## 4 Discussion
A study [28] to access pulp response in a rat tooth model using Fuji Lining LC and Fuji IX showed no response or slight inflammation in most of the samples with mild disorganization of pulp tissue throughout a seven-day interval. This contrasted with our study results in which we found more inflammation and moderate levels of tissue disorganization. The reason for this difference might be because they used different lining and base materials whereas cavities made in our study were deeper, which might explain the results observed. In the above-mentioned study, after 30 days, the pulp tissue in all groups recovered and exhibited a normal manifestation. However, we observed slightly more inflammation in the nano-HA-SiO\({}_{2}\)-GIC group as compared to c-GIC in both occlusal and cervical restorations. Reasons might be ascribed to its nanoscale. When converted to the nanoscale, many materials may show considerable toxicity at the cellular level [5,40,41]. Since the nanomaterials are comparable in size to proteins, DNA, viruses, and biological molecules, part of their effects may lie in the interaction between living things and the environment. Nevertheless, this mechanism of interaction is still not very clear, and necessitates further investigation in the future. [PERSON] et al. [25] performed a biological evaluation of nano-HA-SiO\({}_{2}\)-GIC on human dental pulp stem cells (DPSCs). At the highest concentration of 200 mg/mL, they observed a moderate level of cytotoxicity to DPSCs. This moderate level of cytotoxicity was believed to be attributed to the formation of a component/by-product that leached out from the cement. An earlier study [42] on nano-HA-SiO\({}_{2}\)-GIC showed detection of a high degree of cross-linking of silyl species between the glass particles in the GIC matrix and nano-silica. As a result, during the setting of nano-HA-silica-GIC, lesser glass particles were free to react with the polyacrylic acid (PAA), thereby allowing this unreacted free PAA to be released after the setting of the nano-HA-silica-GIC, and hence causing more inflammation in the pulp tissue [21], as observed in our study. Another interesting point to be mentioned here is that whilst the subsequent inflammatory process will cause the break-down of tissue, low-grade inflammation potentially induced by mechanical trauma and mild necrosis may encourage regenerative mechanisms, including angiogenesis and stem cell differentiation [43]. This may explain our results for nano-HA-SiO\({}_{2}\)-GIC having more inflammation but at the same time better tertiary dentin formation. For the detection of bacteria, our study revealed some promising findings whereby no bacteria were observed in both groups (except for one) which is in line with findings of [PERSON] et al. [29]. However, it is difficult to achieve any association between inflammation of the pulp and the presence of bacteria based on a smaller number of subjects. The absence of bacterial contamination under both types of restoration based on GICs supports two possible explanations. First, the barrier of the tertiary dentin layer, self-repair processes, and alteration of blood vessels, result in prompt healing of the pulp. Moreover, the slow release of fluoride from both c-GIC and nano-HA-SiO\({}_{2}\)-GIC may also constrain the penetration of bacteria into the dentin. The morphometric data of remaining dentin thickness (RDT) analyzed in our study, in terms of the dimension of the rats' molars, established that a reasonable residual dentin thickness of \(\sim\)200 \(\upmu\)m was equivalent in both restoration types (c-GIC and nano-HA-SiO\({}_{2}\)-GIC) and in both groups of occlusal and cervical restorations which is adequate for determining the biological response, as mentioned by [PERSON] et al. [27]. Thus, this parameter in terms of RDT was consistent.