Faculty Collaboration Database

Mechanical behavior and failure analysis of prosthetic retaining screws after long-term use in vivo. Part 4: Failure analysis of 10 fractured retaining screws retrieved from three patients. J Prosthodont 2008 Apr;17(3):201-10

Date

01/22/2008

Pubmed ID

18205736

DOI

10.1111/j.1532-849X.2007.00291.x

Scopus ID

2-s2.0-41649100086 (requires institutional sign-in at Scopus site)   22 Citations

Abstract

PURPOSE: The aim of this study was to perform a failure analysis on fractured prosthetic retaining screws after long-term use in vivo. Additionally, the study addresses the commonly asked question regarding whether complex repeated functional occlusal forces initiate fatigue-type cracks in prosthetic retaining screws.

MATERIALS AND METHODS: Ten fractured prosthetic retaining screws retrieved from three patients treated with fixed detachable hybrid prostheses were subjected to a failure analysis. In patients 1 and 2, the middle three retaining screws of the prostheses were found fractured at retrieval time after they had been in service for 20 and 19 months, respectively. In patient 3, the middle three and one of the posterior retaining screws were found to be fractured at retrieval after they had been in service for 18 months. Low power stereomicroscopy and high-power scanning electron microscopy (SEM) were performed to analyze the fractured surfaces of the retaining screws examining fatigue cracks in greater detail.

RESULTS: Typical fatigue failure characterized by ratchet mark formation was revealed by light microscopy and SEM for all examined screws. Using low magnification light microscopy, ratchet marks were visible on the fracture surfaces of only two screws. SEM examination revealed all three classical stages of fatigue failure, and it was possible to see the ratchet marks on the fracture surfaces of all specimens, indicating a fatigue zone. The final catastrophic overload fracture appeared fibrous, indicating ductile fracture. The final overload ductile fracture surfaces showed equiaxed dimples, suggesting tensile overload in all examined screws except in two specimens that showed an elongated dimple pattern indicating shear/tearing overload forces.

CONCLUSIONS: Fracture of prosthetic retaining screws in hybrid prostheses occurs mainly through a typical fatigue mode involving mostly the middle anterior three screws. Fatigue cracks can grow in more than one prosthetic retaining screw, leading to fracture before the patient or clinician determines that any problem exists.

Author List

Al Jabbari YS, Fournelle R, Ziebert G, Toth J, Iacopino AM

Author

Jeffrey M. Toth PhD Associate Dean for Research in the School of Dentistry department at Marquette University

MESH terms used to index this publication - Major topics in bold

Bite Force
Dental Alloys
Dental Prosthesis Design
Dental Prosthesis Retention
Dental Prosthesis, Implant-Supported
Dental Restoration Failure
Dental Restoration Wear
Dental Stress Analysis
Equipment Design
Equipment Failure Analysis
Hardness
Humans
Microscopy, Electron, Scanning
Stress, Mechanical