Impact of the Coronavirus Disease 2019 Pandemic on Dental Visits in Japan.

PURPOSE: This study aimed to clarify the impact of the coronavirus disease 2019 (COVID-19) pandemic on individual dental-visit behaviour and examine the difference between elderly and other individuals regarding the impact on dental visits. MATERIALS AND METHODS: An interrupted time-series analysis was performed to examine the change in data from the national database before and after the first declaration of a state of emergency. RESULTS: The number of patients visiting a dental clinic (NPVDC), number of dental treatment days (NDTD) and dental expenses (DE) during the first declaration of a state of emergency decreased by 22.1%, 17.9%, and 12.5% in the group under 64 years of age and 26.1%, 26.3%, and 20.1% in the group over 65 years of age, respectively, compared with those in the same month of the previous year. Between March and June 2020, the monthly NPVDC and NDTD were significantly reduced (p < 0.001, p = 0.013) in those over 65 years of age. The DE did not change statistically significantly in either the under 64 group or the over 65 group. There was no statistically significant change in the slope of the regression line in the NPVDC, NDTD, and DE before and after the first state-of-emergency declaration. CONCLUSION: The first state of emergency greatly reduced the NPVDC, NDTD, and DE compared to those in the previous year. In people aged over 65 years, it might still be unresolved 2 years after the postponement of dental treatment owing to the first declaration of a state of emergency.

Short-term efficacy of exercise therapy for temporomandibular disorders: a case control study.

[Purpose] This study compared the short-term outcomes of manual therapy performed by a dentist and home exercises performed by patients as a single exercise therapy program for temporomandibular joint anterior disc displacement without reduction. [Participants and Methods] In this study we included seventeen patients with temporomandibular joint anterior disc displacement without reduction, moderate or greater temporomandibular joint functional impairment, and no treatment interventions. Patients receiving treatment underwent exercise therapy at the time of their first visit, whereas those in the non-treatment group received only an explanation of the condition. We evaluated the clinical symptoms (maximum painless opening distance, pain on motion and mastication, and degree of difficulty in daily life) at the first visit and at the two-week follow-up visit. [Results] For both groups, maximum painless opening distance and degree of difficulty in daily life improved significantly. For the treatment group, the pain on motion and mastication values significantly improved throughout the assessment period. [Conclusion] An exercise therapy program may be useful for the early treatment of temporomandibular joint anterior disc displacement without disc reduction.

Changes in prefrontal cerebral hemodynamics during intermittent pain stimulation to gingiva: Preliminary study using functional near infrared spectroscopy.

BACKGROUND/PURPOSE: Elucidating the transmission mechanism of pain signals from the orofacial area and the corresponding modification mechanism will not only aid in the understanding of pain mechanisms but also provide useful information regarding the development of pain mitigation methods. In this study, the involvement of the pain suppression system in the trigeminal area was investigated through an analysis of the activation status over time in the prefrontal cortex using functional near-infrared spectroscopy (fNIRS). MATERIALS AND METHODS: In 28 healthy, right-handed male volunteers (average age, 30.1 ±â€¯4.2 years) as subjects, a mild, intermittent, acute pain stimulus was administered through the implementation of pocket probing of the gingiva surrounding the right maxillary central incisor. In the prefrontal cortex, the levels of hemoglobin (Hb) were measured using the fNIRS measurement system. Average values of both oxy-Hb and deoxy-Hb were calculated at four stages: rest stage, 20 s prior to the pain stimulus application, and three stages at 20-s intervals within 1 min of stimulation. One-way analysis of variance and multiple comparisons were used to compare representative values to investigate the changes due to pain. RESULTS: Oxy-Hb levels decreased the most during the 20 s stage directly after stimulus application. This change was seen mainly on the contralateral side, after which it returned to the resting baseline level before the stimulus application. CONCLUSION: Our data demonstrate that in healthy males, a mechanism exists to mitigate pain involving the pain suppression system in the 20 s after feeling mild pain to the gingiva.

Short-term effects of range-of-motion exercise on temporomandibular joints of patients who undergo disc displacement with reduction of temporomandibular joint.

[Purpose] We investigated the short-term effects of an exercise therapy program that combined a range-of-motion exercise for the temporomandibular joint with self-traction therapy for patients with temporomandibular joint disorders who undergo disc displacement with reduction of the painful temporomandibular joint. [Participants and Methods] The program involved 31 patients with moderate or higher functional pain. The range-of-motion exercise for the temporomandibular joint was performed at the first visit by the therapist, and the patients were instructed to perform self-traction therapy in the morning and while bathing for the next 2 weeks, until their next visit. The maximum mouth opening distance and the visual analog scale scores at the first consultation and 2 weeks later were compared to assess the changes in pain on motion and mastication as well as the impact of the program on daily activities. [Results] All symptoms of the patients showed significant improvements after 2 weeks of starting the treatment. [Conclusion] The results of this study suggest that an exercise therapy program combining range-of-motion exercises for the temporomandibular joint and self-traction therapy may be an effective conservative therapy for reducing the pain and obstacles experienced by patients with temporomandibular joint disorders who undergo disc displacement with reduction of the painful temporomandibular joint.

Application of Deep Learning in the Identification of Cerebral Hemodynamics Data Obtained from Functional Near-Infrared Spectroscopy: A Preliminary Study of Pre- and Post-Tooth Clenching Assessment.

In fields using functional near-infrared spectroscopy (fNIRS), there is a need for an easy-to-understand method that allows visual presentation and rapid analysis of data and test results. This preliminary study examined whether deep learning (DL) could be applied to the analysis of fNIRS-derived brain activity data. To create a visual presentation of the data, an imaging program was developed for the analysis of hemoglobin (Hb) data from the prefrontal cortex in healthy volunteers, obtained by fNIRS before and after tooth clenching. Three types of imaging data were prepared: oxygenated hemoglobin (oxy-Hb) data, deoxygenated hemoglobin (deoxy-Hb) data, and mixed data (using both oxy-Hb and deoxy-Hb data). To differentiate between rest and tooth clenching, a cross-validation test using the image data for DL and a convolutional neural network was performed. The network identification rate using Hb imaging data was relatively high (80‒90%). These results demonstrated that a method using DL for the assessment of fNIRS imaging data may provide a useful analysis system.

Efficacy of therapeutic exercise for temporomandibular disorders as assessed by magnetic resonance imaging: a case report.

[Purpose] The efficacy of exercise therapy in temporomandibular disorders has been recognized. Here, we present our experience with exercise therapy. [Participant and Methods] A 25-year-old female with a sudden onset of mouth opening limitation in October 2018 was admitted to our hospital in November 2018. Based on our initial findings, the patient was diagnosed with left disc derangement of the temporomandibular joint without reduction. A definitive diagnosis was established following magnetic resonance imaging in December 2018. Subsequently, range-of-motion exercises for the temporomandibular joint as passive movements and self-traction therapy as active movements were conducted. Magnetic resonance imaging was repeated 4 months after the first treatment. [Results] The temporomandibular joint disc remained in anterior dislocation during mouth opening and closing. The mouth opening joint motion was significantly improved compared to the pre-therapy range. The pain-related visual analog scale score also significantly improved. [Conclusion] The range of motion of the temporomandibular joint was improved by range-of-motion exercises for the temporomandibular joint, and was maintained and managed using self-traction therapy. Improvement of the range of motion was confirmed by magnetic resonance imaging.

Brain activity in response to the touch of a hand on the center of the back.

The aim of this study was to validate the possibility of using functional Near-Infrared Spectroscopy (fNIRS) to measure changes in cerebral blood flow in response to a hand being placed on a participant's back, and to identify the areas of enhanced activity in the brain. Nineteen female adult volunteers participated in the study. An experienced school nurse touched the center of the participant's back between the shoulder blades with the palm of her hand. Cerebral blood volume dynamics were measured with a 52-channel fNIRS system. Significantly higher oxygenated hemoglobin (oxy-Hb) concentration levels were recorded by channels 11, 14, 21, 22, 24, 32, 35, 45, 46, and 49 during the touching period than during the resting period. These channels indicated enhanced activity in the supramarginal gyrus, the middle frontal gyrus, the superior temporal gyrus, and the inferior frontal gyrus. The ability to detect changes in cerebral blood flow using this method indicates the possibility of measuring changes in cerebral blood flow using fNIRS when a person is touched on the back. fNIRS has been shown to be useful for studying the effects of touch.

Pilot study of the short-term effects of range-of-motion exercise for the temporomandibular joint in patients with temporomandibular joint disc displacement without reduction.

[Purpose] This study investigated the effectiveness of a short-term exercise program combining range-of-motion exercise for the temporomandibular joint and self-traction therapy in patients with temporomandibular joint disc displacement without reduction. [Subjects and Methods] The study participants comprised 36 females with jaw trismus and moderate to severe functional pain. The range-of-motion exercise for the temporomandibular joint was performed at the first visit by the therapist, and the patients were instructed to perform self-traction therapy in the morning and during daily bathing until the next visit 2 weeks later. Maximum mouth opening distance and the visual analogue scale score were used to compare pain on motion and mastication as well as the impact of the program on daily activities at the first consultation and 2 weeks later. [Results] All symptoms were significantly improved after 2 weeks of treatment. [Conclusion] A program that combines exercise for the temporomandibular joint and self-traction therapy can improve range of motion at the joint in the short term and reduce pain and difficulty associated with daily activity in patients with temporomandibular joint disc displacement without reduction. The results of this study suggest that such a program can serve as an effective conservative treatment.

Can sonographic features be efficacy predictors of robotic massage treatment for masseter and temporal muscle in patients with temporomandibular disorder with myofascial pain?

OBJECTIVE: The aim of this study was to detect sonographic predictors for the efficacy of massage treatment of masseter and temporal muscle in temporomandibular disorders (TMDs) patients with myofascial pain. METHODS: Thirty-seven TMD patients with myofascial pain (6 men and 31 women, a median age of 45 years) were enrolled. An oral rehabilitation robot massaged the patient's masseter and temporal muscles with a standard massage pressure of 10 N for 16 min. The standard treatment protocol was set five sessions every 2 weeks. The median total duration of treatment was 9.5 weeks. Efficacy of treatment was evaluated based on maximum mouth opening and visual analog scale scores of muscle pain and daily life impediments. The intramuscular echogenic bands and elasticity index ratios of the masseter muscles were evaluated on sonographic or sonoelastographic images obtained before treatment and after the third and last treatment sessions. RESULTS: The sonographic features detected different changes after the third treatment session between the therapy-effective and therapy-ineffective groups: in the therapy-effective group, the frequency of visibility of the distinct echogenic bands increased, and the elasticity index ratio decreased. CONCLUSION: Sonographic features after the third treatment session may be useful as predictors of therapeutic efficacy.

Regional brain activity during jaw clenching with natural teeth and with occlusal splints: a preliminary functional MRI study.

OBJECTIVE: The purpose of this study was to investigate regional brain activity during jaw clenching with natural teeth and with two types of occlusal splints using functional magnetic resonance imaging (fMRI). METHODS: Sixteen healthy volunteers were enrolled in this study. Blood oxygenation level-dependent (BOLD) fMRI signals were compared under three conditions: during clenching with natural teeth, with a soft splint, and with a hard splint. For each condition, 30-second jaw clenching followed a 60-second rest, and was repeated three times, with intervening 30-second rests. SPM 8 was used for the fMRI analysis. RESULTS: Blood oxygenation level-dependent signals during clenching with natural teeth increased in BA44, 45, and the cerebellum. Blood oxygenation level-dependent signals increased in those areas and in BA17, 18 during clenching with a soft splint. Use of the hard splint increased the BOLD signals in BA6 and BA20, 37 in addition to the areas previously mentioned. Blood oxygenation level-dependent signals in the left BA6, the left BA20, 37, and the right BA44, 45 were significantly higher during clenching with a hard splint than with natural teeth. These regions are associated with motor coordination, memory, and cognition, respectively. CONCLUSION: Jaw clenching with a hard splint caused activity in the widest brain regions, including the associated area with motor coordination.

Potential clinical application of masseter and temporal muscle massage treatment using an oral rehabilitation robot in temporomandibular disorder patients with myofascial pain.

OBJECTIVES: To investigate the safety, suitable treatment regimen, and efficacy of masseter and temporal muscle massage treatment using an oral rehabilitation robot. METHODS: Forty-one temporomandibular disorder (TMD) patients with myofascial pain (8 men, 33 women, median age: 46 years) were enrolled. The safety, suitable massage regimen, and efficacy of this treatment were investigated. Changes in masseter muscle thickness were evaluated on sonograms. RESULTS: No adverse events occurred with any of the treatment sessions. Suitable massage was at pressure of 10 N for 16 minutes. Five sessions were performed every 2 weeks. Total duration of treatment was 9·5 weeks in median. Massage treatment was effective in 70·3% of patients. Masseter muscle thickness decreased with treatment in the therapy-effective group. CONCLUSION: This study confirmed the safety of massage treatment, and established a suitable regimen. Massage was effective in 70·3% of patients and appeared to have a potential as one of the effective treatments for myofascial pain.

Measurement of cerebral blood volume dynamics during volitional swallowing using functional near-infrared spectroscopy: an exploratory study.

The aim of this study was to examine cerebral blood volume dynamics during volitional swallowing using multi-channel functional near-infrared spectroscopy (fNIRS) to understand the basic cortical activation patterns. Fifteen volunteers (age, 26.5±1.3 years, mean±SD) performed volitional swallowing of a 5-ml bolus of water as a task. A 52-channel fNIRS system was used for measuring oxy-Hb levels. We determined the oxy-Hb concentration changes in each channel by calculating the differences between rest and task oxy-Hb levels. Differences in rest and task data were assessed using a paired-t test (p<0.05). A significant increase in oxy-Hb was found in 21 channels. The cortical regions that exhibited increased oxy-Hb concentration included the bilateral precentral gyrus, postcentral gyrus, inferior frontal gyrus, superior temporal gyrus, middle temporal gyrus, and supramarginal gyrus. These data provide a description of cortical activation patterns during volitional swallowing using fNIRS, which will be useful for the evaluation of dysphasia and the effects of the rehabilitation [Corrected].

Experimental pain in the gingiva and its impact on prefrontal cortical hemodynamics: a functional near-infrared spectroscopy study.

Evaluating alterations in brain activity in response to pain stimulus can help understand the mechanisms underlying pain perception. We measured oxygenated hemoglobin (oxy-Hb) levels using functional near-infrared spectroscopy (fNIRS) in order to assess prefrontal cortex activation after inducing a pain stimulus to the gingiva. Twenty-three right-handed, healthy male subjects (mean age: 29.3±3.6 years) were subjected to a mild pain stimulus to the tissue around the right maxillary central incisor. The periodontal pain stimulus (PPS) was elicited from a pocket probe, and a multi-channel fNIRS system with its accompanying 22-channel probes was used for measuring oxy-Hb levels. Mean oxy-Hb levels for each channel were calculated on the basis of values obtained at rest and during the PPS load, for 1min each. The change in oxy-Hb level was calculated by subtracting oxy-Hb at rest from oxy-Hb levels during PPS load. Oxy-Hb levels in each channel during both conditions were then compared using the paired t-test and Bonferroni correction. Pain stimulation caused oxy-Hb levels to decrease in virtually all areas of the prefrontal cortex, particularly, in the superior frontal gyrus, the middle frontal gyrus, and the orbital part of the superior, middle, and inferior frontal gyrus, on the brain side contralateral to the pain load. This measurement could prove beneficial as an index for objective pain evaluation.

Efficacy of massage treatment technique in masseter muscle hardness: robotic experimental approach.

The study aimed to clarify the masseter muscle hardness in patients with myofascial pain, to examine their changes after massage, and to analyze whether the hardness can be an index for massage treatment. Sixteen patients with myofascial pain (12 with unilateral and 4 with bilateral masseter muscle pain) and 24 healthy volunteers were enrolled in this study. The masseter hardness between patients and the healthy volunteers was compared. The changes in the hardness in patients after massage were examined. The relation of the hardness with massage regimens and efficacies was analyzed. There was a significant right-and-left difference of the hardness in patients, although there was no difference in the healthy volunteers. The hardness decreased after massage. The pretreatment asymmetry index of the hardness showed a significant correlation with the massage pressure. It was concluded that there was a significant difference between the right and left masseter hardness in patients with myofascial pain. After massage treatment, the masseter hardness and right-and-left difference decreased. The hardness may be an index for determining the massage pressure.

Masseter muscle sonographic features as indices for evaluating efficacy of massage treatment.

OBJECTIVE: The aim of this study was to clarify the sonographic features of the masseter muscle as indices for judging the efficacy of massage treatment. STUDY DESIGN: Fifteen patients with temporomandibular disorder (10 with unilateral and 5 with bilateral muscle pain) underwent massage treatment alternately on the bilateral masseter and temporal muscles with an oral rehabilitation robot. Sonography was performed before and after treatment, and the masseter thickness and existence of anechoic areas were evaluated. RESULTS: The thickness on the symptomatic side in the unilateral group significantly decreased after treatment. Anechoic areas were shown in 20 muscles (66.7%) before treatment, and disappeared or were reduced in size in 17 muscles (85.0%) after treatment. The pretreatment thickness was significantly related to visual analog scale (VAS) scores regarding posttreatment muscle pain and massage impression. The existence of anechoic areas was relevant to VAS scores regarding muscle pain. CONCLUSION: Masseter thickness and existence of anechoic areas might be related to the therapeutic efficacy regarding muscle pain.

Magnetic resonance T2-weighted IDEAL water imaging for assessing changes in masseter muscles caused by low-level static contraction.

OBJECTIVE: The aim of this study was to clarify the changes, using magnetic resonance (MR) images, in the masseter muscles caused by low-level static contraction. STUDY DESIGN: Ten healthy male volunteers were enrolled in the study. The MR scans were performed before, immediately after, and 10 minutes after low-level static contraction. Two imaging sequences were acquired: a diffusion-weighted image and an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) image. The apparent diffusion coefficient (ADC), the signal-to-noise ratio (SNR), and the thicknesses of the right and left masseter muscles were examined. RESULTS: The ADC and SNR immediately after exercise were significantly higher than those before exercise and 10 minutes after exercise. The muscles were significantly thicker immediately after exercise than before exercise and 10 minutes after exercise. CONCLUSION: We confirmed the presence of edema in the masseter muscles caused by low-level static contraction using MR images.

Asymmetric activation of motor cortex controlling human anterior digastric muscles during speech and target-directed jaw movements.

Like most of the cranial muscles involved in speech, the trigeminally innervated anterior digastric muscles are controlled by descending corticobulbar projections from the primary motor cortex (M1) of each hemisphere. We hypothesized that changes in corticobulbar M1 excitability during speech production would show a hemispheric asymmetry favoring the left side, which is the dominant hemisphere for language processing in most strongly right handed subjects. Fifteen volunteers aged 24.5+/-5.3 (SD) yr participated. All subjects were strongly right handed as reported by questionnaire. A surface electromyograph (EMG) was recorded bilaterally from digastrics and jaw movement detected by an accelerometer attached to a lower incisor. Focal transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability of the digastric representation in M1 of both hemispheres during four tasks: 1) static isometric contraction of digastrics; 2) speaking a single word; 3) visually guided, nonspeech jaw movement that matched the jaw kinematics recorded during task 2; and 4) reciting a sentence. Background EMG was well matched in all tasks and jaw kinematics were similar around the time of the TMS pulse for tasks 2-4. TMS resting thresholds and digastric muscle-evoked potential (MEP) size during isometric contraction did not differ for TMS over left versus right M1. MEPs elicited by TMS over left, but not right M1 increased in size during speech and nonspeech jaw movement compared with isometric contraction. We conclude that left corticobulbar M1 is preferentially engaged for descending control of digastric muscles during speech and the performance of a rapid jaw movement to match a target kinematic profile.

Focal transcranial magnetic stimulation of motor cortex evokes bilateral and symmetrical silent periods in human masseter muscles.

OBJECTIVE: To determine whether a single hemisphere exerts distinct inhibitory influences over masseter muscles on each side, and to compare features of the masseter cortical silent period (CSP) evoked by transcranial magnetic stimulation (TMS) with previous reports from limb and other cranial muscles. METHODS: Focal TMS was applied over the motor cortex jaw area in 14 normal subjects. In one experiment, TMS intensity was constant (1.1 or 1.3x active motor threshold, T) and masseter muscle activation varied from 10% to 100% of maximal. In another experiment, muscle activation was constant (20% maximal) and TMS intensity varied from 0.7 to 1.3T. RESULTS: In all subjects, TMS evoked a silent period of similar duration in masseter muscles on both sides. Masseter CSP duration increased at higher TMS intensities, but was not affected by muscle activation level or the size of the excitatory response evoked by TMS. Weak TMS produced a bilateral CSP without short-latency excitation. The masseter CSP was short ( approximately 100ms at 1.3T), yet this was not due to maintenance of excitatory drive from the unstimulated hemisphere, as the masseter CSP was not prolonged with dual-hemisphere TMS. CONCLUSIONS: Intracortical inhibitory circuits activated by TMS have a relatively weak effect on corticotrigeminal neurons supplying masseter, and effects are equivalent for corticobulbar efferents directed to contralateral and ipsilateral masseter motoneuron pools. SIGNIFICANCE: Trigeminally innervated masseter muscles exhibit weak, bilaterally symmetric inhibition following focal TMS. This method can be used to investigate abnormalities of intracortical inhibition in movement disorders or focal lesions affecting the masticatory muscles in humans.

Ultrasonographic features of the masseter muscle in female patients with temporomandibular disorder associated with myofascial pain.

OBJECTIVE: The purpose of the present study was to examine ultrasonographic appearances in female patients with temporomandibular disorder (TMD) associated with myofascial pain in comparison with healthy volunteers. STUDY DESIGN: The thickness of the masseter muscle in 25 female patients with TMD was measured at rest and at maximum contraction using ultrasonography. The visibility and width of the internal echogenic bands of the masseter muscle were also assessed and the muscle appearance was classified as 1 of 3 types: type I, characterized by the clear visibility of the fine bands; type II, thickening and weakened echo-intensity of the bands; type III, disappearance or reduction in number of the bands. RESULTS: There were significant differences in the thickness at rest and the increase ratio by contraction between the patient and control groups. The distribution of muscle types showed a significant difference between the 2 groups. CONCLUSION: The ultrasonographic features of the masseter muscle in TMD patients with myofascial pain were clarified and they might be related to muscle edema.