Bite registration technique for TMJ-patients

How pain in the TMJ comes about, or why certain patients, referred to as „TMJ-patients“, develop all sorts of pains and aches in the head and neck region, is subject to a seemingly endless controversy. However, to the clinical practitioner confronted with a patient seeking help for such problems, randomized double-blind studies are not the answer. He needs to know if and how he can help this individual person in front of him, not what statistic calculations he or she may be part of.

Bite cushions have been a valuable asset here, in that they make it possible to take the factor „occlusion“ out of the equation for a while and observe what happens. The neuromuscular system, instead of holding the mandible such that closure will result in a stable contact between the teeth, can let go, because any kind of closure from any resting position will result in a balanced contact of the bite cushion. Over time, involved muscles are likely to relax and the patient can observe how his symptoms react while the doctor takes notice of specifics, like lateral or sagittal changes in the mandibular posture, in order to determine which aspects of the bite may be causing the problem.

If a patient recovers from his symptoms by wearing a bite cushion, scientific statistics have lost their relevance for his case. The next step would be to identify the particulars of the mandibular position on the bite cushion and to check if the symptoms of the patient can be controlled as well by providing identical occlusal support in a fixed occlusal position, f. i. by using a bite splint. However, transferring the occlusal relation from the mouth to dental casts in an articulator can be a challenge.

The FreeBite® has been developed to provide extra posterior occlusal support, by extending the bite cushions all the way to the back molars. A slight wedge-shape of the cushions insures the first contact at the back teeth with every bite. This is the opposite sensation from what most TMJ-patients experience when they have trouble in finding full support on their back teeth. The bite cushions can be filled with water, but for the purposes of this registration technique this would not be ideal, since water is not compressible, thereby  limiting the range of vertical positions the mandible can assume while being supported on the cushions bilaterally. In our clinical comparison of actual heights of different bite cushions, the blue columns in the diagram are taller for a particular group of devices, the FreeBite air, signifying the greater range of compression available as opposed to a water filling.

The purpose of the following bite registration technique is to maintain the mandibular position associated with symptomatic relief on the FreeBite air while avoiding joint compression during the bite registration by keeping the mandible supported on the posterior teeth as the desired mandibular position is assumed. In addition, this technique allows the bite registration to be taken exactly at the desired vertical dimension so that any changes in vertical in the articulator and associated errors can be avoided.

Select a FreeBite air of suitable height („CMD" for neutral vertical, „CCD" for deep bites). Place it between the patients teeth. Also, try turning it upside down, as the upper and lower side of the FreeBite are not a mirror image of each other. Use the more comfortable side up and make sure that the incisors are not biting on the anterior connecting tube. Have patient lightly chew on the FreeBite, opening the mouth every 3–4 chewing strokes in order to reposition the FreeBite with the tongue for optimal symmetry and support for the posterior teeth.

Muscle relaxation will occur in as little as 1015 minutes of FreeBite chewing. Warn patient not to clench on the FreeBite, as this would prevent muscle relaxation.

Observe shifts in the alignment of the dental midlines and in the sagittal overjet of the front teeth as the mandible assumes a progressively more relaxed position.

Affix marks to the tips of the nose and chin. After 10–15 minutes, remove the FreeBite from the patient’s mouth. While the FreeBite is out, the patient must not bite on his or her teeth! 

Measure the distance between the marks as the patient relaxes his or her mandible so that the lips come into unstrained contact. This distance represents the vertical dimension at physiologic rest, which is 1-2 mm greater than the ideal vertical dimension at occlusal contact.

Replace the FreeBite air between the patient’s teeth and check if the desired vertical dimension is accessible by biting on the cushions until the distance between the marks reaches that measured at physiologic rest minus 1-2 mm (interocclusal space).

With the patient in an upright position, apply fast setting Futar® fast between the incisors. 

Have the patient bite down on the FreeBite air until the desired vertical dimension is reached as measured between the marks. Once again, the lips should come together without effort.

After the material has set, remove the FreeBite from the patient’s mouth and make sure that the incisors will fit into the indentations in the material after opening the mouth and closing lightly while maintaining an upright body and head posture. Re-check the distance between the marks as the patient lightly rests the incisors in those indentations.

Apply Futar fast onto the molars and premolars on both sides and have the patient again loosely close until the incisors just touch the indentations in the already hardened anterior part. Futar will passively mold to the posterior teeth without the need to actively bite down. 

After a few moments, the material will have set and can be removed from the patient’s mouth. The FreeBite air is replaced between the patient’s teeth and the patient again chews on it as before in order to prepare for the final check of the occlusal record.

After a few minutes, the FreeBite is again removed and exchanged for the bite registration. Maintaining an upright body posture, the patient opens his or her mouth and then lightly lets it „fall“ closed. The indentations on the bite registrations should be hit accurately without sliding on prematurities. When biting onto the material, the patient should feel an even and symmetrical loading of his back teeth on both sides. A hard setting material such as Futar fast provides for a much more precise feedback at this stage than more elastic materials can.

The end result should be a bite registration which captures the mandibular position in a position where the musculature is relaxed and balanced and the temporo-mandibular joints are not compressed. It also represents the exact vertical dimension where f. i. a dental splint can be fabricated. We have been teaching this technique to dentists for the past two years and practically everybody is able to obtain valid occlusal records in this way, regardless of dexterity. However, there are two possible factors which can prevent success:

1. Missing posterior teeth. 
2. Premature tooth contacts.

The FreeBite can only work as desired if there are posterior teeth to support the mandible and unload TMJ’s. 

If tooth contacts occur before the desired vertical dimension is reached, a balanced neuromuscular occlusal record cannot be obtained. In this case the operator has three choices:

  1. Compromise the vertical dimension and take the bite a little higher than originally intended. Care should be taken that the patient can still close his or her lips without effort.
  2. Eliminate the premature contact so that the correct vertical dimension becomes accessible.
  3. Compromise the neuromuscular balance of the occlusal record by allowing just enough slide on the prematurity so that the correct vertical dimension can be reached (usually the least desirable option).

Please also note that impressions for dental casts often times are taken with alginate. The silicone used for bite registrations may create impressions with more detail, preventing the dental casts from seating all the way on the occlusal record. The depth of the occlusal indentations in the record should be reduced in this case until the dental casts seat all the way.

This is a direct link to where the FreeBite air may be obtained. Please observe that the „CMD“ shape is also available in clinic packs at a greatly reduced price!

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