The habit of biting one’s nails, scientifically termed onychophagia, is a common behavior often dismissed as merely a nervous tic or cosmetic issue. This repetitive action is prevalent, affecting an estimated 20% to 30% of children and up to 45% of adolescents. While the physical effects on the fingers and nails are obvious, the continuous mechanical stress applied to the mouth introduces a spectrum of oral health complications. Chewing on fingernails subjects the teeth and surrounding structures to forces they are not designed to withstand.
Enamel Wear and Tooth Chipping
The constant, forceful engagement of the front teeth with the nails causes mechanical trauma that damages the protective outer layer of the tooth. Repeated friction from biting down on the fingernails leads to gradual wear, creating microscopic abrasions and thinning the enamel, particularly on the edges of the incisors.
Over time, this erosion can expose the underlying dentin, a softer layer beneath the enamel. This often leads to increased tooth sensitivity when consuming hot or cold foods and beverages. The sustained, irregular pressure also increases the risk of microfractures, or small cracks in the tooth structure. These breaks compromise the tooth’s integrity, making it susceptible to chipping or cracking, which may necessitate restorative dental work.
How Nail Biting Affects Alignment and Braces
The teeth are held in place by a delicate balance of forces, and the continuous lateral pressure from nail biting can disrupt this equilibrium. The habit acts as an uncontrolled orthodontic force, causing teeth to shift out of their proper positions. This movement may lead to malocclusion, or a misalignment of the bite, or cause new gaps to form between the front teeth.
For individuals undergoing orthodontic treatment, nail biting can hinder progress and even reverse the desired tooth movement. The force exerted on the teeth can weaken the tooth roots, a condition known as root resorption, which is a concern when wearing braces. The habit also frequently leads to damage of the orthodontic hardware itself, causing brackets to detach or wires to bend, which requires unplanned dental visits to repair the equipment.
Risks to Gums, Jaw, and Overall Oral Hygiene
Beyond the hard tissues of the teeth, the habit poses risks to the surrounding soft tissues and the jaw joint. Sharp or jagged nail fragments can easily cause injury to the gingival tissue, leading to cuts and inflammation known as gingivitis. Repeated trauma can also contribute to gum recession, where the gum tissue pulls away from the tooth, exposing the sensitive root surface.
The constant engagement of the jaw muscles in non-chewing activity puts stress on the temporomandibular joints (TMJ), which connect the jawbone to the skull. This repetitive strain can lead to Temporomandibular Joint Dysfunction (TMD), resulting in symptoms such as chronic pain, clicking sounds, or difficulty opening the mouth fully. The habit may also increase the likelihood of developing bruxism, or chronic teeth grinding, as the jaw muscles become overused.
Fingernails harbor dirt, debris, and numerous pathogens because of constant hand contact with surfaces. When nails are bitten, these bacteria and microorganisms are transferred directly into the mouth, increasing the risk of oral infections. This unsanitary transfer can contribute to the development of gum disease and may introduce bacteria that can lead to systemic issues if they enter the bloodstream through small cuts in the mouth lining.