Nail biting, clinically known as onychophagia, is a common habit often triggered by anxiety, stress, or boredom. This repetitive behavior involves biting and chewing on the fingernails and sometimes the surrounding skin. An overbite, or deep bite, is a type of malocclusion where the upper front teeth excessively overlap the lower front teeth vertically. This article explores the relationship between the chronic forces of nail biting and the development or worsening of a dental overbite.
The Physics of Tooth Movement
Teeth are not rigidly embedded in the jawbone; instead, they are suspended within the socket by a network of fibers called the periodontal ligament (PDL). This ligament acts as a shock absorber, allowing for slight tooth mobility during normal functions like chewing. Orthodontic treatment relies on the principle that sustained pressure applied to a tooth causes a biological response in this supporting structure.
The application of prolonged force, even at a low magnitude, produces bone remodeling. When a tooth is pushed, the PDL compresses, triggering osteoclasts to resorb the bone. Simultaneously, where the PDL is stretched, osteoblasts deposit new bone to fill the space. This selective bone removal and addition allows the tooth to migrate slowly through the jawbone. Intermittent, heavy forces, such as those from chewing food, are resisted by the PDL and do not cause movement.
Nail Biting’s Specific Impact on Alignment
Nail biting introduces chronic, non-functional mechanical forces that can influence tooth position and bite alignment. While the habit rarely initiates a severe, genetically determined overbite, the repetitive pressure can significantly exacerbate existing malocclusions. The constant contact of the lower teeth against the fingernails and the nails pushing against the upper front teeth creates an irregular force system.
This sustained pressure often results in labial tipping, pushing the upper front teeth forward and away from the lower teeth. This increases the horizontal overlap, known as an increased overjet or “protrusion.” Over time, this forward movement can also create small gaps (diastema) between the upper incisors. The force may also contribute to a reduced overbite or alter the resting position of the lower jaw, affecting the overall bite relationship.
Other Dental and Systemic Risks
Beyond the potential for misalignment, chronic nail biting carries several other negative consequences for oral and general health. The grinding friction of teeth against the hard nail surface can lead to enamel erosion and microfractures on the front teeth. This can also cause chipping or cracking, particularly on the edges of the incisors, leading to increased tooth sensitivity.
The consistent strain on the jaw muscles and joints from the clenching action can contribute to temporomandibular joint (TMJ) dysfunction. Symptoms of this disorder include pain, clicking, or difficulty opening and closing the mouth. The habit also introduces bacteria and viruses trapped under the fingernails into the mouth, increasing the risk of gum inflammation (gingivitis) and other infections. In severe, long-term cases, the forces may even contribute to root resorption, the shortening of the tooth roots.
Practical Steps for Stopping the Habit
Addressing nail biting requires a multi-faceted approach, often starting with increased self-awareness of the behavior. One straightforward physical deterrent involves applying bitter-tasting, over-the-counter polishes to the nails, which makes the habit unpleasant. Covering the nails with bandages or wearing gloves can also serve as a physical barrier to prevent the biting action.
Behavioral strategies focus on identifying triggers, such as stress or boredom, and substituting the habit with a healthier activity. Replacing the biting with a stress ball, a fidget toy, or chewing gum can help keep the hands and mouth occupied. If the habit is severe, persistent, or linked to anxiety, consulting a dentist or a therapist for habit-reversal training may be necessary.