Biomedical Engineering Reference
In-Depth Information
Fig. 11.11
Regional activation of the orbicularis oris muscle (deep vs. superficial and marginal vs.
peripheral) changes the shape of the lips, the degree of opening, and the magnitude of protrusion
for the same level of muscle activation. From Ref. [
10
]. Copyright 2013 by American Speech-
Language-Hearing Association. Adapted with permission
11.4.3 Teeth Support Lip Protrusion
In addition to intrinsic properties andmorphology of the lipmuscles, we also expected
that mechanical coupling with the underlying rigid structures of the jaw, maxilla and
teeth is needed to provide the mechanical support necessary for lip protrusion. We
tested this hypothesis by simulating two conditions: lip protrusion with and without
teeth support. Such conditions are straight-forward to simulate because contact con-
straints in the model can be turned off, in which case there is no resistance to the lips
from interpenetrating the teeth and vice versa.
Simulations are shown in Fig.
11.12
and were found to support our hypothesis of
the importance of skeletal support. The lack of skeletal and teeth support resulted in
reduced protrusion of the lips and was generally disruptive of the rounding gesture.
11.4.4 Jaw Opening and Lip Closure
We believe that coupling of the jaw and face is a functionally important aspect of
speech movements. We expected that jaw opening would affect the lips, e.g. by
reducing the capacity to produce lip closure due to this coupling. Lip closure is
known to be possible even at low jaw positions during speech movements such as
bilabial consonants /b/ or /p/ [
35
]. Through simulation, we wanted to assess which
