A loose denture is unsettling, causing difficulty speaking, discomfort, and reduced ability to chew effectively. This loss of stability means the prosthetic moves or shifts unexpectedly, creating sore spots. Looseness is common because the mouth is a dynamic biological environment, constantly changing. When a denture begins to slip, the cause falls into one of three primary areas: changes in underlying anatomy, degradation of the appliance, or an issue from the initial fabrication. Understanding the specific reason is the first step toward correcting the problem and restoring comfort and function.
Changes in Jawbone and Gum Structure
The most frequent biological reason for long-term denture looseness is the progressive loss of the jawbone ridge. When teeth are removed, the alveolar bone that housed their roots is no longer stimulated and begins to resorb, or shrink away, in a process known as disuse atrophy. This remodeling is most noticeable in the first year following tooth loss, but it continues gradually throughout life. Studies indicate that horizontal bone loss can reach up to 63% within the first six months after extraction, continuing at an estimated rate of 0.5% to 1.0% per year thereafter.
This continuous shrinkage fundamentally alters the shape of the mouth’s foundation, which the denture base is molded to fit. As the bone ridge becomes smaller and flatter, a gap forms between the denture and the gum tissue, breaking the suction seal necessary for retention. The lower jaw (mandible) tends to resorb faster than the upper jaw, making lower dentures particularly susceptible to instability. The gum tissue resting on the bone also changes shape as the underlying structure diminishes, exacerbating the lack of contact and encouraging the denture to shift. This means a denture will inevitably require professional adjustment, such as a reline or rebase, to compensate for the reduction in supporting tissues.
Wear, Damage, or Material Degradation
Looseness can result from a physical breakdown of the denture appliance, which is typically made from acrylic resin. One common issue is material warpage, where the acrylic base changes shape and no longer conforms precisely to the mouth’s contours. This warpage is frequently caused by poor cleaning habits, such as soaking the denture in excessively hot water, which makes the acrylic malleable. Allowing the denture to dry out completely can also cause the acrylic to shrink and warp, negatively affecting the fit.
Over many years of use, the artificial teeth can wear down and become flattened, affecting bite stability. This loss of tooth height disrupts the balanced way the upper and lower dentures meet, leading to uneven contact points. When the bite is unstable, forces are transmitted unevenly to the underlying gums, causing the denture to tip or flip during chewing, instantly breaking the seal. Plaque and hard calculus deposits on the denture surface can also change the contour, causing inflammation of the gum tissue underneath, which then swells and changes shape.
Initial Improper Fit
Sometimes, a denture feels loose or unstable from the very beginning, indicating an error during the impression or fabrication stages. The foundation of a well-fitting denture relies on an accurate mold, or impression, of the patient’s mouth. If the initial impression contains flaws, such as bubbles or voids, or if the tray used was the wrong size, the resulting dental model will be inaccurate. Consequently, the final denture will lack the necessary precise contact for stability.
Errors can also happen during the laboratory fabrication process, even with a perfect impression. For instance, mistakes in setting the vertical dimension—the correct height of the denture when the mouth is closed—can result in a prosthetic that is too tall or too short, leading to unstable contact points and jaw strain. If the edges of the denture base are incorrectly shaped or too short, they cannot establish the necessary peripheral seal to maintain suction, causing the appliance to lift or dislodge during speaking or eating. When a denture is delivered shortly after extractions, initial looseness is often due to the swelling subsiding, requiring adjustment shortly after the initial fitting.