| Objective: To establish mandibular protraction model of beagle dogs with Herbst functional appliance, and inject exogenous prostaglandin E2(PGE2) on the temporomandibular joint articular cavity. In order to investigate the effect of injecting exogenous prostaglandin E2 and its plus Herbst functional appliance on the mandibular condylar growth of late growth beagle dogs, which could provide experimental basis for further research.Methods: 24 male beagle dogs aged 8 months were randomly divided into four groups(n=6 in each group): natural growth group, mandibular protraction group(Herbst group), injected prostaglandin E2 group(PGE2 group), mandibular protraction plus injected prostaglandin E2 group(Herbst+PGE2 group). Mandibular protraction group and injected prostaglandin E2 plus mandibular protraction group were applied with Herbst functional appliance; Injected prostaglandin E2 plus mandibular protraction group and injected prostaglandin E2 group were injected 0.1 ml of prostaglandin E2(dose of 0.05 mg) into bilateral temporomandibular joint articular cavity; Natural growth group and mandibular protraction group were injected 0.1 ml of saline into bilateral temporomandibular joint articular cavity as control. Prostaglandin E2 and saline were injected once every 3 days for 60 days respectively. Cone-beam CT(CBCT) was taken respectively before applied with Herbst functional appliance and after removed of Herbst functional appliance for all beagle dogs of four groups at the same time. The original images scanned by CBCT were reconstructed with In Vivo5 software and then measured the relevant parameters of temporomandibular joint. At the end of experiment, all beagle dogs were sacrificed under the over-dose of anesthesia injected. Bilateral mandibular condyles were taken to analyze by hematoxylin-eosin staining after decalcification. Immuohistochemical method was used to localize and examine the expression of type II collagen in the middle-post part of the condyle and then for hemi-quantitative imaging analysis. The SPSS20.0 software was used for statistical analysis. The differences between before and after experiment in each group were tested with Paired t-test. The differences between before and after experiment in all measurements between PGE2 group, Herbst group, PGE2+Herbst group and natural growth group were compared by using analysis of variance(ANOVA). The LSD test was applied to assess the differences between two groups randomly when there was a difference in the test.Results: 1. There was no statistical difference of all parameters on natural growth group before and after experiment(P>0.05). After experiment, the measurement of CBCT showed that both the condylar height and condylar anteroposterior diameters had a small amount of increase, which the differences were statistically significant(P<0.05), but the condylar longitudinal distances,condyle width,condylar transverse diameter, glenoid fossa width and glenoid fossa depth had no statistically significant difference among the four groups(P>0.05). At the same time, the increment of the condylar height and condylar anteroposterior diameters on three experimental groups were more than natural growth group after experiment(P<0.05); In addition, the increment of the condylar height and condylar anteroposterior diameters on PGE2 group and Herbst+PGE2 group were more than Herbst group after experiment(P<0.05); After experiment, the condylar height and condylar anteroposterior diameters on Herbst+PGE2 group increased, and also had significantly statistical difference, comparing with PGE2 group(P<0.05). 2. Results of hematoxylineosin staining showed the cartilage thickness of three experimental groups increased significantly in comparison with natural growth group in the middle-post part of the condyle. The number of cells increased and the volume of cells also enlarged in hypertrophic layer. The cartilage thickness from thick to thin was Herbst+PGE2 group, PGE2 group and Herbst group respectively. 3. Results of immunohistochemical staining indicated that type II collagen was mainly expressed in extracellular matrix of the chondroblast layer and the hypertrophic layer. The coloration of DAB was tan. There was a little expression of type II collagen in calcified layer, but the fibrous layer expressed seldomly. The expression of type II collagen was hardly detected in natural growth group. In the middle-post part of the condyle, the expression of type II collagen in three experimental groups were more than natural growth group(P<0.05); The type II collagen in both PGE2 group and Herbst+PGE2 group had greater express, and the difference existed statistical significance(P<0.05), when compared with Herbst group; Furthermore, the expression of type II collagen in Herbst+PGE2 group increased more than PGE2 group(P<0.05).Conclusion: 1. Only injecting appropriate dosage of exogenous PGE2 into the temporomandibular joint articular cavity could have a certain amount growth on the mandibular condyle of late growth beagle dogs. 2. Only appling with Herbst functional appliance could have a certain amount growth on the mandibular condyle of late growth beagle dogs. 3. Injecting appropriate dosage of exogenous PGE2 into the temporomandibular joint articular cavity plus appling with Herbst functional appliance could have a certain amount growth on the mandibular condyle of late growth beagle dogs, and the growth was more obvious on the combination of both of them. |
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