July 09, 2020
In dentistry, a lot of anatomical and physiological processes are inter-related. In order to understand one component, it is important to understand the more vital smaller components. This applies to Lucia Jig as well. In order to understand Lucia Jig, it is important to know about centric relation, condyles and a few associated muscles.
The upper and lower teeth coincide with each other systematically because of the way they are arranged in the mouth. A major portion of it is dependent on the position of the lower jaw. The lower jaw is movable and its motility is dependent on the temporomandibular joint. This is a joint that is situated at the region of the ears. The part of the temporomandibular joint that causes movement of the lower jaw is the condyle. This condyle moves in a "fossa" which is a space that connects the lower jaw (mandible) to the fixed area of the skull it is related to (temporal lobe). When this condyle is present at the most upper and backward position in the fossa, the given position between the upper and lower jaws at that instance is called the centric relation.
The centric relation is majorly dependent on the muscles that are related to the condyles and the lower jaw. These are the same muscles that also help in chewing. In dentistry, a centric relation is often obtained by the dentists when they need to fabricate dentures and appliances in order to correct the inter-relation of teeth and thus the overall stability of the oral cavity. It is important to note that the centric relation is recorded irrespective of whether the teeth are in contact or not. Hence, one of the techniques to record this centric relation by relaxing the associated muscles and making sure that the back teeth are not in contact with each other is called the Lucia Jig.
A Lucia Jig is a technique that uses a hook-shaped jig as its main component. This comes in two dimensions and can be used depending on the distance between upper and lower teeth. A "Whale Tail" or "Tongue Depressor" are used in conjunction with the jig in some cases. Lucia Jig has a recess in which a flowable material is inserted. After this, the jig is inserted in between the upper central teeth. The patient is asked to close his mouth in a way that the lower central teeth touch the jig. This leads to the upper and lower back teeth staying away from each other.
The dentist then puts a thin paper known as an articulating paper between the jig and the lower central teeth. The patient is asked to make back and forth grinding movements. The articulating paper's dye leaves an impression on the jig indicating whether both the lower central teeth are in proper contact with the jig. If not, the dentist needs to make necessary adjustments. Re-insertion of the jig is done, and in a similar way by making certain movements, the most retruded position is recorded. This is ensured when a mark on the jig is left by the articulating paper.
The movements also make sure that only a selective muscles responsible for chewing are relaxed. A couple of other muscles move the condyle in its possible that causes centric relation. It is important to note that the patient should feel no strain or discomfort in the temporomandibular joint or the jaws during this process. This preliminary procedure terminates only when the patient feels relaxed.
Later, following the drying of teeth, a flowable material is injected on the chewing surfaces of the teeth. This material is injected starting from the back teeth, moving then to the front teeth. This material needs to be 4-5 mm teeth so that the cusps on the chewing surface are properly recorded. When the record is obtained, the material is carefully removed and the excess material is trimmed. If the patient's lower incisors are not in alignment the Lucia Jig can be used on those incisors as well. There will be no change in the accuracy of recording centric relation.
Lucia Jig is one of the best procedures for recording central relation. It takes approximately 20 minutes for the Lucia Jig to be recorded. But it can be time consuming at times and is not indicated in patients with dysfunction or pain in temporomandibular joint.