OBJECTIVES: To determine the shrinkage-stress and shrinkage-strain upon polymerisation of polymer filling materials with varying filler particle size.
METHODS: Four light-sensitive resin-composite materials were available for testing, all with a filler volume fraction of 56.7%. Filler particle size varied between the materials (450nm to 1500nm).
The bonded disk method was used to determine shrinkage-strain. Samples were placed within a 15mm diameter brass ring upon a rigid glass slab and compressed to form a 8mm disk. A flexible glass cover slip provided the upper surface. A uni-axial LVDT, positioned centrally over the cover slip, recorded displacement following irradiation. The signal from the LVDT was fed to a PC via an analogue to digital converter.
A Bioman instrument was used for stress measurement. It consists of a cantilever load cell free at one end with an integral clamp holding a circular steel rod. The rod is orientated such that it is vertical and perpendicular to the load cell axis. Facing the bottom of the rod is a rigidly held glass slab. The sample was placed in the gap (0.8mm) between the rod and the glass and irradiated through the glass. The stress-induced displacement of the free end of the load cell was amplified via a wide-range strain indicator attached to a PC to collect raw data.
For stress and strain, data were captured for sixty minutes and the mean maximum values calculated.
RESULTS:
There was a trend for higher shrinkage-strain and higher-shrinkage stress as filler particle size decreased, though this was not significant (p=0.45).
|
Filler |
Strain MPA |
SD |
Stress % |
SD |
|
Irregular 450nm |
2.993 |
0.028 |
8.443 |
0.413 |
|
Irregular 700nm |
2.956 |
0.021 |
7.595 |
0.270 |
|
Irregular 1000nm |
2.902 |
0.028 |
7.103 |
0.194 |
|
Irregular 1500nm |
2.908 |
0.088 |
6.995 |
0.163 |
CONCLUSION:
Filler particle size influences shrinkage-strain and shrinkage-stress of polymer materials and may have clinical significance.