The effects of Er:YAG laser irradiation on enamel caries prevention

Objectives: Several studies were performed to examine the effects of lasers and fluoride on dental hard tissues with several different applications. During the last few decades, many studies, using different kinds of laser pre-treatment of enamel in inhibiting subsequent artificial caries-like lesions in the laboratory. However, in the recent literature, very little information has been known about Er:YAG lasers' effective role of inhibition of enamel demineralization. Therefore, the aim of this study was to examine the effect of Er:YAG laser irradiation, and APF gel alone and in combination on carieslike lesion formation in extracted human molar tooth enamel in vitro.

Methods: Twenty extracted human non-carious molar teeth were selected. The teeth were covered with nail varnish, leaving two windows(approximately 4mmx2mm) on both the buccal and lingual surfaces at the middle third of the crown. The windows were randomly assigned to four groups, which were no-treatment control(A), Er:YAG laser irradiation alone(B), APF gel(Sultan/topex Neutral Ph Gel,Sultan Dental Products Ltd) treatment alone(C) and Er:YAG laser irradiation before APF gel treatment(D). Er:YAG laser unit(KaVo KEY Laser 3,KaVo Dental GmbH) was used with low-fluence irradiation at 100 mJ with 2 pps(pulse per second), and 1.0 mm spot size. Then a two-day pH-cycling was performed, with an 18-hour demineralization followed by a 6-hour remineralization. Sections(two per tooth segment) of 120±20 µm in thickness were obtained from each window. Mean lesion depth was measured using polarized light microscope. Kruskal-Wallis test and Mann-Whitney U test were used for evaluation of treatment effects. Bonferroni correction was used in multiple comparison.

Results: Mean lesion depths(±standard deviation) were 134±32 micrometers for group A, 90±18 µm for group B, 109±25 µm for group C, and 74±23 µm for group D. Mean lesion depths of all treatment groups were significantly less than those for the matched no-treatment control group(Mann-Whitney U). Er:YAG laser irradiation before APF gel treatment significantly reduced lesion depth compared with the no-treatment control and APF gel treatment alone(Mann-Whitney U).

Conclusion: Er:YAG laser irradiation in combination with fluoride treatment was improved resistance to enamel dissolution and reduced the mean lesion depth.