Influence of curing time and distance on microhardness of eight light-cured liners.

Eight visible-light-activated liners were evaluated to assess the degree of polymerization by microhardness comparison. Knoop hardness number values were measured on 1.0 mm-thick specimens with varied exposure times (20, 40, 60 seconds) and distances from the curing source (0, 3, 6 mm). Statistical analysis of the nine groups within each material revealed significant differences for time and distance (P < 0.05). Application of the light for at least 40 seconds resulted in significantly higher Knoop hardness number values than specimens cured for 20 seconds. The highest Knoop hardness values were obtained if the tip of the light source was 3 mm away from the light-activated liner.