epidemiological studies have been supporting that the gingivitis is practically universal in children and adolescents , but destructive forms of periodontal disease may also occur although this is lower in young people than in adults [ 2 , 3 ] . thus , the american academy of periodontology withdrew the age factor of the classification system of periodontal disease . although previous data revealed a more surface problem in children and adolescents , some studies pointed out the presence of more advanced forms of periodontal disease , since severe gingivitis [ 1 , 46 ] until chronic periodontitis [ 7 , 8 ] with periodontal pocket , clinical attachment loss [ 911 ] , and alveolar bone loss [ 1215 ] . some studies also showed that periodontal attachment loss and alveolar bone loss are uncommon in children , but its prevalence increases in 12- to 17-year - old adolescents when compared with children from 5 to 11 years [ 13 , 1620 ] . a multinational study in 8.730 subjects from 15 to 17 years old was accomplished by hansen et al . , which represented a global sample ( 18 centers of 16 countries ) , and the authors stated that the early periodontal destruction in 15-year - old young people seems to be a common phenomenon in the whole world . although these studies have found that the alveolar bone loss was a common finding in adolescents , the diagnosis of bone loss in pediatric patients has been neglected . demonstrated that 40% of patients diagnosed in adulthood with periodontitis had already presented alveolar bone loss in deciduous dentition . several studies showed the prevalence of periodontal disease in young and adolescent patients using x - rays as a method of diagnosis [ 17 , 18 , 2227 ] . although there are limitations in the x - ray conventional technique , it represents an available and acceptable method when the technical standardization can be obtained because it is very useful . the studies that use x - rays to check the alveolar bone loss aim to obtain information about periodontal disease to diagnose if the images indicate a disease condition or a normalcy variation . in this way , some studies reported various findings considering the subjectivity of the parameters and analyses , focusing on some of the problems about this methodology . however , the x - rays have shown a strong correlation between the clinical and radiographic findings   and a good correlation with the clinical attachment loss , especially using the interproximal ( bitewing ) x - rays , which have shown to be a valuable method for the detection of incipient bone loss . thus , the interproximal ( bitewing ) radiography has been the most used method to check bone loss in young people [ 1719 , 22 , 25 , 32 ] . the radiographic examination can be a useful method for the determination of the early reabsorption of alveolar bone crest , considering the extent of the gingival problem in children and young people . the aim of this study was to verify the prevalence of alveolar bone loss in adolescents by means of the interproximal x - rays . this research was approved by the research ethics committee of university center of educational foundation of barretos  unifeb . a survey was carried out at elementary public schools in barretos city ( so paulo , brazil ) to check the availability of 15-year - old students for voluntary participation in the research . some schools were randomly chosen according to their location through the method of stratified sampling to obtain a representative sample of the city . the adolescents were taken to the dental clinics of the university center of the educational foundation of barretos ( unifeb ) by bus , kindly loaned by the road company rio grande ( barretos , so paulo , brazil ) for safety transportation and without any cost for the students and institution ( unifeb ) . parents or guardians should sign a written consent form for authorization of the adolescents for the participation in the study . thus , initially 380 patients from the 400 obtained were examined . the criterion for exclusion of the subject in the sample was based on the absence of at least one proximal surface of a first upper molar and a first lower molar for the readings . the radiographic examination was obtained through two x - rays shots per patient ( one on each side ) , using the interproximal technique in the region of premolars and molars [ 16 , 19 , 25 ] . an x - ray machine was used at 70  kv 8  ma ( dabi atlante , ribeiro preto , sp , brazil ) , and the x - ray shots were standardized by the use of positioners to the interproximal technique ( bitewings , indusbello , londrina , brazil ) . the shots were carried out within all the standards of biosecurity , using lead apron and rapid exposure ektaspeed films ( kodak , so paulo , brazil ) , packed in pvc plastic film . the films were evaluated by an investigator ( emb ) that evaluated the radiographs in an appropriate negatoscope in a dark room , with the screen covered by paper and dark suitable window for accommodation of the film for the examinations . the measurements were carried out by a single examiner ( emb ) on different days with two days apart , evaluating a maximum of 40 x - rays per day . the measurements were made from the distance from the cementoenamel junction until the alveolar bone crest , with the support of a magnifying glass and precision caliper ( mitutoyo , tokyo , japan ) . a distance greater than 2  mm between the cementoenamel junction and the alveolar bone crest was considered as bone loss [ 1719 , 25 ] . the bone crest was defined as the most coronal level in which the periodontal membrane retains its normal thickness . subsamples of three radiographs were read again , with one - week interval for the proof and determination of reproducibility and reliability of the data . the intraexaminer diagnostic confidence was evaluated by kappa statistics , reaching a concordance level of 88% . the measurements were performed from the distal surface of the canine teeth up to the mesial surface of the second molars fully erupted . surfaces with superposition of dental elements , presence of dental braces or cases with no possibility of determining the cementoenamel junction were excluded , as well as teeth in eruption process , and films with processing problems or that presented errors in the x - rays shot . then , 54 patients were excluded from the 380 patients initially examined , and the study was followed with 326 subjects . the cochran test ( q ) was used for comparison between the numbers of lesions . the results showed that the proportion of women was higher than men in the sample ( p < 0.0001 ) . table 2 shows the distribution of types of alveolar bone loss ( horizontal and vertical ) according to the gender . the data showed higher proportion of bone loss in men than in women ( p = 0.03 ) . there was greater predominance of horizontal bone loss than vertical lesions ( p < 0.0001 ) . the distribution of the number of horizontal and vertical lesions ( 1 , 2 or 3 ) can be verified in table 3 . it is verified that men showed higher proportion in the total number of lesions than women ( p = 0.03 ) , and that the majority showed one or two lesions . some authors reported that the distance considered as normal in young individuals would be from 1 to 2  mm between the cementoenamel junction and the bone crest [ 34 , 35 ] . it has also been recommended that this distance could be greater than 3  mm ; however , in the present study , it was considered a distance greater than 2  mm between the cementoenamel junction and the alveolar bone crest , following the guidelines of some studies [ 1719 , 25 ] . moreover , there was uniformity in the age of sample to avoid its influences , because the distance from cementoenamel junction to alveolar bone crest seems to increase with age . some authors also emphasize the possibility of an underestimation in the verification of the incipient periodontitis by x - rays methods , whether by deflection of angulation , difficulties of identification of the cementoenamel junction , evaluation only in posterior teeth , and even by other aspects of the radiographic technique . in the present study , all the procedures were standardized , such as x - rays shots , revelation , and readings of the sample in the attempt to avoid errors . our results are in agreement with the observations by hansen et al .   that revealed that the alveolar bone loss showed an average of 10.2% , nearly to the percentage obtained in our findings ( 10.4% ) . from the three brazilian centers that participated in the multinational study of hansen et al . , two of them named as brazil 1 and brazil 3 ( araraquara and porto alegre ) demonstrated average values of 8.95% and 8.70% , respectively . these values were also close to 10.4% verified in the present study , as well as the percentage of 10.2% obtained in the global sample , and in the result obtained by hansen et al .   of 11.3% . conversely , some findings showed higher percentage of alveolar bone loss in younger individuals [ 18 , 19 , 22 , 25 ] . examined a sample of 304 schoolchildren with low socioeconomic conditions in belo horizonte ( brazil ) , from 13 to 16 years old , and found 27.6% of alveolar bone loss . in the same way , similar results had already been observed in the global study by hansen et al .   in the sample of brazil 2 , and a small sample was discarded due the high rate of bone loss ( 26.6% ) . the highest values presented in populations of low socioeconomic conditions had been observed previously by albandar et al .   and aass et al . . our results showed a percentage of 8.9% and 1.5% for horizontal and vertical defects , respectively . these findings are similar to those found by hansen et al . , which demonstrated a prevalence of 8.85% for horizontal types and 1.35% for vertical lesions , and even by hansen et al .   that found 10.8% and 0.5% for horizontal and vertical defects , respectively . this proportion was also verified in the study by gjermo et al .   that found 51.8 for horizontal defects and 16.2 for the vertical types , in a sample of low socioeconomic condition moreover , our results showed higher prevalence of one lesion defects ( 67.7% ) , followed by two ( 26.5% ) and three lesions ( 5.6% ) , which was similar to the findings by hansen et al .   that found percentages of 64.80% ( one lesion ) , 24.68% ( two lesions ) , and 7.01% ( three lesions ) , respectively . .   also found high prevalence of one and two lesions in younger individuals ( 97.5% ) , as well as gjermo et al . that showed higher prevalence of one lesion ( 40.7% ) in people with low socioeconomic condition . additionally , the men showed higher prevalence of bone loss ( 14.95% ) than women ( 8.2% ) , whose tendency had already been revealed by some authors [ 1719 , 25 ] . considering that the alveolar bone loss may increase with age , it is important to focus in the young population to prevent the development of periodontal diseases . thus , other studies in young people are encouraged for evaluating the progression of alveolar bone loss in prospective studies , as well as for verification of their relationship with the clinical aspects . it can be concluded that the interproximal radiography was an efficient method for the detection of alveolar bone loss , revealing low prevalence in adolescents and predominance of horizontal bone defects .
purpose . 
 the aim of this study was to verify the prevalence of alveolar bone loss in brazilian adolescents through the interproximal x - rays analysis . methods . 
 bilateral and standardized interproximal ( bitewing ) x - rays were performed in 15-year - old adolescents ( n = 326 ) , and the processing of films and measurements of alveolar bone levels were accomplished by a single examiner . a distance between the cementoenamel junction ( cej ) and the alveolar bone crest more than 2  mm 
 was considered as periodontal bone loss . 
 results . 
 the results showed percentage of bone loss of 10.4% with predominance of horizontal defects ( 8.9% ) over the vertical types ( 1.5% ) . 
 it was verified higher individual distribution of one lesion ( 67.6% ) than two ( 26.5% ) or three lesions ( 5.6% ) , and higher occurrence was detected in men ( 14.95 ) than in women ( 8.21 ) . conclusion . 
 it can be concluded that the interproximal radiography was an efficient method for the detection of alveolar bone loss , revealing low prevalence in adolescents and predominance of horizontal bone defects .