Viscoelasticity of Human Oral Mucosa

Abstract

The dynamic behavior of oral soft tissues supporting removable prostheses is not well understood. We hypothesized that the stress and strain of the mucosa exhibited time-dependent behavior under masticatory loadings. Displacement of the mucosa on the maxillary residual ridge was measured in vivo by means of a magnetic actuator/sensor under vertical loading in partially edentulous individuals. Subject-specific finite element models of homogeneous bone and mucosa were constructed based on computed tomography images. A mean initial elastic modulus of 8.0 × 10(-5) GPa and relaxation time of 494 sec were obtained from the curve adaptation of the finite element output to the in vivo time-displacement relationship. Delayed increase of the maximum compressive strain on the surface of the mucosa was observed under sustained load, while the maximum strain inside the mucosa was relatively low and uninfluenced by the duration of the load. The compressive stress showed a slight decrease with sustained load, due to stress relaxation of the mucosa. On simulation of cyclic load, the increment of the maximum strain and the evidence of residual strain were revealed after each loading. The results support our hypothesis, and suggest that sustained and repetitive loads accumulate as surface strain on the mucosa.

Determination of oral mucosal Poisson’s ratio and coefficient of friction fromin-vivocontact pressure measurements

“…While FEA provides a feasible approach to modelling load transfer, it is difficult to assign realistic mucosa properties (Inoue et al 1985). Although the previous studies (Sawada et al 2011;Wakabayashi and Suzuki 2013) attempted to derive the nonlinear moduli of mucosa via the same approach as hard tissues, data regarding its volumetric deformation have not been identified specifically. More importantly, the effect of the apparent Poisson's ratio has been largely disparaged due to lack of data (Inoue et al 1985).…”

“…The mucosa was modelled with a hyperelastic material for its nonlinear responses (Kydd and Daly 1982;Sawada et al 2011). Driven by the unit volume strain energy, a third-order Ogden strain energy constitutive equation (Bergomi et al 2011;Limbert et al 2003) was derived from the in vivo data documented by Kishi (1972) by leastsquare fitting.…”

“…The oral mucosa plays a critical role in distributing masticatory force from the denture to the underlying bony ridge (Sawada et al 2011;Ahmad et al 2013). Some associative clinical complications often cause pain and discomfort in patients due to excessive contact pressures (Ogawa et al 2003;Isobe et al 2013).…”

“…Significant interest has arisen and extensive studies have been undertaken regarding the biomechanical responses of mucosa under denture treatment. Both instant nonlinear elastic responses (Scapino 1967;Kishi 1972;Kydd et al 1974;Kanbara et al 2012) and time-dependent viscous responses (Inoue et al 1985;Lacoste-Ferré et al 2011;Sawada et al 2011;Wakabayashi and Suzuki 2013) of the mucosa have been examined via experimental and numerical approaches. This highly vascularized tissue consists of considerable amount of interstitial fluids, and the substantial fluidic exchange occurs with surrounding tissues under compression (Scapino 1967;Kydd and Daly 1982).…”

“…In fact, apparent Poisson's ratio (n) of mucosa has not been considered as a critical factor in some literature (Inoue et al 1985). Previous FE studies have assumed a rather broad range of possible values, from 0.30 to 0.49 (Lacoste-Ferré et al 2011;Sawada et al 2011;Kanbara et al 2012;Ż mudzki et al 2012a, 2012bWakabayashi and Suzuki 2013). From a biomechanics perspective, the effect of apparent Poisson's ratio has not been adequately addressed thus far.…”