in order to formulate a correct orthodontic diagnosis , accurate and thorough documentation of anamnesis , intra- and extraoral clinical examinations , model analysis , radiographic analysis , and cephalometric and photographic studies is required . in diagnosis , it is particularly important to obtain an accurate measurement of overjet , as this describes the sagittal relationship between the upper and lower central incisors . after crowding , excessive protrusion of the upper central incisors is the most frequent cause of malocclusion in caucasian subjects . it is generally accepted that increased overjet is due to a growth deficit of the jaw rather than poor positioning of the dental elements but no significant data regarding this has been published as yet . anb angle on the other hand indicates a skeletal discrepancy between the jaws , which must be brought back into harmony during treatment . this value , as well as being influenced by the anteroposterior relationship between the jaws , is not always an indicator of a real imbalance in the patient as it may also be influenced by the vertical height of the face or the position of the nasion . however , consideration of another parameter , the inclination of the upper and lower incisors with respect to the osseous base , may help to establish the correct relative protrusion of the teeth . thus , a relationship between overjet and skeletal parameters is evident , but the challenge in planning adequate treatment can be understanding how to interpret and correctly correlate dental and skeletal values . in this study , the following parameters were considered : overjet as the dental parameter , anb as the skeletal parameter , and inclination of the incisors with respect to the osseous base , that is , the impa angle and the u1-bispinal plane  ( ans / pns ) angle , as the dentoskeletal parameters . values corresponding to these parameters were obtained from analysing of digital volumetric tomographs acquired via cbct ( cone - beam computed tomography ) . this system allows us to procure images suitable for detailed study of a patient 's anatomy and to examine the structures present at a high level of accuracy and precision . the aim of this study was therefore to evaluate the degree to which a dental parameter of immediate clinical relevance ( overjet ) correlates to skeletal ( anb ) and dentoskeletal ( impa angle and u1-bispinal plane angle ) parameters to provide a potential diagnostic aid . from a sample of 73 subjects aged between 18 and 40 years , 42 subjects ( 25 females , 17 males ) all in integral permanent dentition , unaffected by maxillofacial syndromes or evident trauma , lacking a history of orthodontic or surgical treatment , and without insalubrious habits were selected ; furthermore , all subjects with metallic prostheses in the incisal region were excluded , as these devices are known to provoke scattering phenomena , as were subjects with anb angle < 0 , as these subjects were not statistically significant in number . the sample was further divided into 2 groups : group 1 comprising 25 subjects in skeletal class i with anb angle 04 , and group 2 constituted by 17 subjects in skeletal class ii , with anb angle x > 4. cbct ( cone - beam computed tomography ) was performed on each subject using the newtom 3 g volume scanner ( qrsr1 , verona ) , which employs a conical beam x - ray emission technique that markedly reduces the quantity of radiation absorbed by the patient , to obtain the images . the settings applied were fov 12  inches , 110  kv ( ap - ll ) , 2.00  ma ( ap ) , 1.00  ma ( ll ) , exposure time 5.4  s , and section thickness 0.50  mm . each cbct ( cone - beam computed tomography ) was then analysed via nnt newtom 3 g software by an orthodontist with experience in using this programme . for each left and right cbct ( cone - beam computed tomography ) the following parameters were measured : anb angle : anterior - posterior relationship of the maxilla with the mandible is measured in degrees , overjet ( oj ) : sagittal relationship between the upper and lower central incisors is measured in millimeter , impa angle : inclination of the lower incisor with respect to the mandibular plane defined as axis between gonion ( go ) and menton ( me ) is measured in degrees , u1-bispinal plane angle : inclination of the upper incisor with respect to the bispinal plane . the bispinal plane is defined as axis between the anterior nasal spine ( ans ) and the posterior nasal spine ( pns ) is measured in degrees . anb angle : anterior - posterior relationship of the maxilla with the mandible is measured in degrees , overjet ( oj ) : sagittal relationship between the upper and lower central incisors is measured in millimeter , impa angle : inclination of the lower incisor with respect to the mandibular plane defined as axis between gonion ( go ) and menton ( me ) is measured in degrees , u1-bispinal plane angle : inclination of the upper incisor with respect to the bispinal plane . the bispinal plane is defined as axis between the anterior nasal spine ( ans ) and the posterior nasal spine ( pns ) is measured in degrees . all cbct ( cone - beam computed tomography ) measurements were subsequently repeated by the same operator in order to permit reliable evaluation of the data found . moreover , to quantify the degree of error , an msa ( measurement systems analysis ) was performed which utilises a dahlberg 's d test , whose formula is s = d/2n . dahlberg 's test revealed the absence of statistically significant systematic errors in measurement . however , the systematic error was subsequently calculated using student 's t - test for paired data and yielded a significance level of 0.05 ( table 1 ) . to measure the anb angle , a secondary reconstruction was performed for each cbct wherein 3d mip ( 3d maximum intensity projection ) images were created ; this format was selected as it consents application of units of measurement to the image to be exported . to measure overjet and impa , right and left panoramic sections in which the relationship between the upper and lower incisors was clear were taken , permitting identification of the menton and right and left go for calculation of the impa and consenting the degree of overjet to be established . finally , in order to measure the inclination of the right and left upper central incisors with respect to the bispinal plane , a secondary reconstruction of each cbct ( cone - beam computed tomography ) was obtained so as to procure sagittal sections of the upper jaw perpendicular to the line passing through the centre of each radicular canal . for each of these sections , the angle between the incisor axis and the bispinal plane , the latter passing through the data obtained ( see table 2 ) were subsequently analysed statistically using multiple linear regression in order to evaluate the existence of a statistically significant correlation between dental and skeletal parameters , both in the sample as a whole and for the disparate groups 1 ( anb angle : 04 ) and 2 ( anb angle > 4 ) . two distinct analyses were performed : the first to analyse the entire sample and the second to evaluate separately group 1 ( anb angle : 04  mm ) and group 2 ( anb angle > 4 ) . in both analyses , oj right was equated to anb , impa right , 11/ans - pns , and 21/ans - pns . in a distribution analysis , only the dependent variable oj right was found to have an altered trend . however , given the numerosity higher than 30 , it was possible to hypothesise that the distribution of oj right also tends towards the normal . at this point , multiple linear regression analysis was carried out : first the correlation indices were applied and oj right was found to correlate positively , to a statistically significant degree , with anb ( r = 0.4872 ; p = 0.001 ) ; then a multiple linear regression test revealed that oj right only correlated in a statistically significant manner with anb and 21/ans - pns ( table 3 ) . eliminating the two variables found to be nonsignificant , the following expression was formulated for the final model : 
 ( 1)oj  right=10.56 + 0.60anb+0.1021/ans - pns , 
 with anb ( p = 0.000060 ) and 21/ans - pns ( p = 0.003187 ) being highly significant , as was the intercept ( p = 0.007069 ) . fisher 's goodness - of - fit index also yielded a highly significant value ( p = 0.00006 ) . subsequently oj left was considered as the dependent variable and equated with anb , impa left , 11/ans - pns , and 21/ans - pns . via distribution analysis , the only variable found to have abnormal distribution was the dependent oj left itself . however , given the numerosity higher than 30 , it was possible to hypothesise that the distribution of oj left also tends towards the normal . multiple linear regression analysis was also carried out for this variable : the correlation indices revealed that oj left had a positive , statistically significant correlation with anb ( r = 0.4872 ; p = 0.001 ) , and the multiple linear regression test showed that oj left is correlated in a statistically significant manner with anb and 21/ans - pns ( table 4 ) . elimination of the variable found to be nonsignificant ( impa left ) yielded a final model which can be expressed as 
 ( 2)oj  left=10.17 + 0.56anb+0.1021/ans - pns , 
 with anb ( p = 0.000596 ) , 21/ans - pns ( p = 0.009593 ) , and the intercept ( p = 0.002 ) being highly significant . a highly significant value was also obtained upon application of fisher 's goodness - of - fit test ( p = 0.0007 ) , although the linear determination index was low ( r = 0.313 ) . as per the entire sample , ( anb  0 < x < 4 ) , neither of the linear correlation indices oj right and oj left were found to be correlated to any of the predictor variables . furthermore , multiple linear regression analysis for oj right ( table 5 ) and oj left ( table 6 ) showed that no independent variable was significant and , therefore , no model could be constructed . in group 2 ( anb > 4 ) , analysis of the correlation indices yielded similar results . in fact , neither oj right nor oj left were found to correlate significantly with any of the predictor variables , although multiple linear regression analysis applied to oj right revealed a statistically significant correlation between this parameter and anb ( table 7 ) . however , after elimination of the nonsignificant variables , regression analysis showed that no model could be constructed . linear regression analysis of oj left , on the other hand , gave statistically significant values for anb and 21/ans - pns ( table 8) . thus , eliminating the two nonsignificant values , a definitive final model was obtained in which anb ( p = 0.002990 ) and 21/ans - pns ( p = 0.003550 ) were highly significant , as was the intercept ( p = 0.003348 ) . the model can therefore be expressed as 
 ( 3)oj  left=22.03 + 1.05anb+0.1921/ans - pns . the indicator of linear determination r is high enough ( r = 0.589 ) to validate the above model . among the factors which must be evaluated to formulate a correct diagnosis and a suitable treatment plan , the anteroposterior relationship between the jaws is a particularly relevant parameter . as proposed by the abo ( american board of orthodontist ) , overjet , in association with other parameters such as overbite , impa , presence of open bite or crossbite , or entity of crowding , is a useful indicator in evaluation of the diagnostic complexity . the aim of this paper was to establish by what degree a dental parameter ( overjet ) is able to predict the entity of the skeletal parameter anb and the dentoskeletal parameters impa and upper incisor - bispinal plane axis . the sample in this study was constituted by subjects of the dental clinic of the university of ferrara postgraduate school in orthodontics , all in integral permanent dentition , not treated orthodontically and not affected by systemic pathologies . subjects presenting skeletal class iii were excluded as they were not present in a statistically significant number . the use of cbct ( cone - beam computed tomography ) was further justified by the fact that the effective dose of radiation that the patient receives ( 56.2  milli sv ) is significantly lower than that emitted by traditional fan beam systems ( ct multislice 429.7  milli sv ) and is similar to values discharged during orthopantomography or conventional teleradiography ( 10.4  milli sv ) [ 10 , 11 ] . from analysis of the entire sample , it emerges that overjet , both left and right , was correlated in a statistically significant manner ( p < 0.001 ) with anb , despite the index of linear determination being rather low : in the first case ( right side ) r = 0.391 , and in the second ( left side ) r = 0.313 . this was probably due to the fact that overjet is influenced by the inclination of the upper and lower incisors , while anb also varies according to the anteroposterior position of the nasion , the inclination of the sn plane , and the inclination of the jaws . another factor able to modify the width of anb , even if the relationship between the jaws remains constant , is the inclination of the occlusal plane . in contrast , no correlation was revealed between overjet and impa , while a weak correlation emerged between overjet and left upper incisor - bispinal plane . this is likely to be due to the difficulty in establishing the position of the incisors with respect to the osseous base with a sufficient degree of reliability , as the dentoalveolar values are subject to greater compensatory variations [ 15 , 16 ] . from the analysis of the two distinct groups , regarding skeletal first class subjects , it was not possible to formulate any type of correlation , neither on the left nor the right , between overjet and the other variables examined . this can be explained by the fact that skeletal class i subjects are generally less  harmonic ,  that is , exposed to a greater number of compensatory variations , in both sagittal and vertical directions , sufficient to render the creation of a mathematical model able to predict their entity impossible [ 1719 ] . concerning skeletal class ii on the other hand , it was possible to construct , for the left side , a good model to correlate overjet and anb , characterised by a high significance value ( p = 0.002990 ) and a good linear determination index r = 0.589 . analogous to that revealed for the entire sample , no correlation with the impa and only a slight correlation with the left upper incisor - bispinal plane was determined . in the study conducted by zupancic et al . in exclusive class ii subjects , the overjet was found to be  a statistically significant predictor of the skeletal relationship in the sagittal plane  . however , in our study , it was not possible to construct a statistically significant model for the right - hand side . the difference between the two sides has no precise justification but is probably linked to the low number of test subjects in the sample . in contrast to previous studies performed on conventional teleradiographs , the present study offers the advantage of analysing precisely and accurately the anatomical structures both from the left side and from the right , thereby permitting radiographic artefacts , superimpositions , and flaws produced by an inevitable and omnipresent asymmetry of the face to be eliminated [ 20 , 21 ] . the results of the study conducted on the entire sample indicate how a dental parameter such as overjet can be a reliable predictor of anb angle , and to a lesser extent the u1-bispinal plane . however , if the cases of skeletal class i and class ii are considered separately , different results are obtained . in fact , in the cases of skeletal class i ( group 1 ) , it was not possible to establish a correlation between the variables analysed . in contrast , the class ii cases reflected the entire sample in that oj left was found to predict both anb angle and 21/ans - pns to a sufficient degree , despite not being in correlation with impa .
aim . to evaluate the degree of correlation between a dental parameter of immediate clinical relevance ( overjet ) with skeletal ( anb angle ) and dentoskeletal parameters such as the impa angle and upper incisor - bispinal angle . 
 materials and methods . a sample of 42 subjects , all in complete permanent dentition and without a history of orthodontic treatment or systemic pathologies , was subdivided into 2 groups : group 1 consisted of 25 subjects with anb angle 04 ( skeletal class i ) , and group 2 was made up of 17 subjects with anb angle > 4 ( skeletal class ii ) . 
 each subject underwent cone - beam computed tomography ( cbct ) . 
 for each right and left cbct , the following parameters were measured : ( 1 ) anb , ( 2 ) oj ( overjet ) , ( 3 ) impa angle , and ( 4 ) upper incisor - bispinal angle ( u1/ans - pns ) . 
 results . 
 analysis of the entire sample revealed that both right and left overjets were correlated in a statistically significant fashion ( p < 0.001 ) with anb . 
 no correlation between overjet and impa emerged , while a weak correlation between overjet and the left u1-bispinal plane was ascertained . 
 conclusions . 
 overjet may be a reliable predictor of anb , and to a lesser extent the u1-bispinal plane , particularly in skeletal class ii .