Craniofacial Muscles

250 Z.-J. Liu
Fig. 14.7 The estimated overall tongue shape in relation to three phases of jaw movement during
chewing. Column A : dorsal view; Column B : sagittal ( right-side ) view. ( a ) Opening phase;
( b ) closing phase; ( c ) occlusal (power stroke) phase. Arrows indicate the direction of deformational
changes (modi fi ed from Liu et al. 2008c , with permission)
not show closer correlation with the amount of EMG activity in intrinsic than
extrinsic tongue or jaw muscles.
In summary, the estimated tongue shapes during three stages of chewing are
sketched in Fig. 14.7 . Compared to the overall shape during jaw opening phase
(Fig. 14.7a ), elongation in the body and narrowing and thickening in the posterior
body are the main deformations during the jaw closing phase (Fig. 14.7b ). During the
power stroke, the tongue extensively widens and shortens, along with its thinning in
the posterior body (Fig. 14.7c ). Taking all of these dimensional and volumetric
changes together, it can be concluded that increases in the widths are greater than
decreases in the length and thickness, and their combination is most likely responsible
for the volumetric expansion during the power stroke. On the other hand, decreases in
the widths and length are greater than the increase in the thickness, and their combination
is most likely responsible for the volumetric contraction during jaw closing.
14.3 Tongue Volumetric Reduction and Consequences
of Motor Function
14.3.1 Mass Reduction and Tongue Kinematics
Abnormalities in tongue size and morphology have been implicated in various clinical
diseases such as malocclusion, OSA, dysphagia, Beckwith-Wiedemann and
Down’s syndromes, and cerebral palsy. Tongue volume reduction is a valuable
approach for treating symptomatic macroglossia and some related functional disorders
(Deguchi 1993 ; Davalbhakta and Lamberty 2000 ; Wolford and Cottrell 1996 ;
Ruff 1985 ; Herren et al . 1981 ; Li et al . 2002 ; Stuck et al . 2005 ) . Given the fact that
the tongue is a volume-dependent muscular organ due to the nature of its hydrostat