The mouth does not physically shrink like an atrophying muscle, but the surrounding structural components—the jawbone, teeth, and soft tissues—undergo changes. These changes collectively reduce the internal volume of the oral cavity and shorten the lower third of the face. This process creates the visual effect of a smaller, more sunken-in mouth area. The perceived reduction is a consequence of shifts in the underlying anatomy, primarily involving the breakdown and remodeling of bone and dental tissue.
Changes in Jawbone Structure
The most definitive physical reduction of the oral cavity is rooted in the aging of the jawbone, specifically the alveolar process. This specialized bone structure houses the tooth sockets and depends almost entirely on the presence of teeth. The alveolar bone undergoes constant renewal through a balanced process involving bone-forming cells (osteoblasts) and bone-resorbing cells (osteoclasts).
When a tooth is lost, the mechanical stimulation provided to the surrounding bone through the periodontal ligament ceases, disrupting this balance. Without this functional input, the osteoclasts’ activity outpaces the osteoblasts’, leading to alveolar bone resorption. This results in a progressive reduction in the height and width of the jaw ridge, diminishing the physical size of the jaw structure.
This bone loss is particularly rapid in the first few months following tooth extraction, but it continues throughout life, especially without tooth replacement. The width and height of the alveolar ridge can shrink significantly, sometimes losing 40% to 60% of its volume in the initial phase after removal. The overall effect is a mandible and maxilla that are physically smaller and less supportive of the facial structures.
Impact of Teeth Wear and Loss
Changes to the teeth significantly contribute to the perceived shortening of the mouth area and facial collapse. Daily chewing and grinding cause mechanical wear, known as dental attrition, which shortens the length of the teeth over time. This gradual wearing down of the enamel and underlying dentin reduces the overall height of the bite.
When multiple teeth are lost or severely worn, the Vertical Dimension of Occlusion (VDO)—the vertical distance between the upper and lower jaws when closed—decreases. This loss of vertical support causes the jaw to over-close, visibly shortening the lower third of the face and creating a “sunken-in” facial profile. The loss of posterior molar support is damaging, as it places excessive stress on the remaining anterior teeth, often accelerating their wear or causing them to shift forward.
Teeth naturally experience mesial drift, a lifelong process where they slowly shift toward the midline of the face. This movement, combined with the gradual shrinkage of the jawbone, often leads to increased crowding and misalignment, particularly in the lower front teeth. This crowding further alters the internal architecture and functional relationships of the mouth.
Soft Tissue and Facial Profile Changes
While the underlying bone structure reduces physical volume, changes in the soft tissues are primarily responsible for the appearance of a smaller mouth. The lips lose definition and volume due to the degradation of structural proteins in the skin and muscle. The loss of collagen and elastin fibers in the lip tissue reduces elasticity and firmness, causing the lips to thin and flatten.
The orbicularis oris muscle, the ring of muscle surrounding the mouth, experiences atrophy with age. This loss of muscle tone and volume causes the lips to lose their projection and can lead to an inversion, or rolling inward, of the vermillion border. The combined effect of thinning lips and a reduced VDO creates the appearance of perioral wrinkles, such as marionette lines and vertical lip lines.
Mitigating Age-Related Oral Changes
Maintaining proper oral hygiene is the foundational step in mitigating age-related oral changes, as it prevents diseases that accelerate bone and tissue loss. Brushing twice daily and flossing once daily helps control periodontitis, a major contributor to alveolar bone resorption and subsequent tooth loss. Regular professional cleanings and check-ups are necessary to identify and manage early signs of wear or gum disease.
Replacing missing teeth is one of the most effective ways to prevent further structural collapse of the mouth. Dental implants are beneficial because they provide the necessary mechanical stimulation to the jawbone, which helps slow or stop bone resorption. For those experiencing excessive tooth wear, custom-fitted night guards can protect teeth from grinding and clenching (bruxism), preserving the existing tooth structure and VDO. Adequate intake of calcium and Vitamin D also plays a supportive role in maintaining overall bone density, including the jawbone.