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Objective: To evaluate the intra-arch displacements of the molars and the change in molar relationship following the use of a maxillary lip bumper combined with a bite plate. Materials and Methods: The material comprised study casts taken before and after the treatment of 40 consecutive patients with mixed dentition. The sagittal and transversal displacements were evaluated by a three-dimensional digitizer using the palatal rugae as an indirect fixed reference. The displacements were expressed as translation mesiodistally and buccolingually and rotation around the long axis and tipping mesiodistally. The change in molar relationship was measured to the nearest millimeter at the level of the occlusal plane. Results: The tooth movements were predominantly of distal rotation (mean, 9.7°; range, 6.5° to 26°) and distal tipping (mean, 5°; range, 5.8° to 18°). The distal displacement was a modest mean (mean, 0.3 mm; SD, 1.6 mm) and more pronounced to the buccal (mean 1.6 mm; SD, 1.5 mm). The molar relationship improved in all but four sites, and a full Class I was obtained in 65 of 80 sites. Conclusions: The early treatment with the lip bumper and bite plate can be recommended from a cost-benefit point of view. [ABSTRACT FROM AUTHOR]