IADR Abstract Archives
Correlatng Strain Measurements with Degree of Conversion in Commercial Composites
Objectives: To find a correlation between the degree of conversion (DC) and the polymerization shrinkage strain (ε) of commercial dental composites using Raman spectroscopy and digital image correlation (DIC).
Methods: An open ended mold was constructed by milling a channel (2mm(H) x 4mm(L) x 6mm(W)) into a block of PFTA. Dental restorative composite (3M Z100 (Z) or FiltekTM Z250 (Y)) was placed in the mold. Carbon black was dusted onto the long surface of the uncured composite to impart optical contrast for DIC. Samples were cured with a 15 s exposure to an LED curing light (1242 mW/cm2) through the open-end while recording strain on the surface using DIC. After removing the inhibition layer from the long surface, the DC was acquired at 50 locations on the long surface using Raman spectroscopy. DC was calculated using the ratio of the absorption peaks intensity at 1637 cm-1 (C=C) and 1609 cm-1 (aromatic) in the following equation.
![DC = (1-[(Ac=c/Aar)polymer/(Ac=c/Aar)monomer])*100](/data/abstract/iadr/43am/Paper_186739_abstract_25348_0.gif){kind=small}
(1)
Results: Average shrinkage strain measurements at t = 20s ranged from 1.15 to 0.13% for Z and 1.04 to 0.11% for Y. Average degree of conversion for the samples ranged from 37.47 to 4.31% for Z and 38.29 to 0.00% for Y. All values had a large degree of variability leading to negative correlation values when plotted against one another (r2 =
-0.5 and -0.12 for Z and Y, respectively)
Table 1: Average degree of conversion and shrinkage strain of samples Z and Y (t = 20s) at certain depths away from the end exposed to the curing light. Plus-minus values are the standard deviation.
Depth | Z | Y | ||
x [mm] | DC [%] | ε [%] | DC [%] | ε [%] |
0.5 | 23.05 ± 6.99 | 1.15 ± 0.14 | 38.29 ± 6.20 | 0.87 ± 0.31 |
1 | 28.78 ± 5.00 | 1.10 ± 0.28 | 31.11 ± 5.59 | 1.04 ± 0.22 |
1.5 | 14.09 ± 10.89 | 0.99 ± 0.47 | 21.99 ± 4.26 | 0.92 ± 0.25 |
2 | 22.52 ± 3.67 | 0.99 ± 0.39 | 32.56 ± 12.87 | 0.89 ± 0.19 |
2.5 | 37.47 ± 15.98 | 0.78 ± 0.57 | 25.59 ± 14.91 | 0.74 ± 0.04 |
3 | 33.12 ± 18.94 | 0.89 ± 1.04 | 27.49 ± 20.30 | 0.69 ± 0.11 |
3.5 | 18.51 ± 16.13 | 0.43 ± 0.45 | 22.07 ± 13.07 | 0.57 ± 0.22 |
4 | 25.37 ± 14.79 | 0.31 ± 0.20 | 23.22 ± 10.29 | 0.11 ± 0.22 |
4.5 | 12.86 ± 15.50 | 0.19 ± 0.22 | 12.88 ± 11.92 | 0.34 ± 0.31 |
5 | 4.31 ± 6.20 | 0.13 ± 0.15 | 0.00 ± 0.00 | 0.11 ± 0.19 |
Conclusion: The correlation of shrinkage strain, using DIC, to DC, using Raman Spectroscopy, was not statistically significant for the conditions of this experiment. Further work is needed to refine the experimental methods to reduce error.