## 1 Introduction
It can be performed in cases of pulp necrosis secondary to trauma, decay, or dental anomalies. As for endodontic treatment, the success rate of these techniques is influenced by efficiency of bacteria eradication and recontamination prevention [2]. The principal objective of temporary restorations is to provide a tight seal of the access cavity, to prevent reinfection of root canal system/vital pulp from microorganisms present in saliva [5] and to guarantee protection of other materials located in cavity access/chamber floor or root canal system [6; 7; 8; 9]. Previous studies demonstrated that bacteria present in natural human saliva will penetrate in <30 days through an entire root canal system obturated by a lateral or vertical condensation techniques [10]. Another advantage of temporary filling materials is the reduction in time to re-open cavity access in case of worsening of pulpal/periapical signs/symptoms or failure of vital pulp therapy with subsequent need of endodontic treatment [6; 11]. The most commonly used materials for short-term temporizations contains zinc oxide eugenol and zinc oxide/calcium sulphate [1]. These compounds possess antimicrobial properties and good sealing properties, determined by its hygroscopic nature and high setting expansion [12; 13]. Moreover, are simple to apply in cavity access with bulk techniques and easy to remove. Previous studies, evaluating marginal leakage of different temporary restorations, concluded that zinc oxide/calcium sulphate materials had better marginal seal in Class 1 and Class 2 cavity access preparations [6]. However, these materials lack mechanical properties and need to be minimum 3.5 mm in thickness [14] to prevent total leakage. Moreover, no mechanical loading would be preferable to maintain their stability in tooth cavity [15]. In addition to temporary filling material, a \"spacer\" or \"barrier material\" placed apically to the provisional restoration can be used in most clinical situations [16]. In endodontics, spacers can prevent unwanted materials (also the same temporary material) entering and blocking the canal space in multiple visit approach endodontic treatments [17]. In addition, spacers reduce the time required to access the root canal system and reduce the risk of chamber floor damage during removal of the temporary material [18]. Spacers can also be soaked with medicaments in specific emergency procedures [19]. When pullectomy is not achievable, an emergency procedure for temporary relief of symptomatic acute pulpitis can be pulotomy eventually associated to soaked pellets used as chamber floor medicaments [20; 21; 22]. One of these medicaments is eugenol, that can rapidly inhibit bacteria and kill viruses, with an analgesic effect to relieve the pain of patients [23]. Another chamber floor medicament is m-cresyl acetate that allows the removal of bacterial biofilm and is less irritating for periapical tissues than other compounds such as p-chlorophenols [24]. The probability of eliminating pain is related to the extent of the inflamed/necrotic tissue removal. However, if there is no sufficient time to for a complete removal of pulpal tissue (pulpectomy), pulpotomy will give a better pain-relieving effect compared with incomplete canal instrumentation [20]. Spacers soaked with water can be used to provide a suitable humidity source in therapies (vital pulp therapies, apexogenesis, apexification, and perforation repair) using calcium-silicate cements, that needs humidity for their setting time and bioactive properties. Calcium silicate-based cements, also called hydraulic cements, have gained popularity due to their excellent biological and physiochemical properties. The chemical basis of the setting mechanism of these sealers consists of a hydration reaction in which water is absorbed from dentin tubules, and a calcium silicate hydrate gel and calcium hydroxide are produced. Moreover, the latter is able to react with the phosphate ions to precipitate and form hydroxyapatite (HA).