Endodontic File Geometry for Flexibility and Enlarged Chip Space
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Solution Overview
Problem
Endodontic rotary files fail due to cyclic fatigue, particularly at the apical end, necessitating a design that balances torsional strength and flexibility to prevent breakage within the root canal.
Innovation Solution
An endodontic instrument with a reduced cross-sectional area and enlarged chip space, featuring a cross-section that occupies less than 40% of the total area at each diameter, providing increased flexibility and reduced torque strength while maintaining integrity during use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the cross-sectional area of the instrument is reduced to access curved root canals, then the instrument can reach narrow anatomical structures, but the instrument becomes more prone to cyclic fatigue and fracture
Solution Approach 1:
The instrument combines two different metal alloys with complementary properties: a nickel-titanium (NiTi) alloy core that provides superelasticity and resistance to cyclic fatigue, and a stainless steel outer layer that provides strength and rigidity. This composite structure allows the instrument to maintain both flexibility for navigating curved canals and strength to prevent fracture during operation
2Strength
If the instrument has high torque strength to prevent separation at the apical stop, then the instrument can maintain positional stability, but the instrument generates excessive torque that may cause canal transportation or ledging
Solution Approach 1:
The instrument features a non-uniform cross-sectional design where the thickness of the metal walls varies along the length of the instrument. The apical end has greater thickness and strength to maintain positional stability at the apical stop, while the coronal portions have reduced thickness to minimize torque generation and prevent canal transportation. This localized variation in structural properties allows the instrument to satisfy conflicting requirements at different locations
3Stability of the object's composition
If the instrument design is optimized for flexibility to navigate curved canals, then the instrument can follow canal anatomy, but the instrument generates heat during reciprocating motion that may cause thermal injury
Solution Approach 1:
The instrument utilizes the temperature-dependent superelastic properties of nickel-titanium alloy, which exhibits different mechanical behaviors at different temperatures. The material's phase transformation characteristics allow it to be more flexible at operating temperatures, enabling navigation of curved canals, while the controlled reciprocating motion and material properties work together to limit heat generation and prevent thermal injury to surrounding tissues
Data Source
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AI summary
An endodontic instrument of this disclosure has less torque strength but greater flexibility and enlarged chip space compared to the prior art. In embodiments, only two flutes are spiraled about the instrument's length L to form two non-landed cutting edges between D2 and D16, the cutting edges merging to form a land at about D1. The tip end is rounded. The helical angle α increases from the handle end toward the tip end, a number of spirals per unit length being at least two times greater toward the tip end than toward the handle end, a cross-section of the length L consisting of two convex portions intersecting at each cutting edge or a wave-shape having one concave portion and one convex portion intersecting at each cutting edge, the cross-section occupying less total area than would a same size endodontic instrument having a triangular cross-section and providing greater chip space.