What is muscular disturbance?
Muscular disturbance plays a major role in Temporomandibular (TMJ) joint dysfunction. In many cases of TMJ syndrome, inflammation and muscle spasm occurs give rise to pain, inability to open the mouth wide(trismus), and in sever cases, jaw lock. TMJ joint dysfunction is a term to describe a collection of signs and symptoms pertaining to the Temporomandibular joint degneration and/or the disturbance of the muscle of mastications. Patient most often referred to these symptom as clicking, crepitus, tinitus, headache pains for a period of time, sore muscle and jaw. Occasionally, these symptoms come and go, and may be disappear after a while. This “silent stage” may be a precursor to the more serious joint degeneration, or just part of the adaptation which the joint-occlusion-muscle complex adapt to operate at the satisfactory threshold, borderline level. Nevertheless, patient will almost always benefit from early intervention in order to avoid possible joint degeneration. In many cases, symptom can be relieved or reduced greatly with treatment.
What happen to the muscle surrounding the osteroarthitic TMJ?
The primary purpose for the muscle is to keep the parts of the joint they straddle in contact. With the disc no longer interposed between the condyle and eminence, these bones articulates against each other and degenerate. The degeneration brings about wearing down the articular surface and shorten, which causes the muscles straddling the joint to shorten its contracting length (the muscle pull distance is shortened). When the muscle pull distance is shortened, the strength increases and further rub the bones against each other and further wear down its articulating surface. This vicious cyle of shortening, break down, shortening, is established.
What are the muscles involved with the TMJ joint-occlusion complex?
The muscle of mastication work synchronously in pairs to help guiding masticatory movement such as opening and closing of the mandible.
The major muscle pairs that involve with opening (depressor muscles) are:
- Digastric: This is a sling muscle, arises from the mastoid notch, attached to the tendon on the hyoid bone, and sling forward to the digastric fossa of the mandible. Its contraction pulls the mandible down and back. This muscle will be exquisitely sensitive to palpation if the mandible is chronically posteriorized
- Inferior head of lateral pterygoid muscle: originates from the lateral surface of the lateral pterygoid plate and inserts at the neck of the condyle. Its contraction pulls the neck of condyle and cause the mandible to glide forward (This occurs after the condyle has rotated and mandible open about 21mm). This muscle will exhibits soreness and pain to palpation upon chronic dysfunction
The major muscle pairs that involve with the closure(elevator muscles) of the mandible are:
- Temporalis: Divided into the anterior portion which elevates the mandible and the posterior portion which retracts the mandible. Its middle portion both elevates and retracts. This muscle can be palpated and show tenderness in TMJ patient
- Masseter: Originates from the medial surface of zygomatic arch and inserts into the lateral surface of the ramus and angle of the mandible. Its contraction produces a powerful force to elevate the mandible. This muscle shows excessive tonus in clenching or bruxing patient
- Medial Pterygoid: Originates from the medial surface of the lateral pterygoid plate and inserts on the medial surface of the angle of the ramus of mandible forming the fascial sling with the masseter muscle
There are the suprahyoid muscles which plays minor role (except for the digastric muscles which depress the mandible) in guiding the movement of mandible and swallowing. They are: Geniohyoid, Mylohyoid, Platysma, and the Digastric.
The superior head of the lateral pterygoid muscle arises from the infratemporal surface of the greater wing of sphenoid and inserts on the anteromedial portion of the TMJ disc. In TMJ patient that exhibits clenching and bruxism, the superior head of the lateral pterygoid muscle contracts at the end of power stroking during closure of the mandible. Unilateral contraction of the inferior head of the lateral pterygoid contributes to the lateral movement of the mandible.
How is the splint designed to help balance the muscle involved in TMJ dysfunction patient?
The splint is designed to:
- Position the mandible such that the muscle involved can be function in harmony by eliminating all the interference and stimulatory factor from the occlusion.
- Artificially decompresses the tissue of the TMJ and allow the disc to function between the articulating surfaces of the condyle and the glenoid fossa.
- By discluding the teeth, the splint help to reduce the proprioception into the central nervous system and thus “deprogram” the mandible from its position. Now the mandible is positioned by the balancing and harmonious functioning of the muscles, not by the occlusion of the teeth.
- Restores foreshortened masticatory muscles to their resting length. As this occurs, the electrical activity of muscles will decrease since the muscles are allowed to rest more between function.
- Restores the component parts of the TMJ to the normal physiological position, allows for a normal range of function concerning condyle-disc-eminence complex, and stabilizes and limits TMJ functional movements to promote healing to the tear or fibrosed ligaments.
What are the various splint designs and their application?
Maxillary appliances are popularized by crown and bridge restorative dentist due to the fact that they usually restored the mandibular teeth first and therefore want this arch to be unencumbered by the presence of the splint. However, it binds up with the maxillary and palatine bones and interfering with their movement. I always try to place the splint on the mandibular arch for this very reason. It is also unesthetic and therefore poor patient compliance. The followings are the available splint designs:
- Smooth surfaces – myalgia patients
- Central occlusion
- Pull forward (SVED)
- Distalization of the mandible
- Thompson (pivot) – for closed lock
- Palatal expansion
- Sagittal – for incisal interference
- Entirely flat – myalgia patients
- Pull forward – for bilateral reciprocal clicks, unilateral reciprocal clicks, and unilateral closed locks
- Pivot – for bilateral closed-lock TMJs
- Flexible nightguard
- Preformed nightguard
- Fillings on second molar or second premolar to increase the vertical
- Posture erector or correct forward head posture and chronic cervical extension
If the problem is musculature in nature with no joint derrangement (no clicking or popping or crepitus), a flat mandibular splint is used. In the case of unilateral or bilateral reciprocal clicks, a pull forward splint should be used, constructed at the point anterior to that at which the click occurs. In the case of bilaterally closed locked TMJ joints, pivotal splint is used to move both condyles inferiorly simultaneously. When the patient begin to click, the splint is converted to a pull forward splint constructed slightly anterior to the point of the click. Whenever patient exhibits a closed lock unilaterally, the pull forward splint will be deliverred with the use of the molt retractor with local anesthesia or manually to allow decompression of the tissues or in some case the disc will be able to pop into place. Finally, flat or pivotal splint for the unilateral or bilateral reciprocal clicking joint should be avoid because the mandible drops posteriorly during sleep causing the clicking joint to become closed-locked.
How do we know that the splint is working as expected?
Often we need to change our splint design as the joint complex evolves into different stage during healing. Overally, these are the positive signs of a “working” splint design:
- No joint noise
- Interincisal opening of 48 mm or more
- No deflection or deviation from opening
- Working excursion of 12 mm or more
- Condyle centered or anterior of center of fossa, radiologically
- Condyle travel past eminence and is separated from it radiologically by 2mm (average thickness of the disc)
- New cortical bone formation if previously degenerated, radiologically
What else do we need to do after the splint therapy has deemed successful?
The next phase of TMJ treatment usually involves orthodontic therapy and crown and bridge. In extreme case, we may need orthonagthic surgery and/or orthodontics and crown and bridge. Rarely will the post treatment stabilization only require equilibration. Equilibration usually will only effective in short symptomatic period, young patient whom the joint complex has not undergone osseous change and his or her dentition does not develop compromising and pathological malocclusion.
What are the contraindication in long term usage of the splint without moving forward to reconstructing the occlusion?
In many case, due to financial limitation, patient is unable to move forward into the second phase of reconstructive treatment. The splint will then act as part of the palliative treatment (supportive treatment) and the symptom may relapse due to many factors to be mentioned below. Long term usage of the splint will:
- Posterior open bite: this phenomena happened when the patient continously function with the splint and depressed the mandibular posterior teeth. Anterior disclusion will cause the anterior teeth to supraerupt and further worsen the posterior open bite.
- Fremitus: the phenomena which the anterior teeth contact prematurely during swallowing or functioning, results in traumatic occlusion to the opposing maxillary anterior teeth due to supraeruption of the mandibular anterior teeth. The fremitus will cause localized vertical bone loss, inflammation to the periodontium of the anterior teeth, and may result in periodontal abscess.
- Clicking, popping, and headache may return due to loss of vertical dimension (due to intruding mandibular posteriror) and supraeruption of anterior introducing interference and malocclusion.
I believe if the patient is unable to move to second phase, the splint should be worn intermittently to provide the teeth with antagonistic action and thus avoid these complications to occur. The splint now is function palliatively to alleviate the symptoms of TMJ dysfunction.
These are the protocol of which Dr. Bui, D.D.S., M.S., follows in his treatment modality. It is not necessary the same or equivalent with other operator. Our method may be different, but the final result should be toward eliminating or relieving the TMJ dysfunction. I would like to extend my gratitude to Dr. Brendan C. Stack, D.D.S, M.S. and Dr. John E. Scott, D.D.S., M.S. for all my trainings and educations.