Temporomandibular Muscle Disorders Research Articles

Pain, dynamic postural control, mental health and impact of oral health in individuals with temporomandibular disorder: A cross-sectional study

IntroductionSome studies claim that functional changes in TMD affect the stomatognathic system (SS) and could contribute to the emergence of pain and changes in postural control. PurposeTo characterize and to compare pain, dynamic postural control (DPC), mental health and impact of oral health (QoL) in different types of temporomandibular disorders (TMD). MethodCross-sectional study with 116 participants evaluated by a validated TMD protocol and divided into three groups, muscle TMD (TMD-M, n = 32), joint TMD (TMD-J, n = 30) and muscle-joint TMD (TMD-MJ, n = 54).Chewing pain, DPC, anxiety, depression, sleep quality and impact of oral health on QoL were measured. One-way ANOVA, Kruskal-Wallis, Pearson's Chi-square test and eta-square effect size were used to data analysis. ResultsTMD-J showed less subjective pain than TMD-M (p = 0.014) and TMD-MJ (p = 0.021).TMD-J also presented greater height (p = 0.022) and body mass (p = 0.041) than the TMD-MJ and TMD-M, respectively. The DPC evaluation with sensory organization test 1 (SOT1, open eyes, platform and cabin fixed) in the medio-lateral direction (ML) was higher (p = 0.027) for TMD-J than TMD-M. TMD-MJ had a higher level of depression (p = 0.041) than TMD-J, and a greater impact of oral health on QoL (p = 0.035) than TMD-M. ConclusionMasticatory pain was lower in the TMD-J. There was a reduction in DPC in the ML of SOT1 in the TMD-J owing to the greater height of the patients in this group. The TMD-MJ had higher levels of depression and negative impact of oral health. In general, poor oral health reduces QoL in patients with TMD.

Effect of low-level LASER therapy versus CAD/CAM Michigan splint on patients with Temporomandibular Muscle Disorders: a randomized clinical trial

Effect of low-level LASER therapy versus CAD/CAM Michigan splint on patients with Temporomandibular Muscle Disorders: a randomized clinical trial

Test-retest reliability of the isometric contraction test (IC test) of the masticatory muscles in subjects with and without temporomandibular muscle disorders

Test-retest reliability of the isometric contraction test (IC test) of the masticatory muscles in subjects with and without temporomandibular muscle disorders

Clinical factors affecting depression in patients with painful temporomandibular disorders during the COVID-19 pandemic

Temporomandibular disorders (TMD) are a multifactorial condition associated with both physical and psychological factors. Stress has been known to trigger or worsens TMD. We aimed to investigate whether the novel coronavirus disease-2019 (COVID-19) pandemic aggravates depression in patients with painful TMD, and the factors that affect their level of depression. We included 112 patients with painful TMD (74 females, 38 males; mean age: 35.90 ± 17.60 years; myalgia [n = 38], arthralgia [n = 43], mixed joint–muscle TMD pain [n = 31]). TMD was diagnosed based on the Diagnostic Criteria for TMD Axis I. Physical pain intensity was recorded using the visual analog scale (VAS); psycho-emotional status (depression: Beck Depression Inventory [BDI], anxiety: Beck Anxiety Inventory [BAI], and generalized stress related to COVID19: Global Assessment of Recent Stress [GARS]) was investigated twice (before [BC] and after COVID-19 [AC]). Additionally, factors affecting BDI-AC were investigated. BDI (p < 0.001), BAI (p < 0.001), GARS (p < 0.001), and VAS (p < 0.01) scores were significantly increased at AC than BC. The depression, anxiety, and stress levels were significantly positively correlated, and the AC and BC values of each factor showed a high correlation. In the mixed TMD group, BDI-AC was positively correlated with VAS-AC (p < 0.001). In the multiple regression analysis, clenching habit was the strongest predictor of an increase in the BDI scores from moderate to severe, followed by psychological distress, muscle stiffness, female sex, BAI-AC, and TMJ sounds. COVID-19 has negatively affected the psycho-emotional state of patients with painful TMD, and several clinical factors, including female sex and clenching habits, have influenced depression.

Therapeutic approach to patients with chronic orofacial pain with temporomandibular disturbed

Temporomandibular disorder (TMD) is a term that encompasses a series of dysfunctions and disorders that affect the temporomandibular joint (TMJ), masticatory muscles and associated structures. These disorders are characterized by a set of signs and symptoms that may include joint noises, such as clicking and crackling, tooth wear, limited mandibular movement, accompanied or not by facial, cranial and periauricular pain. Here, we reported the clinical conduct of a patient with muscle TMD. Patient with chronic pain complaint in the cervico-craniofacial region, signs of bruxism, mouth opening limitation and masseteric hypertonia. The diagnosis was TMD of bilateral masseteric muscle origin, without trigger points. Heat thermotherapy was prescribed, myofacial and myofunctional physiotherapy, rigid Michigan stabilizer plate making, postural correction, and cognitive-behavioral therapy. The patient presented a gradual evolution of the clinical condition and after 90 days reported remission of approximately 95% of the symptomatological complaints, such as an improvement in the quality of sleep at night, without medication assistance, reduction in pain crises, and full mouth opening (44mm). It is concluded that the correct diagnosis and full patient adherence to the treatment proposed in this study provided relief in painful symptoms and biopsychosocial aspects.

Matrix Metalloproteinase-2 Gene Polymorphisms Decrease Chances of Muscle TMD Development in Brazilian Population

Introduction: Muscular Temporomandibular disorders or masticatory disorders are characterized by orofacial pain and functional limitations associated with oral dysfunctions, emotional changes and/or genetic factors. Matrix Metalloproteinases (MMPs) are proteolytic enzymes that constitute the extracellular matrix and play an important role in the skeletal muscle adaptation. Objectives: To evaluate the association between polymorphisms in the Matrix Metaloprotease-2 (MMP2) gene and the presence of muscular disorders. Methods: RDC/TMD questionnaire was applied for clinical diagnosis of Temporomandibular Disorders (TMD) in the study sample and three diagnosis groups were formed: control group (n=154), muscular TMD (n=122) and joint TMD (n=49). Genomic DNA was obtained from saliva samples and six single nucleotide polymorphisms in the MMP2 gene were selected. Results: A tendency of association between the presence of the CT genotype (rs243865) and the absence of muscular TMD was observed when compared to the control group (p=0.05). There was a significant prevalence of the polymorphic CT+TT (rs243865) genotypes in the control group (p=0.04) compared to the muscular TMD group (p=0.05). Confirming these results, TCCACC MMP2 haplotype showed higher association (p=0.01) with protection against muscular TMD. Conclusion: Polymorphism in the MMP2 gene (rs243865) is related to protection against muscular TMD.

Effect of a single dry needling session in temporomandibular disorders

Introduction Temporomandibular disorders embrace a heterogeneous group of pathologies with manifestations in the orofacial region, head and neck. They are defined as a group of musculoskeletal and neuromuscular conditions that involve the temporomandibular joint, the masticatory muscles and the associated structures through interactions and reciprocal influences. They may present one or more signs or symptoms: orofacial pain, pain in the masticatory muscles or a combination of both [1]. According to available literature, pain tolerance threshold at pressure and pain intensity decrease after dry needling intervention [2]. The aim of the present study is to evaluate the effect of a single dry needling session in patients with temporomandibular muscle disorder with pain. Material and methods a longitudinal quasi-experimental study with 26 patients with a diagnosis of temporomandibular muscle dysfunction (group I), on the masseter and temporal muscles, according to the Research Diagnostic Criteria for temporomandibular disorder. Patients were randomly picked up from the waiting list of the physiotherapy appointment at Clinica Egas Moniz (CEA) and randomised into two groups: 13 in the experimental group (G1) and 13 in the control group (G2). The groups were evaluated simultaneously but were not submitted to any intervention. The pain tolerance threshold was evaluated at pressure (2 kg), pain intensity measured with numeric pain rating scale (NPRS), before (T0) and after (T1) the intervention, and one week after (T2) the intervention. The intervention consisted of applying the dry needling technique to the painful points of the masseter. Statistical analysis performed in SPSS with a significance level of 5%. All the assumptions of the Helsinki Declaration have been fulfilled and a informed consent for clinical case of Clinica Dentária Egas Moniz approved by the ethic commission of Instituto Universitário Egas Moniz. Results G1 group was formed by 12 female and 1 male subjects with an average and standard deviation of 22.78 ± 3.75. G2 group was formed by 13 female with an average and standard deviation of 23.42 ± 2.45. Pain tolerance threshold at pressure values increased from T0 to T2 in G1 group (p < .001) with averages and standard deviations respectively for: T0 8.34 ± 1.75; T1 79,886 ± 2.10; T2 1.78 ± 0.79. The pain intensity values decreased in T2 when compared to T0 in the G1 group (p < .001) with averages and standard deviations respectively for: T0 7.56 ± 1.36; T1 7.86 ± 1.52; T2 0.89 ± 0.72. Discussion and conclusion Dry needling promotes an increase in pain tolerance threshold values and a decrease in pain intensity values in patients with temporomandibular muscle disorder after a single session, reinforcing their importance in the treatment of themselves.

Effectiveness of acupuncture, ozonio therapy and low-intensity laser in the treatment of temporomandibular dysfunction of muscle origin: a randomized controlled trial

Abstract Introduction One of the most common causes of orofacial pain is temporomandibular disorder (TMD). Objective The aim of this study was to compare the effectiveness of acupuncture, ozone therapy and laser therapy in the treatment of muscle TMD patients through a randomized controlled trial. Material and method Twelve professors and postgraduate students from the University of Passo Fundo, diagnosed with TMD, aged between 23 and 50 years old, of both sexes, were evaluated. Individuals were randomly divided into 3 groups: G1: laser therapy, G2: acupuncture, and G3: ozone therapy. TMD diagnostic questionnaires (RDC / TMD), Quality of Life Questionnaire (OHIP-14), Pain Scale (VAS) and maximum mouth opening were applied. Descriptive statistics and percentage were used for sample characterization, which were presented using absolute and relative frequency distributions. Qualitative variables were analyzed with Wilcoxon tests p≤0.05. Result There was no statistically significant difference between treatments. Regarding pain and maximum mouth opening, the groups showed no statistical difference when individually analyzed, but when compared in general, they did (p=0.002 and p=0.003). Conclusion It can be considered that all treatments were able to decrease pain and improve maximal opening capacity related to muscle TMD. It can also be concluded that the TMD-related quality of life, in relation to the pain variable, was generally effective when compared before and after the interventions.

Association Between Polymorphisms in the Genes of Estrogen Receptors and the Presence of Temporomandibular Disorders and Chronic Arthralgia

The high prevalence of painful temporomandibular disorders (TMDs) in women suggests that estrogen and its receptors play a fundamental etiologic role in the development of this joint pathology through complex action mechanisms. The aim of this study was to evaluate the possible association between polymorphisms in the ESR1 (estrogen receptor-1) and ESRRB (estrogen-related receptor-β) genes and the risk of simultaneous development of TMDs and pain in other joints in the body. All participants were clinically evaluated for the presence of TMD (Research Diagnostic Criteria for TMD) and asked about the presence of chronic joint pain. The control group consisted of 72 patients without TMD and without pain. Participants with arthralgia were divided into 3 groups: with muscular TMD (n=42), with articular TMD (n=16), and without TMD and with systemic arthralgia (n=82). Eight single-nucleotide polymorphisms in the ESR1 (rs12154178, rs1884051, rs2273206, rs7774230) and ESRRB (rs1676303, rs4903399, rs10132091, rs7151924) genes were investigated. The χ2 test and Student t and Mann-Whitney tests were used to assess the relevance of nominal and continuous variables, respectively. A P value less than .05 was considered significant. The TT (timin/timin) genotype for the ESR1 (rs2273206) gene was strongly associated with the risk of developing muscle TMDs and temporomandibular joint pain (P=.04). For the ESRRB (rs1676303) gene, an association was observed between the CC (cytosine/cytosine) genotype and the presence of articular TMDs associated with other chronic arthralgia (P=.02). These results were confirmed by the increased risk of developing articular TMDs associated with the C allele (P=.04). This study supports the hypothesis that changes in the ESR1 and ESRRB genes influence the presence of TMDs associated with chronic joint pain.

Atuação fonoaudiológica em disfunção temporomandibular em dois casos: análise comparativa dos efeitos da terapia tradicional e o uso da bandagem terapêutica associada

Objetivo: verificar e comparar os efeitos da terapia fonoaudiológica tradicional e o uso associado da bandagem terapêutica no tratamento de disfunções temporomandibulares musculares em dois casos. Descrição e histórico de procedimentos: O estudo foi composto por dois indivíduos do sexo feminino, ambos com trinta e três anos de idade, diagnosticados com disfunção temporomandibular através do Research Diagnostic Criteria for Temporomandibular Disorders. O primeiro indivíduo denominado como TT foi submetido à terapia fonoaudiológica tradicional em disfunção temporomandibular e o segundo indivíduo denominado como TB, além desses mesmos recursos contou com a utilização de bandagem elástica no músculo masseter bilateral. Os seguintes parâmetros foram verificados de forma qualitativa e descritiva: sinais e sintomas, intensidade de dor e amplitude dos movimentos funcionais mandibulares. Resultados: Os sinais e sintomas presentes no início da terapia foram cessados em ambas as terapêuticas. O paciente TB teve o quadro álgico reduzido em um número reduzido de sessões em relação ao seu par. Ambas as terapêuticas mostram-se efetivas quanto ao aumento de excursões mandibulares. Conclusão: A fonoterapia utilizando-se de técnicas tradicionais e a aplicação da bandagem elástica associada a estas demonstram benefícios terapêuticos em sujeitos com disfunção temporomandibular. O uso da bandagem elástica aparenta ter promovido eficiência terapêutica em menor tempo.

Use of botulinum toxin type a in temporomandibular disorder

ABSTRACT Temporomandibular disorder (TMD) may be defined as a set of clinical scenarios involving the masticatory muscles, the temporomandibular joint (TMJ) and associated structures. Currently, 40 to 75% of the population has some sign of temporomandibular disorder, mainly pain located in the muscles of mastication in the pre-auricular region. The present clinical case was diagnosed as muscle temporomandibular disorder secondary to parafunction, as well as muscle hyperactivity due to surgical displacement of the left temporal muscle on two occasions, one for placement of aneurysm clips and the other for tumor excision from the supraorbital region on the left side. The patient sought medical and dental attention for 10 years due to constant headaches, tiredness and pain in the cheeks. The patient tried numerous bite-guards and pharmacological therapies to no avail. The American Academy of Orofacial Pain Questionnaire was applied combined with the Criteria for Research and Diagnostics (DRC) and a decision was made to use botulinum toxin type A in the masseter and temporalis muscles. An analog pain scale was applied over 90 days. Three days following the application of botulinum toxin type A, the patient reported a significant improvement with complete resolution of pain (level 0) after 90 days. At 12 weeks from starting treatment, facial muscle physiotherapy was introduced to strengthen the muscles of mastication and the patient remained pain-free, which allowed the preparation and adaptation of a snap-on prosthetic appliance. In conclusion, the use of botulinum toxin in patients with temporomandibular disorder should be considered as a viable therapeutic option.

Use of Magnetic Neurostimulator Appliance in Temporomandibular Disorder

Temporomandibular disorder (TMD) is ranked the second leading cause of orofacial pain after toothache, and there is no effective standard treatment for all cases. Therefore, much research has been conducted in the therapeutic areas of TMD, such as acupuncture and electrotherapy, for this purpose. The aim of this research was to evaluate application of the neuromagnetic stimulator device Haihua model CD-9, used within the precepts of acupuncture in treating TMD-related pain symptoms and limited mouth opening. Analysis and discussion of this study were based on pain intensity index and range of mouth-opening evaluation before and after each session. Nine patients diagnosed with muscle TMD, referred by the surgery sector of Center Dental Specialties (CEO – I) in Piracicaba-São Paulo participated in this research. Considering the simplicity of the technique and good results obtained, use of this device is suggested as an additional therapeutic tool for relief of TMD symptoms.

Effectiveness of low-level laser therapy on pain intensity, pressure pain threshold, and SF-MPQ indexes of women with myofascial pain.

Women with temporomandibular disorders (TMD) frequently report pain areas in body regions. This process is associated with central sensitization phenomena, present in chronic pain. The low-level laser therapy (LLLT) has been reported as a therapeutic option for the painful TMD treatment. The aim of this study was to analyze the effect of LLLT on pain intensity (visual analogue scale, VAS), pain sensitivity in orofacial and corporal points (pressure pain threshold, PPT), and on Short Form-McGill Pain Questionnaire (SF-MPQ) indexes of women with myofascial pain (subtype of muscle TMD). Ninety-one women (18-60years) were included in the study, among which 61 were diagnosed with myofascial pain (Research Diagnostic Criteria for Temporomandibular Disorder-Ia and Ib) and were divided into laser (n = 31) and placebo group (n = 30), and 30 were controls. The LLLT was applied at pre-established points, twice a week, eight sessions (780nm; masseter and anterior temporal = 5J/cm2, 20mW, 10s; TMJ area = 7.5J/cm2, 30mW, 10s). Pain intensity, pain sensitivity, and the SF-MPQ indexes were measured at the baseline, during laser sessions, and 30days after treatment. For intra-group comparisons, the Friedman test was performed, and for inter-group, the Mann-Whitney test. Increased pain sensitivity was found in women with myofascial pain when compared to controls (p < 0.05). There was a reduction in pain intensity for both groups after LLLT. The LLLT did not change the PPT for any group (p > 0.05). Active laser and placebo reduced the indexes of sensory, total pain, and VAS, maintaining the results after 30days; there was a reduction in the affective pain rating index for both groups, with no maintenance after 30days for placebo, and the present pain intensity decreased in the laser group and did not change in the placebo after LLLT. In conclusion, the LLLT active or placebo are effective in reducing the overall subjective perception of myofascial pain (VAS and SF-MPQ indexes); however, they have no effectiveness in reducing the pain sensitivity in orofacial and corporal points (PPT increase).

Retrospective review of patients referred to a temporomandibular dysfunction care setting of a Brazilian public university

ABSTRACT BACKGROUND AND OBJECTIVES: The objective of this study is to describe the restrospective analysis of medical records of patients with temporomandibular disorder in a healthcare service of a Brazilian public university. The prevalence of signs and symptoms of temporomandibular disorder, associated factors, diagnosis and observations related to the treatment were recorded. METHODS: Two hundred and thirteen medical records were assessed by one single surveyor from March 2013 to December 2014. Information about sociodemographic factors, prevalence of symptoms of temporomandibular disorder and treatment need were collected (Fonseca Anamnestic Index), clinical examination, diagnosis, treatments and referral to other professionals. RESULTS: The majority of patients were female (81.7%), single (53.0%), students (23.3%) between 20 and 29 years of age (26.8%). Pain was reported by 50.4% of patients. According to FAI, 41.8% of patients were classified with severe synptoms of temporomandibular disorder and 73.2% identified with the need of treatment. Presence of temporomandibular disorder symptoms (p = 0.001) and need of treatment (p <0.001) were significantly associated to the female gender. The most prevalent diagnosis was muscle temporomandibular disorder (41.5%) and the most affected muscle was the masseter (21.3%). The most common treatments were occlusal splint (27.6%) and counseling (22.6%). CONCLUSION: The greater demand for temporomandibular disorder treatment came from young patients, single, female, complaining from pain. The prevalence of temporomandibular disorder symptoms was high, muscular disorders was the most prevalent findings and most of the treatments were reversible and conservative. The frequency of referral to other specialties related to temporomandibular disorder was low.

Clinical study on head and jaw position of patients with muscle temporomandibular disorder

BACKGROUND AND OBJECTIVES: Temporomandibular disorder is a collective term encompassing a wide range of clinical orofacial joint and muscle problems. The stomatognatic system is part of the postural system, so changes in one system may interfere with the other. This study aimed at observing whether there is change in jaw and head position before and after temporomandibular disorder treatment. METHODS: Participated in the study 16 volunteers, aged above 18 years, of both genders, who looked for assistance in the dentistry course clinic of a Public University, with diagnosis of temporomandibular disorder according to Diagnostic Criteria for Temporomandibular Disorder Research. Volunteers were submitted to X-rays (teleradiography with analysis of cephalometric points); posture in physiologic centric relation was evaluated by computerized photogrammetry and pain intensity was evaluated by the visual analog scale from zero to 10. Patients were evaluated before and after 8 weeks of treatment. RESULTS: Pain has decreased from 6.43±2.84 to 2.17±2.39, before and after treatment, respectively (p<0.05). Vertical head alignment, in initial angle, has changed from 21.84o±17.49o to 11.38o±14.61o (p<0.05). Jaw position has changed from A-NB (angle indicating mandible-jaw relationship in the anterior posterior direction): 4.95±2.52mm to A-NB: 4.64±2.52mm (p<0.05). CONCLUSION: Muscle temporomandibular disorder changes vertical head alignment and interferes with jaw position.

Biopsychosocial factors of Axis II of the Research Diagnostic Criteria for Temporomandibular Disorders in individuals with muscular temporomandibular disorder and migraine

BACKGROUND AND OBJECTIVES: To relate biopsychosocial variables of Research Diagnostic Criteria for Temporomandibular Disorders to groups of patients with temporomandibular disorders, temporomandibular disorders and migraine and a control group. METHODS: This is a cross-sectional observational study where 280 consecutive patients were evaluated and distributed in three groups: group I (140 control individuals); group II (65 individuals with muscle temporomandibular disorders) and group III (75 individuals with migraine and muscle temporomandibular disorders). Exclusion criteria were individuals with clinical history of muscle inflammatory processes, muscle spasms, contractures and acute temporomandibular joint traumatic injury. RESULTS: Group III individuals had association with severe depression (p<0.001), level 4 in pain severity (p=0.004), unspecific physical symptoms without severe pain (p<0.0001) and unspecific symptoms with severe pain (p<0.00001). There has been significant difference between females and males in group III (Z=2.59; p=0.001), with longer pain duration among females. The percentage of females in group III was significantly higher as compared to males (p=0.004). CONCLUSION: The relationship between variables and the three groups has shown a higher number of individuals with more severe symptoms in group III. So, it is understood that migraine is a morbid condition often associated to temporo mandibular disorders, worsening symptoms referred by patients. There is the need for multidisciplinary evaluation of these individuals to optimize treatment and minimize morbidity, costs and the number of medical visits.

Correlation between facial types and muscle TMD in women: an anthropometric approach.

Temporomandibular disorders (TMD) affecting the articular disc and/or the facial muscles are common among the population, recording a higher incidence in women age 20-40 years. The aim of this study was to investigate the correlation between facial types and muscle TMD in women. This study comprised 56 women age 18 to 49 years, seeking treatment for TMD at the School of Medicine, Federal University of São Paulo. All of the study individuals were diagnosed with muscle TMD, based on the Research Diagnostic Criteria (RDC). Facial type was determined using the Facial Brugsch Index and classified as euryprosopic (short and/or broad), mesoprosopic (average width) and leptoprosopic (long and/or narrow). The data were submitted to the Chi-square test and ANOVA-Tukey's test to conduct the statistical analysis. The faces of 27 individuals were classified as euryprosopic (48%), 18 as mesoprosopic (32%), and 11 as leptoprosopic (20%). A statistically significant difference (Chi-square, p = 0.032) was found among the facial types, in that leptoprosopic facial types showed the lowest values for muscle TMD. A greater number (p = 0.0007) of cases of muscle TMD were observed in the 20 to 39 year-old subjects than in the subjects of other age segments. In conclusion, women with euryprosopic facial types could be more susceptible to muscle TMD. Further studies are needed to investigate this hypothesis.

Psychological aspects of temporomandibular disorder patients: evaluations after acupuncture treatment

BACKGROUND AND OBJECTIVES: Depression and somatization are emotional features present in chronic temporomandibular disorder pain patients. This study aimed at evaluating results after acupuncture on psychological aspects of females with chronic muscle temporomandibular disorder pain. METHODS: Sample was made up of 40 females, aged between 18 and 45 years, submitted to two procedures: acupuncture and splint. Patients were evaluated for one month by the Research Diagnostic Criteria for Temporomandibular Disorders questionnaire Axis II before and after treatment. Treatment expectation before treatment was also evaluated by a visual analog scale with verbal anchors: negative expectation and positive expectation. RESULTS: There has been chronic pain improvement in 53.3% of acupuncture patients and in 60% of splint patients. For severe depression, 11.1% of acupuncture and 50% of splint patients have improved. Patients with severe somatization had 16.7% improvement with acupuncture and 44.4% with splint. There has been negative correlation (p<0.05) between treatment expectation and somatization (including and excluding pain items) for the acupuncture group. CONCLUSION: Both groups have improved some psychological aspects (depression and somatization) after a short period of treatment.

Chronic pain conditions in women.

There are inconsistent data on the age/sex prevalence pattern of back pain and on chest pain. However, it is possible that for chest pain, the rates are higher in younger women and older men. Neck pain, joint pain, and fibromyalgia all appear to increase with age in both genders, whereas abdominal pain and tension-type headaches decrease with age, and migraine headache and TMD appear to peak in the reproductive years. A concluding example illustrates how epidemiologic data can be used to enhance our understanding of the causes of pain. A higher prevalence in women and a peak prevalence during the reproductive years as seen in TMD suggest that either biologic or psychosocial factors unique to women in this period of life could increase the risk of developing or maintaining this pain. As female reproductive hormones can play a role in migraine, at least for some women, it would be interesting to examine whether hormones play a role in TMD. The situation that occurs when menopause is followed by hormone replacement therapy (HRT) provides a natural experiment similar to a laboratory experiment in which female animals are deprived of the natural sources of hormones and then hormones are replaced exogenously. In women, of course, the decision to receive HRT may be associated with a number of psychosocial variables that might also influence pain. Recognizing these limitations, data from records of a large health maintenance organization were examined to ascertain whether use of estrogen or progestin (or both) in postmenopausal women might be associated with the occurrence of TMD pain and, thus, whether the hormone hypothesis might be worthy of further investigation. More women with TMD than controls used estrogen replacement therapy, and slightly more patients than controls used progestin. The use of estrogen significantly increased the odds of having TMD. Progestin use showed a weaker association, which did not hold up after other factors were controlled. However, the risk of TMD appears to increase with increasing doses of estrogen. A review of the epidemiologic literature indicates that there are definite age and sex differences in the prevalence of many chronic pain conditions. There is little basic information about the source of these differences, such as different onset rates, different probabilities of recurrence, or different durations of pain, or combinations of these in women and men. Nevertheless, a systematic examination of the existing epidemiologic data may be an important step in helping pain researchers to generate hypotheses in the search for a better understanding of chronic pain in both sexes.