Abstract:

Objective

To explore the effect of photoactivation mode soft-start on the polymerization shrinkage and the degree of surface hardness conversion of three kinds of posterior composite resins （Ecusphere-Carat， Filtek P60， Tetric Ceram HB）.

Methods

Compared with the conventional photoactivation mode， each kind of composite was put into 10 cylinder containers with a diameter of 0.7 cm and a height of 0.4 cm， and every 0.2 cm layer of composite was cured using photoactivation mode soft-start for 40 s. The width of marginal gap between the composite and the container was estimated using scanning electron microscope （SEM）； Compared with the conventional photoactivation mode， each posterior composite has 7 specimens for both the experimental and the control group which are all prepared in the same way， the vickers diamond hardness of the samples' surface were measured with microhardness tester.

Results

The width of margin gap of EcuShere-Carat， Filtek P60 and Tetric Ceram HB with the conventional photoactivation mode were （15.32±1.78）μm、（15.72±1.97）μm and （16.14±1.74）μm respectively.The width with soft-start were（14.83±3.34）μm，（13.64±1.92）μm and（14.18±2.01）μm. There was statistical difference between two kinds of photoactivation mode （P ＜0.05）. The surface hardness with the conventional photoactivation mode were （116.76±12.00）MPa、（159.14±5.90）MPa and（119.59±5.00）MPa； which with soft-start were （109.74±5.77）MPa、（154.81±3.99）MPa and（114.11±6.42）MPa， lower than those with conventional mode. There was statistical difference between the two kinds of photoactivation modes （P ＜0.05）.

Conclusions

The photoactive mode soft-start can reduce the polymerization shrinkage of posterior composites， but it can also bring side effect to the surface hardness. The microhardness of Filtek P60 is higher than the other two composites.

Key words: Soft-start, Posterior composite resin, Polymerization shrinkage, Margin gap, Surface microhardness