Relationship between vertical dentofacial morphology and respiration in adolescents

Relationship between vertical dentofacial morphology and respiration in adolescents Henry W. Fields, DDS, MS, MSD, ° Donald W. Warren, DDS, PhD, b Keith Black, DDS, = and Ceib L. Phillips, PhD ~

Chapel Hill, N.C. The relationship between vertical dentofacial morphology and respiration has been debated and investigated from various approaches. The purpose of this study was to use contemporary respirometric techniques to compare the breathing behavior of normal and long-faced adolescents. Sixteen normal and 32 long-faced subjects 11 to 17 years of age were chosen clinically and verified by means of a discriminant function. Vertical and anteroposterior facial form was assessed from lateral cephalometric radiographs according to the following measurement criteria: six skeletal angular, eight skeletal linear, four dental linear, and three skeletal ratios. Breathing behavior was quantified according to tidal volume, minimum cross-sectional nasal area, and percent of nasal breathing as assessed by pneumotachography, measurement of differential pressures, and inductive plethysmography. The data indicated that the normal and long-faced groups were significantly different with respect to lower face form, and each group in the study was comparable to groups that had been chosen by previous investigators. Multiple regression analysis demonstrated that the normal and long-faced groups had similar tidal volumes and minimum nasal cross-sectional areas, but the long-faced subjects had significantly smaller components of nasal respiration. These results illustrate that groups without significant differences in airway impairment can have significantly different breathing modes that may be behaviorally based, rather than airway-dependent. (AM J ORTHODDENTOFACORTHOP1991 ;99:147-54.)

C l i n i c i a n s and researchers continue to question the relationship between craniofacial morphology and respiration. '-9 Much of the controversy appears to result from the lack of objective criteria used to assess facial form and respiratory behaviors. Recent developments in techniques for the evaluation of both facial form and respirometric variables make it possible to explore this relationship further. Patients should be selected for study according to their true facial form. Choosing subjects according to the vertical position of the teeth and extrapolating vertical skeletal form on this basis can be misleading, '° so alternative strategies for selecting subjects are necessary. Clinical impressions can be used successfully to choose subjects for investigations of selected vertical • Professor, Departments of Orthodontics and Pediatric Dentistry, School of Dentistry, University of North Carolina. ~Kenan Professor and Director. Oral-Facial and Communicative Disorders Program, Department of Dental Ecology and the Dental Research Center, School of Dentistry, University of North Carolina. 'Private practitioner, Asheville, N.C. aResearch Associate Professor, Department of Orthodontics, School of Dentistry, University of North Carolina. Supported by National Institute for Dental Research Grants DE 06957, 07105, 08708, and 05215. 8/1/18582

facial proportions." Optionally, sets of morphologic variables can be used to separate patients objectively into long-faced and normal groups--a method that is superior to using a single variable to discriminate between vertical facial types. ~°,'~ Considerable progress also has been made in assessing modes of respiration. Previously, investigators often used undisclosed, subjective, or unreliable methods to evaluate and label respiration as either nasal, oral, or a combination of these two modes. ~2~4Lateral cephalometric radiographs have been used to quantify airway size and patency. 's Although positive correlations have been found between airflow and airway measurements from cephalometric radiographs, '6 the validity of evaluating a three-dimensional structure with a two-dimensional radiographic projection is questionable. ~7 Several investigators have used measures of nasal resistance to determine airway dynamics? ,~8,~ Measurement of airway resistance involves the simultaneous recording of airflow and pressure drop across a specific structure. The rate of airflow is measured with a pneumotachygraph, and the pressure drop is measured with differential transducers. Nasal resistance values are always recorded at a given airflow rate or a standard 147

148

Am. J. Orthod.Dentofac.Orthop. February1991

Fields et al.

T a b l e I. Sample description

Group Normal Long face

[

No. 16 32

I

Zgerange(yr)

Mean age O'r) (SD)

11-16 11-17

13.9(1.7)

pressure level. Although nasal resistance measurements are valid and reliable when used appropriately, this method does have certain limitations. 2° It assumes laminar flow, even though some nasal airflow is turbulent. Another problem is that the relationship between nasal resistance and nasal airway impairment is nonlinear. 2t When a subject's nasal breathing is severely impaired, airflow may be so low that testing at some flow rates is difficult. Nasal resistance cannot be correlated with respiratory mode, which is defined by the proportion of nasal to oral breathing. 2t'22 A system for objective measurement of respiratory behavior should provide continuous monitoring of successive respiratory cycles; it should measure both inspiratory and expiratory airflow, provide simultaneous measurements of oral and nasal airflow, interfere minimally with normal respiratory behavior, and have a high degree of reliability and reproducibility?3 Gurley and Vig 23 developed the Simultaneous Nasal and Oral Respiratory Technique (SNORT) to quantify respiratory mode and meet the previously mentioned criteria, but this method was found to entail some difficulty during calibration and in maintaining patient comfort in the breathing chamber. ~4 Newer iterations of this technique have addressed these shortcomings. 25'26 Warren 2° demonstrated a technique that assesses nasal airway impairment by estimating minimum crosssectional nasal area during breathing. This technique gives some indication of the potential for nasally impaired or normal respiratory function. Warren et al. 27 also described an alternative approach for measuring oral and nasal respiration and tested its reliability. Their technique involved inductive plethysmography, which enabled the investigators to assess respiratory modes without enclosing the subject's head in an airtight box. The calibration routine is simple, 2s and the technique can be used for both infants and children. 29"3° The subjective nature of many studies that have investigated the interaction between vertical facial morphology and respiration raises serious questions about their validity. The purpose of this study was to use newly developed respirometric techniques to compare breathing behaviors in a group of adolescent boys and girls who had normal vertical facial morphology with a similar group that had excess anterior lower face

[

Boys

137 20

6

t8

[

Girls I0 ,,

height or a tendency toward long face. Objective quantification of possible differences should provide a better basis for determining whether adverse breathing behaviors influence dentofacial development. MATERIALS AND METHODS Selection of subjects Sixteen subjects with normal facial dimensions and 32 subjects with long faces were chosen from a group of patients seeking treatment at the University of North Carolina School of Dentistry (Table I). All the subjects were between 11 and 17 years of age and in good health, with no underlying systemic or identifiable craniofacial syndrome, as determined by medical history. All had intact dentitions and no signs or symptoms of temporomandibular joint dysfunction. Quantification of facial morphology The initial designation of each subject as being of either a "normal" or "long face" type was made by two clinicians, whose judgment was based primarily on the relative percentage of total anterior face height (softtissue nasion to soft-tissue menton) contributed by the anterior lower face height (subnasale to soft-tissue menton). Long face subjects had a disporportionally large anterior lower face height. A previous study showed that clinical judgment of facial proportion can discriminate between long face and normal subjects on the basis of cephalometric characteristics with sufficient accuracy to produce groups similar to those designated as deviant or normal by other investigators) ° A discriminant analysis, which had been tested previously on independent groups of subjects and which had yielded a jacknife classification accuracy greater than 90% when compared with clinical impressions, 31 was applied to all subjects clinically selected for this study. The subjects were given final classifications as either long face or normal, based on the results of the discriminant analysis. Lateral cephalometric radiographs were obtained with the subject's head in a natural position, achieved by having the patient gaze at a distant point while taking one step forward and adjusting to a comfortable posture. 32 Each radiograph was obtained within 12 months of the breathing assessments. True horizontal and ver-

VohLme 99 Number 2

Vertical morphology and respiration hz adolescents 149

N S

SN/

Go

B

Fig. 1. Angular measurements and linear measurements CoGo and Go-Mc used to quantify anteroposterior and vertical facial morphology.

Fig. 2. Linear measurements used to quantify facial skeletal morphology. ATFH and PTFH are not shown, but AUFH + ALFH = ATFH and PUFH + PLFH = PTFH.

P PLANE tical planes were registered on each film, which was traced on matte acetate paper, and 140 hard-tissue and soft-tissue landmarks were indicated with a 0.5 mm lead pencil. Bilateral structures were averaged to provide a mean outline. The points were then digitized. From the completed multiple tracings and digitizations, the landmarks and digitizing errors were identified. The tracing point location and digitizing errors for these methods, which have been reported previously, 3' ranged from 0 to 2.12 mm for landmark identification and 0 to 0.15 mm for digitizing. Twenty-one dental and skeletal measures were used to evaluate the craniofacial structures from the lateral perspective in the anteroposterior and vertical planes o f space. This set of measures contained eight skeletal linear measures, six skeletal angular measures, four dental linear measures, and three skeletal facial height ratios. Figs. 1, 2, and 3 describe these measures. Quantification of respiratory mode and measurement of nasal cross-sectional area The assessment of respiratory modes involved, first, measuring the volume of air inspired, then ascertaining the nasal component of this total. To determine total air inspired, or tidal volume, respiratory inductive plethysmography was used as previously described, 27 and the values were calibrated against a spirometer. The nasal component o f tidal volume was measured by placing a small cap over the nose and connecting it through a tube to an integrated pneumotachograph. The ratio of the nasal volume and tidal volume was then

H

~LDH

M PLANE Fig. 3. Linear measurements used to quantify vertical dentoalveolar morphology. Maxillary measures are perpendicular to the palatal plane, and mandibular measures are perpendicular to the mandibular plane.

multiplied by 100 to provide the percentage of nasal respiration. The technique for measurement of minimum sectional area also has been reported previously. :° This method assumes that the smallest cross-sectional area of a structure can be determined if the differential pressure across the structure is measured simultaneously with rate of air flow through it. The pressure drop across the nose was measured by placing one catheter in the mouth and another in the nasal mask and attaching the catheters to pressure transducers. Air flow was measured with a heated pneumotachograph attached to the

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Am. J. Orthod.Dentofac.Orthop. February1991

Table II. Morphologic measurements and results of unpaired t tests for comparisons of adolescents with long face and normal facial height (magnification × 7.5%)

Variable Skeletal angular measures (degrees) SNA SNB ANB Gonial SN-PP SN-MP Skeletal linear measures (ram) Go-Me Co-Go ATFH PTFH AUFH PUFH ALFH PLFH Dental linear measures (mm) AUDH PUDH ALDH PLDH Skeletal ratios PTFH/ATFH AUFH/ALFH AUFH/ATFH

]

Longface(n = 32) Mean (SD)

l

Normalface(n =16) Mean (SD)

I

p value

79.5 76.4 3,4 133.1 7.2 39.1

(4.0) (4,0) (2,3) (6.0) (3,6) (4,8)

80.6 78.5 2.4 129,7 6.6 30.9

(4.5) (4.7) (1.3) (1.3) (2,8) (3.9)

0.43 0. l 1 0.13 0.06 0.42 0.0031

72.0 58.5 127.1 86.0 54.6 43.2 70.5 35,7

(6.4) (5.1) (6.9) (6.2) (4.1) (4.4) (5.3) (5,6)

70.8 57.1 114.6 83.7 52.8 43.0 60.7 33.5

(5.1) (3.5) (5.4) (6.0) (2.9) (3.0) (4.0) (4.5)

0.52 0.32 0.0001 0.22 0.23 0.87 0.0001 0.19

30.8 24,3 42.2 32.5

(2.3) (3.4) (3.9) (3.2)

26.3 20.7 38.2 28.9

(3.2) (2.6) (2.6) (2.6)

0.0001 0.0004 0.0006 0.0003

0.73 (0.05) 0.87 (0.07) 0.46 (0.02)

0.0004 0.0001 0.0001

0.68 (0.04) 0.77 (0.08) 0.43 (0.02)

mask. The mask was modified to ensure that there was no impingement on the nasal airway during data collection. As the subjects breathed in and out through the nose, the computer calculated the minimum cross-sectional area of the nasal airway. Subjects were subsequently grouped into breathing categories, based on their percentage of nasal respiration, and characterized as "nasal," "predominantly nasal," "mixed nasal and oral," "predominantly oral," or "oral" breather, as suggested by Warren et al. 33 Descriptive statistics were calculated for the subjects with normal and long faces and these statistics were compared to existing data to determine the representativeness of the discriminate analysis group assignments. Unpaired t tests were used to determine whether significant differences existed between subjects with long and normal facial skeletons for specific morphologic variables. The level of significance was set at 0.002 because of the large number of comparisons. A full-model multiple regression analysis was used to test the assumption of parallelism for the regression lines of tidal volume, percent of nasal breathing, minimum cross-sectional area, and breathing category, ae-

cording to age and gender, before an analysis of covariance was used to compare the groups with normal and long facial shapes. The full model analysis and analysis of covariance were performed according to the general linear model (GLM) procedure in SAS. 3~ The F tests for the three hypotheses of parallelism, no interaction, and no group difference, based on the adjusted mean scores, were performed as outlined by Kleinbaum, Kupper, and Muller. 3~ The level of significance was set at 0.05. A nonparametric analysis of covadance also was completed on the breathing categories according to age and gender as covariates. A 0.05 level of significance also was set for this test. RESULTS

Descriptive statistics for the two groups are given in Table II. The comparison between them indicated that the subjects with long faces had significantly greater mandibular plane angles, anterior total face height, anterior lower face height, and increased vertical dental dimensions. The proportions of posterior total face height to anterior total face height, anterior upper face height to lower or anterior total face height, and anterior lower face height to anterior total face

Volume99 Number2

Vertical morphology and respiration in adolescents 1 51

Table III. Unadjusted and adjusted mean values for respiratory variables

I

Group Unadjusted means Normal face Long face Long-normal Adjusted means (controlled for age and gende0 Normal face Long face Long-normal

Tidal volume (ml)

Minimum X sec area (mrr?)

[

Nasal respiration

523.4 616.9 93.5

43.6 36.3 - 7.3

85.2 63.5 - 21.7*

4.4 3.7 - 0.8t

537.9 609.6 71.7

43.6 36.1 - 7.5

84.9 63.6 - 21.3*

4.4 3.7 - 0.7

(%)

Breath category (1-5)*

*1, Oral breathing; 2, predominantly oral; 3, mixed oral-nasal; 4, predominantly nasal; 5, nasal. iDifferences between normal and long face groups p <-- 0.05 level.

Table IV. Distribution of subjects according to respiratory behavior category

Respiratory behavior category Group

Oral*

Predominantly oral

Normal face n= 16 Long face n = 32

0

0

2

5

9

5 (16%)

(12%) 4 (12%)

(31%) 8 (25%)

(56%) 12 (38%)

3 (10%)

I

Mixed orallnasal

I

Predominantly nasal

Nasal

*Number in categoryl(percent of group).

height were significantly different between the two groups and deviated in the expected direction. Comparisons of the unadjusted means by unpaired t tests between the two groups for the respiratory variables of tidal volume, minimum cross-sectional area, percentage of nasal respiration, and breathing category showed that the percentage of nasal respiration was significantly reduced in the group with long faces. These differences also were reflected in the significantly increased distribution of subjects with long faces who were found to use oral or predominantly oral breathing (Table III). When these data were analyzed and controlled for age and gender, the only remaining significant difference in the adjusted mean values between the groups was the reduced percentage of nasal respiration in the group with long facial skeletons. The nonparametric analysis of covariance also indicated no significant differences in the distribution of subjects with respect to breathing category between the group containing subjects with normal facial length and the one containing subjects with long faces (Table IV). DISCUSSION This study again suggests that it is possible to classify subjects as having either normal or long faces on

the basis of a discriminant analysis, and to obtain resuiting groups that are comparable to those of other studies, z0.31Most of the angular dimensions for adolescent subjects are consistent with those found for children or adults? °'31"36The linear measurements are intermediate between those found for children and for adults in both the long face and normal face categories. 1°'3Z'3+Some of the mean differences between the groups are not of the magnitude of those found in previous studies, in which the subjects were assigned strictly by clinical impression. This discrepancy may have resulted because the discriminant function assigned subjects to groups as having either predominantly long or normal faces without assigning an arbitrary classification cutoff point other than 0.5 to determine the extent of the normal or long attributes. However, inspection of the data reveals that only three subjects in the long faces group had less than a 75: 25 ratio of long to normal characteristics. This finding suggests that very few of the subjects had borderline faces. Nevertheless, the discriminant function method of group assignment may have a tendency to reduce the magnitude of the morphologic differences between the groups. Long face subjects in this study had significantly

152 Fields et al. longer anterior lower faces, expressed as increased steepness of the mandibular plane angle. All facial height ratios--both posterior to anterior and upper to lower--revealed statistically significant differences between the normal and long face groups because of the excessive contribution of anterior lower face height in the long face subjects. These ratios are consistent with those found for clinically selected children with long faces, but they are not similar to those for clinically selected adults with long faces, who showed differences only for posterior/anterior skeletal ratios '° when compared to the normal group. The group of long face adolescent subjects in this study also had increased dentoalveolar components in all areas, a finding similar to that for children in the same category, but not for long face adults, t° In many ways, then, the adolescents with long faces are morphologically more similar to long face children than to long face adults. This study, like Our previous studies, '°,3' was unable to detect mean differences in palatal plane orientation, upper face height measures, or ramus length between the two groups. Nahoum s7 ~'eported differences in palatal plane orientation and upper face height measures between groups with open bite and nonopen bite, while Schendel et al. 36 found no difference in upper facial height between long face and normal subjects but reported significantly shorter ramus length in long face subjects with open bite. The lack of significant differences between groups for these variables in this study may, in part, be that open bite and nonopen bite subgroups of the long face group were not segregated for data analysis because of the small sample sizes. Because recent data revealed changes in the nasal airway during adolescence3s an analysis of covariance was performed to ensure that differences between groups were not the result of unequal distributions of subjects by age and gender. The adjusted and unadjusted mean values for tidal volume fell within a wide range from 300 to 800 ml. These values are considered to be dependent on body type and were not significantly different between groups. The adjusted mean minimum cross-sectional nasal areas for the normal and long face groups of 46.3 mm 2 and 36.3 mm 2, respectively, compare favorably with the value for normal face adults (approximately 65 mm2), 39 for normal face adolescents at the ages of 14 years (47 mm2) and I 1 years (38 mm2), 38and for normal face children at 6 years of age (21 mm2). a8 Growth in adolescence or late adolescence apparently contributes to further increases in airway size. The significant differences found in the percentage of nasal respiration indicate that more of the long face adolescents had some component of oral breathing. This

Am. J.

Orthod. Dentofac. Orthop. February 1991

was not caused by the patency of the airways, which were, on the average, reduced but not significantly different from normal, according to estimates of minimal cross-sectional nasal area, as noted above. The group with normal facial height had a mean of approximately 85% nasal breathing, compared to the long face group for which mean nasal breathing was approximately 63%. Data for children and adolescent subjects indicate that the percentage of children with nasal breathing increases between 6 and 14 years of age and that, for children who are the mean age of this sample (13.9 years), 70% to 80% nasal breathing is expected. 38 Therefore, the appropriate respiratory mode was evident among the normal subjects, but not among the long face group. How can these data be reconciled with studies that have found a difference in breathing patterns between subjects with long and normal faces, 2'5,'6,4° at the same time that they agree with other studies that have found no difference in quantifiable airway variables between these subject groups~ '9"17.z9First, we believe that the methods used in this study are the best available for selecting subjects according to objective information about dentofacial morphology and respiratory behavior. This fact makes comparison to previous studies difficult and possibly irrelevant. Previous studies may have been correct or incorrect for the wrong reasons, simply because of the methods used. Nonetheless, there are some unattractive explanations for the failure of this study to reveal a realtionship between the patency of the nasal airway and the mode of respiration, an outcome that is consistent with the overall modest relationship between cross-sectional nasal area and respiratory mode found in a previous study. 3s These explanations include the possibility that we did not measure a relevant functional variable when minimum cross-sectional nasal area was evaluated. Another alternative is that our interpretation is incorrect. On the other hand, the differences in breathing mode observed in this study may have been established by the subjects early, and they may have remained unchanged, even when the need to use the oral airway was eliminated or when normal transition or maturation to an increased nasal breathing pattern should have occurred. There is corroborating evidence that breathing mode may not always be related to airway patency, even when nasal airway dimensions are adequate4 ' that is, although an impaired nasal airway almost invariably results in sbme oral breathing, s3 the converse does not always apply. Persons with normal airways may breathe orally to some extent out of habit, rather than of necessity. Hairfield et al. 41 observed a persistence of mouthbreathing in subjects with cleft palate, even after surgery had resulted in an adequate airway.

Volume 99 Number 2 S o m e long face subjects h a v e been identified in early c h i l d h o o d , while in o t h e r subjects this characteristic appears to develop in a d o l e s c e n c e , w h i c h indicates they do not appear to f o l l o w a single pattern. Postural changes m a y be responsible for the m o r p h o l o g i c changes in the face and m a y h a v e been established early as an adaptation for previous airway deficiencies. T h e adaptive posture m a y h a v e resulted in altered m u s c l e forces that can have an impact on dental and skeletal structures. S o l o w et al. 42 a d v a n c e d this theory that also was first noted by Warren and Spalding. 4~ M a n y questions remain with respect to the relationship b e t w e e n respiratory b e h a v i o r and facial m o r phology, and, therefore, a causal relationship should not be implied. Until these inconsistencies are r e s o l v e d , intervention to alter the nasal airway and thus to influe n c e dentofacial growth is unjustified. Continued, careful investigation o f the relationships b e t w e e n vertical dentofacial m o r p h o l o g y and respiration appears to close o n e d o o r and open m a n y m o r e . In this study, it w o u l d b e tempting to attribute differences in breathing patterns to respiratory variables, but those m o s t c o m m o n l y cited are not presently culpable. C o n t i n u e d delineation o f respiratory behavior, postural variables, and other functional variables in g r o w i n g subjects with various dentofacial m o r p h o l o g i c characteristics w o u l d be useful.

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40. Bresolin D, Shapiro PA, Shapiro GG, Chapko MK, Dassel S. Mouthbreathing in allergic children: its relationship to dentofacial development. AM J ORI'HOD 1983;83:334-40. 41. Hairfield WM, Warren DW, Seaton D. Prevalence of mouthbreathing in cleft lip and palate. Cleft Palate J 1988;25;135-8. 42. Solow B, Kreiborg S. Soft-tissue stretching: a possible control factor in craniofacial morphogenesis. Scand J Dent Res 1977; 85:505-67. 43. Warren DW, Spalding PM. Dentofacial morphology and breathing: a century of controversy. In Melsen B, ed. Controversies in orthodontics, Berlin: Quintessence-Verlage, 1990. Reprint requests to:

Dr. Henry Fields Department of Orthodontics School of Dentistry University of North Carolina Chapel Hill, NC 27514-7450