The Management of Temporomandibular Dysfunction (TMD) is the seventh article in a series to address applications of Botulinum neurotoxin. Feel free to review the other articles posted on The Intronix Technologies Blog.
The following article is presenting a short review of TMD applications of BoNT, with a focus on the benefit of using the Myoguide™ EMG/ESTIM BoNT injection guidance system.
The article presents some background specifically aimed at the management of Temporomandibular Dysfunction (TMD). The information within, is simply informative and not considered to be instructive, in any way. Please have a look at the article and the appropriate reference materials for more details
TMD is a common cause of chronic facial pain and is known to interfere with personal relations, professional duties, and overall quality of life.
Appropriate diagnosis allows physicians to identify the disorder and initiate an effective therapeutic plan. Botulinum toxin can provide long-term relief of TMD by reducing the intensity, frequency, and duration of recurrent episodes. BoNT injections can be an attractive option for adjunctive therapy in patients who have failed initial conservative therapy and systemic pharmacotherapy .
The temporomandibular joint (TMJ) is one of the few synovial joints with an articular disc. The TMJ functions as both a hinge joint and a sliding joint.
Adduction of the mandible (mouth closing) is performed by the actions of the masseter, temporalis, and medial pterygoid muscles.
Abduction (mouth opening) is performed by the lateral pterygoids and digastric muscles.
Lateral deviation occurs by the action of the contralateral lateral pterygoid muscles.
Protrusion of the mandible occurs when right and left lateral pterygoid muscles contract simultaneously.
TMD is the term used to describe orthopedic and myofascial disorders that affect the Temporomandibular Joint (TMJ). Temporomandibular joint dysfunction, or TMJ dysfunction, is used interchangeably. The prevalence of TMD is between 30% and 44%, with up to 25% of the population seeking professional care .
Symptoms are commonly related to pain surrounding the joint and may include headache, periauricular pain, neck pain, decreased jaw excursion, jaw locking, and noise at the joint with movement.
TMD is divided into two categories:
Myofacial TMD is associated with pain originating from hyperfunctioning muscles of mastication, which has led to chronic myositis.
Arthrogenic TMD is associated intracapsular pathology yielding pain in the joint itself.
Diagnosing Temporomandibular Dysfunction (TMD)
The diagnosis of TMD is based on history and physical exam findings.
Patients should be asked about:
- Nighttime bruxism
- Jaw soreness
- Morning headaches
- Use of orthodontic appliances
- History of trauma
- Personal habits
- Anxiety/ recent stressors
Signs and symptoms of TMD may include:
- Joint or muscular pain with or without jaw opening/closing
- Limited jaw movement,
- Cracking or popping sounds at the TMJ with movement
- Ear fullness or tinnitus (shared border with TMJ)
- Boring orbital or periorbital pain (neurogenic or muscular in origin > hyperfunctioning temporalis)
Treatments for TMD include:
- Nonpharmacologic therapy
- Conservative pharmacotherapy
- Open surgery
The initial management consists of nonpharmacologic management and typically include:
- avoiding triggers
- adjusting diet
- pain management
- physical therapy
- warm compresses
Patients with bruxism should be referred to a dentist and can be evaluated for an occlusal splint.
Systemic pharmacotherapy for TMD may be used as adjunctive therapy and includes:
- Anti-inflammatory agents
- Muscle relaxants
- Tricyclic antidepressants (in some cases) [9–12].
Less conventional approaches include:
- Cognitive behavioral therapy [13–15]
Selected patients with Arthrogenic TMD may benefit from:
- Intra-articular corticosteroid injections
- Arthroscopic surgery.
Despite the effectiveness of analgesic pain medications, response to opioid therapy is often incomplete with approximately three quarters of patients suffering from persistent pain .
Botulinum toxin (BoNT) injection has therefore become an attractive choice as supplemental therapy in patients with Temporomandibular Dysfunction (TMD), who do not achieve a complete response with conservative management and pharmacotherapy .
Botulinum Toxin (BoNT)
As we discussed in the blog post “ Orofacial Applications of Botulinum Neurotoxin”, Botulinum toxin (BoNT) is a neurotoxin produced by the bacterium Clostridium Botulinum. There are seven types of BoNT (A–G) which bind and cleave one of several neuronal cellular proteins including SNAP-25, Syntaxin or VAMP/Synaptobrevin.
The outcome of BoNT application results in the inhibition of release of acetylcholine (Ach) from the motor neuron terminals resulting in muscle weakness or paralysis. Duration of action depends on cellular regeneration mechanisms, which can take 3-6 months.
The pain-relieving effect of BoNT was reported during the treatment of oromandibular dystonia and cervical dystonia [18–22].
These days, BoNT is used for pain relief in numerous conditions including:
- Tension headaches
- Migraine headaches
- Post-herpetic neuralgia
- Myofacial TMD [23–27]
With respect to TMD chronic local muscular contracture has been known to cause inflammation and localized muscular hypoxia leading to chronic myofascial pain . However, the analgesic effect of BoNT comes from more than just muscle-based stress relief.
BoNT has a direct effect on nociceptors and the parasympathetic nervous system . Inflammatory mediators like calcitonin gene-related peptide (CGRP), substance P and glutamate are also regulated by SNARE and VAMP docking proteins and, their release is inhibited by BoNT. The effect of BoNT also effects pain processing, which reduces central pain sensitization.
A-delta sensory fibers, which mediate acute pain, and A-beta fibers, which mediate touch and pressure, are not mediated by neuropeptide release and are unaffected by BoNT. Thus, BoNT does not interfere with the perception of acute pain nor does it cause local anesthesia.
BoNT Injection For The Management of TMD
The most commonly affected muscles are:
- Temporalis muscle
- Masseter muscle
- Lateral Pterygoid muscles.
The Temporalis muscle and Masseter muscle are almost always involved and usually manifest as direct muscle pain .
Lateral Pterygoids involvement  usually manifests as:
- buccal pain
- lateral jaw deviation
There have been observations, in cases of Oromandibular Dystonia, that repeated injections of BoNT into Masseter and Temporalis muscles can lead to hyperactivity of the Medial Pterygoid. The expectation is that regardless of the Lateral Pterygoids being injectected, it may also be prudent to assess the Medial Pterygoid based on the clinician’s overall assessment of the patient .
Referred pain from the Medial Pterygoid is poorly circumscribed in regions of the mouth, hard palate and below and behind the TMJ 
Injections are best carried out under the electromyographic guidance (EMG guidance). The Temporalis and Masseter muscles are usually injected transcutaneously. Asking the patient to clench their teeth will support confirmation, using EMG localization .
Identification of the Lateral Pterygoid muscle is done intraorally. EMG guidance is recommended. The hypodermic needle electrode is placed between the Pterygoid Plate and the coronoid process of the mandible in order to access the Lateral Pterygoid muscle. Confirmation of insertion in the Lateral Pterygoid is effected by evoking EMG with lateral jaw movements .
The intraoral approach to the Medial Pterygoid allows palpation of the muscle before injection. The muscle can be located directly behind the last molar when you push your finger into the tissue. Once located the hypodermic needle electrode is inserted medial to the jaw and lateral to the Pterygo-mandiular raphe; piercing through the buccinator muscle . Asking the patient to activate the muscle will provide EMG confirmation.
There has also been discussions about accessing Medial Pterygoid by using a Tomogram/MRI- based- fabricated splint. These splints are created to be inserted and fixated intraorally, in order to provide a stable platform and pathway to the injection site . There are several additional steps, however, this procedure can add a lot of surety to the procedure.
It is known that BoNT diffuses out, within 1 cm from each injection site. The affected areas may be left untreated if an inadequate number of sites are infiltrated within a single muscle group. To avoid an incomplete response, it is advocated to use lower concentrations at multiple sites with larger injection volumes .
Injections for the management of TMD, are best carried out under the electromyographic guidance (EMG guidance).
Myoguide™ can play an essential role in these procedures by supporting EMG guidance procedures with both EMG audio and visual feedback.
Numerous studies have shown that BoNT  provides long-term relief of recurrent episodes of myofacial TMD by:
- Decreasing the intensity
- Decreasing the frequency
- Decreasing the duration
These studies reported significant reductions in their subjective and objective pain scores, and all patients with restricted mouth opening had some degree of improved range of motion.
They also reported successful treatment of various conditions that fall under the general category of TMD such as bruxism and clenching, oromandibular dystonias, trismus, masseter and temporalis hypertrophy, and headaches .
In a study of roughly 100 patients with TMD, there was a 70% response rate to BoNT-A injections to the masseter, temporalis and lateral pterygoid muscles. The response was defined as a 50% or greater reduction of subjective pain and/or frequency of pain .
Another study showed that BoNT injections into Masseter and Temporalis muscles led to a reduction in subjective measures of pain and tenderness to palpation. These results were greatest at 8 weeks following the injections. There was also a noted decrease in the average daily use of pain medication of the course of the 16-week study .
The Value of EMG Guidance in The Management of Temporomandibular Dysfunction (TMD)
These studies clearly illustrate that we all do better finding the optimal spots to locate the hypodermic needles when using EMG guidance, regardless of whether the muscle is located easily on the surface or deeper.
It is the confirmation that you are indeed in the muscle you have identified requiring treatment, that is the point of the matter. This will lead to improved results and a lower incidence of iatrogenic effects.
There are many compelling reasons to use EMG guidance. The first is that EMG ensures that the needle is located in a muscle. The second is confirmation that the needle is in a muscle that is actively contracting in association with the disorder.
Speelman and Brans showed that even the most experienced “blind” injectors were frequently inaccurate in identifying needle placement in muscles of the neck .
Comella and colleagues illustrated that BoNT injection for spasmodic torticollis increased magnitude of benefit with electromyographic assistance. The article involved comparing experienced investigators using EMG versus palpation and showed that EMG was superior in terms of reducing side effects and obtaining clinical benefit .
Recent studies showed that both expert and novice needle placements improve with guidance when compared without, even in large easily accessible muscles .
A recent review article by Grigoriu et al, showed strong evidence that instrumented guided injections (Ultrasound, EMG, STIM) were more effective than manual needle placement for the treatment of Spasmodic Torticollis, and both upper and lower limb spasticity .
These studies clearly illustrate that we all do better finding the optimal spots to locate hypodermic needles, when using EMG guidance, regardless of whether the muscle is located easily on the surface, or deeper, or whether the needle insertions are being carried out by novice or experts.
Myoguide™ is equipped with what is essentially a single channel EMG machine with a full featured, built in stimulator.
Myoguide™ EMG/ESTIM BoNT injection guidance system is designed to amplify EMG signals from muscle and provide audio and visual feedback to assist clinicians in locating areas of muscle activity.
The other useful feature is Myoguide’s ability to mute the audio. This is a design feature for times when it is better to operate in silence and rely upon the visual signal display. This is pertinent in cases where patients are easily startled or are likely to have issues with hearing EMG audio.
Myoguide also has an integrated and well featured stimulator, capable of stimulation in either 1.0 mA or 0.1 mA steps, for muscle, nerve, and motor endplate location procedures.
Myoguide supports injection of neuromodulators and both chemodenervation and neurolytic procedures, as well as, peripheral nerve stimulation. Learn more about how to use Myoguide
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