## 1 Introduction  
Ion-releasing dental restoratives, especially fluoride, have garnered increased attention, owing to their anti-cariogenic effects and enhanced remineralization of dental hard tissues, especially in pathologic conditions [1, 2, 3]. There are several fluoride-containing dental restoratives available on the market, including glass ionomers, resin-modified glass ionomers (RMGI), polyacid-modified composites (compomers), giomers, and composites [1]. Glass ionomer cements chemically bond to tooth structure, and their fluoride release ability provides a caries-preventive effect [4]. RMGI is a hybrid material of traditional glass ionomer cement with a small supplement of light-curing resin [5]. Giomer is based on the incorporation of surface pre-reacted glass-ionomer fillers into a resin matrix. It has fluoride-releasing property which might enhance the antibacterial effects in restoration [6]. Recently, a new 'alkasite' restorative material was introduced, comprising an alkaline filler, which releases acid neutralizing ions along with fluorides, calcium and hydroxide ions along changes of the oral environment [7]. Alkaling glass fillers were shown to be able to raise the pH and form fluorapatite in media containing phosphate, which could explain the low incidence of secondary caries in alkasite restorations [8]. Ion release from fillers has been reported to induce the remineralization of dental hard tissues in previous studies [9]. Fluoride-containing restorative materials may feature greater longevity, a reduced incidence of marginal failure, an elevated concentration of fluoride in contingent plaques, and antibacterial action when compared with non-fluoride-releasing materials [10].  
Intraoral pH can be largely influenced by dietary intake, but also by intrinsic factors, such as regurgitation [11], and by the flow rate and buffering capacity of saliva [12]. In a healthy oral cavity, the pH is maintained near neutrality (6.7-7.3) by saliva [13]. In pathological conditions, such as periodontitis and dental caries, changes in the microbial and environmental dynamics may yield a shift of the pH level in lesions. The pH, after a sucrose rinse on localized plaque, can decrease to a cariogenic pH of 4-4.5 [14]. Bacterial acid production results in a decrease in pH, which may be the driving force behind the carious process [15]. Natural tooth surfaces and filling materials are not only affected by bacterial acids, but also by strong acids that induce erosion. This may be induced by extrinsic acids (soft drinks) and intrinsic acids (refluxed gastric acids). During reflux episodes, gastric acid attacks the tooth structure with a pH of 1.5-3.1 [16; 17].  
The aim of this study was to evaluate the bond strength to the dentin of three different ion-releasing restorative materials: a gomer, an RMGI, and an alkasite restorative material and the marginal integrity of class V restorations. The null hypotheses were that (1) the type of materials, (2) various pH conditions, and (3) the locations in the margin (enamel or dentin) would have no significant effect on the bond strength to the dentin and the marginal microleakage of the class V restorations.