The perception of a “flat” face when viewed from the side, a concept known as limited facial projection, is rooted in the three-dimensional relationship of the skull. Facial projection describes how far forward the forehead, midface, and chin sit relative to a vertical line. This structural arrangement is determined by inherited bone structure and environmental factors that guide growth. Understanding the underlying anatomy and developmental influences provides a scientific explanation for why some profiles appear more recessed than others.
The Skeletal Foundation of Facial Projection
The profile’s appearance is fundamentally defined by three major bony structures of the face. The upper jaw, known as the maxilla, forms the central part of the midface, supporting the nose and the upper teeth. The zygomatic bones, commonly called the cheekbones, articulate with the maxilla and contribute significantly to the width and forward projection of the upper face. These bones collectively form the foundation of the midface contour.
The lower jaw, or mandible, is the only movable bone of the facial skeleton and houses the lower teeth. The relative positioning of the maxilla and the mandible sets the overall horizontal balance of the profile. When one or both of these jaw structures are positioned slightly backward, the face naturally lacks projection from the side. The angle and size of these bones are the primary determinants of whether a profile is considered straight, convex, or concave.
Primary Causes: Inherited Craniofacial Patterns
The most significant factor determining a flat profile is the inherited architecture of the craniofacial skeleton. Familial and ethnic traits strongly dictate the final size and anterior-posterior positioning of the jawbones. This skeletal pattern is a polygenic trait, meaning it is influenced by the simultaneous action of multiple genes passed down through generations.
A set-back lower jaw, known scientifically as mandibular retrognathism, is a common inherited pattern that contributes to a convex profile and a perception of flatness. This occurs when the mandible is slightly smaller or positioned further back relative to the maxilla and the rest of the skull. Twin studies have confirmed a high degree of heritability for these skeletal dimensions.
Similarly, a naturally underdeveloped midface, often due to a slightly retruded maxilla, can also create a flat or recessed appearance. The combination of a set-back maxilla and a normal or slightly set-back mandible often results in a profile that lacks forward projection in its central third. These inherited variations in skeletal relationships are the fundamental reason for differences in profile shape across the population.
Developmental Factors Shaping Profile Growth
While genetics provides the blueprint, functional habits during childhood and adolescence can modify the expression of that inherited potential. The process of facial growth is highly adaptable to environmental forces, often referred to as epigenetic factors. Consistent habits related to breathing and resting posture exert continuous pressure on the developing bone.
Chronic mouth breathing, often caused by nasal obstruction, forces the tongue to rest low in the mouth. When the tongue is not resting against the palate, it fails to provide the necessary upward and outward pressure on the maxilla. This lack of pressure can impede the forward development of the midface, leading to a narrower upper jaw and a less projected profile.
The low tongue posture associated with mouth breathing also encourages the lower jaw to rotate backward and downward. This rotation increases the vertical dimension of the face and contributes to an appearance of a receded chin and a less defined jawline. Promoting proper nasal breathing and correct tongue posture guides the maxilla and mandible toward their full, genetically determined forward growth potential.
How Soft Tissues and Age Affect Profile Appearance
Even with a strong underlying bone structure, the appearance of the profile is heavily influenced by the overlying soft tissues. The thickness and distribution of subcutaneous fat pads contribute significantly to facial projection and contour. These soft tissues smooth the transitions between facial regions, creating a fuller, more youthful profile.
As part of the natural aging process, the facial skeleton itself undergoes changes, which further exaggerate a recessed profile. The maxilla is susceptible to bone resorption, especially around the nasal opening and the eye sockets, causing the midface to appear to fall backward. This loss of bony support, combined with the gradual atrophy and downward repositioning of facial fat pads, creates hollowing in the cheeks and a less projected appearance over time.
Furthermore, a reduction in collagen and elastin causes the skin to lose its firmness, leading to skin laxity and sagging. This descent of the soft tissue envelope, particularly along the jawline, can obscure the bony contour of the chin and mandible. Therefore, the perception of flatness may be a combination of inherited skeletal positioning and the inevitable effects of soft tissue and bone changes over a lifetime.