Mandibular molar protraction as an alternative treatment for edentulous spaces: Focus on changes in root length and alveolar bone height

Background The authors conducted a retrospective cohort study to investigate external apical root resorption (EARR) and alveolar bone loss (ABL) after protraction of the mandibular molars by using miniscrews. Methods The authors protracted 51 mandibular molars in 37 adults into an edentulous area by using sliding mechanics with a lever arm or a miniscrew-supported root spring. The authors measured root length and alveolar bone height on panoramic radiographs and corrected according to the crown length registration method. The authors measured the amounts of crown movement (CM) and root movement (RM) on the superimposed lateral cephalometric radiographs along the mandibular occlusal plane. The authors used a linear mixed model to determine the risk factors for EARR and ABL. Results All edentulous spaces closed successfully in an average of 31.7 months, and the average CM and RM were 4.97 and 8.64 millimeters, respectively, with an RM:CM ratio of 2.81. The root length decreased significantly by 0.80 mm (5.53%), but EARR of more than 2 mm occurred in only 4.0% of molars. The alveolar bone height was reduced significantly by 0.56 mm, but ABL of more than 2 mm occurred in only 2.0% of molars. Linear mixed model results revealed that EARR and ABL correlated only with RM and age, respectively. Conclusions Protraction of the mandibular molars into an edentulous area by using miniscrews was effective and safe, especially in younger adults. Practical Implications Protraction of the mandibular molars can be considered as an alternative treatment to conventional prosthetic treatment in the restoration of edentulous space, especially in young adults, if patients accept longer treatment duration.