INTRODUCTION

Rapid maxillary expansion (RME) is a common way to correct a narrow maxilla in adolescents. In addition, it helps eliminate mandibular shifts upon closure, provides more space for erupting maxillary teeth, and lessens dental arch distortion and potential tooth abrasion from dental interferences.^1–4 The skeletal effects for the maxillary hard tissue changes are well documented, but there are fewer studies that examine RME effects on the nasal soft and hard tissue. Furthermore, the previous studies that have evaluated nasal tissue changes have been limited and contradictory, and utilized a variety of data intake modalities, making their findings unclear.

The earliest study was by Berger et al.⁵ in 1999, which analyzed photographic renderings of facial changes associated with maxillary expansion. They found an increase in nasal width post-orthopedic and surgical expansion that was maintained 1 year after treatment. Filho et al.⁶ also used facial analysis to assess nasal morphology in children following RME and found contradictory results to Berger et al.,⁵ concluding that RME had no impact on nasal morphology. Johnson et al.⁷ used a caliper and clinical measurements reporting significant increases of alar width (defined as greater alar cartilage) in the RME group in age groups 11 to 13 compared with a normative sample group, but this increase did not show a clinically significant effect. Santariello et al.⁸ analyzed nasal dimensions in pre-pubertal patients during clinical sessions similar to Johnson et al.⁷ and were in agreement that RME induced an increase in alar width. These studies used a variety of methods from photographic analysis to in-person clinical exams and were limited to only evaluating nasal changes immediately following RME. These methods can introduce various errors, including frontal photographic error, examiner bias, and patient movement during clinical exams. Studies that have employed a variety of traditional two-dimensional cephalometrics neglect structures lateral to the midline, cannot measure the transverse dimension, and have difficulty in reliably identifying soft tissue landmarks.

Recent cone beam computed tomography (CBCT) studies introduced a more accurate and reproducible method in evaluating in the transverse dimension. In 2012, Kim et al.⁹ was one of the first CBCT studies to evaluate nasal soft tissue changes. This was followed by Badreddine et al.^10,11 in 2018, who studied changes in the noses of mouth-breathing patients using multislice computed tomography scans. These studies focused on the short-term nasal soft and hard tissue changes after expansion.

This is the first study to compare the long-term effect of RME on nasal tissue with a nontreatment control group using CBCT. The goal of this study was to evaluate the short-term and long-term effects of RME on nasal soft and hard tissue and compare the effects with a control group using CBCT.

MATERIALS AND METHODS

The study consisted of 63 patients, of which 35 patients (18 girls, 17 boys; average age 9.39 ± 1.4) were diagnosed with a constricted maxilla, treated with RME, and placed in the treatment group (TG). The remaining 28 patients (16 girls, 12 boys; average age 8.81 ± 1.6) were only subjected to routine records and placed in the control group (CG). All patients were evaluated at the private practice office of Dr Boucher. Exclusionary factors included patients with severe skeletal asymmetries, craniofacial anomalies, and syndromic patients and patients with prior orthodontic treatment or any other surgeries in the craniofacial complex. This retrospective study was approved by the Institutional Review Board, University of Pennsylvania, under Institutional Review Board Protocol 829908.

After initial routine records, patients of the TG were delivered a full coverage bonded rapid palatal expander extending from the maxillary primary or permanent canine to the maxillary first molar (Figure 1). The expanders had four predrilled holes in the palatal acrylic prior to cementation to measure the extent of expansion. With a digital caliper, the distance between the anterior and posterior holes were measured and averaged. Patients and parents were instructed to perform two turns per day (0.2 mm/turn) until adequate expansion was reached.

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A CBCT was taken as part of the initial (T1 and T1′) records of all 63 patients (35 for TG and 28 for CG) on an I-CAT machine (Imaging Sciences International, Hatfield, Pa). For the patients of the TG, immediate post-RME CBCT images (T2) were taken approximately 66 days after initial delivery. A smaller window of exposure was taken at post-RME, decreasing the time from 20 to 10 seconds, halving the amount of radiation exposure to the patients. Fixed comprehensive orthodontic treatment, including wires and brackets, were only placed after post-RME. A subsequent progress CBCT was taken for 25 patients of the TG (T3) 2.84 years after post-RME. Generally, T3 CBCTs were taken for the phase II records when the secondary teeth had erupted, and it was clear that the malocclusion was not fully corrected during the phase I treatment. Progress records as part of phased treatment is the standard of care for most orthodontists and is advocated by the American Board of Orthodontics. One of the reasons for the attrition at T3 was that some patients required no additional treatment after palatal expansion.

The CG consisted of a total of 28 patients who had visited from November 2006 to July 2016 and presented for an orthodontic consultation, where the clinical examination revealed a malocclusion, records were taken, and following the review of records, treatment was not initiated for 1 to 2 years. Some patients were referred to an otolaryngologist for a consultation related to hypertrophy of the adenoids and tonsils, several sought second opinions and returned later, and others postponed treatment for financial reasons. The control patients had skeletal Class 1 or mild to moderate Class 2 attributed to mandibular retrognathia. Most patients had anterior arch perimeter deficiencies. Of 28 patients, 6 had posterior crossbite. Updated records were taken at T3′, an average of 2.25 years after T1′.

All CBCTs were anonymized, oriented, and standardized in Dolphin Imaging (version 11.9; Dolphin Imaging & Management Solutions, Chatsworth, Calif). Orientation was completed in three planes of space from the frontal and lateral views. From the frontal, inferior rims of the orbit were placed symmetrically and parallel to the floor. The midsagittal line was placed at the soft tissue of nasion, through the pronasale, to the middle of the chin. From the lateral views, the Frankfort horizontal line (inferior border of the orbital rim to porion) was oriented parallel to the floor. The coronal line was placed just posterior to the condyle. The right lateral view was turned to be superimposed as closely as possible to the left lateral view without a cant. Soft and hard nasal tissue points were chosen as landmarks that would give accurate measurements of any changes that occurred in the nasal complex post-RME. They are shown and defined in Tables 1 and 2 and Figure 2a,b,c. The landmarks were measured in millimeters on the CBCTs in three dimensions in Dolphin Imaging.

Table 1.  Definition of Soft and Hard Tissue Landmarks^a

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Table 2.  Description of Measurements

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Descriptive statistics of the data, including means (M), standard deviations (SD), and 95% confidential intervals, were calculated for T1, T2, and T3 for the treated group and T1′ and T3′ for the control group. Differences between timepoints and within a treatment group were evaluated by paired t-tests or Wilcoxon signed-rank tests. Long-term comparisons between treatment and control groups were evaluated by independent-sample t-tests or Wilcoxon rank-sum tests. Nonparametric tests were used when the Shapiro-Wilk test was statistically significant at a P value < .05. P values for the 40 pairwise comparisons were adjusted using Hochberg's step-up Bonferroni method and considered statistically significant when <.05. SAS version 9.4 (SAS Institute Inc, Cary, N.C.) was used for these analyses. To assess the reliability of the numerical measurements of all variables, all samples from both groups were repeatedly measured after 2 weeks by the same investigator (P.S.) according to Houston.¹² The power was calculated for detecting group differences in T1 to T3 change in alar base width. Using group sample sizes of 25 and 28 and pooled SDs of 0.879,¹³ there was an estimated 98% power to detect a 1-mm difference between groups.

RESULTS

Immediate Post-RME Nasal Soft and Hard Tissue Changes

Table 3 shows the descriptive statistics of the soft and hard tissue variables for TG. Table 4 depicts the comparison of T1 and T2 values of the soft and hard nasal tissue variables of the TG. At the alar base width, there was a mean increase of 1.60 mm (P < .0001). For alar width, nasal length, and nasal height, there was an increase of 0.65 mm, 0.14 mm and 0.34 mm, respectively (P > .05). With the skeletal tissues, there was an increase of pyriform height of 1.77 mm (P < .0001) and of pyriform width of 3.57 mm (P < .0001) when comparing T1 and T2 of the TG. For nasion–anterior nasal spine (ANS) height and ANS–posterior nasal spine (PNS) length, there were increases of 1.04 mm and 0.34 mm, respectively (P > .05).

Table 3.  Descriptive Statistics of the Soft and Hard Tissue Variables for TG^a

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Table 4.  Comparison of the Soft and Hard Tissue Variables for TG^a

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Long-Term Comparison of TG vs CG

Table 5 shows the descriptive statistics of the soft and hard tissue variables for CG. Table 6 depicts the comparison of T1′ and T3′ values of the soft and hard nasal tissue variables of the CG. The control group showed significant differences regarding all measurements except pyriform width from T1′ to T3′, demonstrating the effect of growth (Table 6). The increase in pyriform width was 0.30 mm (P = .056). Table 7 illustrates the comparison of changes that occurred between T1 and T3 (TG) and T1′ and T3′ (CG). There was no significant difference in the nasal soft and hard tissue measurements except for pyriform height and pyriform width attributed to the RME (P < .05).

Table 5.  Descriptive Statistics of the Soft and Hard Tissue Variables for CG^a

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Table 6.  Comparison of the Soft and Hard Tissue Variables for CG

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Table 7.  Long-Term Comparison of Changes of the Soft and Hard Tissue Variables Between T1 and T3 (TG) and T1′ and T3′ (CG)

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DISCUSSION

Based on the intimate relationship of the maxilla and the nasal cavity,¹⁴ there has been a growing interest for orthodontists to study the effect of expansion on the nasal anatomy and its impact on nasal physiology relative to the airway. In this study, the nasal soft and hard tissue changes after RME and the stability of these changes were examined. In addition, the use of CBCT scans was a more reliable way to diagnose and analyze the changes that occurred during expansion.

The short-term effect outcomes showed a 1.6 mm increase of the alar base width, which was closer to the underlying skeletal change. This was in agreement with previous studies showing less than 2 mm widening of the alar base.^5,7,15 Studies that were reliant on facial photographs and in-person clinical measurements reported various outcomes. Baysal et al.¹³ reported that alar base width was greater by approximately 1 mm in the RME treatment group after a 6-month retention period. Badreddine et al.¹¹ reported that, after RME, the alar base width, alar width, and height of the nasal soft tissues increased, whereas changes did not occur in the control group. Berger et al.⁵ reported a 2-mm increase in alar width, which was maintained 1 year after tooth-borne expansion. Johnson et al.⁷ reported that alar base width increased 1.98 mm in the treated group compared with the control group, but the difference might not be clinically significant on the impact to the whole face. On the contrary, Filho et al.⁶ showed no impact on nasal morphology using facial analysis, concluding that RME was incapable of influencing the nasal soft tissues. Torun reported no significant differences observed in soft tissue alar base, nostril width, nostril height, and nasolabial angle.¹⁶ Discrepancies in the extent of nasal soft tissue changes with RME may be attributable to different measurement methods, expansion protocols, age groups, and/or amounts of expansion. Another potential side effect after RME could be the development of a dorsal hump,^5,17,18 which was not found in the patients in this study. The short-term nasal hard tissue change showed a significant increase in pyriform height and width, which was consistent with Badreddine et al.,^10,11 Cordasco et al.,¹⁹ Palaisa et al.,²⁰ and Fastuca et al.²¹

For the long term, this study examined how RME affected patients' nasal growth in comparison with the nontreatment CG. The differences between T1 and T3 values in the TG (Δ T1–T3, average 2.84 years) was compared with the differences between T1′ and T3′ in the CG (ΔT1′–T3′, average 2.25 years). There were no statistically significant differences across all measurements except for the nasal hard tissue pyriform height and pyriform width. This suggests that the significant soft tissue changes that occurred during expansion will, over time, regress to the mean of normal growth and development. In other words, the significant nasal soft tissue changes were immediate, and RME did not have a long-lasting impact on an adolescent's nasal soft tissue anatomy. This may be attributed to continuous growth of the nose and soft tissue elasticity. In the CG without RME (average age 8.81 ± 1.6), a significant increase over all nasal soft and hard tissue measurements except pyriform width (P = .056) was observed during the follow-up period, which was supported by other studies.^22,23 The amount of change in pyriform height and pyriform width in TG showed a significant difference compared with CG, probably attributed to the RME effect. The long term RME effect on the nasal hard tissue is supported by previous studies. Long-term maintenance of a significant increase in nasal cavity width for 12 months²⁴ and 5 years²⁵ were reported in studies and a previous systematic review.²⁶

Immediate and long-term changes after RME in growing patients showed a significant increase in nasal cavity dimension and volume, reducing the resistance of nasal airflow.^26–31 In this study, the RME group showed 3.57 ± 1.2 mm (immediate) and 2.66 ± 1.0 mm increases of pyriform width in 2.84 years, which were consistent with other studies.³² In a previous systemic review,³² RME increased nasal geometry and the increase in transverse nasal measurements ranged from 2 to 4 mm. RME increased the nasal cavity volume by about 0.10% of the pre-expansion volume.¹⁹ In addition, Izuka et al.³³ reported that RME positively impacted the quality of life of mouth-breathing patients with maxillary atresia by increasing the nasal cavity volume significantly and reducing subsequent respiratory symptoms. Interestingly, RME increased the mucociliary clearance in patients who had maxillary atresia, having positive effects on nasal physiology and increasing nasal cavity volume.¹⁴ On the other hand, Langer et al.³⁴ concluded that RME did not influence nasal resistance in their long-term evaluation. Itikawa et al.³⁵ and Matsumoto et al.³⁶ examined the effects of RME on nasal cavity dimensions of young children and observed a significant increase in nasal transverse bony width. However, no difference in nasal volume was detected as a result of mucosal compensation. Nasal bony expansion was followed by a mucosal compensation at a 3-month follow-up study using acoustic rhinometry and rhinomanometry.³⁷ In the current study, the change of nasal mucosal tissue could not be examined precisely using CBCT. Furthermore, the wide variability of the nasal mucosa, which is influenced by several factors such as nasal cycle, body posture, age, infection, exercise, medication, and ultradian rhythm, made it very difficult to compare.^38–41 Therefore, the effect of RME on airway should be carefully interpreted, and RME cannot be indicated only for the improvement of nasal breathing because of the wide variability of individual responses.²⁸

CBCT is being widely used in orthodontic field for diagnosis and treatment planning, and it is considered as one of the most reliable methods for evaluating facial soft and hard tissue changes.^9,42 It has several strengths including lower costs, lower radiation dose, shorter scanning time, and overall accuracy compared with conventional multislice computed tomography scans.^43–46 In addition, CBCT allows the simultaneous evaluation of both skeletal and related soft tissue changes. Previously, studies used several different methods to evaluate nasal soft tissue changes, including photography,⁵ in-person clinical measurements,⁴⁷ three-dimensional facial scans,²¹ and tomography,¹⁶ showing the wide range of outcomes. For those reasons, CBCT was used to assess the changes in the nasal soft and hard tissue in this study.

This study had some limitations resulting from the retrospective design. There was attrition in T2 and T3. Not all treatment groups had T1, T2, and T3 records. Possible reasons for attrition were described in the Material and Methods section. In addition, the power analysis was based on soft tissue changes after RME and not on the control group as the reference value for a control group was not found. However, the sample size was large enough to detect statistically significant findings.

CONCLUSIONS

• The results of this study suggest that, although RME produces some significant increase on the nasal soft tissue immediately after treatment, in the long-term this gain appears to be clinically similar to that observed in untreated control patients.

• The significant increase on the nasal hard tissue immediately after RME was maintained at long-term follow-up. There was a statistically significant difference in nasal hard tissue change between TG and CG at long-term follow-up attributed to the RME effect.

• A well-controlled future prospective study is recommended to overcome the current limitations from the retrospective study design.

• This is the first study to compare the long-term effect of RME on nasal tissue with a nontreatment CG using CBCT.