LOGIN
 
Share Page:
Back

Volume 19 , Issue 1
January/February 2004

Pages 124132


Preload Loss in Gold Prosthesis-Retaining Screws as a Function of Time

Andrew Cantwell, BDentSci, MClinDent, MSc, FDSRCS/John A. Hobkirk, PhD, BDS, FDSRCSEng, FDSRCSEd, DrMed HC


PMID: 14982365

Purpose: Screwed joints are widely used in implant dentistry, and their failure is a significant problem that may be related to loss of preload. Preload is the compressive force generated across a joint when a screw is tightened and is responsible for keeping a joint closed. For a given torque, preload is limited by the frictional resistance of the contacting screw threads, flange, and opposing joint surfaces. This study tested the hypothesis that following correct placement, prosthetic gold screws lose preload over time. Materials and Methods: The study used standard Nobel Biocare components. Strain gauges mounted on a standard abutment formed a transducer to measure preload. Five sets of new prosthetic gold screws, gold cylinders, and standard abutment screws were assembled in turn on the top of an implant body, using the transducer abutment. The gold screws were tightened with a Nobel Biocare Torque Controller set to 10 Ncm, when it had an output of 12.06 0.8 Ncm with 95% repeatability. Preload was monitored for 15 hours; then the screws were removed and examined under a scanning electron microscope. Results: Preload ranged from 157.5 to 488.9 N (mean 319.6 N), with a mean reduction over 15 hours of 24.9%, with 40.2% of this occurring within 10 seconds of tightening. Discussion: Torsional relaxation of the screw shaft, embedment relaxation, and localized plastic deformation of the gold alloy and opposing titanium threads were the most likely explanation for this phenomenon. Conclusions: New prosthetic gold screws suffer significant loss of preload following placement. INT J ORAL MAXILLOFAC IMPLANTS 2004;19:124132


Full Text PDF File | Order Article

 

 
Get Adobe Reader
Adobe Acrobat Reader is required to view PDF files. This is a free program available from the Adobe web site.
Follow the download directions on the Adobe web site to get your copy of Adobe Acrobat Reader.

 

© 2014 Quintessence Publishing Co, Inc JOMI Home
Current Issue
Ahead of Print
Archive
Author Guidelines
About
Accepted Manuscripts
Submission Form
Submit
Reprints
Permission
Advertising
Quintessence Home
Terms of Use
Privacy Policy
About Us
Contact Us
Help