Altering the dimensions of the mouth typically refers to two distinct goals: increasing the vertical distance between the upper and lower teeth (the gape or maximum opening), or permanently increasing the horizontal, lateral width of the lips and smile. The limits of modification depend on whether the goal is temporary flexibility or a permanent structural change to the soft tissue and underlying skeleton. Understanding the anatomy that controls the mouth’s movement and fixed size is essential for assessing the possibility of achieving either form of widening.
The Anatomy of Mouth Size and Opening
The size and movement of the mouth are governed by a complex interplay of muscle, skin, and joint mechanics. The structure of the lips is primarily formed by the Orbicularis Oris muscle, a multi-layered ring of muscle fibers that encircles the mouth. This muscle acts to close and pucker the lips, and its complex network interlaces with fibers from other facial muscles, providing strength and precise control for actions like speaking and eating.
The lateral width, or the distance from one corner of the mouth to the other, is largely fixed by the points where muscle fibers anchor into the skin at the commissures (the corners of the mouth). The elasticity of the surrounding facial skin and the length of the muscle fibers establish a rigid outer boundary for the relaxed mouth width. Permanent alterations to this lateral dimension require modifying the tissue at these fixed commissural points.
The maximum vertical opening, or gape, is controlled by the Temporomandibular Joint (TMJ), which connects the jawbone to the skull. Normal Maximum Mouth Opening (MMO) typically ranges from 35 to 40 millimeters in adults, measured between the cutting edges of the upper and lower incisors. Jaw movement is a two-part process: a pure rotational or hinge movement up to about 25 millimeters, followed by a translation, or gliding movement, of the jaw joint forward. The soft tissues and the flexibility of the TMJ ligaments determine the absolute limit of this vertical stretch.
Limits of Non-Surgical Modification
Non-surgical methods, such as stretching exercises or specialized devices, can sometimes increase the vertical flexibility of the mouth but cannot significantly alter the fixed lateral width. Repetitive stretching can improve the range of motion of the jaw, potentially increasing the maximum vertical opening by a few millimeters through enhanced joint and muscle flexibility. This temporary increase in gape works within the existing anatomical limits of the TMJ and the surrounding musculature.
The permanent horizontal width of the mouth is constrained by the length of the Orbicularis Oris muscle and the fixed points of the commissures. No amount of stretching or exercise can permanently lengthen muscle fibers or relocate the skin anchor points that determine the mouth’s width. Applying excessive force to attempt lateral widening can lead to muscle strain or damage the TMJ, potentially causing pain and dysfunction.
Orthodontic devices like palatal expanders can widen the upper jaw’s bone structure to correct crossbites, but this skeletal change does not directly increase the lateral dimension of the lips or the smile. For adults, non-surgical palatal expansion is challenging because the midpalatal suture has fused, meaning any widening achieved is often due to dental tipping rather than true skeletal enlargement. Non-surgical approaches are largely limited to improving the flexibility of the vertical opening and cannot achieve permanent lateral widening.
Surgical Procedures for Permanent Change
The only reliable method for achieving permanent lateral widening of the mouth is through surgical intervention. These procedures are often adaptations of techniques developed to correct microstomia, an abnormally small mouth opening resulting from burns or congenital conditions. The primary procedure used for increasing lateral width is a combination of commissurotomy and commissuroplasty.
A commissurotomy involves making an incision at the corner of the mouth to extend the labial fissure. This is followed by a commissuroplasty, which reconstructs the new corner of the mouth. This delicate reconstruction requires rearranging the surrounding facial muscles, particularly the Orbicularis Oris fibers, to ensure the mouth remains fully functional and retains its sphincter-like action. Surgeons often utilize local tissue flaps, such as V-Y advancement or mucosal flaps, to cover the resulting defect and provide a natural appearance.
The procedure is complex and carries specific risks, including noticeable scarring at the new corners of the mouth. To counteract the tendency of the tissue to contract and relapse, surgeons may overcorrect the width by a few millimeters and recommend specialized splints during recovery. While surgery provides a path for permanent lateral change, it is typically reserved for cases of reconstruction or significant aesthetic modification due to the complexity, recovery time, and potential for a visible scar.