Purpose: While attention has been focused on the relationship between masticatory dysfunction or tooth loss and general health, the effects of masticatory dysfunction on brain function remain poorly understood. In this article, we discuss the effects of masticatory dysfunction on brain function based on our own animal experiments.
Research overview: Study 1. Eighteen rats were divided into a tooth extraction group that had their upper molars extracted at 4 weeks old, an anesthesia group administered an equivalent amount of anesthesia, and an untreated group that did not undergo any procedure or receive any anesthesia. Tetanic stimulation was administered by cerebral microdialysis and glutamate discharge was measured during hippocampus function. The tooth extraction group exhibited significantly lower glutamate discharge. Study 2. Sixteen 5-week-old rats were divided into a tooth extraction group that had their upper molars extracted at 5 weeks old, and a control group that only received an equivalent amount of anesthesia. Glutamate discharge in the hippocampus was measured during a passive avoidance learning experiment using a telemetry biosensor system. While the tooth extraction group had significantly lower discharge during acquisition trials, no group differences were seen during retention trials.
Discussion: In addition to causing masticatory disturbance, early loss of molars may also lower release from glutamate synapses in the hippocampus and potentially lead to impaired neurobiochemical functioning.
Conclusion: These studies indicate that early loss of molars may be one factor triggering impairments in learning and memory.

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System neuroscience is a subdiscipline of neuroscience that studies the function of neural circuits and systems. Such examinations are conducted using neural circuits to analyze sensory information, external shape perception, decision making, and executive motor functions, as well as higher cognitive functions such as learning, memory, and consciousness. In this topical review, we report f-NIRS studies of sensorimotor cortical areas, which are related to orofacial sensorimotor functions, using healthy control subjects and dystonia patients with focal oromandibular involuntary movement. In addition, we present studies of prefrontal cortex areas related to oral sensorimotor cognition, chewing execution and related denture efficacy, and clinically unexplained symptoms of oral dysesthesia as comorbidities of psychiatric disorders such as depression, anxiety, and somatoform disorders. Furthermore, we present findings showing that r-TMS may promote cortical plasticity and improve some symptoms associated with chronic intractable neurological diseases in the oromandibular and maxillofacial regions.

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Purpose: There are many kinds of diseases that can cause glossalgia, and it is not always easy to determine the differential diagnosis. Therefore, establishment of screening procedures for organic factors of glossalgia is important to obtain the correct diagnosis. We statistically analyzed the findings in patients with various lingual abnormalities.
Methods: Patients were 104 persons consisted of 12 males and 92 females. Medical history taking, intraoral and extraoral examinarion, panoramic x-ray radiography, blood examination, culture, and salivation test were performed. It was also determined whether local analgesic or nonsteroidal anti-inflammatory drug relieved the pain or not.
Results: Glossalgia-related diseases consisted of oral candidiasis, xerostomia, glossitis, glossodynia and other diseases. The major part of oral candidiasis lacked a change in organic appearance. Concerning xerostomia, a sense of thirst was also lacking. Local analgesic or nonsteroidal anti-inflammatory drug showed a limited effect on glossodynia. The prevalence of taste disorder or hypozincemia in glossodynia was less than that in other diseases. On the other hand the prevalence of palm sweating in glossodynia was greater than that in other diseases.
Conclusions: Culture and salivation test were necessary for the diagnosis of either oral candidiasis without a change in organic appearance or xerostomia without a sense of thirst. If these examinations were not performed, these cases might be diagnosed as glossodynia. The presence of pain on tongue tip and the absence of food-induced pain or oppressive pain were specific findings of glossodynia. Lingual mucous damage could not be directly correlated with pathology of glossodynia judging from the nature of glossalgia and the result of analgesic effects. Taste disorder and hypozincemia were found to be nonspecific findings of glossodynia. It was suggested that glossodynia is related to dysautonomia, and palm sweating is a specific finding of glossodynia.

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Patient: A 39-year-old man experienced electric shock-like pain around the right eye when he touched his toothbrush to his right maxillary molar tooth. After removing of the crown of the tooth and opening his root canal at the dental office, his pain was relieved. However, the next month, the pain appeared again. Although he was administered nonsteroidal anti-inflammatory drugs, the pain was not relieved. The pain aggravated and occurred more frequently, because of which he visited our clinic. At the first visit, he experienced the electric shock-like pain attack around the right eye for a few seconds. Eating and talking triggered the pain. At that time, he was prescribed carbamazepine (100 mg/day) for the treatment and differentiation of trigeminal neuralgia, with which the pain relieved. Magnetic resonance imaging (MRI) scan showed neurovascular compressions at the root entry zones of the bilateral trigeminal nerves. The carbamazepine dose was increased to 300 mg/day, and the pain was under control. Subsequently, carbamazepine dose was reduced to 200 mg/day, and the pain was under control for a while; however, the pain eventually aggravated. Therefore, we increased the carbamazepine dose to 300 mg/day and additionally Goreisan (7.5g/day) was administered. Both these drugs relieved the pain. Thus far, the pain has been under control with the same prescription.
Discussion: When patients complain of eye pain, the causes can be ophthalmological diseases or headaches besides trigeminal neuralgia. In this case, the cause of pain was trigeminal neuralgia because carbamazepine was effective, and MRI scan showed neurovascular compression.
Conclusion: Trigeminal neuralgia of the first branch is rare. The patients rarely visit dental clinics because the pain appear out of the dental region. However dentists should carefully discriminate because there is a case that eye pain is precipitated from oral trigger areas, like this case.

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