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Preload loss in gold prosthesis-retaining screws as a function of time
Andrew Cantwell1, John A Hobkirk
1Eastman Dental Institute for Oral Health Care Sciences, University College London, United Kingdom.
The International Journal of Oral & Maxillofacial Implants
|February 26, 2004
Summary
New prosthetic gold screws in implant dentistry experience significant preload loss shortly after placement. This loss, averaging 24.9% over 15 hours, can compromise the stability of screwed joints.
Area of Science:
- Biomaterials Science
- Dental Implantology
- Mechanical Engineering
Background:
- Screwed joints are crucial in implant dentistry for maintaining joint closure.
- Loss of preload in these joints is a significant concern, potentially leading to failure.
- Preload is determined by frictional resistance and is essential for joint stability.
Purpose of the Study:
- To test the hypothesis that prosthetic gold screws lose preload over time after correct placement.
- To quantify the extent and rate of preload loss in new gold screws.
Main Methods:
- Utilized standard Nobel Biocare components and a strain gauge transducer to measure preload.
- Assembled five sets of prosthetic gold screws and associated components on an implant body.
- Tightened gold screws to a specific torque (10 Ncm) and monitored preload for 15 hours.
Main Results:
- Initial preload ranged from 157.5 to 488.9 N (mean 319.6 N).
- A mean reduction of 24.9% in preload was observed over 15 hours.
- A substantial 40.2% of the total preload loss occurred within the first 10 seconds post-tightening.
Conclusions:
- New prosthetic gold screws exhibit significant preload loss immediately after placement.
- Likely causes include torsional relaxation, embedment relaxation, and plastic deformation of screw and implant threads.
- This preload reduction can impact the long-term stability and success of dental implant restorations.