Objective: To prepare dense zirconia-silica ceramic nanofibers and to study their reinforcement effects on fluoride-releasing dental composites. Method: Zirconia-silica nanofibers were prepared by a reactive sol-gel electrospinning method using a mixture of zirconia/silica (80/20) sols prepared by hydrolysis of zirconium propoxide and tetraethyl orthosilicate (TEOS), respectively. As-prepared gel nanofibers were dried and calcinated. The resulting ceramic nanofibers (100-200 nm) were treated with silane before mixing with the fillers. Nine groups of experimental composites (n=10) were formulated using 70 wt% F-releasing glass filler (mean 0.8µm, Caulk/Dentsply), part of which (0, 2.5% or 5%) were replaced by nanofibers, and 30 wt% monomers (BisGMA:EBPADMA:HDDMA 40:40:20; or for fluoride-releasing composites: BisGMA:EBPADMA:HDDMA:F-releasing-monomer 30:30:20:20). The specimens were prepared by either heat-cure (1%BPO, 100oC for 2 hrs) or light-cure (Optilux 501, 80s each in three segments) in 2×2×25mm stainless steel molds. The specimens were tested on Instron 5566 testing machine (crosshead speed 1 mm/min) for flexure strength, flexure modulus and energy at break after they were stored in 37°C deionized water for 24h. Fluoride release from some light-cured composites was also measured. The data were analyzed using ANOVA and Tukey's B tests.
Results: (mean ± SD)
Composites | Nanofiber Content (wt%) | Flexure strength (MPa) | Flexure Modulus (GPa) | Energy at break (mJ) | |
Heat-cured | Control-1 | 0 | 104.2±14.8b | 8.55±0.64c | 7.33±2.57b |
Exp-1 | 2.5 | 128.2±22.3a | 9.08±0.59b,c | 10.7±4.08a | |
Exp-2 | 5 | 122.7±27.3a | 8.93±0.57b,c | 9.71±3.56a | |
Light-cured | Control-2 | 0 | 102.6±9.4b | 8.43±0.32c | 8.15±1.76b |
Exp-3 | 2.5 | 142.7±17.1a | 9.59±0.7a,b | 11.9±2.61a | |
Exp-4 | 5 | 137.7±21.0 | 10.07±0.63a | 10.84±3.67a | |
Light-cured F-releasing composites | Control-3 | 0 | 91.4±13.8c | 8.42±1.02c | 5.18±1.55b |
Exp-5 | 2.5 | 126.8±16.1a | 9.83±0.71a,b | 8.41±2.16a,b | |
Exp-6 | 5 | 126.3±17.2a | 9.87±0.61a,b | 7.56±3.47b | |
The groups with the same superscript letters have no significant difference (p>0.05)
Conclusion: zirconia-silica ceramic nanofibers were successfully prepared. Incorporation of 2.5wt% zirconia-silica ceramic nanofibers can significantly increase the mechanical properties of fluoride-releasing composites. Sponsored by NIH/NIDCR grant 1R21DE18349.