# Dentin Bond Strength of Calcium Silicate-Based Materials: A Systematic Review of In Vitro Studies
## 1 Introduction  
In the root canal filling phase, the use of a sealing cement, which acts as an interface between the gutta-percha and the tooth structure, is essential [1]. Calcium silicate-based cements (CSCs) are materials that stimulate tissue regeneration and have a hydrophilic profile and excellent biocompatibility properties, due to their similarity to biological hydroxyapatite [2]. They have an intrinsic osteoinductive capacity, achieving a good hermetic seal due to the formation of a chemical bond with the tooth structure [2]. They have different levels of radiopacity and a great antibacterial capacity [2]. Among the most studied CSCs we can find Biodentine, EndoSequence BC sealer, EndoSequence Root Repair Material, ProRoot MTA, and EndoSeal [3]. CSCs are also bioactive. Bioactivity is defined as a material's ability to form hydroxyapatite on its surface and develop a mineral attachment or adhesion to the dentin substrate through the ionic interchange with surrounding tissue fluids [4]. Adhesion to dentin is a necessary characteristic for a root canal sealing cement. The aim is to achieve a three-dimensional union between gutta-percha, cement, and dentin, resulting in a hermetic seal of all the root canals. In this way, all anatomical irregularities of the root canal should be well filled to prevent any space or interface that could cause a bacterial or oral fluid filtration [1]. The challenge arises in achieving hermetic sealing when faced with undesirable conditions like perforations, resorptions, or open apices. Consequently, there is a demand for a restorative material capable of strong adherence to the dentin of the root canal. This material must also uphold the integrity of the material-dentin interface in static conditions andresist displacement. The effectiveness of this bond is influenced by the inherent properties of the materials involved and may also be influenced by the presence of the smear layer on the dentin surface. [5]. One of the tests most used to evaluate the adhesive property of a sealing cement is the so-called \"push-out bond strength\" test [6]. It consists of applying tensile forces to the root in its longitudinal axis to evaluate the share bond strength or dislocation resistance of a material [6]. The results depend on many variables such as the filling technique, tooth type, portion of the tooth studied, slice thickness, storage time, and loading speed [6]. The measurement is carried out in megapascals using a universal testing machine. Pressure is exerted with the plunger to separate the elements, and the measurements are recorded with computerized software [4]. Alternative methods for assessing the adhesive capability of a sealing cement include scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). SEM enables the observation of high-magnification images (ranging from 50\(\times\) to 10,000\(\times\)). In this technique, an electron beam scans the surface of the sample, and the resulting signals are captured by a detector. Commonly used detectors in SEM include secondary electron detectors (ETD or SE1/SE2 in high vacuum or LFD in low vacuum) and backscattered electron detectors (BSED). While high vacuum provides superior magnification, it needs sample conductivity. As teeth and dental materials are non-conductive, preparing the sample involves applying a layer of gold (Au), which may potentially damage the sample [7]. CLSM operates with a laser beam serving as a light source and an electronic system for image processing. This technique utilizes extremely thin cross-sections (0.5-1.5 nm), resulting in high-resolution optical images. The elimination of light interference caused by different optical fields in the sample thickness contributes to the clarity of the images. The laser beam traverses a narrow space referred to as a pinhole, reflects off the sample, returns to the microscope for refocusing, and passes through the pinhole once more.