Orthodontic measurements and nasal respiratory function after surgically assisted rapid maxillary expansion: an acoustic rhinometry and rhinomanometry study

Abstract

The present study sought to assess nasal respiratory function in adult patients with maxillary constriction who underwent surgically assisted rapid maxillary expansion (SARME) and to determine correlations between orthodontic measurements and changes in nasal area, volume, resistance, and airflow. Twenty-seven patients were assessed by acoustic rhinometry, rhinomanometry, orthodontic measurements, and use of a visual analogue scale at three time points: before surgery; after activation of a preoperatively applied palatal expander; and 4 months post-SARME. Results showed a statistically significant increase ( p < 0.001) in all orthodontic measurements. The overall area of the nasal cavity increased after surgery ( p < 0.036). The mean volume increased between assessments, but not significantly. Expiratory and inspiratory flow increased over time ( p < 0.001). Airway resistance decreased between assessments ( p < 0.004). Subjective analysis of the feeling of breathing exclusively through the nose increased significantly from one point in time to the next ( p < 0.05). There was a statistical correlation between increased arch perimeter and decreased airway resistance. Respiratory flow was the only variable to behave differently between sides. The authors conclude that the SARME procedure produces major changes in the oral and nasal cavity; when combined, these changes improve patients’ quality of breathing.

Maxillary constriction is a transverse or sagittal discrepancy in the size of the maxilla and mandible. Its aetiology involves multiple factors, which may be congenital, developmental, traumatic, or iatrogenic in origin. The condition may also be associated with other skeletal–dental abnormalities.

The clinical aspects of transverse maxillary deficiency include dental crowding, anterior open bite and posterior crossbite, malocclusion, high and narrow palatal vault, and lip incompetence due to maxillo-mandibular discrepancy. In addition to these dentofacial abnormalities, major craniofacial changes may also be present, such as narrowed nasal cavity and alar base, reducing nasal permeability and increasing airflow resistance; coupled with skeletal–dental abnormalities, these changes may lead to a higher frequency of mouth breathing.

Correction of transverse maxillary deficiencies may be carried out using orthopaedic and orthodontic techniques or by a combined orthodontic and surgical approach; the choice will depend on the patient’s potential for bone growth and on the extent of correction desired. The various techniques used in maxillary (palatal) expansion are: slow (orthodontic) maxillary expansion; rapid maxillary expansion; and surgically assisted rapid maxillary expansion.

Rapid maxillary expansion with orthodontic appliances is used to great effect for correction of transverse maxillary deficiency in children and adolescents. With growing interest in the orthodontic treatment of maxillary deficiency in adults, many issues have become frequent. According to Lehman Jr. and Haas, rapid maxillary expansion in adults is frequently associated with failure, such as lateral tilting of the teeth and alveolar bone, difficulty distracting the midpalatal suture, mucosal necrosis induced by the expander, and recurrence of deficiency. Effective correction of true unilateral deficiency is impossible with conventional rapid maxillary expansion, because the effects of the latter are always bilateral.

Difficulty opening the midpalatal suture in adults has historically been attributed to suture fusion. Indeed, Silverstein and Quinn showed that orthopaedic rapid palatal expansion in the presence of mature sutures can lead to dental tipping, relapse, and open bite after removal of fixators, in addition to pressure, pain, and necrosis under the expander when it is activated against already ossified sutures; these forces also cause bone defects and gingival recession. These complications may be avoided by concurrent surgical therapy aimed at releasing bone structures that would offer resistance to orthodontic expansion forces, with a minimally invasive procedure.

Surgically assisted rapid maxillary expansion (SARME) entails decreasing bone resistance to maxillary expansion by means of osteotomy of the maxillary walls and buttresses, thus permitting an increase in the transverse maxillary dimension. This technique provides better dental arch stability, aesthetically superior results due to the absence of negative space (distance between the inner commissure of the lips and the buccal surface of the molars, seen during forced smiling), and increased long-term periodontal quality.

In addition to favourable cosmetic, functional, and occlusive outcomes after any of the aforementioned treatments for maxillary constriction, studies on orthodontic maxillary expansion have shown through the use of acoustic rhinometry, which is currently considered the most reliable method for assessing nasal volume and permeability, that nasal breathing is improved due to widening of the nasal cavity, which in turn is brought about by a repositioning of the lateral nasal walls. Acoustic rhinometry is based on the analysis of sound waves reflected within the nasal cavity, and allows assessment of nasal geometry and volume. Rhinomanometry is an aerodynamic method that quantifies transnasal pressure and airflow resistance within the nasal fossae.

There have been few reports on the influence of SARME on respiratory function, but there is growing interest in it, not only about the influence of SARME but also the nasal cavity changes after other maxillary surgical procedures, such as Le Fort I osteotomy.

No published studies have associated changes in nasal area, volume, resistance, and airflow with orthodontic measurements of increased transverse maxillary dimension after SARME. The present study therefore sought to determine, with the aid of maxillary arch study models, acoustic rhinometry, and rhinomanometry, the changes that occur in orthodontic measurements, nasal cavity geometry, and nasal respiratory function in patients who undergo SARME. Another aim was to conduct a subjective, visual analogue scale (VAS)-based analysis of respiratory function before and after SARME. The study also sought to ascertain the correlations between orthodontic measurements and nasal area, volume, resistance, and airflow changes, thus establishing the rhinological importance of maxillary expansion (an oral and maxillofacial procedure).

Materials and methods

This study received prior approval from the Research Projects Ethics Committee Research Protocol no. 750/06 of 13 September 2006, and received funding support from the State of São Paulo Research Foundation, FAPESP (grant n° 06/58768-8 of 4 October 2006).

The study sample comprised 27 patients with maxillary constriction referred for SARME. The study included patients 16 years of age or more, with complete or nearly complete dentition (presence of the maxillary first premolars and first molars in good periodontal condition was mandatory, as they are required for support of the Hyrax expander that would be placed prior to surgery), a diagnosis of maxillary constriction, and orthodontic referral for surgical expansion.

Patients were excluded from the study if they had nasal airway disturbances due to mechanical abnormalities such as nasal septum perforations, synechia, polyps or other primary nasal diseases, a history of prior nasal surgery, local or systemic conditions that contraindicated general anaesthesia, or craniofacial syndromes or malformations.

Patient selection was carried out by the lead researcher on the basis of patient history, oral examination, and panoramic scanning X-rays of the maxilla and mandible. ENT triage was carried out by a single specialist physician on the basis of physical examination and nasal endoscopy.

Assessment of nasal geometry and physiology was conducted by the researcher with a Rhinometrics model SRE 2000 acoustic rhinometry/rhinomanometry device (RhinoMetrics, Interacoustics A/S, Assens, Denmark). The device was handled by a single operator, in a temperature-, noise-, and moisture-controlled room equipped with an Oregon Scientific hygrometer/thermometer, under supervision, and in accordance with the standards proposed by the Standardization Committee on Acoustic Rhinometry (presented at the 18th Congress of the European Rhinologic Society, Barcelona, 2000). Each patient underwent acoustic rhinometry on three separate instances: before surgery (preoperative); after surgery (immediate), immediately after activation of the Hyrax appliance was completed; and 4 months postoperatively (late), when the patient was cleared to remove the Hyrax expander and begin orthodontic treatment with fixed braces immediately.

Prior to testing, each patient remained in the examination room for 10 min for acclimatization and then sat comfortably, resting their head against the chair. For acoustic rhinometry assessment of minimal cross-sectional area (MCA) and volume (VOL), the equipment was calibrated according to software guidance and the long adapter was connected to the appropriate probe (right or left nasal fossa), which adapted to the nostril without deforming it. In order to prevent sound waves from escaping, a gel provided with the equipment was used to seal the space between the probe and the nostril. Patients did not breathe while the software collected data. For rhinomanometric study of transnasal pressure (AP) and respiratory flow (FLOW), both probes were adapted to the equipment and to the patient’s nostrils, after calibration, according to software guidance, and the patient was asked to breathe normally with the probes in place while rhinography proceeded.

All rhinologic variables were measured with and without application of a nasal vasoconstrictor (oxymetazoline hydrochloride, 0.5 mg/ml solution, sprayed twice into each nostril 5 min prior to testing).

Respiratory function was also analysed from the patient’s standpoint at the three separate instances, by means of a VAS, a 10-cm rule on which patients were asked to mark the point, from 0 to 10 cm, which corresponded to how much of their breathing was felt to be exclusively nasal.

Study models were cast at the three assessment times: preoperative, at the end of surgery, and at 4 months after surgery, to measure changes in the maxillary orthodontic measurements. On these models, a compass and calliper were used to measure anterior–posterior arch length and maxillary arch perimeter, as well as transverse measurements of the maxilla between the cusps of the canines, the palatal cusps of the first premolars, and the mesiobuccal cusps of the upper first molars. The measurements on the dental casts were made by two different observers at the different time points and were measured a third time if a difference was detected between both scores. The models showing the measurements in the arch are shown in Fig. 1 .

Fig. 1
The model showing: (A) measurements of anterior–posterior arch length; (B) measurements of maxillary arch perimeter; (C) transverse measurements of the maxilla between the cusps of the canines, the palatal cusps of the first premolars, and the mesiobuccal cusps of the upper first molars.

With the Hyrax appliance in place, patients underwent SARME under general anaesthesia. The technique was as follows: an incision was made at the back of the maxillary buccal sulcus, from the mesial aspect of the canine to the mesial aspect of the first molar, bilaterally, with a V-shaped incision between the maxillary central incisors and exposure of the anterior and lateral maxillary walls by mucoperiosteal elevation. This was followed by horizontal corticotomy of the lateral wall of the maxilla, 5 mm above the apices of the teeth, extending from the piriform aperture and ending posteriorly to the zygomatic buttress, without reaching the pterygomaxillary fissure, in both maxillae. The nasal lateral wall and the septum were not osteotomized. The midpalatal suture was then separated by applying an osteotome between the maxillary central incisors. After releasing the midpalatal suture, the expander appliance was activated eight quarters of a turn (2 mm) and diastema between the central incisors was noted.

5–7 days post-procedure (initial healing period), activation of the expander appliance was begun, one-quarter of a turn in the morning and one-quarter of a turn at night. An orthodontist provided regular follow-up, completed activation and stabilized the expander.

Statistical analyses

A pilot sample of 10 patients was used to calculate the sample size required for the study. According to statistical analysis of the partial data obtained, with an estimated standard deviation of 0.30 for MCA values, a confidence interval of 95%, and based on the calculation of a sample for pairwise comparison, the sample required for reliable data was calculated as 15 patients.

Orthodontic and respiratory function data have three levels of the independent variable each (initial or T1, immediate post surgery or T2, and late measures with 4 months follow-up or T3), and the difference scores were calculated for each of the 27 subjects comparing T1 with T2, T2 with T3, and T1 with T3. If only standard ANOVA tests were used in these statically different variances there will be an increase in Type I errors. Because of that, an adjustment factor based on the amount of variance heterogeneity were used, the Huynh–Feldt-corrected ANOVA, followed by the Bonferroni multiple-comparison correction, used for repeated measures ANOVA. The significance level was defined as 5% ( p < 0.05) for all tests.

Respiratory function data were compared with orthodontic measurements in an attempt to assess the statistical correlation between variables. Pearson’s correlation was used for this purpose. Values between −1 and +1 were considered as representing the existence of a statistical correlation.

Results

Mean participant age was 25.33 years (range 17–44 years). Most patients were female (59.3%). All orthodontic measures changed, on average, significantly ( p < 0.001), from instance to instance, showing that orthodontic measurements increase with surgery and that this increase is sustained over time ( Table 1 ).

Table 1
Orthodontic measurements at different points in time and their comparisons.
Variable Point in time Mean SD Median Min. Max. N p
Perimeter Initial 74.59 4.72 75.0 63 82 27
Immediate 83.41 4.67 84.0 72 93 27 <0.001
Late 81.56 4.99 83.0 69 91 27
Length Initial 27.11 1.89 27.0 24 31 27
Immediate 27.89 1.97 28.0 24 31 27 <0.001
Late 27.74 2.26 28.0 24 31 27
13–23 Initial 33.26 2.14 33.0 28 38 27
Immediate 41.19 2.43 41.0 37 47 27 <0.001 *
Late 39.67 2.72 39.0 36 46 27
14–24 Initial 33.44 5.92 31.0 26 44 27
Immediate 42.93 6.35 40.0 32 54 27 <0.001 *
Late 42.44 6.44 40.0 31 54 27
16–26 Initial 49.85 3.63 51.0 41 55 27
Immediate 59.63 3.36 60.0 53 66 27 <0.001 *
Late 59.00 3.52 59.0 52 65 27
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Orthodontic measurements and nasal respiratory function after surgically assisted rapid maxillary expansion: an acoustic rhinometry and rhinomanometry study
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