The visibility of upper teeth when the mouth is naturally closed is known as resting incisor display. This characteristic varies significantly among individuals. While often viewed as a cosmetic concern, excessive teeth show at rest can indicate underlying anatomical variations in the jaw, teeth, or surrounding soft tissues. Understanding the components that contribute to this display helps determine if intervention is needed.
The Anatomy of Teeth Display
The amount of upper tooth structure visible when the lips are relaxed is called maxillary incisor show. This measurement is a key parameter in facial aesthetics that changes throughout a person’s life. In young adults, the normal range of upper central incisor display at rest is typically between 2 and 4 millimeters.
This measurement varies by gender; young adult females typically show 3 to 4 millimeters, while males average 1 to 2 millimeters. This display decreases with age as the upper lip lengthens and loses elasticity, often resulting in minimal or no upper incisor show by the time a person reaches their fifties. When the lips cannot comfortably meet without straining the chin muscles, the condition is known as lip incompetence, which contributes to excessive incisor show.
Primary Causes of Excessive Incisor Show
Excessive incisor show, which may include visible gum tissue, stems from three distinct anatomical categories: skeletal, dental, and soft tissue factors. Often, a combination of these elements is responsible for the overall display.
Skeletal Factors
Skeletal factors relate to the underlying structure and vertical dimensions of the jawbones. The most common skeletal cause is Vertical Maxillary Excess (VME), where the upper jaw (maxilla) has grown too long vertically. This overgrowth positions the upper teeth and gum tissue too low, pushing them past the border of the relaxed upper lip. The resulting long lower facial third makes the teeth and gums appear prominent.
Dental Factors
Dental factors focus on the position and length of the teeth themselves. Excessive incisor show can be due to dentoalveolar extrusion, which is the over-eruption of the upper front teeth and their supporting bone. This vertical positioning pushes the biting edge of the incisors further down than is ideal, even if the jawbone is normal size. Teeth can also appear excessively long if the gums have not receded properly during development, a condition known as altered passive eruption.
Soft Tissue Factors
Soft tissue factors involve the lips and the muscles controlling their movement and rest position. A naturally short upper lip is a frequent soft tissue cause of excessive incisor display. Another element is hyperactivity of the upper lip elevator muscles, which affects the resting lip position. When the upper lip cannot naturally cover the teeth and gums, the chin muscles must strain to force a lip seal, which is the physical manifestation of lip incompetence.
Functional and Health Implications
While the visual aspect motivates consultation, the inability to maintain a natural lip seal leads to several non-cosmetic health consequences. Chronic lip incompetence often forces the individual to breathe through the mouth, a habit known as mouth breathing.
This persistent open-mouth posture significantly reduces the protective flow of saliva, leading to chronic dry mouth (xerostomia). A lack of saliva increases the risk of dental decay, gingivitis, and other gum diseases because the teeth are constantly exposed to a less protected environment.
Mouth breathing is also linked to systemic issues, including an increased risk of sleep-disordered breathing and obstructive sleep apnea. Furthermore, the continuous strain to seal the lips can affect facial development in growing children, potentially contributing to a long, narrow facial structure and a high, narrow palate.
Options for Correction and Management
The appropriate management strategy is determined by correctly identifying the underlying cause or combination of causes. A thorough evaluation by a dental specialist, such as an orthodontist or oral surgeon, is necessary to develop a treatment plan.
Orthodontic Management
For cases primarily involving dental factors, such as over-erupted incisors, orthodontic treatment is the primary solution. Specialized braces or clear aligners can be used to slowly move (intrude) the upper front teeth back into the jawbone. This process can be enhanced by using Temporary Anchorage Devices (TADs), which are small, temporary screws placed in the jawbone to provide a stable anchor point. Orthodontic intrusion effectively reduces the vertical height of the teeth and surrounding gum tissue, decreasing the resting incisor display.
Surgical Intervention
Severe skeletal discrepancies, particularly Vertical Maxillary Excess, often require surgical intervention for definitive correction. Orthognathic surgery, specifically a Le Fort I osteotomy, involves carefully repositioning the entire upper jaw higher into the facial skeleton. This procedure shortens the vertical dimension of the midface and corrects the excessive display, often in conjunction with pre- and post-surgical orthodontics.
Soft Tissue Management
If the cause is a short or hyperactive upper lip, soft tissue procedures offer targeted management. Lip repositioning surgery can be performed to restrict the upward movement of the upper lip muscles, reducing excessive gum display. For cases of muscular weakness or poor resting posture, myofunctional therapy involves exercises to strengthen the muscles of the lips and tongue. This therapy helps establish a natural, relaxed lip seal and promotes proper nasal breathing.