Monitoring Mandibular Position

One of the strong points of the FreeBite system is that it allows the patient and/or the operator to compare two jaw positions to each other:

  • Habitual Occlusal Position (HOP): Where the teeth normally fit. May be associated with the symptoms presented by the patient.
  • Orthopedic Mandibular Position (OMP): Where the mandible settles as muscles relax and compression of one or both TMJ’s is released. May be associated with symptomatic relief.

Normally, it is complicated and costly to construct a different bite and it becomes apparent only afterwards if the new bite actually works better. The FreeBite will support the mandible in a variety of positions while insuring that the TMJ’s are unloaded in the process. Therefore, treatment results from a chiropractic manipulation, manual therapy or osteopathic techniques can express themselves in changes of the mandibular position while the mandible remains supported when biting. It therefore becomes of particular interest quantify such changes. While computer assisted electronic measurements provide a convenient means to do so with great precision, not all dentists have access to such costly equipment, not to mention other therapists. However, there are simple means by which changes in mandibular position can be monitored:

  1. Dental Midlines
  2. Sagittal Overjet of Incisors
  3. Point of First Occlusal Contact

Dental Midlines (DM) are where the left and right upper and lower incisors touch, or the middle of the gap between them if they do not touch. Dental midlines do not always match up, for instance due to the upper dental midline deviating from the cranial center (due to a turned lateral incisor on one side, orthodontic treatment, etc.), or due to the lower dental midline deviating from the mandibular midline for similar reasons. Probably the most common cause for mismatched dental midlines is, however, a mandibular shift towards one side in occlusion. This can happen for a variety of reasons, manual bite registration techniques for dental restorations being. If the dentists tries to manually retrude the mandible into a hinge axis position, he operates against the bilateral resistance of joints, muscles, ligaments and fascia. This bilateral resistance is unlikely to be perfectly symmetrical, resulting in an uneven retrusion on both sides and a side shift of the mandibular DM toward the side offering less resistance. When using the FreeBite it is therefore important to compare the relationship the dental midlines assume when biting down on the teeth in intercuspation with that assumed as the chewing muscles relax and TMJ’s decompress on the FreeBite. The latter relation of the DM is monitored with the FreeBite between the teeth and after it has been worn at least for 30-60 minutes. 

The Sagittal Overjet of Incisors (SOI) is the measurement from the upper incisal edge to the anterior surface of the lower central incisors. This can be done by placing a small ruler cut off at ”0“ against the front of the lower central incisors and reading the value under the upper incisal edge. Again, this value is measured twice, once with the teeth together at maximal intercuspation and once with the FreeBite between the teeth and after it has been worn for 30-60 minutes. A decrease of this value means that the mandible has shifted forward.

The Point of First Occlusal Contact (PFOC) occurs when the patient assumes an upright, but unstrained head and body position, opens his mouth, then relaxes it and finally closes it lightly until the first tooth just touches its antagonist. This can be repeated a few times to assert consistency. After wearing the FreeBite for at least 30-60 minutes, it is taken removed and the mouth is again opened and then closed lightly while the first dental contact is monitored. A PFOC shifting towards the anterior teeth can have two meanings: 

  1. The mandible has shifted forward while the chewing muscles relaxed.
  2. There is more space between the posterior teeth, because the TMJ’s have decompressed and returned to an unloaded joint space.

Most commonly found will be a combination of 1. and 2. The PFOC is a much more sensitive measure than the SOI and will change even with minimal shifts which cannot be determined by the use of a ruler. However, if the PFOC changes massively, may be to such an extend that the posterior teeth cannot even be brought into contact with some force exerted by the chewing muscles, this is an indication of a previously existing compression of the TMJ’s, especially if the SOI has hardly changed. The release of a unilateral joint compression is usually accompanied by a shift of the lower DM and the PFOC to the opposite side.

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