Analysis of contribution of collagen fibre component in viscoelastic behaviour of periodontal ligament using enzyme probe

The aims of this study are to observe microscopic changes in the periodontal ligament (PDL) collagen fibres after collagenase treatment, to analyse stress–relaxation behaviour of PDL specimens treated with collagenase, and to elucidate the contribution of the collagen component to the viscoelastic behaviour of the PDL. Transverse sections of rat mandibular first molars (n=24) were treated in vitro with 0, 8, 16, or 24 units of bacterial collagenase for 4 h at 37 °C. Histological specimens were then prepared, and image analyses were done for polarised light microscopic appearances of collagen fibres. Further, stress–relaxation tests were performed for PDL specimens treated with 8 units of collagenase (n=7) and control specimens (n=7). Image analysis showed that higher concentrations of collagenase reduced greater area occupied by the PDL collagen fibres and birefringent retardation of the fibres. The amount of stress–relaxation during 600 s was 1.37 times greater in the collagenase-treated specimens than in the controls. The observed values of the stress–relaxation process were well described by a function with three exponential decay terms. The relaxation parameters of the first and second terms did not show significant differences, but those of the third term did so between the collagenase-treated and control specimens. The ratio and relaxation time of the third term for the collagenase-treated specimens were significantly less than those for the controls. These findings suggest that in the long-term relaxation component of the stress–relaxation process of the PDL the viscoelastic properties of the collagen fibres may play an important role.