Purpose: The purpose of this study was to evaluate whether or not bone quality has an effect on the biomechanical behavior of a tooth connected to an implant, when a rigid and a nonrigid attachment are used. Materials and Methods: Models of fixed partial dentures supported by a tooth and an implant were developed. These models were then imported into finite element analysis software to study the impact of forces on different types of attachments (rigid vs nonrigid) and bones (types 1 to 4). Each fixed partial denture was subjected to a vertical load of 200 N on the premolars and 230 N on the molar. The materials were considered linear, isotropic, and homogenous. Eight different scenarios were tested. The von Mises criterion was used to display the stress in five structures: fastening screw, implant, attachment, cortical, and trabecular bone. The displacements of the tooth and the implant were also examined. Results: The calculated maximum observed stress values differed among the simulated scenarios. The biggest values of stress concentrations were observed at the lingual cervical areas, the implant-cortical bone interface, the implant-crown interface, the butt-joint contact of the implant-abutment screw, and the apical parts of the tooth and implant. The main difference between the rigid and nonrigid connection was observed between the natural tooth retainer and the pontic. In the rigid connection, the movement of the natural tooth retainer was smooth. In the nonrigid connection, the attachment exhibited a partial buccal displacement. Von Mises stresses among the different tested structures ranged between 24 and 840 MPa. Conclusion: The quality of the bone and the rigidity of the connection between a natural tooth and an implant influence both the generated stresses and the displacement of the tooth and the implant. The highest stresses for the implanttrabecular bone interface, the neck of the implant, and the fastening screw were observed in type 3 bone when a rigid connection was used. The lowest stresses for the implant-cortical bone interface, the neck of the implant, and the connector were registered in type 1 bone, when a rigid connection was used. The smallest tooth and implant displacement was observed in type 1 bone, when a rigid connection was used, while the biggest tooth and implant displacement was registered in type 4 bone when a nonrigid connection was used. Keywords: biomechanics, bone types, finite element analysis, implant displacement, nonrigid attachment, rigid attachment, tooth displacement, tooth-implant connection