Correlation of Pharyngeal Airway Dimensions with Maxillomandibular Skeletal Relation and Mandibular Morphology in Subjects with Skeletal Class I and Class II Malocclusions and Different Growth Patterns: A Cephalometric Study in Selected Local Population.

OBJECTIVES: To test the hypothesis that there is no positive correlation between skeletal Class II and mandibular morphology with pharyngeal dimensions in subjects with different growth patterns.
MATERIALS AND METHODS: Lateral cephalograms of 60 patients were collected and divided into 2 groups, comprising of 30 in each group. Group 1 consisted of cephalograms of patients having Class I malocclusion, and was further divided into subgroups. 1a) Class I with normal growth 1b) Class I with vertical growth. Group 2 consisted of cephalograms of patients having class II malocclusion and was further divided into subgroups 2a) Class II with normal growth, 2b) Class II with vertical growth.
RESULTS: The results showed that the estimated marginal mean for upper pharyngeal width in class I malocclusion group was 8.56 mm, for class II malocclusion group was 7.80 mm, for normal growth individuals was 9.73 mm and that for vertical growth individuals was 6.63 mm. The estimated marginal mean for lower pharyngeal width in class I malocclusion group was 9.62 mm, in class II malocclusion group was 9.10 mm, in normal growth individuals was 8.95 mm and that in vertical growth individuals was 9.77 mm. The estimated marginal mean for pharyngeal area in class I malocclusion group is 330.13 sq.mm, in class II malocclusion group is 308.17 sq.mm, in normal growth individuals is 328.47sq.mm and that in vertical growth individuals is 309.83 sq.mm.
CONCLUSIONS: The null hypothesis for this study, as per the statistical analysis, has been rejected. Copyright:

INTRODUCTION

The size of the nasopharyngeal airway space is of importance in its relationship to the morphology of the face, the mandible included, because with reduction of the nasopharyngeal airway space, nasal breathing becomes difficult or impossible, and mouth breathing becomes necessary.[1]

Some authors associated mouth breathing and Class II malocclusions, and others reported associations of vertical growth patterns with obstruction of the upper and lower pharyngeal airways concurrently with mouth breathing. If this relationship actually exists, Class II malocclusions and vertical growth patterns must have natural anatomical predisposing factors.[23456]

Thus it may be hypothesised that mandibular morphology and position are closely associated with the dimensions of the airway. Taking all the above factors into consideration, it was decided to evaluate the correlation between pharyngeal airway dimensions, mandibular morphology and maxillomandibular skeletal relation

AIMS AND OBJECTIVES

Comparative evaluation of pharyngeal width in skeletal class I subjects with that in skeletal Class II subjects,

Comparative evaluation of pharyngeal width and height with mandibular ramus width and height in subjects with Class I malocclusion and Class II malocclusion and with either normal or vertical growth pattern.

Comparative evaluation of the area of pharyngeal space in subjects with Class I and Class II malocclusion and with either normal or vertical growth pattern.

MATERIALS AND METHOD

Lateral cephalograms of 60 patients were collected from the existing records.

Inclusion Criteria: Subjects with no previous orthodontic treatment, Subjects with skeletal Class I malocclusion and skeletal class II malocclusion, 8 to 14 years of age. Selection criteria for Class I malocclusion -ANB of 2° ± 2°, WITS analysis of 2mm to -3mm. Selection criteria for Class II malocclusion- ANB>4°, WITS analysis >2mm. Selection criteria for growth pattern -Angle used to determine the growth pattern was FMA(°) according to Downs analysis - normal growth(17° – 28°), vertical growth pattern ( > 28°). Exclusion Criteria: Craniofacial deformities, Asymmetries, Missing teeth, History of sleep disorders, snoring, sleep apnea, Adenoidectomy, pathology in the pharynx,horizontal growth patterns.

METHOD OF STUDY

Group 1 consisted of cephalograms of Class I malocclusion, divided into subgroups as 1a) Class I with normal growth and 1b) Class I with vertical growth

Group 2 consisted of cephalograms of class II malocclusion, divided into subgroups as 2a) Class II with normal growth and 2b) Class II with vertical growth

All the cephalograms were traced manually on acetate paper by 1 investigator using the viewer box in a dark room. Within a week after the first measurement, 20 (5 from each group) randomly selected radiographs were retraced and remeasured by the same examiner. The casual error according to Dahlberg's formula (Se2 = d2/2n)[7] and the systematic error with dependent t tests at P .05 were calculated.

The following cephalometric measurements were selected for pharyngeal dimensions.

Pharyngeal height (distance Pht) as: between points Pn'and Pp'. [Figure 1]

Figure 1

Superimposition

Width of pharynx is measured as per McNamara's Analysis. [Figure 1]

a) Upper pharyngeal width (distance a) as: distance between a point on the anterior half of posterior outline of soft palate to the closest point on the pharyngeal wall.

b) Lower pharyngeal width (distance b) as: distance between a point of intersection of posterior border of tongue and the inferior border of mandible to the closest point on the posterior pharyngeal wall.

Statistical Analysis methods:

Software usedfor statistical analysis is Windows based statistical package Medcalc® version 12.7.5.0 (MedCalc Software bvba, Ostend, Belgium; http://www.medcalc.org; 2013). Measurement data is expressed as means with SEM. All testing is done using 2-sided tests with alpha 0.05.

The pharyngeal and mandibular dimensions were compared for differences using a Two-Way ANOVA with class as first factor and growth as second factor.

RESULTS

The findings have been tabulated in [Tables 1 and 2], and the significant changes have been highlighted as bold.

Table 1

Mean upper pharyngeal width (mm) in different classes and growth types

	n	Mean	SEM	95% CI	Mean difference	95% CI for difference	‘p’
Class type
Class I	30	8.57	0.47	7.62-9.50	0.77	−0.56-2.09	0.25
Class II	30	7.80	0.47	6.86-8.74
Growth type
Normal	30	9.73	0.47	8.79-10.67	3.10	1.77-4.43	<0.0001
Vertical	30	6.63	0.47	5.69-7.57

SEM: Standard error of mean, CI: Confidence interval

Table 2

Mean upper pharyngeal width (mm) in sub-groups

Class type	Growth type	n	Mean	SEM	95% CI
Class-I	Normal	15	9.27	0.66	7.94-10.59
	Vertical	15	7.87	0.66	6.54-9.19
Class-II	Normal	15	10.20	0.66	8.87-11.52
	Vertical	15	5.40	0.66	4.07-6.73
Two-way ANOVA	Sum of squares	df	Mean square	F	‘p’
Class	8.8	1	8.82	1.34	0.252
Growth	144.15	1	144.15	21.93	<0.001
Class*Growth	43.35	1	43.35	6.59	0.013

Significant changes have been highlighted as bold. SEM: Standard error of mean, CI: Confidence interval

DISCUSSION

A number of researchers during the last 50 years used variety of radiographs to study the pharyngeal airway space.[8910] Cameron et al, in their study compared computed tomography (CT) and cephalometric films in subjects with skeletal malocclusion and found a significant positive relationship between nasopharyngeal airway size on cephalometric films and its true volumetric size as determined from CBCT scan in adolescents.[8] Though, in this day and age, CBCT offers accurate three dimensional information about the extent of the airway, cephalograms are more easily accessible and offer a more economical and reasonably reliable estimate of 2- dimensional pharyngeal space measurements. Also the radiation exposure for CBCT ( 0.15 mSv) is higher as compared to lateral cephalometric exposure (0.03 mSv).[11]

Results showed that subjects with Class I and Class II malocclusions and vertical growth pattern had significantly narrower upper pharyngeal airway [Table 1] than Class I and Class II subjects with normal growth pattern confirming the previous studies.[2121314]. In subjects with vertical growth pattern the saddle angle is increased which leads to a more downward and forward position of the superior wall of the pharynx resulting in a narrower upper pharyngeal airway measurement.

The upper airway width showed no significant association with type of malocclusion; this corroborated previous findings.[15]

Mandibular ramus width and pharyngeal height showed a more positive correlation for class II malocclusion type and normal growth pattern as the mandibular plane was more horizontal and therefore resulted in a larger measured pharyngeal height.

This study showed that the upper pharyngeal width was found to be narrower in individuals with vertical growth pattern as compared to individuals with normal growth pattern, in both Class I and Class II malocclusions.

CONCLUSIONS

Our results showed that,

Sagittal malocclusion type does not influence upper pharyngeal width. Malocclusion type and growth pattern do not influence lower pharyngeal airway width

Mandibular ramus height and pharyngeal height showed a more positive correlation for class I malocclusion type and normal growth pattern. No significant correlation was found between mandibular ramus width and pharyngeal width for malocclusion type in either normal or vertical growth pattern subjects.

The null hypothesis for this study therefore, has been rejected