Introduction: Rapid maxillary expansion (RME) has been shown to increase nasal
permeability and reduce nasal airway resistance. Numerous studies have examined the
relationship between rapid maxillary expansion and the change in airway resistance,
or have looked at the relationship between airway resistance and natural head position
(NHP). Few studies, to date, have examined the relationship between RME and the
change in NHP resulting from the consequent change in nasal airflow and decreased
nasal resistance.
Hypothesis tested: The null hypothesis is that rapid maxillary expansion has no
significant effect on airway patency which in turn influences craniocervical
angulations.
Nature of study: prospective, longitudinal, non-randomised study of 43 consecutive
adolescent patients who presented with uni- or bilateral crossbites in the permanent
dentition, and who required rapid maxillary expansion as part of their overall
orthodontic treatment
Methods: Cephalograms in natural head position were taken before, immediately
after, and one year after RME and the craniofacial angulations obtained were
compared with an historical control group from an earlier study.
Results: No significant changes in the craniofacial angles were found immediately
after expansion. One year post-expansion, however, NSL/VER had reduced by 3.14°, (p<0.01), indicating a drop in head position, while OPT/HOR reduced by 2.13°
(p<0.05), and CVT/HOR had reduced by 2.55° (p<0.05), indicating a more forward
inclination of the cervical spine.
Conclusions: The results of this study suggest that when the nasal airway resistance
decreases as a result of RME, changes in craniocervical angulations do take place, but
this takes some time to occur. The decrease in head elevation relative to the true
vertical is consistent with previous studies where increased nasal airflow has
occurred. The forward inclination of the cervical spine, which, while statistically
significant, may not be clinically significant, suggests that a possible small increase in
airway resistance at the lower levels of the airway results from the increased nasal
airflow. In order to accommodate this, the cervical spine inclines forward to increase
the cross-sectional area of the lower airway and thereby achieving a possible
equalisation of the total airway resistance between the nasal and the pharyngeal
components.
The null hypothesis (that rapid maxillary expansion has no effect on craniocervical
angulations in the long term) is not supported in this study.
