Objective: To determine the relationship of E-space preservation with lingual holding arches to mandibular permanent second molar impaction.
Methods: Two hundred consecutively treated patients undergoing nonextraction treatment for incisor crowding were entered into the study. Lower incisor crowding was assessed by the Little Irregularity Index. Treatment involved E-space preservation via a passive lingual arch placed prior to exfoliation of the second primary molar. Panoramic and cephalometric radiographs were analyzed for any significant relationship of mandibular permanent second molar impaction relative to molar angulation, spacing, growth pattern, and skeletal relationships.
Results: Twenty-nine patients had at least one impacted second molar (14.5%). Of a possible 400 mandibular second molars, 34 were determined to be impacted (8.5%). Only the mandibular first molar-second molar angulation was found to be significant (P < .001). Pretreatment intermolar angulation of 24 degrees had a positive predictive value of 1.
Conclusion: Impaction of permanent second mandibular molars in patients undergoing nonextraction via E-space preservation with a passive lingual arch is 10 to 20 times more prevalent than that observed in the general population. Risk of impaction is best predicted by the pretreatment intermolar angulation between first and second permanent mandibular molars.