Bioactivity and Physico-Chemical Properties of Dental Composites Functionalized with Nano- vs. Micro-Sized Bioactive Glass

Abstract

Bioactive resin composites can contribute to the prevention of secondary caries, which is one of the main reasons for failure of contemporary dental restorations. This study investigated the effect of particle size of bioactive glass 45S5 on chemical and physical composite properties. Four experimental composites were prepared by admixing the following fillers into a commercial flowable composite: (1) 15 wt% of micro-sized bioactive glass, (2) 15 wt% of nano-sized bioactive glass, (3) a combination of micro- (7.5 wt%) and nano-sized (7.5 wt%) bioactive glass, and (4) 15 wt% of micro-sized inert barium glass. Hydroxyapatite precipitation and pH rise in phosphate-buffered saline were evaluated during 28 days. Degree of conversion and Knoop microhardness were measured 24 h after specimen preparation and after 28 days of phosphate-buffered saline immersion. Data were analyzed using non-parametric statistics (Kruskal-Wallis and Wilcoxon tests) at an overall level of significance of 5%. Downsizing the bioactive glass particles from micro- to nano-size considerably improved their capability to increase pH. The effect of nano-sized bioactive glass on degree of conversion and Knoop microhardness was similar to that of micro-sized bioactive glass. Composites containing nano-sized bioactive glass formed a more uniform hydroxyapatite layer after phosphate-buffered saline immersion than composites containing exclusively micro-sized particles. Partial replacement of nano- by micro-sized bioactive glass in the hybrid composite did not impair its reactivity, degree of conversion (p > 0.05), and Knoop microhardness (p > 0.05). It is concluded that downsizing bioactive glass particles to nano-size improves the alkalizing potential of experimental composites with no negative effects on their fundamental properties.

Keywords: bioactive glass filler; degree of conversion; dental resin composites; hydroxyapatite; microhardness; nanoparticles.

Figure 1

pH (mean ± standard deviation) as a function of immersion time.

Figure 2

Degree of conversion measured after 24 h and 28 days. Within each measuring time, same uppercase letters indicate statistically homogeneous groups for top surfaces, while same lowercase letters indicate statistically homogeneous groups for bottom surfaces. Asterisks (*) indicate significant differences between measuring times, within each material/surface combination.

Figure 3

Knoop microhardness measured after 24 h and 28 days. Within each measuring time, same uppercase letters indicate statistically homogeneous groups for top surfaces, while same lowercase letters indicate statistically homogeneous groups for bottom surfaces. Asterisks (*) indicate significant differences between measuring times, within each material/surface combination. Square brackets indicate significant differences between the top and bottom surfaces.

Figure 4

Scanning electron microscopy images of specimen surfaces immediately after preparation and after 28 days of storage at 37 °C in phosphate-buffered saline (PBS) for the control (a,b), micro-BG (c,d), nano-BG (e,f), hybrid-BG (g,h), and micro-inert composites (i,j). Insets show higher magnification of crystals formed on specimen surfaces.

Figure 5

Relative amounts (in weight %) of calcium and phosphorus identified on the surface of BG-containing composites before and after PBS immersion.