Study population and design
This study enrolled subjects who were seeking orthodontic treatment and who had never been treated before. Signed informed consent was obtained from the parents of the subjects prior to entry into the study, and the protocol was reviewed and approved by the local ethical committee. The following enrolment criteria were observed: (1) age between 7 and 17 years, (2) intermediate or late mixed, or early permanent phases of dentition, and (3) good general health with absence of any nutritional problems. The subjects were scheduled for enrolment at their first clinical examination, when dental panoramic radiographs and lateral cephalograms were taken. A total of 300 subjects, constituting a subset of a previous study , were enrolled in the study: 192 females and 108 males (mean age, 11.4 ± 2.4 years; range, 7.0 to 17.0 years).
Assessment of individual dental maturity
Assessment of dental maturity was carried out through the calcification stages, according to the method of Demirjian et al.  (stages D to H), from the panoramic radiographs of the left-side mandibular teeth. Briefly, these stages are defined as:
Stage D. When (1) the crown formation is complete down to the cemento-enamel junction; (2) the superior border of the pulp chamber in the uniradicular teeth has a definite curved form, with it being concave towards the cervical region; the projection of the pulp horns, if present, gives an outline shaped like the top of an umbrella; and (3) the beginning of root formation is seen, in the form of a spicule.
Stage E. When (1) the walls of the pulp chamber form straight lines, the continuity of which is broken by the presence of the pulp horn, which is larger than that in the previous stage and (2) the root length is less than the crown height.
Stage F. When (1) the walls of the pulp chamber form a more or less isosceles triangle, with the apex ending in a funnel shape, and (2) the root length is equal to or greater than the crown height.
Stage G. When the walls of the root canal are parallel and its apical end is still partially open.
Stage H. When (1) the apical end of the root canal is completely closed, and (2) the periodontal membrane has a uniform width around the root and the apex.
An experienced orthodontist (LC) who was blinded to the skeletal maturation stages assessed the dental maturity of the mandibular canines, the first and second premolars, and the second molars.
Assessment of individual skeletal maturity
Assessment of skeletal maturity was carried out through the cervical vertebral maturation (CVM) method  on lateral cephalograms. This method comprises six stages (CS1 to CS6) for cervical vertebral maturation. An experienced orthodontist (GP) who was blinded to the dental maturation stages assessed the skeletal maturity of the subjects. Finally, the subjects were clustered into three groups according to their growth phases, as pre-pubertal (CS1 and CS2), pubertal (CS3 and CS4), and post-pubertal (CS5 and CS6) .
For each canine and second molar, and within each dental maturation stage, the prevalence of the growth phases was calculated. To establish the clinical performance of each dental maturation stage for the diagnosis of each CVM stage, the positive likelihood ratios (LHRs) were calculated, along with the 95% confidence intervals (CIs) . These positive LHRs provide estimates of how much a given dental maturation stage changes the odds of having a given growth phase. Here, a positive LHR indicates that a subject who tests positive for any clinical parameter (i.e., any dental maturation stage) has a high probability of having the given condition that needs to be diagnosed (i.e., any skeletal maturation stage). The positive LHR incorporates both the sensitivity and the specificity of the test, and it provides a direct estimate of how much a test result changes the odds of having a condition .
With a positive LHR ≥10 considered as the requirement for a satisfactorily diagnostic performance , all of the maturational stages of the individual teeth that satisfied this condition for the identification of either pre-pubertal or post-pubertal growth phases were excluded from the analysis of possible combinations of maturational stages. According to these data, the canine stages G and H and the second molar stages F and G were considered as possible combinations, for which the diagnostic performance for the identification of the growth phases was calculated. These stages were combined using either two or three stages per combination. In the case of three stages, for instance, canine stage G was combined with second molar stage F and G; similarly, canine stage H was combined with the same second molar stage F and G. The positive LHRs were retrieved for each combination, along with the 95% CIs; again, a threshold value ≥10 was used to assess a reliable diagnostic performance for the identification of growth phase on an individual basis [15, 18].
The weighted kappa statistics for intra-examiner agreement were >0.88. A p value less than 0.05 was used for rejection of the null hypothesis.