J Adv Prosthodont.  2018 Dec;10(6):415-421. 10.4047/jap.2018.10.6.415.

Screw loosening and changes in removal torque relative to abutment screw length in a dental implant with external abutment connection after oblique cyclic loading

• Lee JH
• Cha HS

• KMID: 2429374
• DOI: http://doi.org/10.4047/jap.2018.10.6.415

Abstract

PURPOSE
This study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading.
MATERIALS AND METHODS
External connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a 30° angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons.
RESULTS
All assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P < .001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647).
CONCLUSION
Within the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

Keyword

Screw length; Implant; Cyclic loading; Removal torque; Screw loosening

MeSH Terms

Dental Implants*
Torque*
Dental Implants

Figure

• 

  Fig. 1 A photograph of the abutment screws used in the current study. From left to right, the screws are 1.4 – 3.8 mm in length (in 0.4 mm increments) with 3.5 – 9.5 threads (in one thread increments).

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  Fig. 2 Schematic of the cyclic loading experiment. The implant-abutment-abutment screw assemblies were designed to receive loads at a 30° angle relative to the loading axis.

• 

  Fig. 3 Distribution of the RTVs before and after cyclic loading.

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