Urban-rural differences in the prevalence of having a family dentist and their association with income inequality among Japanese individuals: a cross-sectional study.

BACKGROUND: Few reported studies evaluate the status of those who have a family dentist (FD) by regional differences and the socioeconomic factors associated with this status. This study aimed to assess the prevalence of having an FD among Japanese individuals across three samples of municipality type: urban, intermediate, and rural areas, and determine the factors associated with having an FD. METHODS: This was a cross-sectional study involving a web-based survey. In total, 2,429 participants (comprising men and women aged 20-69 years) were randomly selected from among the registrants of a web research company: 811 urban residents, 812 intermediate residents, and 806 rural residents. In each area, we categorized the participants into those who had an FD (FD group) and those who did not (non-FD group). A multivariate modified Poisson regression analysis was used to determine the factors associated with the FD group as compared to the non-FD group. RESULTS: The proportion of the FD group was lowest in rural areas (42.3%), followed by intermediate (48.6%) and urban areas (49.7%). The regression analysis revealed a statistically significant tendency between associated factors in the two groups; that is, the higher the household income, the more likely that the family belonged to the FD group (prevalence ratio (95%CI), JPY 4-6 million: 1.43 (1.00-2.03), JPY ≥ 8 million: 1.72 (1.21-2.44)). CONCLUSIONS: Rural areas have the lowest proportion of people with an FD among the three areas, and income inequality is associated with having an FD. Thus, when planning policies to encourage individuals to have an FD to manage their oral health, it is necessary to consider regional differences.

Regular Dental Check-Ups Are Associated with Choosing Uninsured Dental Restoration/Prosthesis Treatment in Japan.

Since Japan has implemented Universal Health Coverage (UHC), most dental treatments are covered by public health insurance. Therefore, when receiving fixed dental restoration/prosthesis (FDRP) treatment, such as inlays, crowns, and bridges, the patient can choose whether or not it is covered by insurance. This study aimed to evaluate whether those who receive dental check-ups regularly chose uninsured FDRP treatment. Data were collected from 2088 participants, who had undergone FDRP treatment, via a web-based survey and analyzed. Among them, 1233 (59.1%) had received regular dental check-ups (RDC group) and 855 (40.9%) had not (non-RDC group). The multivariate logistic regression model showed that compared to the non-RDC group, those in the RDC group were statistically significantly associated with higher rates of good oral health behaviors (brushing teeth ≥ 3 times daily, odds ratios (OR):1.46; practiced interdental cleaning habitually, OR: 2.22) and received uninsured FDRP treatment more often (OR: 1.59), adjusted for socioeconomic factors. These results suggest that health policy interventions to promote access to RDC among individuals may improve the oral health of people and reduce the financial burden on the public health insurance system.

People's Willingness to Pay for Dental Checkups and the Associated Individual Characteristics: A Nationwide Web-Based Survey among Japanese Adults.

This study aimed to determine the willingness-to-pay (WTP) values for dental checkups and analyze the association between the values and individual characteristics. This cross-sectional study was conducted using a nationwide web-based survey, and 3336 participants were allocated into groups that received regular dental checkups (RDC; n = 1785) and those who did not (non-RDC; n = 1551). There was a statistically significant difference in the WTP value for dental checkups between the RDC (median: 3000 yen [22.51 USD]) and non-RDC groups (2000 yen [15.01 USD]). In the RDC group, age 50-59 years, household income <2 million yen, homemaker and part-time worker employment status, and having children were significantly associated with decreased WTP values; male sex, household incomes ≥8 million yen, and tooth brushing ≥3 times daily were associated with increased WTP values. In the non-RDC group, age ≥30 years, household incomes <4 million yen, and having ≥28 teeth were significantly associated with decreased WTP values; household income ≥8 million yen was associated with increased WTP values. Conclusively, WTP values for dental checkups were lower in the non-RDC group than in the RDC group; in the non-RDC group, those with lower household income aged ≥30 years were more likely to propose lower WTP values, suggesting the need for policy intervention to improve access to RDC.

Effect of local administration of eicosapentaenoic acid on the jaw-opening reflex in rats.

Although eicosapentaenoic acid (EPA) application in vitro inhibits voltage-gated Na+ (Nav) channels in excitable tissues, the acute local effect of EPA on the jaw-opening reflex in vivo remains unknown. The aim of the present study was to determine whether local administration of EPA to adult male Wistar rats could attenuate the excitability of the jaw-opening reflex in vivo, including nociception. The jaw-opening reflex evoked by electrical stimulation of the tongue was recorded by a digastric muscle electromyogram (dEMG) in pentobarbital-anesthetized rats. The amplitude of the dEMG response was significantly increased in proportion to the electrical stimulation intensity (1×-5× threshold). At 3×, local administration of EPA dose-dependently inhibited the dEMG response, lasting 60 min, with maximum inhibition observed within approximately 10 min. The mean magnitude of dEMG signal inhibition by EPA was almost equal to that observed with a local anesthetic, 1% lidocaine, and with a half dose of lidocaine plus a half dose of EPA. These findings suggest that EPA attenuates the jaw-opening reflex, possibly by blocking Nav channels of primary nerve terminals, and strongly support the idea that EPA is a potential therapeutic agent and complementary alternative medicine for the prevention of acute trigeminal nociception.

Factors Affecting the Career Continuation of Newly Graduated and Reinstated Dental Hygienists Who Participated in a Technical Training Program in Japan.

This study aimed to identify (1) what newly graduated dental hygienists and reinstated dental hygienists consider important for preventing early turnover in their own professions and for encouraging them to continue in the profession more generally and (2) relevant factors among hygienists intending to continue working in the field. An anonymous, self-administered questionnaire survey was distributed to 215 Japanese dental hygienists who participated in the technical training programs (response rate: 72.6%). Of them, 143 participants were classified into two groups: newly graduated (NGDH, n = 32) and those reinstated to work (RDH, n = 111). Follow-up for lack of skills was most often selected as important for preventing early turnover among both groups and follow-up for lack of knowledge was significantly selected in the RDH group (p < 0.001). Regarding factors important for career continuation, NGDHs significantly selected gaining job satisfaction, whereas RDHs significantly selected working support. Relevant factors contributing to participants' intentions to continue in the profession were job satisfaction (NGDH, OR = 8.37; RDH, OR = 8.83), career outlook (RDH, OR = 3.11), and job turnover experience because of marriage and parenting (RDH, OR = 2.70), thereby suggesting the importance of raising awareness regarding career progression and job-related rewards among dental hygienists, their educators, and the government through ongoing career education.

Characteristics of Individuals in Japan Who Regularly Manage Their Oral Health by Having a Family Dentist: A Nationwide Cross-Sectional Web-Based Survey.

Dental healthcare systems may differ between countries; however, having a family dentist is generally important for proper oral health management. This study aims to analyze the proportion of people in Japan who have a family dentist, and their characteristics. A nationwide web-based survey with 3556 participants (1708 men and 1848 women) showed that 45.6% of men and 54.1% of women had a family dentist (FD group). A multiple logistic regression analysis revealed that men in the FD group mostly belonged to older age groups (≥70 s, OR: 2.41), received higher household incomes (≥8000 K JPY, OR: 1.47), brushed their teeth three or more times daily (OR: 1.60), practiced habitual interdental cleaning (OR: 3.66), and fewer lived in rural areas (towns and villages, OR: 0.52). Regarding the women, the majority belonged to older age groups (60 s, OR: 1.52; ≥70 s, OR: 1.73), practiced habitual interdental cleaning (OR: 3.68), and fewer received lower household incomes (<2000 K JPY, OR: 0.61). These results suggest that despite Japan being a country with a public insurance coverage system for both men and women, having a family dentist is associated with disparities in individual socioeconomic factors, particularly age and household income.

Factors Associated with Regular Dental Checkups' Discontinuation during the COVID-19 Pandemic: A Nationwide Cross-Sectional Web-Based Survey in Japan.

Managing oral health through regular dental checkups (RDCs) can help prevent dental diseases. Our study aimed to investigate the proportion and characteristics of those who stopped receiving RDCs owing to the coronavirus disease 2019 (COVID-19) pandemic. A nationwide web-based survey in Japan in September 2021 (3556 participants) revealed that 62.4% of participants had habitually received RDCs before COVID-19. Of these (n = 2219), 71.5% had received RDCs since the pandemic and 28.5% had not. Multiple logistic regression analysis revealed the following characteristics of those without RDCs since the pandemic: female (male, OR: 0.58, 95%CI: 0.45−0.74), lower household income (<2000 K JPY, OR: 1.45, 95%CI: 0.94−2.23; 2000 K−< 4000 K JPY, OR: 1.46, 95%CI: 1.08−1.98), fewer teeth (20−27, OR: 0.63, 95%CI: 0.39−1.03; ≥28, OR: 0.60, 95%CI: 0.36−0.98), and no interdental cleaning habits (OR: 0.51, 95%CI: 0.41−0.63). These results suggest that the disruption to RDCs owing to the pandemic is related to individual socioeconomic factors. Additionally, these individuals have poor oral health, which may be worsened by such barriers.

Relationship between career education experience among final-year dental hygiene students and their perspective towards work and profession: A nationwide survey in dental hygiene schools of Japan.

OBJECTIVES: This study aimed to clarify the relationship between the experience of receiving career education among final-year dental hygiene students and their views regarding their work and profession, as part of research on the working style of dental hygienists. METHODS: An anonymous, self-administered survey was sent by post to all the 162 dental hygienist schools in Japan with dental hygiene students in their final year in November 2019. The main questions were regarding student attributes, career aspirations, their perspective on work and profession and whether or not they received career education at a dental hygienist training school. Analysis was conducted by cross-tabulation and logistic regression. RESULTS: Completed questionnaires were sent to us by 150 schools (response rate 92.6%), with a response from 6,270 students. The students who had received career education had significantly higher awareness and plans for the profession and a positive attitude towards the work (p < 0.01). Following adjustment for age, sex, educational attainment, length of the course of study and timing of class the results shows that there was a significant relation between the experience of the career education with having future plans (odds ratio = 2.11, 95% confidence interval = 1.88-2.38, p < 0.01). CONCLUSIONS: It was observed that the experience of receiving career education just before graduating from dental hygienist school was related to an increased positive attitude of the students towards their work and profession. Further long-term investigations are necessary to evaluate the effects of career education among dental hygiene students and their attitude towards their profession.

Are Public Oral Care Services Evenly Distributed?-Nation-Wide Assessment of the Provision of Oral Care in Japan Using the National Database of Health Insurance Claims.

The provision of oral health care services is one of the global challenges under the realization of universal health coverage in many countries. Despite the increasing importance of oral health care in an aging society, the disparities in the provision of oral care in Japan have not been clarified. Therefore, this study investigated the status of oral and dental care provision using the National Database of Health Insurance Claims and Specific Health Checkups (NDB) at the level of prefectures and secondary medical care areas. Additionally, a multiple regression model was applied to identify the influence of human resources in oral care services and economic factors on the standardized claims data ratio (SCR) of total dental receipts. The results showed that the total amount of oral care provided tended to be higher in metropolitan areas, with bimodal peaks in children aged 5-9 and adults in their 70s. The SCR for dental caries showed little difference nationally, but SCR for periodontal disease tended to be higher in prefectures including metropolitan areas. In a multiple regression model, the number of dentists and prefectural income per capita influenced the SCR of total dental receipts. In secondary medical care areas, some depopulated areas are supplemented by adjacent areas. These results suggest that oral health care services in the national health insurance system are generally well provided; however, they are likely to be influenced by human resources and economic disparities, and regional differences may occur in the care of periodontal diseases.

Current status of supply of and demand for dental technicians in Japan: Evaluation and countermeasures against the decrease in the number of dental technicians.

In recent years, the number of dental technicians (DTs) in Japan has fluctuated around 35,000. However, this number is expected to decline dramatically in future, given the increase in the number of older DTs and marked decline in the number of younger DTs. This is a review of various reports analyzing the supply of and demand for DTs in Japan and a description of prospective measures to ensure a sufficient supply of DTs in future. Several previous reports have suggested that the number of DTs will fall more rapidly than the demand. However, there are only few quantitative assessments of the supply of and demand for DTs, and extensive investigation of how the decrease in numbers will affect the future of dental services is required. The role of each Japanese dental profession, that is, dentists, dental hygienists, and dental technicians, is well-defined; they are to provide dental services to the Japanese people. Therefore, it is necessary to maintain the required number of each dental profession in future. For clarity on the social situation of DTs and to help in taking immediate measures, it is important to analyze the supply and demand of DTs from various perspectives, such as region.

Gender Differences in Work Status during Early Career of Dentists: An Analysis of National Survey Cohort Data of 10 Years in Japan.

Few studies have evaluated gender differences in young dentists' career focusing on career breaks and return to work. We created a cohort dataset for dentists registered in 2006 using the national survey between 2006-2016 (men, 1680; women, 984), and examined the work setting of dentists by gender 10 years after registration. The proportion of dentists on career break increased each survey year, and was more pronounced in women than in men (2006 to 2016, men, 11.2% to 14.2%; women, 7.9% to 31.0%). The proportion of those who had career breaks between 2006-2016 was 44.8% in men and 62.9% in women. In the multiple logistic regression for examining the associations between those who returned to work compared to those working continuously, in women, the odds ratios (OR) were significantly higher in those working in dental clinics (owner, OR: 5.39; employee, OR: 3.10), and those working part-time (OR: 2.07); however, in men, there was no significant association with part-time work. These results suggest during early career phase, female dentists are more likely than males to take career breaks and choose part-time on returning. These gender differences should be considered for ensuring adequate workforce in dentistry in the future.

Analysis of Factors Related to Working Status of Dental Hygienists in Japan.

The super-aged society of Japan is experiencing an increased demand for dental hygienists, of which there is currently a shortage. This study aimed to investigate the factors related to the working status of dental hygienists in Japan. We conducted a survey by mailing a questionnaire on employment to 1444 dental hygienists and obtained 537 valid responses. We conducted a bivariate analysis using either a chi-square test or t-test as well as a multiple logistic regression analysis to determine the factors related to working status. The overall employment rate was 68.2%, with a significant difference between age groups (p < 0.01). Approximately 80% of respondents considered working hours and human relations at the workplace to be important, and more than 70% of respondents considered wages as important. Finally, the following four variables were found to be significantly associated with employment status: training course attendance, a desire to work full-time, consideration of wages as important, and consideration of working hours as important. These findings suggest that it is necessary to improve working conditions and environments, including wages and working hours, as well as provide a more robust system of continued professional development for dental hygienists to increase the workforce.

The Relationship between the Sense of Coherence of Dental Hygiene Students in Their Graduation Year and Their View of the Profession and Attitude to Work: A Cross-Sectional Survey in Japan.

OBJECTIVE: The need to make sense of coherence in placement support for student dental hygienists has been shown. On this basis, this study investigated the relationship between the sense of coherence of student dental hygienists and their view of the profession and attitude to work in order to clarify how they perceive their prospects for employment. METHODS: The subjects were graduation-year students at all of the dental hygienist training institutions in Japan, and anonymous, self-administered questionnaires were sent to the institutions by post in 2019. The results were analyzed by χ2 tests, as well as one-way analysis of variance and multiple comparisons using Tukey's test, with the level of significance set at 5%. RESULTS: Of 6270 questionnaires that were returned, 6264 were analyzed. The sense of coherence (SOC) component senses were manageability (F(26,221) = 5306.06, p < 0.01), meaningfulness (F(26,222) = 4373.48, p < 0.01), and comprehensibility (F(26,216) = 3986.12, p < 0.01), with meaningfulness scoring significantly higher than the other two (p < 0.01). Analysis with SOC scores divided into the low, medium, and high groups showed a relationship between the SOC of student dental hygienists and their view of the profession and attitude to work (p < 0.01), such that higher SOC scores were associated with a better view of the profession and a better attitude to work (F(26,225) = 282.18, p < 0.01). CONCLUSIONS: The results suggest that education that increases SOC in dental hygienist training programs may positively affect future prospects for student dental hygienists.

Resveratrol suppresses nociceptive jaw-opening reflex via 5HT3 receptor-mediated GABAergic inhibition　.

Systemic administration of the dietary constituent, resveratrol, was previously shown to inhibit the nociceptive jaw-opening reflex (JOR) via the endogenous opioid system. The present study investigated whether resveratrol could similarly affect the JOR under in vivo conditions via 5HT3 receptor-mediated GABAergic inhibition. We used electrical stimulation of the tongue in pentobarbital-anesthetized rats to evoke the JOR, which was recorded as the anterior belly of the digastric muscle electromyograms (dEMG). Intravenous administration of resveratrol (2 mg/kg) reduced the dEMG amplitude in response to three times the determined threshold electrical stimulation, with maximum inhibition reached within approximately 10 min. These inhibitory effects on the JOR were reversible to control levels after approximately 20 min. Pretreatment of rats with either 5HT3 receptor antagonist, ondansetron (0.25-1 mg/kg, i.p.), or GABAA receptor antagonist, bicuculline (0.5-1 mg/kg, i.p.), significantly and dose-dependently attenuated the inhibitory effects of resveratrol on dEMG amplitude compared with untreated controls. These findings suggest that resveratrol also attenuates the nociceptive JOR via 5HT3 receptor-mediated GABAergic inhibition. The present study therefore provides new insight into a possible mechanism underlying resveratrol-induced trigeminal antinociception via the descending pain control system and highlights a potential therapeutic agent for complementary alternative medicine.

Local anesthetic effect of docosahexaenoic acid on the nociceptive jaw-opening reflex in rats.

Although docosahexaenoic acid (DHA) administration suppresses sodium channels in primary afferent sensory neurons, the acute local effect of DHA on the trigeminal nociceptive reflex remains to be elucidated, in vivo. Therefore, the aim of the present study was to investigate whether local administration of DHA attenuates the nociceptive jaw-opening reflex (JOR) in vivo in the rat. The JOR evoked by electrical stimulation of the tongue was recorded by a digastric muscle electromyogram (dEMG) in pentobarbital-anesthetized rats. The amplitude of the dEMG response was significantly increased in proportion to the electrical stimulation intensity (1-5 x threshold). At 3 x threshold, local administration of DHA (0.1, 10 and 25 mM) dose-dependently inhibited the dEMG response, and lasted 40 min. Maximum inhibition of the dEMG signal amplitude was seen within approximately 10 min. The mean magnitude of inhibition of the dEMG signal amplitude by DHA (25 mM) was almost equal to the local anesthetic, 1% lidocaine (37 mM), a sodium channel blocker. These findings suggest that DHA attenuates the nociceptive JOR via possibly blocking sodium channels, and strongly support the idea that DHA is a potential therapeutic agent and complementary alternative medicine for the prevention of acute trigeminal nociception.

Systemic administration of the dietary constituent resveratrol inhibits the nociceptive jaw-opening reflex in rats via the endogenous opioid system.

The aim of the present study was to investigate whether, under in vivo conditions, systemic administration of resveratrol could attenuate the rat nociceptive jaw-opening reflex (JOR) via the endogenous opioid system. The JOR evoked by electrical stimulation of the tongue was recorded as digastric muscle electromyograms (dEMG) in pentobarbital-anesthetized rats. The amplitude of the dEMG increased significantly in proportion to the intensity of electrical stimulation (from 1× to 5 × threshold for the JOR). dEMG amplitude in response to 3× threshold electrical stimulation of the tongue was dose-dependently inhibited by intravenous administration of resveratrol (0.5-2mg/kg). Maximum inhibition of dEMG amplitude was seen within approximately 10min. These inhibitory effects were reversible, with dEMG responses returning to control levels after approximately 20min. Pretreatment of rats with naloxone resulted in significant, dose-dependent attenuation of the inhibitory effects of resveratrol on dEMG amplitude compared with control. These findings suggest that resveratrol inhibits the nociceptive JOR via the endogenous opioid system. Further, the findings of the present study strongly support the idea that resveratrol, which is not known to have any toxic side effects, combined with an opioid could be a potential therapeutic agent for the prevention of acute trigeminal nociception.

Local administration of resveratrol inhibits excitability of nociceptive wide-dynamic range neurons in rat trigeminal spinal nucleus caudalis.

Although we recently reported that intravenous administration of resveratrol suppresses trigeminal nociception, the precise peripheral effect of resveratrol on nociceptive and non-nociceptive mechanical stimulation-induced trigeminal neuron activity in vivo remains to be determined. The aim of the present study was to investigate whether local subcutaneous administration of resveratrol attenuates mechanical stimulation-induced excitability of trigeminal spinal nucleus caudalis (SpVc) neuron activity in rats, in vivo. Extracellular single-unit recordings were made of SpVc wide-dynamic range (WDR) neuron activity in response to orofacial mechanical stimulation in pentobarbital-anesthetized rats. Neurons responded to non-noxious and noxious mechanical stimulation applied to the orofacial skin. Local subcutaneous administration of resveratrol (1-10mM) into the orofacial skin dose dependently and significantly reduced the mean number of SpVc WDR neurons firing in response to both non-noxious and noxious mechanical stimuli, with the maximal inhibition of discharge frequency in response to both stimuli being seen within 5min. These inhibitory effects were no longer evident after approximately 20min. The mean magnitude of inhibition by resveratrol (10mM) of SpVc neuron discharge frequency was almost equal to that of the local anesthetic 1% lidocaine (37mM). These results suggest that local injection of resveratrol into the peripheral receptive field suppresses the excitability of SpVc neurons, possibly via inhibition of Na(+) channels in the nociceptive nerve terminals of trigeminal ganglion neurons. Therefore, local subcutaneous administration of resveratrol may provide relief of trigeminal nociceptive pain, without side effects, thus contributing to the suite of complementary and alternative medicines used as local anesthetic agents.

Regional cerebral blood flow in patients with orally localized somatoform pain disorder: a single photon emission computed tomography study.

AIM: Somatoform pain disorder is characterized by persistent and chronic pain at one or more sites without an associated general medical condition and in which psychological factors are thought to play a role. This study aimed to investigate the pathological features of somatoform pain disorder localized to the oral region by single photon emission computed tomography (SPECT). METHODS: Ten patients (nine females and one male; average age 55.0 ± 14.4 years) having somatoform pain disorder with oral symptoms participated. SPECT was performed using N-isopropyl-4-[(123) I] iodoamphetamine intravenous injections, and regional cerebral blood flow (rCBF) was assessed by three-dimensional stereotactic surface projections. We also selected 12 healthy individuals (seven females and five males; average age 61.8 ± 13.2 years) to act as controls. RESULTS: Both the patient and control groups showed no atrophy or infarction on CT or magnetic resonance imaging. The patient group showed higher rCBF in the subcortical area, especially in the thalamus and cingulate gyri, than the control group. In contrast, the patient group showed lower rCBF in the bilateral frontal and occipital lobes as well as in the left temporal lobe. CONCLUSIONS: These results suggest that the biological process involved in somatoform pain disorder of the oral region is characterized by changes in limbic and cortical functions. The finding that somatoform pain disorder with oral symptoms is associated with brain functional changes will help to develop treatment regimes for this disorder and clarify the underlying pathology.

Clinical investigation of patients who develop neuropathic tooth pain after endodontic procedures.

INTRODUCTION: This study aimed to determine the characteristics of patients with neuropathic tooth pain (NTP) who were selected from a group of patients who developed persistent pain after undergoing endodontic procedures. METHODS: Of 271 patients who had chronic persistent pain that did not respond to previous endodontic procedures and were referred to the Endodontic Team of the Nippon Dental University Hospital, 16 patients (5.9%; mean age, 46.8 years; 13 women) who fulfilled the diagnostic criteria for NTP were recruited. The inclusion criteria for the patients were the presence of chronic persistent pain and other pain-related symptoms, despite the absence of major pathology. RESULTS: Pain predominantly occurred in the maxilla (14 patients). In 10 patients (62.5%), NTP developed after retreatment. Daily application of tricyclic antidepressants produced pain relief in 11 patients (68.8%). CONCLUSIONS: These results indicated that NTP is a rare type of chronic intractable endodontic pain and that careful diagnosis of NTP is important.

Systemic administration of lidocaine suppresses the excitability of rat cervical dorsal horn neurons and tooth-pulp-evoked jaw-opening reflex.

Although systemic lidocaine has been demonstrated to have analgesic actions in neuropathic pain conditions, the effect of intravenous lidocaine on trigeminal pain has not been elucidated. The aim of the present study is to investigate the effect of intravenous lidocaine administration on the excitability of the upper cervical dorsal horn (C1) neuron having convergent inputs from both tooth-pulp (TP) and facial skin as well as nociceptive jaw-opening reflex (JOR). After electrical stimulation of TP, extracellular single-unit recordings from 19 C1 neurons and the digastric muscle electromyogram (dEMG) were made in pentobarbital-anesthetized rats. These neurons also responded to non-noxious and noxious mechanical stimulation (touch and pinch) of facial skin, and every neuron was considered to be a wide dynamic range (WDR) neuron. The TP-evoked C1 neuronal and dEMG activities were dose-dependently inhibited by systematic administration of lidocaine (1-2 mg/kg, i.v.). After intravenous injection of lidocaine, the unit discharges induced by both touch and pinch stimuli were inhibited, and the size of the receptive field for pinch was also significantly decreased. The mean spontaneous discharge frequencies were significantly inhibited by the application of lidocaine. These changes were reversed within -20 min. These results suggest that in the absence of neuropathic pain intravenous lidocaine injection suppresses the trigeminal nociceptive reflex as well as the excitability of C1 neurons having convergent inputs from TP and somatic afferents. Systemic lidocaine administration, therefore, may contribute to the alleviation of trigeminal-referred pain associated with tooth pain.