Replacing missing teeth with dentures requires precise steps to ensure the final appliance is functional and comfortable. Since patients without teeth lack natural references to align the jaws, an intermediary device is needed to accurately record this relationship. This device, known as the “wax bite” or “occlusion rim,” is a temporary, adjustable tool that serves as a placeholder for the artificial teeth during the fitting process.
What Is the Wax Bite and Why Is It Necessary?
The wax bite is composed of two main parts: a stabilized baseplate and a wax rim. The baseplate, often made from acrylic or shellac, is custom-made to fit securely over the patient’s gums, mimicking the fit of the future denture base. It must be stable and retentive so the patient does not have to consciously hold it in place during measurements.
The wax rim is a thick, horseshoe-shaped block of wax attached to the baseplate, representing the position and bulk of the future denture teeth. This rim acts as an adjustable surface for the dentist to record the precise relationship between the upper and lower jaws. It is used to determine the correct placement of the artificial teeth, verify proper jaw alignment, and assess aesthetic qualities like lip support and smile line. Since the wax is pliable when warmed, the dentist can easily add or remove material to achieve the perfect height and contour before fabrication.
Determining the Vertical Dimension
One of the first measurements taken with the wax bite is the Vertical Dimension (VD), which is the measured height between the upper and lower jaws. VD has two forms: the Vertical Dimension of Rest (VDR), the distance when the jaw is relaxed, and the Vertical Dimension of Occlusion (VDO), the distance when the teeth are in contact. The difference between these two points, typically two to four millimeters, is known as the resting interocclusal space or “freeway space,” which is necessary for comfortable function.
Setting the VDO too high constantly strains the facial muscles, causing discomfort, fatigue, and an audible clicking sound when the patient speaks or chews. Conversely, setting the VDO too low results in the chin appearing too close to the nose, giving the face a prematurely aged or collapsed appearance. The dentist uses instruments like a Willis gauge to measure the distance between two marked points, adjusting the height of the wax rims until the correct VDO is established.
Recording Centric Relation
Once the correct vertical height is established, the second measurement, Centric Relation (CR), must be recorded. Centric Relation is defined as the most stable, repeatable, and retruded position of the condyles—the rounded ends of the lower jawbone—within their sockets, independent of where the teeth contact. This measurement determines the horizontal and lateral alignment of the dentures, which is necessary for stability and proper chewing function.
Since edentulous patients lack natural teeth to guide the jaw into a repeatable bite, the dentist must gently manipulate the lower jaw to guide the condyles into this ideal socket position. Techniques are used to ensure the patient’s muscles are relaxed, such as asking them to swallow or curl their tongue to the back of the mouth. Registration materials, like paste or softened wax, are applied to the occlusion rims to capture this precise horizontal relationship at the predetermined VDO. Grooves cut into the wax rims help lock the upper and lower rims together, creating a stable index for the laboratory.
Transferring Measurements to the Final Denture
The precisely adjusted wax bite, containing the patient’s VDO and CR records, is sent to the dental laboratory. This wax bite is used to mount the patient’s plaster models, or casts, onto a mechanical device called an Articulator. The Articulator is designed to accurately mimic the patient’s jaw movements, including the recorded jaw relationship.
The dental technician uses the articulator to set the artificial teeth onto the wax rims, aligning them according to the recorded vertical and horizontal measurements. The wax setup is often returned for a final “try-in” appointment to confirm aesthetics and function. This ensures the final appliance provides a comfortable fit, proper function, and a natural appearance before it is processed into its final acrylic form.