## 4 Discussion
So, our study data indicate that a valuable evaluation can be performed between the two types of restoration (c-GIC and nano HA-SiO\({}_{2}\)-GIC) and two groups (oclusal and cervical), and hence, the reproducibility of rat molars for restorations was supported. Also, the shape and width of the upper first molars of Wistar rats are appropriate to deliver enough histological sections, permitting us to assess the results and conclude meaningful assessments [32]. These time intervals were selected because a study performed on the pulps of rat molars showed that the inflammatory reaction subsided in 8 days, and tertiary dentin formation was initiated in 2 weeks, resulting in a proper hard tissue denitinal bridge formation in 2 consecutive weeks [27]. In our study, the negative controls showed some deposition of tertiary dentin which was in the range of 31-44 \(\upmu\)m (Grade 0) because of attrition. It can be suggested that some tertiary dentin formation was seen in occlusal aspects (beneath the cuspal tips) of the molars with and without restoration due to the continuous tooth grinding nature of the rats and subsequent adaptation to the masticatory stresses resulting in deposition of tertiary dentin which is also reported by [PERSON] et al. [44]. For that purpose, morphometric analysis was carried out to compare the TD thickness of the first molar and second molar, and the different grading system mentioned above was utilized (Table 1). Also, this point emphasizes the importance of having another parameter included in the study, which was cervical restorations. In cervical restorations, the same grading system mentioned above was followed, as we also observed some TDF in second molars in the cervical area, which was in the range of 21-30 \(\upmu\)m (Grade 0). This physiological cervical dentin deposition was also observed by [PERSON] et al. [44] as a discrete deposition of asymmetrical dentin in the mesio-cervical area of the pulp corresponding to the exposure of denitinal tubules associated with cervical root dentin. In both occlusal and cervical restorations, the grading and scoring criteria we used differentiates between the TDF due to attrition and TDF due to restoration with biomaterials. GIC is known to have good outcomes in terms of tertiary dentin formation. As mentioned in a clinical trial [45], when GIC was evaluated as an Traumatic restorative technique, the tertiary dentin was found in almost 90% of the teeth inspected, though the degree of deposition was small. This was almost observed in our study occlusal group at 1-week duration, in which four out of eight teeth in the c-GIC group, and to a greater extent in the nano-HA-SiO\({}_{2}\)-GIC group, in which six out of eight teeth showed some level of tertiary dentin formation. Our findings of early tertiary dentin formation by both groups are in line with a study by [PERSON] [34], who reported that after three days of cavity preparation, odontoblasts that were newly differentiated replace the damaged odontoblasts and ultimately by five days after cavity preparation, they began to produce reparative dentin. Also, an immunoelectron-microscopic study by [PERSON] and co-workers demonstrated that a large amount of osteocalcin mRNA expression was found in odontoblasts 3 days post cavity preparation [46]. Osteocalcin is a major non-collagenous protein of the dentin matrix which forms the basis of newly formed tertiary dentin. In our study, at a 1-month interventional period, all samples of both types of restorations showed a Grade 2 level of tertiary dentin formation. Concerning cervical restorations, almost all first molars from both c-GIC and nano-HA-SiO\({}_{2}\)-GIC groups revealed a favorable response of the dentin-pulp complex in terms of tertiary dentin formation. However, results were better for nano-HA-SiO\({}_{2}\)-GIC restorations, in which the extent of the newly formed tertiary dentin was similar to the thickness and extent of the cavity, which is an encouraging outcome. A study by [PERSON] et al.