Dental caries is one of the most common oral diseases, and white spot lesions are non-cavity lesions of early enamel caries, which are also common around fixed orthodontic appliances. At present, there are many treatments for white spot lesions, but due to variable limitations and conditions, no consensus has been reached on the clinically recommended best solution for the treatment of early dental caries yet [22–24]. In recent years, biomimetic mineralization of demineralized enamel has gradually come into view by researchers.
GERM CLEAN, a new biological polypeptide oral spray, occupies a certain market in China as a mature product. According to the manufacturer's instructions, this spray has a broad-spectrum antibacterial effect, is harmless to probiotics, and can promote mucosal repair. The antimicrobial effects on Streptococcus mutans and dual-species biofilm formed by Streptococcus mutans and Candida albicans of this product were confirmed by previous studies [19, 20]. Its’ remineralization ability was investigated in this experiment. The result that the mineral loss in the GC group was less than that in the DDW group suggested that GERM CLEAN had remineralization properties and could inhibit mineral loss to a certain extent. Moreover, the result of polarized light microscopy also supported this conclusion. It showed that the demineralization depth became shallower after the treatment of GERM CLEAN, which became deeper after the treatment of DDW, but GERM CLEAN was less effective than fluoride, that is in accord with the recent study [20]. For the surface roughness, GERM CLEAN manifested a better effect than the previous study [20], which may be due to GERM CLEAN of 50% mass fraction was used and the shorter pH cycling time of the previous study, while this study used the stock solution of GERM CLEAN. However, as for the lesion depth in the GC group, although it was shallower than that in the DDW group, there was no statistical difference between the two groups. This finding is contrary to the previous study [20], this result may be explained by the fact that we chose human molars as experimental subjects but the previous study used bovine permanent incisors as experimental subjects. There are differences in structures, the organic content and inorganic content between human and bovine teeth [25]. It was also noticed that the samples treated with NaF showed the smoothest surface, the least mineral loss, and the shallowest lesion depth, while these in the GC + NaF group were similar to those in the NaF group. This result reflected that the combined application of GERM CLEAN and NaF had no enhancement effect in terms of promoting remineralization.
In the present research, whether applied GERM CLEAN alone or GERM CLEAN combined with NaF, the observed remineralization effect were weaker than the peptides reported in the previous studies [20], the reason may be that GERM CLEAN has weak acidity with a pH of 6.5. The previous study reported that acidic amino acids could regulate the orientation of hydroxyapatite cyrstals [26]. The peptides with obvious mineralization effects such as Sp-H5 [27], QP5 [14] and 8DSS [13] reported in the literature could combined with calcium ions, promoted the hydroxyapatite nucleation, growth, and aggregation. In addition, when the two peptides combined with fluoride, the peptide-calcium phosphate compounds could induce more mineral deposition by binding to fluoride. Since the combined application of GERM CLEAN and NaF had no enhancement effect in terms of promoting remineralization, GERM CLEAN may cannot bind to fluoride, but the related remineralization mechanism remains to be further discussed. According to the latest review [28], there are forty-three synthetic antimicrobial peptides, but only four antimicrobial peptides promoting remineralization or preventing demineralization including Sp-H5 [27], CS-QP5 [29], TVH19 [30] and DR9-RR14 [31], and the four studies used laboratory or animal models. More clinical researches are needed before these antimicrobial peptides used for clinical treatment, while GERM CLEAN has been a clinical available antimicrobial peptide.
At present, the clinical methods for the treatment of early enamel caries, such as topical fluoride application, micro-grinding, bleaching, resin penetration, and direct or indirect repair, have some limitations, including dental fluorosis, tooth sensitivity, and damage to tooth tissue. However, the biomimetic mineralization of enamel using peptides is still in research, and there is still a long way to clinical transformation. As a marketed antimicrobial peptide, GERM CLEAN is a mature product, and the clinical safety of GERM CLEAN can be guaranteed. Due to the obvious antibacterial activity and mineralization promoting effects, GERM CLEAN still has broad application prospects in the clinical practice of early enamel caries.