 μm thick for ADP (a) with funnel-shaped resin tags (TG); XE (d) exhibited a thin hybrid layer with cylindrical TGs. When silver methenamine was used, both ADP (b) and XE (e) exhibited spotted nanoleakage patterns at the bottom of the hybrid layer. Ammoniacal silver nitrate yielded intense silver observed in the bonding interfaces for both ADP (c) and XE (f). Clusters of silver deposits were observed at the interaction area between the adhesive and resin composite for XE (↖). Specimens bonded with ADP showed water trees in the adhesive layer (pointer). (RC) Resin composite; (D) Dentine