# A Statistical Procedure for Exploring a Skeletal Age-Explicative Tool for Growing Patients
## 2 Materials and Methods  
This observational and retrospective study was approved by the Ethical Committee of the University of L'Aquila (protocol 135261, ID 22/2023). The research was performed in accordance with the Declaration of Helsinki from 1975 and subsequent revisions, and written informed consent was obtained from every suitable subject before collecting data. Participants were recruited among patients treated at the Orthodontic Clinic of the Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila from January 2011 to December 2019. They were selected after screening, in chronological order, according to the following inclusion criteria:  
1. Age between 6 and 16 years old;
2. OPG;
3. X-ray of the second phalanx of the third finger of the right hand;
4. Collection of biometric data such as height, weight, and wrist circumference;
5. All data must have been collected within a time window of a maximum of three months. The exclusion criteria were:  
1. Systemic pathologies affecting growth;
2. Bone pathologies and/or previous fractures of the upper limbs;
3. Multiple dental agenesis or oligodontia. One of the data collected was the grade of maturation of the second phalanx of the third finger, using a well-established method. The grade of maturation of the second phalanx of the third finger is a validated method used in dentistry for assessing skeletal age. It was introduced by [PERSON] and [PERSON] in 1980 [13], who defined five stages considering the changes in the shape of the epiphysis and metaphysis of the second phalanx of the middle finger. Lately, it was improved by [PERSON] and [PERSON] in 2002 [18; 24] with the addition of another stage, and finally, the staging was more precisely described by [PERSON] et al. [2], who defined six stages as described in Table 1 and represented in Figure 1. \begin{table}
\begin{tabular}{c c c} _Stage_ & _Bones’ Maturation_ & _Phase of the Growth_ \\ _MPS1_ & the epiphysis is narrower than & the patient is more than one year \\  & the metaphysis & before the puberral growth spurt \\ _MPS2_ & the epiphysis is at least as wide as & the patient is one year before the \\  & the metaphysis & onset of the puberral growth spurt \\ _MPS3_ & the epiphysis is either as wide as or & the patient is at coincidence of the \\  & wider than the metaphysis & puberral growth spurt \\ _MPS4_ & the epiphysis begins to fuse with & the patient is during the \\  & the metaphysis & deceleration of the curve of growth \\ _MPS5_ & the epiphysis is mostly, but not & the patient toward the end of the \\  & completely fused with the metaphysis & puberral growth spurt \\ _MPS6_ & the epiphysis totally fused with & the patient is at the end of the \\  & the metaphysis & puberral growth spurt \\  & & \\ \end{tabular}
\end{table} 
Table 1: Stadiation of the middle phalanx of the third finger according to [PERSON] et al. [1]. Figure 1: Representation of the six stages of skeletal maturation of the middle phalanx of the third finger according to [PERSON] et al. [1]. Therefore, it is a categorical assessment method. Over the years, different authors have demonstrated the reliability of this method [15; 16; 17; 18], and since the radiography of the middle phalanx of the third finger is practical and easy to record, many dental clinicians use it routinely to assess skeletal age. Indeed, this radiogram can be taken with the intraoral radiographic machine, which is present in any dental clinic. Therefore, with a single intraoral radiography of the third finger of the hand, the clinician can have information about the skeletal maturation of the patient in a very quick and practical way without requiring additional examination (for instance X-ray of left hand and wrist). Data collection  
The evaluation of radiographs was performed by three operators (MT, RE, MD). Two operators performed the categorization, while a third author was asked to arbitrate when the first two operators were not in agreement.