Health Science Reviews

By Robyn-Lee Manchest

Ever wondered if your jawline could help solve a crime? For forensic scientists, it might just be the key to unlocking your biological identity. On today’s episode of “Jaws”, we dive into a fascinating study by Toneva et al. (2023), which explores sex-related differences in the size and shape of the human mandible using cutting-edge 3D analysis. These researchers gave ancient jawbones a high-tech digital makeover to see if subtle variations in form could reliably reveal whether a mandible once belonged to a male or a female. But that’s not all… the study also investigates how age influences the accuracy of this method.
Why the Mandible?
Sex estimation is a cornerstone of forensic and anthropological investigations. When skeletal remains are recovered, knowing whether bones belong to a male or female helps narrow down the identity. The mandible (your lower jawbone) is often used for this purpose because it’s one of the most durable bones in the human body and is frequently recovered intact.
Behind the (Jaw) Scenes: How the Study Worked
A total of 190 Bulgarian individuals (98 males and 92 females) were analysed using computed tomography (CT) scans. These individuals were further divided into two age groups: those under 40 and those over 40.
Researchers generated 3D models of each mandible and placed 45 anatomical landmarks on each jaw. These landmarks were then processed through a method called generalized Procrustes superimposition, which standardizes the data for shape analysis.
They used statistical tools like principal component analysis (PCA) and discriminant analysis (DA) to determine how well mandible shape and size could predict sex.
Key Findings
Size Matters Most
When it comes to sex estimation, bigger really does mean bolder… well, at least in the human mandible. Male mandibles were found to be significantly larger than female ones across both age groups. With the use of size alone, the researchers achieved an impressive 87% accuracy in predicting sex.
Shape Helps, But Only When Paired with Size
Significant shape differences were observed between males and females, particularly when shape and size were analysed together. This combo produced an accuracy of 78%. However, once size was statistically removed, the shape differences alone dropped to 53% accuracy, which is essentially a coin toss.
Turns out, shape doesn’t like to work alone.
Age Shifts the Picture
Here’s where things got interesting. Age affects how size influences shape, a concept known as allometry. In younger males, shape differences were more size-related. In older males, this effect faded, suggesting that aging bones slowly blur the sharp lines between male and female traits.
Interestingly, females didn’t show much age-related variation in shape, indicating that male jaws may be more sensitive to aging.
Jawlines That Tell Tales: The Anatomical Clues
The mandible holds several sex-related secrets that even the most experienced poker face can’t hide:
Ramus: Female mandibles usually have a shorter, more upright posterior ramus, while males show a longer, slightly slanted structure.
Coronoid Process: Males tend to have a shorter, forward-pointing projection. Females? Longer and more vertical.
Gonial Angle: Males generally show a more everted (flared) angle, contributing to a broader jawline. Females display a flatter, more inverted angle.
Symphysis (chin): Male chins are typically higher and retracted, resulting in a more square profile, while female chins are rounder and more forward-facing.
Inferior border of the mandible: Males often have a sharper and more notched contour near the preangular notch. In females, this border is smoother and more curved.
Put these features together, and you’ve got a biological blueprint that forensic scientists can use with striking precision.
Final Thoughts: Jaws Don’t Lie
This study shows that your jaw does more than just chew, it speaks volumes about who you are. Thanks to 3D imaging and geometric morphometrics, forensic scientists are able to read the skeletal signatures we carry in our bones. From size and shape to how these features change with age, your mandible is like a silent witness, one that tells your story even after you’re gone.
So, next time you catch a glimpse of your jawline in the mirror, just remember… it’s not just bone, it’s evidence.
REFERENCE
Toneva, D.H., Nikolova, S.Y., Fileva, N.F. & Zlatareva, D.K. 2023. Size and shape of human mandible: Sex differences and influence of age on sex estimation accuracy. Legal medicine (Tokyo, Japan). 65:102322. DOI:10.1016/j.legalmed.2023.102322.