Dental caries is a very common condition, and although it has become less common, it still represents a serious public health risk. Caries symptoms range from the earliest molecular alterations in the tooth's apatite crystals to an apparent white spot lesion (WSL) or eventual cavitation. The white spot lesion looks chalky because minerals are being lost from both the surface and the underside of the enamel. A relatively simple and noninvasive caries preventive regimen in treating white spot lesions with low-level laser irradiation, either alone or with topical fluoride treatment. This treatment results in reduced enamel solubility and dissolution.

The study was reviewed and approved by the "Ethical research committee "of the Faculty of Dental Medicine for Girls; at Al-Azhar University, Cairo, Egypt. This study was conducted on 90 teeth with white spot lesions (WSLs) detected clinically on the buccal surface of teeth. The patients with WSLs were selected randomly from the operative dentistry clinic at the Faculty of Dentistry, Girl's Branch, Al-Azhar University After examination, the teeth will be assigned into six groups of 15 teeth with white spot lesions each according to the remineralizing material used: * The first group (A1B1): The teeth with WSL will be treated with nano-hydroxyapatite +fluoride with laser application. * The second group (A1B2): The contralateral teeth will be treated with nano-hydroxyapatite +fluoride without laser application. * The third group (A2B1): The teeth with WSL will be treated with nano-hydroxyapatite + xylitol with laser application. * The fourth group (A2B2): The contralateral teeth will be treated with nano hydroxyapatite+ xylitol without laser application. * The fifth group (A3B1): The teeth with WSL will be treated with 5% sodium fluoride varnish with laser application. * The sixth group (A3B2): The contralateral teeth will be treated with 5% sodium fluoride without laser application.