May 28, 2021
A proper bite means a proper synergy and harmony between the upper and lower teeth and the jaws. The importance of having a proper bite is not restricted to the teeth but also the surrounding muscle attachments. Skeletal and dental discrepancies can often lead to unrest in the normal bite to the extent that it causes interferences in normal functioning. In order to achieve the optimal occlusion after orthodontic treatment or a major restorative dental work, a device named leaf gauge can be used.
Leaf gauge and centric relation
Before we get to the leaf gauge, let us briefly understand what a centric relation (CR) is. The lower jaw is movable. Its movement in all three planes allows us to speak and chew. It is connected to the skull through a joint located near our ears. This is the temporomandibular joint. The lower jaw has a round head-like part (condyle) on both its ends that fits within a depression or fossa in the skull near the ear. The movement of the condyles within the fossa is what allows us to make the necessary movements of the lower jaw. When the condyle is positioned in the most furthest and the most superior portion of the fossa, it is said to be in centric relation. The centric relation can be obtained irrespective of the position of the teeth.
A dental leaf gauge can help in getting the centric relation of a patient. The centric relation needs to be obtained when patients require a fixed, removable or an implant-supported prosthesis. The leaf gauge was first introduced in 1973. Since, then its fabrication has evolved and it has been used for both occlusal adjustments and for muscle spasms.
It is made of mylar, polyester, polycarbonate or acetate. Each leaf is 0.1mm thick. The dentist holds a bunch of these leaves in his hand. Next, he positions the leaf gauge in such a way that it touches the upper front teeth. The dentist now asks the patient to bite in a way that the lower front teeth touches the leaf gauge. Till here, the dentist can hold any number of leaves and the basic goal is to ensure that the back teeth of both jaws are not in contact with each other. From here, the dentist removes or adds the leaf accordingly.
The dentist will then ask the patient to ensure that his or her back teeth touch each other. Initially, it might take the patient some time to adapt, but when the back teeth contact each other, it is recorded as a first point of contact. This means that the muscles of the patient are now released from tension and a proper point of contact is established. Now, in order to record the centric relation, the dentist adds a few more leaves to once again separate the back teeth minimally. The dentist now records the bite of the back teeth by adding some silicone impression material between the bite. Once the material hardens, bite is registered. The material is removed carefully such that the impression made by the tips on the teeth are preserved.
Leaf gauges need to be sterilized by moist heat at 132°C for 4 minutes. This is done in an autoclave. Once this cycle ends, the leaf gauge is left in the chamber for 30 minutes for drying. They need to be cooled down for an hour before being reused. The way the leaf gauge is stored also contributes to its shelf life. Leaving the device in a wet or dusty area can effect its handling characteristics. A set of laf gauge can be used multiple times. It is up to the clinician as to how many times can he or she use the same leaf gauge after autoclaving it.
A leaf gauge is a handy tool that can help the patient to record a perfect bite irrespective of the position of the teeth. Moreover, the recorded bite is completely done by the patient's own neuromusculature and is not a forced procedure. It allows for subtle occlusal adjustments if needed and can help in easing the musculature. An anterior jig is another device that performs the same function as leaf gauge and has also been advocated for clinical use.