Geometric optimization for development of glide path preparation nickel-titanium rotary instrument.

INTRODUCTION: This study was done to develop a glide path preparation nickel-titanium rotary instrument by size optimization procedures and evaluate the properties of the prototype.

METHODS: G-1 and G-2 files were tested for cyclic fatigue, torsional resistance, and screw-in force. The cyclic fatigue resistance was compared by measuring the number of cycles to failure by using a 90° curved metal canal (n = 10). The torsional resistance was evaluated at 3 levels (2, 4, and 6 mm from the file tip) by measuring the ultimate torsional load (n = 10 each level). The screw-in forces (n = 5) were measured during sequential pecking in a simulated resin block to the end of foramen by using the customized shaping device (AEndoS). Meanwhile, finite element models of G-1 and G-2 files were made by reverse engineering, and their bending stiffness and torsional properties were calculated. By analyzing the results from mechanical tests and finite element analysis, a universal G (uG) file was designed to have intermediary mechanical properties, and then the prototype was fabricated by the manufacturer. Cyclic fatigue and torsional resistance tests and screw-in force with the uG were compared with G-1 and G-2 files.

RESULTS: The prototype of uG file showed higher cyclic fatigue resistance than the G-2 file and intermediary torsional strength and screw-in forces between the G-1 and G-2 files.

CONCLUSIONS: The prototype production from a size optimization procedure produced appropriate mechanical properties for the purpose of development.