To investigate the effects of laser irradiation and fluorid application on surface micro-hardness, fluoride uptake and acid resistance on initial carious lesions in vitro

In this study, individual and combined effects of the APF gel and Er:YAG laser application on enamel surface which artificially created initial caries. These applications' effects on demineralization and remineralization were compared using various study groups. For this purpose, on the initial decay formed surface of enamel, microhardness change, superficial fluoride uptake and mineral loss after acid treatment were evaluated. In this study, 15 bovine teeth are used for the determination of surface microhardness test and the 15 teeth are used to determine fluoride uptake and the acid resistance. After separated from each crowns from roots, teeth is divided into 4 equal parts and a total of 120 samples were obtained. 60 samples used in surface microhardness test were embedded in the acrylic metal molds. After grinding and polishing procedures, 3×3 standart windows on labial surfaces were prepared. Remaining surfaces was coated with acid resistant nail varnish. Initial surface microhardness measuring the Vickers hardness value (VSN) were calculated. After the initial decay were created, enamel surface microhardness measured again. In the formation of experimental and control groups according to the surface microhardness values on enamel after demineralization, stable distribution is made and after the demineralization the average surface microhardness values in each group has been noted to be close to each other. Samples which were prepared and initial caries were generated are divided into 5 groups of 12 samples in each group. Groups are defined as; Control group (K) with no treatment has been performed, the group apply only APF gel (F), before Er:YAG laser after APF gel treatment group (L+F), before APF gel after Er:YAG laser treatment group (F+L), the group apply only Er:YAG laser (L). After applying the treatments mentioned in the experimental groups, samples were exposed to a final pH cycle and surface microhardness values are measured. In KOH-soluble fluoride uptake experiment, remaining 60 samples were used. After 3 × 3 mm adhesive tape adhered to the enamel samples, the remanining surfaces were covered with blue wax. In this experiment, in addition to the groups identified in the microhardness test another control group which was not kept in demineralization solution was added and totally 6 groups were obtained. After each enamel specimen was kept in 1 ml 1 M potassium hydroxide (KOH) for 24 hours, the same amount TISAB III solution was added and then fluoride measurements were made. For the determination of the acid resistance, samples identified for fluoride uptake were used. Samples were incubated for 30 seconds in 1 ml of hydrochloric acid. After transferring the acid solution in which tooth enamel was dissolved into the polyethylene tubes, calcium, magnesium and phosphorus ion concentrations analysis were determined using inductive coupling plasma mass spectrometer. In all treatment methods which initial caries formed on enamel, surface microhardness values (VSN) was found statistically significantly higher compared to the control group which no treatment was made (p=0,0001). However, the surface microhardness values obtained after these applications can not get the initial values, and were found statistically significantly lower (p=0,0001). The most effective method for increasing the surface microhardness of the tooth enamel was determined that APF application after Er:YAG laser application. The VSN values obtained in this group compared to the group which only the APF jel applied before the application of Er:YAG laser was determined to be statistically significantly higher (p=0,033). When the concentration of soluble fluoride KOH data are evaluated, the difference between the control and experimental groups were found to be statistically significant (p=0,0001). The highest uptake of fluoride is Er:YAG + APF group and the lowest values Er:YAG laser group which administered alone was found. The evaluation of the acid resistance, calcium concentration dissolves in tooth enamel, only the APF applied group was found to be statistically significantly lower than all other groups. Between the experimental groups, the highest calcium concentration Er:YAG + APF was found in groups. Magnesium and phosphorus concentrations were determined in control and experimental groups in mean that there is no statistically significant difference was seen. KOH soluble fluoride concentration and the determination of dissolved tooth enamel in hydrochloric acid, between the concentrations of calcium (r = -0.342 p = 0.008) and phosphorus (r = -0.322 p = 0.012) were determinened as statistically significant negative correlation. As a result, under the conditions of this in vitro study, APF application following the Er:YAG laser application increase the surface microhardness and KOH soluble fluoride uptake on the initial decay formed enamel surface was observed. However, there is no statistically significant effect on the acid resistance of tooth enamel. Therefore, evaluating the effect of the Er: YAG laser applications with various parameters using in conjunction with the different fluoride applications should be study to be a need for in vitro and in vivo studies is believed.