Assessment of the effect of maxillary protraction appliance on pharyngeal airway dimensions in relation to changes in tongue posture

Abstract

Background:

Literature is controversial in regard with alterations in pharyngeal airway dimensions subsequent to maxillary protraction. The correlation between maxillary protraction and sagittal airway dimension was investigated in association with tongue and soft palate position in skeletal Class III children. The results were compared with those of an untreated Class III and a Class I malocclusion control group.

Materials and Methods:

In this cross-sectional study pre- and post-treatment cephalometric radiographs of 19 Class III patients (6 males, 13 females; mean age, 7.93 ± 0.96 years) treated with facemask were analyzed. The correlation between treatment changes in craniofacial morphology and those in the upper airway, tongue, and soft palate was evaluated. These results were compared with those of a group of 16 Class I malocclusion patients (1 male, 15 females; mean age, 7.31 ± 0.7 years) and a group of 15 untreated Class III patients (4 males and 11 females; mean age, 7.46 ± 0.1 years). A paired t-test, the Shapiro–Wilk test and Mann–Whitney U-test was used. The level of significance was established as P < 0.05.

Results:

Nasopharyngeal airway measurements PNS-ad1 and PNS-ad2 significantly increased by 2 mm and 2.1 mm, respectively. Statistical analysis revealed that maxillary protraction had a positive relationship with PNS-ad1 and PNS-ad2.

Conclusion:

Nasopharyngeal airway dimensions can be improved in the short term with maxillary protraction in skeletal Class III children.

INTRODUCTION

Orthopedic and dentoalveolar effects of maxillary protraction have been broadly discussed in the literature.[1,2,3,4]

The relationship between forward displacement of maxilla and dimensions of pharyngeal airway has been proposed and investigated;[5,6,7,8,9,10,11,12] the issue, however, is very controversial.

Several studies confirmed the existence of a positive correlation between maxillary protraction and the improvement of pharyngeal airway dimensions.[5,6,7] Other studies investigated the synergistic effect of maxillary protraction and expansion and concluded that the treatment could positively improve naso- and/or oro-pharyngeal airway dimensions in short term.[8,9]

Kaygısız et al. showed long-term improvements in nasopharyngeal airway dimensions after treatment with reverse-pull headgear,[10] Pamporakis et al. demonstrated an insignificant increase in the volume of upper and lower airway following treatment,[11] and Baccetti et al. showed no significant short- or long-term changes in sagittal oropharyngeal and nasopharyngeal airway dimensions after maxillary protraction.[12]

The position of hyoid bone, soft palate, and tongue posture are considered as important variables that control airway dimensions.[7,13]

The association of tongue posture with characteristics of the maxilla and mandible has been investigated. It has been shown that Class III participants have a significantly lower tongue posture as compared to Class I participants,[14] and upper airway obstruction has been associated with this low tongue posture.[15]

In addition, a higher tongue posture has been shown by Ozbek et al.[16] and Iwasaki et al. following rapid maxillary expansion.[15]

It can be hypothesized that facemask therapy, through anterior repositioning of the maxilla, may alter tongue posture and consequently the airway dimensions as RME does.

Moreover, due to anatomic attachment of maxillary bone and soft palate, it can be presumed that positional changes in the maxilla could also affect position of the soft palate.

Few of the previous studies[9,12] included a suitable control group with normal growth of the airway to investigate this matter; therefore, the purpose of this study was to assess the association of tongue posture and pharyngeal sagittal dimensions in Class III patients treated with facemask in comparison with an untreated Class III and a treated Class I group.

MATERIALS AND METHODS

Sample size and inclusion and exclusion criteria

This was a before-after cross-sectional retrospective study of 34 patients who were diagnosed as having skeletal Class III deformity, defined as maxillary retrusion with normally positioned mandible (SNA <77, 76≤ SNB ≤80, ANB <1)[17] and 16 patients with skeletal Class I relationship, Class I molar relationship, and a mild malocclusion. There were 39 female and 11 male patients with average age of 7.56 ± 0.58 years in the range of 5–9 years old at the treatment onset. The participants were selected from the files of a private clinic and orthodontic department of Shiraz University of Medical Sciences. The records of all patients were retrospectively selected on the basis of the following criteria:

1. Availability of before (T1) and after (T2) treatment lateral cephalograms. T2 was defined as 9–12 months after T1. Only cephalograms taken at rest and in the natural head position that included the second and fourth cervical vertebrae were included in the study

2. Patients having one or more of these criteria were excluded from the study: History of trauma to the face and jaws, apparent facial asymmetry, presence of any syndrome related to orofacial region, cleft lip and/or palate, obstructive sleep apnea or even habitual snoring, chronic upper respiratory tract infections and diseases, previous history of adenoidectomy/tonsillectomy, and vertical growth pattern. The data for excluding these criteria were gathered from patient's medical and dental history and cephalograms

3. The patients having these criteria were included in the study: Participants aged between 5 and 9 years, anterior crossbite, straight or concave profile, Class III molar relation, and existing scleral show.

Patients were divided into three groups:

Group 1: Sixteen patients (1 male and 15 females; mean age, 7.31 ± 0.7 years) with skeletal Class I relationship, Class I molar relationship, and a mild malocclusion. These patients were treated with either removable or fixed appliances.

Group 2: Fifteen patients (4 males and 11 females; mean age, 7.46 ± 0.1 years) with anterior crossbite, a Class III molar relationship, maxillary skeletal retrusion with no congenital anomalies, or mandibular deviation.

Group 3: The same diagnostic criteria for Group 2 were used. Of these, nineteen patients (6 males and 13 females; mean age, 7.93 ± 0.96 years) who had been successfully treated using a maxillary protraction appliance (delaire-type facemask) and no maxillary expansion were chosen.

Radiography

All cephalograms chosen had been taken at one radiographic clinic with the same equipment (cephalometer PM 2002 EC Proline, KV 85; Planmeca, Helsinki, Finland) in which the film distance to the X-ray tube have had been fixed at 150 cm and the film distance to the midsagittal plane of the patients' head have had been fixed at 15 cm as suggested by the manufacturer.

Lateral cephalograms

The cephalograms were hand traced on a 0.003-inch thick, 8 × 10-inch matte acetate tracing paper (Truvision, Ortho Technology Inc., Tampu, Florida, USA; distributed by Emergo Europe, Molenstraat, Netherlands) with HB pencil.

Skeletal landmarks are depicted in Figure 1 and determined according to Jacobson.[18] Soft-tissue landmarks and airway, soft palate, and tongue measurements are defined in Table 1.

Figure 1.

Skeletal and soft-tissue landmarks.

Table 1.

Soft-tissue landmarks

Figure 2.

Soft tissue landmark (1) ANS (SP); (2) E; (3) ii; (4) is; (5) Mc; (6) mc; (7) O; (8) Pt; (9) Pw; (10) TT; (11) U.

Figure 3.

Soft tissue land mark (1) Tg1; (2) tg2; (3) tg3; (4) tg4; (5) tg5; (6) tg6; (7) tg7; (8) TGH; (9) TGL; (10) Pt-Pw.

Statistical analysis

To estimate the reliability of a single measurer, measurements were retaken in 3 weeks. A paired t-test with a significance level of ≤0.01 was conducted on two measurements to check for any significant differences in the measured items recorded in two different measurements. After no significant difference was confirmed, the mean values of the two measurements were adopted for statistical analyses. All statistical analyses were performed using SPSS version 12.0 for Windows (SPSS Inc., Chicago, IL, USA). The result of the Shapiro–Wilk test confirmed that the variables followed normal distribution (P > 0.05). The mean and standard deviation at the first encounter (T1), at treatment completion (T2), and of the difference between them (T2–T1) were statistically analyzed using paired t-test. A Mann–Whitney U-test was used to assess the significance of the differences in every parameter between the groups. The level of significance was established as P < 0.05.

RESULTS

Among the airway parameters, minimum lingual airway (MLA), AD1 to PNS, and AD2 to PNS significantly increased after treatment only in the treated Class III malocclusion group. In addition, both VRL to U and VRL to EP increased significantly after treatment in the treated Class I group (P < 0.05).

Soft palate measurements showed no significant changes with treatment. [Table 2]

Table 2.

Mean and P values of parameters before and after treatment in the three groups of the study

However, the partial length of tongue in the anterior region of the tongue (Tg6) decreased significantly after treatment in treated Class I malocclusion group; tongue height (TGH) increased significantly in the untreated Class III malocclusion group, and the distance of root part of tongue from the posterior pharyngeal wall (Pt-Pw) showed a significant increase in treated Class III group.

The comparison between the three groups showed that there were no significant changes in soft palate and airway values before and after treatment but that there was a significant difference between before and after values of TGH and Pt-Pw. Comparison between each of the two groups showed that this significance was due to the difference between the 2^nd and the 3^rd group.

DISCUSSION

Growth modification and orthognathic surgery cause not only tooth movement but also changes in the skeletal dimension; it can, therefore, be hypothesized that size and position of the adjacent soft tissues are also altered. The results of this study confirmed the significant effect of skeletal change caused by an MPA on changes in the size of the airway, tongue, and soft palate during treatment.

Among the airway parameters, minimum airway dimension behind the base of the tongue (MLA), airway dimension at the level of basion-PNS plane (AD1 to PNS) and airway dimension at the level of PNS-So (AD2 to PNS) significantly increased after treatment only in the treated Class III malocclusion group. In addition, both VRL to U and VRL to EP increased significantly after treatment in the treated Class I malocclusion group.

Soft palate measurements showed no significant changes with treatment.

As for tongue measurements, however, Tg6 decreased significantly after treatment in Class I malocclusion treatment group; TGH increased significantly in the 2^nd group and Pt-Pw showed a significant increase in Group 3.

In contrast, Pamporakis et al.[11] reported no significant changes in the upper airway dimension during treatment; Hiyama et al.,[5] however, associated a greater forward maxillary growth with a greater increase in the superior upper airway dimension which is in line with the results of this study.

Hiyama also mentioned the influential effects of changes in head posture on upper airway dimension. In our study, this confounding effect has been controlled by choosing cephalograms with the head in natural position.

A limitation of Hiyama's study was the absence of an untreated control group; therefore, changes in the upper airway dimensions during natural growth could not be elucidated. In our study, a group of untreated Class III patients was radiographically followed to overcome this limitation. These patients were chosen among those who prepared pretreatment radiographic records but did not begin their treatment for personal reasons and came back to seek treatment in a few months.

The results of this follow-up confirm the findings of Ozbek et al.[21] who demonstrated only negligible changes in the upper airway dimension during a 1.8-year observation period in untreated participants. Furthermore, in a study by Kilinç et al., change in the upper airway space in untreated Class III patients was trivial during the follow-up of 9.8 months.[9] Therefore, the increase in the upper airway dimension can be related to the increased maxillary growth induced by MPA treatment, and the increase in upper airway dimensions should not be anticipated unless patients are treated with an MPA.

These results are, however, not in accordance with the results of a study by Taylor et al. in which two periods of accelerated change (6–9 years and 12–15 years) were identified for pharyngeal soft tissues.[22]

Hiyama et al. attributed the increase in upper airway dimensions after maxillary protraction to a possible anterior repositioning of the tongue in the enlarged oral cavity. They explained that the change in tongue posture could have induced the soft palate to a more anterior position, which might have resulted in an increase in the superior upper airway dimension.[5]

In our study, the increase in airway space behind the soft palate was trivial; this may be attributed to the growth of soft palate that is needed to maintain velopharyngeal seal as was discussed by Akcam et al.[23] The space posterior to tongue, however, was increased significantly, and this is in agreement with Hiyama et al.'s discussion on the subject[5] and may be related to a more forward position of the tongue subsequent to facemask therapy since the distance between the base of tongue to Pt-Pw was also increased.

The increase in airway space behind tongue in treated Class I patients may also be related to a more forward position of the tongue due to the space created through protrusion of lower incisors during nonextraction treatment of these patients.

Our results were in agreement with those of Primozic et al. who showed that Class III participants have a significantly lower tongue posture as compared to Class I participants, with most of the difference found at the posterior regions and no significant difference at the anterior areas.[14] With maxillary protraction in our study, patients attained an increased TGH and a resultant decreased tongue-to-palate distance.

Lee et al. showed that after treatment with an MPA, the tongue increased in length without thickness change.[6] In our study, the thickness of tongue also remained unchanged after maxillary protraction.

Measurement of airway space after treatment with maxillary protraction appliance showed that PNS-ad1 and PNS-ad2 were, respectively, positioned 2 mm and 2 ± 0.2 mm superiorly. This is consistent with the result of studies by Lee et al., Sayinsu et al., and Kaygisiz et al.,[6,8,10] which showed an increase in nasopharyngeal rather than oropharyngeal space.

Contrary to our results, however, Bacceti et al. could not demonstrate a favorable change in the oro- and/or naso-pharyngeal airway dimensions after facemask therapy in comparison to an untreated control group. This discrepancy in results may be attributed to a longer treatment and follow-up period in their study. It could, therefore, be concluded that any improvement in airway dimensions may be lost to physiologic compensations in the future.

Akcam et al.[23] reported that airway space decreased in patients with the clockwise rotation of the mandible. Patients with vertical growth pattern were excluded from this study; however, the clockwise rotation of the mandible during facemask therapy was an inevitable side effect of the treatment. Therefore, it can be concluded that airway space would be more significantly increased through application of mechanics that control mandibular rotation.

In our study, the effect of deviated growth pattern in Class III individuals was controlled by simultaneous evaluation of untreated Class III patients. There was, however, limited three-dimensional evaluation of airway space because of unavailability of the costly cone-beam computed tomography (CBCT) views. In studies on upper airway space using CBCT, space area, anteroposterior width, horizontal width, and upper airway volume can be measured. Therefore, a limitation of this study was that two-dimensional views were used to evaluate a three-dimensional entity.

CONCLUSION

1. The nasopharyngeal airway dimensions can be improved in short term with maxillary protraction in skeletal Class III children

2. Pharyngeal airway space will not increase in untreated Class III patients

3. Tongue attains a more forward position after maxillary protraction and nonextraction treatment of Class I malocclusion.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.