Evaluation of the Effectiveness of Low Power Diode Laser with different wavelengths in Dental caries Prevention (In Vitro Study)

Abstract

Dental caries is chronic infectious disease affecting all population .Conventional ways of prevention by fissures sealant and fluoride application ,these two main methods inherited draw back as fluoride only act on smooth surfaces 2 and fissures sealant may partially or completely lost. New technology for caries prevention by lasers either in high or low powers. The main objective of this study is to investigate the effectiveness of low power Diode lasers, with different wavelengths, in caries prevention (in Vitro study), while specific objectives are to assess effectiveness of irradiation time on the prevention process and to compare different wavelengths in their effectiveness in caries prevention. True experimental post test design was done in two phases, first by measurement of caries like depth by polarized light microscopy and the second phase, by measurement of the amount of calcium dissolution after irradiation by different wavelengths. For the first phase four wavelengths of diode lasers were used, 532 nm (4 mW), 671 nm (100 mW), 675 nm (30 mW) and 810 nm (20 mW). A fifth group was added as a control (without irradiation). The specimens were prepared by coating the extracted human premolar teeth with acid resistance nail varnish leaving only 2x2 mm of the enamel surface uncovered. For each wavelength, samples were divided into three groups for three irradiation time as 4, 8 and 12 minutes. Each group of irradiated samples and the control were immersed in lactic acid (3.5 pH) and incubated for 21 days under controlled temperature of 37 C°. After the incubation period the teeth samples were sectioned longitudinally dissecting the 2x2 enamel window and slides 3 were prepared for microscopic examination. For the second phase the experiment aimed to measure the amount of calcium dissolved after irradiation, two wavelengths were used, 532 nm (100 mW) and 671 nm (100 mW). Samples were prepared by cutting each tooth into two cubic specimens of 4x4 mm enamel surface (one for irradiation and the other as control). The five surfaces of the cubic were coated by acid resistance nail varnish leaving the 4x4 enamel surface uncovered. Irradiation was done for each wavelength with different time as 4, 8, 12 and 16 minutes. Specimens were immersed in 3 mL lactic acid (pH 4.4) for 24 hours under controlled temperature of 37 C°. The amount of calcium dissolution was measured by atomic absorption spectrophotometery using flame photometer. Data was displayed in a form of tables and figures. Statistical analysis was done using ANOVA, Chi squire and T. test. Statistical significant differences were measured, with the level of P value less than 0.05. The results of microscopic examination showed that the depth of the caries like lesion in 810 nm and 675 nm wavelengths, for different irradiation time was more than that in control group (no effect), while the 671nm and 532 nm lasers wavelengths revealed depth of 70 μm and 112 μm, respectively, compared with 180 μm in control group. Increasing irradiation time decrease the depth of caries like lesions as in 532 nm, 4 min (230 μm), 8 min (160 μm ) and 4 12 min (112 μm), while 671 nm , 4min (170 μm ), 8 min (100 μm ) and 12 (70 μm). The results of calcium dissolution showed that the percentages of teeth having less calcium content are more in laser groups. Eight minutes time, revealed highest percentages of irradiated sample with less calcium content (671 nm gave 81.25% while 532 nm gave 78.60 %).The mean of calcium (μm /mL) dissolved in acid decreased when increasing irradiation time with p value less than 0.05. In conclusion diode laser of wavelengths 532nm and 671 nm showed promising results in caries prevention, increasing irradiation time to resistance to acid dissolution. 5 certain value, increase