TMJ Surgeon.com TMJ splints and MRI imaging, Part I

One of the most commonly used non-surgical management devices is the bite splint or oral orthotic appliance.  As discussed  previous blog (12/29/10.   Refer to work of Simmons, Katzberg, Westesson, Lundh, Okesson et al), orthotics that engage the teeth on the lower jaw and are used to posture the lower jaw slightly forward until orthopedic function improves are called Anterior Repositioning Appliances (ARA).  The appliances have bee studied have have been shown to have the ability to correct a Wilkes II derangement as long as they are worn.  This is followed by   Non-surgical treatment, usually with orthodontic movement of the teeth to a position that mimics the action/jaw position of the orthotic,  is then advocated to place the teeth in a position to emulate the ARA.  This can be successful is some cases and under the correct state  of circumstances.  For this treatment to be scientifically valid, it must be accompanied by imaging that directs the  non-surgical treatment  in order to validate it.  (Tomography, CT scan, MRI etc.)

Occasionally, this treatment may not be completely successful and orthopedic instability returns.  The reason this can happen is that there is a significant weakening if not outright detachment or tear of the disc/capsule from the lateral condyle such that orthopedic forces (shear and torque)  delivered to the disc/capsule are greater  than the integrity of the ligament attachments and instability remains or worsens during even the best of orthodontic care.

Orthotics play a great role in diagnosis of the integrity of this disc/capsule attachment to the lateral condyle as shown below.

 FIGURE 1

Figure 1 is a coronal scan of a patient with the teeth together in the closed mouth position.  There is no orthotic or splint (ARA) in place.  The left side of the MRI phots is the lateral side.  Note the irregularity of the lateral condyle pole and its surfaces, suggesting eary osteophyte (bone spur) formation.

 FIGURE 2

Figure 2 represents the same joint with the ARA in place.  Despite its use, the joint still remains painful, is unstable and locks, alternating between Wilkes II and III.  Observe closely the lateral disc/capsule attachement to the lateral pole of the condyle  shows a detachment or tear in the disc/capsule in the vicinity of the osseous irregularities of the lateral condylar pole.  In this case, the ARA has decompressed the joint in order for MRI to reveal the torn attachments.(The disc/capsule is the intermediate grey image that is an extension of the condyle of the jaw and articulating with the fossa at the base of the skull. Continued instability of the joint despite the use of the appliance and continued dysfunction of the joint during  joint loading while eating are significant findings of an injury or acquired problem which will not respond to non surgical management.  Note that sagittal two dimensional views of this condition can be normal (See Wilkes/Piper classification blog).  Three dimensional scanning with and without the
ARA are necessary for complete and accurate diagnosis in these cases.  The ARA also improves the ability of MRI to visualize all components clearly in the decompressed or slightly open joint translating position.

Surgery performed at this stage of development of derangement preserves the integrity of critical joint structures which must adapt to the physical/mechanical needs of curvilinear general plane motion.   Eriksson et al experimentally produced TM joint derangement by detaching the disc/capsule in the lateral and posterior lateral regions of adaptation of the disc/capsule to the condyle of the jaw.  Experimentally detaching the disc/capsule from other areas surrounding the condyle did not.  The biomechanical reason for this is that this area is a region where tension forces during all types of joint function  converge and are concentrated    The act of joint translation and unstable and damaging forces of shear and torque during mouth opening and condyle translation  will create significant damage to an unstable disc/capsule over time.  Examples of irreversibly damaged discs are presented elsewhere in this web site (see previous blogs).

SUMMARY

Orthotics, “bite splints” and ARAs have  played  an important role historically in  TMJ non-surgical  management.  MRI imaging reveals they do a good job of “decompressing” a painful joint.  They change the dynamics of how the disc capsule is loaded during mouth closing , tooth engaged maneuvers.  However, they have no ability to change the biomechanics of when the joint is loaded maximally during open mouth maneuvers. (See Koolstra et al reference).  Once the integrity of the lateral disc/capsule attachment to the condyle is lost, shear and torque force generated throughout the fibrous disc tissue will result in irreversible tissue damage if this component of biomechanical and orthopedic instability is not corrected .

Eriksson L, Westesson PL, Macher M et al:  “Creation of disc displacement in human tempormandibular joint autopsy specimens.”  J Oral and Maxillofacial Surg. 1992;  50:869-73.

Koolstra JH and vanEijden TMGJ:  “Combined finite-element and rigid-body analysis of human jaw joint dynamics”, Jnl of Biomechanics 38(2005) 2431-2439.

Kirk, WS and Kirk, BS: “A biomechanical basis for primary arthroplasty of the temporomandibular joint”.  Oral and Maxillofacial Clinics of North America 18 (2006) 345-368.