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CEPHALOMETRIC NORMS FOR PAKISTANI SAMPLE FOR THE SKELETAL VARIABLES OF MCNAMARA ANALYSIS.

Byline: MASOOMA HAMEED, AMJAD MAHMOOD and ROZINA NAZIR

Abstract

Objective of the study was to determine cephalometric skeletal norms for Pakistani sample according to McNamara analysis.

It was a cross-sectional study, conducted on the standardized lateral cephalometric radiographs of 28 males and 72 females. Subjects falling in the age range of 18 to 23 years, having skeletal Class I jaw relationship, normal vertical dimension and no history of orthodontic treatment were included in the study. Lateral cephalometric radiographs were traced and McNamara analysis was performed. Both the maxilla (-0.2+-3.7mm) and mandible (-5.9+-1.3mm) were positioned backward. The mean of effective mandibular length and Frankfort to mandibular plane angle were found to be 124+-6.6mm and 25.0Adeg+-4.6Adeg respectively. The mean values of cephalometric variables for Pakistani adults were significantly larger than the McNamara established norms.

The current study results showed statistically significant differences in most cephalometric values of McNamara Analysis, between Pakistani adults and McNamara established norms. Pakistanis have distinct cephalometric values, therefore, for Pakistani Orthodontic and Orthognathic surgery patients it is advisable to use these as a standard in treatment planning.

Key Words: Cephalometric norms; McNamara analysis; Orthognathic surgery.

INTRODUCTION

Lateral cephalogram is one of the basic aids in diagnosis and treatment planning in orthodontics. Several cephalometric analyses have been introduced to diagnose and study the patients' malocclusion. McNamara analysis is one of the well-defined and specific analysis among them. This describes not only the position of teeth within bone but also the relationship of jaws with the cranial base.1 This made McNamara's analysis a suitable tool for the diagnostic purposes for both regular orthodontic patients as well as for orthognathic surgery and growth modification patients. In this analysis James McNamara studied European-American population and developed norms for them.2,3

Genetics play an important role in determining the facial characteristics of individuals. Hence, the variation in facial characteristics and diversity in the size and shape of different facial attributes ask for establishing norms for each ethnic group separately. The norms made by McNamara for European-Americans differ from those established for other ethnic groups. However, these norms are in routine use since several years, which is not justified both ethically and scientifically as it may result in false diagnosis leading to faulty treatment plan. These ethnic variations in cephalometric norms have also been reported in many previous studies.2,3

Khan et al4 conducted a study to establish norms according to Jaraback's analysis for Pakistani population and compared the mean of cephalometric values with Jaraback's norms. According to results, there were significant difference in mean values between Pakistani sample and Caucasians.

Shaikh et al5 made cephalometric norms for esthetically pleasing Pakistani faces and compared them with established norms for Caucasians. The study results showed significant difference in the mean cephalometric values between Pakistani population and Caucasians.

Several studies6-9 were conducted to establish cephalometric norms for Pakistani population. However, none of them established the norms for the McNamara analysis. Since, reliable norms for Pakistani subjects are not available yet; European-American norms are being used for the assessment of orthodontic patient. This rationality stimulated the authors to conduct this study with an aim to determine the cephalometric skeletal norms for Pakistani sample using McNamara analysis.

METHODOLOGY

Current study was approved from Ethical Review Committee of Margalla Institute of Health Sciences, Rawalpindi (MIHS). Informed written consent was taken from the patients fulfilling the inclusion criteria. Total 540 patients' records were taken from the archive of orthodontics department of MIHS and analyzed, out of them 100 patients (28 males and 72 females) met the inclusion criteria. Patients falling in the age 18-23 years,4 skeletal Class I relationship (ANB angle 0-4o)10 with normal vertical skeletal dimension (SNMP 25.5Adeg +- 5.3Adeg)11 were included. Patients with history of orthodontic treatment, trauma, any syndrome and patients undergone orthognathic and plastic surgery were excluded from study.

Lateral Cephalograms of the selected patients were taken and McNamara analysis was performed using lead pencil (Goldfish HB with 0.5mm lead thickness) on tracing sheets (sheet of transparent lead acetate paper measuring 8X10 inch and 0.003 inch thickness) and readings were noted. All statistical analyses were performed using SPSS 21.0. Descriptive statistics (mean and standard deviations) were calculated for all cephalometric variables. To estimate the error of method, 30 Cephalometric radiographs were randomly selected and were retraced and re-measured in an interval of one month by a colleague. Method errors were calculated by using Dahlberg's formula.12 The t test was employed to compare the mean cephalometric values of Pakistani adults with McNamara established norms. The results of the test were considered significant at p < 0.05.

TABLE 1: CEPHALOMETRIC MEASUREMENTS USED IN MCNAMARA ANALYSIS

McNamara variables###Definitions13

Point A to Nasion perpendicular###A vertical line is constructed perpendicular to the Frankfort horizontal

(Point A-NP)###and extended inferiorly from the nasion. The perpendicular distance

###is measured from point A to the nasion perpendicular.

Pog to Nasion perpendicular###The perpendicular distance is measured from the pogonion to the

(Pog-NP)###nasion perpendicular.

Effective midface length (Co-point A)###Distance from condylion (Co) to point A.

Effective mandibular length (Co-Gn)###Distance from condylion (Co) to anatomic gnathion(Gn).

Maxillo-mandibular difference###Effective midface length minus effective mandibular length.

(Mx-Md differential)

Lower anterior face height (Ans-Me)###A line is measured from the anterior nasal spine to the menton.

Frankfort to Mandibular plane###The angle between the anatomic Frankfort plane and the mandibular

angle (MP-FH)###plane, Gonion-Menton.

TABLE 2: COMPARISON BETWEEN CEPHALOMETRIC MEAN OF PAKISTANI ADULTS ND MCNAMARA NORMS

S.###Variables###Present Study###McNamara Norms

No.###P value

###Mean###SD###Mean###SD

1###Point A-NP (mm)###-0.2###+-3.7###0.4###+-2.3###0.06

2###Pog-NP (mm)###-5.9###+-1.3###-1.8###+-4.5###0.003*

3###Co-point A (mm)###98.2###+-5.4###91###+-4.3###0.001*

4###Co-Gn (mm)###4.9###+-6.6###120.2###+-5.3###.04*

5###Mx-Md differential (mm)###26.8###+-3.7###29.2###+-3.3###0.05*

6###ANS-Me (mm)###68.9###+-4.8###66.7###+-4.1###0.06

7###MP-FH (Adeg)###25.0Adeg###4.6Adeg###22.7Adeg###+-4.3Adeg###0.04*

TABLE 3: COMPARISON BETWEEN CEPHALOMETRIC MEAN OF PAKISTANI MALES AND MCNAMARA NORMS

S.###Variables###Pakistani Males###McNamara Norms for

No.###Males###P value

###Mean###SD###Mean###SD

1###Point A-NP (mm)###-0.2###+-5.0###1.1###+-2.7###0.05*

2###Pog-NP (mm)###-6.1###+-6.0###-0.3###+-3.8###0.003*

3###Co-A (mm)###101.7###+-4.7###99.8###+-6.0###0.045*

4###Co-Gn (mm)###133.4###+-5.2###134.3###+-6.8###0.06

5###Mx-Md differential (mm)###31.8###+-4.4###34.5###+-4.0###0.06

6###ANS-Me (mm)###76.1###+-4.5###74.6###+-5.0###0.05*

7###MP-FH (Adeg)###24.90###+-5.70###21.30###+-3.90###0.04*

TABLE 4: COMPARISON BETWEEN CEPHALOMETRIC MEAN OF PAKISTANI FEMALES AND MCNAMARA NORMS

S.###Variables###Pakistani Females###McNamara Norms for

No.###Females###P value

###Mean###SD###Mean###SD

1###Point A-NP (mm)###-1.6###+-4.0###0.75###+-2.5###0.04*

2###Pog-NP (mm)###-6.7###+-6.5###-1.05###+-4.2###0.003*

3###Co-A (mm)###89.0###+-6.41###95.40###+-5.2###0.02*

4###Co-Gn (mm)###115.8###+-7.1###127.25###+-6.1###0.004*

5###Mx-Md differential (mm)###26.8###+-5.8###31.85###+-3.7###0.03*

6###ANS-Me (mm)###68.0###+-6.3###70.65###+-4.5###0.06

7###MP-FH (Adeg)###25.19Adeg###+-5.4Adeg###22.0Adeg###+-4.1Adeg###0.05*

RESULTS

There were total 100 patients, 28% (n=28) males and 72% (n=72) females. Descriptive statistics (mean and standard deviations) were calculated for McNamara cephalometric variables. Method error for linear and angular measurements was calculated by using Dahlberg's formula. Method errors of cephalometric measurements was calculated to be less than 0.9 mm for linear measurements and 0.5Adeg for the angular measurements which were insignificant.14

The mean cephalometric values of Pakistani adults and comparison with McNamara established norms are shown in Table 2. The maxilla Point (A-NP=-0.2+-3.7mm) and mandible (Pog-NP=-5.9+-1.3mm) were placed posterior to cranial base. The mean effective midface (Co-point A) and mandibular length (Co-Gn) were 98.2+-5.4mm and 124+-6.6mm respectively. The mean of lower anterior facial height (ANS-Me) and FH to mandible plane angle (MP-FH) were 68.9+-4.8mm and 25.0Adeg +-4.6Adeg respectively.

The mean cephalometric values of Pakistani males and comparison with McNamara established norms are shown in Table 3. In Pakistani adult males, maxilla point (A-NP=-0.2+-5.0mm) and mandible (Pog-NP=-6.1+-6.0mm) were placed posterior to cranial base. The mean effective midface (Co-point A) and mandibular length (Co-Gn) in adult Pakistani males were 101.7 +-4.7mm and 133.4+-5.2mm respectively. The mean of lower anterior facial height (ANS-Me) and FH to mandibular plane angle (MP-FH) were 76.1.9+-4.5mm and 24.9Adeg+-5.7Adeg respectively.

The mean cephalometric values of Pakistani females and comparison with McNamara established norms are shown in Table 4. In Pakistani adult females, maxilla (A-NP=-1.6+-4.0mm) and mandible (Pog-NP= -6.7+-6.5mm) were placed posterior to cranial base. The mean effective midface (Co-point A) and mandibular length (Co-Gn) were 89.0 +-6.4mm and 115.8+-7.1mm respectively. The mean of lower anterior facial height (ANS-Me) and FH to mandibular plane angle (MP-FH) were 68.1.9+-6.3mm and 25.49Adeg+-5.7Adeg respectively.

DISCUSSION

It has been observed that variables like racial origin, gender, age and face type contribute to facial variation. Skeletal and dental differences between racial groups were considerable. These differences play an important role in deriving objectives for achieving excellent orthodontic treatment results for any specific population.

Current study determined skeletal cephalometric norms for Pakistani sample according to McNamara analysis and compared the mean values with McNamara established norms. The study results were similar to Al Jasser and Garcia study results who found racial differences in their research, but they performed another analysis instead of McNamara analysis in their study.15,16,17

Aljame et al18 found that adolescent Kuwaitis had reduced chin prominence and steeper mandibular plane angle that resulted in increased profile convexity. These findings showed similarities to the current study's results by observing reduced chin prominence but posteriorly placed pog was the contributing factor for reduced chin prominence in current Pakistani sample. Frankfort to mandibular plane angle was found to be normal in current study.

Al-Barakati and Talic1 conducted a study, in which total 65 (36 males and 29 females) dental students of Saudi population were included to establish cephalometric norms according to McNamara analysis. They concluded that Saudi population had distinct facial features, convex profiles, increased lower facial height. Increased vertical dimension might explain tendency for backward mandibular growth rotation resulting in reduced chin prominence. While in current study reduced chin prominence was not due to increased facial height but due to backward position of pog from Nasion perpendicular. The mean of the cephalometric values were different from McNamara established norms but showed similarities to present study's results.

Miyajima and McNamara2 compared 54 Japanese adults with 125 European-American adults. The Japanese adults were having smaller sagittal facial dimensions, larger vertical facial dimensions and bimaxillary protrusion with an acute nasolabial angle. The facial axis angle in Japanese explained downward direction of facial development. Their study result was in contrast to current study observation, which observed greater antero posterior facial dimensions and bimaxillary retrognathism. Current study included the patients with skeletal class I jaw relationship while Japanese adults were selected on the bases of ideal occlusion with well balanced faces in their study.

Park et al19 described the skeletal pattern of Koreans and stated that they have a similar skeletal pattern as that of Caucasians, with slightly larger facial convexity and bimaxillary proclination. Hajighadimi20 conducted a study and concluded that Iranians had more retrusive skeletal pattern, convex profiles, high mandibular plane angle and bimaxillary dental protrusion. These findings are in partial agreement with current study's findings.

Alam et al21 established norms for Bangladeshi adults according to McNamara analysis and compared the mean cephalometric values with Caucasians norms. They stated that both the maxilla and mandible were positioned anterior to cranial base, which is in contrast to current study's results. Both the maxilla and mandible have a tendency to be positioned forward, but the mandible was more forward which gives a clinical impression of Class III skeletal pattern while current study observed tendency towards skeletal class II pattern with convex profile. Their study results showed dissimilarities from current study's findings, might be due to different study inclusion criteria which included only patients with Class I incisor relationship with satisfactory aesthetics.

The results of the current study established that the norms made for specific population should be used as standard for successful orthodontic treatment for that specific population and should not be used for other populations. Further studies are required with larger sample size to get more results that are significant.

CONCLUSION

When compared McNamara established norms with the current study, it was observed that Pakistani subjects displayed distinct facial features, greater convex profiles, reduced chin prominence and tendency towards Class II facial pattern. Therefore, Pakistanis have distinct cephalometric values, so for Pakistani Orthodontic and Orthognathic surgery patients it is advisable to use these as a standard in treatment planning.

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Publication:Pakistan Oral and Dental Journal
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Date:Dec 31, 2017
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