Inhibition of the proliferation of human periodontal ligament fibroblasts by hyaluronidase

Hyaluronan (HA) exists in various living tissues as one of the major matrix macromolecules, and is well known to play an integral role in cell differentiation and proliferation. The present study was conducted to elucidate whether or not the proliferation of periodontal ligament (PDL) cells are affected specifically by the degradation of HA by hyaluronidasze (HAase). Human PDL fibroblasts were isolated and cultured with and without 15-150U/ml bovine testicular HAase from 1 to 11 days after seeding. The cells were also cultured with anti-CD44 antibody of 2 microg/ml. For the control against the anti-CD44 antibody treatment, 2 microg/ml IgG was used. The HA-dependent pericellular matrix was visualized by particle-exclusion assay. The number of cells was counted by MTT assay during the proliferation. The mRNA levels of HA synthases (HASs), HAases (HYALs) and CD44s were examined by a quantitative real-time PCR analysis. The cell proliferation was inhibited by the treatment with HAase and anti-CD44 antibody in cultured PDL fibroblasts. HASs mRNAs were down-regulated, whereas HYALs mRNAs were up-regulated significantly by the treatment with HAase and anti-CD44 antibody. The CD44s mRNA level exhibited no significant changes. These results suggest that HA may contribute to modulate the proliferation of cultured human PDL cells through a CD44-mediated mechanism.     

Biomechanical response of bovine temporomandibular joint disc to prolonged tensile stress

This study was designed to evaluate the influence of prolonged tensile stress on the viscoelasticity of the temporomandibular joint (TMJ) disc. Twenty discs from 10, 3-year-old cattle were used. Tensile stress of 1.5 MPa was applied to specimens from the discs for 10, 20, 40 and 60 min. Following the prescribed period of tension for creep, the specimens were removed from the tension device and any recovery observed for 20 min. In all specimens, strain increased at the onset of stress application and reached almost steady conditions after 5 min. Although, the strain became slightly larger when the creep time was longer, no significant differences were found in the strains between any two tests with different periods of creep. The residual strain increased significantly with creep duration, and similarly the degree of recovery decreased significantly. In 10- and 20-min creep tests, the residual strains were 0.1 and 1.0%, the specimens in 40- and 60-min tests revealed irreversible changes in length. It was concluded that continuous loading for >40 min causes creep damage in bovine TMJ disc, and that prolonged sustained tension affects the recovery of joint homeostasis.     

Influence of mechanical properties of two resin cements on durability of bond strength to dentin after cyclic loading

The purpose of this study was to evaluate how the different mechanical properties of two luting agents (acrylic resin cement and resin composite cement) influenced their bond strength to dentin, after cyclic loading that simulated chewing. Stainless steel rods were bonded to the flattened dentin surfaces with each luting agent. After immersion in water for 24 hours, half the specimens of each group were tested for tensile bond strength and the remaining half were subjected to a vertical load (75.6 N, 1.2 Hz) using an acrylic stylus--which upon contact with the specimen would rotate counterclockwise and then counter-rotate. Bond strength of the resin composite cement with self-etching was found to be significantly lower than the other adhesive systems. After 100,000 cycles, the bond strength of resin composite cement was significantly decreased while acrylic resin cement showed no decrease in bond strength.