A night guard, often called an occlusal splint, is a custom-fitted dental appliance typically worn over the upper or lower teeth during sleep. These devices are designed to cover the biting surfaces of the teeth, acting as a physical barrier. The primary goal of a night guard is to protect the dental structures from excessive force, mitigating damage related to involuntary grinding and clenching. Understanding the mechanical function of a night guard clarifies its distinction from appliances designed to maintain tooth alignment.
The Primary Role of Night Guards
The intended function of a night guard centers on managing the forces generated by jaw muscles, particularly those associated with nocturnal bruxism. Bruxism involves repetitive jaw-muscle activity, characterized by clenching or grinding of the teeth, which can exert significant pressure on the oral system. The night guard acts as a cushion to absorb and distribute this mechanical stress across the dental arch, preventing tooth wear, fractures, and damage to existing restorations like crowns or veneers.
Beyond physical protection, the appliance plays a role in stabilizing the bite and promoting muscle relaxation. By providing a flat, smooth surface for the opposing teeth, a full-coverage splint can eliminate premature contacts and allow the temporomandibular joint (TMJ) to assume a more relaxed position. This altered bite relationship helps to reduce the hyperactivity of the masticatory muscles, such as the masseter and temporalis, which frequently become fatigued or sore from clenching. The even distribution of force minimizes strain on individual teeth and the TMJ structures.
Night Guards vs. Retainers: Preventing Tooth Shifting
Night guards are not designed to prevent teeth from moving and are generally ineffective for this purpose. Their design is fundamentally different from devices meant for stabilization. The intent of a night guard is to protect the teeth by distributing force, like a shock absorber, rather than holding them rigidly in place. While a well-fitting, full-coverage splint may incidentally prevent some minor shifting by stabilizing the bite, this is a secondary effect.
Orthodontic retainers, conversely, are specifically fabricated to maintain the position of teeth after they have been moved by braces or aligners. Retainers, whether fixed wires bonded to the back of the teeth or removable clear plastic appliances, are engineered to prevent orthodontic relapse. The purpose of a retainer is to stabilize the teeth while the surrounding bone and soft tissues solidify around the new alignment. If an individual has completed orthodontic treatment, the retainer is the appropriate appliance for long-term stabilization, not the night guard.
The materials and construction of the two devices reflect their distinct purposes. Night guards are typically made from thicker, more durable acrylic or plastic to withstand the intense, destructive forces of grinding. Retainers are often thinner and made of a more precise plastic or a combination of wire and acrylic, which is not built to absorb heavy grinding pressure. Attempting to use a retainer for bruxism risks damaging the appliance, while using a night guard to maintain alignment fails to provide the necessary rigid retention.
Unintended Tooth Movement Caused by Night Guards
In certain circumstances, a night guard can inadvertently cause minor changes in tooth position or bite alignment. This unintended movement occurs when the appliance is poorly fitted, worn incorrectly, or used for an extended period without professional monitoring. Since teeth can move under sustained pressure, a night guard that applies uneven force to specific teeth can gradually push them out of alignment.
A common adverse effect is the development of an “open bite,” where the front or back teeth no longer meet when the jaw is closed. If a partial-coverage guard only covers the front teeth, the back teeth may slowly erupt or the front teeth may be slightly pushed down, leading to a gap. The risk of these unintended occlusal changes is highest with over-the-counter or “boil-and-bite” guards, which do not offer the precise customization of a professionally fabricated splint. Regular dental check-ups are necessary to ensure the night guard continues to fit correctly and to prevent alterations to the bite.