Hardness and Elastic Modulus of Nano-whisker Reinforced Sealant

Objectives: the present study aimed to investigate the effect of nano-whisker particles on hardness and elastic modulus of pit and fissure sealant. Methods: experimental chitin nano-whisker particles (approximately 30 nm in diameter and 400 nm in length) were synthesized and incorporated (15.5% by weight) in a pit and fissure sealant (Prevocare, Thailand). The whisker reinforced sealant was cured with a visible light-curing unit in the cylindrical mould according to the manufacturer's instruction. The flat surface of cured sealant cylinder was ground and polished to the final finish with 0.05 micron of alumina oxide powder. The polish sealant cylinder was then mounted on the testing stage of nano-hardness tester (UMIS, CSIRO, Australia). The Prevocare sealant was also cured and polished as control following the same procedure. Series of 25 indentations for maximum indenting forces of 5 and 10 mN were carried out on both experimental and control specimens. At each indentation, hardness and elastic modulus were calculated from the loading and unloading curve, respectively. Results: hardness and elastic modulus (subjected to 5 mN force) were 0.13 +/- 0.002 and 3.09 +/- 0.05 GPa for control and 0.19 +/- 0.002 and 3.82 +/- 0.03 GPa for reinforced sealant. Hardness and elastic modulus (subjected to 10 mN force) were 0.11 +/- 0.002 and 2.93 +/- 0.04 GPa for control and 0.17 +/- 0.002 and 3.62 +/- 0.03 GPa for reinforced sealant. The average indentation depths were from 0.97 – 1.14 and 1.44 – 1.69 microns for 5 and 10 mN, respectively. Results showed significant differences of hardness and elastic modulus (Student t-test, p < 0.05) between the experimental and control groups for all forces used. Conclusion: incorporation of nano-whisker particles at 15.5% by weight into sealant significantly increased the hardness and elastic modulus.