***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: It has been suggested that occlusal interferences may lead to pain and tenderness of the masticatory muscles . Tender jaw muscles are more sensitive to pressure pain , as assessed by means of pressure algometry . We tested the effects of occlusal interferences on the pressure pain threshold of the jaw muscles by means of a double-blind r and omized crossover experiment carried out on 11 young healthy females .  Golden strips were glued either to an occlusal contact area ( active interference ) or to the vestibular surface of the same tooth ( dummy interference ) and left for 8 d each . Pressure pain thresholds of the masseter and anterior temporalis muscles were assessed under interference-free , dummy-interference and active-interference conditions . The results indicated that the application of an active occlusal interference , as used in this study , did not influence significantly the pressure pain thresholds of these muscles in healthy individuals & NA ; Tenderness and pain thresholds in pericranial muscles were studied in a general population . A r and om sample of 1000 adults aged 25–64 years was drawn as part of the Glostrup Population Studies , and 740 adults were examined . This study was part of a multifacetted , epidemiological study of different headache disorders according to the new headache classification . Manual palpation and pressure pain threshold with an electronic pressure algometer were performed by observers blinded to other information such as the person 's history of headache , previous illness and mental state . The muscles most commonly tender to manual palpation were the lateral pterygoid ( 55 % ) , the trapezius ( 52 % ) , and the sternocleido‐mastoid muscles ( 51 % ) . Females were more tender than men in all the muscles examined by manual palpation . In total , the young age group was more tender than the old age group ( P = 0.03 ) . Pressure pain thresholds on temporal muscles showed lower thresholds in women than in men ( P < 10−3 ) , and in the total population thresholds increased with age ( P < 0.05 ) . No side‐to‐side difference in tenderness by manual palpation was found , while the right side showed increased pain thresholds in right‐h and ed individuals ( P < 10−4 ) . No side‐to‐side difference was found in left‐h and ed persons . This study provides data about the normal population and forms the neccesary basis for evaluating the importance of muscle tenderness in headache subjects and other selected groups Abstract The aim of this study was to investigate the effect of injection of serotonin ( 5‐HT ) into the masseter muscle on pain and allodynia/hyperalgesia .  Twelve female patients with fibromyalgia ( FM ) and 12 age‐matched female healthy individuals ( HI ) participated in the study . The current pain intensity ( CPI ) and the pressure pain threshold ( PPT ) of the superficial masseter muscles were assessed bilaterally . 5‐HT in one of three r and omized concentrations ( 10−3 , 10−5 , 10−7 M ) or isotonic saline was then injected into either of the two masseter muscles in a double‐blind manner . After the injections the CPI and PPT were recorded ten times during 30 min . The injections were repeated twice with the other concentrations of 5‐HT after 1 and 2 weeks , respectively . In the FM‐group there was a non‐significant increase of CPI after injection that lasted during the entire 30‐min period irrespective of whether 5‐HT or saline was injected . Neither did the PPT change significantly . In the HI‐group pain developed significantly after injection irrespective of whether 5‐HT or saline was injected , but significantly more so after 5‐HT at 10−3 M than saline injection . CPI decreased quickly and then remained on a very low level for most of the experiment . 5‐HT at both 10−5 M and 10−3 M caused a significantly greater decrease of PPT than saline . In conclusion , our results show that 5‐HT injected into the masseter muscle of healthy female subjects  elicits pain and allodynia/hyperalgesia , while no such responses occur in patients with fibromyalgia Certain types of jaw-muscle pain may be managed with pharmacologic treatment . This study evaluated the effect of topical and systemic nonsteroidal anti-inflammatory drugs on  acute postexercise jaw-muscle soreness . Ten men without temporom and ibular disorders performed six 5-minute bouts of submaximal eccentric jaw exercise . The outcome variables were pressure pain thresholds and pain tolerance thresholds at the masseter muscles , and maximum voluntary occlusal force . Surface electromyography from the masseter muscles was used to assess the development of muscle fatigue during the exercise period . Three treatment modalities were tested in a placebo-controlled , double-blind approach : ( A ) placebo gel and placebo tablets ; ( B ) nonsteroidal anti-inflammatory drug gel ( 2 g , 5 % ibuprofen ) and placebo tablets ; and ( C ) placebo gel and nonsteroidal anti-inflammatory drug tablets ( 400 mg ibuprofen ) . The subjects used their medication 3 times a day for 3 days in the postexercise period . In the exercise period , the mean power frequency of the electromyography signal , pressure pain threshold , pain tolerance threshold , and maximum voluntary occlusal force decreased significantly ( analysis of variance , P < .01 ) . In the postexercise period , the effect of treatment on pressure pain thresholds was significant ( F[2,9 ] = 4.41 , P = .02 ) . On day 3 , treatment with topical nonsteroidal anti-inflammatory drugs was associated with significantly higher pressure pain thresholds as compared to treatment with systemic nonsteroidal anti-inflammatory drugs ( P < .05 ) and placebo ( P < .05 ) . Treatment effects on pain tolerance thresholds and on maximum voluntary occlusal force were nonsignificant . The results demonstrated that repeated eccentric jaw exercise caused muscle fatigue and low levels of postexercise pain and soreness .  Topical nonsteroidal anti-inflammatory drugs seem to have some advantages over systemic nonsteroidal anti-inflammatory drugs for management of exercise-induced jaw-muscle pain Objective To evaluate interrater reliability using 5 newly trained observers in the assessment of  pressure pain threshold ( PPT )  using a fixed-angle algometer . Methods The study design comprised 2 phases . Phase 1 : 5 undergraduate physical therapists were  trained  in algometry at a predefined angle , at a rate of 5 Newtons (N)/s , to the first dorsal interosseous muscle . Each observer then underwent a competency test of the application speed . The aim was to achieve repeated applications at 5 N/s without visual feedback from the algometer . Phase 2 : the 5 observers measured PPT of 13 healthy volunteers , at the first dorsal interosseous muscle . The sequence of observer measurements for each participant was r and omized . Mean PPT values for each observer were analyzed using repeated measures analysis of variance , intraclass correlation coefficient ( ICC2,1 ) , and st and ard error of measurement , with 95 % confidence intervals ( CIs ) . Results No significant differences between observers ' mean values were found ( P=0.094 ) , suggesting no bias . The ICC was 0.91 ( 95 % CI 0.82 , 0.97 ) . The st and ard error of measurement value was 6.27 N/cm2 ( 95 % CI 5.35 , 7.59 ) . Differences in PPT measurements of more than 17.39 N/cm2 ( 1.77 kg/cm2 ) are likely to exceed the magnitude of measurement error , and could be used to indicate true change . This margin of error is , however , somewhat larger than a previously proposed minimum clinical ly important difference in PPT of 14.71 N/cm2 ( 1.5 kg/cm2 ) . Discussion This study provides new evidence that trained observers can apply an algometer at a consistent rate and provide highly reliable measures of PPT in healthy humans , when PPT is calculated as the mean of 3 trials The purpose of this study was to estimate inter-examiner reliability of  head and neck algometry .  Pain perception thresholds were assessed with a mechanical pressure algometer in 21 healthy individuals . Thresholds were assessed at 13 symmetrical points on each side of the head and neck , at the deltoid muscle and at the median finger . The pressure range of the instrument proved insufficient to study the pain perception threshold on the finger , however . Two different examiners carried out one or two examinations in each subject during one day . The sequence of investigations was varied r and omly . The inter-examiner reliability was found to be good , with a mean intra-class correlation coefficient ( ICC ) of 0.75 . Intra-examiner reproducibility was excellent ( mean ICC = 0.84 ) . The mean inter-examiner coefficient of variation was 18.7 % , while the mean coefficient of repeatability ( CR ) was 1.60 kg/cm2 . In comparison , the mean intra-examiner coefficient of variation was 15 % while the mean CR was 1.29 kg/cm2 . Statistically significant differences between examiners were found for the frontal point ( p < 0.01 ) , while a trend towards lower thresholds in one of the two observers was seen in 10 of the 13 non-significant points . Inter-examiner reliability of side differences was excellent , with CR = 1.23 kg/cm2 . In conclusion , manual algometry with a rather inexpensive mechanical device has a good to excellent inter-rater reliability . When study ing patients , however , the possible bias introduced by different examiners should be taken into account , both regarding study design and data analysis & NA ; Tenderness and pain thresholds in pericranial muscles were studied in a r and om sample of 735 adults aged 25–64 years . This study was a part of a multifaceted , epidemiological study of different headache disorders . Manual palpation and pressure pain threshold were performed by observers blinded to the persons ' history of headache . The aim of the study was to evaluate the possible role of pericranial myofascial nociception in headache pathogenesis . Tenderness in migraineurs did not differ from non‐migraineurs . Subjects with episodic tension‐type headache and females with chronic tension‐type headache were more tender than the rest of the population , and males without any experience of headache were less tender than the rest of the male population . A strong positive correlation between tenderness and frequency of tension‐type headache was found ( males : P < 10−4 ; females : P < 10−5 ) , while no relation between tenderness and migraine frequency was seen ( P = 0.43 ) . In subjects having actual headache  at the day of examination tenderness was 32 % increased compared to a matched group with identical usual frequency of headache , but without headache during the examination . A significant relation of tenderness to the recency of last episode of headache was detected in both sexes after control for usual frequency and actual headache ( males : P < 10−3 ; females : P < 10−4 ) . Pressure pain thresholds were largely normal indicating normal pain processing and contradicting the idea that tension‐type headache mainly is due to generally increased pain sensitivity . This study supports the pathogenetic importance of muscular factors in tension‐type headache , while muscular factors are of no primary importance in migraine Temporom and ibular disorders ( TMDs ) are associated with perturbation of proprioceptive and nociceptive function . Recent studies have shown that injection of the neurotrophic protein nerve growth factor ( NGF ) into the masseter muscle causes sensitization to mechanical pressure stimuli ; however , it is not clear if vibration sense and jaw stretch reflexes as measures of proprioceptive function as well as glutamate-evoked pain are also altered . We tested the hypothesis that NGF-induced mechanical sensitization would be associated with changes in vibration sense and stretch reflex sensitivity as well as facilitation of glutamate-evoked pain responses . A double-blind , r and omized and placebo-controlled study was conducted on 14 healthy men . In one session subjects received an injection of NGF ( 5 μg in 0.2 ml ) into the masseter muscle and in a control session an injection of buffered isotonic saline ( 0.9 % , 0.2 ml ) . Subjects assessed their pain intensity on a 0–10 cm visual analogue scale ( VAS ) for 15 min after the injections . Pressure pain thresholds ( PPT ) , vibration sense and jaw stretch reflexes were recorded at baseline and 1 , 2 , 3 and 24 h post-injection . The sensitivity to injections of glutamate into the masseter muscle ( 1 M , 0.2 ml ) was assessed after 24 h. ANOVAs were used to assess significant differences . NGF did not cause more pain than isotonic saline , but significantly reduced PPTs 1 , 2 , 3 and 24 h post-injection ( P < 0.001 ) whereas isotonic saline had no effects on PPTs ( P = 0.583 ) . The injection of glutamate after 24 h was associated with reduced PPTs in both sessions , but the PPTs remained lower in the NGF pretreated masseter than in the control masseter ( P < 0.001 ) . Ratings of vibratory stimuli and the normalized amplitude of the jaw stretch reflex were not affected by the NGF-induced sensitization ; however , after glutamate injection a significant increase in the stretch reflex was observed in the injected masseter muscle in both sessions ( P = 0.002 ) . There were no significant differences in the perceived pain intensity of the glutamate injection between the masseter muscle pretreated with NGF or control ( P > 0.414 ) 
    Output:
    
The masseter muscle seemed to be more sensitive than the other 2 muscles , in both females ( healthy : masseter 194.1 ± 62.7 kPa < frontalis 277.5 ± 51.1 kPa < temporalis 282.1 ± 70.8 kPa ) and males ( healthy : masseter 248.2 ± 48.4 kPa < temporalis 314.8 ± 63.3 < frontalis 388 kPa ) .
Females had lower PPT values than those of males in temporalis , masseter , and frontalis muscles .