a quantitative assessment of respiratory patterns and their effects on den to facial development

A quantitative assessment of respiratory patterns and their effects on dentofacial development

Article Outline

Abstract Materials and methods

o Sample o Orthodontic assessment o Cephalometric analysis o Measurements of breathing

Nasal power and nasal airway resistance Head-out body plethysmograph

o Statistical analysis Results

o Plethysmograph measurements Verification studies Percent mouth breathing

o Nasal power and nasal airway resistance Verification studies Relationship to percent mouth breathing

o Perception of breathing modeo Dental and skeletal relationships

Discussion Acknowledgements References Copyright

Abstract

The purpose of this study was to assess the effects of quantitatively determined breathing patterns on dentofacial development in growing children. Forty-nine subjects ranging in age from 10 to 16 years participated in the breathing pattern assessment portion of this project. Oral, nasal, and total airflow were measured at separate times by means of a head-out body plethysmograph technique and the values were compared with the subjects' and parents' subjective perceptions of their breathing modes. These breathing pattern measurements also were compared to nasal airway resistance and nasal power. Temporal variation and cyclic respiration, which may play important roles in quantitative evaluations of childrens' breathing patterns, also were addressed. In addition, objective assessments of possible associations between dentofacial structure and respiration were made on 45 of these

children. Most subjects' exhibited was either an oronasal or a completely nasal respiratory pattern. However, significant variation in breathing measures was evident among a number of subjects whose breathing was measured twice on the same day and on different days. No significant correlations were found between objectively measured and subjectively determined impressions of respiratory patterns. In addition, there was no association between nasal airway resistance or nasal power and plethysmograph recordings of percent of mouth breathing. Comparisons of measured breathing modes and dentofacial characteristics revealed a weak tendency among mouth breathers toward a Class II skeletal pattern and retroclination of maxillary and mandibular incisors. In contrast, subjective perception of mouth breathing was associated with increased anterior facial height and greater mandibular plane angles. Nasal power and resistance were not correlated with either dental or skeletal variables. This study presents evidence that determination of respiratory pattern is a complex issue for which methods must be refined and performed longitudinally. (AM J ORTHOD DENTOFAC ORTHOP 1990;98:523-32.)

Animal and human studies have demonstrated some relationship between nasal airway function and dentofacial form. Longitudinal investigations in primates by Harvold1, 2 and Miller3, 4 have revealed that mouth breathing can influence lip, tongue, and mandibular positions and lead to marked variation in skeletal and dental morphology. Linder-Aronson's studies5, 6, 7, 8 on human subjects with enlarged lymphoidal tissues also have suggested a relationship between respiratory pattern and dentofacial form. Skeletal differences were described in the vertical, transverse, and anteroposterior planes of space. Bresolin9, 10 noted distinguishing features in mouth-breathing subjects with allergies, including increased anterior facial height, larger gonial angle, narrower maxillary arch, deeper palatal height, and a more retrognathic profile. Trask11 described similar findings for allergic and non-allergic siblings.

Despite these findings, the effects of breathing pattern on facial form are still subject to debate. Quantitative analysis of respiratory mode has been an obvious methodologic difficulty in most studies. Efforts have been based on subjective opinions of breathing patterns or on indirect physiologic measurements taken at one time. Quantifying the proportions of oral and nasal breathing at repeated intervals is a prerequisite to any conclusion regarding the effects of respiratory function on facial form. The purpose of this project was to achieve quantitative evidence with respect to breathing patterns in growing children to evaluate the influences of these patterns on dentofacial development. Airflow measurements for the oral and nasal components of respiration were obtained by a head-out body plethysmograph technique on two separate visits. The values were compared with those obtained by three different methods of assessing respiratory pattern: subjective perception of breathing mode and measurement of nasal airway resistance and nasal power. Associations between dentofacial structure and the various measures of respiratory function were analyzed. The importance of temporal variation in respiration also was considered in the analysis of breathing pattern.

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Materials and methods

Sample

Forty-nine children, 18 boys (36.7%) and 31 girls (63.3%), participated in the first measurement of breathing patterns. Thirty-six of these subjects were willing to return to be studied a second time on a separate day. The subjects were between the ages of 10 and 16 years, with an average age of 13 years 1 month. The subjects were selected according to age and interest in participation. Their cephalometric radiographs were analyzed to evaluate possible associations between facial structure and respiration. Four of the subjects were eliminated from this part of the study because they did not fulfill one or more of the additional criteria: (1) white origin; (2) no pacifier or thumb-sucking habits beyond 5 years of age; and (3) no history of facial trauma.

Because of restrictions on radiographic exposure, the sample included both patients without prior orthodontic treatment and those in an early phase of treatment. Twelve (24.5%) had received no orthodontic treatment, 16 (32.7%) were in an early phase such as being treated with space-maintaining appliances or headgear, and 21 (42.9%) were wearing standard edgewise appliances during an early alignment period. The sample included both extraction and nonextraction cases, but patients with prior maxillary expansion were excluded. This information was obtained from patient records and clinical examination.

In addition, each subject, along with his or her parent(s), was asked to fill out a brief questionnaire concerning their subjective impressions of the participant's breathing pattern. One subject was unable to give an opinion.

Orthodontic assessment

Examination of radiographs and models of patients was performed by one investigator (N. U.) to identify the following variables:

1.Number and type of teeth (deciduous or permanent)

2.Right and left first molar and canine relationships (Angle classification)

3.Open bite (defined from the cephalometric radiograph as space between maxillary and mandibular incisal edges with reference to the occlusal plane)

4.Posterior crossbite

5.Maxillary and mandibular intermolar widths (as defined by the distance between the mesiolingual cusp tips of the right and left first permanent molars)

Cephalometric analysis

The cephalometric radiographs were obtained from patient records. Each subject's pretreatment radiograph was analyzed. The subjects' names were covered, and each was randomly assigned a code number that was used throughout the study. Tracings of each film were made by the primary author (N. U.) on 0.003-inch matte acetate with an 0.5 mm pencil. Fifteen landmarks were identified (Fig. 1), and 19 cephalometric relationships were measured (Table I).

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Fig. 1.

Cephalometric landmarks.


Intraexaminer reliability was determined by a random selection of 10 cephalograms that were retraced and remeasured. Pearson product moment correlation coefficients, ranging from r = 0.83 to 0.99, were calculated for each measurement.

Measurements of breathing

Nasal power and nasal airway resistance

Nasal power is commonly defined as the rate of energy required to move air through the nose.12 Nasal airway resistance is the ratio of the air pressure differential across the nasopharynx over the rate of nasal airflow.13 Resistance is derived from the relationship between pressure and nasal airflow at one specific flow rate during the respiratory cycle. Nasal power, however, provides an estimate over a continuous time interval, yielding a more precise and reproducible assessment of nasal airway obstruction.12 Posterior rhinomanometry was employed to measure both nasal power and nasal airway resistance. The rhinomanometer consisted of an airtight face mask that covered the nose. Two catheters measured the pressure drop between the mouth and the nose. One was placed in the posterior oropharynx with a tight lip seal; the second was connected to the well-adapted nasal mask. A pneumotachograph (Fleisch No. 2) also was attached to the face mask to measure nasal airflow. The rhinomanometer was connected to a microcomputer, which

calculated nasal power and resistance from the pressure and flow signals. Nasal airway resistance was computed as the reciprocal of the slope of the curve at zero flow from pressure plotted against airflow. Nasal power was calculated by integrating the pressure-flow curves over three consistent respiratory cycles. The subject was instructed on its use and asked to breathe through the nose to establish a regular breathing pattern. An average of three measurements was computed for inspiration and expiration immediately before and directly after the head-out body plethysmograph portion of the experiment.

Head-out body plethysmograph

Mode of respiration was assessed by the head-out body plethysmograph shown in Fig. 2.


Fig. 2.

Schematic diagram of the head-out body plethysmograph.

This system measures airflow during respiration. It is a noninvasive procedure in which each subject is placed into an airtight box with his or her head out. An airtight seal is maintained by means of a pliable sheet of rubber-dam material that is held in place around the neck with a tubular sandbag. Without information about our purpose, the participant was instructed to breathe normally for 10 minutes through a rubber mouthpiece.

Total airflow from the subject was measured by the displacement of air in the airtight box caused by the relative movements of the thoracic cage and abdomen. The amount of oral flow could be compared with total airflow. A mouthpiece was connected to a pneumotachograph, which measured oral airflow and translated the measurements into an electronic signal. Both oral and total flow signals were recorded on X-Y axes every 30 seconds for 10 minutes. When the total flow equaled the orally respired flow, the X-Y graph plotted a signal of approximately 45°. Deviation from this angle indicated nasal airflow. During the last three measurements, nose clips were used to induce total oral breathing. The value thus obtained was used as the baseline at which oral breathing represented total respiratory airflow. Thus the percent of mouth breathing could subsequently be calculated.

Statistical analysis

Pearson correlation coefficients were calculated to identify temporal variation and to verify all breathing measurements. Sex, age, number of previous measurements, time of day, and perception of breathing mode were analyzed separately. Means and variances for percent of mouth breathing were compared with subjective perceptions of breathing modes. A t test was performed to ascertain whether the subjective assessments of respiratory patterns

differed significantly from the quantitative measurements of their breathing modes. Pearson correlation coefficients were computed to determine whether there was a relationship between nasal power or nasal resistance and the percent of mouth breathing. Scatter diagrams were plotted for nasal power, nasal airway resistance, and percent of mouth breathing to determine whether there were threshold levels at which mouth breathing became the predominant mode of respiration. Multiple linear regression analysis was used to assess differences in skeletal and continuous dental parameters. Discrete dental variables were analyzed with the X2-test by dividing the groups into those identified as ≤ 10% or > 10% mouth breathing. Covariables were adjusted for age and sex. The significance level for all tests was accepted at p ≤ 0.05.


Results

Plethysmograph measurements

Verification studies

Verification of the measurements for percent of mouth breathing, nasal power, and nasal airway resistance was obtained by remeasuring 27 randomly selected subjects. Periods of 20 to 60 minutes were allowed between measurements. Pearson correlation coefficients for the plethysmograph's recording of percent of mouth breathing at the two different times were computed and are found in Table II.


Although the univariate or overall correlation was strong, the mouth breathing of 6 of the 27 subjects varied more than 15% on the same day (from 16.2% to 63.9%), accounting for the large variation seen. In addition, the sample was divided according to sex, percent of mouth breathing measured, and the subject's perceptions of respiratory pattern to ascertain whether these variables had been influential in the plethysmographic measurements. The variability between measurements was not influenced by perception of breathing mode. It appeared that female subjects and those who registered less than 10% mouth breathing had significantly stronger correlations and may have had less variation in breathing modes. However, it should be noted that one male subject significantly affected the correlation coefficient. When the value for this one subject was eliminated, no statistically significant difference was evident between the sexes.

The total variation in the measurements for percent of mouth breathing could have been due either to differences in two sets of measurements for the same individual at different times, or to variations between different subjects. The intraclass correlation was calculated to assess the contribution of variation from these two separate sources. The correlation was 0.885, demonstrating that the variation in the two measurements for one particular subject was not great. However, the variation among different subjects accounted for a high proportion of the total variation.

Percent mouth breathing

The oral component of respiration varied between 0% for nose breathers to 100% for total mouth breathers. The results for the first measurement were plotted according to the subjective perceptions of breathing patterns and can be seen in Fig. 3.


Fig. 3.

First-visit plethysmograph measurements plotted according to subjects' or parents' perceptions of breathing pattern. Percent of mouth breathing was calculated as the mean of a 10-minute recording on the head-out body plethysmograph.

sixteen subjects (32.7%) registered as total nose breathers, while only two (4.3%) registered as 100% mouth breathers. Most subjects used an oronasal breathing pattern in the range of 40% to 80%. No one measured between 5% and 40% oronasal breathing for either the first or the second visit.

The correlation between breathing patterns on different days was less strong than the correlation between patterns on the same day. Ten of the 36 subjects measured on the second visit registered a variation from the first day of greater than 15%. Five of these 10 switched from complete nasal breathing to predominantly mouth breathing, and 2 changed from oral breathing to total nasal respiration. In addition, female subjects had significantly less variation than male subjects. Perceptions, time of day, and season did not appear to have significant influences on the temporal variation in percent of mouth breathing.

The evident variation made it difficult to categorize subjects as mouth breathers or nose breathers. Therefore, measurements from the first visit, the second visit, and an average of these two values were all used for statistical comparisons requiring classification of breathing patterns. Findings were reported only if significant relationships were identified for all three of these separate classifications of breathing pattern.

Nasal power and nasal airway resistance

Verification studies

The verification measurements for nasal power and nasal airway resistance were divided according to those taken before and after the plethysmograph portion of the experiment that was performed on the same day. Two subjects were unable to perform the breathing exercise required by the procedure. Lack of patency between the pharynx and the oral cavity from contraction of the pharyngeal musculature in persons who were unable to complete the procedure have been described in previous research.14 The small mean differences between readings and the strong correlation coefficients for nasal power (r = 0.91) and nasal airway resistance (r = 0.99) of expiration values taken after the plethysmograph led us to use these measures in analyzing relationships between percent of mouth breathing and dental and skeletal variables.

Relationship to percent mouth breathing

The Pearson correlation coefficients were calculated and scatterplots were derived for measured percent of mouth breathing and nasal power/nasal airway resistance. No statistically significant correlation, threshold level, or apparent relationship could be found between plethysmograph measurements of oral breathing and either the degree of nasal resistance or the amount of work required to breathe through the nose (Fig. 4).


Fig. 4.

First-visit plethysmograph measures (as percent of mouth breathing) plotted against nasal power (in milliwatts).

Perception of breathing mode

Information provided by the subjects or their parents was used for comparisons between measured and perceived breathing patterns. Both an estimation of percent of nasal and oral breathing and a categorization of patients as nose or mouth breathers were requested. A t test was performed to determine whether the perceived breathing pattern was significantly different from the quantitatively measured breathing pattern (Fig. 3), nasal power, or nasal airway resistance. There was no evidence that a subject's or a parent's impression of breathing mode had any statistically significant relationship to any of these objective assessments of respiratory function.

Dental and skeletal relationships

The variability in the dental parameters examined could not be explained by the percent of mouth breathing measured. Angle classification and presence or absence of either crossbite or anterior open bite were not explained significantly by respiratory mode. Also, no relationship was found between maxillary or mandibular intermolar width and measured percent of oral breathing. Age and sex did not affect these results.

As subjects increased the degree of mouth breathing, there was a weak but significant tendency toward a Class II skeletal pattern and retroclined maxillary and mandibular incisors. Significant findings for the multiple linear regression analysis comparing cephalometric measurements and percent of mouth breathing are shown on Table III.


The r2 values give the percentage of the variation seen in the cephalometric measurements that was explained by mouth breathing after adjustment for age and sex. ANB was correlated most strongly with mouth breathing. Thirty-eight percent of the 0.41° increase in ANB was explained by a 10% increase in mouth breathing. The maxillary and mandibular incisor positions also were affected significantly. With every 10% increase in mouth breathing, maxillary and mandibular incisors decreased 1.0° for 1 SN and 1L MP, respectively. In the vertical plane, no relationships were found to be statistically significant after adjustments had been made for age and sex.

Estimated perception of mouth breathing by parents and subjects also was used to classify individuals. As with the plethysmograph breathing measurements, no statistically significant dental relationships were found. Significant cephalometric results are shown in Table IV.


Vertical relationships, including anterior facial height and mandibular plane, were most affected. As perceived mouth breathing increased by 10%, SN-MP increased by +0.70° and PP-MP by +0.80°; 13:0% of this variation in cephalometric values was explained by mouth breathing in the cases involving increased SNMP and in 21.5% of the variation with increased PP-MP. Anterior facial height, as measured by N-Me, also increased by 0.70 mm with every 10% increase in perceived mouth breathing. There were no significant findings with respect to the anteroposterior plane or incisor position.

Analyses of the associations between dentofacial variables and nasal airway resistance, as well as nasal power, were also performed. No statistically significant dental or cephalometric relationships were found.


Discussion

The results of this study revealed that the plethysmograph measurements of the oral and nasal components of breathing, as well as the subjective perception of respiratory pattern, could not be associated with either nasal power or nasal airway resistance. In the past, nasal power has been examined infrequently in studies assessing respiratory activity and its effects on facial development. In one study, Trask11 reported greater nasal power readings for mouth-breathing siblings with allergies, compared with their nonallergic siblings. Unfortunately, although nasal power appears to be a more sensitive measure of estimating nasal obstruction,12 studies using nasal resistance as the criterion for assessing respiratory activity have been more popular in determining relationships between dentofacial variables and breathing pattern.15, 16, 17 In agreement with our findings, Hartgerink and Vig17 have reported a lack of association between nasal resistance and respiratory pattern when 38 orthodontic patients were compared with a group of 24 control subjects between the ages of 8 and 14. On the other hand, in a study of 100 adult subjects, Warren18 reports that airway impairment and obligatory mouth breathing occur at a threshold of 4.9 cm H2O/L/sec of nasal airway resistance, which corresponds to a nasal cross-sectional area of 0.4 cm.2 Although the sample in our study came from a much younger population, there was no threshold level at which nasal resistance was associated with quantitatively assessed mouth breathing and therefore no demonstrable relationship between them. Consideration, however, must be given to the disparate samples with respect to remaining facial and nasal growth, atrophy of lymphoidal tissues, and other age-related factors. These variables may have influences on nasal airway function, making comparisons difficult between the two study groups.

The measurement of nasal airway resistance itself should be examined. Warren18 states that as a nasal airway is impaired, resistance increases. The body responds with obligate mouth breathing, thereby reducing the degree of resistance. This measurement represents the cross-sectional area of the nasal cavities and does not appear to reveal directly a person's pattern of breathing. Direct measurements of oral and nasal components of respiration have been accomplished by Gurley and Vig19 and by Keall and Vig.20 The simultaneous nasal and oral respirometric technique, or SNORT, is capable of separating nasal and oral airflow through a system of valves, transducers, and flow meters to make recordings.

In the present investigation, respiratory patterns were obtained by direct measurement of oral and total airflow with the head-out body plethysmograph. A significant degree of variation was evident in some children whose breathing was measured twice within 1 hour. However, the variation in measurements obtained by this system was similar to that in a report on the inductive plethysmographic technique described by Warren et al.21 The device used assessed nasal and tidal air volume without enclosing the subject in an airtight box.

Although the validation methods were different, the intraclass correlations to assess variation within subjects ranged between 0.760 and 0.929 for Warren's technique and 0.885 for our study. Despite the apparent strong correlations between the head-out body and inductive plethysmograph techniques, these methods must be received with caution because of the possibility for individual variations that a summary correlation statistic cannot reveal.

Our evaluation of the breathing modes of growing children measured on different days showed variations that may be attributed to inherent fluctuations in respiratory activity. Nasal breathing cycles, which have a 3-hour average periodicity with a range of 1 to several hours, have been found to occur in 80% of adults.22, 23 The patency measured in each nostril varies, and yet the total resistance remains constant. Children, however, do not maintain uniform conductivity from alternating nasal patency.24 Instead, nasal passage obstruction is random in nature and will fluctuate throughout the day with periods of congestion. Van Cauwenberge and Deleye24 reported that the duration of the cycle in children averages 57 minutes, although this will vary immensely on an individual basis. This recognized cyclic nature of respiration could explain the numerous “switchers” that alternated from total nasal breathing to complete oral respiration and, conversely, on separate visits. The variation in measurements recorded on the same day within an hour also could be a product of the nasal breathing cycle.

The possibility that the variation measured in our study might be a result of the method itself cannot be discounted. Although the plethysmograph is noninvasive, awareness that the airway is being assessed is an inherent difficulty in any evaluation. Attempts to breathe normally with a mouthpiece in place easily could influence a person to increase the oral component of breathing. This has been suggested in a recent study by Hairfield and associates.25 Adult subjects had greater oral airflow during respiration when plastic tubing was placed in the mouth. An inverse relationship was found between the degree of mouth breathing and the distribution of airflow through the nose. Although this suggests the possibility of technique-induced breathing patterns, there are several reasons not to consider the plethysmograph measurements as entirely invalid. First, it is notable in this study that half of those whose breathing varied more than 15% on the same day also had high variations when measured on two separate days. This finding supports a theory of more profound cyclic respiration in certain persons. In addition, the correlation between measurements taken within an hour was significantly stronger than the correlation between measurements recorded on separate days. Furthermore, the plethysmograph values were taken over a 10-minute period and were averaged over this entire interval to adjust for the possibility of fluctuations or spurious measurements caused by postural adaptations to the measuring device. Despite these findings and precautions, it appears that both inherent respiratory fluctuations and difficulties in technique, as well as nasal power and nasal airway resistance, may contribute to variations in plethysmograph measures.

Measures for percent of mouth breathing in this study revealed that the subjects were either total nasal breathers or combined oral and nasal breathers. Only two subjects measured 100% oral respiration. Therefore, the term mouth breathing should be reconsidered. Pure mouth breathing appears to be unusual. From these and other findings,26, 27 oronasal breathing seems more common. This theory is in agreement with that of Hartgerink and Vig,17, 28 who also demonstrated that 100% mouth breathing occurred infrequently. The

absence of measurements between 5% and 40% mouth breathing also is notable. Perhaps a threshold exists after which oronasal breathing varies on a continuum. No absolute definition of mouth breathing can be described; only an arbitrary designation could be postulated with the present level of knowledge.

In this study, an increase in the oral component of respiration was associated weakly with a skeletal Class II pattern and retroclination of maxillary and mandibular incisors. Although the correlation was statistically significant, its clinical importance is questionable because of the degree of association measured. However, previous reports have shown similar findings. Freng29 studied 11 patients with restricted nasal respiratory function due to choanal atresia. Sagittal differences were affected significantly. Retrognathia of both the maxilla and the mandible were observed, while vertical facial dimensions were similar for both control subjects and patients. Linder-Aronson6 has reported that children with nasal obstruction from enlarged adenoidal tissue are characterized not only by a more retrognathic profile and retroclined maxillary and mandibular incisors but also by distinctive vertical facial features. Increased total and lower anterior facial heights, as well as steeper mandibular planes, typified children with nasopharyngeal obstruction. In contrast, Hartgerink and Vig17 examined vertical relationships and found no association with an objective measurement of percent of nasal respiration. Solow et al.30 studied 24 children with no history of nasal obstruction. Mandibular retrognathia and retroclination of the maxillary incisors were found in association with obstructed nasopharyngeal airway, defined radiographically and rhinomanometrically. Despite these findings in previous studies, comparisons are difficult to make. Classifications of subjects as mouth breathers and nasal breathers were dissimilar. Associations were made between very different samples, so interpretation must be made with this fact in mind.

Our findings also indicated a lack of association between either nasal power or nasal airway resistance and dentofacial characteristics. In a study by Trask et al.,11 no relationship was found between nasal power and facial form (Trask, 1989 personal communication). Watson et al.15 examined 51 subjects to compare nasal airway resistance and sagittal skeletal dimensions. No relationships were determined between nasal resistance and the cephalometric parameters analyzed. In a report by Vig et al.,16 28 adult subjects were grouped according to vertical facial proportions and lip competency. Values for nasal resistance were measured and found to be unrelated to facial morphology. Similarly, Hartgerink and Vig17 have reported no significant relationships between vertical facial characteristics and the degree of nasal airway obstruction measured by resistance. These conclusions are consistent with our finding that nasal airway resistance was not associated with respiratory pattern. Nasal respiration in children appears to exist despite varying degrees of resistance.

In our report, vertical relationships were found to be related weakly to the subject's/parent's impression of breathing mode. As the degree of perceived mouth breathing increased, anterior facial height and mandibular plane steepness also increased. Subjective opinion as a source of information for determination of nasorespiratory condition has been employed in past studies.6, 10, 11 Previous findings of increased vertical dimensions are in agreement with the results of this report. However, objectively measured respiratory activity did not correlate with subjective perception in this study. Those who perceived themselves as

mouth breathers often based their assessments on open-mouth posture. One can speculate that posture may largely influence vertical facial relationships. Yet Vig28 argues that there is a minimal level of muscular activity for posture. A greater threshold is required to maintain muscular balance for respiration. This larger degree of muscular control may be responsible for variations in dentofacial morphology seen in mouth breathers, which may not be attributed to the weaker neuromuscular requirements of posture only. Another possibility may be that some subjects develop a habitual open position after an earlier period of actual mouth breathing, despite presently measured nasal respiration. Perhaps, then, those who were measured as nasal breathers in this study had been oronasal breathers at one time when influences on dentofacial form were strongest. This theory might allow an understanding of the variations in vertical facial dimensions seen in this and other studies with regard to classifications of individuals by perceived respiratory pattern. The period in which facial development can be most readily influenced by respiratory mode cannot be addressed in a cross-sectional study.

This investigation made initial efforts to assess respiratory patterns objectively and to evaluate influences on dentofacial morphology in children from an orthodontic population. Variations in sagittal relationships and retroclination of incisors were partially explained by plethysmograph measurements with respect to percent of mouth breathing. In contrast, subjective perceptions of respiratory patterns were associated mildly with increases in vertical facial structure. In both objective and subjective assessments of respiratory patterns, associations with dentofacial variables were not adequate to warrant strong generalizations about causal relationships. In addition, nasal power and nasal airway resistance could not be correlated with either subjectively determined or objectively measured oral respiration, or with dentofacial characteristics. From this study, it is clear that the classification of individuals according to respiratory pattern is a complex issue. Furthermore, although the effects of mouth breathing on dentofacial morphology were statistically significant, the magnitude of the variations explained by oral respiration were not great. Stronger correlations and a more thorough analysis of respiratory patterns may be required to support decisions for clinical intervention. Questions also remain as to the timing of the possible effects of respiratory mode on dentofacial form. If the period during which influences are strongest were known, intervention could be timed to have its greatest value. Finally, longitudinal evaluations involving objective assessment of breathing pattern are crucial and deserve further research.


Acknowledgements

We gratefully acknowledge the technical assistance of Garrett Hayashi, Quentin Hanley, and Viviana Rebellodo, as well as the statistical assistance of Dr. Timothy DeRouen and Lloyd Mancl.


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a quantitative assessment of respiratory patterns and their effects on den to facial development

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