الفهرس 
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Abstract
In the present study, we describe the effect of oral administration of 2 different doses of melatonin on the mandibular alveolar bone and gingiva of rats with experimentally induced periodontitis. Fifty-six healthy male albino rats were used in this study. They were randomly divided into 4 equal groups (14 rats each) where group A was a negative control group. In groups B, C, and D; periodontitis was induced by the subgingival placement of a silk ligature wire for 15 days around the right mandibular first molar. After that, ligature was removed from the three groups and only groups C and D were then treated with melatonin. The melatonin dose for group C was 10 mg/kg/day while that for group D was 20 mg/kg/day.
MGI and BI were evaluated in all groups twice during the experiment, once directly after ligature removal and another time before euthanization. After 30 days from the beginning of the experiment, the animals were euthanized, and the right halves of their mandibles were dissected out. The mandibles of 8 rats from each group were prepared for histological examination by using the light microscope as well as histomorphometric analysis, while the mandibles of the other 6 rats of each group were prepared for SEM examination.
1. Results of the clinical evaluation of modified gingival index and bleeding index
MGI and BI statistical analysis after removal of the ligature and melatonin treatment (In groups C and D) showed that there was a significant improvement in the gingival clinical status and reduction in the inflammation in all 3 groups (B, C, and D) under investigation. However, there was more gingival condition enhancement in the melatonin treated groups (C and D) than the untreated group (B). Nevertheless, no significant difference was found between the gingival indices in groups C and D.
2. Light microscopic results
LM results of the control group A revealed normal histological appearance of the alveolar bone and gingiva. Interradicular bone exhibited smooth architecture with dense bony trabeculae. Normal level of intact ABC between first and second molars in relation to the CEJ was also observed. Continuous well-organized PDL fibers of normal thickness were seen connecting both bone and cementum.
On the other hand, group B exhibited irregular alveolar bone with noticeable decrease in the interradicular bone thickness and increased inflammatory cell infiltrate. Interdental bone showed marked apical shifting of the level of the ABC in relation to the CEJ and apical migration of the JE. Moreover, discontinuity, destruction, and marked detachment of the gingival transseptal fibers and PDL fibers were also evident.
In both groups C and D, relative reestablishment of the normal architecture and thickness of the alveolar bone was noted. Interradicular bone showed regular and smooth outline with relative restoration of the ABC in relation to CEJ. Continuous, well organized gingival transseptal fibers and PDL fibers were also noted.
3. Histomorphometric results
• Percentage of bone SA: group A showed the largest mean % of bone surface area followed by group D, then group C, and the least % of surface area was seen in group B. A statistically significant difference was seen between the treated groups (C and D), and the untreated group B. However, there was no significant difference between groups C and D.
• Osteoclast count: the highest mean osteoclast count was seen in group B. There was a statistically significant difference between the results of group B and all the other groups. Both groups C and D displayed greater mean osteoclast count in comparison to group A. However, no statistically significant difference was seen between the mean osteoclast count in groups C and D.
• Distance between ABC and CEJ: the mean greatest distance was present in group B followed by groups C and D that showed very similar mean values. group A showed the least distance between ABC and CEJ. The results of groups B, C, and D showed a statistically significant difference from group A. Similarly, there was a statistically significant difference in the results of the treated groups (C and D) when compared to the untreated group (B). However, there was no statistically significant difference between the results of groups C and D.
4. Scanning electron microscopic results
group A displayed a generalized smooth surface of the buccal cortical plate of bone with a normal level around mandibular first molar. In contrast, the periodontitis group B showed marked generalized roughness with irregular surface topography with severe resorption of the level of the alveolar bone around the mandibular first molar. Both groups C and D showed a marked relative restoration of normal architecture of alveolar bone with smooth surface topography of the outer cortical plate and a considerable restoration in the level of the alveolar bone around mandibular first molar.