[The effect of low-magnitude high-frequency loading on peri-implant bone healing and implant osseointegration in Beagle dogs].

PURPOSE: Low-magnitude, high-frequency（LMHF） loading has been confirmed to play an important role in bone healing. The present study aimed to evaluate the effect of LMHF loading applied directly to titanium dental implants on peri-implant bone healing and implant. METHODS: The mandibular premolars and molars were extracted from six male Beagle dogs. Three months post-extraction, six titanium implants (Aadva Standard Implant Narrow, 3.3 mm×8 mm) were inserted into the mandibular premolar and molar area (three implants per side) in each of the six dogs. In each animal, one side was randomly selected to undergo daily LMHF loading (experimental group), while the other side had no further intervention (control group). The loading was applied directly to the implant abutment using an individual jig and a custom-made loading device (8 µm,100 Hz). The implant stability quotient (ISQ) was tested every week. Three dogs were euthanized after 2 weeks, and three were euthanized after 8 weeks. Tissue samples were fixed and stained for micro-computed tomography(micro-CT) and histomorphometric analyses. The data were statistically analyzed using SPSS 13.0 software package. RESULTS: The experimental group had significantly increased peri-implant bone volume relative to tissue volume in region of interest 2 (100-500 µm) compared with the control group after 2 weeks of loading (P<0.05); however, there was no significant difference between the two groups after 8 weeks (P>0.05). The ISQ value and the micro-CT results did not differ between the two groups during the study period. CONCLUSIONS: LMHF loading positively influences peri-implant bone healing and osseointegration in the early healing period.

[Expression of BMP/Smads in rabbit condylar cartilage during mandibular forward positioning].

OBJECTIVE: To identify the relationship between the expression of BMP/Smads in condylar cartilage and condylar growth modifications in rabbits during mandibular forward positioning. METHODS: Sixty male rabbits with 8 weeks of age were randomly divided into the experimental group (n=36) and control group (n=24). The mandibles of rabbits in the experimental groups were induced to forward position by a functional appliance. The rabbits in the experimental group and control group were sacrificed after 3 days and 1, 2, 4, 8, 12 weeks, respectively. The expression of BMP-2, Smad1/5, 4 and 6 in condylar cartilage was examined by immunohistochemical staining. RESULT: The expression of BMP-2, Smad1/5, 4 and 6 was mainly found in the chondrocytes from the transitional zone and hypertrophic zone, and was also found in the chondrocytes and osteoblasts of the mineralized zone. Compared with those of the age-matched controls, the positive signals for BMP-2, Smad1/5, 4 and 6 in the experimental animals were stronger at early stage (P<0.05), coinciding with the remodeling in condylar cartilage after functional appliance. CONCLUSION: The expression of BMP-2, Smad1/5, 4 and 6 is associated with the adaptive remodeling of the condylar cartilage after functional appliance.

[The temporal and spatial expression of CBFalpha1 in rabbit condylar cartilage during forward mandibular positioning].

PURPOSE: To identify the relationship between the expression of Core binding factor alpha1 (Cbfalpha1) in condylar cartilage and condylar growth modifications in growing rabbits following forward positioning mandibles with functional appliance. METHODS: Sixty rabbits with age of 8 weeks were randomly divided into the experimental group (n=36) and control group (n=24). Rabbits in the experimental groups were induced to forward their mandibles by a functional appliance. The animals in the two groups were killed after 3 days and 1, 2, 4, 8 and 12 weeks, respectively. The temporal and spatial expression of Cbfalpha1 in condylar cartilage was examined by immunohistochemical staining and measured with Image Computer Analysis Software. Date was statistically analyzed by Student's t test and one-way ANOVA. RESULTS: The expression of Cbfalpha1 was mainly found in the chondrocytes from the transitive zone and hypertrophic zone, and was also observed in the chondrocytes and osteoblasts of the mineralized zone. Compared with those of the age-matched controls, the positive signals for Cbfalpha1 of each zone in the experimental animals were significantly stronger (P<0.05), and the highest expression of transitive zone, hypertrophic zone and mineralized zone was detected after 4 weeks of treatment (71.00+/-1.52, 50.00+/-0.75, 82.00+/-0.39). CONCLUSION: The pattern of Cbfalpha1 expression is concerned with the adaptive remodeling of the condylar cartilage after functional appliance.

[The morphology of the cells in the cartilage of rabbit mandibular condyle].

PURPOSE: To study the tissue layers and their function of the cartilage in mandibular condyle in rabbits. METHODS: Six adult Japanese white rabbits were subjected. Their temporomandibular joints were studied by immunohistochemistry for FGFR3 and PCNA, and in situ hybridization for aggrecan and collagen II mRNA expression, as well as ultrastructure. RESULTS: The upper proliferative cells did not express FGFR3, but the lower proliferative cells expressed FGFR3. Only few cells in the upper proliferative layer were PCNA positive, but all cells in the lower proliferative layer were positive for PCNA. No collagen II mRNA expression was found in the upper proliferative cell, but aggrecan and collagen II mRNA coexpressed in the lower proliferative layer. The cells in both layers were different in ultrastructure. CONCLUSION: The cartilage in mandibular condyle should have the 5 following tissue layer: fibrous layer, proliferative layer, transitional layer, cartilaginous layer and calcified cartilaginous layer. The cells in the proliferative layer are undifferentiated and the cells in the differentiated layer are prechondrocytes.

[Gene expression changes of cartilage matrix of condylar cartilage with anterior disc displacement].

OBJECTIVE: To study the gene expression changes in extracellular matrix of condylar cartilage following disc anterior displacement of rabbit TMJ. METHODS: The right sides of 28 joints in 40 rabbits were subjected to surgical operation of disc displacement. The condylar Collagen II and Aggrecan mRNA expression were detected by in situ hybridization. RESULTS: Collagen II and Aggrecan mRNA mainly expressed in the lower zone of condylar chondrocyte. Aggrecan mRNA decreased faster than collagen II following disc displacement, and adjusted to normal later. CONCLUSION: Anterior disc displacement leads to alteration of extracellurar matrix gene expression in the condylar chondrocyte, which means the start of remodeling.