The determination of occlusal height, formally known as the Occlusal Vertical Dimension (OVD), is a procedure in restorative dentistry. OVD represents the vertical distance between the upper and lower jaws when the teeth are in maximum contact, or intercuspation. Obtaining this precise distance is important for the successful completion of major dental reconstructions, such as complete dentures, complex crowns, or implant-supported prostheses. The OVD ensures the jaw relationship is correct, influencing the function and long-term health of the mouth and facial structure.
The Significant Role of Occlusal Height in Dental Health
Establishing the correct OVD impacts three main areas beyond the teeth themselves. Proper occlusal height is necessary for efficient function, primarily affecting the ability to chew and swallow food. If the height is insufficient, the muscles of mastication must work harder in a collapsed position, leading to fatigue and discomfort.
The second area is facial aesthetics, as the OVD directly supports the muscles and soft tissues of the lower third of the face. A diminished height can result in a sunken facial appearance, causing the chin to appear too close to the nose and leading to excessive folding at the corners of the mouth. Correct OVD helps maintain natural lip closure and provides appropriate facial support, contributing to a balanced profile.
The third effect relates to the health of the temporomandibular joints (TMJ), which connect the jawbone to the skull. An improper bite height can place strain on these joints and the surrounding ligaments and musculature. This strain may contribute to symptoms of temporomandibular disorder, such as clicking, pain, or limited jaw movement.
Key Methods Dentists Use to Determine Vertical Dimension
Dentists begin determining OVD by first finding the Resting Vertical Dimension (RVD), the distance between the upper and lower jaws when the jaw muscles are fully relaxed. RVD is measured with the patient’s head upright and the lower facial muscles in a relaxed, postural position, often achieved after the patient swallows and lets the jaw naturally drop. A common method involves marking two points on the face—one on the nose or upper lip and one on the chin—and measuring the distance between them using a ruler or caliper.
The OVD is mathematically derived from the RVD by subtracting the freeway space, also known as the interocclusal rest space. This small gap naturally exists between the biting surfaces of the upper and lower teeth when the jaw is at rest, typically measuring between two and four millimeters. This physiological relationship provides the starting point for calculating the desired occlusal height for the final restoration.
Phonetics offers a way to refine this initial measurement, particularly for patients receiving dentures. The dentist asks the patient to make specific speech sounds, such as the “S” sound, which requires the anterior teeth to come close but not touch. This closest speaking space provides a functional check of the vertical distance, ensuring adequate room for clear speech production. If the space is too small, speech may sound slurred or the teeth may click together.
When a patient has lost all natural teeth, the dentist may rely on existing facial proportions as a guide. Techniques involve measuring the distance from the center of the pupil of the eye to the corner of the mouth, or comparing the length of the middle third of the face to the lower third. While these measurements are not absolute, they provide an anatomical framework to approximate the original OVD.
When available, pre-extraction records are valuable reference points. These records include old photographs, diagnostic casts, or previous dentures. An old denture, if comfortable and functional, can be measured to determine a baseline OVD. Because no single method is universally accurate, dentists frequently use a combination of these techniques to arrive at the best estimate for the individual patient.
Clinical Verification and Adjustment of the Measurement
After the initial OVD is determined, the measurement enters a phase of clinical verification rather than being immediately finalized. This is accomplished using temporary appliances, such as wax rims on record bases or clear plastic mock-ups of the planned final restoration. These trial devices are worn by the patient for a period to test the determined height in a real-world setting.
The patient’s feedback is an important component of this verification process. They assess comfort, the ability to speak clearly, and the ease of eating with the trial height. The dentist also observes the patient for signs of muscle strain or a strained lip appearance, which might indicate the height is too great.
If the OVD is set too high, the patient may experience muscle fatigue or pressure on the TMJ. Conversely, if the height is too low, the patient’s face can appear compressed, and the chewing muscles may not function effectively. The dentist makes micro-adjustments to the trial appliance, often by adding or removing a millimeter of material, until the patient reports the best balance of comfort, function, and aesthetics. This process ensures the final restoration is built to a dimension the patient’s oral system can comfortably tolerate long-term.