###### Abstract  
The objective of this study is to conduct a systematic review of the literatures on the effect of treatment combining 9300 nm carbon dioxide (CO\({}_{2}\)) lasers and fluoride on prevention of enamel caries. A literature search was performed using PubMed, Scopus, and Web of Science. The keywords were ((9300 nm) OR (9.3 \(\upmu\)m) OR (carbon dioxide laser) OR (carbon dioxide lasers) OR (CO\({}_{2}\) laser) OR (CO\({}_{2}\) lasers)) AND ((fluoride) OR (fluorides)) AND ((dental caries) OR (caries) OR (remineralization) OR (remineralization) OR (demineralization) OR (demineralization)). Meta-analysis was performed to compare the change in mineral content by laser irradiation and fluoride treatment (F + L) with that of fluoride treatment (F) and laser treatment (L). The search identified 946 potential publications and five laboratory studies using a chemical model for caroigenic challenge and determining mineral loss of the enamel were included in this review. Meta-analysis comparing F + L with L on enamel showed a standard mean difference of \(-\)1.58 (CI \(-\)2.13, \(-\)1.03). Meta-analysis comparing F + L with F on enamel showed a standard mean difference of \(-\)1.84 (CI: \(-\)2.30, \(-\)1.39), with low heterogeneity (\(l^{2}\) = 49%, \(p\) = 0.04). In conclusion, F + L was better than L and F in preventing enamel demineralization. Keywords:fluoride; caries; prevention; laser; enamel; demineralization; remineralization; carbon dioxide +
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which acts as a temporary fluoride reservoir and can release fluoride ions in an acidic environment [7]. In addition, the topical use of fluoride can delay the progression of lesions and inhibit the formation of biofilm by binding to bacterial cellular components, and it can influence enzymes related to carbohydrate metabolism [8; 9]. Fluoride also inhibits collagenases and thus hinders the degradation of dentine collagen [10]. Another strategy in preventing dental caries is the use of lasers [11]. Lasers can be absorbed by hydroxyapatite, the main mineral composition of dental enamel and dentine [12]. This absorption causes chemical and morphological changes such as the reduction of carbonate content and the recrystallization of hard dental tissues [11]. Compared with lasers at other wavelengths, such as argon lasers or neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, carbon dioxide (CO\({}_{2}\)) lasers have a higher absorption coefficient to enamel. Therefore, carbon dioxide (CO\({}_{2}\)) lasers may be a promising treatment for the prevention of caries [13]. CO\({}_{2}\) lasers have been found to increase the enamel's acid resistance to caries [14]. CO\({}_{2}\) lasers produce various emission laser lines with wavelengths ranging from 9000 nm to 11,000 nm [15]. Laser technology has evolved rapidly in recent years and has been proven as an effective strategy for the prevention of caries. A short-pulsed 9300 nm CO\({}_{2}\) laser is now commercially available and is one of the lasers most highly absorbed by the mineral components of hard dental tissue. This 9300 nm CO\({}_{2}\) laser has higher absorption but lower reflectance in hydroxyapatite than the conventional CO\({}_{2}\) laser (10,600 nm) [16]. Thus, it possesses a more effective energy transfer ability to dental hard tissues. A study showed that irradiation with a 9300 nm CO\({}_{2}\) laser can inhibit more than 60% of enamel caries compared with the negative control [17]. Moreover, because the 9300 nm CO\({}_{2}\) laser better matches the absorption characteristics of dental hard tissues, it can localize heat deposition to the surface and reduce the risks of thermal damage to the pulp [18; 19]. Thus, a 9300 nm CO\({}_{2}\) laser can be used safely and effectively for the prevention of caries. There is a general consensus that topically applied fluoride can reduce demineralization and enhance remineralization via physical and chemical interventions, however, its effect is partial and cannot prevent demineralization completely.