Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

The physicochemical and biological properties of calcium silicate-based cement (CS) associated to microparticulated (micro) or nanoparticulated (nano) zirconium oxide (ZrO 2 ) were compared with CS and bismuth oxide (BO) with CS. The pH, release of calcium ions, radiopacity, setting time, and compression strength of the materials were evaluated. The tissue reaction promoted by these materials in the subcutaneous was also investigated by morphological, immunohistochemical, and quantitative analyses. For this purpose, polyethylene tubes filled with materials were implanted into rat subcutaneous. After 7, 15, 30, and 60 days, the tubes surrounded by capsules were fixed and embedded in paraffin. In the H&E-stained sections, the number of inflammatory cells (ICs) in the capsule was obtained. Moreover, detection of interleukin-6 (IL-6) by immunohistochemistry and number of IL-6 immunolabeled cells were carried out. von Kossa method was also performed. The differences among the groups were subjected to Tukey test (p 0.05). The solutions containing the materials presented an alkaline pH and released calcium ions. The addition of radiopacifiers increased setting time and radiopacity of CS. A higher compressive strength in the CS 1 ZrO 2 (micro and nano) was found compared with CS 1 BO. The number of IC and IL-6 positive cells in the materials with ZrO 2 was significantly reduced in comparison with CS 1 BO. von Kossa-positive structures were observed adjacent to implanted materials. The ZrO 2 associated to the CS provides satisfactory physicochemical properties and better biological response than BO. Thus, ZrO 2 may be a good alternative for use as radiopacifying agent in substitution to BO.

There was a significant regression in the inflammatory reaction in the capsules indicating, therefore, that Biodentine is a biocompatible material.

Niobium pentoxide can be used as radiopacifier for the development of calcium silicate-based materials.

Biodentine and MTA exhibit potential as repair material in the treatment of furcation perforations.