Temporomandibular joints of BALB/c-bm/bm mouse that has spontaneous transverse crossbite

Objectives: Murine brachymorphism (bm) has cartilage with glycosaminoglycans (GAGs) undersulfated. bm mouse is characterized by short thick tail, and shortened but not widened limbs. The phenotype is inherited as an autosomal recessive. Spontaneous anterior transverse crossbite sometimes occurs in about 10% of BALB/c-bm/bm mice (bm homozygotes) inbred. We examined degree of undersulfated GAGs in temporomandibular joint (TMJ) of this mouse. Methods: The mice, those aged 3 weeks (juveniles) or 13 weeks (adults) of BALB/c mice (Control group, n=10), BALB/c-bm/bm mice with normal occlusion (Norm group, n=10), and BALB/c-bm/bm mice with crossbite (Mal group, n=10), were used. After extracting cartilage, sulfated GAGs were measured using demethylmethylene blue assay. Nonparametric test were used for comparison of concentration of sulfated GAGs using the statistical package SPSS® Ver. 8.0. Results: In aging comparison, concentrations of sulfated GAGs on condyles of juvenile mice were higher than those on condyles of adult mice in all 3 groups. In comparison between groups, concentration of sulfated GAGs on condyles in the Mal group was significantly lower than those in the control group and Norm group of adult mice but not juvenile mice. There was not a great difference between the concentrations of sulfated GAGs on condyles located on the mandibular shifted side in the Mal group and those located on the non-shifted side in the Mal group. Conclusion: The results suggest that low-sulfated GAGs on the condyle at the TMJ of BALB/c-bm/bm mice are probably induced by the bm gene and are one of causes of crossbites in these mice.