Chin

The presence of a well-developed chin is considered to be one of the morphological characteristics of Homo sapiens that differentiates them from other human ancestors such as the closely related Neanderthals.

Robinson (1913)[3] suggests that the demand to resist masticatory stresses triggered bone thickening in the mental region of the mandible and ultimately formed a prominent chin.

[11] Coquerelle et al.[9][10] show that the anteriorly positioned cervical column of the spine and forward displacement of the hyoid bone limit the anterior–posterior breadth in the oral cavity for the tongue, laryngeal, and suprahyoid musculatures.

[11] These coordinated bone growth and modeling processes mold the vertical symphysis present at birth into the prominent shape of the chin.

Recent research on the development of the chin[12] suggests that the evolution of this unique characteristic was formed not by mechanical forces such as chewing but by evolutionary adaptations involving reduction in size and change in shape of the face.

Robert Franciscus takes a more anthropological viewpoint: he believes that the chin was formed as a consequence of the change in lifestyle humans underwent approximately 80,000 years ago.

Franciscus believes that this change in the human environment reduced hormone levels, especially in men, resulting in the natural evolution of the chin.

The cleft chin is also a classic example of variable penetrance[20] with environmental factors or a modifier gene possibly affecting the phenotypical expression of the actual genotype.

If the patient suffers from sleep apnea, early maxillomandibular advancement is usually the only causal treatment and necessary to preserve normal life expectancy.