Effect of biofilm exposure on marginal integrity of composite restorations

Abstract

Purpose: To evaluate the effect of bacterial exposure on the marginal integrity of dentin-resin interfaces for composites with and without bioactive glass (BAG).

Methods: Cavity preparations of 5 mm width and 1.5 mm depth were machined into dentin disks by means of a computer controlled milling system. After applying the bonding agent, cavity preparations (n=3-5) were restored by incremental technique with experimental resin composites (50:50 BisGMA/TEGDMA: 72wt% filler) with different filler compositions: control - 67 wt% silanated strontium glass and 5wt% aerosol-silica filler and BAG - 57 wt% silanated strontium glass and 15 wt% BAG-65 wt% silica. Samples were then stored in sterile Todd-Hewitt media or co-incubated with Streptococcus mutans (UA 159), at 37°C, 5% CO2 for 1-2 weeks. For samples co-incubated with a living biofilm, a luciferase assay was performed in order to assess its viability. Surfaces were impressed before and after each storage condition and replicas examined in a scanning electron microscope. Using image analysis software (Image J), the discontinuous margins percentage (%DM) was quantitatively assessed. Data were analyzed using two-way ANOVA followed by Tukey's test (α= 0.05).

Results: Gap size ranged between 7-23 µm. The bacterial exposure significantly increased the %DM in both groups predominantly due to the formation of new gap regions. There was no difference between control and BAG composites regarding %DM and the biofilm viability. Bacterial exposure promoted degradation of composite restoration marginal integrity, with no difference between composites with and without BAG.

Clinical significance: The samples incubated with living biofilm had a higher gap percentage in the margins, confirming the negative effect of cariogenic bacteria on margin degradation. The parameters defined for such synergy can help to understand the multi-factorial aspect of marginal discontinuity and therefore, predict the behavior of composite restorations subjected to the challenging oral environment.

Fig. 1.

SEM image of BAG-containing composite sample, showing simultaneously the presence (B) and absence (A) of gaps along the margin.

Fig. 2.

Relative luminometer units (RLU) representing the viability of S. mutans bacteria after 1 and 2 weeks of co-incubation with samples restored with BAG and control composites.

Fig. 3.

SEM images of control composite samples before and after storage with only media (A,B) and with biofilm (C,D). While no changes can be seen after the storage with media, the presence of bacteria promoted the development of discontinuity along the margin.

Fig. 4.

SEM images of a control composite actual tooth sample after 2 weeks of incubation with biofilm. Left (44×): presence of gap along the margin, except on the selected area (arrows). Right (760×): Magnification of the circled area, showing the presence of enamel (E) along with the dentin (D).