Viscoelastic properties of human periodontal ligament: Effects of the loading frequency and location

Objectives: To determine the viscoelastic properties of the human periodontal ligament (PDL) using dynamic mechanical analysis (DMA). Materials and Methods: This study was carried out on three human maxillary jaw segments containing six upper central incisors and four lateral incisors. DMA was used to investigate the mechanical response of the human PDL. Dynamic sinusoidal loading was carried out with an amplitude of 3 N and frequencies between 0.5 Hz and 10 Hz. All samples were grouped by tooth positions and longitudinal locations. Results: An increase of oscillation frequency resulted in marked changes in the storage and loss moduli of the PDL. The storage modulus ranged from 0.808 MPa to 7.274 MPa, and the loss modulus varied from 0.087 MPa to 0.891 MPa. The tan delta, representing the ratio between viscosity and elasticity, remained constant with frequency. The trends for storage and loss moduli were described by exponential fits. The dynamic moduli of the central incisor were higher than those of the lateral incisor. The PDL samples from the gingival third of the root showed lower storage and loss moduli than those from the middle third of the root. Conclusions: Human PDL is viscoelastic through the range of frequencies tested: 0.5-10 Hz. The viscoelastic relationship changed with respect to frequency, tooth position, and root level.