The purpose of this study was to determine the angular facial norms in the Iranian population between 16 and 30 years of age with skeletal class I occlusion and to discover any sexual dimorphisms in the angular measurements. Many factors, such as ethnicity, are known to impact facial soft tissue profile (
18). The inclusion criteria and overall design of this study was specifically devised to identify normative values for the young Iranian population, which could be used to improve treatment plans in creating facial patterns consistent with accepted norms and a more natural look ( 6, 7, 19, 20). Patients who had undergone orthodontic or facial surgical treatment or subjects with obvious asymmetry or disharmony of facial features were excluded from this study as their artificial features may have confounded our study intended to characterize natural patterns. This study examined patients with normal skeletal class I occlusion, which may not necessarily reflect facial features considered aesthetically pleasing. However, the goal of this study was as an objective characterization of the typical and natural facial features in the young Iranian population, rather than confound the subjectivity of perceived beauty ( 21). This type of assessment is consistent with other major studies in this field for other population sub-groups ( 18). In addition, to ensure evaluating the normative values of the young Iranian population, subjects with known non-Iranian lineage (as could be discerned within the past 2 generations) were excluded. The ability to more easily utilize photogrammetric analysis in the clinical settings is one major driver for selecting this method for this study. In addition to its clinical accessibility, it has made data collection and analysis more efficient and effective. Other available major methods are at a disadvantage, as they necessitate costly equipment and more time consuming data collection ( 18). However, in the case of photogrammetric analysis, only relatively inexpensive equipment and simple procedures are needed to achieve reliable and solid analysis. Photogrammetric analysis allows us to readily utilize digital computation and computer-powered data analysis ( 18). This provides the means to produce graphical representations and perform complex statistical computations, which further extends our capabilities in profile analysis. Furthermore, unlike other available methods, subjects are not exposed to radiation, thus, making it a safer method for population based studies ( 22). As mentioned, one significant, noteworthy benefit of photogrammetric-based results is their accessibility for clinicians and easier application in clinical practice. Most plastic surgeons primarily use photographs for total facial aesthetics procedures ( 23); and when using angular measurements, there is no confounding impact by image re-sizing, and thus, easing its clinical application for both pre-operative planning and post-operative follow-up ( 18, 24). To assess whether sexual dimorphisms exist in the angular facial norms of the population studied in this study, our data analysis focused on comparing the angular data between the female and male gender sub-groups. Our analysis showed statistically significant differences (at a 95% confidence level) between male and female sub-groups in only a few of the measurements: the nasofrontal angle (N-G-Prn), nasal angle (Cm-Sn/N-Prn), and vertical nasal angle (N-Prn/TV). All other measurements showed no statistically significant differences between male and female sub-groups. Judging by this statistical analysis alone, one would conclude many similarities in facial norms between the female and male gender. We challenged the validity of this assessment by considering the variables that could have confounded ability to resolve statistical differences. From a standpoint of subject selection, we found no known or discernible population biases within the defined criteria that would have skewed our data (such as a high ratio of subjects originating from the same familial or tribal background). Data “noise” originating from the setup, data collection methods and measurements was considered. However, while a small level of noise is expected from these sources, no cause for significant levels of data “noise” could be gathered. Furthermore, sample sizes were relatively balanced between male and female sub-groups with significant data points for each (N > 30) to conduct a reasonable statistical analysis. Thus, the resulting standard deviations for the various sub-groups are likely to be strongly reflective of actual sampled variability and we consider the lack of significant differences in the majority of angular measurements to be real. In comparison with other similar studies investigated other population sub-groups, there are similarities however interesting differences when compared to the Iranian sub-population in our study, as expected when comparing ethnic and racial groups. However, it should be noted that the methodology used in our study, while fundamentally similar, was not identical to other photogrammetric studies in this field. In many respects, our methodology most closely resembles that of Malkoc et al. ( 18), which is a well-reputed study and has been referenced and used for comparisons in other ethnic and racial-based photogrammetric studies. While, any small differences in our methods could have introduced some level of bias in our data, no cause or reason for significant bias is identified. Thus, a macro-level and qualitative comparison is deemed valid for the purposes of assessing broad, overall differences of angular norms across different ethnic and racial sub-populations studied with using similar methods as the present study. And thus, the comparisons below between the results of our study with other benchmark studies are merely qualitative and do not assess statistical significance across datasets from different studies. We found statistically significant gender differences in nasofrontal angle (G-N-Prn), nasal angle (Cm-Sn/N-Prn) and vertical nasal angle (N-Prn/TV) which is against Malkoc et al. ( 18) in which no gender differences were reported for these three angles in young Turkish adults. However, our average values in the G-N-Prn, Li-Sm-Pg, N-Trg-Sn and G-Sn-Pg compared closely similar to Malkoc. Whereas, the average values for Sn–Trg–Me were distinctly different (34-35 degrees in Malkoc vs. 39 - 40 degrees in this study). Despite the similarities in average values of certain angles, the Iranian population showed greater gender differences than the Turkish population. Given the close similarity in methods between the two studies, these data comparisons could suggest overall resemblances in certain facial patterns between Turks and Iranians, with greater gender differences in the Iranian population. One study by Fernandez et al. ( 1) on young Caucasians from Galicia found statistically significant sexual differences in the nasofrontal angle, nasal angle and vertical nasal angle. The presence of statistically significant sexual differences in these angles is consistent with our study of the Iranian population. However, there were no similarities in the average values for these angles, suggesting differences between these corresponding features in the Iranian and Galicia populations. In contrast, the nasal angle (Cm-Sn/N–Prn) showed sexual dimorphism in both studies and similar average values between the two studies (male subjects = 72.6 ± 9 degrees, female subjects = 76.2 ± 6 degrees). Thus, this suggests similarity in the nasal angle between the Galician and Iranian populations with corresponding gender dimorphisms. Where the nasal dorsum angle (N–Mn–Prn) also showed significantly (P < 0.05) wider angles in males than in females, our study showed no statistically significant differences between genders. In another study by Anic-Milosevic et al. ( 25) on a young Croatian sub-population found distinct gender differences. It was found nasolabial (female subjects = 109.39 degrees; male subjects = 105.42 degrees; P = 0.018) and mentolabial angles (female subjects = 134.5 degrees; male subjects = 129.26 degrees; P = 0.019) were larger in female subjects, which is different from our finding in the Iranian population where no statistically significant gender differences were found. In addition, when comparing these values with our study, the average values were similar, suggesting similarities in these corresponding features between the Croatian and Iranian populations. Wamalwa et al. ( 22) studied facial angular norms and sexual dimorphisms in a sub-population of Kenyans and Chinese. Their finding was that the nasofrontal angle showed significant sex differences in both black Kenyans and Chinese, which is also consistent with our findings in the Iranian population. However, the average values for the nasofrontal angle between the two genders showed considerably large differences with our study (132 - 138 degrees versus 145 - 149 degrees in our study). In a sample of the Bangladeshi Galo population, Ferdousi et al. showed females had significantly higher values than the males in the nasofrontal angle, the nasomental angle and the angle of facial convexity, where we only found sexual dimorphisms in the nasofrontal angle of the Iranian population. Consistent with our study, Ferdousi et al. found no statistically significant gender differences in the nasolabial angle.Furthermore, we found that the average angle of facial convexity in this study (female subjects = 169.26 ± 4.43 degrees; male subjects = 158.65 ± 12.17 degrees) was similar to our study. Whereas, we found potentially substantial differences in the average values in the nasofrontal angles between our study (145 - 149 degrees) and Ferdousi et al. (130 - 138 degrees) ( 26). In a sub-population of young Igbo adults, Loveday et al. ( 7) showed significant gender differences in nasofrontal and cervicomental angles. However, we only found significant gender differences in the nasofrontal angle. In addition, the average cervicomental angle reported by Loveday et al. (91 degrees) was inconsistent and not considered similar in value with our findings (101 degrees). This was also the case with the nasofrontal angle where we found the Iranian population potentially larger than the Igbo population studied (averages of 145 - 149 degrees versus 130 - 134 degrees). Thus, this suggests potential differences in this angular measurement between the Igbo and Iranian sub-populations. Overall the above assessments show that the Iranian population we studied carries distinctive differences with sexual dimorphisms in comparison to other ethnic populations to which we compared our findings. In light of the objective of this study, we have characterized the angular facial norms in the young Iranian population with skeletal class I occlusion and found certain sexual dimorphisms in the angular measurements. Relative to surgical planning for cosmetic procedures and treatment of facial disorders, we believe our results can be used to re-assess the norms used by clinicians and improve the natural appearance for young Iranian subjects. These results confirm that a database for facial patterns used by clinicians in facial surgery for young Iranian subjects should be racially sensitive, if the goal is to attain a ’natural’ facial appearance that is consistent with Iranian population norms. The differences in our results with benchmark studies of other ethnic groups further validate the need for racial-ethnically tailored cosmetic treatment plans. While this study achieves its objective by assessing preliminary data that shows trends and patterns in angular norms, we believe further work is needed to develop a data set that can be applied to clinical practice. This should entail assessment of a larger study population, in order to improve the confidence and resolution of facial norms in the young Iranian population. Such further study could be used to create a formal database and formulary for angular norms that surgeons can draw upon in clinical practice. 5.1. Conclusion
The results showed gender dimorphism in three of the measurements: the nasofrontal, the nasal and the vertical nasal angles. Another significant finding was the large variability for the mentolabial angle. The result of this measurement should be assessed with caution. Our results could be used as a reference guide for comparison with records of subjects that have the same soft tissue profile, ethnic characteristics and a dental class 1 occlusion and following the same photogrammetric technique. While our preliminary data set shows promise for future clinical application, a further developed database can allow orthodontics and surgeons to determine deviations from Iranian angular norms with angular photogrammetric profile analysis and improve treatment to establish a natural look.