Chemical Effects of Nanosecond High-Intensity IR and UV Lasers on Biosilicate® When Used for Treating Dentin Incipient Caries Lesions

Abstract

The root caries lesions still represent a health problem due to their rapid progression and, therefore, more efficient remineralization strategies are necessary. High-intensity lasers are useful because they modify the microstructure of the irradiated tissue due to heating; however, nothing is known about the effects of these lasers when associated with bioactive materials to remineralize caries lesions. This study evaluated the compositional changes that the Q-switched lasers emitted in the spectral region of infrared (IR, 1064 nm) and ultraviolet (UV, 355 nm) make in Biosilicate® on dentin with incipient caries lesion. Sixty blocks of demineralized root dentin were randomly divided into 6 experimental groups, to be treated with Biosilicate® alone (10% in fetal bovine serum), lasers alone (IR or UV, 5 ns, 10 Hz, 5 pulses/sample, 250 mJ/pulse or 100 mJ/pulse, respectively) or laser irradiations after 24 h of Biosilicate® application. After 24 h immersed in artificial saliva, samples were evaluated by Fourier transform infrared spectroscopy between 450 and 4000 cm⁻¹. Laser irradiation alone reduced the organic, carbonate and water contents of the dentin, with greater effects promoted by the IR-laser as a result of heating. Biosilicate® alone elevated the content of phosphate and carbonate, which suggests formation of carbonated hydroxyapatite (HAC) on dentin. The irradiation with UV-laser after Biosilicate® also promoted an increase in the phosphate content, however there was less conversion of the biomaterial, evidenced by the rise in the intensity of the bands corresponding to the siloxane and amorphous phase of the apatite. Irradiation with IR-laser after Biosilicate®, on the other hand, promoted a significant increase in phosphate content when compared to the group treated with Biosilicate® alone, without the presence of siloxane bands. It was concluded that laser irradiation can augment the bioactivity of the Biosilicate®, evidenced by the greater formation of HAC and, for this, the wavelength of 1064 nm should be used.