Sexual dimorphism in the head and neck area is a particular interest to orthodontists who manipulate the underlying hard tissue in order to alter the overlaying soft tissue. Hard tissue differences between the sexes have been well documented in the literature with the advent of the cephalostat. With the enlightenment of the ‘soft tissue paradigm’, research has been shifted towards revealing differences in the soft tissue. Although overall size difference, with males being larger, has been a commonly recurring theme, elucidating shape differences has been more subtle. A large sample (n=586) of adults with recent European ancestry have been recruited for the study. Five direct anthropometric measurements were taken using calipers while 29 indirect anthropometric measurements were captured using a 3dMD digital stereophotogrammetry system (Atlanta, GA). Seven indices were derived and compared between the sexes. Statistical analysis was performed using a t-test as well as an analysis of covariance (ANCOVA) using height as the covariate measure. Our results confirmed that males were larger than females on all 34 measurements, and 32 of the 34 measurement differences were found to be significant according to the t-test (p<0.001). Although the upper and lower vermilion heights were absolutely larger for males, vermilion height in females was proportionally larger relative to the size of the mouth. Once height was factored in, the number of significant findings decreased to 27 of the 34 measurements according to the ANCOVA (p<0.001). Measurements such as ‘minimum frontal width’, ‘palpebral fissure length (right)’, ‘palpebral fissure length (left)’, ‘nasal protrusion’, and ‘nasal height’ were found to be non-significant when the effects of body size (height) was controlled. Three of the four index comparisons were significant according to the t-test (p<0.001). ‘Upper-middle facial depth index’ was larger in females indicating that they have a more anterior projection of nasion and/or a more posterior projection of subnasale. Females also had a larger ‘middle-lower facial index’ indicating that females have more convexity to their profile shape. Males had a larger ‘nasal index’ suggesting that they have a relatively shorter and wider nose.
Table 1: Direct anthropometric measurements used in the present study (Kolar and Salter, 1997) 15
Table 2: Indirect anthropometric measurements used in the present study (Kolar and Salter, 1997) 16
Table 3: List of craniofacial indices used in the present study 19
Table 4: Descriptive statistics on all 34 craniofacial measurements (mm) 23
Table 5: Results of t-test and ANCOVA for all variables 24
Table 6: Descriptive statistics and t-test results for the seven anthropometric indices 25
List of figures
Figure 1: Boxplot showing the mean age of males and females in the present sample 14
Figure 2: Example of 3D mesh obtained via stereophotogrammetry 18
preface First of all, I would like to mark my appreciation to the University of Pittsburgh, School of Dental Medicine, Department of Orthodontics for the opportunity to pursue this masters research.
I would also like to thank my major advisor, Dr. Weinberg for his dedication and perseverance. And thank you very much Dr. Janet Robison and Dr. Kulkarni in assisting me through this journey. Moreover, I would like to thank Dr. Petrone, select co-residents, and the staff in orthodontics in making this a possibility.
Last but not least, I would like to thank my family and friends for their everlasting love and support.
Although humans show relatively little sexual dimorphism compared with other primates, males and females still differ (on average) on many physical attributes, such as height and muscle mass. It has also been well documented in the orthodontic, forensic and anthropological literature that various aspects of the craniofacial complex differ between males and females. This observation was stated clearly by Enlow and Hans (2008):
“A talented artist can effectively render male versus female faces, and the viewer has no problem recognizing either gender from sketches or portraits of adults. However, many artists, as well as the average citizen, are not really conscious of the actual, specific anatomic differences involved. They just “know.” In our mind’s eye, we have all subconsciously associated, over the years, the topographic characteristics that relate to facial dimorphism.”
The effects of sex on facial form are of particular relevance to orthodontists. Having an accurate picture of the ways male and female faces differ is particularly important in both treatment planning and outcome assessment, a fact evidenced by the orthodontist’s reliance on sex-specific cephalometric norms. Especially in cases where the initial facial state of the patient is drastically altered, such as in craniofacial anomalies, the orthodontist must incorporate facial norms that specifically apply to that case in terms of sex, ethnicity, and age. Dean et al. (1998) highlights this point by stating that the “…use of ‘treatment’ images of the bony skull are likely to produce the best results when they are averages of a craniofacial imagebase subsampled for sex and ethnicity rather than a grand mean.”
The vast majority of studies comparing facial form between males and females have focused on the hard tissue, typically using traditional cephalometrics. Far less has been published on the craniofacial soft tissues. As Proffit et al. (2007) have pointed out, the field of orthodontics is in the process of shifting away from the era of exclusive focus on hard-tissue skeletal relationships and moving into a ‘soft-tissue paradigm’ where priority is placed on achieving harmony of the soft tissue facial proportions rather than producing an ideal occlusal relationship at the expense of anything else. “Facial appearance is judged largely on soft tissue contours, not hard tissue relationships” (Proffit 2000). “Although at the present time quantitative measurements cannot be rigorously applied for soft tissue assessment, the challenge for the future will be to develop methods for doing so” (Proffit 2000). This altered emphasis has put understanding human variations in facial soft tissues front and center in orthodontics. Recent technological advances in 3D surface imaging have now made it possible to capture large amounts of quantitative data on the soft tissues of the face in a way that is fast, non-invasive, and accurate. Armed with this technology, we are now in an ideal position to improve our understanding of the sex differences in the human face, especially pertaining to the soft tissue.
The purpose of the present study is to provide a detailed quantitative assessment of the sex differences of the craniofacial soft tissue in a large sample of healthy adults based on anthropometric measurements obtained through 3D surface imaging.