ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Fig. 1 – Finite element mesh of the orbicularis oris muscle
The material behavior implemented in the finite element analysis considered an
uncoupled, hyperelastic, transversely isotropic strain energy density function for the
passive and active behavior. This constitutive material model was implemented in the
commercial finite element code ABAQUS TM as a user`s material subroutine. The
analysis included the consideration of contact between the opposing lip segments to
obtain displacements, stresses and contact pressures. The contact interaction was
defined as frictionless, and the penalty contact algorithm was considered to define the
normal behavior.
To generate a representative model of the lips, simplifying hypothesis were considered.
The fixation of some points in the model was required to avoid rigid body movement.
Based on the facial anatomy and considering the set of different muscles included in the
orofacial system, the displacements of two points located at the extremes of the model
in the horizontal direction, corresponding to the position of the modiolus, were
restrained because these regions are usually described in the literature as regions of
fixation of the upper and lower fibers of the mouth orbicularis oris as well as of the
remaining muscles in the region.
3.2 Instrument to measure lips force
The instrument to measure lip forces was named FORLAB and is composed of an
intralips insert, a load cell, a data acquisition board and a personal computer (Fig. 2).
Fig. 2 – FORLAB