Sunday, December 20, 2009

Head Posture and Craniofacial Morphology

Linder-Aronson, S and Woodside, DG: Head Posture and Craniofacial  from Morphology Excess Face Height Malocclusion: Etiolog, Diagnosis and Treatment. Quintessence Publishing Co, Inc., Chicago, IL, pg 24-25.

Section Exerpt:
"The physiologic changes alread described can have a profound effect on facial structure.  For example, Solow and Tallgreen <86> foudn that individuals with large head extensions were characterized by larg anteiror face heights, and also both maxillary and mandibular retrognathism and steep inclination of the mandibular plane to the palatal and anterior caranial base planes.

In addition, a correlation study of predictive relationships <83> observe children for 2-4 years before the age of peak velocity in pubertal skeletal growth.  They found that a large head extension was followed by vertical facial development.  This was characterized by backward displacemetn of the temporomandibular joint, reduced growth in maxillary length, reduced racial prognathism, and less-then-average true foward rotation of the mandible.  On the other hand, head flexion was followed by the opposite facial development.

Electromyography (EMG) has also been used to study this phenomenon.  Hellsing et al<44> determined postural activity in the neck muscles in relatin to extension and flexion of the head in adults.  Both the supra- and infrahyoid muscles responded with increased EMG activity during extension and also with 20 degree flexion of the head.  (figure 1-19 shows thi interrelationship between induced oral respoiration, changed head posture, and the EMG activity of the suprahyoid muscles.  Hellsing and L'Estrange<43> also used transducers to measure the changes in lip pressue on the incisors as individuals changed from mouth to nose breathing.  They found that the upper lip pressure decreased when the patient changed from nose to mouth breathing., but increased during 5-degree extension (fig 1-20).  There was a clear correlation between lip pressure and cranial posture.  Thus, in investigations of the effects of long-term alteration in head posture, compensatory muscle function associated with head extension or flexion may be one of the determinants of craniofacial morphogenesis in growing individuals.  These results support the soft tissue stretching  hypothesis suggested by Solow and Kreiborg<8>  This stretching hypohyothesis is named after one of the links in the porposed chain of events (Fig 1-21).  The coordination of different neck muscles is also important for adequate respiration and head posture.  For example, if the head posture is changed by tilting the head backward from the lower cervicla reiong, the nasopharynx will be narrowed.  However, if hte head is tilted backward from the upper cervical vetebrae, the naso pharynx will be widened (Fig. 1-22). <42,84>

These findings indicate that airway obstruction triggers an increased in head extension via upper cervical vertebrae to compensate for nasopharyngeal obstruction.  This facilitates oral breathing by enlargemetn of the naso- and oropharyngeal airway sapce.  This head extension may create a stretching of the soft itissue envelope of the face and neck and thus initiate malocclusion."

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