Journal List > J Korean Acad Prosthodont > v.48(1) > 1034645

Im, Kim, Park, Cha, and Cho: Biomechanical considerations for the screw of implant prosthesis: A literature review

Abstract

Purpose

This article attempted to determine the factors affecting the preload and screw loosening.

Methods

Available clinical studies from 1981 to 2008 from the PUBMED that presented screw loosening data and review articles regarding screw joint stability were evaluated. Eleven studies dealing the biomechanical principles of the screw mechanics were reviewed. Moreover, the results of our data were included.

Results

The frequency of screw loosening was consequently reduced due to the advancement in torque tightening with torque wrench, screw material, coating technique for reducing the frictional force, and thread design, etc. If preload in the screw falls below a critical level, joint stability may be compromised, and the screw joint may fail clinically. The types of fatigue failure of screw were divided to adhesive wear, plastic deformation, and screw fracture.

Conclusion

An optimum preload is essential to the success of the implant-abutment complex. To maintain optimum preload, using a torque wrench and re-tightening at recall time were needed. (J Korean Acad Prosthodont 2010;48:61-8)

REFERENCES

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Fig. 1.
Clinical images and SEM images of fractured screws. Arrow indicates the starting point of crack line.
jkap-48-61f1.tif
Fig. 2.
Marginal bone loss around the fractured abutment screw. From first fracture, the other fractures were consequently happened (Fig. 1).
jkap-48-61f2.tif
Fig. 3.
Estimation of fatigue life of gold screw; theoretical failure and realistic failure.
jkap-48-61f3.tif
Fig. 4.
A, Electronic torque controller; B, Torque limiting device; C, Torque indicating device; D, Contra-angle torque device.
jkap-48-61f4.tif
Fig. 5.
Loosening torque of titanium screw at 20 Ncm and 30 Ncm tightening torques.
jkap-48-61f5.tif
Fig. 6.
Mechanical tolerance of various implants. A, Implantium (Dentium, Seoul, Korea); B, Astra (Astratech, Mo ¨lndal, Sweden); C, GS (Osstem, Pusan, Korea); D, M implant (Shinhung, Seoul, Korea).
jkap-48-61f6.tif
Fig. 7.
Spiralock system of Biohorizon (Detroit Tool Industries, Madison Heights, MI).
jkap-48-61f7.tif
Fig. 8.
Schematic diagram of the mechanism of adhesive wear of screws in implant prostheses. (Upper thread indicates much milder state, while lower thread indicates much severe state of wear).
jkap-48-61f8.tif
Table I.
Screw loosening in single implant prosthesis
Author Observation time Frequency (%)  
Jemt et al. (1991)3 1 Y 27% Cantilever
Jemt et al. (1993)4 3 Y 45% CP Ti screw
Laney et al. (1994)5 3 Y 9.3%  
Henry et al. (1996)6 5 Y 18.3% old gold screw design
Priest G. (1999)7 10 Y 7.1%  
Jung et al. (2008)2 5 Y 5.8% 1996 - 2006 Review
Table II.
Multiple factors for screw loosening
Extrinsic factors Intrinsic factors
Mal-aligned implant position Preload reduction by reduced tension
Off-axis occlusal force Mechanical tolerance
Malocclusion Screw material
Bruxism, Clenching Fatigue resistance of metal
Cantilever  
Insufficient tightening torque  
Misfit between implant and abutment  
Settling effect  
TOOLS
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