Differential bone histomorphometric characters of the mandible in senescence- accelerated mice (SAMP6 and SAMP8): murine models for senile osteoporosis and temporomandibular joint osteoarthritis

Histomorphometric analyses of the mandible and femur were performed in senescence-accelerated mice (SAM) using SAMP6 as a senile osteoporosis (OP) model, SAMP8 as a temporomandibular joint osteoarthritis (TMJOA) model, and SAMR1 as control. Thirty-six male mice at 2 or 4 months of age (6 for each strain and age) were used. The cortical thickness index (CTI), bone area (B.Ar/T.Ar), trabecular width (Tb.Wi), trabecular number (Tb.N), trabecular separation (Tb.Sp), osteoblast perimeter (N.Ob/B.Pm), and osteoclast perimeter (N.Oc/B.Pm) were assessed in the distal femoral metaphysis and in the mandibular ramus including the alveolar bone. Compared with SAMR1, SAMP6 showed lower B.Ar/T.Ar and Tb.Wi in the femur and mandible at 2 and 4 months of age. This strain showed lower CTI in both bones and higher Tb.N and Tb.Sp in the femur at 4 months of age. SAMP8 showed higher CTI in both bones at 2 months of age and maintained a high index in the mandible but not in the femur at 4 months of age; however trabecular bone mass was not reduced. SAMP6 exhibited lower N.Ob/B.Pm in the femur but not in the mandible at 4 months of age, while SAMP8 showed lower N.Oc/B.Pm in the mandible but not in the femur at 2 and 4 months of age. The differential histomorphometric features of the mandible in different SAM strains may imply a difference in mandibular bone property between SAM mice with senile OP and TMJOA genetic background.