This study aimed to clarify the efficacy of a newly developed self-adjusting magnetic attachment (SMAT) that allowed 0.4 mm of vertical and 8 degrees of rotational movements using an in vitro model. Comparison between the SMAT and a conventional magnetic attachment (CMAT) was performed for the retentive force under different dislodgement directions. Lateral forces to the abutment were also compared among the SMAT, CMAT, dome-shaped magnetic attachment, and a ball attachment. The SMAT maintained retentive force more effectively than the CMAT, even in oblique directions of dislodgement. A smaller lateral force to the abutment was found for the SMAT compared to the CMAT or ball attachment.