pain in the masticatory muscles is the most prevalent symptom associated with 
 temporomandibular disorders ( tmd ) , being present in 88.7% of the affected 
 population . ( 2001 ) found a positive 
 correlation between chewing ability and tmj pain and reduced mouth opening capacity , 
 although no significant association was found for noises and muscle tenderness . different types of muscle hyperactivity have been associated with muscle pain , among 
 those bruxism , as well as extensive voluntary repeated maximum contractions , innate 
 weakness in the strength of a muscle accentuated by repeated maximum contractions and 
 continuous use of the muscle . the 
 overuse of the masticatory muscles has also been associated with changes in the blood 
 supply , suggesting that ischemia may occur during contraction above a given 
 threshold . ( 1993 ) 
 studied the validity of six tests to discriminate patients from control subjects and 
 found that passive opening measurement and palpation were the most useful for this 
 purpose . ( 2002 ) concluded 
 that pain can be either increased , decreased or unaltered when assessed the 
 discriminative power of an experimental chewing test in patients with myofascial pain 
 ( mfp ) . the existence of two different pathologies or different pre - exercise pain levels 
 could explain these different reaction . ( 2002 ) carried out a similar study , increasing the exercise time and measuring the pain 
 using the visual analogue scale ( vas ) over 9 min at rest . they concluded that a 
 strenuous chewing exercise is a potential beneficial tool in the diagnostic process of 
 mfp . in spite of that , the phenomenon of pain reduction in a small percentage of the 
 patients with mfp should be further investigated . pressure - pain threshold ( ppt ) has been extensively used in diagnostic studiesof myogenic tmds as well as in therapeutic studies , but little is known about the impact of 
 chewing exercises on ppt measurements of symptomatic patients . ( 2001 ) evaluated those parameters in 15 
 healthy women and did not find significant increase of pain intensity during a 40min 
 soft - gum chewing task nor a significant ppt reduction after the test . investigators have used some exercises to induce muscle pain , such as tooth 
 grinding , experimental 
 chewing , electromyographically controlled clenching , 
 and maximal protrusion . the 
 literature has demonstrated that muscular hyperactivity exerts an important role as an 
 etiological factor in this pain modality , since a symptomatic muscle pain relief has 
 been observed concomitant to reduction in muscular activity . the purpose of this study was to test whether there are distinct pain responses to 
 chewing exercise among patients with mfp with mild to moderate pain , and verify whether 
 this protocol could be used to distinguish patients with mfp from control subjects . the mfp group consisted of 29 consecutive caucasian women ( mean age 29.838.43 
 years , ranged from 18 to 49 ) selected among those seeking for treatment at the 
 orofacial pain clinic of the bauru school of dentistry , university of so 
 paulo , brazil . inclusion criteria followed the diagnostic of mfp ( group ia ) , 
 according to the research diagnostic criteria ( rdc / tmd ) . patients with more than two absent teeth , history of 
 facial or cervical injury , cervical pain or limited range of motion , active 
 periodontal disease or caries , history of general neurological disturbances cervical 
 and/ or masticatory active trigger points were excluded from the study . the diagnosis 
 of tmj disorders , according to rdc / tmd ( diagnostic ii ) were also an exclusion criterion , although 
 individuals with asymptomatic disc displacement joint ( iia , without pain ) concomitant 
 with ia diagnostic ( rdc / tmd ) were 
 allowed to participate . the patients should not have taken any analgesic medication 
 within 24 h prior to the experimental procedure . the control group was comprised by 15 asymptomatic caucasian women ( means age 
 25.471.23 years , ranged from 20 to 35 ) recruited at the regular dental 
 clinics of the bauru school of dentistry . none of the subjects had any facial pain 
 complaint or underwent tmd treatment 6 months prior to the experiment . except for 
 pain , the inclusion criteria for the control group were the same to the used for the 
 mfp group . all participants granted a written informed consent to participate in the 
 study ( 126/2004 ) . all participants filled out the rdc / tmd questionnaire and were examined by one of the authors . the digital 
 palpation was carried out with a pressure of 1.0 kgf to the extraoral sites and 
 approximately 0.5 kgf to the intraoral and articular sites , as recommended by the 
 rdc / tmd . this pressure was 
 previously calibrated using an algometer ( dinamometer model ddk , kratos equipamentos , 
 cotia , sp , brazil ) . due to evidence of low specificity or palpation bias , palpation of the  lateral pterygoid area  , though part of the 
 screening evaluation ( rdc / tmd ) , 
 was replaced by palpation of the deep portion of masseter , in order to maintain the 
 20 sites proposed in rdc protocol , as documented in previous studies . following the clinical examination , an experimental chewing exercise was performed , 
 which was modified from gavish , et al . the test was performed with the same interval time , though 
 with a different chewing material . during the sessions of the chewing test , the subjects were seated comfortably in a 
 dental chair , in an upright position and with their heads leaning back on the 
 headrest . before the chewing test ( p0 ) , the participants were asked to indicate their 
 pain intensity on a visual analog scale ( vas ) , which ranged from 0 mm (  no pain  ) to 
 100 mm (  the worst imaginable pain  ) . each vas was filled out on a separate piece of 
 paper in order to avoid bias of previous vas records . with the aid of an algometer , the ppt of the superficial masseter ( body ) ( m ) , as well 
 as the anterior ( at ) , medium ( mt ) and posterior temporalis ( pt ) muscle was also 
 established bilaterally before the test ( ppt0 ) . with a rate of application of about 
 0.5 kg / cm / s , the pressure was applied until it became painful . at this 
 point , the participant was instructed to push a hand - held button attached to the 
 algometer , so the amount of pressure was automatically recorded by the device . after recording the baseline measurements ( vas and ppt ) , the subjects were instructed 
 to start chewing . they were requested to chew on a stick of chewing gum 
 ( trident , cadbury , bauru , sp , brazil ) for 9 min at the 
 preferred side . after that , individuals were instructed to hold their jaws at a rest 
 position ( lips together and teeth apart ) for additional 9 min , completing the total 
 period test of 18 min . vas was recorded again after 3 , 6 , and 9 min ( p3 , p6 , and p9 , respectively ) after the 
 beginning of the experiment , and during the rest period at 12 , 15 and 18 min ( p12 , 
 p15 , and p18 , respectively ) , while ppt measurements were taken at times 9 ( ppt9 ) and 
 18 ( ppt18 ) . the kolmogorov - smirnov test was used to verify homogeneity in all groups 
 ( p<0.05 ) . the student s t test ( parametric data ) and 
 mann - whitney test ( non - parametric data , p<0.05 ) were used to 
 verify statistically significant differences between control and mfp groups regarding 
 vas and ppt . anova for repeated measures and tukey s test ( parametric data ) and 
 friedman s test followed by the student- newman - keuls test ( =0.05 ) 
 ( non - parametric data ) were used to verify intragroup differences in different moments 
 of ppt records . the statistical analysis was performed using the sigmastat 2.0 
 software ( jandel scientific software , san jose , ca , usa ) . the mfp group consisted of 29 consecutive caucasian women ( mean age 29.838.43 
 years , ranged from 18 to 49 ) selected among those seeking for treatment at the 
 orofacial pain clinic of the bauru school of dentistry , university of so 
 paulo , brazil . inclusion criteria followed the diagnostic of mfp ( group ia ) , 
 according to the research diagnostic criteria ( rdc / tmd ) . patients with more than two absent teeth , history of 
 facial or cervical injury , cervical pain or limited range of motion , active 
 periodontal disease or caries , history of general neurological disturbances cervical 
 and/ or masticatory active trigger points were excluded from the study . the diagnosis 
 of tmj disorders , according to rdc / tmd ( diagnostic ii ) were also an exclusion criterion , although 
 individuals with asymptomatic disc displacement joint ( iia , without pain ) concomitant 
 with ia diagnostic ( rdc / tmd ) were 
 allowed to participate . the patients should not have taken any analgesic medication 
 within 24 h prior to the experimental procedure . the control group was comprised by 15 asymptomatic caucasian women ( means age 
 25.471.23 years , ranged from 20 to 35 ) recruited at the regular dental 
 clinics of the bauru school of dentistry . none of the subjects had any facial pain 
 complaint or underwent tmd treatment 6 months prior to the experiment . except for 
 pain , the inclusion criteria for the control group were the same to the used for the 
 mfp group . all participants granted a written informed consent to participate in the 
 study ( 126/2004 ) . all participants filled out the rdc / tmd questionnaire and were examined by one of the authors . the digital 
 palpation was carried out with a pressure of 1.0 kgf to the extraoral sites and 
 approximately 0.5 kgf to the intraoral and articular sites , as recommended by the 
 rdc / tmd . this pressure was 
 previously calibrated using an algometer ( dinamometer model ddk , kratos equipamentos , 
 cotia , sp , brazil ) . due to evidence of low specificity or palpation bias , palpation of the  lateral pterygoid area  , though part of the 
 screening evaluation ( rdc / tmd ) , 
 was replaced by palpation of the deep portion of masseter , in order to maintain the 
 20 sites proposed in rdc protocol , as documented in previous studies . following the clinical examination , an experimental chewing exercise was performed , 
 which was modified from gavish , et al . the test was performed with the same interval time , though 
 with a different chewing material . during the sessions of the chewing test , the subjects were seated comfortably in a 
 dental chair , in an upright position and with their heads leaning back on the 
 headrest . before the chewing test ( p0 ) , the participants were asked to indicate their 
 pain intensity on a visual analog scale ( vas ) , which ranged from 0 mm (  no pain  ) to 
 100 mm (  the worst imaginable pain  ) . each vas was filled out on a separate piece of 
 paper in order to avoid bias of previous vas records . with the aid of an algometer , the ppt of the superficial masseter ( body ) ( m ) , as well 
 as the anterior ( at ) , medium ( mt ) and posterior temporalis ( pt ) muscle was also 
 established bilaterally before the test ( ppt0 ) . with a rate of application of about 
 0.5 kg / cm / s , the pressure was applied until it became painful . at this 
 point , the participant was instructed to push a hand - held button attached to the 
 algometer , so the amount of pressure was automatically recorded by the device . after recording the baseline measurements ( vas and ppt ) , the subjects were instructed 
 to start chewing . they were requested to chew on a stick of chewing gum 
 ( trident , cadbury , bauru , sp , brazil ) for 9 min at the 
 preferred side . after that , individuals were instructed to hold their jaws at a rest 
 position ( lips together and teeth apart ) for additional 9 min , completing the total 
 period test of 18 min . vas was recorded again after 3 , 6 , and 9 min ( p3 , p6 , and p9 , respectively ) after the 
 beginning of the experiment , and during the rest period at 12 , 15 and 18 min ( p12 , 
 p15 , and p18 , respectively ) , while ppt measurements were taken at times 9 ( ppt9 ) and 
 18 ( ppt18 ) . the kolmogorov - smirnov test was used to verify homogeneity in all groups 
 ( p<0.05 ) . the student s t test ( parametric data ) and 
 mann - whitney test ( non - parametric data , p<0.05 ) were used to 
 verify statistically significant differences between control and mfp groups regarding 
 vas and ppt . anova for repeated measures and tukey s test ( parametric data ) and 
 friedman s test followed by the student- newman - keuls test ( =0.05 ) 
 ( non - parametric data ) were used to verify intragroup differences in different moments 
 of ppt records . the statistical analysis was performed using the sigmastat 2.0 
 software ( jandel scientific software , san jose , ca , usa ) . patients with mfp presented the following values of vas ( present pain : 
 47.7922.27 mm ; mean pain in the last six months : 50.342.03 mm , and 
 maximal pain in the last six months : 67.9319.34 mm ) . they had a mean active 
 mouth opening of 45.9010.95 mm and a mean number of sensitive palpation sites of 
 8.374.73 mm . on the other hand , control group had no pain on the vas ; 
 45.076.55 mm of mean active mouth opening ; and a mean number of sensitive 
 palpation sites of 0.400.63 mm . the most prominent findings were the differences 
 in vas pain intensity and in mean number of sensitive palpation sites ( p<0.001 ) . at p9 , patients with mfp reported a mean pain increase of 18.79 mm , while controls 
 had an increase of 3.33 mm in vas records . none of the patients with mfp reported 
 pain reduction , 7 ( 24% ) reported no change in pain ( mfp ncp ) , and 22 ( 76% ) reported 
 an increase ( mfp incp ) . within the mfp incp patients , the mean increase of pain at p9 
 was 23.59 mm . however , at p12 , two additional patients experienced an increase in 
 pain , elevating the percentage of this subgroup to 82.76% ( 24 subjects ) and reducing 
 the percentage of patients who had no change in pain ( mfp ncp ) to 17.24% ( 5 
 subjects ) . for the control group , 13 ( 87% ) patients had no change in pain and only 2 
 subjects ( 13% ) experienced pain increase at p9 . data concerning pain intensity ( vas ) 
 and their fluctuation over time in both groups at the different measurement points 
 are presented in figure 1 . pain intensity during the chewing test of patients with myofascial pain ( mfp ) 
 and control subjects . * the same number of asterisks indicates no statistically 
 significant differences ( p<0.05 ) ( intragroup analysis ) .  
 significant differences between groups at the same intervals time ( intergroup 
 analysis ) when applied a friedman repeated measures anova on ranks on vas scores of both 
 groups , no statistical difference was found in the control group along the whole 
 experiment ( exercise and rest ) ( figure 1 ) . conversely , the mfp group showed a clear increase on pain intensity from p0 up to p9 . 
 from this point , a slight decrease in the intensity levels was revealed , but not 
 enough to recover to pre - exercise levels ( figure 
 1 ) . there was no significant difference in initial pain intensity ( p0 ) between mfp ncp 
 and mfp incp patients . however , a significant difference in pain intensity between 
 these subgroups was found after chewing ( p=0.002 ) . analysis of covariance of pain levels during the chewing experiments yielded the 
 following : a significant main effect for group ( mfp vs. control , 
 p=0.002 ) and for time ( p<0.001 ) , but not for activity 
 ( chewing or rest ) . also a significant interaction between group , activity and time 
 ( p=0.01 ) was found . these findings reveal the effect of the 
 chewing activity on the pain level in both groups over time , but do not indicate a 
 significant recovery at rest ( figure 1 ) . in the 
 mfp group , the pain increased 18.79 mm at p9 and recovered to levels above ( 13.00 mm ) 
 the preexercise levels . ppts were significantly lower in patients with mfp than in controls at all recording 
 sites and at all the times ( ppt0 to ppt18 ) . figure 
 2 shows ppt fluctuations over periods 0 , 9 , and 18 min ( ppt0 , 9 , and 18 , 
 respectively ) of each muscular site of mfp and control group . data from right and 
 left sides were pooled because ppts obtained bilaterally in the jaws have been shown 
 to be correlated . in the control 
 group , statistically significant reductions on ppt9 were observed only in anterior 
 and posterior temporalis . for the mfp group , ppt9 values were significant reduced for 
 all muscle sites . after the rest period ( ppt18 ) , however , the ppt values remained 
 significantly lower than the pre - exercise figures ( ppt0 ) ( figure 2 ) . pressure - pain threshold ( ppt ) during chewing test [ patients with 
 myofascial pain ( mfp x control ) ] . * significant difference from ppt0 in 
 the same muscle , for the control group . * * significant difference from ppt0 in 
 the same muscle , in the mfp group . mm = superficial masseter body ; mt= medium 
 temporalis ; at= anterior temporalis ; pt= posterior temporalis among the patients with mfp , 18 ( 62.07% ) started the exercise with vas pain between 0 
 and 5 mm ( mfp p0=0 ) . in order to evaluate the weight of this variable on the final 
 result , comparisons between mfp p0=0 and those who started with vas higher than that 
 were made : intergroup evaluation : the mfp p0=0 patients showed ppt0 values significantly higher 
 than those who started exercise with eav greater than 0 ( mfp>0 ) ; and similar 
 to pre - exercise ppts of control group . after chewing , mfp p=0 patients showed ppt9 
 and ppt18 significantly greater than mfp p0>0 and significantly lower than the 
 control group for all recording sites . ppt9 : at all muscles sites , but the anterior temporalis , mfp ncp showed ppts 
 significantly higher than mfp incp . moreover , except the mt and pt , mfp ncp showed 
 ppt9 significantly lower than the control group ( figure 3 ) . it means that ppt9 of mfp ncp were in between the control group 
 and mfp incp . pain during chewing test of patients with myofascial pain who reported a pain 
 increase ( mfp incp ) , x no change in pain ( mfp ncp ) an control subjects ppt18 : after rest ( ppt 18 ) , mpf ncp showed ppt values similar to mfp incp and 
 significantly lower than the control group at all muscle sites but the pt ( figure 4 ) . pressure - pain threshold ( ppt ) during chewing test [ patients with 
 myofascial pain who reported a pain increase ( mfp incp ) x no change in pain 
 ( mfp ncp ) ] . mm = superficial masseter body ; mt= medium temporalis ; at= 
 anterior temporalis ; pt= posterior temporalis with the exception made for the mt , which ppt9 did not change significantly , all 
 other muscles in both subgroups presented similar ppts evolution pattern along the 
 whole experiment , i.e. , ppt9 significantly lower than ppt0 and ppt18 significantly 
 lower than ppt0 and similar to ppt9 ( figure 4 ) . that means that , regardless of vas evolution , the mfp group experienced a decrease of 
 ppt after the exercise , and 9 min of rest are not enough to recover it to 
 pre - exercise levels . the discriminative ability of the test to distinct patients from controls was 
 demonstrated by a sensitivity of 0.76 , a specificity of 0.87 , a positive likelihood 
 ratio ( lr+ ) of 5.69 ( ci95 : 1.99231.012 ) , and a negative likelihood ratio ( lr- ) of 
 0.28 ( ci95 : 0.1280.515 ) . a pre - test probability of 66% ( 0.66 ) , post - test probability 
 to lr+ of 0.92 ( 92% ) and to lr- of 0.35 ( 35% ) it means that the risk of a person who report increase in pain to 
 have mfp is 0.92 ( 92% ) , while the risk of a person who do not change in pain with 
 this protocol to have mfp is 0.35 ( 35% ) . at p9 , patients with mfp reported a mean pain increase of 18.79 mm , while controls 
 had an increase of 3.33 mm in vas records . none of the patients with mfp reported 
 pain reduction , 7 ( 24% ) reported no change in pain ( mfp ncp ) , and 22 ( 76% ) reported 
 an increase ( mfp incp ) . within the mfp incp patients , the mean increase of pain at p9 
 was 23.59 mm . however , at p12 , two additional patients experienced an increase in 
 pain , elevating the percentage of this subgroup to 82.76% ( 24 subjects ) and reducing 
 the percentage of patients who had no change in pain ( mfp ncp ) to 17.24% ( 5 
 subjects ) . for the control group , 13 ( 87% ) patients had no change in pain and only 2 
 subjects ( 13% ) experienced pain increase at p9 . data concerning pain intensity ( vas ) 
 and their fluctuation over time in both groups at the different measurement points 
 are presented in figure 1 . pain intensity during the chewing test of patients with myofascial pain ( mfp ) 
 and control subjects . * the same number of asterisks indicates no statistically 
 significant differences ( p<0.05 ) ( intragroup analysis ) .  
 significant differences between groups at the same intervals time ( intergroup 
 analysis ) when applied a friedman repeated measures anova on ranks on vas scores of both 
 groups , no statistical difference was found in the control group along the whole 
 experiment ( exercise and rest ) ( figure 1 ) . conversely , the mfp group showed a clear increase on pain intensity from p0 up to p9 . 
 from this point , a slight decrease in the intensity levels was revealed , but not 
 enough to recover to pre - exercise levels ( figure 
 1 ) . there was no significant difference in initial pain intensity ( p0 ) between mfp ncp 
 and mfp incp patients . however , a significant difference in pain intensity between 
 these subgroups was found after chewing ( p=0.002 ) . analysis of covariance of pain levels during the chewing experiments yielded the 
 following : a significant main effect for group ( mfp vs. control , 
 p=0.002 ) and for time ( p<0.001 ) , but not for activity 
 ( chewing or rest ) . also a significant interaction between group , activity and time 
 ( p=0.01 ) was found . these findings reveal the effect of the 
 chewing activity on the pain level in both groups over time , but do not indicate a 
 significant recovery at rest ( figure 1 ) . in the 
 mfp group , the pain increased 18.79 mm at p9 and recovered to levels above ( 13.00 mm ) 
 the preexercise levels . ppts were significantly lower in patients with mfp than in controls at all recording 
 sites and at all the times ( ppt0 to ppt18 ) . figure 
 2 shows ppt fluctuations over periods 0 , 9 , and 18 min ( ppt0 , 9 , and 18 , 
 respectively ) of each muscular site of mfp and control group . data from right and 
 left sides were pooled because ppts obtained bilaterally in the jaws have been shown 
 to be correlated . in the control 
 group , statistically significant reductions on ppt9 were observed only in anterior 
 and posterior temporalis . for the mfp group , ppt9 values were significant reduced for 
 all muscle sites . after the rest period ( ppt18 ) , however , the ppt values remained 
 significantly lower than the pre - exercise figures ( ppt0 ) ( figure 2 ) . pressure - pain threshold ( ppt ) during chewing test [ patients with 
 myofascial pain ( mfp x control ) ] . * significant difference from ppt0 in 
 the same muscle , for the control group . * * significant difference from ppt0 in 
 the same muscle , in the mfp group . mm = superficial masseter body ; mt= medium 
 temporalis ; at= anterior temporalis ; pt= posterior temporalis among the patients with mfp , 18 ( 62.07% ) started the exercise with vas pain between 0 
 and 5 mm ( mfp p0=0 ) . in order to evaluate the weight of this variable on the final 
 result , comparisons between mfp p0=0 and those who started with vas higher than that 
 were made : intergroup evaluation : the mfp p0=0 patients showed ppt0 values significantly higher 
 than those who started exercise with eav greater than 0 ( mfp>0 ) ; and similar 
 to pre - exercise ppts of control group . after chewing , mfp p=0 patients showed ppt9 
 and ppt18 significantly greater than mfp p0>0 and significantly lower than the 
 control group for all recording sites . ppt9 : at all muscles sites , but the anterior temporalis , mfp ncp showed ppts 
 significantly higher than mfp incp . moreover , except the mt and pt , mfp ncp showed 
 ppt9 significantly lower than the control group ( figure 3 ) . it means that ppt9 of mfp ncp were in between the control group 
 and mfp incp . pain during chewing test of patients with myofascial pain who reported a pain 
 increase ( mfp incp ) , x no change in pain ( mfp ncp ) an control subjects ppt18 : after rest ( ppt 18 ) , mpf ncp showed ppt values similar to mfp incp and 
 significantly lower than the control group at all muscle sites but the pt ( figure 4 ) . pressure - pain threshold ( ppt ) during chewing test [ patients with 
 myofascial pain who reported a pain increase ( mfp incp ) x no change in pain 
 ( mfp ncp ) ] . mm = superficial masseter body ; mt= medium temporalis ; at= 
 anterior temporalis ; pt= posterior temporalis with the exception made for the mt , which ppt9 did not change significantly , all 
 other muscles in both subgroups presented similar ppts evolution pattern along the 
 whole experiment , i.e. , ppt9 significantly lower than ppt0 and ppt18 significantly 
 lower than ppt0 and similar to ppt9 ( figure 4 ) . that means that , regardless of vas evolution , the mfp group experienced a decrease of 
 ppt after the exercise , and 9 min of rest are not enough to recover it to 
 pre - exercise levels . the discriminative ability of the test to distinct patients from controls was 
 demonstrated by a sensitivity of 0.76 , a specificity of 0.87 , a positive likelihood 
 ratio ( lr+ ) of 5.69 ( ci95 : 1.99231.012 ) , and a negative likelihood ratio ( lr- ) of 
 0.28 ( ci95 : 0.1280.515 ) . a pre - test probability of 66% ( 0.66 ) , post - test probability 
 to lr+ of 0.92 ( 92% ) and to lr- of 0.35 ( 35% ) it means that the risk of a person who report increase in pain to 
 have mfp is 0.92 ( 92% ) , while the risk of a person who do not change in pain with 
 this protocol to have mfp is 0.35 ( 35% ) . despite the small sample size , the experimental and control groups clearly demonstrated 
 different responses after the experimental chewing . the increase in pain intensity in 
 the mfp group along the chewing exercise was significantly higher when compared to the 
 healthy controls . this fact highlights ultimate differences in pain behavior upon 
 function between healthy subjects and patients with mfp . ( 2002 ) and dao , lund 
 and lavigne ( 1994 ) showed mean pain 
 increases of 28.3 e 32 mm , respectively ( values above the smallest detectable 
 difference ) . in the present 
 study , differences in the pre - test pain vas may explain 
 that difference . while the present study obtained mean initial values of vas of 
 12.0318.27 mm ( 18 patients with preexercise vas=0 ) , dao , lund and 
 lavigne ( 1994 ) had 
 35.22.7 mm ( all patients with eav>0 ) and gavish , et al . the frequency of patients which experienced variations in pain intensity during 
 functional exercise was pointed out by earlier studies , as followed : increase in pain 
 ( 48.3% and 84% ) ; no change in pain ( 20% and 10% ) ; and reduction in pain ( 31.7% e 6% ) . 
 in the present study , 76% of the sample experienced pain increase , and 24% reported no 
 change . these finding are 
 in accordance to gavish , et al ( 2002 ) 
 and could be explained due to similar inclusion criteria , which excluded patients with 
 cervical trigger points and arthralgia . dao , lund and lavigne ( 1994 ) hypothesized that the reaction to exercise may be 
 related to the pre - exercise pain level , since the patients who presented a decrease in 
 pain had a level of pre - exercise pain significantly higher(55.84.0 mm ) than 
 those who had an increase in pain ( 27.53.1 mm ) . again , the mean low pre - exercise 
 pain level observed in this study could be responsible for the absence of this 
 occurrence . a more 
 comprehensive sample with patient subgroups for pain intensity ( low , mild and high ) 
 might be necessary to confirm the hypothesis of dao , lund and lavigne ( 1994 ) . also , to avoid confounding 
 factors , the present study ruled out individuals with any sign of referred pain due to 
 trigger points , as well as those that had taken any analgesic medication within 24 h 
 prior to the experiment . thus , a more homogenous sample of patients with mfp with mild 
 ( n=18 ) and moderate ( n=11 ) pain levels was composed . among the control subjects , only 2 showed increased vas after the exercise , while the 
 remaining 13 reported no change in pain intensity . ( 2001 ) , who 
 reported no change on vas in healthy subjects after 40 min of chewing on a soft gum . ( 2005 ) demonstrated 
 cut - off values of ppt to each of muscular sites evaluated in the present study . they 
 found 1.5 , 2.47 , 2.75 , and 2.77 kgf / cm to the superficial masseter ( belly ) , 
 and the anterior , middle , and posterior temporalis , respectively , with specificity of 
 90.8% . in the present study all pre - exercise mean ppts of patients with mfp were below 
 those cut - off values ( 1.40 , 1.60 , 1.85 , and 1.94 kgf / cm respectively ) . however , mean pre - exercise ppts of control subjects to anterior and middle temporalis 
 stayed just below them ( 2.13 and 2.32 kgf , respectively ) , though significantly above the 
 mfp group . at chewing completion ( ppt9 ) , all ppts of patients with mfp were lower than baseline 
 ( ppt0 ) , whereas the control group showed significant reduction of ppt only for the 
 anterior and posterior temporalis , with subsequent recovery to similar ppt0 levels at 
 ppt18 . ( 2001 ) who gave further evidence that the 
 human jaw muscles in healthy subjects recover quickly after prolonged gum chewing , 
 demonstrating that the amount of masticatory loading did not affect muscle tenderness in 
 healthy subjects . based on ppt evolution of the control group , mfp ncp and mfp incp , it could be assumed 
 that the pain / ppt behavior during the exercise in patients with mfp seems to be 
 associated to the pre - exercise pain ( vas ) and ppt levels . nevertheless , it is not 
 possible to compare these findings with those of dao , lund and lavigne ( 1994 ) due to differences in pre - exercise 
 pain levels . after chewing ( p9 ) , mfp ncp patients , showed a more similar pattern to mfp incp than to 
 the control group . despite of this similarity , this fact may be explained by the differences 
 between the ppt0 values , significantly and almost significantly greater than those of 
 incp patients ( p=0.012 for pt , 0.057 for mm ; and 0.051 for at ) . the differences in ppt9 
 values between mfp ncp and incp patients could be also due to pre - exercise ppt values . patients with mild vas pain tend to present a mild vas pain reaction on to exercise and 
 those with moderate vas pain trend do present , also , a moderate reaction to exercise . similarly , the ppt0 values seem to be the main factor to the tenderness exacerbation 
 during function . pain stimulation or exacerbation in patients with mfp due to chewing is well 
 demonstrated as one of the most important characteristics of musculoskeletal pain . mcmillan and blasberbg ( 1994 ) have 
 described similar findings in subjects with mfp . ( 2001 ) described that the 
 exercise - induced pain and fatigue has been related to ischemia and to accumulation of 
 metabolic waste products . indeed , it has been shown that during activity of the jaw 
 muscles , muscle blood flow may be hampered , probably due to an increased intramuscular 
 pressure and nipping of the vessels entering the muscle . however , nielsen , et 
 al . ( 1990 ) demonstrated that 
 subjects with muscle pain in craniomandibular muscles , regardless the location of the 
 pain and the muscle involved , recruit the anterior temporalis and masseter muscles less 
 often and with lower activity . the sensitization of muscle nociceptors is probably the peripheral mechanism underlying 
 local tenderness and the pain upon function of a pathologically altered muscle , related 
 to the release of endogenous substances , such as prostaglandin and bradykinin . central 
 mechanisms also contribute for this event in chronic pain patients , as very well 
 documented . despite the presence of some patients with mfp who did not change in pain to exercise , 
 this protocol presented an or value greater than the majority of combined orthopedic 
 tests in a previous study . those 
 authors studied the discriminative ability of six orthopedic tests and combinations to 
 distinguish different subtypes of tmd ( myogenous and arthrogenous ) . for this reason , the sensitivity of this test was higher than the minimal acceptable level ( 0.75 ) 
 reported by widmer , lund and feine 
 ( 1990 ) . the findings of the 
 present study ( lr and or ) indicate an adequate discriminative ability of this protocol 
 to distinguish patients with mfp from healthy controls . however further studies with a 
 more representative sample of patients with mfp with low , moderate and severe 
 intensities of pain are necessary . the findings of the present study give further evidence that : 1 ) there are at least two 
 subtypes of patients with mfp who can be expected to respond differently to experimental 
 chewing , either with an increase in pain or not ; 2 ) probably because of different 
 reactions to exercise within the mfp group , this protocol showed an adequate 
 discriminative ability ; and 3 ) the pre - exercise pain / ppt levels seem to influence 
 coherently the pain / ppt response to exercise in patients with mfp with mild and moderate 
 pain .