IADR Abstract Archives
Matrix Shrinkage Stress: Significance of the Monomer Structures
Objectives:
The interfacial integrity of composite resins depends on many factors, especially the polymerization shrinkage stress related to the dimethylacrylate based matrix of these products. The aim of this study is to analyse the monomer influence on the shrinkage stresses of 7 photoactivated matrices.
Methods:
1. A centrifugal mixer, SpeedMixer* was used to prepare the matrices:
- three pure monomer matrices: bis-GMA, TEGDMA and UEDMA.
- four co-monomer matrices: bis-GMA/TEGDMA (70/30 and 50/50 in weight %) and UEDMA/TEGDMA (88,5/11,5 and 66,5/33,5 in weight %).
In order that the matrices should be light-curable, 0.2 wt% of CQ and 0.2 wt% of CEMA were dissolved in each of the monomer mixtures.
2. A rheometer RFS II* determined the viscosity of the matrices at ambient temperature.
3. A mechanical testing machine INSTRON 5569* equipped with a 2 kN load cell recorded the samples stresses (150 mg; C = 2,4; n = 5) polymerized over a period of 80s using the conventional high power density curing mode (1.200 mW/cm-2) of the Optilux 501* light-curing unit.
Results:
|
Matrix (wt%) |
Viscosity (Pa.s) |
Shrinkage Stress (MPa) |
|
bis-GMA |
1188 |
0.3 |
|
UEDMA |
22 |
6.8 |
|
TEGDMA |
0.01 |
14.2 |
|
bis-GMA/TEGDMA (70/30) |
3.5 |
4.4 |
|
UEDMA/TEGDMA (88,5/11,5) |
3.5 |
8 |
|
bis-GMA/TEGDMA (50/50) |
0.28 |
8.2 |
|
UEDMA/TEGDMA (66,5/33,5) |
0.28 |
10.6 |
The calculation of the simple Pearson correlation (a < 0.05) showed that a correlation [TEGDMA]/shrinkage stress and a negative viscosity/shrinkage stress correlation existed.
Conclusions:
In the light of a synthesis between our results and those in the literature, it would seem that the viscosity of the matrices studied and the concentration of the diluting monomer (TEGDMA) of the co-monomer matrices, are the determining elements influencing the development of shrinkage stresses. A better understanding of the phenomenology of the internal stresses necessitates an evaluation of the volume contraction and the degree of conversion of these matrices.