A comparative study of unilateral dislocated mandibular condyle fractures in the rabbit.

PURPOSE: The purpose of this study was to clarify the influence of patients age and the degree of dislocation on the healing of mandibular condyle fractures. MATERIAL AND METHODS: Sixty-two Japanese white rabbits (30 adolescent and 30 adult ones) were used. They underwent unilateral condylar neck osteotomy. The proximal fragments were positioned differently. In group I animals, the fragments were reduced into the original position, in group II animals the small fragment was dislocated 55-90 degrees to the ramus. In group III animals the proximal fragment was dislocated 135 degrees to the ramus. Gross and microscopic assessment was performed 4, 6, 8, 12 and 24 weeks postoperatively. RESULTS: In adolescent animals, complete healing of the fracture was observed, irrespective of the degree of dislocation. In the adult animals, there was complete healing of the fractures in groups I and II. In group III animals, there was a decrease of ramus height accompanied by some fibro-cartilaginous changes. CONCLUSION: Even in rabbits condylar deformation has been found following heavily dislocated artificial condylar fractures in adult animals. This result will help to decide for or against surgical treatment of condylar fractures in humans.     

Expression of cathepsin K mRNA during experimental tooth movement in rat as revealed by in situ hybridization

The expression of cathepsin K. a novel collagenolytic enzyme specifically expressed in osteoclasts, was investigated in the rat maxillary dentoalveolar unit during experimental tooth movement by in situ hybridization histochemistry with a non-radioisotopic cRNA probe for rat cathepsin K. Orthodontic elastics were inserted into the interproximal space between the maxillary first and second molars of 7-week-old male SD rats according to Waldo's method and sections prepared from tissues obtained at 12 hr, 1, 2, 3, 4, 7, and 12 days after orthodontic force application. Cathepsin K mRNA expression was detected in the mono- and multinuclear osteoclasts on the pressure side of the alveolar bone at 12 hr after force application, and the distribution and number of cathepsin K mRNA-positive osteoclasts increased time-dependently on the pressure side. At 3-4 days, a marked increase in cathepsin K mRNA-positive osteoclasts was found not only on the pressure side but also on the tension side of the alveolar bone in response to tooth movement. At 7-12 days, the cathepsin K mRNA-positive osteoclasts on both sides had disappeared. These findings suggest that the recruitment of osteoclasts on the pressure side begins during the initial stage of orthodontic tooth movement and the site-specific early induction of cathepsin K mRNA may cause an imbalance in the relative resorption activities on the pressure and tension side incident to such movement.     

Greater development of 1,2-dimethylhydrazine-induced colon cancer in a rat model of type 2 diabetes mellitus

Several clinical cohort and case-control studies have suggested a link between diabetes and colon cancer. Otsuka Long-Evans Tokushima Fat (OLETF) rats spontaneously develop type 2 diabetes mellitus and Long-Evans Tokushima Otsuka (LETO) rats are non-diabetic. The relationship between type 2 diabetes mellitus and colon cancer was examined in these rats. The carcinogen 1,2-dimethylhydrazine was administered subcutaneously once weekly for 10 weeks, and the animals were killed and necropsied in week 29. All OLETF rats and 80% of the LETO rats developed cancer. The number of colon cancers per rat was significantly greater in the diabetic than in the non-diabetic rats. Although the tumours tended to be larger in diabetic rats, the difference was not statistically significant. No significant differences were observed in the depth of invasion or histological type of cancer in the two groups. Type 2 diabetes mellitus may enhance the generation and growth of colon cancer.