## 1 Introduction  
Caries in primary dentition have a prevalence of up to 90% worldwide [1]; in Italy, prevalence varies from about 43% at age 12 to 21% at age 4 [2,3]. Many different factors influence the results of a restorative treatment: patient's compliance, adherence to post-treatment recall programs, state of dentition development, assessment of caries risk and, most importantly, which material is chosen for the restoration [4]. This last factor may be directly influenced by the patient's compliance, because a scarce compliance often makes it difficult (if not impossible) to isolate and access the lesion properly. For restoring posterior primary teeth, the available restorative materials include glass ionomer cement (GIC), resin modified glass ionomer cement (RMGIC), high-viscosity glass ionomer cement (HVGIC), amalgam (AM), composite resin (CR), pre-made steel crowns (SSC), and compare (CP) [4]. Some of these materials are also used for cementation of orthodontic brackets [5]. There is both a lack of agreement and of scientific evidence in dental literature regarding which restorative material is the best choice to restore caries in primary dentition [6,7]. The choice between the different materials available for restoring primary is influenced by different aspects, including repeatability of the used technique, substrate characteristics, cavity design, and aesthetic requirements [8]. Glass ionomer cements (GICs) are provided in a base/catalyst formulation, with a basic powder and an acid liquid that need to be mixed. The base powder composition is based on three components: silica (SiO\({}_{2}\)), aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) and fluorite (CaF\({}_{2}\)). The liquid component is usually a mixture of organic acids [9,10]. This material is self-curing, thanks to a reaction between the liquid polymer acids and the basic particles (acid-base reaction). The first phase of hardening is completed after about 4 min and continues in the following hours up to 10 days after the first phase [11]. GICs adhere to tooth structure thanks to chemical and micromechanical adhesion. The first of these is provided by the formation of ionic bonds between polialchenoic acid and calcium, and the second is provided by the hybridization between the material and the collagen fibers on the surface. Because there is no need to use etchants and adhesives, and the material is self-curing, it becomes clear that there is an high potential in using GICs in less compliant and younger patients where proper isolation is impossible and working in a quick and precise manner is essential [12]. A key property of the material is the capability of releasing fluoride ions in the surrounding tissues and saliva; they are also able to be \"recharged\" with the application of topical fluoride [13,14]. Thanks to this property, GICs can make the dentin and enamel surrounding the restoration more resistant to acid attacks, thereby preventing secondary caries and caries progression [15, 16, 17, 18]. In spite of the positive aspects of this material, such as the ease of application, quick hardening, and biological active proprieties, there are some drawbacks to glass ionomer cement (GIC) that need to be highlighted. The material is inherently fragile and scarcely resistant to wear, thus making it a material ideal for provisional restorations or restoration of deciduous teeth. Alkasite materials are a subgroup of dual cure resinous materials, usable in greater increments compared to conventional composites. They are available in a base/catalyst formulation. The base (powder) contains glass fillers, pigments, and polymerization initiators, whereas the catalyst (liquid) contains metacrylates and polymerization initiators. In particular, the methacrylates contained in the liquid component are as follows. * Urethane dimethacrylate (UDMA): main component, provides the basic mechanical properties of the material.