The observation that your top teeth, or maxillary incisors, are barely visible when your mouth is slightly open or during casual conversation is a common aesthetic concern. This phenomenon, known as low maxillary incisor display, refers to the vertical relationship between the upper front teeth and the lower border of the upper lip when the facial muscles are at rest. The amount of visible tooth structure at rest is a key indicator of facial aesthetics and youthfulness, as display naturally changes over a lifetime.
Anatomical and Dental Causes of Low Maxillary Display
The primary factor dictating how much of the upper teeth is visible is the length and mobility of the upper lip. A longer upper lip, typically measuring over 22 millimeters in males and 20 millimeters in females, physically covers more of the tooth surface when the mouth is relaxed. The lip’s ability to lift during a smile, known as lip mobility, can also be a factor, with an average lift range of six to eight millimeters from rest to a full smile.
Structural issues with the teeth themselves frequently contribute to reduced visibility. Over time, the biting edges of the incisors can wear down due to factors like grinding, clenching, or acid erosion, a process called attrition. This loss of tooth structure shortens the clinical crown length, directly reducing the vertical dimension of the visible tooth.
This physical shortening can be exacerbated by a deep overbite, a dental relationship where the upper front teeth significantly overlap the lower front teeth. In a deep overbite, the upper incisors are often positioned too far down or the lower incisors have over-erupted, causing the upper lip to conceal the teeth. Past orthodontic treatment that involved intruding, or pushing up, the upper teeth to correct a deep bite may have inadvertently resulted in a lower amount of tooth show at rest. The vertical position of the entire upper jaw, known as the maxilla, also plays a role, as a shorter-than-average distance between the upper jaw and the base of the nose can minimize tooth display.
Functional and Cosmetic Implications
Low maxillary display is largely perceived as a sign of aging, driving many to seek correction for cosmetic reasons. In young adults, the normal display of the upper central incisors at rest is generally three to four millimeters for females and one to two millimeters for males. As a person ages, the upper lip naturally lengthens and loses elasticity, causing the visible portion of the upper teeth to decrease, often to zero millimeters, while the lower teeth become more prominent.
Severe incisal wear, which shortens the teeth, can lead to a traumatic bite where the lower teeth repeatedly strike the gum tissue behind the upper teeth, potentially causing gum recession and bone loss. This loss of tooth height can also complicate the jaw’s function. It may contribute to symptoms of temporomandibular joint (TMJ) disorder, such as jaw pain or clicking, because the jaw may be functioning in a strained position.
The vertical position of the teeth is also important for clear speech. These sounds are correctly formed when the biting edges of the upper incisors lightly contact the wet-dry line of the lower lip. A significantly incorrect tooth position can alter this functional contact, though the body’s oral muscles are often able to compensate for minor discrepancies.
Options for Enhancing Upper Tooth Visibility
If the teeth are physically short due to wear, restorative dentistry can be highly effective. Porcelain veneers or crowns are bonded to the front surface or entire structure of the teeth, respectively. They are designed to physically add length to the biting edge, typically by one to one-and-a-half millimeters, restoring a youthful appearance.
If the teeth are the correct length but are positioned too high within the jaw, orthodontic treatment can adjust their vertical placement. Maxillary incisor extrusion, the process of moving the teeth further out of the gum line using braces or clear aligners, directly increases the visible tooth length. In some cases, temporary anchorage devices, or mini-screws, are used to provide a fixed anchor point to precisely control the extrusive force.
When the appearance of short teeth is caused by excess gum tissue covering the natural tooth, a periodontal procedure can expose more of the existing tooth structure. Aesthetic crown lengthening involves surgically removing excess gum tissue and sometimes a small amount of underlying bone to reposition the gum line higher. This procedure makes the tooth appear naturally longer and can be done before placing veneers or crowns to maximize tooth display.
For a long upper lip that physically covers the teeth, a lip lift procedure can be considered to surgically shorten the distance between the base of the nose and the upper lip. In the most severe cases, where the problem stems from a skeletal discrepancy in the upper jaw’s vertical position, orthognathic surgery may be necessary. A Le Fort I Osteotomy is a surgical procedure that allows the entire maxilla to be repositioned downward, or inferiorly, to permanently increase the display of the upper teeth and re-establish proper facial proportions.