Effects of Loading Frequency Changes on Fatigue Strength of Titanium Dental Implants

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Effects of Loading Frequency Changes on Fatigue Strength of Titanium Dental Implants
14 March 2003
D.A. RUNYAN, and G.A. THOMPSON, US Army Dental Research Detachment, Great Lakes, IL, USA
IADR
Objective: Under normal loading conditions, fatigue cracks in titanium dental implants initiate near singularities leading to a degradation of mechanical strength properties. ISO/DIS 14801.2 allows generating load-cycle diagrams at ¨£ 2Hz in aqueous media with 2 x 106 cycles considered success or >2 and <15 Hz with 5 x 106 cycles considered success. The objective was to determine the effect loading frequency had on the measured fatigue strength of titanium dental implants. Methods: Nobel Biocare AB 3.75 x 15 mm fixtures and 7.0 mm abutments were used for all testing. The implant assemblies were mounted in a specimen holder using Lecoset 100 acrylic so that 2 mm of threads were exposed and the implant was tilted 30 degrees from the loading axis. The testing set-up insured no lateral forces were placed on the implant assembly. Load-cycle diagrams were established in air at room temperature, RO water at 37¨? C and 0.85% sodium chloride at 37¨? C using loading frequencies of both 2 Hz and 15 Hz. using a MTS MiniBionix II servohydraulic testing machine applying a sinusoidal load between a nominal maximum value and 10% of that value. Failure was defined as fracture or 1.8 mm of bending in the implant assembly. Results: The mean fatigue strength for titanium dental implants when loaded at 2 Hz in all three environments is 240N. When loaded at 15 Hz in all three environments the mean fatigue strength is 330N. Using a Student-t test these are statistically significantly different (p< 0.002). Conclusions: While increasing the loading frequency during fatigue testing dramatically shortens testing time from 29 to 4 days, the effects of heat dissipation and corrosion at the fatigue crack tip are altered to such a degree as to bring into doubt the validity of any extrapolations from 15 Hz to 2 Hz.