Having a lower denture shift or dislodge while eating is a common source of frustration. This instability occurs because the mechanics of a lower denture are inherently challenged by the jaw’s anatomy. Unlike the upper jaw, which provides a large, fixed bony palate for suction, the lower jaw offers a significantly smaller and constantly moving foundation. This anatomical difference contributes to frequent movement during chewing and speaking.
Understanding the Sources of Lower Denture Movement
The fundamental difficulty in stabilizing a lower denture stems from the unique characteristics of the mandibular arch and its surrounding soft tissues. The denture-bearing area on the lower jaw, which averages about 14 cm², is substantially smaller than the upper jaw’s surface area (closer to 24 cm²). This reduced surface area means the lower denture cannot achieve the same level of retentive seal or suction as its upper counterpart.
A major factor undermining stability is the constant activity of the surrounding muscles. The lower denture rests on a mobile floor, with the tongue and the muscles of the cheeks and lips continuously acting upon it. The mylohyoid muscle forms the floor of the mouth, and its movement during swallowing and speaking can easily lift the denture if the borders are not perfectly contoured. The tongue itself is a large, strong organ that often dislodges the denture through its movements.
Instability is worsened over time by changes in the jawbone structure. Once natural teeth are lost, the jawbone is no longer stimulated by chewing forces, leading to a process called resorption, where the bone shrinks and deteriorates. This bone loss happens about four times faster in the lower jaw compared to the upper jaw, causing the supporting gum ridge to flatten. As the underlying ridge shrinks, the denture loses its close fit and begins to rock or shift.
Immediate Adjustments and Remedies for Better Grip
When a denture begins to move, the first step is often to utilize external aids to improve retention. Denture adhesives (creams, powders, or strips) work by filling the microscopic gap between the denture base and the gum tissue to enhance the seal. For maximum effectiveness, the denture must be clean and completely dry before applying a thin, even layer of adhesive. While adhesives offer immediate relief, excessive reliance on them can mask a deeper problem with the denture’s fit, delaying the need for professional adjustment.
Adjusting eating habits can immediately improve the denture’s performance during meals. Instead of biting and chewing with the front teeth, which acts as a fulcrum and tips the lower denture up, focus on chewing slowly with your back teeth. A technique known as bilateral chewing involves placing food on both sides of the mouth simultaneously to distribute pressure evenly across the dental arch. This balanced force prevents the denture from tilting or lifting on one side, a common cause of dislodgment.
Cutting food into smaller pieces significantly reduces the force required for mastication, minimizing stress on the denture. It is helpful to avoid foods that are sticky or very hard, as these items are more likely to grab onto the denture and pull it away from the gum tissue. Ensuring dentures are clean and moist upon insertion also contributes to a better initial grip.
Clinical Treatments for Lasting Stability
When immediate remedies fail to provide lasting stability, professional intervention is necessary. The first clinical solution is often a reline, a procedure that resurfaces the portion of the denture contacting the gum tissue by adding new material. A hard reline is typically performed in a laboratory, providing a long-term adjustment to compensate for minor bone loss and is recommended every two years. A soft reline uses a more pliable, temporary material to cushion the denture, often used for patients with sensitive gums, but it must be replaced more frequently.
A more extensive procedure is rebasing, which involves replacing the entire pink acrylic base of the denture while preserving the existing teeth. Rebasing is indicated when the teeth are in good condition but the base material is cracked, weakened, or structurally unsound due to age. If the denture is too old (typically beyond five to seven years) or if the teeth are significantly worn down, a completely new prosthesis is required to restore proper function and fit.
For chronic instability, the most effective solution is the use of dental implants to anchor the denture. An implant-supported overdenture is a removable prosthesis that “snaps” onto two to four implants surgically placed in the jawbone. Placing just two implants in the front of the lower jaw can dramatically improve retention and chewing efficiency, providing a stable foundation that traditional dentures cannot match. The implants act like artificial tooth roots, providing stimulation to the jawbone that significantly slows or halts the process of bone resorption, preserving the structure otherwise lost with conventional dentures.