Water uptake and strength characteristics of a nanofilled resin-based composite

OBJECTIVES: To investigate the influence of short- and medium-term immersion on water uptake and mechanical properties of a so-called 'nanofilled' compared with a conventional resin-based composite (RBC). METHOD: For each material (a microhybrid, Filtek Z250, FZ and 'nanofilled' RBC, Filtek Supreme in body and translucent shades, FSB and FST; 3M ESPE, St. Paul, USA) five specimen groups (n=20) were tested. Mean bi-axial flexure strength (BFS) of each group was determined following 24h 'dry' and 24h, 3, 6 and 12 months in a water-bath maintained at 37+/-1 degrees C prior to testing. The extent of water uptake following each storage regime was determined using a near-infrared spectroscopy (NIRS) technique. RESULTS: No significant difference in BFS was identified for each material stored dry or wet for 24h (F=2.7; P=0.07) whilst BFS decreased following 3, 6 and 12 months (F=6.6; P0.05). In contrast, no significant decrease in BFS of FSB (97+/-34 MPa) and FST (112+/-28 MPa) was recorded following 6 compared with 3 months immersion (P>0.05). Storage for 12 months resulted in a further significant strength reduction of FSB and FST (56+/-11, 82+/-12 MPa; P=0.004, P