According to the American Association of Dental Research, it is strongly recommended that unless there are specific and justifiable indications to the contrary, treatment of TMD should be based on the use of conservative, reversible, and evidence-based treatment modalities [2]. Treatment methods include gentle muscle massage, anti-inflammatory medications, and use of oral appliances [5, 6].
This patient developed TMD secondary to injury and had what can be considered a typical example of severe TMD [4]. Treatment should have been performed sooner since it became difficult due to the disease progression. Ultrasound-guided IANB was able to improve the trismus caused by TMD in this case.
In a recent study, Kumita et al. suggested that ultrasound-guided IANB was highly effective in perioperative analgesia in cases of gnathoplasty [7]. Another recent study found that ultrasound-guided IANB was useful in the perioperative management of patients undergoing mandibular sequestrectomy for medication-related osteonecrosis of the jaw [8]. Our results demonstrated that IANB provided effective pain control for 72 h. Furthermore, IANB was not associated with adverse events or prolonged hospitalization. These results also suggest that IANB provides effective postoperative analgesia following mandibular surgery. In the present case, the improvement in mouth opening lasted for 3 days after the procedure, which is consistent with previous reports; however, it is unclear as to why the analgesic effect persisted longer than the duration of action of the local anesthetic. The patient’s satisfaction with IANB was very high as it led to improved feeding. On the third day after the operation, the maximum mouth opening returned to that before IANB. Therefore, we are currently performing treatments such as opening training and manipulation after IANB. She is currently undergoing 1 month of treatment and mouth opening has improved to 45 mm.
Previous reports have described that a mandibular nerve block using the landmark technique was effective in relieving trismus for a short time in several patients [9,10,11,12]. These case reports indicated that the nerve block was effective for pain due to TMD; however, the classical approach carries a risk of vascular lesions or foramen ovale insertion. These complications can result in “total spinal anesthesia” and even pharyngeal penetration [9]. Ultrasound-guided IANB is much easier to perform, has no adverse effects, and may be useful for diagnostic purposes as well. This implies that the inability of a patient to open his/her mouth even after IANB points toward a disorder of the joint disk or deformation of the joint itself. The joint trigger block can be applied to the joint cavity. However, when the muscles involved in the TMJ result in as much pain as in this case, the effect of the joint trigger block may be limited. Since IANB is effective in the mandibular nerve innervation area, the range of effect is broad. The mandibular nerve innervates the masseter, temporalis, internal pterygoid, lateral pterygoid, mylohyoid, geniohyoid, digastric, and tensor veli palatini muscles, and its innervation area includes the mandibular teeth, lower jaw, lower lip, cheek, and tongue.
Further studies on the epidemiology, drug dosage of anesthetics, and accurate assessments of the duration of their action are required to guide the clinical decision regarding treatment of patients with trismus due to TMD.