The relation between nasorespiratory function and dentofacial morphology: A review

The relation between nasorespiratory function and dentofacial morphology: A review

Dr. O’Ryan

Felice S. O’Ryan, D.D.S.,* Dale M. Gallagher, D.D.S.,* John P. LaBanc, D.D.S.,* and Bruce N. Epker, D.D.S., Ph.D.** Fort Worth. Texas It is commonly assumed that nasorespiratory function can exert a dramatic effect upon the development of the dentofacial complex. Specifically, it has been stated that chronic nasal obstruction leads to mouth breathing, which causes altered tongue and mandibular positions. If this occurs during a period of active growth, the outcome is development of the “adenoid facfes” (dentofacial morphology). Such patients characterfstlcally manifest a vertically long lower third facial height, narrow alar bases, lip incompetence, a long and narrow maxillary arch, and a greater than normal mandibular plane angle. These dentofacial traits have repeatedly been attributed to restricted nasorespiratory functlon.1-‘4 It is generally believed that environmental factors can exert subtle or dramatic effects upon dentofacial morphology, depending upon their magnitude, duration, and time of occurrence. The purpose of this article is to present a critical review of the literature concerning the effect of one such environmental factor, nasal airway function, upon dentofacial morphogenesis. This review will critically examine the most frequently cited papers reporting a relationship between nasorespiratory function and dentofacial morphology. In summary, this critical review fails to support a consistent relationship between obstructed nasorespiratory function and the adenoid facies or long-face syndrome. Additional objective evaluations of this relation are encouraged.

Key words: Nasorespiratoryfunction, dentofacial morphology, adenoid facies, long-face syndrome

H

istorically, restricted nasal airway function has been believed to be causally related to specific facial, skeletal, and occlusal features, those of the adenoid facies or long-face syndrome.‘-l4 This syndrome is characterized by various features, including a vertically long lower third facial height, narrow alar bases, lip incompetence, a narrow or “V’‘-shaped maxillary arch, and a high mandibular plane angle. If such a clear-cut relationship between restricted nasorespiratory function and dentofacial morphogenesis exists, then data in the literature should readily support it. If this is so, a scientific basis for rational treatment decisions in growing persons with nasorespiratory impairment is then possible. Many papers have been written concerning the relationship between upper airway function and dentofacial morphology, and a review of the ones most freFrom John *Residents, **Director, Demofacial

Peter Smith Hospital. Oral and Maxillofacial Oral and Maxillofacial Deformities.

0002-9416/82/l

10403+08$00.80/0

Sorgexy. Surgery, and Center for the Correction

0

1982 The C. V. Mosby Co.

of

quently cited in the current literature will be presented. These papers will be divided into two major groups: (1) those dealing with cross-sectional studies and (2) those dealing with longitudinal investigations of the relationship between dentofacial morphology and nasorespiratory function. LITERATURE REVIEW

Clinicians and researchers involved in the treatment of dentofacial deformities have long searched for determinants of facial morphology. Since the turn of the century, nasal airway function has been implicated as an etiologic factor in dentofacial development.1-3, i5 Theories first proposing the existence of a relationship between mouth breathing and facial form stated that oral respiration alters normal air currents and pressures through the nasal and oral cavities, which causes impaired development of these structures.3, s--7 Several authors postulated this to be the result of the oral airstream in mouth-breathing individuals hindering normal downward palatal growth.3, 4 Others believed that the raised negative air pressure difference between 403

I. Control and experimental populations examined by Linder-Aronson’O

Table

Population

No.

Classification

CROS!HECTIONAL

Control Group

I

No adenoids

Group Group

2 3

Small Large

or moderate adenoids

37 33

adenoids

11 XI

Experimenlal Group Group

and, second, longitudinal investigations of nasorespiratory function and its relationship to dentofacial morphology

4

Adenoidectomy

for recurrent

5

media Adenoidectomy

for obstructed

otitis nasal

21 60

breathing r

the oral and nasal passages in mouth breathers lead to development of a deep palatal vault.“-” A second theory held that oral respiration disrupts the muscle forces exerted by the tongue, cheeks, and lips upon the maxillary arch.’ The mouth breather was believed to position the tongue in a more downward and forward manner in the oral cavity, a position in which it could not exert adequate buccal pressure to counteract the inward forces from the lips and cheeks upon the maxilla. H-‘4 This theory exists in the current literature. 12, I4 A third school of thought denies a significant relationship between facial morphology and mode of breathing.‘“-rH Kingsley’” was among the first to consider the V-shaped maxillary arch and deep palate a congenital trait not related to mouth breathing. In a subjective evaluation of 1,033 children, Humphrey and LeightonI reported an approximately equal distribution of malocclusions in nose and mouth breathers.r6 They noted that, of those children who kept their mouths open while breathing, almost half respired nasally. Gwynne-Evans and Ballard” also subjectively evaluated the relationship between facial morphology and breathing conditions over a period of 15 years.17 They reported that orofacial morphology remains constant during growth, regardless of breathing patterns. They also stated that “mouth breathing does not produce deformities of the jaws and malocclusions and does not result in the development of the adenoidal facies.“” LeechI examined the relationship between lip competence and mode of breathing in subjects undergoing evaluation in a research clinic for upper respiratory disease and found that fewer than one third of the lipincompetent persons were mouth breathers. Thus, many theories have been proposed and much confusion remains regarding the relationship between nasorespiratory function and dentofacial morphology. We will now sequentially review, first, cross-sectional studies

tNVESTIGATIONS

[fchronic orul respiration in the growing individucrl causes predictuble jkciul, skeletal, and c1c~~lr4sal ,feutures, these charucteristics should be readily identified by appropriute studies qf humurz beings mam~esting chronic oral respirution. Cross-sectional investigations aimed at evaluating the relationship between nasal airway function and dentofacial morphology have approached the subject by measuring nasorespiratory function in persons with features of the long-face syndrome. In these studies the mode of respiration in persons with selected facial features was evaluated, rather than the reverse (that is, evaluating the dentofacial characteristics in a random sample of chronic mouth breathers). In conducting such investigations the variables of (1) age at occurrence of nasal obstruction, (2) magnitude of obstruction measured quantitatively as the percent nasal versus oral respiration, and (3) duration of oral respiration must be considered, as each will affect the degree to which the dentofacial complex would be altered. To determine the magnitude of nasal obstruction, an objective quantitative means of measuring the amount of oral versus nasal respiratory volume must be employed. Without these data, the breathing patterns of individuals can only be hypothesized. In our review of the literature, we found that five cross-sectional studies were most frequently sited. A brief summary of each paper followed by a critical review will be presented in this section.* Watson and associate?’ calculated nasal airway resistance in forty-five children between the ages of 9 and 17 years by directly measuring transnasal pressures with nasal airhow at a constant expiratory flow rate. No significant relations were found to exist between skeletal type, occlusion, and mode of respiration. Several salient points about this study must be noted. The mode of breathing was determined subjectively by clinical observation. No quantitation of the relative amount of oral versus nasal breathing was documented. Further, the age at onset and the duration of nasal obstruction were not evaluated. Second, only anteroposterior cephalometric dimensions were evaluated. Such an analysis would be better related to nasal resistance if vertical measurements of the facial skeleton were analyzed. This study neither supports nor refutes a possible *The reader is advised to obtain the references

for more d&ted

information.

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Relation

between

relationship between upper airway function and dentofacial morphology. One of the most frequently cited papers dealing with the subject of nasal airway function and dentofacial morphology is by Linder-Aronson.‘* He hypothesized that “enlarged adenoids give rise to mouth breathing, which leads in turn to a change in tongue position and this is then followed by changes that are reflected in the dentitional variables. ” Facial and dental morphology, nasal airflow, and breathing mode were examined in 162 prepubertal children. Two groups, each consisting of eighty-one individuals, were evaluated (Table I). The control population consisted of eighty-one children who were grouped into three categories according to the size of the adenoidal mass as assessed on lateral radiographs. The experimental population consisted of eighty-one prepubertal children who had undergone adenoidectomy for either recurrent otitis media or nasal obstruction. The experimental and control populations were matched for age and sex. All subjects were evaluated via 131 variables selected to examine (1) anamnesic and clinical status, (2) dental relationships, (3) adenoid size, (4) nasal airflow, (5) skeletal and lip relations, and (6) tongue position. The author concluded that adenoids affect the mode of breathing which, in turn, affects dentofacial morphology . The first question that arises concerns the relationship between adenoid size relative to nasopharyngeal area in the groups studied. If nasal obstruction leads to mouth breathing, then the most obstructed group should manifest the most characteristic features of adenoid facies morphology. However, a review of the actual data revealed that the available nasopharyngeal area was essentially the same in the control group with

large adenoids (Group 3) and the group operated for nasal obstruction (Table I). One would expect the volume of airflow through the nasal cavity also to be essentially equal between these two groups; however, Group 3 consistently exhibited the lowest nasal airflow

of all five groups! According to the author’s own line of reasoning, those persons with the largest adenoidal masses and the lowest amount of nasal airflow should exhibit the most characteristic features of the adenoid facies morphology! Interestingly, the persons in Group 3 were considered normal. If the proposed hypothesis (that adenoids affect the mode of breathing) is true, then the group with the largest adenoid mass relative to pharyngeal area would exhibit the least nasal airhow and have the most characteristic features of the adenoid facies morphology. However, the data show that total face height and upper face height are significantly greater in Group 5

nasorespiratory

function

and

dentofacial

morphology

405

(adenoidectomy for obstructed nasal breathing) than in Group 3 (largest adenoids and least nasal airflow). Thus, there is a gross inconsistency between the hypothesis and the data, since Group 3 exhibited much lower nasal airjlow volume than Group 5.

The author states: “Children in Group 5 tend to demonstrate retroinclined upper and lower incisors, a narrow upper arch, a high incidence of crossbite and wide angles between the occlusal line on the one hand and the nasion-sella and mandibular lines on the other.” However, the data show that significant differences in these variables exist only between Groups 1 and 5. Since it is presumed that large adenoids can be obstructive and influence facial morphology, the following question must be considered: Why are there no significant differences among the above variables between Group 1 (without adenoids) and the two groups with large adenoids (Groups 3 and 4)? This is important concerning Group 3, which showed the largest adenoidal masses and the least nasal airflow of all groups. It was also concluded that large adenoids lead to a forward tongue position, and this was said to be indicative of mouth breathing. Tongue position was analyzed in only two groups: Group 1 (without adenoids) and Group 4. Theoretically, the group with the largest adenoid mass and the lowest nasal airflow should have the lowest tongue position. However, tongue position was not analyzed in the most important group: Group 3, the group with largest adenoids and least nasal airflow, Thus, the author cannot make valid conclusions regarding tongue position and adenoid size. Examination of the data in this study indicates that the conclusion that adenoids influence facial morphology is questionable. Finally, the mode of breathing was determined subjectively by clinical observation in these individuals. There were no objective measures of actual nasal versus oral breathing. Yet, the author’s primary purpose

and conclusions were based upon facial, skeletal, and dental morphologic changes that occurred secondary to oral respiration, an entity that was not actually measured! The raw data do not support the conclusions presented by the author in this study. A simple causeand-effect relationship between upper airway function and dentofacial morphology has yet to be established. Sarver*’ quantitatively measured various nasal airflow parameters in three groups of subjects on the basis of their facial heights and lip competence. Group I, the control group, contained nine subjects with normal facial heights and lip competence at rest, Group II consisted of ten subjects with excess vertical lower facial heights, and Group III contained nine patients with normal facial heights but with lip incompetence. These facial characteristics were determined clinically, as

cephalometric radiographs were available for only three patients. Sarver reported a significant difference in nasal airway resistance among the three groups, with Group II having a significantly greater nasal resistance than the other two groups. The parameter of nasal resistance must be examined. This measurement represents the effective minimal cross-sectional area of a tube of fixed dimensions; in this case the tube is represented by the nasal cavities. While these measurements may reveal anatomic relationships (within a physiologic range), they do not indicate a person’s physiologic breathing pattern. That is, what percentage of the tidal volume is actually respired nasally and orally? Many readers may equate a large nasal resistance value with mouth breathing, which may not necessarily be true. Vig and his colleagues” examined three groups of adults categorized as having (1) normal facial features with competent lips, (2) normal facial features with lip incompetence, and (3) long vertical face height. The following respiratory parameters were measured for each subject: nasal resistance to expiratory airflow, average nasal airflow volume per inspiratory and expiratory breathing cycles, duration of breathing cycles, and peak airflow rate. Respiratory measurements were obtained by means of a pneumotachograph attached to a face mask and an oropharyngeal catheter. Significant differences existed in nasal airway resistance values for the three groups. Group 3 had the highest over-all nasal resistance when compared to the normal and lipincompetent groups; however, no statistically significant differences were found for other respiratory parameters. The data that are presented demonstrate a lack of association between nasal resistance and the amount of air passing through the nose. Those individuals with high neressarily those airyTow,.

nasal resistance n’ith the least

values amount

were not of nasal

Martin, Vig, and WarreP further reported the lack of a consistent relationship between nasal resistance and dentofacial morphology. They compared nasal resistance values in thirty-two patients (aged 10 to 15 years) with varying facial morphologies. Cephalometric measurements of dental and vertical skeletal proportions were analyzed. Nasal resistance ranged from 0.4 to 15.9 cm. H,O/L./sec. The results do not convincingly show any significant correlations between nasal resistance and the vertical dentofacial parameters examined. Further, when persons with nasal resistance values greater than 4 cm. H,O/L./sec. were compared to subjects whose nasal resistance measured less than 4 cm. H,O/L./sec., no significant differences in the vertical skeletal measurements could be demonstrated. To

summarize, if’ nasal obstruction during growth con tributes to the long-face syndrome. then these dentofacial features should be apparent in chronic mouth breathers. These cross-sectional studies primarily measured nasal resistance and indicate that there is nor a consistent relationship between nasal resistance and dentofacial morphology. Finally, when the data concerning the presence of adenoids and their relation to nasorespiratory function and dentofacial morphology is critically examined, it can be seen that the amount of nasal obstruction does not appear to be related to nasal airflow or to dentofacial morphology. Whether the characteristic facial type which has been observed in patients with hypertrophic adenoids is hereditary, acquired secondary to musculoskeletal forces, or a combination of these remains to be determined. Thus, the effects of nasorespiratory function upon craniofacial morphology cannot be conclusively proved or disproved by these cross-sectional investigations. These studies provide weak evidence that altered nasorespiratory function affects craniofacial morphogenesis. LONGlTUDiNAL INVESTIGATIONS Longitudinal studies are concerned with the direct effects of nasal airway obstruction upon the muscular function and skeletal morphology of the craniofacial system. Longitudinal investigations all ask the same question: What are the effects of nasal airway obstruction upon the dentofacial complex? They can be broadly divided into two categories: (1) those concerned with the effect of nasal obstruction on tongue and mandibular positions and (2) those concerned with the effect of the presence of adenoids and their influence upon dentofacial morphology. While this grouping is arbitrary, it provides a convenient means of discussing the literature. Effect of upper airway function on tongue and mandibular position Background information about impaired nasorespiratory function and its proposed effect upon the stomatognathic system will be discussed briefly. Two studies investigating this association will then be reviewed critically. The effect of reduced nasorespiratory function on tongue and mandibular positions has been postulated to be that of impaired nasal function causing a downward and forward position of the tongue in the mouth in order to maintain oral respiration. This altered tongue posture causes an inferior repositioning of the mandible and induces concomitant changes in neck and facial muscular activity. The net result is said to be develop-

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Relation between nasorespiratory

ment of dentofacial features characteristic of the longface syndrome. Harvold and associates,‘3, I4 in two studies, examined the effects of altered upper airway function upon tongue posture, mandibular position, and masticatory muscle activity in primates. Since both studies used similar populations and essentially identical methods, they will be reviewed together. Growing monkeys were arranged in pairs on the basis of sex and similarities in facial morphology and dental occlusion. One of each pair served as the experimental animal and the other as the control. The experimental group underwent gradual nasal airway obstruction over a 3-month period. After complete nasal airway occlusion was accomplished, cephalometric, dental, soft-tissue, and electromyographic analyses were done at 3-month intervals and then every 6 months after the nose was reopened. Soft-tissue changes (including lip and tongue morphology) were assessed from clinical photographs and were not measured cephulometrically.

Comprehensive skeletal cephalometric evaluations were performed. In the first study, mean differences in total anterior facial height of 1.75 mm. and 2.75 mm., respectively, were seen between the control and experimental animals, thus representing a mean increase of 1 .U mm. in total facial height in the experimental group. The initial study demonstrated no significant intrapair differences between the control and experimental groups in upper face height, mandibular length, or gonial angle after 9 and 15 months of oral respiration. This however, was not the case in the later studyI in which the same skeletal measurements were used. Changes in anterior facial height were significantly greater in animals whose nasal airways had been occluded as compared to the control group. The position of the tongue and mandible was not quantitated. The initial study presented a detailed evaluation of the dental arch changes seen between the two groups. After 15 months of mouth breathing there was a mean decrease in maxillary intercanine distance measured from the dental models in the experimental group. Although the differences are less than 2 mm., this was significant at the p = 0.01 confidence level. It was not stated whether a significant difference existed at the beginning of the study between the control and experimental groups with respect to dental arch measurements. This makes the magnitude of these changes in dental arch configuration difficult to interpret. Further, it is important to note that occlusions that developed in the experimental group were highly variable, ranging from Class II to Class III relationships. The second study included an electromyographic

function

and dentofacial

morphology

407

evaluation of the masticatory, lip, tongue, and suprahyoid muscles. The authors state that the experimental group showed rhythmic recruitment of the genioglossus and intrinsic tongue muscles as well as the anterior temporalis and lateral pterygoid muscles. Approximately one half of the experimental animals exhibited muscle contractile rhythmicity when measured after 3 years of oral respiration. According to these data, rhythmic recruitment of the orofacial muscles is not a uniform response to mouth breathing. Postural positions of the mandible and the tongue were not measured quantitatively but were assessed clinically. Thus, any associations between skeletal morphology and tongue or mandibular posture are speculative and anecdotal. These studies demonstrate that primates with obstructed nares develop oral respiratory breathing patterns which may result in skeletal, dental, and muscular alterations. Although some skeletal traits were common among the experimental group (such as, increased face height and steeper mandibular angle with a larger gonial angle), the occlusal and muscular adaptations were not uniform or consistent among the experimental animals. While oral respiration can theoretically influence tongue and mandibular position, further experimentation is necessary before definitive conclusions regarding the relationship between dentofacial morphogenesis and mandibular and tongue posturing can be drawn. The effect of adenoids on dentofacial morphology

Grossly enlarged tonsils and adenoids are among the reported causes of oral respiration. While a relationship between nasal obstruction and mouth breathing cannot be denied, a causal association between mouth breathing and altered dentofacial form is unproven. Three studies address the subject of the effects of mouth breathing (resulting from nasal obstruction due to enlarged adenoids) on dentofacial form.24-26 Two of these studies examined the same populations at different time intervals and will be reviewed together.24s 2j The purpose of the first two studies was to examine patients initially, at 1 year,24 and at both 1 and 5 yea@ after removal of the adenoids to see if adenoidectomy is followed by changes in dentofacial morphology and mode of breathing. The hypothesis proposed was that nasal obstruction secondary to enlarged adenoids leads to mouth breathing which, in turn, results in the aforementioned skeletal and dental differences. Prior to adenoidectomy there were significant differences between the experimental and control groups for the skeletal and dental variables evaluated. These variables were evaluated again 1 and 5 years after adenoidectomy . One would

then expect that after adenoidectomy the patients who were initially deemed mouth breathers and postoperatively became nose breathers would demonstrate the largest changes in these variables. In examining the data, we find that several significant points warrant discussion. 1. The subject material is not clearly de$ned. The initial study was made up of the clinical material presented in Linder-Aronson’s previous publication, reviewed earlier.” The present study divided these subjects into two groups- “thirty-seven who underwent adenoidectomy and thirty-seven controls. ” However, it will be recalled that in the original study there were actually three control groups with vurying adenoid sizes, and two groups who underwent udenoidectomy (one group for recurrent otitis media and the other for obstructed nasal breathing) (Table I). It is not clear from this study which of the three control groups was actually evaluated; that is, were adenoids present and, if so, what was their size? Further, it is also not clear which adenoidectomy group was evaluated-the persons operated for otitis media or for obstructed nasal breathing. This is important, as the author’s hypothesis is based upon the presumption that children undergoing adenoidectomy for obstructed nasal breathing will demonstrate skeletal and dentitional changes postoperatively as a result of an increased ability to breathe through the nose, while those operated for otitis media should not. 2. No objective measure oj’ the mode of breuthing MS used. Thus, it is impossible to make any conclusions regarding change in this parameter after adenoidectomy 3. The actual magnitude of some of the measured changes, although stuted to be signijcant, were so smull thut their biologic signiJicance must be yuestioned. The author attributes these changes to a reduction in size of the adenoids, which allows the person to breathe nasally. He fails to address the fact that some of the largest dental changes occurred in those persons who were nose breathers preoperatively and remained nose breathers (intermolar distance and upper incisor angulation) and those classified as mouth breathers preoperatively and who remained mouth breathers (lower incisor angulation)! 4. The author did not evuluute important skeletul vuriubles, such as facial height or mandibular plane angle, which he considered components of the socalled “adenoid facies” morphology in his original study. lr In light of these criticisms, the author’s hypothesis that adenoidectomy can lead to nasal breathing in persons with nasal obstruction, which in turn can lead to

normalization of the dentition, certainly cannot be supported from the data. The later study will be discussed with regard to pertinent results not seen at the l-year examination. In the 5year adenoidectomy study, Linder-Aronson evaluated the same dental variables as in the l-year study.2” In addition, facial height and the relation of the mandible to the maxilla were also evaluated. Two groups of patients were evaluated. The control group was composed of fifty-four children, and thirty-four children who underwent adenoidectomy and “switched from mouth to nose breathing postoperatively” made up the experimental group. The mode of breathing (oral versus nasal) was again determined subjectively by observation. The results, conclusions, and criticisms of this study are similar to those of the previous l-year study. These two studies lend no credence to the hypothesis that nasal obstruction due to enlarged adenoids may be an etiologic factor in development of the “adenoid facies” morphology. It is first necessary to quantitate amounts of mouth and nose breathing before facial and dental changes can be evaluated in relation to mode of breathing. Woodside and Linder-Aronsor?” serially evaluated dentofacial variables in a population of 120 males from the ages of 6 to 20 years to establish population standards for the group, document serial channelization,* and examine the possible relationship between anterior facial height and nasal and nasopharyngeal capacities. This study included 120 males with complete longitudinal orthodontic records taken at the ages of 6, 9, 12, 14, 16, 18, and 20 years. Some were orthodontically treated and some were not, although the exact numbers were not specified. Two smaller populations were evaluated separately with regard to dentofacial features and nasorespiratory parameters. A subgroup of twenty-two persons whose lower anterior facial height (subnasale to gnathion) was considered high (greater than the ninetieth percentile) or who crossed two percentile channels were evaluated separately with regard to their nasal airway capacities. A third group consisted of cephalometric radiographs from thirty-two Swedish children with a mean age of 9.8 years. This group was subdivided into those with chronic nasal obstruction who had adenoidectomies and age- and sex-matched controls. Standard skeletal variables were evaluated serially from cephalometric radiographs in the population of 120 male subjects at the stated ages. The size of the *Channelization existed percentile channel

if the mdividual

growth

curve remained

in the same

Volume 82 Number 5

Relation between nasorespiratory

adenoids relative to the bony nasopharynx was assessed yearly from ages 3 to 20 in the subgroup of twenty-two children. The degree of nasal obstruction in this group was determined from posteroanterior cephalometric radiographs. Head posture, as determined by the angle formed between SN and a vertical reference line, was measured in the Swedish sample. Normal population standards were established for upper and lower anterior facial heights in all three groups. This study showed a steady increase in upper and lower anterior facial heights up to age 18; thereafter, a reduction in growth increments was seen. Growth curves were analyzed relative to presumed airway capacity based on measurements of nasopharyngeal volume in the twenty-two-child subsample. These authors concluded that a relationship exists between airway obstruction in either the nose, nasopharynx, or both and lower facial height. They also concluded that lower anterior face height is independent of other skeletal units and that it is dependent upon the growth direction of the mandible and the neuromuscular factors influencing mandibular posture, such as mouth breathing and head posture. Several important points concerning the population measured must be considered. The group consisting of 120 males was a heterogeneous sample with regard to facial morphology. Several questions arise: (1) Were those subjects who did not receive orthodontic treatment considered normal? If so, by what skeletal and cephalometric criteria? (2) Of those subjects undergoing orthodontic treatment, what type of deformities were being corrected? Were they primarily occlusal, skeletal, or a combination? This is important, as many morphologic groups show patterns of facial growth specific for that group.*’ No clinical measurements of nasal or oral airway function were carried out in these patients. Clearly, it cannot be assumed that two-dimensional measures of “airway obstruction” from the radiographs are a reliable indication of breathing pattern. Interestingly, the mean measurement of lower facial height (71.71 mm. at 20 years) indicates that the population examined had a tendency toward vertical excess as adults. We would expect more than just twenty-two out of 120 subjects to exhibit nasal obstruction if there is a relationship between increased lower facial height and impaired nasal function. However, a weak statistical correlation between airway obstruction and lower facial height was found, In order to demonstrate an association between airway size and facial height, it is necessary to compare the size of the airway in the selected subsample to twenty-two chil-

function

and dentofacial

morphology

499

dren selected at random from the entire population. Without a control group, it is impossible to determine the meaning of a “tendency suggesting” that airway obstruction can explain why lower face height increased in sixteen to twenty-two members of the subsample evaluated for airway obstruction. In light of this critique, we must question the author’s conclusions regarding a relationship between nasal obstruction and facial height and consider it speculative. DISCUSSION

We do not dispute the contention that perhaps some relationship exists between nasal airway function and dentofacial form. Many have assumed that mouth breathing resulting from nasal airway compromise is of major etiologic significance in the development of the long-face syndrome and its accompanying dentofacial abnormalities. A critical review of the literature does not support this contention. Moreover, cases of complete nasal obstruction since birth in patients with bilateral choanal atresia do not demonstrate gross characteristics of the long-face syndrome.28 It is suggested from both the cross-sectional and longitudinal studies that a simple cause-and-effect relationship between nasorespiratory function and dentofacial development does not exist; rather, it is a complex interaction between hereditary and environmental influences. Before any definitive conclusions can be drawn regarding this relationship, one must first answer the following questions: (1) What is the proportion of oral versus nasal breathing in persons with various dentofacial characteristics? (2) Are common dentofacial characteristics apparent when patients are categorized according to a reliable quantitative evaluation of nasal airway function? (3) Does alteration of nasorespiratory function during growth consistently and predictably alter dentofacial morphogenesis? From this literature review, it appears that further study in the direction of quantitating the actual amount of oral and nasal breathing in persons with normal and abnormal dentofacial morphologies is warranted before the true effects of nasorespiratory function on dentofacial growth can be determined. Only after such studies can we attribute various dentofacial characteristics to presumed alterations in nasorespiratory function. CONCLUSIONS

Current literature concerning the effects of nasorespiratory function upon the development of the dentofacial complex has been reviewed. Although several of these articles suggest a direct cause-and-effect relationship between nasal airway obstruction and altered den-

tofacial morphology, further well-controlled studies designed to quantitate the relative amounts of oral versus nasal respiration are necessary before airway obstruction can be implicated as a significant etiologic factor in the development of any specific dentofacial deformity.

IS 16.

17. 18.

REFERENCES I. Meyer, W.: On adenoidal vegetations in the naso-pharyngeal cavity, their pathology, diagnosis and treatment, Med. Chir. Trans. 53: 191, 1870. 2. Times, C. S.: On the developmental origin of the V-shaped contracted maxilla, Monthly Rev. Dent. Surg. 1: 2, 1872. 3. Bloch, E.: Untersuchungen Zur physiologie der nasentamung, 2. Ohrenheilkd. 18: 215, 1888. (Cited in Stoksted, 1951, 1953.) 4. Michel. K.: Die Krankenh. der Nashenhahle, etc., Berlin, 1876. p. 95. (Cited by Morrison, 1931.) 5. Morrison, W. W.: The interrelationship between nasal obstruction and oral deformities. INT. J. ORTHOD. 17: 453-458. 1931. 6. Kantorowitz, A.: iiber den mechanismus der rieferdeformierung bei behinderter, Atmug. Stsch. Monatsschr. Zahnheilkd. 225. 1916. (Cited by Linder-Aronson and B&k&m, 1960.) 7. Wustrow: Zur kritik der ursachen der kieferanomalien, Dtsch. Monatsschr. Zahnheilkd. 1917. (Cited by Linder-Aronson and Bickstriim, 1960.) 8. Angle, E.: Treatment of malocclusion of the teeth, Philadelphia, 1907, S. S. White Dental Manufacturing Co. 9. Leader, S. A.: Nasal and oral respiratory air pressures: Their effect upon the growth and health of dental structures-Some experiments and conclusions, Br. Dent. J. 56: 387-389, 1934. IO. Hartsook, J. T.: Mouthbreathing as a primary etiologic factor in the production of malocclusion, J. Dent. Child. 13: 91-94, 1946. Il. Meyers, R. E.: Handbook of orthodontics, Chicago, 1960, Year Book Publishers, Inc. 12. Linder-Aronson, S.: Adenoids: Their effect on mode of breathing and nasal airflow and their relationship to characteristics of the facial skeleton and the dentition, Acta Otolaryngol. Supp. 265: l-132, 1970. 13. Harvold, E. P., Vargervik, K., and Chierici, G.: Primate experiments on oral sensations and dental malocclusions, AM. J. ORTHOD. 63: 494-508, 1973. 14. Harvold, E. P., Tomer, B. S., Chierici, G., and Vargervik, K.: Primate experiments in oral respiration, AM. J. ORTHOD. 79: 359-372, I98 I.

19.

20.

21.

22.

23. 24. 25.

26.

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