## 4 Discussion  
Since secondary caries at the cavo-surface margins is the prime reason for the failure of any restoration, restorative materials that are biocompatible and promote tertiary dentin formation are highly desirable. This study inspected a potential bioactive novel nano-hydroxyapatite-silica-glass ionomer cement in an animal model and investigated the reaction of the dentin-pulp complex in tooth cavities of rats. Our study outcomes provide evidence that nano-HA-SiO\({}_{2}\)-GIC exerts mild to moderate dentin-pulp complex reactions comparable to conventional GIC and therefore attains adequate biocompatibility. The methodology used in this study permits us to characterize: (i) the different effects of occlusal and cervical types of restoration on dentin-pulp complex; (ii) the differentiation of tertiary dentin which is formed due to normal physiological processes (such as tooth grinding and attrition) with the tertiary dentin that is formed because of biological effects of the material; and (iii) the reproducibility of the cavity preparation in molars of rats by using ImageJ analysis. Judgment between TDF resulting from normal physiological effects and what is consequential from the restorative material is a critical point, mostly explored by the investigation of longer duration observation that is the 1-month interventional period [27; 29]. Rat molar teeth are an excellent model for studying dentin-pulp complex response after restoration due to their anatomical and genetic similarities to humans [27; 33]. Regarding pulp tissue disorganization, the response of both types of restorations at 1-week intervals in both occlusal and cervical type restorations was more restricted to the odontoblastic layer disruption in the pulp area corresponding to the cut dental tubules. However, after a 1-month interval, the normal palisade arrangement of cell bodies of odontoblasts in the outermost zone of the pulp was restored. A study by [PERSON] [34], who utilized the same animal model, reported that odontoblasts returned to their normal arrangement, although they were observed to be severely injured right after the preparation of cavities, which was also observed in our study. The morphological design of our study does not permit us to differentiate whether these odontoblast cells were previously existing  
Figure 7: (**A–C**) (4\(\times\), 10\(\times\) and 40\(\times\)) (where (**B,C**) are magnified view of red encircled area of (**A**): Microscopic view of cervical restoration with nano-HA-SiO\({}_{2}\)-GIC. A very organized continuation of dental tubules can be seen with a normal palisade appearance (yellow arrow) of odontoblasts on either side of newly formed tertiary dentin, with dilated blood vessels. A clear distinctive pre- dentin can also be seen (red arrows). or newly differentiated odontoblast cells from undifferentiated ecto-mesenchymal cells from the core of the pulp. However, this is more common in various attacks [2]. In our study, we did not observe any case of pulpal necrosis in both types of restoration, which is in line with the study by [PERSON] et al. [35] who also observed that high fluoride-releasing materials such as GIC and silver diamine fluoride did not cause any necrosis. There are two main causes of inflammation after any cavity preparation followed by restoration. Firstly, the inflammation occurs due to abrupt movement of the dental fluid caused by cutting dentin, which usually resumes its normal status in 8 to 19 days [36]. Secondly, inflammation occurs due to the response of the restorative material, which may be because of discharge of some unknown components. For GIC, the unreacted groups have been shown to have mild to moderate cytotoxic effects on cell cultures [37], mainly depending on the type of additives being added in GIC [38]. [PERSON] et al. [39] reported that at the seventh day, a mild inflammation of the pulp related with local tissue disruption was witnessed in the majority of the teeth filled with c-GIC, and this was also observed in our study.