## 1 Introduction  
Impaction of the third molar is the most common of all tooth impactions occurring in the oral cavity. Third molars appear on routine radiographs of patients from 5 to 16 years of age, whereas the time of eruption ranges from 18 to 24 years [1; 2; 3]. This long duration for calcification and eruption may also play a role in the subsequent impaction of third molars [4; 5]. A recent systematic review and meta-analysis revealed a mean prevalence of third molar impaction in 24.4% of the population worldwide [6]. The odds of third molar (M3) impaction were found to be 57.7% higher in the mandible than in the maxilla, without any difference between men and women. In dental practice, the clinical decision of whether to extract third molars remains controversial [7; 8]. Various factors have been analyzed in different studies to examine their role in determining third molar impaction: deficient mandibular growth, absence of interproximal attrition in modern humans, limited retromolar space, direction of condylar growth, etc. [9]. The main predictors of third molar retention are lack of eruption space (limited retromolar space) and angulation of the third molar [10; 11; 12; 13; 14]. Some studies show that these linear and angular measurements can be used to estimate the eruption potential and the risk of retention of mandibular third molars. Evaluating the eruption potential allows timely removal of third molars while avoiding other complicated pathologies (dental, osseous, or nervous) in relation to the tooth eruption process [15]. Predicting third molar eruption is a key task in various clinical scenarios/settings: in orthodontic treatment, to estimate the indication for surgical removal, and in multidisciplinary treatment, to assess the need for orthodontic traction of a retained third molar to replace a deteriorated lower molar or prevent post-treatment complications due to lack of eruption. Third molar eruption is a complex, multifactorial process, and the excessively high rate of asymptomatic third molar extraction may be due to a lack of reliable and simple predictive tools [7; 16]. A recent systematic review established that retained asymptomatic third molars rarely remain disease-free over time, with the likelihood of disease rising with increasing age. Thus, increased retention time seems to be associated with greater morbidity [16]. Moreover, the presence of symptomatic indications for surgical third molar extraction also increases with age [17]. The goal of the present study is to evaluate the reliability and validity of the Panoramic Dental Application (PDApp) tool among Caucasian adolescents and young adults. In previous works, we developed software tools with a friendly graphical user interface (GUI) to perform quantitative analysis of medical and biological images using machine learning algorithms [18; 19]. In this paper, we propose PDApp, which predicts the eruption/retention potential of third molars. This software is intended to perform the following functions:  
1. Provide a friendly GUI to interactively work with radiological images and draw lines and angles for analysis. 2. Measure lines and angles in the images. 3. Use machine learning algorithms to automatically classify third molars in the images. 4. Allow data sharing among researchers to review the results at any time. 5. Operate fast enough to analyze images in real time. In a recent analysis, [PERSON] and [PERSON] (2018) used linear measurements and the radiological retention coefficient (RRC) to determine the eruption status of third molars [20]. This study was performed using diagnostic digital panoramic radiographs of 184 Caucasian patients of both sexes, aged 18 to 27, which were taken from the archive of the radiological dental center and anonymized. All subjects had full dental arches with radiographically confirmed lower third molars and were divided into two groups according to their eruption status (retained (R)/erupted (E)).