Samples from each strain at 6 weeks and 5 months (N = 6) were tested for enamel mechanical hardness. Samples were stored in a moist environment in the presence of 0.1% thymol to retard bacterial growth [31 (link)].
Since enamel is a brittle material, the Knoop hardness test was indicated. In this test, only a small indentation is created by a pyramidal diamond point, which is pressed into the polished enamel surface with a known force, for a specific dwell time. The resulting indentation is measured using a microscope. The Knoop hardness number KHN is the ratio of the load applied to the indenter, P (kgf) to the unrecovered projected area A (mm2): KHN = F/A = P/CL2. Where: F = applied load in kgf; A = the unrecovered projected are of the indentation in mm2; L = measured length of long diagonal of indentation in mm; C = 0.07028 = Constant of indenter relating projected area of the indentation to the square of the length of the long diagonal.
Experiments were done perpendicularly to the external surface of the enamel [22 (link)]. At the start of sample preparation the enamel surface were polished to obtain a flat surface. Blocks were then submitted to baseline microhardness analysis using a microhardness tester (IndentaMet 1100 Series, Buehler Ltd., Lake Bluff, IL, USA) with a knoop diamond under a load of 25 grams for 5 seconds. One indentation was made.
Since enamel is a brittle material, the Knoop hardness test was indicated. In this test, only a small indentation is created by a pyramidal diamond point, which is pressed into the polished enamel surface with a known force, for a specific dwell time. The resulting indentation is measured using a microscope. The Knoop hardness number KHN is the ratio of the load applied to the indenter, P (kgf) to the unrecovered projected area A (mm2): KHN = F/A = P/CL2. Where: F = applied load in kgf; A = the unrecovered projected are of the indentation in mm2; L = measured length of long diagonal of indentation in mm; C = 0.07028 = Constant of indenter relating projected area of the indentation to the square of the length of the long diagonal.
Experiments were done perpendicularly to the external surface of the enamel [22 (link)]. At the start of sample preparation the enamel surface were polished to obtain a flat surface. Blocks were then submitted to baseline microhardness analysis using a microhardness tester (IndentaMet 1100 Series, Buehler Ltd., Lake Bluff, IL, USA) with a knoop diamond under a load of 25 grams for 5 seconds. One indentation was made.