Overdenture attachment selection and the loading of implant and denture-bearing area. Part 2: A methodical study using five types of attachment.

In general, an implant is loaded via axial and horizontal forces. Besides this, moment loading can also occur. The aim of this study was to investigate how different prosthetic connectors with overdentures develop force transfer to implant and bone as well as to the denture-bearing alveolar ridge. Five connectors were investigated on a stereolithographic model fabricated according to a real patient situation. The model was fitted with strain gauges on the "bone" distal and medial to the implants and with vertical force transducers in the alveolar "bone" under the denture-bearing area. The parallel-sided rigid telescopic connector developed the highest moment loading of the implant (P<0.001), which would suggest restraint in the use of this connector. The bar construction also showed somewhat high moments but these may have been at least partly exaggerated by the individual patient situation. Loading results through the non-rigid telescopic copings, single spherical attachments and magnet overdentures demonstrated a low level of implant moment loading which would in part result from horizontal forces caused by denture forward shift during force application. The denture-bearing area loading was different with all attachments (P<0.001) and was related to the rigidity of the connector and reached the highest values with the non-rigid telescopic coping. The clinical implications of the various findings are discussed.