The Effect of Viscosity and Application Mode of Phosphoric Acid on Bond Strength of GlassFiber Post

Abstract

Background: When a phosphoric acid is used, before applying an adhesive system, it is known that obtaining an effective adhesion to the root canal walls is a challenge. The aim of the present study was to evaluate the influence of phosphoric acid viscosity and application mode on the push-out bond strength (BS) values of fiberglass post to root dentin. The conditioning pattern on the root dentin was also evaluated.

Materials and methods: The roots of 44 endodontically treated premolars were divided into 4 groups, of eleven teeth each, according to the combination of the main factors: phosphoric acid viscosity (liquid or gel) and application mode (passive or sonic). After application of the two-step etch-and-rinse adhesive system, the fiberglass posts were cemented with a dual-cure resin-cement. Roots were sectioned transversely into six 1-mm slices for push-out BS test at 0.5 mm/min. Some roots of each group were selected for evaluation of the conditioning pattern by scanning electron microscopy. BS results (three-way ANOVA and Tukey's test) and the conditioning pattern (Kruskal-Wallis test and Mann-Whitney test) were statistically evaluated (α= 0.05).

Results: The highest BS value was observed with a liquid phosphoric acid under sonic application mode (p < 0.05), being all other groups similar to one another (p < 0.05). Also, the highest BS value was observed in the cervical third, followed by the medium and the apical thirds (p < 0.05). The sonic application produced better smear layer removal and opening of dentinal tubules for both viscosities (p = 0.015).

Conclusion: A better bonding of fiberglass posts to root canals can be achieved when the post spaces are conditioned with a liquid phosphoric acid under sonic application.

Keywords: acid etching; fiberglass reinforced polymer; post and core technique.

Figure 1

Number of specimens (%) according to the fracture pattern modes observed in the different experimental groups.

Figure 2

Number of specimens with opened dentinal tubules (%) observed in the different experimental groups. Groups identified with same lowercase letters indicate values statistically similar (p > 0.05).

Figure 3

Representative SEM images of each third ((A) cervical; (B) medium; (C) apical) of the conditioning pattern observed in the experimental groups. It was observed that, in all thirds, the liquid and gel applied as passive technique shows dentinal surfaces with smear layer debris (black hands) and partially opened tubules due to the presence of smear plugs (white hands). On the other side, in the groups where the liquid and gel etchants were applied in the sonic mode, it was a more complete opening of the dentinal tubules (red hands).