Jaw trainers are small devices designed to be placed between the teeth, where users repeatedly bite down against resistance. The devices are marketed as a way to “work out” the muscles of the jaw and face, primarily aiming to create a more defined or “chiseled” jawline through muscle growth. The mechanism relies on resisting the natural biting and chewing motion to hypertrophy the masseter muscles. However, dental and medical professionals have raised concerns about the safety of these devices, urging a closer look at the potential for damage to the delicate structures of the mouth and jaw.
Effects on the Temporomandibular Joint
The temporomandibular joint (TMJ) acts as a sliding hinge connecting the jawbone to the skull. Jaw trainers overload this joint by applying high, repetitive forces that are far removed from the normal function of chewing food. This excessive stress significantly increases the risk of developing Temporomandibular Disorders (TMD), a condition characterized by pain and dysfunction in the joint and surrounding muscles.
The constant, forceful engagement can lead to inflammation within the joint capsule and cause strain on the delicate ligaments and tissues. Overworking the masseter muscle creates an imbalance that can further destabilize the joint. This strain can manifest as chronic pain, stiffness, and a reduced ability to open the mouth comfortably.
A severe consequence of this repetitive force is the potential for displacement of the articular disc, the cartilage that cushions the joint. Once this disc is pushed out of its proper position, it often results in painful clicking, popping, or grinding sounds (crepitus) during jaw movement. A displaced disc can be a serious and potentially permanent injury, which is difficult or impossible to reverse with treatment.
Risks to Teeth and Bite Alignment
The forces generated by biting down on resistance trainers pose direct threats to the hard structures of the mouth. These devices apply pressure at unnatural angles to the teeth, which can effectively act as “unintentional orthodontics.” Over time, this sustained, misdirected pressure can cause the teeth to shift out of their correct positions.
This unwanted movement can lead to malocclusion, or a misaligned bite, making it difficult to chew properly and potentially requiring extensive orthodontic treatment. The pressure is particularly damaging to the teeth themselves, risking dental wear, chipping, or cracking, especially on the molars or incisors used to hold the device. Furthermore, the high forces can damage existing dental restorations like fillings, crowns, and veneers, compromising their integrity and requiring replacement.
The act of non-nutritive chewing can also have systemic effects on oral health by stimulating the production of stomach acid. This can lead to gastrointestinal problems such as acid reflux. Over time, stomach acid brought up into the mouth can erode the enamel on the back of the teeth, increasing sensitivity and the risk of cavities and decay.
Anatomical Limitations of Jaw Training
The primary goal of using jaw trainers is typically to achieve a sharper, more defined jawline. True jawline definition is determined by two fixed factors: the underlying skeletal structure of the mandible (jawbone) and the distribution of fat and skin laxity in the lower face. Jaw trainers cannot alter the shape or length of the bone.
The only change these devices reliably produce is hypertrophy of the masseter muscles, causing them to get bigger. Ironically, instead of creating the desired chiseled look, this muscle over-bulking can result in an overly square, wide, or unnatural appearance. This aesthetic outcome is often the opposite of the sought-after result, as the face may look heavier or bulkier due to the enlarged muscle volume.
The masseter is already one of the most frequently used muscles in the body, constantly engaged during talking, swallowing, and eating, making it built for endurance rather than rapid growth. Excessive resistance training on a muscle that is already well-developed is often counterproductive and may contribute more to muscle fatigue and joint strain. The professional consensus is that the significant risks of joint damage and dental harm far outweigh the limited, and often negative, aesthetic changes these devices can produce.