Change of HA molecular size and boundary lubrication in synovial fluid of patients with temporomandibular disorders.

The collapse of lubrication function caused by changes of synovial fluid (SF) is regarded as the main aetiology of temporomandibular disorders (TMD). Hyaluronan (HA) is one of the principal components of SF. Both physicochemical properties and cell biological functions of HA mainly depend on its molecular size. The present study was designed to analyse the HA molecular size and boundary-lubricating ability of SF in the patients with TMD and compare them with that from normal controls. Temporomandibular disorders patients were divided into three subgroups: displaced disc with reduction (DDR), disc without reduction (DDNR) and disc perforation (DP). After obtaining SF samples, we analysed the molecular size of HA by high-performance liquid chromatography, and boundary-lubricating ability (coefficient of friction, COF) of SF by a friction apparatus. The results suggested that there was no significant difference in molecular size of HA among the groups of health control, DDR and DDNR, while the DP group presented a lower molecular size when compared to other ones. Boundary-lubricating ability test showed that COF of SF in TMD patients were significantly higher than that of healthy controls. In the patients' subgroups, no statistical difference was observed between the group of DDR and DDNR, while DP group presented a higher COF when compared to the group of DDR or/and DDNR. Collectively, the increased values of COF, which corresponded to the decrease of HA molecular size, indicated that the distinct changes of HA molecular size and boundary-lubricating ability in the SF occurred with TMD.