Mandibular transverse dentoalveolar and skeletal changes associated with lip bumper and rapid maxillary expander: A cone-beam computed tomography study

Introduction: Currently, there is little consensus regarding the spontaneous uprighting of the mandibular dentoal-veolar complex in response to maxillary expansion, which poses the question about the necessity of combining mandibular treatment with rapid maxillary expansion to coordinate the maxilla and mandible transversely. This study aimed to evaluate the effects of the bonded rapid maxillary expander (RME) alone compared with RME with lip bumper (LB) treatment on the mandibular transverse changes. Methods: This retrospective study analyzed 3 groups: the control group with no orthodontic or orthopedic treatment (23 patients [14 females, 9 males]; mean age 9.13 years at T1 and 11.24 years at T2); the RME group with no mandibular treatment (22 patients [9 females, 13 males]; mean age 8.73 years at T1 and 12.04 years at T2); and RME + LB group (23 patients [16 females, 7 males]; mean age 9.45 years at T1 and 12.18 years at T2). Three-dimensional superimposition of the mandibular images was performed with cone-beam computed tomography taken at prephase and postphase I treatment (growth and development check records for the control group) to conduct the angular and linear measurements at the dental, alveolar, and skeletal levels. The intergroup comparisons were performed using the Mann -Whitney U-test. Results: Accompanying slight molar self-uprighting during the normal mandibular growth period observed in the control group, transverse growth was also observed in both alveolar and basal bone levels of the mandible, but no significant changes in the alveolar bone inclination occurred. The bonded RME slightly increased the mandibular first molar uprighting but not the mandibular widths at the tooth or alveolar levels. Adding a LB significantly increased the intermolar width and molar uprighting while decreasing the alveolar bone inclination but did not increase the amount of mandibular transverse growth at the bone level. Conclusions: RME alone did not significantly increase the transverse dimension of the mandible. RME + LB significantly increased mandibular intermolar width, uprighted the mandibular molars, and reduced the alveolar bone inclination. (Am J Orthod Dentofacial Orthop 2023;163:407-25)