Objective: The aim of this systematic review and meta-analysis is to identify the risk factors of external root resorption (ERR) on second molar (M2) due to presence of impacted third (M3) molar based on cone- beam computerised tomography (CBCT) findings.
Material and methods: Search of PubMed via MEDLINE, SCOPUS, and Experta Medical dataBASE (EMBASE) was performed to identify studies assessing the risk factors of ERR in M2 due to the presence of impacted M3.
Results: M2 in close proximity to mesio-angular impacted M3 had 50% higher risk of root resorption than with vertical impacted M3 (RR 0.50 95% CI [0.35, 0.73], p = .0003). Presence of the impacted M3 in the lower arch with ERR in M2 was higher (38.3%) than in the upper arch (33.8%). With respect to the inclination of impacted M3, the incidence of ERR was higher with transverse, horizontal and mesio-angular impacted M3 with 54.5%, 47.5% and 44.5% of occurrence, respectively.
Conclusion: ERR in M2 was significantly affected by the contact with impacted M3 and most importantly, the inclination of M3. The presence of mesio-angular, horizontal or transverse impacted M3 in close proximity to apical or middle portion of M2 could possibly be a strong risk factor for ERR in M2.
Keywords: Risk factors; impacted third molars; meta-analysis; root resorption; second molar; systematic review.