To measure the hardness of bulk fill and conventional resin composite materials and assess hardness changes after 24h dry and 75% ethanol/water solution (75% EW) storage.
Method:
Six bulk fill (SureFil SDR, Venus bulk fill, x-tra base, Filtek bulk, Sonic fill, and Tetric EvoCeram bulk fill) and eight conventional resin-composite materials (Grandioso flow, Venus Diamond flow, X- flow, Filtek Supreme Ultra Flowble, Grandioso, Venus Diamond, TPH Spectrum, and Filtek Z250) were tested. Cylindrical specimens (2mm and 4mm thickness for conventional and bulk fill materials respectively) were prepared (n=5). Initial and 24h post-cure top and bottom Vickers hardness values were measured. Specimens were then stored for 24h in 75% EW and hardness was measured again. Results were analysed using one-way analysis of variance (ANOVA), Bonferroni post hoc test, and paired sample t-test at α=0.05 significance level.
Result:
All materials showed significant increase of hardness after 24h of dry storage which ranged from 100.1% (± 19.9) for SureFil SDR to 9.1 % (± 4.0) for Grandioso flow. 24h post-cure hardness values ranged from (14.8 ±0.8) for Venus bulk fill to (97.6 ± 2.5) for Grandioso. Bottom/top hardness ratios higher than 0.9 were exhibited by all materials. All materials showed significant decrease of hardness after 24h of storage in 75% EW in relation to their 24h post-cure hardness values. SDR had the highest percentage decrease of 74.2% (± 1.9). The percentage increase of hardness after 24h of dry storage was positively correlated to the percentage decrease of hardness after 24h of storage in 75% EW (R2= 0.8).
Conclusion:
Hardness of all materials significantly increased over 24 hours. Bottom/top surface hardness ratios of bulk fill composites are comparable to those of conventional materials in spite of their increased increment thickness. Hardness of all materials significantly decreased after 24h storage in 75% EW.