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Table of Contents   
ORIGINAL RESEARCH  
Year : 2015  |  Volume : 26  |  Issue : 5  |  Page : 451-461
Upper airway dimensions and sleep efficiency - three-dimensional imaging analysis and assessment of the nasopharyngeal appliance


1 Department of Prosthodontics, SRM Dental College, SRM University, Ramapuram, Chennai, Tamil Nadu, India
2 Department of Medical Research, SRM University, Kattankulathur, Kancheepuram, Tamil Nadu, India
3 Department of Orthodontics, Priyadharshini Dental College, Thiruvallur, Tamil Nadu, India

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Date of Submission02-Aug-2013
Date of Decision31-Mar-2014
Date of Acceptance11-Sep-2015
Date of Web Publication17-Dec-2015
 

   Abstract 

Background: Reduction of upper airway (UA) dimensions during sleep is contemplated to cause reduced sleep efficiency (SE) but a definitive association is not affirmed. Efficacy of nasopharyngeal appliance (NPA) in management of UA resistance syndrome (UARS) has not been compared with mandibular repositioning splint (MRS). This study intended to assess relation of UA dimensions to SE and effectiveness of NPA.
Materials and Methods: Research had two phases: Case-control study to determine association between UA and SE; randomized control trial (with independent concurrent trial groups and double-blind design) to analyze treatment outcome with NPA. Subjects were categorized to three groups of 20 in each: A control group of healthy subjects (Group A); two "Randomly Assigned" sample groups of subjects with reduced SE (Groups B and C). Preliminary questionnaire for sleep analysis, Final data collection sheet (first and second case sheets) were recorded, cephalometric variables analyzed, and diagnostic overnight polysomnography was done to match and confirm selection criteria. Three-dimensional computed tomography was done to analyze airway dimensions before and after appliance placement. ANOVA and post-hoc tests were used for statistical analysis of results.
Conclusions: Reduced UA dimension during sleep is associated with reduced SE; NPA gives better improvement for UARS than MRS.

Keywords: Continuous positive airway pressure, microarousal, obstructive sleep apnea, polysomnography, sleep fragmentation, upper airway resistance syndrome

How to cite this article:
Venkat R, Vasanthakumar M, Balakrishnan D, Deenadayalan P. Upper airway dimensions and sleep efficiency - three-dimensional imaging analysis and assessment of the nasopharyngeal appliance. Indian J Dent Res 2015;26:451-61

How to cite this URL:
Venkat R, Vasanthakumar M, Balakrishnan D, Deenadayalan P. Upper airway dimensions and sleep efficiency - three-dimensional imaging analysis and assessment of the nasopharyngeal appliance. Indian J Dent Res [serial online] 2015 [cited 2020 Feb 17];26:451-61. Available from: http://www.ijdr.in/text.asp?2015/26/5/451/172021
Upper airway resistance syndrome (UARS) is a respiratory distress associated with upper airway (UA) during sleep. This syndrome is distinctive in sense that, unlike obstructive sleep apnea (OSA), clinical signs are less noticeable and thereby diagnosis of the condition is challenging. [1] In contrast to OSA, individuals with UARS do not show polysomnographic signs of reduced oxygen saturation and apnea-hypopnea index (AHI) of >5 to 30/h of sleep. [2] Nevertheless, it is contemplated that UARS leads to sleep disturbances and is a more common condition than OSA, with high prevalence rate of one in every five individuals. [3]

Dimensions of UA have been studied for wakeful subjects in supine position and reduction of UA size in OSA patients has been stated. [4] Such an association has not been verified between UARS individuals and healthy subjects during sleep by means of a three-dimensional (3D) imaging analysis of UA. More significantly, airway dimensional changes during sleep and its effect on sleep efficiency (SE) have not been investigated.

The first aim of this research was to determine whether subjects having a reduction of UA dimension during sleep exhibit sleep fragmentation (SF), microarousals (MA), and reduced SE due to respiratory disturbance.

In subjects with severe OSA, improvement in the condition has been proven to be best attained with continuous positive airway pressure (CPAP) therapy and oral appliances (OAs) in subjects with noncompliance to CPAP. [5] In contrast, CPAP therapy is not justified in subjects with UARS, due to less severity of symptoms. Mandibular repositioning splint (MRS) which is recommended as the modality of choice, [6] is based on the concept of tongue repositioning and preventing narrowing of the oropharyngeal part of UA. UA narrowing at nasopharyngeal region will not be corrected by this splint and hence a new appliance design is indicated .

A previous research publication by the principal author of this manuscript, done elsewhere, [7] proposed a new appliance design, nasopharyngeal appliance (NPA), and compared the efficacy of both MRS and NPA. The clinical predictors, nasal, and oral endoscopy analyses revealed better outcome with NPA. However, the effectiveness of NPA in improving UA dimensions during sleep in UARS subjects must be compared with healthy subjects.

Hence, the second aim of this research was to compare efficacy of NPA and MRS in improving UA dimensions during sleep in UARS subjects.

Objectives

  • To determine whether subjects with reduction of UA dimension during sleep will exhibit SF, MA, and reduced SE due to respiratory disturbance.
  • To compare efficiency of NPA and MRS in improving UA dimensions during sleep in UARS subjects.
Null hypothesis

A null hypothesis was derived from the research questions: "An adult with reduced UA dimensions in sleep does not have a definitive risk of SF, MA, and reduced SE in comparison to a subject without airway reduction. The new NPA does not exhibit better improvement of UA dimension in subjects with UARS in comparison to conventional modality of MRS." Study was designed to test this hypothesis.


   Materials and methods Top


Experimental design

The research had two phases: A Case-control study design to determine whether there is association between reduced UA dimensions in supine position to SF, MA, and UARS; a randomized control trial (with Independent-Concurrent trial groups and double-blind study design) to compare treatment outcomes between MDS and NPA. All the participants were informed about testing methods; time/duration of visit; medico-legal risks; terms of liability; compensation and written consents were taken. Ethical issues were dealt by official declaration to participants about medico-legal terms and code of ethics to safeguard their rights. Ethical sanction and methodology approval for the research were registered at Research Review Board-Directorate of Medical Research-SRM University-Chennai. Periodic monitoring of research progress was done by Doctoral Committee formulated by the University and by the Research Co-ordination Committee of the Institution.

Sampling method

The sample comprised of total 60 subjects -20 healthy individuals (Control group - Group A), 40 subjects (by "Random Assignment" method with stratified sequence) with respiratory distress related sleep disturbance (20 as Group B and 20 as Group C). A priori test (prospective power analysis) was conducted through a pilot study to estimate the minimal sample size required to achieve adequate statistical significance. Also, based on this analysis of statistical power, it was determined that the P < 0.05 (significance level of 5%) for the null hypothesis to be rejected.

Selection criteria

Participants were selected through inclusion criteria with separate norms for control/sample groups and were matched for demographic, clinical, geographic, and temporal factors [Table 1]a].
Table 1:

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Further, during the process of subject selection, the subjects of control and sample groups were matched for cephalometric variables, which denote their craniofacial skeletal architecture. Lateral cephalometric imaging was done for all subjects after positioning the subject using a cephalostat in Kodak 8000C digital panoramic and cephalometric system. Tracings were done manually, and all the subjects of the control and sample groups were matched for 6 cephalometric parameters using the baseline reference values [Table 1]b].

Participants underwent following series of sampling methods to confirm selection criteria:

  1. Preliminary questionnaire for sleep analysis (first case sheet): For identification of sleep disturbance and daytime sleepiness scale; elimination of medical problems/drugs/behaviors/habits that may influence sleep
  2. Final data collection sheet (second case sheet): For confirmation of inclusion criteria and matching samples of Groups A, B, and C; to affirm suitability of subjects
  3. Cephalometric analysis of craniofacial parameters: To match the samples of all groups for similar craniofacial skeletal architecture and to avoid any differences between the subjects of control and sample groups regarding craniofacial pattern
  4. Overnight diagnostic polysomnography (ODP): To confirm diagnosis of sleep disturbance secondary to UARS in Groups B and C; to confirm healthy sleep pattern in Group A (Control) subjects
  5. Sleep-fragmentation index (SFI): To confirm MA and SF in subjects of Groups B and C; to confirm absence of above conditions in Group A.
The diagnosis based on case sheets, cephalograms, ODP reports, and SFI was done by one observer - a Dental Surgeon with training on orofacial pain and sleep medicine (who did not have a prior idea of the sample grouping) with opinions from the specialists team comprising of a ENT surgeon, a general physician, a sleep medicine specialist, radiologist, an orthodontist, and 2 dental surgeons. Information regarding whether a subject belonged to control or sample group was concealed from the observer, the specialists team and the subject to have "double-blind effect" for minimizing bias.

Anticipated variables in study were Predictor variables of presence/absence of subjective symptoms of sleep disturbance and Outcome variables of (1) polysomnographic data; (2) SFI; (3) variation in craniofacial pattern among subjects; and (4) dimensions of UA; confounding factors that may influence results were eliminated by (1) matching age; body mass index; body type; ethnicity of control; and sample groups; (2) elimination of medical problems/drugs/habits/behaviors which may influence sleep; (3) matching all the subjects for craniofacial pattern by cephalometric analysis of common variables; (4) double blind effect during sampling and observation.


   Testing protocol Top


Overnight diagnostic polysomnography

Each of the participants from control and sample groups was admitted to sleep laboratory on the evening of study. ODP was performed in sound proof room with one-way glass and subjects were analyzed during nonpharmacologically induced sleep by seven point electroencephalogram (EEG), right and left electrooculograms (EOG), and electrocardiogram (ECG). Following investigation were carried out [Figure 1] (1) sleep latency (using EEG) - in minutes; (2) SE - duration of sleep/number of hours in bed (EEG); (3) sleep stages (EEG and EOG) graphical representation - transition from nonrapid eyeball movement (NREM) to rapid eyeball movement (REM) and percentage of each stage; (4) oxygen de-saturation percentage (oximentry), UA air-flow (nasal cannula analysis) and thoracic/abdominal respiratory movements (piezoelectric strain gauges); (5) arousal states (by EEG) - brain waves, tracheal sounds (microphone), muscular movements (Tribalis EMG); (6) cardiac rhythm changes (ECG); (7) inspiratory air flow (nasal cannula-pressure transducer); and (8) respiratory effort related arousals (RERA) with nasal pneumotachograph.
Figure 1: Overnight Diagnostic Polysomnography for sleep analysis

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Interpretation of polysomnography data

Sleep study reports contained investigation of SE and arousal data. Summary of report included SFI, spontaneous-arousal index, AHI, RERA index, SE, sleep maintenance competence, general sleep pattern, and diagnosis based on these values.

Sleep fragmentation index

From the EEG data of polysomnogram, SFI was derived through the recommended formula. [15]



This index denotes sleep-fragmentation and degree of MA. It was affirmed from ODP and SFI that subjects of Group A (Control) do not exhibit reduced SE/high SFI/MA secondary to UARS, whereas subjects of Groups B and C showed these signs.

Upper airway dimension measurement

Computed tomography (CT) was done on subjects after nonpharmacologically induced sleep during the course of ODP. Imaging was done during NREM sleep Stage 2 of sleep as shown by polysomnographic data and with subjects in supine position. CT scanning was done during the course of the overnight polysomnography and the subjects were kept under observation of sleep lab and radiology laboratory assistants throughout the night time during polysomnography. CT imaging was done only when the polysomnogram showed NREM Stage 2 sleep and when subject was in supine position. Base of skull sequencing was followed with CT machine - Siemens SOMATOM Definition AS/AS with FAST CARE (Global Siemens Health Care, Siemens AG, Germany) with settings of 110 kV, 50 mA, 75-77 s, voxel size 0.33 mm, 180 slice configuration, slice thickness of 1 or 0.3 mm and dimension of 13 mm × 13 mm. UA patency was measured by computerized method (Fuji Synapse Vincent Software, Synapse 3D Fujifilm, FUJIFILM Medical Systems U.S.A., Inc.) and measurements (surface area in mm 2 ) were taken from base of skull CT (slide 80/180) at the oropharyngeal level with hard tissue reference points of transverse process and foramen [Figure 2].
Figure 2: Measurement of upper airway patency done from computed tomography images by computerized method (Fuji Synapse Vincent software)

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3D CT Imaging was done for evaluating UA volume and surface area. The superior border of UA was defined by a plane drawn parallel to the Frankfort plane and going through the most distal point of the bony hard palate; and the inferior border of UA was set by a plane drawn parallel to the Frankfort plane and going through the most anterior-inferior point of the second cervical vertebrae. UA volume was measured between the borders derived from these two hard tissue reference planes. Volume analysis was done by Fragmentation and Processing technique [Figure 3] using  Amira 3.1 software (Mercury Computer Systems 3D Viz - FEI Visualization Sciences Group, France). Measurements were taken from the 3D images developed using the software [Figure 4]. Measurements were made for volume, anterior-posterior width (a-p width), lateral width and surface area at the narrowest points in retroglossal and retropalatal regions. Statistical analysis of the data was done with ANOVA and post-hoc tests.
Figure 3: Fragmentation and Processing technique- three-dimensional imaging of upper airway -Amira 3.1 software (Mercury Computer Systems three-dimensional Viz group)

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Figure 4: Three-dimensional images of upper airway developed for dimensional analysis

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UA dimensions measurements were made for all subjects - Group A of healthy individuals; Groups B and C with and without MRS and NPA, respectively, to evaluate and compare treatment outcome with appliance therapies. No specific instructions were given to subjects regarding co-operation during scanning process as the subjects needed to be in NREM Stage 2 sleep, no active participation or co-operation was expected from the subjects. Appliances were fabricated using materials and techniques as stated by the principal author in prior publication. [7] MRS was fabricated in such a way that mandible will get advanced by 5 to 6 mm in all subjects. Subjects to whom NPA is to be prescribed were instructed about the usage and postplacement care. poly-methyl--meth-acrylate acrylic allergy was ruled out through history/patch test before delivering this appliance to any subject. First 12 h after placement of NPA, all subjects were kept under observation in sleep lab overnight to observe any adverse effects. Subjects were also trained in wearing the appliance during this period. Subjects with exaggerated gag-reflex and irritability were advised to discontinue NPA and were withdrawn from further participation in the study (there was a 6% overall dropout rate based on this reason). All subjects were trained in appliance wear for 3 weeks prior to the UA imaging analysis of Group B with MRS [Figure 5] and Group C subjects with NPA [Figure 6] [Figure 7] [Figure 8].
Figure 5: Group B subject with mandibular repositioning splint

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Figure 6: Nasopharyngeal appliance

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Figure 7: Group C subject with nasopharyngeal appliance

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Figure 8: Nasopharyngeal appliance - level of engagement of posterior extensions of the appliance

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Statistical analysis

The results obtained were tabulated and analyzed for statistical significance. Differences within and between control (Group A) to sample Groups B and C were analyzed by ANOVA statistical test (P < 0.0001) and post-hoc test. Statistical analysis was done between Groups B and C to compare the treatment outcomes of MRS and NPA using ANOVA test (P < 0.0001).


   Results Top


Airway patency values (in mm 2 ) for subjects in Group A (mean: 423.9), Group B without and with MRS (mean: 288.1 and 375.7), and Group C without and with NPA (mean: 280.5 and 406.4) were noted and statistical analysis done (P < 0.0001) [Table 2]. 3D UA measurements (volume, a-p width, lateral width and area at retroglossal and retropalatal regions) were calculated for all three groups with Groups B and C before/after MRS/NPA placement (mean values of UA volume in mm 3 - Group A: 9929.2, Group B without and with MRS: 9025.8, 9387.2, and Group C without and with NPA: 9006.2, 9896.7, respectively) [Table 3]. Statistical analyses were done to evaluate differences within and between control (Group A) to sample Groups B and C and results tabulated [Table 4] and [Table 5]. Statistical analysis was done between Groups B and C to compare the treatment outcomes of MRS and NPA [Table 6]. The null hypothesis was rejected based on the outcome of the statistical analysis.
Table 2: UA patency (surface area) values for control and sample Groups (in mm2)


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Table 3: Mean values of three - dimensional UA measurements


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Table 4: Analysis of UA dimensions within and between control (Group A) to sample groups (Groups B and C)-ANOVA test


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Table 5: Analysis of UA dimensions within and between control (Group A) to sample Groups (Groups B and C) -Post-hoc test


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Table 6: Analysis of treatment outcomes between MRS (Group B) and NPD (Group C)-ANOVA test


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Results revealed that subjects in Group A exhibit significantly higher values of UA patency, volume, area, anterior-posterior and lateral widths at retroglossal and retropalatal regions than Group B and C subjects [Figure 9]. Subjects in Group C showed better improvement in the airway dimensions after NPA placement than subjects in Group B after MRS placement [Figure 10].
Figure 9: Histogram revealing comparison of upper airway dimensions - Group A (control) to Groups B and C

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Figure 10: Frequency polygon comparing treatment outcome - between mandibular repositioning splint (Group B) and nasopharyngeal device (Group C)

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   Discussion Top


UA, a dynamic constituent of respiratory system, is contemplated to influence SE by altering airflow during sleep, resulting in RERA. UA consists of two components: muscular and collapsible oropharyngeal region; cartilaginous laryngeal-tracheal regions. The fundamental dissimilarity between these two segments results in inherent collapsible tendency of UA during sleep. Unlike cartilaginous component, muscular segment of oropharynx is dependent on muscle tonus and head posture for patency.

It is affirmed that sleep influences changes in skeletal-muscle tonus such as: Decreases tonus during NREM sleep Stages II, III, and IV of sleep; [16] partial muscle paralysis during REM sleep stage due to the action of inhibitory neurotransmitter Glycine. During respiratory airflow, a balance of forces must exist between dilatory and collapsible forces of pharyngeal and primary respiratory muscles, respectively. [17] This balance is lost during sleep as a result of reduced skeletal-muscle tonus.

It can be hypothesized that reduction in muscle tonus and loss of balance between forces can result in reduced UA dimensions during sleep. This may act as a risk factor for reduced SE with SF and MA secondary to respiratory disturbance, a condition termed as UARS. The assumption that UA reduction during sleep affects SE was tested by this study.

Region specificity of UA obstruction is critical in management of UARS. Increased collapsibility of UA and reduced dilatory muscle activity during inspiration are considered vital for identifying the region of obstruction. [18] Importance of velopharynx and posterior palatal regions in UA obstruction has been affirmed. [19] It is documented [20] that 56-75% of UA obstruction in OSA subjects show initial obstruction in oropharyngeal and retropalatal regions; 25-44% at base of tongue and 0-33% at hypopharynx. A proportionally longer soft palate is considered as risk factor for respiratory disturbance in sleep. [21] The area posterior to soft palate is stated as site of inspiratory narrowing during sleep in majority of normal subjects and important site of pharyngeal collapse in OSA patients. [22]

It is evident from such observations that pharyngeal and soft palatal muscles play a critical part in UA dimensional changes during sleep. Nevertheless, current modalities of managing UARS with OA intend to prevent UA obstruction by positioning tongue in anterior relation and preventing airway obstruction by tongue fall back. MRS is the commonly preferred OA therapy for UARS, and it does not approach/resolve the obstructions at velopharyngeal/soft palate/nasopharyngeal regions. Also, long term usage of MRS in OSA/UARS patients has been proven to cause tooth migration, [23] occlusal alterations, [24] and craniofacial postural changes. [25]

A new appliance design, NPA, put forward by the principal author of this manuscript elsewhere, [7] was proposed for managing UARS by correcting UA obstruction at nasopharyngeal/soft palate regions. Preliminary evaluations and comparison of treatment outcomes revealed better results with NPA than MRS. [7] The current study was designed to categorically evaluate effectiveness of NPA in improving UA dimensions during sleep in UARS subjects in comparison with healthy subjects.

Diagnostic overnight polysomnography was done for all the subjects as it is considered a reliable diagnostic tool for sleep evaluation. [26] SFI was used for evaluating SF and arousals since it is asserted as a practical tool for sleep analysis. [27]

Imaging was done when a subject was in NREM Stage 2 of sleep as shown by polysomnographic data and with subject in supine position, as supine position is shown to increase the airway collapsibility than lateral recumbent position [28] and head rotated supine position. [29] NREM Stage 2 of sleep was chosen with two justifications: Partial muscle paralysis is a characteristic of REM sleep stage, [16] thereby increasing collapsible tendency of UA even in healthy individuals and making the differentiation between healthy and UARS subjects very difficult; NREM Stage 2 of sleep accounts for 45-50% of total sleep cycle [16] and has a significant role in UA obstruction related sleep disturbance.

Cephalometric analysis, previously used for UA imaging, is considered inadequate [30] and CT imaging analysis is stated to be useful for assessing UA dimensions. [31] 3D CT imaging and computerized analysis have been used for UA imaging in OSA subjects with affirmative results, [32],[33],[34],[35] justifying the choice of 3D CT imaging analysis as a methodology for the current study.

Statistical analysis of data revealed that subjects in Group A (control) exhibit higher values UA dimensions than Groups B and C subjects [Figure 9]; Subjects in Group C showed better improvement in the UA dimensions after NPA placement than Group B after MRS placement [Figure 10].

From these findings, conclusions were derived for the sample: There is definite association between reduced UA dimensions and reduced SE, high MA, and SF; NPA can give better treatment outcome than MRS by improving the UA dimensions. The null hypothesis was rejected based on these verdicts.

On a summarizing note, the theme of this research was to develop a new appliance for management of UARS based on the principle of "cause-effect-management" triad. Existing modalities of OAs intend to correct the constriction of UA during sleep by preventing tongue "fall back." Recent clinical reports and trials have been stated in literature regarding new OA modalities for management of UARS and OSA which have been proven to be effective. [36],[37],[38],[39] These existing and recently reported appliance designs basically prevent UA narrowing by engaging the retroglossal zone only. Nevertheless, documented literary evidence, as discussed earlier, suggests that retropalatal zone is the more common area of UA narrowing during sleep. [18],[19],[20],[21],[22] A new appliance design (NPA) for management of UARS by correcting the retropalatal zone of constriction during sleep was stated by the principal author elsewhere and preliminary analysis was done to test the efficacy. [7] This research was planned to critically analyze the effectiveness of NPA by comparing it with conventional MRS through a definitive, 3D imaging analysis of UA. The findings of this study indicate that NPA can produce better desired outcome of improved UA dimensions during sleep in UARS subjects. Also, it is asserted that 3D CT imaging analysis of UA during sleep can be used as a reliable tool for definitively diagnosing UARS subjects and also for assessing posttreatment outcome after appliance placement.


   Conclusions Top


The null hypothesis stated in the research design was rejected for the sample. Generalizing this decision to the population was done with satisfactoriness, since probability sampling method by random assignment was followed during subject inclusion. Hence the research findings lead to following conclusions.

  1. Adult subjects with susceptibility of reduced UA dimensions during sleep will exhibit sleep fragmentation, MA, and reduced SE in comparison to subjects without reduction in UA dimensions during sleep
  2. Nasopharyngeal appliance (NPA) is more efficient than MRS in improving the UA dimensions during sleep in UARS subjects as based on the findings from this study
  3. Additionally, derived conclusions were attained from the findings of this study as stated below
  4. Management of UARS should be based on the zone of constriction of UA, rather than based on the severity of symptoms as it is commonly perceived. This study with 3D imaging of UA demonstrated the different possible zones of UA constriction, thereby advocating the importance of categorizing UARS subjects based on zone of constriction and managing each type consequently as according to "cause-effect-management" principle
  5. It can be ascertained from the study that NPA can be a better OA modality in managing specific type of UARS subjects who have a retropalatal zone of UA constriction, since this appliance engages the retropalatal zone of UA
  6. As the retropalatal zone is affirmed in the literature as the more common area of UA narrowing, NPA can have a major role in management of UARS subjects, among all the OA modalities.
Acknowledgments

(1) The research was supported in groundwork by Prof. Hajime Minakuchi and Prof. Takuo Kuboki, Department of Oral Rehabilitation and Regenerative Medicine; (2) Institutional Review board-Okayama University Graduate School of Medicine-Dentistry and Pharmaceutical Sciences-2-5-1, Shikata-cho, Kita-ku-Okayama, Japan-7008525. (3) Preliminary study was pursued on the topic through International Scientific Exchange of Indian Prosthodontic Society and Japan Prosthodontic Society. (4) Progressive research was supported by Directorate of Research-Faculty of Medical Sciences-SRM University-India-603203. (5) Prof. B. Muthukumar, Head, Department of Prosthodontics-SRM Dental College-SRM University-Ramapuram-Chennai. (6) Development of 3D CT Imaging was guided by Takumi Ogawa and Yuko Shigeta-Tsurumi University and Junior College, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama-shi, Japan.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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Correspondence Address:
R Venkat
Department of Prosthodontics, SRM Dental College, SRM University, Ramapuram, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.172021

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