Date of Award
Master of Science (MS)
Objective: The objective of this study was to determine the influence of fluoride and stress on the mechanical properties of nickel-titanium open coil springs. Materials and Methods: Sentalloy nickel-titanium open coil springs (15 mm length) were divided into five groups. A control group was tested mechanically in as-received condition. The other four experimental groups were exposed to artificial saliva (Fusayama-Meyer solution) at 37oC for 12 weeks in a 2x2 factorial design with fluoride exposure and stress (compression) as the two factors. Those springs which were under compression were held at 5 mm in length for the entirety of the testing period. Fluoride exposure was two minutes per day in a 1500 ppm NaF solution. In each group, n=10. The experimental groups were then tested mechanically via compression on a universal testing machine following the 12-week exposure period to measure force characteristics. Results: No significant differences in activation force were seen between the coil groups, whereas significant (p<0.05) differences were observed in deactivation forces between the control and compressed/fluoride group and also between the control and the non-compressed/non-fluoride group. Ranges of mean deactivation force values between all groups were less than only 6 and 14 grams of force at 4 mm and 8 mm respectively. Conclusions: Clinically relevant daily fluoride exposure (1500 ppm) and continuous compression for twelve weeks did not result in clinically significant changes in force values of the nickel-titanium open coil springs, indicating they are likely to deliver consistent forces during the course of treatment.