Chewing food primarily on one side can alter the shape of the face, a concern rooted in biological principles of muscle and bone adaptation. While no human face is perfectly symmetrical, the subtle differences we all possess can become more noticeable due to habitual actions. This article explores unbalanced chewing, known as unilateral mastication, and the morphological changes it causes.
Understanding Facial Asymmetry
Facial asymmetry refers to a noticeable lack of correspondence between the right and left sides of the face. Minor asymmetry is considered normal, often resulting from genetics or natural developmental variation. Asymmetry becomes a concern when it is acquired or significantly pronounced, falling into categories such as dental, skeletal, muscular, or functional. Functional asymmetry, which relates to movements or habits like chewing, is the category most relevant to this discussion. Unlike structural asymmetry that involves major bone or congenital issues, functional asymmetry develops post-natally due to external forces and repetitive strain.
The Mechanics of Mastication
Chewing is a complex process driven by four pairs of powerful muscles collectively known as the muscles of mastication. The primary muscles responsible for elevating the jaw and generating the biting force are the masseter and the temporalis. The masseter is visible at the angle of the jaw, and the temporalis is located on the side of the head. These muscles work in tandem with the medial and lateral pterygoid muscles to control the complex movements of the mandible, or lower jaw. The mandible pivots at the temporomandibular joint (TMJ), which acts as the hinge connecting the jawbone to the skull. Any repetitive imbalance in the force applied by these muscles can place uneven stress on the joint and the surrounding bone structure.
How Unilateral Chewing Creates Imbalance
The persistent habit of chewing predominantly on one side applies the principle of “use it or lose it” to the facial musculature. The preferred chewing side (PCS) experiences increased workload and muscular activity, leading to muscular hypertrophy where the masseter and temporalis muscles on the working side enlarge and strengthen. This enlargement results in a visible difference in facial contour, often giving the chewing side a wider, squarer appearance at the jaw angle. Conversely, the non-chewing side undergoes a relative decrease in activity, which can lead to a slight atrophy or weakening of its muscles. This muscular imbalance creates functional and aesthetic asymmetry.
Skeletal and Dental Effects
Over time, this asymmetrical muscular force can influence the underlying skeletal structure through bone remodeling. Studies suggest that in growing individuals, this habit can lead to asymmetric mandibular growth, with the jaw on the chewing side potentially becoming shorter, higher, and bulkier. The constant, uneven mechanical stress also affects the TMJ, causing an asymmetrical trajectory of the condyle—the rounded end of the jawbone—which increases the load on the non-preferred side. Furthermore, the teeth on the preferred side bear the brunt of the grinding action, leading to uneven dental wear patterns and potential misalignment. This uneven wear can worsen the asymmetry by creating a less efficient bite on the non-chewing side, further reinforcing the habit.
Strategies for Achieving Balanced Chewing
Addressing a unilateral chewing habit begins with conscious awareness and retraining the neuromuscular pathways. Practicing bilateral chewing involves alternating between the left and right sides of the mouth. For tougher foods, it is helpful to switch sides every few bites to distribute the workload evenly. Mindful eating techniques can help break the subconscious habit. Some physical therapy exercises, including those focusing on correct tongue posture and gentle jaw movements, can also encourage more symmetrical muscle engagement.
If the unilateral chewing habit is driven by an underlying issue, professional consultation is necessary. Pain, missing teeth, or a misaligned bite (malocclusion) can force an individual to favor one side. Dentists or orthodontists can address these root causes, perhaps with restorative dentistry or orthodontic treatment, to eliminate the physical barrier to balanced chewing. In cases of severe muscle hypertrophy, treatments like botulinum toxin injections may be used to temporarily reduce the bulk of the overdeveloped muscle, aiding in the retraining process.