The classification of third molars regarding their position leads to different treatment behaviors among professionals, especially when they are asymptomatic and without associated pathologies [3]. Some professionals are influenced by the strong preventive philosophy in dentistry, while others are influenced by the number of pathologies associated with mandibular third molars [13].
Overall, when only one panoramic radiograph at the end of orthodontic treatment was examined (XR1), the prognostic accuracy for lower third molars eruption was similar to the chance of accuracy by chance, even for orthodontists (59.9%) or OMFSs (58.3%). When adding another serial radiograph obtained 2 years later (XR1+XR2), no significant difference was observed among orthodontists (Table 2); however, among OMFSs, there was a lower accuracy in cases of spontaneous eruption.
When analyzing spontaneously erupted lower third molars (n=44), it was observed that the prognostic accuracy rate for XR1 was similar (p=0.19) for both groups of specialists (63% for OMFSs and 65.7% for orthodontists, (Table 3). However, when a second serial radiograph was included, the accuracy was worsen for OMFSs (55.3%). OMFS tends to indicate more extraction of teeth that will erupt spontaneously. For orthodontists, the accuracy was not improved when a second serial X-ray is evaluated.
In cases where lower third molars were impacted (n=24), the prognostic accuracy was similar to the probability of a right choice by chance for OMFSs (50.1%) and orthodontists (49.1%). When XR1+2 are examined, OMFSs improved significantly their accuracy (71.8%, p<0.0001). Orthodontists also indicated more extraction, but to a lesser extent than OMFSs (59.8%, p<0.0001). Thus, these findings confirm that there is a bias observed among specialists, since decision-making inevitably implies an element of subjectivity and individual variations can be expected [13]. Surgeons tended to indicate more extractions than orthodontists, regardless of whether the third molar will erupt spontaneously or will impact.
The concordance of the responses pointed out by orthodontists and OMFSs on the approach adopted for the third molars impacted or spontaneously erupted (n = 68), in general, was poorer for both group of evaluators when only one radiograph was examined when compared to the diagnosis obtained with the two radiographs (XR1+2) (p<0.0001). This agreement differs from that obtained in previous studies [10], where, through the analysis of a single panoramic radiograph, an excellent agreement was observed. Because they are different clinical cases, it is likely that the level of agreement depends fundamentally on the case analyzed.
The risk of impaction was the main motivator that led the specialists to indicate extractions of the third molar in our findings (Table 5), in contrast to the justifications found in a previous study [10], which pointed out that the risk of developing diseases was the key motivator leading orthodontists and OMFSs to indicate third molar extractions in their findings. This data may be associated with the eruption pathway of the lower third molars with their angulation directed to mesial that may cause a more intimate contact with the adjacent tooth. Advanced root development and the end of the retromolar space growth are widely reported as determinants of the impaction of the third molar; these have caused an increase in the indication of the impaction as a risk factor.
The influence of third molar eruption on the anterior crowding of the lower incisors has been studied [14]. However, this association is not significant and does not justify removal of the third molars [6, 15]. Systematic reviews contraindicate the prophylactic removal of third molars in order to avoid late crowding in the anterior region of the mandible [11], since none of the orthodontists, when evaluating only one or both panoramic radiographs, cited the crowding of lower incisors as justification for extraction of the lower third molars (Table 5). This is contrary to the results of previous studies [16], in which many orthodontists (30.3%) and OMFSs (55%) report that L3Ms are capable of producing crowding.
This research used a more comprehensive and known radiographic view in the clinical area to evaluate the lower third molars, the panoramic radiograph. The advantage of these radiographs is a complete overview of the dentition in relation to the stage of dental development, number of teeth, dental malformations, eruption, and resorption processes [3, 17]. The problem in evaluating the eruption of the third molar on panoramic radiographs is the difficulty of accurately evaluating skeletal parameters; this method does not replace the clinical evaluation of the patient. Thus, radiographic image formation is directly affected by the shape of the image layer, which varies among different panoramic X-rays. The evaluation parameters of the panoramic radiograph, whether taken at the end of the orthodontic treatment or as a long-term evaluation, do not offer as many requirements to confirm what will occur with the lower third molars, according to the professionals interviewed.
A previous study [18] reported no differences between panoramic and multiplanar CBCT images regarding the assessment of prognosis of third molars. However, there were significant differences in relation to the professional decision regarding the prognosis of these teeth, where OMFS have indicated more extractions than orthodontists.
The likelihood of impacted third molars causing future pathological changes may be exaggerated [7]. Many impacted or untreated third molars erupt normally and never cause clinically important problems. In addition, third molar surgery is not risk free; complications and suffering after surgery should be considered. Therefore, prophylactic removal should be performed if there is good evidence that it will benefit the patient. Thus, computed tomography is considered a more accurate technique to evaluate the involvement of anatomical structures, such as the mandibular canal, with the lower third molars [3].
The mean age of the patients in our study was 14.2 years old on the first panoramic radiograph and 17.1 years old on the second radiograph. The sample of patients in the control group of spontaneous eruption was larger and easier to acquire in comparison to the impaction group. This suggests that the third molars erupt more spontaneously in larger numbers than they are impacted.
Third molars become more upright until age 25 and can erupt normally, usually between 18 and 24 years of age. The final age for diagnosis of eruption or impaction is, on average, 21 years old [15]. The present study included third molars that had no clinical symptoms; therefore, the teeth examined represent a selective sample.
The retrospective nature of this research increases the possibility of bias and was a limiting factor in this study. This research has limited external validity, as only orthodontic patients were included in the sample and not all clinicians perform this number of radiographs for all their patients. The absence of sample size calculation also becomes a limiting factor in this research. The findings and conclusions of this study should be limited to patients with both mandibular molars present. Unilateral conditions may behave differently [2].
Since there is no reliable way to predict the risks of pathological changes related to impacted third molars, the most conservative strategy would be to monitor the life cycle of these elements through radiological monitoring at regular intervals [19]. On the other hand, when these teeth are involved with some painful symptomatology, there is a general consensus that extraction is necessary.
