|Year : 2017 | Volume
| Issue : 2 | Page : 51-57
Assesment of changes in the sagittal pharyngeal airway dimensions post twin-block therapy using polar planimeter
Kiran Chand1, Sanjay Jacob2, Anila Charles3
1 Department of Orthodontics, Sibar Dental College, Guntur, Andra Pradesh, India
2 Department of Orthodontics, Saveetha Dental College, Vellapanchavadi, Chennai, Tamil Nadu, India
3 Department of Orthodontics, SRM Dental College, Ramapuram, Chennai, Tamil Nadu, India
|Date of Web Publication||8-Jun-2017|
Department of Orthodontics, SRM Dental College, Ramapuram, Chennai - 600 089, Tamil Nadu
Background and Aim: An inordinate percentage of orthodontic patients present with Class II mandibular deficient problems. Mandibular deficiency is one of the major risk factors for developing obstructive sleep apnea (OSA). If functional appliance therapy for mandibular development also increases the pharyngeal airway dimensions the risk for developing OSA in these patients will be minimized. The aim of the present study is to evaluate the changes in the sagittal pharyngeal airway dimensions (SPAD) after twin-block functional appliance therapy in adolescent patients with mandibular retrognathism, utilizing linear, and area measurements. Materials and Methods: A total of 14 patients with an age range of 12–14 years, both the genders having skeletal Class II malocclusion with a deficient mandible were selected and twin-block functional therapy was initiated. Lateral cephalograms were taken at the start of functional jaw orthopedic treatment (time point T1) and at its completion (time point T2) after 4–5 months. Specific areas and distances were measured and analyzed. Results: The area measures increased significantly while the linear measurements showed a non significant increase. The oropharynx (P = 0.008) area displayed the most significant increase followed by nasopharynx (P = 0.014) and laryngopharynx (P = 0.028). Conclusion: Functional appliance therapy utilizing twin-block appliance in Class II malocclusion patients with retrognathic mandible was efficient in increasing the SPAD.
Keywords: Class II, obstructive sleep apnea, polar planimeter
|How to cite this article:|
Chand K, Jacob S, Charles A. Assesment of changes in the sagittal pharyngeal airway dimensions post twin-block therapy using polar planimeter. SRM J Res Dent Sci 2017;8:51-7
|How to cite this URL:|
Chand K, Jacob S, Charles A. Assesment of changes in the sagittal pharyngeal airway dimensions post twin-block therapy using polar planimeter. SRM J Res Dent Sci [serial online] 2017 [cited 2017 Aug 20];8:51-7. Available from: http://www.srmjrds.in/text.asp?2017/8/2/51/207655
| Introduction|| |
An unconscionable percentage of orthodontic patients present with Class II mandibular deficient problems. An effective method of treatment for these patients during adolescence is “Growth Modification Appliances.” The literature is abound with numerous investigations suggesting various modes by which functional appliances transform a Class II skeletal relationship to Class I through possible changes in skeletal relationships and neuro-muscular adaptations.
Pharyngeal airway dimensions were found to be decreased in Angle Class II division 1 patient.,
Decreased pharyngeal airway dimensions may lead to the posteriorly positioned tongue and soft palate, predisposing the patient to impaired respiratory function, possibly leading to obstructive sleep apnea (OSA). A high number of OSA patients includes skeletal Class II patients characterized by a deficient mandible. Hence, mandibular retrognathism is considered one of the major risk factors for OSA.
Various removable and fixed functional appliances used routinely to stimulate mandibular growth in skeletal Class II growing patients. Similar oral appliances are also used in adult OSA patients to improve the patency of upper airway (UA).
Although many studies have evaluated the nature of Class II correction by various functional appliances in growing skeletal Class II children, there are only a few studies that mention the effects on the sagittal pharyngeal airway dimensions (SPAD) changes following functional appliance treatment.,,,,,,,,,,,,,
However, most of the studies have considered only linear measurements for evaluating the changes in the pharyngeal airway. Aboudara et al. had shown that the sagittal airway area measurements correlate with the three-dimensional volumetric changes more than the linear measurements. Henceforth, assessment of airway utilizing area measurements associates more with volumetric changes in pharyngeal volume than the linear measurements. Thus, the present study was designed to evaluate the efficacy of the twin-block appliance in the improvement of pharyngeal airway dimensions in adolescents having skeletal Class II malocclusion with retrognathic mandible utilizing sagittal pharyngeal airway area measurements and linear measurements.
| Materials and Methods|| |
This study was approved by the Institutional scientific review board and the Human ethical committee. Patients for this study were selected from the outpatient department of the Department of Orthodontics. Patients who were willing to participate were requested to sign the consent form after due explanation of the procedure. A total of 14 patients with an age range of 12–14 years, both the genders were selected for this study based on the following selection criteria.
Adolescents in their peak growth with a skeletal maturity indicator 4–6, as evaluated by hand-wrist radiographs. Patients diagnosed with skeletal Class II malocclusion and having a clinically retrognathic mandible. Angle's Class II molar relationship with ANB >4 mm and overjet >5 mm. Patients with any history of respiratory illness, previous orthodontic treatment or orthopedic treatment, abnormal phenotypes (clefts or syndromes), and Angles Class II division 2 malocclusion were excluded from the study.
All patients were fitted with the standard twin-block appliance (with appropriate sagittal advancement). Construction bites were taken 2–3 mm beyond the freeway space. Either a one-step or a two-step advancement was performed, depending on the severity of sagittal discrepancy. Patients were reviewed at regular intervals of 20–30 days and overjet, over-bite, mid-line deviations and molar relationships were recorded at each appointment. During the active phase of treatment, the patient was instructed to wear the appliance 24 h a day. Patients were advised to keep their lips together to form a seal when the appliance was being worn. Orthopedic phase (functional appliance therapy) was continued till the required sagittal advancement was attained, followed by a retention phase of 6 months.
All cephalometric radiographs were obtained before the initiation and end of treatment with Sirona Galileos imaging unit. The radiographs were traced and digitized utilizing Epson B300 scanner at 300 dpi.
Pharyngeal airway analysis
Various landmarks [Figure 1] are marked to differentiate the pharyngeal airway into nasopharyngeal airway area (NPAA), oropharyngeal airway area (OPAA), laryngopharyngeal airway area (LPAA) [Figure 2]. The upper border of NPAA is delineated by a line extending from the harmonium (H) to the posterior nasal spine. The lower extent of the NPAA is traced by marking a line at the tip of the soft palate parallel to the Frankfort horizontal (FH) plane extending to the posterior wall of the pharynx [Figure 3]. The OPAA and LPAA are differentiated by a line drawn at the level of the tip of epiglottis parallel to the FH plane to the posterior wall of the pharynx. The lower border of the LPAA is taken as a line drawn parallel to FH plane and passing through the anteroinferior most point (C5AI) of the fifth cervical vertebra. The McNamara's pharyngeal airway analysis was performed to obtain the routine linear measurements of the UA and lower pharyngeal air-way (LA).
|Figure 1: Cephalometric land marks. ANS: Anterior nasal spine, C5AI - antero inferior most point of fifth cervical vertebra. H: Harmonium - the point where the vomer bone meets the cranial base, Or: Orbitale, PO: Porion, PNS: Posterior nasal spine, TSp: Tip of the soft palate, TEg: Tip of epiglottis|
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|Figure 2: Cephalometric sagittal pharyngeal airway area measurements used in the study. NPAA: Nasopharyngeal airway area, OPAA: Oro pharyngeal airway area, LPAA: Laryngo pharyngeal airway area|
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|Figure 3: Cephalometric sagittal pharyngeal airway linear measurements used in the study (mm) UA: Upper airway, LA: Lower airway|
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The digitized lateral cephalograms were calibrated and linear measurements were obtained utilizing ImageJ software (version 1.48), developed by the National Institutes of Health (NIH), Washington, USA.
The boundaries of the upper, middle, and lower pharyngeal airway were traced manually and the area measurements were obtained utilizing Compensating Polar-Planimeter, model Lasko L10.
The IBM SPSS Statistics 25.0 for Windows (IBM Co., Armonk, NY, USA) was used for statistical analysis. For descriptive analyses, the means, standard deviations (SDs) and ranges of the measurements at the pre treatment and post treatment time points were computed. Paired t- test was used to test for significant longitudinal changes. A P < 0.05 was chosen to assign statistical significance for all tests.
To evaluate the intra-operator reliability, the measurements of the pre- and post-treatment cephalograms of all the 14 patients were repeated by the same operator after a wash-out period of 2 weeks, and the reliability of all the measurements was assessed using the Intraclass correlation coefficient.
| Results|| |
After a washout period of 2 weeks, all the lateral cephalograms are traced for the second time, and all the measurements were repeated. The reliability of all measurements was found to be within clinically acceptable limits. While the reliability of area measurements was found to be between 0.992 and 0.993 for pre treatment measurements [Figure 4] and 0.929–0.994 for post treatment measurements, [Figure 5] the linear measurements showed reliability between 0.986 and 0.990 for pre treatment and 0.960–0.993 for post treatment measurements.
|Figure 4: Cephalometric sagittal pharyngeal airway linear measurements used in the study - pre treatment|
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|Figure 5: Cephalometric sagittal pharyngeal airway linear measurements used in the study - post treatment|
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Changes in the SPAD during the treatment period [Table 1].
|Table 1: Comparison of pre treatment and post treatment measurements of various parameters representing pharyngeal airway dimensions (n=14)|
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The comparison of pre treatment and post treatment measurements of the pharyngeal airway dimensions showed a significant increase in the airway area dimensions while the linear measurements showed a non significant increase. When the area measurements are considered the OPAA was greatly increased compared to other measurements with a P = 0.008 followed by NPAA (P = 0.014) and LPAA (P = 0.028). The changes in the linear measurements (UA, LA) were insignificant with P values of 0.269 and 0.361, respectively.
| Discussion|| |
The pharyngeal airway had been an area of interest to the orthodontic community due to the reciprocal effects of the growth of pharynx and surrounding hard tissue structures on each other (the mutual adaptability between form and function, i.e., function may adapt to altered form and vice-versa, the size and shape of the structures may adapt to altered function-Moss).
The collapse of the pharyngeal airway results in sleep disordered breathing (SDB) which when left untreated predisposes the patient to OSA Young et al.; estimated that 2% of women and 4% of men in the middle age meet the criteria for sleep apnea syndrome. Hochban and Brandenburg showed that more than one-third of OSA patients prove to have pharyngeal narrowing combined with more or less distinct maxillary and mandibular deficiency.
Orthodontic literature has ample studies showing decreased pharyngeal airway dimensions in patients with skeletal Class II malocclusion having retrognathic mandible. Most of the studies showed positive correlation between the length of the mandible and pharyngeal airway space.,,,, It is believed that the retro-positioned mandible results in a more posterior tongue position; thereby leading to a reduction in pharyngeal airway space and a resultant decrease in airflow during sleep, predisposing the individual to SDB.
If orthodontic treatment modalities exist that positively or negatively affect the pharyngeal airway volume, they can play a significant role in the orthodontist's diagnosis and treatment planning. The functional appliance therapy in skeletal Class II patients for retrognathic mandible has been shown to improve pharyngeal airway space as stated in the studies by.,,,,,,,,,
Why twin-block appliance is selected for the study?
In comparison with other functional appliances, a number of advantages result from using separate upper and lower appliances with occlusal bite blocks. Twin-blocks are constructed in a protrusive bite that effectively modifies the occlusal inclined plane by means of acrylic inclined planes on occlusal bite-blocks. Occlusal inclined planes give greater freedom of movement in anterior and lateral excursion and cause less interference with normal function. The functional mechanism of the occlusal bite-blocks is very similar to that of natural dentition. The patient can eat with the appliance in the mouth and the full forces of occlusion are harnessed as corrective forces for dental and facial development in the twin-block technique.
The un-favorable cuspal contacts of distal occlusion are replaced by favorable proprioceptive contacts of the inclined planes of the twin-block correcting the malocclusion and freeing the mandible from its locked distal position. Muscle behavior is immediately altered through the placement of inclined planes between the teeth. The muscles of mastication must adapt to the altered balance of occlusal forces by guiding the mandible into the protrusive function. This guidance results in rapid soft tissue adaptation to achieve a new position of equilibrium in muscle behavior.
This study was performed to evaluate the effects of twin-block functional appliance therapy on the SPAD in skeletal Class II patients with retrognathic mandible. This study adds to the existing literature by utilizing area measurements of all the three regions of pharynx (nasopharynx, oropharynx, and laryngopharynx) for assessing the pharyngeal airway dimensions. The pharyngeal airway area measurements were selected, as they have been shown to correlate more with volumetric measurements, when compared with linear measurements. Reliability of the measurement [Table 2].
Aboudara et al. stated that the overall area-to-volume linear regression showed a positive association between the measurements with a moderately high correlation coefficient value r = 0.75, P< 0.001).
Linder-Aronson found a high level of correlation between the results of posterior rhinoscopy and radiographic cephalometry. Jeans et al. suggested that linear measurements of the soft tissues of the nasopharynx are unreliable and the measurements of areas are more meaningful in the studies of the UA.
The theory behind the present investigation was that advancing the mandible using a functional appliance could potentially increase the pharyngeal airway volume. The reason being, as the mandible is positioned forward the associated musculature and soft tissue would be hyper-propulsed as well, thus increasing the airway dimensions.
The longitudinal changes in the study revealed that Twin-Block functional appliance clearly has a characteristic effect on the SPAD, when analyzed utilizing area measurements. The effect of the treatment is not distributed uniformly throughout the pharyngeal airway region. Treatment affects some regions of the pharyngeal airway more than others. The oropharynx (P = 0.008) showed the most significant increase in area measurements followed by nasopharynx (P = 0.014) and laryngopharynx (P = 0.028).
Changes in the nasopharyngeal airway area
The NPAA measurement which was 382.352±- 20.439 mm 2 before twin-block therapy had increased to 423.392 ± 22.033 mm 2 after the twin-block therapy. The NPAA area showed a mean increase of 41.04 ± 14.498 mm 2 with a P = 0.014 (significant).
Changes in the oropharyngeal airway area
The OPAA value which presented with a mean value of 218.712 ± 30.310 mm 2 before the twin-block therapy, increased to 250.919 ± 29.643 mm 2. The mean difference between the pre- and post-treatment value was 32.207 ± 10.390 mm 2 with a P = 0.008 (highly significant).
Changes in the laryngopharyngeal airway area
The LPAA measurement which was 451.446 ± 25.646 mm 2 before twin-block therapy had increased to 487.811 ± 23.369 mm 2 after the twin-block therapy. The LPAA area showed a mean increase of 36.365 ± 14.665 mm 2 with a P = 0.028 (significant).
Changes in the upper airway
Before the twin-block therapy the mean value of UA measurement was 7.6 ± 0.799 mm. With the twin-block therapy the UA value increased to 8.207 ± 0.821 mm. The mean change was 0.607 ± 0.525 mm which is not statistically significant (P = 0.269).
Changes in the lower airway
The mean pre treatment value of LA was 9.257 ± 0.722 mm. After the twin-block therapy the mean value of LA was 9.707 ± 0.861 mm with a mean increase of 0.450 ± 0.475 mm. The increase in the LA measurement is nonsignificant as the P value for the increase is 0.361.
While the area measurements indicated significant increase for all the pharyngeal airway regions, the linear measurements UA (the smallest distance between the soft palate and the posterior pharyngeal wall), LA (the smallest distance between the base of the tongue and the posterior pharyngeal wall) showed an increase in pharyngeal airway dimensions which are not significant (P value; UA - 0.269, LA - 0.361).
When the norms established by McNamara (1984) for UA and LA are considered, which are 15–18 mm and 10–12 mm, respectively, the subjects have not attained the normal values even after the twin-block functional appliance therapy (UA = 8.207 ± 0.821, LA = 9.707 ± 0.861).
The present findings for PAA are in agreement with previous studies Hänggi et al., Ozbek et al. However, LA has showed a significant increase in the studies by Ozbek et al., Hänggi et al., Jena et al., The findings of LA in the study, matches with that of Kinzinger et al.
The discrepancy between the area and linear measurements in calibrating the changes produced in the pharyngeal airway dimensions can be explained by the facts that, the antero-posterior dimension of the naso-pharynx seems to be determined at an early age, after which this distance is relatively similar for most normal adult human beings. King et al. stated that the growth of the pharynx occurs only in vertical direction after the age of 12 years.
- The amount of increase in pharynx airway produced by the normal growth and that can be attributable to the twin-block therapy cannot be differentiated
- Two-dimensional measurements on the lateral cephalometric radiographs cannot reveal the changes in the third dimension (transverse dimension of the airway) (since the three-dimensional imaging is associated with high radiation dose and as the area measurements of the pharyngeal airway correlate more than the linear measurements, with three-dimensional measurements; the conventional lateral cephalogram when utilizing area measurements still remains as a reliable diagnostic tool for monitoring the pharyngeal dimensions).
One must be careful directly applying the findings of the current study to the treatment of OSA, as sleep apnea is studied in patients who are asleep and in a supine position. Furthermore, and most importantly, sleep apnea is multifactorial and largely correlated to body mass index followed by neck circumference and pharyngeal flaccidity.
Pharyngeal airway has been given prime importance in the growth and development of the craniofacial region. Any aberrations in the normal structure of the pharynx predispose the patient to various conditions such as OSA and craniofacial abnormalities.
Patients having a skeletal Class II pattern with retrognathic mandible have been found to have reduced pharyngeal airway dimensions in various studies.,,,,, These patients are at a greater risk of developing OSA.
Functional appliance therapy in recent times has been the mainstay, for the correction of skeletal discrepancies in growing adolescents. Of all the functional appliances, twin-block is the most widely utilized, due to its design. If the correction of the retrognathic mandible in the skeletal Class II patients by the twin-block appliance also improves the pharyngeal airway dimensions, it would result in decreasing the risk of predisposition to develop OSA.
Even though, three-dimensional imaging with cone beam computed tomography provides the most accurate assessment of the pharyngeal airway, it has some inherent disadvantages such as high radiation dosage, and high cost of the inventory. The area measurements of the pharyngeal airway on the lateral cephalogram have been shown to have a high correlation with the volumetric measurements. The reduced radiation dosage, wide-spread availability, and cost effectiveness of the lateral cephalogram have made it a reliable method for assessment of the pharyngeal airway. Based on the above facts, the study was undertaken and a total of 14 patients were selected for this study who matched the objectives of the selection criteria. The patients were explained about the treatment protocol and the consent form was signed before initiating the procedure. The patients who were selected for this study were ideally suited for undergoing functional appliance therapy with a twin-block appliance. The twin-block therapy was initiated and continued till the required amount of sagittal advancement was attained. Pre- and post-treatment lateral cephalograms were taken. The study reveals that all 14 patients exhibited statistically significant increase in the pharyngeal airway dimensions. The increase was most significant in the oropharynx followed by nasopharynx and laryngopharynx.
| Conclusion|| |
The present study utilized sagittal pharyngeal airway area measurements, and linear measurements (McNamara, 1984) to assess the changes produced by functional appliance therapy with twin-block in the pharyngeal airway dimensions.
Growing adolescents (in the pubertal growth spurt) having skeletal Class II pattern with a retrognathic mandible, treated with twin-block functional appliance resulted in improvement in the Class II skeletal pattern by enhancing the growth of mandible.
Significant increase in the pharyngeal airway area measurements, particularly in the oropharynx followed by nasopharynx and laryngopharynx.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]