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Long JH. Locating centric relation with a leaf gauge. J Prosthet Dent. 1973; 29:(6)608-610
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Centric relation contact position (CRCP) is the relationship of the maxilla to the mandible when the condyles are in an anterior/superior position in their fossae and tooth contact has just occurred. Provided that the TMJ remains healthy, CRCP is constant and reproducible throughout life and appears to be functionally comfortable. Accordingly, CRCP records serve as a useful reference from which restorative and prosthodontic treatment can be planned.
One frequently reported method of recording CRCP is the bimanual manipulation technique, first described by Dawson.1 This is where the operator supports the patient's mandible during the retruded arc of closure until the first tooth contact (CRCP) is felt by the patient. This process is repeated while the assistant marks CRCP using articulating paper. Some clinicians believe this technique is prone to operator error and that it is difficult to be certain when the mandible is in CRCP using this method.2,3
An alternative, and perhaps simpler, method of locating and recording CRCP is to use the leaf gauge.4-6 This simple, reusable device consists of around 50 flexible mylar strips, or leaves, that are riveted together. Each leaf has a uniform thickness of around 0.1 mm and these are sequentially numbered to provide a convenient record of the exact vertical opening between the incisors (Figure 1).
Figure 1. The leaf gauge.
To record CRCP using the leaf gauge, the operator must first identify the point of initial contact. This may be achieved using the following sequence:
An arbitrary number of leaves are selected from the leaf gauge and placed between the anterior teeth, at the midline, parallel to the lingual plane of the maxillary central incisors;
The patient is asked to close on his/her back teeth until a lower incisor touches the underside of the leaf gauge;
Leaves are then added or subtracted, as required, until the patient can just barely feel a posterior tooth touch while closing firmly on the leaf gauge;
Further leaves are then added, one at a time, until the patient no longer feels any posterior tooth contact;
This is checked by asking the patient to slide the mandible forwards, backwards and then to squeeze his/her teeth together.
After around 15–20 seconds, the patient will again be able to feel a posterior tooth contact, due to relaxation in the musculature or joints;
The operator must then add leaves, one at a time, until the patient can squeeze for 2–5 minutes without feeling any posterior tooth contact;
At this point, the mandible is described as being ‘tripodized’ in its centric relation position with the right and left condyles;
Leaves can then be removed, one at a time, until a point of contact is again felt. With the leaf gauge in situ, this point of contact is marked with articulating paper by again asking the patient to slide forward, backward and to squeeze (Figure 2).Marking the initial point of contact with the leaf gauge in situ.
To make the CRCP record, the following sequence is suggested:
After identifying the point of initial contact, leaves are added back in, and the number noted, to achieve tooth separation of 1–1.5 mm;
This degree of separation prevents posterior tooth contact, eliminates periodontal proprioception, and ensures that the registration is as thin as possible;7
The leaf gauge is then removed, and the patient is instructed not to close his/her teeth together again, so that the proprioceptive effect of tooth contact is eliminated;
Silicone bite registration material is injected around the maxillary posterior teeth on both sides, and continued up to the level of the canine teeth;
The leaf gauge is re-inserted, using the same number of leaves, and the patient is asked to slide forward, back and to squeeze. The gauge prevents the patient from closing completely through the recording material, which would result in an inaccurate record;7
Once set, the registration material is removed and sent to the laboratory;
If needed, a second record is taken in the same way and the accuracy of both records is checked on the mountings.
The leaf gauge is a valuable yet simple device that simplifies diagnostic centric relation records. It may be useful for patients in whom mandibular manipulation is difficult.
