Experimental Study On Mechanism Of Defense And Repair Of Rat's Dental Pulp After Laser Irradiation

Objective:Through establishment of animal model of dentine hypersensitivity(DH) w ith rats irradiated by pulsed CO₂ laser at the dose of dentinal desensitization, to observe the expression of HSP70, TGF- β1, BMP-2 at different periods an d regions in rat's dental pulp (RDP) and the microscopic changes under trans mission electron microscope(TEM). The biological significance of these change s during the injury defense and self-reparative process are analyzed to provide insight into the injury and repair mechanism of dental pulp after laser irradiat ion. Methods:45 female Sprague-Dawley (SD) rats, 18 weeks old, were made into models of DH and fed routinely for 10 days and were randomly divided into 5 groups of 9 rats each: A (sacrificed after 4 hours of laser irradiation);B (sacrificed after 3 days of laser irradiation);C (sacrificed after 2 weeks of laser irradiation);D (sacrificed after 4 weeks of laser irradiation);N (sacrificed without laser irradiation). After sacrificing the rats, 40 specimens (eight for each group), which were taken from rats' upper left 1st, 2nd, 3rd molar combined with some jaw bones, were acquired immediately for HE staining and immunohistochemical analysis. Upper left first molar of a rat randomly from each group was split and the freshly coronal pulp was obtained for TEM observation. Average optical density (OD) values of all immunohistochemical images and results of HE staining were measured with Image-Pro Plus 5.0 image analysis software. Ultramicrostructural changes of RDPwere observed and analyzed. Statistical methods: Kruskal-Wallis method, Nemenyimethod, one-way ANOVA and LSD-/ test with SPSS 11.5.Results:Results of HE staining after pulsed CO2 laser irradiation: statistical results of vacuole change of the odontoblast and vascular engorgement, hemorrhage of dental pulp were as following: there were statistical difference between A and C, A and D, A and N (P<0. 05), no statistical difference between A and B. Inflammation cell infiltration of RDP came to peak in Group B and recovered normal after 4 weeks. Some tertiary dentine was observed in Group D. Statistical results of immunohistochemistry staining: HSP70 expression state in coronal pulp: Group A has statistical differences with the other four groups. TGF- P 1 expression state in coronal pulp: Average OD value of Group C was highest in 5 groups. BMP-2 expression state in coronal pulp: Average OD value of D group was highest in 5 groups. Discovery under TEM: Group A and Group B: Perinuclear space of odontoblasts distended slightly;rough endoplasmic reticulums (RERs) distended mediumly, some of them were vesicle shape and presented degranulation phenomena;a part of cristae mitochondriales (Mi) and matrix were degraded. Phagocytic cells' bodies were large with multi-ecphyma, plenty of cellular organs, lysosomes and phagocytotic vesicles. Group C and Group D: similar to Group N, there were plenty of cytoplasm, RERs, ribosomes (RIs), mitochondrias, well-developed Golgi's complexes which have multilayer applan vesic, bu and bullule. RER had a lot of attached RI and free polyribosomes. Mi was orbicular-ovate and has cristae lamellar.Conclusion: (D RDP undergone reversible inflammation changes after laser irradiation at the dose of 10.5 J/mm2 which can be used safely. (§) HSP70arose specially when RDP received heat stimulation and played a role duringthe later period of pulp repair. (3) TGF- 3 1 and BMP-2 were presented in n ormal or impaired RDP. The dynamic changes of expression showed that the two factors defended RDP in the early period, then participated in the self-rep arative process and promoted the formation of reparative dentin. @ Ultramicro structural changes showed that RDP had the ability of self defense and repair.