The Occlusal Height, formally known as the Vertical Dimension of Occlusion (VDO), is the precise measurement of the distance between the upper and lower jaws when the teeth are in maximum contact or the jaw is closed. Determining this distance accurately is an important step in restorative dentistry, particularly in the fabrication of complete dentures, full-mouth reconstructions, and other prosthetic treatments. An incorrect VDO can compromise chewing efficiency, affect facial appearance, and potentially lead to problems with the jaw joint.
Determining the Vertical Dimension of Rest
Finding the correct Occlusal Height requires establishing the Vertical Dimension of Rest (VDR). VDR is the height of the face when the jaw is in its comfortable, relaxed position, with the muscles in a state of tonic equilibrium. This position is considered a relatively constant skeletal reference point, even after tooth loss.
The VDR is the baseline measurement from which the VDO is calculated, using the concept of the “Free-way Space” or Interocclusal Distance. Free-way Space is the small, natural gap between the upper and lower teeth when the jaw is at rest. In a healthy adult, this space typically measures between 2 and 4 millimeters.
The formula for the Occlusal Height is essentially the VDR minus the Free-way Space (VDO = VDR – Free-way Space). To find the VDR, a clinician will use simple physiological methods, such as instructing the patient to sit upright, swallow, and then relax their jaw muscles. Repeating the letter ‘M’ or having the patient lick their lips and swallow are also common techniques used to guide the mandible into its relaxed, postural position for measurement.
Physiological Methods for Measuring Occlusal Height
Once the VDR is established, several physiological methods are used to determine the initial VDO, relying on muscle memory, facial structure, or pre-existing records. One technique involves the patient’s tactile sense, where an adjustable device is used to change the vertical distance until the patient subjectively reports the position feels most comfortable and correct. This relies on the patient’s proprioception, or their subconscious sense of jaw position, to guide the closure.
Another approach uses established facial proportions to estimate the height, a method often associated with the Willis Gauge. This technique suggests that certain vertical measurements on the face, such as the distance from the pupil of the eye to the corner of the mouth, should equal the distance from the base of the nose to the bottom of the chin when the teeth are closed at the correct VDO. While this method provides a useful starting point, it is based on general averages and may not apply perfectly to individuals with asymmetrical features.
Clinicians also rely on any available pre-extraction records when possible, which provide a reference to the patient’s original, healthy VDO. This can include old profile photographs taken with the teeth closed or previous dental casts and dentures, which are measured and compared to the new proposed height.
Functional and Aesthetic Verification Techniques
After establishing the initial VDO, dynamic methods are employed to verify and refine the measurement, focusing on function and appearance. One of the most important verification tools is phonetics, specifically assessing the “Closest Speaking Space”. This is the minimal vertical distance between the upper and lower teeth during the pronunciation of sibilant sounds, such as ‘S’ or ‘Ch’.
An ideal closest speaking space should be a small gap, typically around 1 to 1.5 millimeters, between the incisal edges when these sounds are made. If the VDO is set too high, the teeth will audibly click together during speech due to an encroachment on this space. Conversely, if the VDO is too low, the speech may sound muffled or indistinct.
Aesthetic evaluation is another crucial step, as the VDO significantly impacts the lower third of the face. The correct height provides proper lip support, avoids a tense, stretched look, and ensures the chin is not overly prominent. If the height is insufficient, the lower face can appear collapsed or prematurely aged.
The final verification is the patient’s comfort, particularly during functional movements like chewing and speaking. Temporary diagnostic restorations are often used to test the new VDO over a period, allowing the patient’s muscles to adapt and confirm the measurement is functional before a permanent restoration is placed.
Clinical Consequences of Incorrect Occlusal Height
Errors in determining the Occlusal Height can lead to significant clinical problems. When the VDO is set too high, symptoms are related to excessive muscle strain and joint compression. Patients may experience muscle fatigue, pain in the jaw and surrounding muscles (myalgia), and difficulty swallowing.
An excessive VDO can cause the lips to strain to close (lip incompetence) and may lead to trauma to the soft tissues underneath a denture. The increased vertical force can also result in tooth sensitivity and accelerated pathologic bone resorption.
Conversely, setting the VDO too low results in an over-closed position, which can lead to problems like temporomandibular joint disorders (TMD) characterized by clicking or popping in the joint. The collapsed facial appearance often looks aged, and the lack of lip support can cause angular cheilitis (painful cracks at the corners of the mouth). An insufficient VDO also drastically reduces the functional efficiency of chewing.