Cephalometric Norms in an Omani Adult Population of Arab Descent *

Objectives: This study aimed to establish cephalometric norms for an Omani population of Arab descent and to compare these with established cephalometric values for Caucasians. Methods: This cross-sectional study was conducted at the Military Dental Centre and Oman Dental College in Muscat, Oman, between May 2014 and October 2016. A total of 150 Omani patients between 20–29 years old seeking orthodontic treatment were included. All participants had a symmetrical face, class I molar and canine relationships, proper intercuspation, a normal overjet/overbite (<3 mm) and mild spacing/crowding of the teeth (≤3 mm). Lateral cephalography was performed in centric occlusion with the lips relaxed and the head in a natural position. Cephalometric measurements were then compared with Eastman Standard norms. Results: The Omani subjects were found to have a slightly retrusive maxilla, an increased angle between the maxillary and mandibular planes and shorter facial heights in comparison to the Eastman Standard norms. Furthermore, incisor relations were edge-to-edge in nature and the interincisal angle was reduced, suggesting that the Omani subjects had more proclined incisors. In addition, the lips were more protrusive and the nasolabial angle was more obtuse. Conclusion: In the Omani sample, increased proclination of the incisors was observed in comparison to Eastman Standard norms. As such, slightly more proclined incisors should be considered acceptable and natural among Omani patients of Arab descent. The cephalometric findings of this study may be helpful in the diagnosis and treatment planning of orthodontic problems among Omanis of Arab descent.

2][3] While minor differences between an individual's cephalometric values and those of the respective norms is routine, major differences may indicate a structural deviation.Knowledge of the T he diagnosis of potential orthodontic anomalies necessitates the comparison of an individual patient's cephalometric values with those of established norms. 1 However, the patient's ethnic background needs to be taken into consideration

Advances in Knowledge -To the best of the authors' knowledge, this study is the first to establish cephalometric norms for an Omani population of Arab descent.
Application to Patient Care -Establishing cephalometric norms for Omanis of Arab descent could help dentists to detect any orthodontic deviations for diagnostic or treatment purposes.

Methods
This cross-sectional study was conducted at the Military Dental Centre and Oman Dental College in Muscat, Oman, from May 2014 to October 2016.A sample of 150 Omani patients aged 20-29 years old seeking orthodontic treatment at these two institutions were selected.All subjects were of Arab descent from both parents' side, without any history of interracial marriages occurring for at least two generations.Each subject underwent a clinical examination by two orthodontists to ensure they had a symmetrical face (in which a line drawn from the forehead to the chin would yield measurements conforming to the mathematical concept of the golden ratio), class I molar and canine relations with proper intercuspation and an acceptable overjet and overbite (<3 mm), mild spacing/crowding (≤3 mm), no transverse discrepancies and no detectable lateral and sagittal way in which an individual's cephalometric values differ from accepted norms will allow clinicians to conclude whether the anomaly is dento-alveolar or skeletal in origin and undertake corrective measures if necessary. 4n a comparison of cephalometric norms between Egyptian adolescents and those of a sample in Iowa, USA, Bishara et al. concluded that Egyptian boys tended to have bimaxillary dental protrusion and greater posterior facial heights (PFHs), whereas Egyptian girls had mandibular dental protrusion and more convex skeletal profiles. 5In a Jordanian population, Hamdan et al. concluded that, in comparison to a British sample, Jordanians had reduced lower facial heights and more proclined upper incisors (UIs) and lower incisors (LIs); this finding was substantiated by a reduced interincisal angle. 3Al-Awwad et al. compared the cephalometric norms of a sample of adult Kuwaitis with those of previously published Caucasian norms, reporting that the Kuwaiti subjects had more proclined incisors and significantly more obtuse nasolabial angles; moreover, females had more protrusive lower lips with more proclined LIs compared to males. 6Another study found that adolescent Kuwaitis had a steeper mandibular plane (MN) and a more convex profile, with reduced chin protrusion and more protrusive dentition compared to published norms. 4halhoub et al. established cephalometric radiographical norms for Saudi Arabian adults by comparing normal facial proportions with a North American sample; the Saudi subjects showed reasonably normal dental relationships, with no severe anteroposterior, vertical or transverse skeletal discrepancies. 7In western Saudi Arabia, previous findings have suggested that western Saudis have an increased A point/ nasion/B point (ANB) angle due to the retrognathic shifts.Medically compromised subjects and those with congenital abnormalities, facial trauma, missing/ extracted teeth or a history of orthodontic treatment, orthognathic surgery or plastic surgery were excluded from the study, as such individuals were deemed not to represent the typical facial characteristics of an Arab Omani population.
The sample size was calculated using nMaster software, Version 1.0 (Department of Biostatistics, Christian Medical College, Vellore, India) based on the following formulae: Where Sp is the target population, Z is the confidence interval (1.96), a is the α error (assumed to be 1%), B is the β error (assumed to be 10% at a power of 90%), D is the effect size (i.e. the mean difference between males and females) and SD is the standard deviation.The mean and SD of randomly selected variables, including the ANB, sella/nasion (SN) line to the maxillary plane (MP) and the lower dental facial height (LDFH), defined as the distance between the LI tip to the MN, was estimated based on 15 male and 35 female subjects.The minimum sample size was therefore calculated to be 35 subjects of each gender.However, in order to improve the statistical power of the results, the sample size was increased to a total of 150 subjects.
All of the subjects underwent routine twodimensional (2D) lateral cephalography in centric occlusion with the lips relaxed and a natural head position, in which the Frankfort plane was parallel to the floor.The cephalograms were taken from a distance of 150 cm away using an Orthophos XG 5 SD X-ray unit (Dentsply Sirona, York, Pennsylvania, USA).Although three-dimensional (3D) cephalometric analyses have recently gained popularity, recent research has indicated that 3D analysis does not ensure more accurate results than conventional 2D analysis. 28Subsequently, digital versions of the lateral cephalograms were examined using Dolphin imaging software, Version 11.8 (Dolphin Imaging & Management Solutions, Chatsworth, California, USA).A single examiner identified anatomical landmarks on the cephalogram directly on the monitor using markings on a ruler to calibrate the magnification.
A dot was placed and moved around on the image until the examiner was satisfied that the position of the landmark had been accurately recorded.After all of the landmarks were clearly identified, various linear and angular measurements were automatically generated by the program [Figure 1].In order to assess if any errors were made while localising the landmarks, 10 random radiographs were retraced after three weeks to determine examiner error and confirm the reproducibility of measurements at a 95% confidence interval.There were very few measurement errors for all of the variables tested, except for PFH, measured from the sella to the gonion, which resulted in an intra-class correlation coefficient of 0.504 for the male subjects.Table 1 lists the definitions used in the measurement of each cephalometric parameter.Microsoft Excel, Version 2007, (Microsoft Corp., Redmond, Washington, USA), and the Statistical Package for the Social Sciences (SPSS), Version 10.0 (IBM Corp., Armonk, New York, USA), were used for data entry and analysis.The data were tested for normalcy as per previously described methods. 29The results were presented as means ± SD for continuous variables and numbers and percentages for discrete variables.Due to the large sample size and normal distribution of the results, parametric tests were applied.Each of the parameters for male and female subjects were compared using an independent samples t-test.1][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The level of statistical significance was set at P <0.050.
Ethical approval to conduct this study was obtained from the Research & Ethical Review & Approval Committee of the Ministry of Health in Oman (#MH/DGP/R&S/30/2013).All of the subjects included in the study were informed of the nature and purpose of the study and the radiographic procedures involved.Verbal consent was provided for the use of the radiographs for research purposes, under the condition that the subjects' anonymity was maintained.

Discussion
During orthodontic evaluation, a cephalometric analysis can reveal important anatomical information regarding the internal structures of the facial complex, particularly in terms of skeletal and dento-alveolar anomalies. 30While various cephalometric norms have been published in an attempt to define normal skeletal characteristics, most attempts have utilised populations of North American or European Caucasians. 10,11,31,323][34][35][36][37][38][39][40][41] The present study was undertaken to establish cephalometric norms for a young population of Omanis of Arab descent.[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] With regards to skeletal parameters, the Omani subjects had a significantly smaller SNA angle in comparison to the Eastman Standard norms, suggesting a retro-positioned maxilla. 12[39][40]42 Nevertheless, results  from the present study showed no significant difference with Eastman Standard norms regarding the sagittal relationship between the maxilla and the mandible (i.e. the ANB angle). 128][39][40]42 On the other hand, the angle between the palatal and MN planes was significantly higher among the current sample of Omani adults in comparison to Eastman Standard norms. 14Furthermore, the SN-MP angle was significantly higher among the Omani subjects by 1.57 degrees. 13It can therefore be concluded that Omanis have slightly more divergent basal planes, as well as a more caudally tipped palatal plane.This is in accordance with a previous study conducted in Saudi Arabia, but in contrast to Hamdan et al. 's findings among Jordanian adolescents. 2,36][17] Thus, it seems that Omanis have considerably smaller anterior facial heights, which is in accordance with Hamdan et al. 's findings. 3In addition, the upper PFH and overall PFH of the Omani subjects were significantly shorter, by 12.4 mm and 6.3 mm, respectively, compared to Eastman Standard norms. 13However, lower PFH was similar to that of Eastman Standard norms. 18This is in contrast to the findings of Bishara et al. and Behbehani  et al. among Egyptian and Kuwaiti adolescents, respectively. 5,37The Wits appraisal value for the studied Omani population was also significantly different to that of Eastman Standard norms. 19n terms of dental parameters, both the overjet and overbite values for the studied Omani population were significantly lower than those of Eastman Standard norms. 20,21Moreover, the angles between the UI and MP and the LI and MN were increased by 3.9 and 4.1 degrees, respectively, while the interincisal angle was decreased by 13.8 degrees, suggesting that the Omani subjects had more proclined incisors compared to Eastman Standard norms. 10,138][39][40]42 Protrusion of the LI and the distance between the LI and facial plane was also increased by 1.8 mm and 1.5 mm, respectively. 22,2338][39][40]42 Finally, the LDFH of the Omani subjects was shorter than those of Eastman Standard norms by 2.8 mm. 15,16ithin soft tissue parameters, both the upper and lower lips were more protrusive in the current Omani sample in comparison to Eastman Standard norms, by 7.9 and 1.2 mm, respectively. 22Behbehani et al. reported similar findings in a Kuwaiti population. 37n the current study, the nasolabial angle was also significantly more obtuse by 3.6 degrees in comparison to Eastman Standard norms. 22egarding gender differences within the studied Omani population, females had a significantly greater sagittal relationship between the maxilla and mandible, as evidenced by their ANB values.This feature was further supported by the females having a more positive Wits appraisal value.These findings suggest that Omani females display a more retrusive mandible, which is in contrast to reported findings from other Arab populations. 3,5,42In addition, females in the current study had significantly more proclined LIs compared to males, as expressed by the LI-MN angle; this is in accordance with findings of Bishara et al. 5 This study is subject to certain limitations.As noted earlier, Oman is a heterogenous country and is native to individuals of various ethnicities and races, with Arabs representing only a portion of the total population. 9Therefore, in order to determine accurate and specific cephalometric norms for the Omani population, a larger sample comprising all of the different tribes existing in the country should be evaluated.

Conclusion
In comparison to Eastman Standard norms, the Arab Omani subjects were found to have a slightly more retrusive maxilla and an increased MP-MN angle.Their vertical facial heights were also significantly shorter than those of Eastman Standard norms.The Wits appraisal value for the Omani subjects was also comparatively reduced, nearing zero.In terms of dental parameters, the incisor relations of the Omani subjects were edge-to-edge in nature and the interincisal angle was reduced, suggesting more proclined incisors.With regards to soft tissue parameters, the lips of the Omani subjects were significantly more protrusive and the nasolabial angle more obtuse compared to the Eastman Standard norms.These findings suggest that certain cephalometric parameters, such as slightly more proclined incisors, should be considered acceptable and normal within the Arab Omani population, despite differing from Eastman Standard norms.c o n f l i c t o f i n t e r e s t

Figure 1 :
Figure 1: Example of a cephalogram with (A) identified anatomical landmarks and (B) automated cephalometric measurements generated using imaging software.ANS = anterior nasal spine; UI = upper incisor; LI = lower incisor.

a 2 SD 2 Table 1 :
of males + SD of females Sp − pooled SD = Definition of various cephalometric parameters used in the current study Parameter Definition Skeletal SNA Position of the maxilla in relation to the skull base (i.e. the angle between the SN and NA planes) SNB Position of the mandible in relation to the skull base (i.e. the angle between the SN and NB planes) ANB Sagittal relationship between the maxilla and mandible (i.e. the angle between the NA and NB planes) SN-MP Vertical relationship between the maxilla and cranium (i.e. the angle between the SN and ANS and PNS planes) PPL-MN Angle between the PPL and MN LAFH Distance between the Me and MP (i.e.distance between the Me and ANS) UAFH Distance between the N and MP (i.e.distance between the N and ANS) LAFH/TAFH Ratio of LAFH to the TAFH (i.e.ratio of the N-ANS to the ANS-Me) LPFH Distance between the Go and MP (i.e.distance between the Go and PNS) UPFH Distance between the S and MP (i.e.distance between the S and PNS) PFH Distance between the S and Go Wits appraisal Extent to which the jaws are related to each other* Dental Overjet Horizontal overlap of the incisors from the labial aspect of the LI to the incisal edge of the UI Overbite Vertical overlap of the incisors from the incisal edge of the UI to the incisal edge of the LI UI-MP Angle between the UI axis and MP LI-MP Angle between the LI axis and MP UI-LI Angle between the UI and LI axes LI protrusion Distance between the incisal edge of the LI and the line joining point A to Po LI-FP Distance between the incisal edge of the LI and the line joining N to Po B-NPo Distance between point B and the line joining N to Po LDFH Distance between the tip of the LI and the MP Soft tissue UL-EP Distance between the UL and Ricketts' E line † LL-EP Distance between the LL and Ricketts' E line † NLA Angle between the Co and Sn of the UL Chin thickness Distance between the hard and soft tissue Po SNA = sella (S)/nasion (N) point A; SNB = SN point B; ANB = A point/N/B point; MP = maxillary plane; ANS = anterior nasal spine; PNS = posterior nasal spine; PPL = palatal plane; MN = mandibular plane; LAFH = lower anterior facial height (AFH); Me = menton; UAFH = upper AFH; TAFH = total AFH; LPFH = lower posterior facial height (PFH); Go = gonion; UPFH = upper PFH; LI = lower incisor; UI = upper incisor; Po = pogonion; FP = facial plane; LDFH = lower dental facial height; UL = upper lips; EP = E plane; LL = lower lips; NLA = nasolabial angle; Col = columella; Sn = philtrum.*Measured by drawing perpendicular lines from points A and B on the maxilla and mandible, respectively, to the occlusal plane through the region of overlapping cusps of the first premolar and first molars.† Measured by drawing a line from the tip of the nose to the soft tissue Po.