الفهرس 
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Abstract
The aim of this study was to investigate the effect of addition of dexamethasone, vitamin D3 , or chitosan to mineral trioxide aggregate (MTA) on the inflammatory pulp response and gene expression level of dentin sialophosphoprotein (DSPP) and matrix extracellular phosphoglycoprotein (MEPE) after pulp capping of mechanically exposed dental pulps in dogs.
Pulp exposure was performed in teeth of six dogs, which were classified into 3 groups of 2 dogs each, according to the evaluation period. group I: 7days, group II: 21 days, and group III: 60 days. Each group included 40 teeth, with a total number of 120 teeth.
Each group was subdivided into 4 subgroups (A, B, C, and D) of 10 teeth each according to the capping materialused for pulp capping as follows: Subgroup A; combination of MTA and Dexamethasone, Subgroup B; combination of MTA and Dexamethasone with Vitamin D, Subgroup C; combination of MTA with Chitosan compound and Subgroup D; MTA only (control). Each subgroup was subdivided into 2 subdivisions according to the method of evaluation. Subdivision 1; gene expression analysis and subdivision 2; histopathological examination.
Our results showed a significant expression of DSPP with MTA and Dexamethasone at 3 weeks, up to 18.8 relative fold change, while with MTA and Dexamethasone with Vitamin D, a significant upregulated gene expression of DSPP up to 29.4 relative fold change was detected at the same evaluation period.
The addition of osteogenic supplements to MTA did not significantly enhance the level of mRNA expression of MEPE during pulp capping in all the evaluation periods (7, 21, or 60 days). However, MEPE was downregulated in relation to the control (MTA only) in most of the samples.
There was no significant difference in the inflammatory cell score between different capping materials in the same observation period. On the other hand, a significant difference was found after the comparison of the three evaluation periods of MTA+Dexamethasone subgroup, where the 3 weeks evaluation period showed higher inflammatory cell score than that of the 1 week or the 2 months evaluation periods. Moreover, there was no significant difference in inflammatory cell count between all the capping materials of 1 week period and at 3 weeks evaluation period. On the other hand, there was a significant difference between the tested materials at 2 months evaluation period where MTA+Dexamethasone+Vitamin D subgroup recorded the highest statistically significant mean count.
Dentin bridges were not detected at 1 week evaluation period among all tested materials. Also, there was no significant difference between the tested capping materials regardingthe dentin bridge thickness at 3 weeks or 2 months evaluation periods.
Based on the results obtained from this study, it can be concluded that:
1. Dexamethasone, with or without vitamin D3 and chitosan, are synergistic odontogenic inducers with MTA for odontoblasticdifferentiation of dental pulp cells in dogs.
2. The additives added to MTA resulted in upregulation of the gene marker DSPP.
3. The additives added to MTA had no effect on expression of the gene marker MEPE.
4. All tested materials are comparable as regard to inflammation at 1 and 3 weeks.
5. MTA+Dexamethasone+Vitamin D showeda high mean inflammatory cell count than other tested groupsat 2 months evaluation period.
6. Allgroups produced comparable thickness of dentin bridge at 3 weeks or 2 months.