Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials

Abstract

This study prepared composites for core build-up containing Sr/F bioactive glass nanoparticles (Sr/F-BGNPs) and monocalcium phosphate monohydrate (MCPM) to prevent dental caries. The effect of the additives on the physical/mechanical properties of the materials was examined. Dual-cured resin composites were prepared using dimethacrylate monomers with added Sr/F-BGNPs (5 or 10 wt%) and MCPM (3 or 6 wt%). The additives reduced the light-activated monomer conversion by ~10%, but their effect on the conversion upon self-curing was negligible. The conversions of light-curing or self-curing polymerization of the experimental materials were greater than that of the commercial material. The additives reduced biaxial flexural strength (191 to 155 MPa), modulus (4.4 to 3.3), and surface microhardness (53 to 45 VHN). These values were comparable to that of the commercial material or within the acceptable range of the standard. The changes in the experimental composites' mass and volume (~1%) were similar to that of the commercial comparison. The color change of the commercial material (1.0) was lower than that of the experimental composites (1.5-5.8). The addition of Sr/F-BGNPs and MCPM negatively affected the physical/mechanical properties of the composites, but the results were satisfactory except for color stability.

Keywords: bioactive glass; calcium phosphate; color stability; composite resins; core build-up; flexural strength; mass/volume changes; polymerization; surface microhardness.

Figure 1

SEM images and EDX results of Sr-BGNPs and MCPM, respectively.

Figure 2

The representative FTIR spectra of experimental core build-up material (S10M6) and MF upon light-curing and chemical-curing. Peaks at 1300 and 1320 cm^–1 [ν (C-O)] and 1636 cm^–1 [ν (C=C)] of methacrylate groups [51] were reduced upon polymerization.

Figure 3

Degree of monomer conversion upon (A) light-activation and (B) chemical activation. Stars indicate p < 0.05. Error bars are SD (n = 5).

Figure 4

The degree of monomer conversion (self-cured) versus time (20, 30, 60, 300, 600, 900, and 1200 s) from the representative sample.

Figure 5

(A) Biaxial flexural strength and (B) biaxial flexural modulus of materials at 24 h and 4 weeks. The boxes indicate the first quartile (Q1) to the third quartile (Q3), the horizontal line in the boxes represents the median, the whiskers represent the maximum and minimum values, and “+” represents the mean value (n = 5). The same letters represent p < 0.05 of the data compared within the same materials at 24 and 4 weeks. The dashed and solid lines with stars indicated p < 0.05 of data compared among different materials at 24 h and 4 weeks, respectively.

Figure 6

The SEM images of the fracture surface of the representative specimens after the BFS testing. MCPM (blue arrows) and precipitation of calcium phosphates (red arrows) were observed on the experimental core build-up material containing MCPM and Sr-BGNPs. (White arrows) are borosilicate glass [52] and resin matrix.

Figure 7

The elemental composition of (A) MCPM and (B–D) calcium phosphates containing F or Sr in the fracture surface of the representative specimens. The calcium phosphate precipitates were only observed in the specimens containing MCPM and Sr/F-BGNPs.

Figure 8

Vickers surface microhardness (VHN) after immersion in deionized water for 24 h. The boxes represent the first quartile (Q1) to the third quartile (Q3), the horizontal line in the boxes represents the median, the whiskers represent the maximum and minimum values, and “+” represents the mean value (n = 5). The same letters represent p < 0.05 of the data compared within the same materials at 24 h and 4 weeks. The dashed and solid lines with stars indicated p < 0.05 of data compared among different materials at 24 h and 4 weeks, respectively.

Figure 9

Plots of (A) mass change and (B) volume changes versus immersion time (square root of an hour) for all materials after immersion in de-ionized water for up to 8 weeks. Error bars are SD (n = 5).

Figure 10

(A) The averaged mass change and (B) volume change at a late time (336, 504, and 672 h). The boxes represent the first quartile (Q1) to the third quartile (Q3), the horizontal line in the boxes represents the median, the whiskers represent the maximum and minimum values, and “+” represents the mean value (n = 5). Star indicated p < 0.05.

Figure 11

Color difference (∆E₀₀) of all material after immersion in water for 1 week. The boxes represent the first quartile (Q1) to the third quartile (Q3), the horizontal line in the boxes represents the median, the whiskers represent the maximum and minimum values, and “+” represents the mean value (n = 5). Stars indicated p < 0.05.