A CAD-CAM-derived needle guide for safe treatment of oromandibular dystonia

Oromandibular dystonia affects the function of the mouth, tongue, and jaw, often resulting in difficulty chewing, eating, speaking, and swallowing. The most effective way to treat it is with botulinum toxin therapy – Botox^® injections. However, the muscles that cause the problem are not always easy to access. Dr Kazuya Yoshida at Kyoto Medical Center, Japan, has developed a computer-aided design/computer-aided manufacturing (CAD/CAM)-derived technique that enables the medical practitioner to accurately and safely inject into the lateral pterygoid muscle, considerably improving the quality of patient care.
Oromandibular dystonia is a neurological syndrome characterised by involuntary muscle contractions affecting the mouth, jaw, and tongue. It causes jaw closing, jaw opening, repetitive involuntary movements, and abnormal jaw positions, and can make chewing, eating, speaking, and swallowing very difficult for the affected individual.

A number of diseases and conditions can lead to oromandibular dystonia, including hereditary causes, injuries, medications, neurological diseases such as Parkinson’s, and strokes; meanwhile in some cases the reasons behind the syndrome remain unclear.

Involuntary mouth opening and botulinum toxin therapy

Injection of botulinum toxin (Botox^®) is the treatment of choice for oromandibular dystonia. Botox^® is a medication made from a toxin produced by the bacterium Clostridium botulinum that causes muscle paralysis (absence of muscle tone). For example, in patients with jaw opening dystonia (involuntary mouth opening), the lateral pterygoid muscles contract involuntarily, so the patient is unable to close their mouth. In this case the lateral pterygoid muscles need to be injected with botulinum toxin. For this treatment to work, however, the injection must be accurately administered.

These muscles can be accessed from outside the mouth, however this approach has been found to increase the risk of bleeding or mouth dryness, and anxiety for patients, while accessing the muscles from inside the mouth is similar to injections patients might have experiences during dental procedures, and therefore more familiar. Accessing the muscles from the inside also reduces the risk of damage to the maxillary artery and, because the teeth close at the insertion point, the injection is easier to guide. Because the risk of damage and side effects increases with the number of injections, accuracy in the injection site is critical for safe and effective treatment.

“Accuracy in the injection site is critical for safe and effective treatment of jaw opening dystonia.”

However, the lateral pterygoid muscles are among the less-understood muscles of the human body. They are anatomically complex, can differ in structure between individuals, and are often difficult to access. Because of these complications, Botox^® injections into the more accessible jaw closing muscles are currently performed more often, which means it’s hard for practitioners to develop the skill and confidence required for freehand needle insertion into the lateral pterygoid muscles. To solve this problem, Dr Kazuya Yoshida at Kyoto Medical Center, Japan, has developed an innovative needle-guidance technique using computer software that combines data from computed tomography (CT) images of the jaw, and the scan data of a model of the jaw.

CAD/CAM needle guide

Computed tomography (CT)-based surgical templates have already been successfully used in other fields to ensure precise implant insertion. Yoshida thought of using this method to secure an accurate and safe procedure for botulinum toxin injections in the lateral pterygoid muscles. To achieve this, he modified an existing dental implant template to accommodate the Botox^® injection. He then designed a customised computer-aided design/computer-assisted manufacture (CAD/CAM)-derived needle guide which he then tested on patients with jaw opening dystonia.

Jaw opening dystonia study

Seventeen out of 42 patients that were diagnosed with jaw opening dystonia between August 2015 and July 2016 at Kyoto Medical Center were randomly selected for the team’s study. The diagnosis in all cases was established by performing an electromyography (EMG), a test to measure the function of the lateral pterygoid muscles. CT scans of the area with 0.5mm-wide slices were performed for each patient, the images of which were stored in a special format (Digital Imaging and Communications in Medicine – DICOM). At the same time an impression of each patient’s upper jaw (maxilla) was taken using an alginate impression material; this impression was then used to create a plaster model of the jaw. The next step was to take images of the jaw models, which were then imported and fused with the respective CT images for each patient using special clinical software.

The information on the position and shape of the muscles provided by the combination of two and three-dimensional images was analysed to determine two points, ten to 15mm apart, for injection of botulinum toxin into the inferior head of the muscle. These were used as landmarks to adjust the insertion position of the needle into the center of the targeted muscle. Based on these images and their analysis, Yoshida created a CAD/CAM-derived needle insertion guide for each patient. Two metal guide sleeves were then created on each side of the guide, for the insertion of the injection needle.

During the procedure, the guide was fixed over the patient’s teeth. Next, an injection needle was inserted through one of the metal sleeves, to take measurements of the muscle’s activity via EMG monitoring and check correct placement of the injection. After the measurements and verification of the correct positioning, the botulinum toxin was injected into the lateral pterygoid muscle through the metal sleeves. Thirteen of the patients were initially given the botulinum toxin therapy without the guide, with the guide being used for their subsequent treatment. The rest of the patients only had the guided injections.

Improved efficacy and safety

Yoshida evaluated the results of the treatments using a scoring system based on the severity and number of the patients’ symptoms and complaints. Based on these scores, there was a significant improvement of the patients’ functional problems when using the guide compared to the times the guide wasn’t used. More specifically, the mean improvement without the guide was found to be 54.3%, while the improvement observed with the guide was 66.3%. Besides using the clinicians’ scores, Yoshida also evaluated the patients’ subjective feedback after the completion of their treatments. The results showed that the patients were significantly happier with the outcome of the guided treatment compared to the outcomes of freehand injections.

Besides providing a more precise and effective method to administer the treatment, the customised guides also enabled easier insertion of the needle inside the muscle, without any complications. The study’s results overall suggest that the method is very safe. The EMG showed that the electrode was accurately placed the first time in each case.

A promising new method

Yoshida’s study is the first time this innovative use of customised CAD/CAM-derived needle insertion guides for Botox^® injections into the lateral pterygoid muscles has been reported. It clearly showed that the guides provide an easier, more efficient, and – most importantly – a safer method to deal with jaw opening dystonia. ‘The needle was easily inserted without any complications in all the procedures in this study,’ reports Yoshida, ‘and the results suggest that this method is highly safe’.

“The CAD/CAM-derived insertion guide could enable patients to be treated locally, without lengthy and multiple trips to specialist clinics.”

Although the objective evaluation of changes in the patients’ symptoms is difficult in oromandibular dystonia, the study did demonstrate that there was significant improvement for the patients using the guide compared to when they had the freehand injections, even by a very skilled practitioner.

Besides facilitating the administration of botulinum toxin, the method could potentially be modified in the future for studies of the role of the lateral pterygoid muscle, something that would give us more information about this complex and poorly understood structure. Such insertion guides could also be used with other muscles, enabling the development of techniques that could help overcome similar challenges in other areas of the human body.

Making dystonia treatment accessible

Most importantly though, the CAD/CAM-derived needle insertion guide could become a very useful tool in the hands of clinicians who are less experienced and less skilled in the procedure. Yoshida believes that jaw opening and jaw deviation dystonias are often misdiagnosed or overlooked, and that the actual prevalence of such conditions is higher than generally estimated. This makes this new development even more important, as patients can be diagnosed and treated locally, without lengthy and multiple trips to specialist clinics.

This hope is enhanced by the ongoing technological developments in telemedicine, that will enable easier and better access to remote digital data, making it possible for follow-up examinations and treatments to be performed by the patient’s own clinician.

References

• Yoshida, K, (2018) Computer-aided design/computer-assisted manufacture-derived needle guide for injection of botulinum toxin into the lateral pterygoid muscle in patients with oromandibular dystonia. Journal of Oral and Facial Pain and Headache, 32(2), 13–21.
• Yoshida, K, (2018) Botulinum neurotoxin injection for the treatment of recurrent temporomandibular joint dislocation with and without neurogenic muscular hyperactivity. Toxins, 10(5), 174.
• Yoshida, K, (2016) How do I inject botulinum toxin into the lateral and medial pterygoid muscles? Movement Disorders Clinical Practice, 4(2), 285.

Research Objectives

Improving the accuracy, effectiveness, and safety of botulinum toxin therapy for oromandibular dystonia, using a computer-aided design/computer-assisted manufacture-derived needle guide.

Funding

This work was supported by JSPS KAKENHI Grant Numbers JP24592946 and JP22111201.

Bio

Dr Kazuya Yoshida is Head of the Department of Oral and Maxillofacial Surgery at Kyoto Medical Center. He applies a comprehensive range of treatments including medication, botulinum toxin therapy, injections of local anaesthetic (muscle afferent block therapy), and surgery (coronoidotomy) for involuntary movements, including oromandibular dystonia, bruxism, and oral dyskinesia.

Contact
Department of Oral and Maxillofacial Surgery
National Hospital Organization, Kyoto Medical Center
1-1 Mukaihata-cho, Fukakusa,
Fushimi-ku, Kyoto 612–8555, Japan

E: [email protected]
T: +81 75 641 9161
W: sites.google.com/site/oromandibulardystoniaenglish

A CAD-CAM-derived needle guide for safe treatment of oromandibular dystonia