Effects of Dentine Pretreatment Solutions Containing Flavonoids on the Resin Polymer-Dentine Interface Created Using a Modern Universal Adhesive

Abstract

The aim of the present study was to evaluate the influence of several experimental pretreatment crosslinker solutions on the resin polymer-dentine interface created using a representative universal adhesive system, by means of microtensile bond strength testing (μTBS), nanomechanical properties and ultramorphology confocal laser scanning microscopy (CLSM). Five experimental solutions containing different flavonoids were applied as dentine pretreatment after acid etching. A control pretreatment group containing no flavonoid was also employed. A representative modern universal adhesive was then applied, followed by a 3 mm thick composite built up. Specimens were sectioned into sticks and submitted to a μTBS test or nanoindentation analysis along the interface (24 h or 25,000 thermocycles). The ultramorphology of the polymer-resin interface was also evaluated using CLSM. The results were analyzed using two-way ANOVA and Bonferroni's post hoc test (α = 0.05). All flavonoids improved short- and long-term μTBS values (p < 0.01), while only some specific such solutions improved the nanomechanical properties (p < 0.05) and preserved the structural morphology of the interface after aging. Pretreatment of acid-etched dentine using specific flavonoid-containing solutions may be a promising approach to improve both the nanomechanical properties and the durability of modern universal adhesive systems.

Keywords: flavonoids; microtensile bond strength; nanoindentation; nanoleakage; universal adhesive system.

Figure 1

Graphical representation of the overall experimental design used in this study.

Figure 2

Bar graph showing mean values and standard deviation (SD) of the µTBS values (Mpa) obtained in the experimental groups at 24 h (blue) and after 25,000 cycles of thermocycling (red). Bars connected by horizontal black lines are not significantly different for both intervals (pre-set alpha of 5%). Asterisks indicate significant differences between intervals (pre-set α = 0.05).

Figure 3

Distribution of failure pattern in the experimental groups at 24 h (A) and after thermocycling (B).

Figure 4

(a) Representative CLSM image (63X, Zoom 2X, depth: 10 μm) of the fluorescein infiltration in specimens of CON, QUE, and HES groups at 24 h. The presence of fluorescein was noted in some regions within the HL (pointer). (b) Representative CLSM image (63X, Zoom 2X, depth: 10 μm) of the nanoleakage in the experimental RUT, PLA, PRO, and NAR groups after 24 h. No leakage was noted within the HL in these groups (pointer). Some fluorescein was noted within the dentine tubules (white arrows). Resin composite (RC), adhesive layer (AL), hybrid layer (HL), dentine (D).

Figure 5

(a) Representative CLSM image (63X, Zoom 2X, depth: 10 μm) of the fluorescein infiltration observed in the specimens in the CON group after thermocycling. Orange shaded hybrid layer as a result of the mixture between fluorescein and rhodamine B was noted (pointer). (b) Representative CLSM image (63X, Zoom 2X, depth: 10 μm) of the nanoleakage in the experimental QUE and NAR groups after thermocycling. Infiltration of fluorescein was noted at the bottom of the hybrid layer (pointer), as well as the presence of fluorescein surrounding resin tag ends (white arrow). (c) Representative CLSM image (63X, Zoom 2X, depth: 10 μm) of the nanoleakage in the experimental RUT, PRO, and PLA groups after thermocycling. Infiltration of fluorescein at the bottom of the hybrid layer was noted (pointer). Presence of fluorescein surrounding the resin tag ends (white arrow). Resin composite (RC), adhesive layer (AL), hybrid layer (HL), dentine (D).

Figure 6

Flavonoid and surfactant molecules: proanthocyanidin (A), hesperidin (B), quercetin (C), rutin (D), naringin (E), SPAN 20 (F).