temporomandibular disorder ( tmd ) is a blanket term for a group of conditions that generate 
 pain and involve the muscles and/or anatomic components of the temporomandibular joint . the most common signs and symptoms of tmd are sensitivity of the muscles of the head and 
 neck ( including the muscle of mastication ) , pain in one or both joints , limited mouth 
 opening , limited lateral movements and protrusion of the mandible , clicking sounds ( clicking 
 and crackling ) , facial deformity and headache2 , 3 . ringing in the ears , the sensation of ear 
 fullness , earache , sensation of hypoacusis ( diminished hearing ) and dizziness may also be 
 present4 . numerous clinical conditions , 
 such as poor posture , malocclusion and bruxism ( teeth clenching / grinding ) , may be related to 
 the muscles of mastication , the temporomandibular joint and associated structures , giving 
 rise to tmd2 . the literature also suggests 
 that occlusal abnormalities may be causes of headache , tmd and facial pain6 , 7 and 
 may affect facial growth and esthetics , leading to a tendency toward either vertical or 
 horizontal facial growth ( long face or short face pattern , respectively)8 . our research group previoulsy showed that 
 the occurrence of headache in children and adolescentes with signs / symptoms of tmd is 
 frequent , regardless of gender and intensity of signs and symptoms of tmd9 . considering these aspects , the aim of the present study was to test associations between 
 signs / symptoms of tmd and aspects of facial profile , parafunctional habits and the number of 
 occlusal contacts in adolescents to determine which of these factors are associated with 
 clinical symptoms / signals of tmd in adolescents . an observational , cross - sectional study was carried out involving male and female 
 adolescents enrolled at the jos de paiva neto education institute , sao paulo , brazil . parents / guardians received information regarding the objectives and procedures of the study 
 and agreed to their child 's participation by signing a statement of informed consent in 
 compliance with resolution 196/96 of the brazilian national health council . this study 
 received approval from the local human research ethics committee under process number 
 332780 . the inclusion criteria were an age between 14 and 18  years and having all four first molars 
 erupted . the exclusion criteria were current medical or psychological treatment , 
 dento - facial anomalies , history of surgery or trauma in the region of the temporomandibular 
 joint and orthopedic or orthodontic treatment of the jaws . all participants were assessed using to the helkimo index , which is an assessment tool for 
 the diagnosis of tmd that is frequently administered to the age group in question10 , 11 . this index classifies individuals in to severity categories based on 
 clinical signs of tmd , and is divided into five subscales addressing limitations in 
 mandibular range of motion , limitations in temporomandibular joint function , pain in the 
 muscles of mastication , pain in the temporomandibular joint , and pain during mandibular 
 movements12 . the clinical 
 examination consisted of an extraoral and intraoral inspection of the teeth , the 
 determination of the type of occlusion and occlusal abnormalities as well as palpation of 
 the muscles of mastication and the temporomandibular joint . subjects were interviewed about 
 addressing clicking sounds , facial pain , difficulty with chewing , and parafunctional habits . 
 based on the criteria of the helkimo index , each item received a score of 0 , 1 or 5 . the sum 
 of the item scores allows classification of individuals into one of four categories : no 
 symptoms of tmd ( 0 points ) , mild symptoms of tmd ( 1 to 4 points ) , moderate symptoms of tmd 
 ( 5 to 9 points ) and severe symptoms of tmd ( 10 to 25 points)12 . the participants were classified into four groups based on the 
 results of the index and physical exam : without tmd ; with mild tmd ; with moderate tmd ; and 
 with severe tmd . the tracking of headache was made according to the criteria of the international headache 
 society ( 2004)13 . the 
 number of days that headache is less than or equal to 180/year ( less than 15/month ) b. headache lasting 30 minutes to 7 days c. at least two of the following pains:1 . mild to moderate intensity ( may limit , but not prevent activities ) 3 . 
 bilateral location 4 . photophobia and phonophobia are absent or only one is present e. not due to another disease in the statistical analysis we used the chi - square test and fisher 's exact test , with a 
 level of significance of 5% ( p<0.05 ) . ns : not significant fisher 's exact test p=0.002 * eighty - one adolescents ( mean age : 15.64  years ; standard deviation : 1.06  years ) were 
 evaluated . the prevalence of tmd was 74.1% 
 ( n=60 ) in the overall sample and 87.2% among the female participants ( n=34 ) . tmd was 
 significantly associated with the female gender ( p=0.009 ) , clicking sounds ( p=0.026 ) , 
 headache ( p<0.001 ) and the parafunctional habit of nail biting ( p=0.002 ) ( table 1 ) . in the analysis of the degree of severity and gender , a statistically significant 
 association was found between severe tmd and the female gender ( p=0.002 ) ( table 2 ) . the present results demonstrate there are statistically significant associations between 
 tmd and the female gender , clicking sounds , headache and the parafunctional habit of nail 
 biting . with regard to the degree of severity the greater prevalence of tmd among females may be attributed to hormonal , postural , 
 emotional , occlusal and functional factors as well as genetic predisposition14,15,16 . the present findings are in agreement 
 with previous reports on the gender difference in the adolescent population1 , 17 . it should be stressed that the use of the helkimo index was based on it being easy to 
 understand by individuals in the age group studied , and the fact that this assessment tool 
 is frequently employed for the diagnosis of tmd10 , 
 11 . as tmd has a multifactor etiology , individuals with this disorder may exhibit anxiety , 
 stress , occlusal abnormalities and postural problems as well as parafunctional habits , 
 leading to the exacerbation of signs and symptoms , with a negative impact on social 
 activities , physiological aspects and quality of life18 , 19 . diurnal and nocturnal 
 bruxism ( teeth clenching / grinding ) , biting on objects , forward thrust of the mandible , and 
 nail biting are among the harmful oral habits called parafunctions20 , 21 . in the present 
 sample , nail biting was found among 84.2% of the cases of tmd , followed by teeth clenching . the statistically significant association between tmd and nail biting is in agreement with 
 findings described in a previous study19 , 22 . in contrast , other studies have found no 
 association of these variables with tmd23 , 24 . nonetheless , these and other 
 parafunctional habits should be taken into consideration due to the association with 
 emotional factors as well as the issue of placing excessive load on the stomatognathic 
 system25 which may be a trigger factor 
 in the emergence of tmd . however , 
 individuals with the short face pattern generally have a posteriorly inclined cervical 
 spine , whereas those with the long face pattern have reduced curvature of the cervical 
 spine26 . it is important to investigate 
 these characteristics , as orofacial abnormalities and habits have been reported to be 
 associated with postural problems18 , 27 . among the symptoms , gonalves et al . found an association between different subtypes and severities of 
 tmd and primary headache , suggesting that the central facilitation of nociceptive inputs and 
 the involvement of tmd with muscle pain may be important in such cases28 . clicking sounds may be present due to different factors , such as trauma , genetic 
 malformation of bone and cartilage surfaces , syndromes and parafunctions . clicking sounds 
 upon opening the mouth may occur due to the anterior dislocation of the disc with or without 
 reduction and consequent friction between the anterior region of the head of the condyle and 
 the posterior band of the disc during the translation of the condyle , causing the joint to 
  click  . crackling may occur due to degenerative disc problems , with the leakage of synovial 
 fluid between the supra and infra disc compartments16 , 26 . in the present study , joints noises were presented by clicking in 82.4% of the participants with tmd , which is in 
 agreement with studies reporting this to be a frequent sign of this disorder7 , 29 . premature occlusal contact constitutes a possible cause of headache , facial pain and tmd , 
 affecting chewing function and causing asymmetry of the stomatognathic system . these 
 disorders may be secondary consequences of the change in occlusal position due to joint and 
 muscle pain , leading to deviation of the mandible and excessive pressure on the joint and 
 bilamellar region . in the growth phase , occlusal interferences may exacerbate symptoms due 
 to the functional deviation of the mandible as well as periodontal alterations due to pain . these functional alterations between the dental arches may have negative neuromuscular 
 consequences for the structures of the head and neck , triggering the development of tmd , 
 with a negative impact on quality of life30 , 31 . based on the present findings , tmd is more prevalent among females and headache is one of 
 the most closely related symptoms . clicking sounds ( represented by clicking ) are found in 
 the majority of cases . therefore , the sum of two or more factors may be necessary for the 
 onset and perpetuation of tmd .
[ purpose ] to assess the association between the oclusal characteristics , headache , 
 parafunctional habits and clicking sounds and signs / symptoms of tmd in adolescents . 
 [ subjects ] adolescents between 14 and 18  years of age . 
 [ methods ] the participants were 
 evaluated using the helkimo index and a clinical examination to track clicking sounds , 
 parafunctional habits and other signs / symptoms of temporomandibular disorder ( tmd ) . 
 subjects were classified according to the presence or absence of headache , type of 
 occlusion , facial pattern and type of bite . in statistical analyse 
 we used the chi - square 
 test and fisher 's exact test , with a level of significance of 5% . 
 [ results ] the sample was 
 made up of 81 adolescents with a mean age of 15.64  years ; 51.9% were male 
 . the prevalence 
 of signals / symptoms of tmd was 74.1% , predominantly affecting females . 
 signals / symptoms of 
 tmd were significantly associated with clicking sounds , headache and nail biting . 
 no 
 associations were found between signals / symptoms of tmd and angle classification , type of 
 bite and facial pattern . 
 [ conclusion ] headache is one of the most closely associated 
 symptoms of tmd . 
 clicking sounds were found in the majority of cases . 
 therefore , the sum 
 of two or more factors may be necessary for the onset and perpetuation of tmd .