# Assessment of Fluoride-Releasing Materials in Remineralization of Adjacent Demineralized Enamel
## 1 Introduction  
Dental caries remains a prevalent problem in both children and adults. The tight proximal surfaces of teeth are considered areas at high risk for the development of caries lesions. Enamel caries or white spot lesions (WSLs) are the first clinical signs of demineralization and start as non-cavitated. The untreated lesion can become a cavitated lesion that promotes biofilm accumulation and food impaction. In general, lesions that extend to dentine require invasive restorative treatment [1]. It is expected that proximal restoration with the ability to promote ion-releasing actions could potentially help repair the non-cavitated adjacent lesion.  
The selection of dental materials is an important step in the treatment process and in preventing future caries. Fluoride-containing restorative materials can promote remineralization and reverse early enamel caries lesions in contact with the restoration [2, 3]. The remineralization process, which is essential for repairing early enamel caries lesions, isdriven by supersaturated calcium and phosphate ions [4]. However, the process is significantly enhanced by the presence of fluoride ions when pH rises. This enhancement can reprecipitate the minerals and form acid-resistant fluorapatite, thereby boosting mechanical strength [5]. Saliva and toothpaste-derived fluoride play a crucial role in promoting remineralization by converting hydroxyapatite to less soluble fluorapatite. Furthermore, fluoride-containing restorative materials, with their unique ability to recharge fluoride from daily fluoride products, offer an innovative approach to caries prevention by continuously releasing fluoride ions [6; 7; 8].  
Glass ionomer cements (GICs) are fluoride-releasing materials that were first introduced in the late 1960s [9]. Many studies have shown their benefits both in vitro and in clinical use [2; 3; 10]. Resin-modified glass ionomer cement (RMGIC) and highly viscous glass ionomer cement (HVGIC) such as Fuji II LC(r), Fuji IX(r), and EQUIA Forte(r) (GC Corporation, Tokyo, Japan) are the most widely used and critically acclaimed fluoride-releasing materials and have been extensively researched in recent studies [3; 7; 8; 11].  
The alkasite resin-based composite (Cention N; CN) is an innovative, dual-cured dental restorative material that features aesthetic properties. Its composition includes fluoride and alkaline fillers. This material can be used as an alternative to amalgam in class II posterior restorations [12; 13; 14]. CN has a good sealing ability with less microleakage compared to conventional GIC and composite restorations [14]. In one study, CN showed the highest flexural strength, followed by resin composites and RMGIC, respectively [15]. Moreover, CN displayed high microhardness properties capable of withstanding masticatory forces [16] and provides proximal tight contact comparable to a resin composite when used in restoring class II cavities [17].  
A substantial amount of fluoride ions can be released from the alkasite resin-based composite. A previous study showed that in acidic pH, self-cured CN demonstrated the highest fluoride ion release, followed by light-cured CN and GICs, respectively, over a long-term duration [18]. CN also raises the pH in degradation and releases calcium in addition to fluoride. Fluoride release from restorative materials has been proven to promote the remineralization of adjacent enamel caries lesions [19; 20]. However, there are insufficient studies comparing CN to other restorative materials in promoting the remineralization of enamel caries of the adjacent tooth.  
Therefore, the aim of this in vitro study was to investigate the ability of fluoride-releasing restorative materials to remineralize artificially demineralized proximal enamel adjacent to the restoration. The null hypothesis was that there would be no statistically significant difference in the lesion depth (LD) and mineral density (MD) of proximal demineralized enamel following contact with CN, RMGIC, HVGIC, or resin composite materials.