Indian Journal of Dental Research

ORIGINAL RESEARCH
Year
: 2005  |  Volume : 16  |  Issue : 4  |  Page : 147--50

Pharyngeal airway changes following mandibular setback surgery


Ramesh V Babu, Vinod Narayanan, K Murugesan 
 Department of Oral and Maxillo facial Surgery, Saveetha Dental College & Hospitals,162/Poonamallee High Road, Chennai 600 077, India

Correspondence Address:
Vinod Narayanan
Department of Oral and Maxillo facial Surgery, Saveetha Dental College & Hospitals,162/Poonamallee High Road, Chennai 600 077
India

Abstract

Treatment of dentofacial deformities with jaw osteotomies has an effect on airway anatomy and therefore mandibular setback surgery has the potential to diminish airway size. The purpose of this study was to evaluate the effect of mandibular setback surgery on airway size. 8 consecutive patients were examined prospectively. All patients underwent mandibular setback surgery. Cephalometric analysis was performed preoperatively and 3 months post operatively with particular attention to pharyngeal airway changes. Pharyngeal airway size decreased considerably in all, patients thus predisposing to development of obstructive sleep apnea. Therefore, large anteroposterior discrepancies should be corrected by combined maxillary and mandibular osteotomies.



How to cite this article:
Babu RV, Narayanan V, Murugesan K. Pharyngeal airway changes following mandibular setback surgery.Indian J Dent Res 2005;16:147-50


How to cite this URL:
Babu RV, Narayanan V, Murugesan K. Pharyngeal airway changes following mandibular setback surgery. Indian J Dent Res [serial online] 2005 [cited 2020 Sep 25 ];16:147-50
Available from: http://www.ijdr.in/text.asp?2005/16/4/147/29906


Full Text

 INTRODUCTION



Treatment of dentofacial deformities with jaw osteotomies has an effect on oropharyngeal morphology. Consequently, mandibular advancement has been successfully used to increase airway size in patients with obstructive sleep apnea However, less encouraging results have also been published. On the other hand, mandibular setback surgery is known to reduce airway size [3].

Reduction in airway space after setback surgery had probably been a causative factor in the patients developing partial upper airway obstruction [3],[10]. Hence, interest was evoked in studying other patients treated with the use of the sane approach.

The aim of the study was to evaluate the long term effect of mandibular setback surgery on airway size and particularly, to examine whether the presented patient had any specific features, which may have contributed to the development of partial upper airway obstruction.

 MATERIALS AND METHODS



The study consisted of 8 patients whose mean age was 22years. All the patients included in the study were male patients.

All the patients with natural dentition and good quality pre-operative and post operative lateral cephalograms were included for the investigation, all of them underwent mandibular set back surgery alone to correct their skeletal class III discrepancy.

Surgical technique included bilateral sagittal split osteotomy (Epker Modification) with maxillo-mandibular fixation (MMF) for six weeks in all the cases [Figure 1,2].

Lateral cephalograns were performed with the subject standing with his head in cephalometer in a natural head position and teeth in the intercuspal position. A tracing was made on each cephalogram and conventional hard and soft tissue cephalometric points.

The following are the skeletal and pharyngeal reference points on lateral skull radiograph [Figure 3].

Pharyngeal Points

TB - Point on posterior aspect of tongue closest to dorsal pharyngeal wall

UP - Point on posterior aspect of soft palate closest to dorsal pharyngeal wall.

PhW1- Point on dorsal pharyngeal wall closest to TB

PhW2- Point on dorsal pharyngeal wall closest to UP

The linear measurement between TB and PhW 1 was calculated parallel to frank fort horizontal plane preoperatively and post operative at the interval of 3 months.

Similarly linear measurement between UP and PhW2 was calculated parallel to Frankfort horizontal plane preoperatively and post operatively at an interval of3 months.

'The difference between these readings established the amount of decrease in posterior airway size after mandibula setback surgery.

Preoperative and Postoperative SNB angles, ANB angles, Gonial angles, S-Na/MP angles, Na-S-Ah angles were measured and recorded.

Similarly preoperative and post operative linear measurements between ANS-Me, Na-Me, S-Go, S-Ah were measured and recorded.

All these additional readings were calculated to reveal possible association between changes in the mandibular parameters in relation to changes in airway sizes.

For both the preoperative and postoperative readings, mean values were calculated and noted. [Figure 4,5].

 RESULTS



Table 1

At operation and during the follow-up period, the SNB anglewas found to have decreased on an averageby 9°.

The ANB angle increased by an average of 4.8°which was statistically highly significant. There was a marginal decrease in the gonial angle i.e. 1.4°. There was no significant increase in anterior facial height i.e. (Na-Me) or in lower facial height (ANS-Me). On the other hand there was an average increase in the posterior facial height (S-Go) by 3mm. Hyoid bone showed anterior repositioning by 2.8° Preoperative airway size was found to be on average 15mm retropalatially and retrolingually in antero-posterior direction. Post operative airway size was found to be on an average 11 nun retro-palatially and 12mm retro-lingually respectively a decrease which was statistically significant. Analysis revealed a statistically significant correlation between decrease in airway and the mandibular measurements. Based on the results there was 26.6% of reduction in pharyngeal airway size in antero­posterior direction retropalatinally. There was 20% reduction in pharyngeal airway size in anteroposteriorly direction retrolingually.

 DISCUSSION



In the present study, airway size has been evaluated by using a 2 - dimensional view of a three dimensional structure. A good correlation between the airway dimension measured on lateral cephalograms and on 3 dimensional computer tomography has validated the use of the lateral cephalograms in airway size analysis [1],[7].

The development of helical CT scanning technique in combination with 3D rendering techniques enable the use of high quality 3D CT images [1],[2].

The information in the CT image data involves both hard and soft tissue structures. It is possible to design a 3D CT imaging technique to allow visualization of the pharyngeal airway. Hence in future, it is better to use 3D CT rendering techniques for these kind of study purposes [1].

Since adaptive changes are known to occur in soft and hard tissues, after osteotomies, it would be better if the patients were examined at intervals of 1 year, 2 years and 5 years postoperatively.

The present correlation analysis indicates that airway reduction is related to the amount of mandibular setback. Therefore, knowledge of minimal critical airway size would be of great importance when osteotomies are planned to avoid the possible development of sleep related breathing disorders.

Postoperatively, hyoid bone movement in an anterior direction suggests that this is a physiologic adaptation to prevent hyoid related encroachment on the pharyngeal airway [6],[7],[8].

Most studies indicate that hyoid bone returns to its original position at the long term followup [6]. In our study, we could not come to this conclusion as long tern follow up needs to be evaluated.

Pharyngeal airway space below 10mm at mandibular plane is one of the main indications for surgical treatment by maxillo mandibular advancement in patients with obstructive sleep apnea [9].

So one should be cautious when planning a surgical mandibular setback of more than 10mm. This is more relevant if the patient has a pharyngeal airway of less than 12-10mnn. For these patients, it might be better to consider maxillary advancement or split the difference and advance the maxilla halfway and set the mandible back over the remaining distance.

Obesity is a main cofactor contributing to sleep revealed breathing disorders [5]. Therefore, mandibular set back in patients with marked obesity should also be considered with caution.

Complete polysomnographic diagnosis, which is absolutely essential for all patients with sleep related breathing disorders (SRBD) is available in fully equipped laboratories [10]. These particular tests should be done preoperatively and postoperatively for similar studies with larger samples.

In our study, all the patients were lean and had no breathing difficulties postoperatively.

 CONCLUSION



There was 26.6% of reduction is pharyngeal airway size in antero-posterior direction retropalatinally and 20% in retrolingual direction.

In conclusion, it is evident that mandibular setback surgery may cause narrowing of the posterior airway and may be a causative factor in the gradual development of a breathing disorder like sleep apnea [4].

This may particularly occur if predisposing factors, such as specific craniofacial type and /or obesity are present or individual neuromuscular adaptation is insufficient to compensate for reduction in airway size [5].

Therefore, careful airway analysis should be performed, particularly in correction with large anteroposterior discrepancies.

Once indicated by skeletal and airway analysis, such cases should be corrected by combined maxillary and mandibular osteotomies.

In cases of minimal anteroposterior discrepancies, performing amaxillary osteotomy, rather than mandibular setback surgery may be considered.

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