Biomechanics of oral mucosa

Abstract

The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity/permeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure-pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.

Keywords: hydrostatic pressure; hyperelastic; oral mucosa; pressure–pain threshold; residual ridge resorption; viscoelastic.

Figure 1.

(a) Schematic diagram (left) and histological diagram of the healthy mucosal anatomy [34]; (b) SEM images of the vascular network within the rabbit palatine mucosa by corrosion casts [35]; (c) histological image of the mouse mucosa underneath the denture without occlusal load [13] and (d) histological image of the mouse mucosa beneath a denture [13].

Figure 2.

(a) The frequencies of different linear elastic moduli adopted in existing FE studies; (b) a simplified model to present a unit of mucosa–bone structure; (c) the compressive stress–strain relationships between different material models (linear elastic, multi-phasic elastic and hyperelastic); and (d) the maximum mucosa thickness changes in the different material models of mucosa under increasing loads up to 100 N in the test model.

Figure 3.

(a) The schematic diagrams of common viscoelastic material models; (b) the viscoelastic responses of different parameters in the test model, compared to the clinical data; (c) the frequencies of different Poisson's ratios adopted in existing FE studies; (d) the volume-averaged strain responses by the different Poisson's ratios of mucosa under 100 N in the test model.

Figure 4.

(a) The schematic diagram of the finite-element model in the friction coefficient test; (b) the maximum contact pressure against increasing friction coefficients in different material models.

Figure 5.

(a) The distribution patterns of the VM stress in bone and the hydrostatic pressure in mucosa compared to residual ridge resorption under CT (white: before denture insertion; cyan: 1 year after denture insertion); (b) the PPT thresholds determined using the clinical data from the literature; (c) the vertical displacement of a removable partial denture under an occlusal load of 60 N on the first molar and (d) the mucosa hydrostatic pressure pattern versus the residual ridge height reduction.