Changes in nasal airway resistance associated with rapid maxillary expansion H. Garland Hershey, Donald W. Warren,
D.D.S., MS.,* Bruce D.D.S., Ph.D.,***
Chapel Hill, N. C.
he skeletal and dental effects of rapid maxillary expansion have been well documented,1-3 and the procedure is generally agreed to be a reliable method for correcting maxillary alveolar constriction. In contrast to the consistent dental findings, there has not been agreement on the effect of the procedure in reducing nasal airway resistance. Some authors4-” have enthusiastically supported the expansion procedure as a means of reducing or eliminating a mouthbreathing problem, while others7 remain skeptical of its effect on the nasal airway. Recent advances in aerodynamic instrumentation have made it possible to measure nasal airway resistance accurately without subjecting a patient to discomfort or radiation.* The availability of this sophisticated instrumentation and the controversy regarding the effects of maxillary expansion on nasal airway resistance prompted this investigation. Specific objectives of the study were to answer the following questions : 1. How much change in nasal airway resistance can be expected after rapid maxillary expansion I 2. How permanent are the changes in nasal resistance? Does change noted at the time of maximum sutural expansion remain stable through the 3-month retention period ? This investigation was supported in part by NIH Research DE 02668 from the National Institute of Dental Research 05333 from the Division of Research Facilities and Resources. *Associate Carolina
Professor School of
of Orthodontics Dentistry. 1229
Chairman, of Dentistry.
Grants and by
3. Is there a consistent relationship between the amount of maxillary expansion and subsequent c.hange in nasal resistance? 4. 110~ closely does a patient’s subjective statement regarding change in the ability to breathe through the nose correlate with actual change in nasal resistance ? 5. Is there a difference in change in nasal resistance between patients treated with a wire-and-acrylic appliance and patients treated with an allwire appliance ? 6. Are there differences in nasal resistance readings between orthodontic patients who required rapid maxillary expansion therapy and in orthodontic patients who did not require rapid maxillary expansion therapy? In other words, do patients with narrow palates and posterior cross-bites have greater nasal airway resistance than normal patients? Materials
A sample of seventeen subjects was used, all of whom required rapid maxillary expansion for correction of constricted maxillary dental arches. The six boys and eleven girls were between 11 and 14 years of age, and all but three were described by their parents as “mouth breathers.” Each subject underwent a rapid maxillary expansion procedure, the expansion device consisting of bands cemented on the maxillary first molars and first premolars and rigidly connected to an expansion screw located in the center of the palate. Acrylic was applied to the framework of six of the expansion appliances in order to distribute forces to the alveolar process. The appliances were activated two or three quarters of a turn on the day the appliance was inserted and, on ensuing days, one quarter turn in the morning and one quarter turn in the evening until the desired suture opening was achieved. The appliance was used as a retainer for 3 months, at which time it was removed. Records consisting of dental casts, postero-anterior radiographs of the skull, and nasal resistance readings were collected before treatment, after maximum expansion, and after 3 months of retention. The width of the maxillary arch was measured on the casts before treatment and after maximum expansion by recording the diameter between the tips of the distolingual cusps of the maxillary right and left first molars. The outlines of the two nasal cavities were traced on the postero-anterior radiographs, and their diameters (binasal cavity width) were measured at their greatest concavity (lateral nasal point). Nasal resistance was calculated from the parameters of pressure and airflow during breathing by means of an equation modified from Ohm’s law. Nasal resistance (R) is equal to the ratio of pressure drop across the nose (AP) over the volume rate of nasal air emission (V) of air passing from the pharynx
the nose (R = F)T
Nasal pressure drop was measured by means of two catheters, each having an internal diameter of 1.5 mm. The first catheter was placed in the oropharynx as far posteriorly as could be tolerated, and the second catheter was placed within a well-adapted nasal mask (Fig. 1). To avoid irritation of the nasal mucosa or en-
I Mean and SD. (0.50 L./set.) Mean and S.D. (0.25 L./see.)
7.1 f 2.1
4.2 f 2.1
4.4 zk 2.7
4.8 3~ 2.3
9.41 1.21 maxillary first be no change
Initial to stabilization (mm.1
molar width in maxillary
Binasal cavity width
Initial to stabilization (mm.)
Note that because the retention, there could of retention.
Maxillary first molar width
2.03 0.81 fixed by the molar width
Stabilization to retention (mm.) 0.33 0.34 rigid appliance throughout from stabilization to end
croachment upon the natural air passage, no instruments were inserted into the nares.9 The subjects were cautioned not to bite or otherwise occlude the oropharyngeal catheter. Care was taken to ensure that saliva did not enter the oropharyngeal catheter, although such an event would be apparent on the pressure record. A sitting posture with the head erect was chosen because it afforded the best condition for free respiration, whereas a reclining posture may cause an increase in the blood flow through the conchae, eliciting changes in the cyclic activity of the nasal cavities.1° Each subject was instructed to inhale as normally as possible through his mouth, to close his lips around the oropharyngeal catheter, and then to exhale through his nose. When a regular breathing pattern was established, the resulting pressure and air-flow patterns were recorded simultaneously on photosensitive paper by a Honeywell 1508 Direct Writing Recorder. Nasal air flow was measured with a heated flow meter connected to a well-adapted nasal mask, which was positioned away from the nostrils so that it would not obstruct air flow or cause air turbulence which could affect the validity of the measurements. Nasal resistance was calculated at flow rates of 0.25 and 0.50 1~.per second. These rates of air flow were compatible with normal respiratory patterns of breathing and also provided a basis for comparison of the results with those of other studies. After an otolaryngologist had been consulted, the nasal cavity of each subject was inspected before each recording to obtain a clinical impression of the anatomy of the nasal airway. The form of the calcified structures (turbinates and septum) and clinically evident irregularities of the nasal mucosa were noted. Each subject was asked if he had any respiratory ailments, and no measurements were made when there was a positive response. The subjects were asked to relate any change in nasal permeability that they had subjectively observed, and the stage of treatment at which the change had become evident was recorded.
Changes in nasal airway
Measurements of nasal resistance obtained before and after treatment are listed in Table I. The mean nasal resistance at 0.50 L. per second before treatment was significantly higher (p < 0.0005) than the mean nasal resistance measured after expansion. The mean nasal resistance at 0.25 L. per second before treatment was also significantly higher (p < 0.005) than the mean nasal resistance after expansion. The mean nasal resistance measured at the time of stabilization of the appliances and after 3 months’ retention were not significantly different. The values for changes in binasal cavity width and maxillary first molar width are found in Table II. Mean nasal cavity width before treatment was compared to the mean width after stabilization by means of a paired t test. The mean nasal cavity %,vidth after stabilization of the appliance (28.88 mm.) was significantly higher (p < 0.005) than the mean nasal cavity width before treatment (26.76 mm.). The mean nasal cavity width after 3 months of retention (29.23 mm. ) was significantly higher (p < 0.005) than the mean nasal cavity width at stabilization of the appliance (28.88 mm.). The mean maxillary first molar expansion was 9.4 mm. Since the appliance was used for retention and was absolutely rigid, the molar width after 3 months of retention was the same as the molar width after maximum expansion for each subject and thus was not remeasured. In order to determine the subjective responses to the maxillary expansion procedure, fifteen of the patients were asked if they had noticed any change in their ability to breathe through the nose after initiation of treatment. Seven of the fifteen subjects replied that it became easier for them to breathe through the nose as the palate was expanded. The change was usually noticed 1 to 2 weeks after the start of appliance activation. The other eight subjects did not notice any change in their breathing and were termed negative responders. A comparison of expansion results between subjects who responded positively about breathing changes and those who responded negatively about breathing changes showed that the two groups did not differ significantly when change
MAXILLARY Fig. 2. Scatter binasal
diagram relating change width (initial to stabilization).
FIRST MOLAR WIDTH CHANGE IN MILLIMETERS in
in nasal resistance and change in nasal cavity width were considered. As a check for randomness of the samples, first molar expansion and initial nasal resistance of the two groups were compared and were not found to differ significantly. A comparison of expansion results for the all-wire appliances versus the wireand-acrylic appliances showed that first molar expansion, initial and final nasal resistance, and change in nasal cavity width were statistically similar for the two appliance types. Linear regression analyses were computed for change in nasal resistance versus change in nasal cavity width, change in nasal resistance versus maxillary molar width expansion, and change in nasal cavity width versus maxillary molar width expansion. Scatter diagrams were constructed for the three relationships (Figs. 2 to 4). The data points of the three relationships tested demonstrated high variability, low predictability, and weak linear relationships between the variables. The correlation coefficient (“r”) relating nasal resistance change to nasal cavity width change was 0.34. The correlation coefficient relating change in nasal resistance to change in maxillary molar width was 0.42. The correlation coefficient relating change in nasal cavity width to maxillary molar expansion was 0.22. Discussion
Rapid maxillary expansion corrected the cross-bites of the subjects under investigation and concurrently provided an average reduction in nasal resistance of 45 per cent. There was no significant difference between nasal resistance measured after maximum expansion and nasal resistance measured after 3
Changes in nasal airway
Or 110 NASAL Fig. 3. Scatter (initial
diagram to stabilization).
CAVITY WIDTH CHANGE MILLIMETERS in nasal
9.08.00 7.0. 6.05.0-
7.0 MAXILLARY Fig. 4. Scatter resistance
diagram relating to stabilization).
. . I
FIRST MOLAR WIDTH CHANGE MILLIMETERS in maxillary
months of retention. These findings indicate that the reduction of nasal resistance accompanying maxillary expansion was substantial and was stable at least through the 3-month fixed-retention period. It would be desirable to obtain measurements of nasal resistance 1 or 2 years after removal of fixed retention to test the long-term stability of nasal resistance change. The initial nasal resistance of the subjects in this study was higher than nasal resistance of a normal sample and a nose-breathing sample investigated earlier.ll HunteP used instrumentation and methods identical to those used in the present investigation to compile nasal resistance readings on fourth-grade schoolchildren who had not received any orthodontic treatment. His subjects mere divided into three groups: nose breathers, mouth breathers, and a “high nasal resistance” group. Comparison of our subjects with those in the three groups in Hunter’s study reveals a number of interesting relationships. Hunter’s nosebreathing (normal) sample had nasal resistance which was significantly lower than that of our patients before treatment and statistically similar to our patients after expansion. For both the mouth-breathing and “high resistance” groups from Hunter’s study, the nasal resistance was statistically similar to that of our patients before expansion and significantly higher than that of our patients after expansion. These findings indicate t,hat patients requiring rapid maxillary expansion (that is, patients with a constricted palate and posterior dental cross-bite) have a nasal resistance which tends to produce a mouth-breathing pattern of respiration. After maximum expansion, nasal resistance of the subjects in the present investigation was statistically similar to nasal resistance of nose breathers and significantly lower than the nasal resistance of mouth breathers. Thus, nasal resistance highly indicative of mouth-breathing tendencies was reduced to levels commonly associated with children who normally breathe through their noses. This does not necessarily mean that all patients whose high nasal resistance is reduced to within the normal range will necessarily discontinue the mouth-breathing habit, as Watson and co-workers’1 have shown. Changes in nasal resistance from the stabilization of the appliance to the end of the 3-month retention period were slight and not significant statistically. Five patients showed further decrease in nasal resistance, and eight showed some increase in nasal resistance. Surprisingly, there was very low correlation (r = 0.22) between change in maxillary molar width and change in nasal cavity width. The scatter diagram of maxillary first molar expansion versus binasal cavity width expansion (Fig. 2) demonstrated a variation in nasal cavity width change of more than 2.5 mm. with the same amount of molar expansion. The data demonstrate high variability, low predictability, and a weak linear relationship between the variables. For example, Fig. 2 indicates that, of the three patients who experienced first molar expansion of approximately 9 mm., two showed nasal width increase of less than 1 mm. while the third showed an increase in excess of 3 mm. of nasal width. Nasal cavity width increased significantly during the retention period, but nasal resistance did not change appreciably. Residual stress stored in the expansion appliance and in the bones of the midface at the completion of the proce-
Changes in nasal airway
dure probably accounted for the change in nasal cavity width observed during the retention period as Zimring and Isaacson I3 have shown. In cases where significant change in nasal resistance did not occur, either at stabilization or after 3 months of retention, two factors may have limited the benefits of the procedure: (1) smelling of the nasal mucosa due to airborne irritants or allergy and (2) location of the nasal stenosis in an area superior and posterior to the parts of the nasal passages which are effectively widened by maxillary expansion, for example, large adenoids. Data from the present investigation indicate that we can expect an increase in binasal cavity width of from 1 to 3 mm. when maxillary first molars are expanded 8 to 11 mm. A nasal cavity width increase in that range was associated with a nasal resistance reduction (at 0.50 L. per second) of about 4 cm. water/L./second, with the greatest reduction in nasal resistance generally occurring in those patients with the highest initial nasal resistance. Subjects with initial nasal resistance greater than the mean nasal resistance for the maxillary expansion group showed an average nasal resistance reduction of 7.1 cm. water/L./second at maximum expansion. Subjects with initial nasal resistance less than the mean nasal resistance of the experimental group demonstrated a reduction in nasal resistance of only 1.8 cm. water/L./second. Apparently, a patient with a fairly adequate nasal airway does not show as dramatic a change in nasal resistance as one who experiences great difficulty with nasal respiration. Seven of fifteen subjects claimed that nasal respiration was less difficult following maxillary expansion, and eight subjects reported no change. A comparison of the two groups revealed no significant differences in either mean nasal cavity width change or mean nasal resistance change. There are two possible explanations for the different responses, in view of the lack of statistical difference. First, the change in the nasal cavity occurs gradually over a 3- to a-week period and may not be obvious to the less observant child. The other possibility is that several of the children who noticed no change had fairly competent nasal passages before treatment. An increase in nasal permeability would not seem as dramatic to them as it would seem to a child who has experienced great difficulty breathing through his nose. Some investigators 1, 3 have advocated the use of acrylic attached to the framework of the appliance to provide palatal support of the expansion forces. Statistical comparison of the expansion results of six wire-and-acrylic expansion devices with expansion results of eleven all-wire expansion appliances revealed no significant differences in molar expansion, initial nasal resistance, nasal resistance change, or nasal cavity expansion. It should not be inferred from these statements that no differences exist between the two types of expander. Such parameters as amount of molar tipping or amount of alveolar bending were not investigated. Measurement and comparison of these and other parameters bet,ween the two groups would be necessar.v before it could be concluded that one type of expansion device was or was not superior to the other. Larger samples of the two groups would also be desirable. Data collected in this study describe actual changes in nasal resistance and should not be compared to the data published by earlier investigators in the or-
A?u. J. CWth,od. Mcwch 1976
thodontie literature. \Vertz” measured the volume of air passing through the nose at different levels of respiratory effort, rather than nasal resistance. He used a warm-wire anemometer to record volume flow rate as cubic feet per minute. Measurements of air volume do not provide a valid index of change in cross-sectional area of the nose, since a subject with a small nasal passage could exhibit the same air volume rate record as a subject with a larger nasal passage, simply by greater breathing effort at the time of the reading.‘” Air-flow measurements are dependent on the patient’s respiratory effort, while nasal resistance measurements recorded at a specific flow rate are not. Similarly, although Linder-Aronson and AschanlJ termed their measurement “nasal resistance,” they measured only the pressure change of air passing through the nose, Nasal resistance in the present investigation was a ratio of pressure change to rate of air flow and cannot be compared directly to the “nasal resistance” of Linder-Aronson and Bschan. Several subjects described in Table I showed changes inconsistent with the mean changes of the other subjects. Individual variation in nasal resistance from one measurement to the next may have several causes other than rapid maxillary expansion treatment, including cyclic hourly change in the degree of swelling of the nasal mucosa, variation in allergic response to irritants, incipient or lingering upper respiratory infections, variation in linearity or frequency response of the instrumentation, and/or seasonal variation of nasal resistance All of the preceding causes may contribute to the standard deviation of the sample. Although the standard error was not excessive, identification and elimination of such sources of error could further reduce the standard error of the sample and therefore increase the statistical significance of the results. A retrospective review of the present investigation revealed several areas which could benefit from further study, including an investigation of the longterm stability of nasal cavity expansion and nasal resistance reduction, variation in nasal resistance with the time of day and season of the year, and the influence of inflammation of the nasal mucosa on nasal resistance. Rapid maxillary expansion has the potential for providing relief in many cases of nasal stenosis. Quite often the orthodontist is confronted with borderline cases which present the option of expansion of the palate or buccal tipping of posterior teeth. Borderline patients who breathe through their mouths without an obvious reason, such as enlarged adenoids, should be treated with rapid maxillary expansion. The procedure will not cure every case of mouth breathing, and patients will not always notice dramatic increases in nasal permeability. However, data from the present investigation indicate that rapid maxillary expansion does provide consistent reduction of nasal resistance as well as significant widening of the nasal passages. Summary
Records consisting of nasal resistance measurements, postero-anterior radiographs, and dental casts were obtained on seventeen patients before they underwent rapid maxillary expansion. These records were retaken after maximum expansion of the appliance and after 3 months of retention. Measurements of nasal resistance, binasal cavity width, and maxillary first molar width were made
for each subject at each stage of treatment. The following conclusions were derived : 1. Rapid maxillary expansion produced a significant reduction in nasal resistance measured at both 0.50 L. per second and 0.25 IA. per second air flow. The reduction of nasal resistance by maxillary expansion was stable through a 3month period of retention. 2. There was very low correlation between the amount of maxillary first molar expansion and change in nasal resistance. A41so, changes in nasal resistance showed low correlation with the amount of nasal cavity widening which occurred during the expansion procedure. 3. Change in nasal cavity width was not closely related to the amount of maxillary first molar expansion. 4. The patient’s subjective opinion of changes in his ability to breathe through the nose was not closely related to the amount his nasal resistance was reduced. 5. The change in nasal resistance of subjects who noticed an improvement in their ability to breathe through the nose was not significantly different from nasal resistance change in children who did not notice any change in their breathing. 6. When subjects treated with an all-wire expansion appliance were compared to subjects treated with a wire-and-acrylic appliance, the two groups were not significantly different with respect to maxillary first molar expansion, nasal cavity widening, or changes in nasal resistance. Differences in amount of molar tipping or alveolar bending were not investigated. 7. Patients requiring rapid maxillary expansion treatment for constricted maxillary arches have significantly higher nasal resistance than other orthodontic patients and nonorthodontic subjects. The rapid maxillary expansion procedure reduced the nasal resistance of those treated to a level which was not significantly different from that of subjects with maxillary arches of normal dimensions. 8. The reduction in nasal resistance achieved with the expansion procedure was not lost after 3 months of retention. 9. Where indicated, rapid maxillary expansion is not only an effective method for increasing the width of narrow maxillary arches but also reduces nasal resistance from levels associated with mouth breathing to levels compatible with normal nasal respiration. The manuscript.
1. Haas, A. J.: Rapid expansion of the midpalatal suture, Angle Orthod. 2. Haas, A. J. : Palatal expansion: ORTHOD. 57: 219-255,197O. 3. Wertz, R. A.: Skeletal and dental AM. J. ORTHOD. 58: 41-65,1970. 4. Gerlach, H. G. : Apical base after Report 32: 266-278, 1956. 5. Korkhaus, G.: Present orthodontic 1960.
maxillary dental 31: 73-86, 1961. Just the beginning changes rapid
of the maxillary in
6. Timms .I I). .J. : Some mrdic~al aspects of rapid maxillary expansion, Hr. .I. Orthotl. 1: I”7-1X d 1 1974 . i. Wertz, R. A. : Clmnges in nasal airflow incident to rapid maxillary expansion, Anglo Ortlrod. 38: I-11, 1968. 8. TVarrcn, I). W., Uuxny, L. P., ant1 Fischer, N. I).: Nasal patkrvay resistance in normal and cleft palate and/or lip subjects, .J. Dent. Res. Supp. No. 445, Marck, 196s. 9. Asckan, G., Drettner, H., and Range, H. : En ohjektiv metod for matning och regist,rering av nasand ningsmots tnndet, Fork. Sven. Otolaryngol. Foren. No. 2 (cited in LinderAronson and Aschan,i~ 1963). 10. Htoksted, P.: Measurements of resistance in the nose during respiration at rest, n&t Otolaryngol. 109: 143-15’8, 1953. 11. Watson, R., Warren, U. W., atid Fischer, N. I).: Nasal resistance, skeletal classification, and mouth breathing in ortkodontic patients, Aiw. J. ORTHOD. 54: 279-285, 1968. 12. Hunter, B. AI. : Nasal airway r&stance, hreathing patterns, and dentofacial clmracteristics, unpul)lished Master’s Thesis, Department of Orthodontics, University of North Carolina, 1971. 13. Zimring, J. F., and lsaacson, R. J.: Forces produced by rapid maxillary expansion. III. Forces present during retention, Angle Orthod. 35: 178-186, 1965. 14. Lubker, J. F.: Aerodynamic and ultrasonic assessment techniques in speech-dentofacial researck, ASHA Report No. 5, 1970. 15. Linder-Aronson, S., and Aschan, G.: Nasal resistance to breathing and palatal height before and after expansion of the median palatine suture, Odontol. Revy 14: 254-270, 1963.
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