Transverse dimensional changes following rapid maxillary expansion

Abstract

RAPID MAXILLARY EXPANSION has been advocated for the treatment of a narrow maxillary dental arch for over a hundred years. Early investigators found that the effects of maxillary expansion were not confined to the dental complex but also affected craniofacial morphology including the nasal cavity. The purpose of this study was to determine the effects of RME on skeletal, dental and nasal structures in a transverse plane and to relate these changes to nasal cavity function as determined by nasal airway resistance measurements. Twenty-five subjects exhibiting transverse maxillary dental deficiency were compared with 25 age and sex match controls. A number of skeletal, dental and nasal transverse widths and area measurements were selected and subjected to method error analysis. A nasal template was developed that allowed measurement of linear transverse widths and areas within the nasal cavity at different levels. As a result, six skeletal, five dental and seven nasal transverse widths and two nasal cavity area variables were measured and compared between the control group and the anomaly group before and after expansion with RME. Results indicate that there was little difference between the anomaly and control groups before treatment with the exception of maxillary skeletal and dental narrowness. Expansion using RME resulted in increased upper molar width, maxillary width, nasal cavity width and separation of the anterior nasal spine; however all patients did not respond uniformly. Whereas some patients demonstrated large increases in maxillary width, others experienced only moderate or little change. These differences may be related to the degree of ossification of the median palatine suture and to other aspects of maxillofacial maturity. Intranasal changes as a result of RME were restricted generally to the lower half of the nasal cavity and were highly variable, as were changes in nasal airway resistance. Ten patients experienced improvements in either anterior NAR, posterior NAR or both. Six patients had little or no change in either resistance and only three patients experienced increases in both anterior and posterior NAR. Maxillary dental transverse deficiency was successfully treated in all cases at the end of the retention period. Rapid maxillary expansion resulted in separation of the anterior nasal spine in all cases although the extent of separation ofthe median palatine suture was highly individual.As a result of this study it would appear that rapid maxillary expansion is ideally suited to young patients with maxillary skeletal or dental narrowness who have increased anterior nasal airway resistance. Clinically it may be possible to identify those patients most likely to benefit from rapid maxillary expansion by utilising a simple clinical or cephalometric measurement.