Hygroscopic Expansion of Low Shrinkage Composites: A Three Months Report

To investigate the linear hygroscopic expansion of two low shrinkage composites in distilled water and human whole saliva during 12 weeks

Methods:

Three restorative resin composites: Filtek silorane (3M/ESPE) and GC Kalore (GC-International) were studied. Filtek Z-250 (3M/ESPE) was used as control. Ten cylindrical specimens (4X6 mm) were prepared for each test material. Five specimens were stored in distilled water and the other 5 in human whole saliva at 37±1°C for 12 weeks. The length of each specimen was measured immediately after preparation and at 1, 2, 4, 8 & 12 weeks, using an electronic micrometer to the accuracy of 1µ and used to calculate the linear hygroscopic expansion which presented in percentage. Data were analyzed by Repeated measure ANOVA (P<0.05).

Results:

All specimens were significantly expanded during the immersion period in both solutions. The maximum expansion for all materials was seen in 2^nd month. The mean linear expansion (%) for Z250, P90 and GC Kalore following immersion in distilled water was 0.336%, 0.416%, 0.546% and in saliva was 0.288%, 0.417%, 0.387%, respectively.

The linear expansion (%) values for specimens immersed in saliva were not significantly different for all test materials (p>0.05). However, the expansion of GC Kalore in distilled water was significantly different with that of Z250 (p<0.05).

Conclusions:

1. All materials exhibited significant increase in linear expansion (%) during the test period.
2. GC Kalore showed the highest amount of linear expansion among the materials tested.
3. P90 showed similar expansion in comparison to that of Z250 in both medias.