ABSTRACT
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 implant-trabecular 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.
Subject(s)
Dental Implantation, Endosseous/methods , Dental Prosthesis, Implant-Supported , Dental Stress Analysis , Denture Retention/standards , Denture, Partial, Fixed , Alveolar Process/physiology , Biomechanical Phenomena , Bone-Implant Interface/physiology , Dental Abutments , Dental Implants , Dental Stress Analysis/methods , Denture Retention/methods , Finite Element Analysis , Humans , Imaging, Three-Dimensional , Models, Dental , Stress, MechanicalABSTRACT
PURPOSE: The purpose of this study was to evaluate the stress distribution during application of occlusal loads to maxillary anterior single external- and internal-connection implant-supported restorations with different amounts of bone loss and with the use of different metal alloys for restorations and fixation screws. MATERIALS AND METHODS: Models of external- and internal-connection implants, corresponding abutments/crowns, and fixation screws were developed. These models were then imported into finite element analysis software to study the impact of forces on different implant connections and materials. Each prosthesis was subjected to a 200-N compressive shear force applied at 130 degrees relative to the long axis of the implant. The materials were considered linear, isotropic, and homogenous. The parameters changed for each connection type included: bone resorption in relation to the prosthetic platform (no, 2 mm, or 4 mm of resorption); alloys of the restorations (nonprecious vs precious); and alloys of the abutment screws (titanium vs gold). Von Mises stresses were used to display the stress in five models: implant, restoration, screw, cancellous bone, and cortical bone. RESULTS: Statistically significant differences in the stresses of all involved structures occurred when the bone level decreased by 2 mm and by 4 mm. The connection type contributed to statistically significant differences in the stresses in both the restoration and the screw. The alloy type resulted in statistically significant differences in the implant, the superstructure, and the cortical bone stresses. CONCLUSION: As bone resorbed, the stresses generated within the internal-connection implant were greater than those generated in the external-connection implant. The same findings applied for the restoration and for cancellous and cortical bone. The stresses generated in the fixation screw were greater in the external-connection implant than in the internal-connection implant for all bone resorption scenarios.
