Prevalence and predictive parameters of external root resorption caused by retained wisdom teeth.

Objectives: The aim of this study was to estimate the prevalence and severity of external root resorption (RR) caused by retained third molars (M3), to compare the sensitivity of panoramic radiography (PAN) and cone beam computed tomography (CBCT) and to determine predictive factors for root resorption.

Materials and methods: In a retrospective cross-sectional analysis, we included patients (N = 367) who underwent PAN and CBCT imaging between December 2017 and July 2019. Previous orthodontic treatment, age, gender, superimposition of second molars (M2) and M3 on PAN, retention depth, inclination angle and vertical level of contact with the M2 were used as predictor variables. The outcome variable was RR of the M2, graded according to Ericson et al. [1]. Subgroup analyses compared patients with and without suspected resorption in the PAN.

Results: While less than 5% of PANs suggested RR associated with M3, CBCT showed RR in 20% of all M2 with adjacent retained M3. The angle of inclination of M3, patient age and vertical level of molar contact emerged as predictive parameters, with mesial inclination, older age and deeper retention associated with increased severity of M2.

Conclusion: Within the limitations of our study, these data confirm the poor performance of PAN in the diagnosis of RR. CBCT may be helpful in detecting RR in mesioangulated and deeply retained M3 in elderly patients, even when PAN did not suggest pathology.

Clinical relevance: Our study may help to decide whether CBCT should be considered prior to M3 surgery.