In vitro study on passive fit in implant-supported 5-unit fixed partial dentures

Area of Science:

• Dental Materials Science
• Biomaterials Engineering
• Prosthodontics

Background:

• Superstructure fit is crucial for the longevity and success of implant-supported prostheses.
• Fabrication and retention methods significantly influence the passive fit of fixed partial dentures (FPDs).
• Conventional methods may not always achieve an ideal passive fit, potentially leading to complications.

Purpose of the Study:

• To quantify strain development in various cemented and screw-retained fixed partial dentures (FPDs).
• To compare the passivity of fit between different FPD fabrication and retention techniques.
• To evaluate the influence of intraoral bonding on strain development in FPDs.

Main Methods:

• Investigated 40 samples of 4 different FPD types (10 each).
• Utilized a measurement model simulating a patient situation with 3 ITI implant abutments and 2 pontics.
• Mounted strain gauges near implants and on pontics, recording strain during cement setting and screw fixation.

Main Results:

• All investigated FPDs exhibited considerable strain, with no significant difference between cement and screw retention.
• No significant difference in strain was observed between conventional fabrication modes for screw-retained FPDs.
• The lowest strain levels were recorded in prostheses intraorally bonded onto gold cylinders.

Conclusions:

• Intraoral bonding of the superstructure may compensate for clinical and laboratory inaccuracies, potentially yielding the best passive fit.
• Conventional clinical and laboratory procedures cannot guarantee absolute passive fit.
• The strain-gauge technique offers a sensitive, objective method for assessing FPD accuracy, and further investigation into the long-term stability of adhesive bonding is warranted.