## 1 Introduction
* Tricyclodecandimethanol dimethacrylate (DCP): allows for the handling of the material and mixing of the two components and improves the mechanical properties of the material. * Tetramethyl-xylylen-diurethane dimethacrylate (aromatic-alifict UDMA): diminishes the colour variation of the material over time and increases elasticity. * Polyethylene glycol 400 dimethacrylate (PEG-400 DMA) is a liquid monomer that increases the fluidity of the material and bagnability of the surface on dentin and enamel. The fillers contained in the powder component, which are about 78.4% of the material's volume are as follows. * Alluminosilicate (Al\({}_{2}\)SiO\({}_{5}\)) and barium (Ba): increases the strength of the material. * Ytterbium trifluoride (YbF\({}_{3}\)): provides radiopacity. * Isofiller: made of pre-polymerized UDMA fragments, it diminishes polymerization shrinkage. * Calcium, barium, and aluminium fluorosilicate glasses: they increase strength while providing fluoride release. * Calcium fluoro silicate glass: releases basic ions (F\({}^{-}\), Ca\({}^{2+}\), OH\({}^{-}\)) and represents the 24.6% of volume of the material. In order to adhere to the prepared cavity, no etching is needed, while the use of an adhesive is suggested in case of non-retentive design of the cavity. This material has the capability of releasing basic ions when saliva reaches acidic pH levels (i.e., during and after meals), preventing demineralization of tooth tissue and countering the acidic attacks by bacteria. This effect is similar to that typical of bioactive composite resins [19]. Fluoride ions are incorporated in the enamel's crystalline reticle in the form of fluorapatite, which is considerably more resistant to acid attacks compared to conventional enamel apatite. Fluoride also has antibacterial activity, inhibiting acidic production by bacteria such as _Streptococcus mutans_, thus slowing down plaque activity and growth. For this trial, the materials chosen were an alkasite restorative material (Cention-N, Ivoclar Vivadent AG, Schaan, Liechtenstein) and a glass ionomer cement (Fuji-IX, GC Europe, Leuven, Belgium). The use of GIC for Class I carious lesions has been suggested, whereas its use for Class II carious lesions is discussed in the literature and supported by expert opinions [20; 21]. The clinical performance of the alkasite restorative material has been evaluated through the FDI parameters in a 2016 trial, suggesting its use to restore primary teeth and reporting better performance compared to GIC [22; 23]. To evaluate dental restorations, the FDI criteria present three levels of evaluation [24]: aesthetic, biological and functional. Each level is comprised of 16 evaluation criteria divided in sub-groups. * Evaluation of aesthetic properties:
* Surface luster;
* Surface staining;
* Color stability and translucency; and
* Anatomic form. * Evaluation of biological properties:
* Post-operative sensitivity and tooth vitality;
* Secondary caries;
* Tooth integrity and enamel cracks;
* Periodontal response compared to a reference tooth;
* State of the mucosa adjacent to the restoration; and
* Oral and general health. * Evaluation of functional properties:
* Retention and fracture of the restoration;
* Marginal adaptation;
* Wear of the restoration;
* Presence and persistence of the contact point;
* Presence of food impaction;
* Radiographic examination (if available); and
* Patient's view (opinion of the patient or, in this case, of the parent). For all groups, five steps of grading were used for evaluation:  
* 1: Clinically excellent/very good;
* 2: Clinically good;
* 3: Clinically sufficient/satisfactory;
* 4: Clinically unsatisfactory; and
* 5: Clinically poor. This trial's primary focus is to evaluate the clinical properties, in terms of aesthetics, function and biology, of Cention-N alkasite material compared to glass ionomer cement. This is done through the FDI criteria universally used to evaluate direct dental restorations [24].