CHANGES IN THE FIBER ARRANGEMENT OF THE RAT INCISOR PERIODONTAL-LIGAMENT IN RELATION TO VARIOUS LOADING LEVELS IN-VITRO

The relationship between the fibre arrangement of the periodontal liga ment and the load-deformation behaviour was investigated at various lo ading levels. Transverse sections of the rat incisor were loaded in th e eruptive direction in vitro and the deformation fixed at predetermin ed loads. Sections were prepared at these deformation levels. The peri odontal ligaments were examined by polarized-light and scanning-electr on microscopy. At the initial ('toe') part of the load-deformation cur ve, the periodontal fibres were gradually pulled and bent towards the direction of loading; their wavy pattern and periodic dark and bright bands became indistinct. At the next, linear part of the curve, the ru nning direction of the fibres changed gradually until they were straig htened and stretched. At the yielding part of the curve, the periodont al fibres began to rupture. Ruptured fibres adhering to the bone surfa ce returned to their original obliquity and showed periodic dark and b right bands. The fibrous components of the rat incisor periodontal lig ament thus transmit forces to bone at the linear part of the curve whe n the tooth is axially loaded.