Methods:
Three cylinder-shaped composite blocks (diameter: 8 mm, thickness: 10 mm) were prepared using the fiber-reinforced composite EverX Posterior (‘EX-P’, GC), the bulk-fill composite SDR (‘SDR’, Dentsply) and the conventional micro-hybrid composite Filtek Z100 (‘Z100’, 3M ESPE). The top surface of each block was compressed by a slide glass, and light-cured using a polywave LED unit (Bluephase 20i, Ivoclar Vivadent) at 1200 mW/cm2 for 20s. After 24-hour storage (37°C), the blocks were cut in half and the degree of conversion (DC) was mapped using micro-Raman spectroscopy (Senterra, Bruker), with DC calculated as the ratio of peak intensities of the aliphatic 1640 cm-1 and aromatic 1610 cm-1 peaks in cured and uncured materials. The depth effect and distance relative to the specimen center were statistically analyzed using a linear mixed-effects model.
Results:
Mean degree of conversion (%; ±SD) at the different depths (mm).
0-1 |
1-2 |
2-3 |
3-4 |
4-5 |
5-6 |
6-7 |
7-8 |
8-9 |
9-10 |
|
EX-P |
80±2 |
80±3 |
79±3 |
78±2 |
77±3 |
76±3 |
74±3 |
72±3 |
70±4 |
68±5 |
SDR |
79±2 |
79±2 |
79±2 |
79±2 |
78±2 |
78±2 |
77±3 |
76±2 |
74±3 |
72±3 |
Z100 |
74±3 |
74±3 |
72±4 |
69±4 |
65±5 |
61±6 |
46±10 |
31±9 |
|
|
Maximum DC of Z100 was significantly lower (p=0.0011) than that of both bulk-fill composites. In contrast to DC of both bulk-fill composites, DC of the conventional composite decreased more rapidly (p<0.001). Statistics revealed a homogenous DC for both bulk-fill composites, while for the conventional composite DC at the cylinder bottom was up to 10% lower at the periphery than at the center.
Conclusion: The fiber-reinforced composite polymerized homogenously up to at least 6-mm depth; up to 10-mm depth DC only decreased with 15% as compared to maximum DC.