Analysis of stress distribution in a screw-retained implant prosthesis

Four types of implant superstructures were screwed onto implant bodies, and the strains created around the implant bodies were compared and analyzed w ithin the IMZ Implant System. Three IMZ implants were embedded in the cente r of a polyurethane block (30 x 40 x 30 mm), and a total of 16 superstructu res was fabricated by 4 methods: 1-piece cast, 1-piece cast/split soldering soldering, and passive fit. Six strain gauges were placed on the surface o f the block 1 mm apart. Three embedded implants were numbered, and a fixed partial denture was placed on these implants and screwed by a torque wrench using 14.5 Ncm torque. This procedure was repeated 7 times for each fixed partial denture, and each created strain was measured when the last screw w as tightened. In all fixed partial dentures, strains were produced around t he implant bodies when screws retaining the prosthesis were tightened and t he strain was relieved with unscrewing: The magnitude of strain was greater with the 1-piece cast method or the section/solder method than with the so ldering and passive-fit methods. Of the 2 soldering methods, when the screw on the middle implant was tightened before those on the terminal 2 implant s, the magnitude of strain was lower with the soldering method than with th e 1-piece cast/split soldering method. When the order of screw tightening w as changed, there were significant differences in the magnitude of strain a t each gauge with the soldering method. With the passive-fit method, no dif ferences in the magnitude of strain attributable to the order of screw tigh tening could be detected. The magnitude of strain produced around a screw-r etained implant prosthesis was significantly lower with the passive-fit met hod when compared to the other 3 fabricating methods. Furthermore, the impl ants prepared by the passive-fit method were not affected by the order of s crew tightening.