Maxillary Dental Arch Dimensions Following. Pharyngeal-Flap Surgery

Transcription

1 Maxillary Dental Arch Dimensions Following Pharyngeal-Flap Surgery Barry G. KeccerR, D.M.D. Ross E. Lona, JR., D..D., PH.D. Epwarp D. Gop, D.D.S. MicHaeL D. RotH, D.D.S. Pharyngeal-flap surgery (PFS) is a surgical procedure utilized in the treatment of hypernasal speech. The purpose of this study was to evaluate the effect of PFS on the maxillary dental arch. Sixteen patients who had undergone PFS between the ages of 5 and 7 years were selected from the longitudinal growth study of the Lancaster Cleft Palate Clinic. Eight points were marked on the occlusal surfaces of serial maxillary dental models to determine arch width and length. These data were compared to a matched sample of patients from the same growth study who did not undergo PFS. The flap group demonstrated significant reduction in both arch width (at cuspids and molars) and arch length development compared to the control sample, following PFS. These results are not inconsistent with an hypothesis of dental-arch form changes related to possible airway obstruction following PFS, although data on the latter were not available on this sample. KEY WORDS: cleft palate, pharyngeal flap, airway, arch dimensions, longitudinal growth. Improvements in technology and surgical techniques have allowed clinicians to reduce the effects of scar tissue and surgicalrepair on postoperative dentofacial deformities and malocclusion in the cleft-palate population. Because of these improvements, it is possible to evaluate other physiologic factors that may also contribute to altered postoperative growth in the cleftpalate patient. Increased nasal airway resistance and associated altered oropharyngeal muscle function are examples of such physiologic factors that may affect dentofacial growth in the cleft-palate population. Drs. Keller and Long are affiliated with the Division of Orthodontics and Research, Lancaster Cleft Palate Clinic, Lancaster, PA. Drs. Gold and Roth are former residents, Department of Orthodontics, Albert Einstein Medical Center, Philadelphia, PA. Address requests for reprints and all correspondence to: Barry G. Keller, D.M.D., Lancaster Cleft Palate Clinic, 223 N. Lime Street, Lancaster, PA Oral presentation given at Cleft Palate Association meeting in New York City, May 18, This study was supported by National Institutes of Health Grant DE Research efforts and clinical studies have differed widely in their conclusions about the correlation between nasorespiratory function and facial growth. Linder-Aronson (1970, 1973) evaluated patients who were clinically determined to be chronic mouth breathers; he also described the '"'adenoid face.'' Characteristics of this facial type included increased mandibular plane angle, gonial angle, and lower facial height, as well as decreased maxillary arch width and incisor proclination. Other researchers (Harvold et al, 1972, 1981; Miller and Vargervik, 1979; Miller et al, 1982) evaluated facial growth following experimentally induced nasal obstruction in rhesus monkeys. A wide range of growth responses was produced, making it difficult to draw conclusions when relating the growth response to the decreased nasorespiratory function. Other clinical studies relating craniofacial growth to actual mode (nasal versus oral) of respiration have been unable to establish a strong relationship (Vig et al, 1981; Watson et al, 1968). Indeed, it has been shown that neither the patient nor the clinician can adequately assess the mode of respiration in a 248

2 Keller et al, PHARYNGEAL-FLAP SURGERY 249 clinical setting (Vig, 1974). This, then, would raise some questions regarding the conclusions drawn by Linder-Aronson. Warren (1969) has documented an increased nasal airway resistance in cleft patients compared to noncleft controls. In addition, cleft patients who had undergone PFS were found to have even higher nasal airway resistance. The PFS is a procedure performed to improve I speech quality by reducing the velopharyngeal port size, thus decreasing the hypernasality often present in the speech of patients with cleft palate (Harding, 1979). If this procedure, in fact, increases nasal airway resistance, then it may, in turn, alter oropharyngeal muscle function, which could lead to compensatory growth alterations. The pharyngeal flap, then, provides a unique opportunity to study the possible relationship between increased nasal resistance and altered craniofacial growth. The procedure, being a discrete chronologic event, allows for evaluation of growth data before and after the concomitant increase in nasal resistance to identify any altered patterns of growth that may follow. Subtelny and Nieto (1978) studied maxillary growth subsequent to the flap procedure. They found a decrease in forward maxillary growth, which they attributed to a "tethering'*' effect of the flap. The longitudinal data at the Lancaster Cleft Palate Clinic provide for evaluation of both preand postflap growth. Earlier research on this sample, using lateral head films, seemed to demonstrate facial growth changes similar to those described by Linder-Aronson (Long and McNamara 1985). Subsequent work, using posteroanterior cephalometric films, on the other hand, did not show statistically significant changes postoperatively (Long et al, 1984). - The purpose of this study was to evaluate growth changes in dentoalveolar width and arch length following PFS in patients with cleft palate. Growth changes thought to result from the flap procedure were identified through comparison with a matched control group that had not undergone the flap procedure. TABLE 1 Sample of Pharyngeal Flap and Control Patients, Aged 2 to 11 Years, With No Missing Data Condition Flap Control Total Cleft palate only Male Female Unilateral cleft lip Male and palate Female Total the same surgeon on all patients. This same surgeon was also responsible for all primary cleft repairs. Only those patients who had the flap surgery between ages 5 and 7 years were selected for this investigation. Thus 3 to 4 years of serial growth data were available on each patient before the flap procedure, allowing for determination of preflap growth trends. The data shown in Table 1 are for those patients with pharyngeal flap who had no missing data in the 2- to 11- year age range. In addition, medical and treatment histories of all patients were examined. Any patient who had received orthodontic treatment before or during the age ranges examined was excluded from the sample. Patients with any form of craniofacial syndrome were also excluded. The PFS was performed at a mean age of 6.2 years. The criteria used to identify the need for flap surgery were the persistence of hypernasal speech and nasal emission as determined clinically by the speech pathologist. The triangular flap procedure was used for primary lip repair at a mean age of 10 weeks, the vomer flap for hard palate closure at a mean age of 11 months, and a midline closure of the soft palate at a mean age of 16 months. MATERIALS Anp METHODS The longitudinal growth study at the Lancaster Cleft Palate Clinic provided the patient sample used in this investigation. Among the data available in this longitudinal study are study models taken yearly from ages 1 to 15 years. The growth study includes records of 174 patients, 50 of whom had superiorly based pharyngeal flaps for treatment of velopharyngeal insufficiency. The procedure was performed by FIGURE 1 Measurements used for model analysns = UICL, upper incisor to cuspid length; B = UIML, upper incisor to molar length; C = UITL, upper incisor to tuberosity length; D = UCW, upper cuspid width; E = UMW, upper molar width; F = UTW, upper tuberosity width.

3 250 Cleft Palate Journal, July 1988, Vol. 25 No. 3 The control group was also selected from patients included in the longitudinal growth study at the Lancaster Cleft Palate Clinic. Complete records were also available for patients in the ages evaluated, and they were matched to the flap group for cleft type, sex, mandibular growth direction (facial axis angle), and absolute cranial-base size (anterior cranial base) at. ages 3 and 5 years. The cranial-base measurement was used to control for absolute craniofacial size variation. Further matching of control and experimental samples beyond those craniofacial parameters just described was not possible because of limitations of sample size, cleft type, age, and sex. The control group consisted of those patients who, after examination by a speech pathologist, were determined clinically to have adequate velopharyngeal competence and hence did not require a pharyngeal-flap procedure. With the inclusion of 4 years of preflap data, it was hoped that any existing growth difference seen before the flap procedure could be evaluated and separated from those changes evident in the postflap age range. The growth data were taken from study models from ages 2 to 11 years. The models were marked with ink dots on the central incisor edges, cuspid tips, distal marginal ridges of the secondary primary molars (or second bicuspids if erupted), and posterior to the tuberosity. The models were marked by three research assistants and checked independently by the senior author. In cases of early loss or incomplete eruption of marked teeth, the best estimation of normal position was used. A two-dimensional representation of the dental models was obtained by a photocopy method similar to that used previously by Mazaheri et al (1970). The photocopies thus obtained, containing a record of the occlusal surfaces and the 8 points on each arch, were plotted on a Summagraphics digitizing tablet at the Lancaster Cleft Palate Clinic, using the computerized digitizing program at the Center for Human Growth and Development, University of Michigan. A total of 302 models (149 flap group, 153 controls) was then digitized and stored at the Center for Human Growth and Development for later analysis. The model measurements carried out are shown in Figure 1. Three measures of arch width (upper cuspid width= UCW; upper molar width= UMW; and tuberosity width = TABLE 2 Cleft-Palate-Only Group-Descriptive Statistics by Age Before Flap Surgery After Flap Surgery Age UTW KX Control SD UTW X Flap SD_ X = 441 Slope =.465 X =.920 Slope =.385 UMW KX Control SD X Flap SD_ _ X =.501 Slope =.939 X =.304 Slope =.738 UCcw X Control SD Ucw X Flap sdp_ X = 2.67 Slope =.201 =.027 Slope =.560 (C > F) UIML X Control SD UIML X Flap SsD_ _ X =.734 Slope =.780 X =.305 Slope =.355 UICL X Control SD UICL x Flap SD X =.730 Slope =.927 X =.144 Slope =.778 UITL K Control SD UITL X Flap SDp_ _ X =.597 Slope =.8$56 X =.563 Slope =.8$50 UTW = upper tuberosity width; UMW = upper molar width; UCW = upper cuspid width; UIML = upper incisor-to-molar length; UICL = upper incisor-to-cuspid length; UITL = upper incisor-to-tuberosity length.

4 Keller et al, PHARYNGEAL-FLAP SURGERY 251 TABLE 3 Unilateral Cleft-Lip-and-Palate Group-Descriptive Statistics by Age Before Flap Surgery I After Flap Surgery Age C_ _ UTW* X Control SD UTW X Flap SD_ X =.599 Slope =.035 X.252 Slope =.312 _ UMW X Control SD X Flap SD_ X =.937 Slope =.512 X.049 Slope =.613 (C F) UCW X Control SD UCW X Flap SD " X =.019 Slope =.927 (C > F) X.002 Slope =.078 (C F) UIML X Control SD UIML X Flap SD X =.035 Slope =.343 (C > F) X.005 Slope =.374 (C F) UICL X Control SD UICL X Flap SD_ X =.343 Slope =.031 X.941 Slope =.872 UITL X Control SD UITL X , Flap SD_ ) X =.051 Slope =.531 X.002 Slope =.355 * See Table 2 for explanation of abbreviations. UTW) and three measures of arch length (incisor-to-cuspid = UICL ; incisor-to-molar = UIML; and incisor-to-tuberosity = UITL) were carried out in this investigation. Means for each group at each age were plotted to illustrate longitudinal growth changes before the flap procedure (ages 2-6 years) and after it (ages 6-11 years). The Statistical Research Laboratory Computer Program (MIDAS) at the University of Michigan was used to evaluate the data statistically. Significant differences between the groups were examined, using the analysis of covariance between least squares regression lines for each group. RESULTS Tables 2 and 3 (by cleft type) and Table 4 (CPO and UCLP data pooled) summarize the descriptive statistics by age (mean and standard deviation [SD]). The findings of the pooled data are graphically demonstrated in Figures 2 to 7, which can be used to evaluate the longitudinal growth changes over time. Table 4 indicates the statistically significant differences that were revealed following analysis of covariance (AN- COVA) between regression lines in both preflap and postflap age ranges. Included in this table are the results of tests of significance for the data pooled and grouped according tocleft type. As can be seen from Table 5, there are a number of significant differences between the pre- and postflap surgery data within the CPO, UCLP, and pooled groups. In the pooled data, the measurements that are significantly different from the pre- to the postflap age groups are molar width (UMW), cuspid width (UCW), incisor-to-molar length (UIML), and incisorto-tuberosity length (UITL). In all these instances, the control group measurements (Table 4) were larger than the flap group measurements. The significant differences for the pooled data all appear in the postflap age periods with the control and flap groups showing no significant differences in growth in the preflap period. The data were also analyzed statistically by cleft type to determine any possible cleftspecific responses to the flap procedure. In the CPO group, the cuspid width became significantly smaller in the postflap age groups compared with the matched control. No

5 ' 252 Cleft Palate Journal, July 1988, Vol. 25 No. 3 TABLE 4 by Age Pooled Data for Cleft-Lip-Only and Unilateral Cleft-Lip-and-Palate Groups-Descriptive Statistics Before Flap Surgery Age _- UTW* X Control SD UTW X Flap SD_ X =.831 Slope =.080 UMW X Control SD UMW X Flap SD_ X =.712 Slope =.760 UCW X Control SD TCW X Flap SD_ X =.465 Slope =.651 UIML X Control SD UIML X Flap SDp_ X =.322 Slope =.392 UICL X Control SD UICL X Flap SD_ X =.679 Slope =.207 UITL X Control SD UITL X Flap SD_ X =.083 Slope =.557 After Flap Surgery _ , X =.615 Slope = X =.045 Slope =.979 (C > F) X =.005 Slope =.537 (C> F) X =.007 Slope =.173 (C > F) ) X =.282 Slope = , X =.0O11 Slope =.628 * See Table 2 for explanation of abbreviations. other measurements in the CPO group were significantly different between control and flap groups. In the UCLP group, tuberosity width and incisor-to-cuspid length were not significantly affected by the pharyngeal flap. The cuspid width, incisor-to-molar length, and incisorto-tuberosity length all demonstrated significant differences. However, since these differences were found in both pre- and postflap age groups, they could not be attributed to the pharyngeal flap. On the other hand, molar width in the UCLP flap group decreased significantly compared to the control group in the postflap age period. Comparing the results of the pooled data to those for the cleft types grouped makes it possible to determine which cleft type contributed most to the significant differences found. The postflap UCLP changes were obviously mostly responsible for the changes in molar width seen in the pooled sample. The CPO postflap group was likewise responsible for the decrease in cuspid width following the flap. In the incisorto-molar length data and in the incisorto-tuberosity length data, neither cleft type could be clearly identified as the major contributor. Each cleft type most likely changed slightly but not to a statistically significant extent. However, when the two groups were pooled, the combined changes reached a level of statistical significance for these two parameters. The abrupt change seen graphically at age 6 years is a function of the timing of the flap procedure and a temporary change in pre- and postflap sample sizes at age 6 years. At this age, those subjects in the experimental group who had undergone the procedure before age 6 were plotted with the "postflap'' curve. The remainder, receiving their flaps between 6 and 7 years of age, were considered '"preflap'' at age 6 and ''postflap'' at age 7. DIsCcUssION The results presented in this study appear to be relevant to understanding the variables affecting cleft-palate dental arch growth. The longitudinal nature of this growth research allows for an increase in the information available on the growth effects of a specific surgical proce-

6 Keller et al, PHARYNGEAL-FLAP SURGERY AGE [YRS] FIGURE 2 Tuberosity width. Solid line = control group; dotted line = preflap group; broken line = postflap group. dure, the pharyngeal flap. The possible effects that this procedure has on the dentition can be analyzed. Also, these data invite interesting speculation concerning the possible effect of respiratory function on dentoalveolar development. This speculation is strengthened by the possibility that a certain amount of the nasorespiratory compromise in these patients may result from the PFS. It would have been further strengthened with pre- and postflap physiologic airflow data, but these were unavailable in the longitudinal study of the Lancaster Cleft Palate Clinic. Therefore, the argument that the dental effects shown are related to a flap-induced airway obstruction must rely on the assumption that the increased airway resistance found in one sample of pharyngeal-flap patients (Warren et al, 1969) also applied to this sample. However, other physiologic variables not examined in this investigation (size of tonsils and adenoids, mandibular posture, and tongue posture) must also be considered as possible influences ; S AGE IYRS] FIGURE 3 Upper molar width. Solid line = control group; dotted line = preflap group; broken line = postflap group.

7 254 Cleft Palate Journal, July 1988, Vol. 25 No M M a» S5 7 AGE [YRS] FIGURE 4 Upper cuspid width. Solid line = control group; dotted line = preflap group; broken line = postflap group. contributing to the overall dentoalveolar changes demonstrated. The fact that the flap procedure occurred at a specific point in time represents a very testable ''experimental'' paradigm in relating this surgical procedure to dentoalveolar growth. Growth patterns can be established for 4 to 5 years before the flap procedure. The primary surgical repair has been completed by this time and has begun to have its effect on growth through the interaction of scar tissue from the surgical technique superimposed on the original deformity (Kremenak et al, 1967; Ross, 1970; Graber, 1949). This permits a better separation of possible effects of the pharyngeal flap from other factors affecting growth during earlier years. The improved methods of treating patients with clefts have resulted in their growth patterns being relatively free of gross generalized defi Ls AGE [YRS] FIGURE 5 Arch length-incisor-to-molar. Solid line = control group; dotted line = preflap group; broken line = postflap group.

8 Keller et al, PHARYNGEAL-FLAP SURGERY " 5 n r r * , AGE [YRS] FIGURE 6 Arch length-incisor-to-cuspid. Solid line = control group; dotted line = preflap group; broken line = postflap group. ciencies (Krogman et al, 1982; Long et al, 1980; Krogman et al, 1975). The respiratory function hypothesis has been proposed as a method of explaining some of the growth changes seen in cleft patients. Earlier research on data gathered from the Longitudinal Growth Study at the Lancaster Cleft Palate Clinic (Long et al, 1985), the work of Linder-Aronson (1970, 1973), the studies involving nasal airway deformities (Drettner, 1960), and Warren's work, indicating increased nasal resistance in cleft patients (1969), do not allow for a rejection of this hypothesis. The results of this investigation indicate an M M > ! ; 321.* B A GE [YRS] FIGURE 7 Arch length-incisor to tuberosity. Solid line = control group; dotted line = preflap group; broken line = postflap group e

9 256 -_ Cleft Palate Journal, July 1988, Vol. 25 No. 3 TABLE 5 Before- and After-Surgery Data for Cleft-Palate-Only, Unilateral Cleft-lip-and-Palate, and Pooled Groups CPO UCLP Pooled Group Before After A Before After A Before After A UTW* UMW e C > F C > F UCW C C > F C > F UIML C > F C > F UICL e UITL C > F C > F * See Table 2 for explanation of abbreviations. apparent relationship between the pharyngealflap procedure and dentoalveolar changes seen on the models. In general, both length and width development of the maxillary dental arch appear to fall below control values after the flap. An earlier study done at the Lancaster Cleft Palate Clinic on posteroanterior cephalometric data showed no significant changes other than mild maxillary molar width increase (Long et al, 1984). The data presented here would contradict this finding. A possible and more probable explanation would be the marked improvement in accuracy in measuring molar widths on a model over the more variable P-A cephalometric measurements, a point emphasized by Long et al (1984). It is possible that the pooling of the data might obscure the fact that the flap could affect the CPO or UCLP groups uniquely and differently. Therefore, the data were also analyzed for each group separately. Clinically, UCLP patients seem to have much more variable arch width and length dimensions than CPO patients. It appears that the flap may also affect the UCLP group to a greater extent. On the other hand, members of the CPO group seem to have more resistance to arch width and length deformities. Tuberosity width was not significantly altered in any of the groups. This could possibly be explained by the fact that this area represents a more basal skeletal area than a purely dentoalveolar one. The area may also be better supported by such anatomic structures as the pterygoid plates than are other locations in this study. Arch length also showed a decrease in the pooled and UCLP groups. The data, when evaluated in the light of current theories on effects of nasorespiratory function on facial growth, seem to support the dentoalveolar changes that were seen clinically by Linder-Aronson (1970, 1973) and cephalometrically by Long and McNamara (1985). Thus, in this sample, there appears to be a relationship between the flap procedure and the observed dentoalveolar changes. However, a direct causal link between the flap and dentoalveolar changes cannot be made solely on the data shown. One drawback that would prohibit making this link is the lack of airflow data in the longitudinal growth sample. The use of the photocopy method to analyze the individual points must also be considered. A two-dimensional method to evaluate three-dimensional dentoalveolar changes may in itself result in mild experimental error. Additionally, although the statistical method used seemed to be the best choice in evaluating the data at hand, it may have underestimated the sample variability by its use of repeated, nonindependent measures. Finally, a larger sample size and data collected through the early teenage years would be valuable in further evaluating the trends evidenced in our study. Summary The results and discussion of this investigation can be summarized as follows: 1. Pharyngeal flap surgery, as performed on this sample of patients with cleft palate between the ages of 5 and 7 years, was followed by differences in growth curves for several dentoalveolar measurements. 2. These differences were most typically related to a decrease in the width and length of the maxillary arch. 3. Unilateral cleft lip and palate patients seemed to have more profound changes in width and length than did the cleftpalate-only sample. 4. Since pharyngeal flap surgery has been shown to result in increased nasal airway resistance, one is tempted to make a causeand-effect link between changes seen in this study and change in nasorespiratory function. However, no such conclusion can be drawn from these data alone because of

10 Keller et al, PHARYNGEAL-FLAP SURGERY 257 the absence of actual physiologic airflow data for this sample. Future studies of this - nature would be strengthened with this addition. e REFERENCES DRETTNER B. (1960). The nasal airway and hearing in patients with cleft palate. Acta Otolaryngol 52: GRABER TM. (1949). Craniofacial morphology in cleft palate and cleft lip deformities. Surg Gynecol Obstet 88: HARDING RL. (1979). Surgery-velopharyngeal incompetence. In: Cooper HK, Harding RL, Krogman WM, Mazaheri M, Millard, RT ed. Cleft palate and cleft lip: a team approach to clinical management rehabilitation of the patient. Philadelphia: WB Saunders: HArRvoLD EP, TomEr BS, VARGERVIK K, CHIERICI G. (1981). Primate experiments on oral respiration. Am J Orthod 79: HArRvOLD EP, VARGERVIK K, CHIERICI G. (1972). Primate experiments on oral sensation and dental malocclusion. Am J Orthod 61: KREMENAK CR, HuUrrmaAN WC, Oum WH. (1967). Growth of maxillae in dogs after palatal surgery. Cleft Palate J 4:6-27. KROGMAN WM, JAIN RB, Long RE JR. (1982). Possible sex differences in craniofacial growth in clefting. Cleft Palate J 19: KroGMAN WM, MazanxERI M, HarDpNG RL, IsHIGURO K, BARIANA G, MrirER J, CANTER H, Ross P. (1975). A longitudinal study of the craniofacial growth pattern in children with clefts as compared to normal, birth to six years. Cleft Palate J 12: LINDER-ARONSON S. (1970). Adenoids-their effect on mode of breathing any nasal airflow and their relationship to characteristics of the facial skeleton and the dentition. Acta Otolaryngol Suppl LINDER-ARONSON S. (1975). Effects of adenoidectomy on the dentition and facial skeleton over a period of five years. In: Cook JT ed. Transactions of the Third International Orthodontic Congress, St. Louis: CV Mosby. Long RE Jr, Guprton S, McGm.us MG. (1984). Growth in width following pharyngeal flap surgery. The Angle Orthodontist 54:No. 1, _ Lona RE Jr, KorGman WM, OKa SW. (1980). Longitudinal craniofacial growth of children with cleft lip and cleft palate from one month to ten years, compared to noncleft children via lateral x-ray headfilms. II. The lower facial (mandibular) area. Cleft Palate J 17:356. Long RE JR, MCNAMARA JA Jr. (1985). Facial growth following pharyngeal flap surgery: skeletal assessment on serial lateral cephalometric radiographs. Am J Orthod 87: MazaAHERI M, Haromcg R, Cooper J, JonEs T. (1971). Changes in arch form and dimensions of cleft patients. Am J Orthod 60: MILLER AJ, VARGERVIK K. (1979). Neuromuscular changes during long-term adaptation of the rhesus monkey to oral respiration. In: McNamara JA Jr editor. Nasorespiratory function and craniofacial growth. Monograph 9, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, The University of Michigan: MmLER AJ, VARGERVIK K, CHrERICI G. (1982). Sequential neuromuscular changes in rhesus monkeys during the initial adaptation to oral sensation and dental malocclusion. Am J Orthod 81: Ross RB. (1970). The clinical implications of facial growth in cleft lip and palate. Cleft Palate J 7: SUBTELNY JD, NETO RP. (1978). A longitudinal study of maxillary growth following pharyngeal flap surgery. Cleft Palate J 15: ViG PS. (1974). Respiratory mode and morphology types: some thoughts and preliminary conclusions. In: McNamara JA Jr, ed. Nasorespiratory function and craniofacial growth. Monograph 9, Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development, University of Michigan: ViG PS, SARVvER DM, HALL DJ, WARREN DW. (1981). Quantitative evaluation of nasal airflow in relation to facial morphology. Am J Orthod 79: WarREN DW, DuaAny LF, FiscHER ND. (1969). Nasal pathway resistance in normal and cleft lip and palate subjects. Cleft Palate J 6: WaATson RM, WARREN DW, FISCHER ND. (1968). Nasal resistance, skeletal classification, and mouth breathing in orthodontic patients. Am J Orthod 54: