J Korean Acad Prosthodont.  2009 Apr;47(2):125-135. 10.4047/jkap.2009.47.2.125.

Effect of Tightening Torque on Abutment-Fixture Joint Stability using 3-Dimensional Finite Element Analysis

• Eom TG
• Suh SW
• Jeon GR
• Shin JW
• Jeong CM

• KMID: 2195607
• DOI: http://doi.org/10.4047/jkap.2009.47.2.125

Abstract

STATEMENT OF PROBLEM: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. PURPOSE: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. MATERIAL AND METHODS: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques (10, 20, 30 and 40 Ncm) and the external loading (250 N, 30degrees C) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. RESULTS: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. CONCLUSION: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

Keyword

joint stability; screw loosening; tightening torque; preload; FEA

MeSH Terms

Alloys
Dental Implants
Fatigue
Finite Element Analysis
Head
Joints
Neck
Plastics
Titanium
Torque
Alloys
Dental Implants
Plastics
Titanium

Figure

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  Fig.1. Schematic diagram of experimental materials.

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  Fig. 2. Schematic diagram of this study.

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  Fig. 3. Preload measuring device.

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  Fig. 4 . 3-dimensional FE-model and mesh shape.

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  Fig. 5. Contact and boundary conditions of FE-model.

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  Fig. 6. Application method of Loading Condition on the abutment screw.

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  Fig. 7. Principle of preload calculation.

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  Fig. 8. Preload according to holding time of tightening torque 30 Ncm.

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  Fig . 9. Axial normal stress distribution for each tightening torque.

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  Fig. 10. Experimental value, theoretic value or analytic value about preload.

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  Fig. 11. Equivalent stress distribution for each tightening torque.

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  Fig. 12. Equivalent stress distribution for each tightening torque under external loading.

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