## 1 Introduction  
Do dental clinicians need to extract all third molars? On May 2000 in the UK, National Institute for Health and Care Excellence (NICE) published the guidelines about the extraction of third molars. The NICE guidelines recommended that third molar extraction should be limited to teeth with pathologies such as caries lesion, peri-apical lesions, recurrent periodontitis, lesion to the second molar, cyst/neoplastic lesions, etc. [1].  
Still, in the last decades, the frequency of third molar extraction by oral surgeons and general dentists has been increasing [2]. Some cohort studies reported that between \(30\%\) and \(60\%\) of people who have retained their asymptomatic, unreported wisdom teeth will need of at least one extraction in the next future (\(4\)-\(12\) years after their first evaluation). In fact, third molars tend to change position towards the coronal and mesial direction, resulting in the damage of second molars or becoming partially erupted, thus meaning at a higher risk of caries or pericornitis [3].  
It is believed that the presence of the third molar is a phenomenon of human vestigality so that the prevalence is very high and various according to population and familiarity [4].  
In Sweden, 72% of the young population aged between 20 to 30 years has, at least, one impacted lower third molar and, in the UK, it is estimated that every year, 4 people out of 1000 will need a third molar extraction [5].  
A retrospective cohort study of [PERSON] et al. (2020) including 1682 patients reported that the common reasons to avoid third molars extraction are: right eruption with function in occlusion (31.9%), patient preference (31.5%), and absence of symptom in patients >30 years old (17.5%) [6]. Compromised health status and advanced age were often included in the decision regarding whether to retain the third molars or not. One-third of the referred patients had reasons to retain one or more third molars. These findings might facilitate the future development of a consensus statement.  
Prevalent literature indicates that wisdom teeth surgery is often performed by general dentists, however, the cost-benefit relationship and the complication rate should be carefully considered before initiating any treatment plan [2].  
A retrospective study of [PERSON] and co-workers (2019) suggested that impacted teeth with no pathologies could be left in site monitoring the evolution. In those cases, Orthopan-tomography (OPG) is very useful to monitor the evolution of impacted third molar but cone-beam computed tomography (CBCT) is needed to predict the surgical risk [7].  
It is well reported that Orthopantomography (OPG) is routinely used as a primary diagnostic exam in third molar surgery, and it is useful in the initial decision-making process [1,8]. Typical radiological signs of high risk of inferior alveolar nerve (IAN) damage are the darkening of the roots; a deflected root; narrowing of the root; diversion or loop of the inferior alveolar canal [9].  
Despite this knowledge, some studies reported that there is an incidence of 17% of transitory nerve damage in patients who presented these signs in OPG plus 2% of permanent nerve damage [10].  
The present retrospective study was performed to assess whether specific OPG findings could predict the risk level of a third molar extraction and, therefore, the putative need for further patients X-ray exposure to CBCT to have a better understanding of the anatomy.  
The aim was to evaluate the pre-operative position of wisdom teeth as seen on OPGs and to compare this position with the one found on CBCT. The null hypothesis was that the radiolucent area at the apical portion of third molar roots as observed on OPG-(Y-sign)-does not match with the impaction of the root into the lingual cortical bone on the CBCT of the same patient.