Airway Analysis in Skeletal Class I and Class II Subjects with Different Growth Patterns: A 2D Cephalometric Study.

OBJECTIVE: A two-dimensional cephalometric study was carried out to assess the airway among individuals with Class I and Class II skeletal base.
MATERIALS AND METHODS: Class II subjects were further categorized into horizontal and vertical growers and average growth patterns to check the possible relationship between the facial skeleton and pharyngeal airway. Lateral cephalograms of 150 subjects were obtained using standard protocol in natural head position (NHP). Nasopharyngeal and oropharyngeal linear, and angular and nasopharyngeal area measurements were obtained using standardized tracing technique. Analysis of variance (ANOVA), level of significance, and post hoc Turkey's test were performed to assess the correlation between skeletal pattern of the individual and airway dimension. Gender discrimination was assessed using independent sample t test.
RESULTS: In linear measurements, significant differences were observed among upper pharynx (0.039), adenoid tissue 1 (0.036), and adenoid tissue 2 (0.01). In angular measurements, differences were observed with angle of nasopharynx (0.008). The nasopharyngeal area measurements were also associated with significant difference (0.038) with Class II vertical growers less than those with Class I average and Class II horizontal groups.
CONCLUSION: Class II vertical growers had significantly reduced nasopharyngeal airways. Copyright:

INTRODUCTION

The pharynx comprises nasopharynx and oropharynx. They carry out of the two important functions of stomatognathic system called respiration and deglutition efficiently and in unison.[1] The close relationship between the pharyngeal structures and the dentofacial complex pattern therefore attracts the orthodontist’s attention.[23]

Cephalometrics is an important diagnostic tool in orthodontics and helps for analyzing craniofacial complex for anatomic and spatial variations, thereby helping in diagnosis and treatment planning of the subject in question. Cephalometrics has been considered as the most widely used imaging and diagnostic modality in literature.[4]

There has been always a controversial debate between the airway obstruction and dentofacial developmental pattern. Watson et al.[5] studied relation between malocclusion and airway obstruction and concluded that no association existed between aforesaid parameters. Aronson[6] found positive correlation between craniofacial skeleton and airway adequacy carried out by rhinomanometric measurements. Hence, this study was undertaken to test whether there is any association between pharyngeal airway and type of malocclusion.

Aims and objectives

The aims of this study were to assess the airway dimensions in skeletal Class I and Class II individuals, and to evaluate the relationship between airway and growth pattern.

MATERIALS AND METHODS

The sample consisted of 150 subjects with age group of 17–25 years.

Patients enrolled in the present investigation were categorized based on cephalometric measurements for skeletal base and growth pattern. For assessing the anteroposterior jaw relations, ANB angle[1] and Beta angle[7] were considered. On the basis of these parameters, the sample was categorized into skeletal Class I and Class II. For assessing the growth pattern, FMA and Go-Gn-SN were chosen and were applied for Class II sample to categorize into horizontal and vertical growers.[8] Each group was further subdivided into males and females.

The groups include the following:

Twenty-five female subjects with skeletal Class I with average growth pattern

Twenty-five male subjects with skeletal Class I with average growth pattern

Twenty-five female subjects with skeletal Class II with horizontal growth pattern

Twenty-five male subjects with skeletal Class II with horizontal growth pattern

Twenty-five female subjects with skeletal Class II with vertical growth pattern

Twenty-five male subjects with skeletal Class II with vertical growth pattern

The inclusion criteria of the study included normal healthy subjects without clinical signs and symptoms of pharyngeal pathology and no prior history of orthodontic treatment.

Methods

The study was explained to all the subjects and informed consent was obtained. Digital cephalograms were obtained using a standardized technique.

Standardization for obtaining digital cephalogram

All the lateral cephalograms were recorded in natural head position (NHP). A mirror was placed one and half feet away from the cephalostat and the subject’s head was secured in cephalostat (Orthophos XG5/DR5/CEPH from Sirona, The Dental Company, New York, USA) and was asked to look into his own eyes with lips relaxed. The subject was also asked to clench on the posterior teeth adopting the position they normally show during the day. A bead line was hung from the roof of the cephalostat. The exposure parameters of the lateral cephalogram included exposure time: 9.4s, voltage: 73kV, and current: 15 mA.

Exposure is carried out following forceful expiration before next inspiration.[910] The subjects were instructed not to move the tongue and head and not to swallow during exposure. All the cephalograms were exposed with same exposure parameters and using the same machine.

The tracings were carried out by single calibrated examiner. Nasopharyngeal linear ([UP], [LP], [AD1], and [AD2]) [Figures 1 and 2], angular (saddle angle, angle of nasopharynx and vertical angle of nasopharynx) [Figure 3], and areal measurements [Figure 4] were calculated. The area of the bony nasopharynx is a trapezoid formed by the following planes:

Figure 1

Nasopharyngeal linear measurements

Figure 2

Nasopharyngeal linear measurements

Figure 3

Nasopharyngeal angular measurements

Figure 4

Nasopharyngeal area measurements

AA-PNS

Ba-N

Palatal plane

Pterygoid vertical

The trapezium is formed by superiorly by Ba-N plane; inferiorly by palatal plane extension; anteriorly by pterygoid vertical and posteriorly by Atlas Anterior line (AA). The area of the adenoid tissue contained within the trapezoid depicts the nasopharynx.[11]

Formula for calculating the area of naos pharynx is as follows: NP area = d [h – dtanϴ/2].

The cephalograms were also traced for oropharyngeal linear measurements (MPW, TPPW, and LPW) [Figure 5]. In total, 10% of the lateral cephalograms were retraced after 1 week to check for intra-examiner reliability.

Figure 5

Oropharyngeal linear measurements

All the analysis was performed using Statistical Package for the Social Sciences (SPSS) software program, version 14.0. Intergroup comparisons were performed using analysis of variance (ANOVA) test. If P value was significant, then a post hoc Turkey’s test was performed to check which two groups were statistically different from each other. A value of P < 0.05 was set to be statistically significant.

RESULTS

Nasopharyngeal measurements

In linear measurements, statistically significant differences were observed in the values of upper pharynx (UP), adenoid tissue 1 (AD1), and adenoid tissue 2 (AD2) with Class II vertical group less than those with Class I average group with P = 0.039, 0.036, and 0.01, respectively [Table 1].

Table 1

Definition of surface landmarks used in cephalometric analysis

Land mark	Abbreviation	Definition
Sella	S	The deepest point on the anterior curvature of the sella tursica
So	So	Midpoint of the sella basion line.
Nasion	N	The intersection of the internasal and frontonasal sutures , in the midsagittal plane
Anterior nasal spine	ANS	The tip of the bony anterior nasal spine at the inferior margin of the piriform aperture, in the midsagittal plane.
Posterior nasal spine	PNS	This is a constructed, radiographic, lateral cephalometric point, located at the intersection of the continuation of the anterior wall of the pterygopalatine fossa and the floor of the nose.
Subspinale	Point A	The deepest midline point on the premaxillae between the ANS and prosthion.
Supramentale	Point B	The most posterior point in the concavity between infradentale and pogonion.
Condylion	Co	The center of the condyle, found by tracing the head of the condyle and approximating its centre.
Porion	Po	The highest bony point on the upper margin of external auditory meatus.
Orbitale	Or	The lowest point on the inferior bony margin of the orbit.
Gonion	Go	It is a constructed point at the junction of ramal plane and the mandibular plane.
Gnathion	Gn	It is the most antero-inferior point on the symphysis of the chin.
Basion	Ba	The most posterior limit of the lowest point in the midline on the anterior margin of the foramen magnum.
Uvula	U	Tip of soft palate
Vallecula	V	The most posteroinferior point on the base of the tongue
Adenoid 1	AD1	Intersection of the line PNS-ba (basion) and the posterior nasopharyngeal wall
Adenoid 2	AD2	Intersection of the line PNS-midpoint of sella (so) and the posterior nasopharyngeal wall.
C2	CV2P	The most posterior point on the inferior margin of the outline of the body of the second cervical vertebra.

In angular measurements, the significant differences were found in angle of nasopharynx and saddle angle with Class II group less than those with Class I average group with P = 0.008 and 0.0190, respectively [Table 2].

Table 2

Nasopharyngeal angular measurements

S. no.	Parameter	Group	Mean	SD	P Value	Post hoc test
1	BA-S-PNS	Class I average ( 1 )	62.56	4.90	0.008	1 > 3
		Class II horizontal ( 2 )	60.92	4.0
		Class II vertical ( 3 )	59.72	4.55
2	S-BA-PNS	Class 1 average	61.12	7.49	0.825	–
		Class II horizontal	61.70	3.90
		Class II vertical	61.70	4.01
3	SA	Class I average (1)	126.16	4.16	0.019	3 > 1
		Class II horizontal (2)	127.82	4.97
		Class II vertical (3)	128.64	4.12

SD = standard deviation

P value less than 0.05 is considered significant

The areal measurements revealed vertical group values being less than those with Class I average group and Class II horizontal groups (P = 0.038) [Table 3].

Table 3

Nasopharyngeal area measurements

S. no.	Parameter	Group	N	Mean	SD	P Value	Post hoc test
1	NP	Class I average (1)	50	898.94	71.32	0.038	1 > 3
		Class II horizontal (2)	50	888.15	162.67
		Class II vertical (3)	50	838.68	122.31

SD = standard deviation

P value less than 0.05 is considered significant

Oropharyngeal measurements

No statistically significant differences were observed in any of the parameters as tested by ANOVA [Table 4].

Table 4

Oropharyngeal linear measurements

S. no.	Parameter	Group	N	Mean	SD	P Value	Post hoc test
1	MPW	Class I average	50	15.48	4.15	0.064	–
		Class II horizontal	50	13.96	3.81
		Class II vertical	50	14.02	2.8
2	TPPW	Class I average	50	12.62	2.83	0.168	–
		Class II horizontal	50	11.98	3.58
		Class II vertical	50	13.18	3.00
3	LPW	Class I average	50	19.44	4.67	0.226	–
		Class II horizontal	50	18.34	3.83
		Class 2 vertical	50	19.78	4.48

SD = standard deviation

No gender differences were observed following independent t test [Tables 5–7].

Table 5

Gender differences in nasopharyngeal linear measurements

Group	Parameter	Boys		Girls		P Value
		Mean	SD	Mean	SD
Class I average	UP	17.00	2.75	15.92	3.91	0.265
	LP	12.68	1.43	12.44	2.75	0.702
	AD1	30.52	6.14	29.00	5.01	0.342
	AD2	26.24	2.76	25.12	4.04	0.258
Class II horizontal	UP	16.84	3.87	15.48	2.89	0.166
	LP	12.36	2.74	11.76	3.21	0.48
	AD1	28.84	4.92	30.20	5.90	0.381
	AD2	24.56	2.02	23.40	3.07	0.121
Class II vertical	UP	14.76	2.88	15.00	2.94	0.772
	LP	12.68	2.28	12.16	2.72	0.468
	AD1	30.56	6.17	28.96	3.66	0.27
	AD2	24.36	3.21	23.92	2.80	0.608

UP = upper pharynx, LP = lower pharynx, AD1 = adenoid tissue 1, AD2 = adenoid tissue 2, SD = standard deviation

Table 7

Gender differences in oropharyngeal linear measurements

Group	Parameter	Boys		Girls		P Value
		Mean	SD	Mean	SD
Class I average	MPW	16.12	3.72	14.84	4.52	0.134
	TPPW	13.04	2.47	12.20	3.15	0.3
	LPW	20.4	5.47	18.48	3.56	0.148
Class II horizontal	MPW	13.88	3.32	14.04	4.32	0.884
	TPPW	12.6	2.94	11.36	4.09	0.225
	LPW	18.60	3.62	18.08	4.08	0.636
Class II vertical	MPW	14.52	2.08	13.52	3.34	0.21
	TPPW	13.72	2.7	12.64	3.25	0.208
	LPW	20.88	4.68	18.68	4.07	0.082
	LPW	20.88	4.68	18.68	4.07	0.082

SD = standard deviation

DISCUSSION

The higher frequency of nasopharyngeal obstruction in growing children and the association of it to the growth of craniofacial skeleton demands for an economical, easily assessable, simple tool to diagnose the airway obstruction. The adenoid size when assessed using lateral cephalograms was found to have clinically useful correlations particularly with respect to area measurements.[1213]

Lateral cephalograms of all the subjects were obtained in NHP with subjects standing in orthoposition.[141516] Cooke and Wei[171819] also stated that NHP reproducibility was better with mirror method. The exposure was carried out at the end of expiration before next inspiration as this method has the added advantage of recording airway better because during quiet breathing airway resistance is greater during expiration than inspiration.[910]

The use of lateral cephalometric radiographs to evaluate the airway is to an extent compromised as we are trying evaluate the complex three-dimensional (3D) structure of pharynx using 2D imaging.[18] Malkoc et al.[20] stated that “if certain technical requirements are fulfilled such as maintaining NHP, lateral cephalometry can provide useful information in estimating tongue and nasopharyngeal volume.” This observation was also made by Handelman and Osborne,[11] who found that lateral cephalograms give a decent picture of pharyngeal airway size among children of all age groups.

Class II vertical growers had significantly narrower upper pharyngeal airways than Class I average and Class II horizontal growers, confirming previous results in the literature of de Freitas et al.[8] and Dunn et al.[21] Analyzing these results, inference can be drawn that upper airway width is influenced by craniofacial growth.[21] The results of other linear nasopharyngeal measurements such as AD1 and AD2 also showed that individuals with Class II vertical growth pattern had significantly lesser values than Class I average and Class II horizontal growers [Table 1]. This was in accordance with the results of the studies of Martin et al.[14] No statistically significant difference was observed in lower pharynx values among the three groups. With respect to the angle of nasopharynx, Class II group had significantly lower values than Class I average group. No statistically significant differences were observed in relation to depth of nasopharynx among the three groups [Table 2].

The comparison of mean nasopharyngeal area values showed that subjects with Class II vertical growth pattern had significantly lower values compared to Class I average group [Table 3]. The comparison of mean oropharyngeal linear measurements showed that there were no statistically significant differences among the three groups [Table 4]. This is in accordance with the study of Ucar and Uysal,[22] on orofacial dimensions in different growth patterns. Linder-Aronson and Leighton[23] and Daraze et al.[24] suggested that “oropharyngeal space appears to be larger than normal when the nasopharyngeal airway is smaller,” although they did not evaluate this correlation directly.

The sample was also analyzed for gender discrimination in pharyngeal airways. No statistically significant differences were observed in nasopharyngeal and oropharyngeal measurements among the three groups.

CONCLUSION

The following conclusions can be drawn from this study:

Class II vertical growers have less nasopharyngeal linear measurements (UP, AD1, and AD2) than Class I average growers.

Class II vertical growers have less nasopharyngeal angular measurements (angle of nasopharynx) than class I average growers.

Class II vertical growers have less nasopharyngeal area than Class I average growers and Class II horizontal growers.

No statistically significant differences were observed in oropharyngeal linear measurements among the three groups.

No gender differences were observed in any of the parameters among the three groups.

Short comings of the study

The sample has been restricted to Class I and Class II groups. The sample can be broadened to include Class III subjects also.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 6

Gender differences in nasopharyngeal angular and area measurements

Group	Parameter	Boys		Girls		P value
		Mean	SD	Mean	SD
Class I average	BA-S-PNS	61.24	3.81	63.88	5.56	0.056
	S-BA-PNS	61.20	9.51	61.04	4.89	0.941
	SA	126.24	3.89	126.08	4.49	0.893
	NP	958.11	267.83	873.24	183.24	0.197
Class II horizontal	BA-S-PNS	60.08	3.46	61.76	4.39	0.14
	S-BA-PNS	62.64	4.03	60.76	3.60	0.088
	SA	127.56	6.21	128.08	3.43	0.716
	NP	905.39	151.68	870.92	174.34	0.459
Class II vertical	BA-S-PNS	59.60	4.17	59.84	4.98	0.854
	S-BA-PNS	61.96	4.17	61.44	3.92	0.651
	SA	128.12	3.98	129.16	4.27	0.378
	NP	872.35	135.48	805.00	99.13	0.051

SD = standard deviation