A critical appraisal of studies on cyclic fatigue resistance of engine‐driven endodontic instruments

Abstract

The endodontic literature contains a plethora of studies on static and dynamic cyclic fatigue resistance tests performed on a large array of rotary or reciprocating nickel–titanium endodontic instruments. It was the aim of this review to summarize the currently available evidence to point out the different outcomes from static versus dynamic tests and to assess whether cyclic fatigue tests provide useful data and information for clinical practice. An electronic literature research in the database PubMed was performed using appropriate search terms, and the titles and abstract were screened for relevance. Language was restricted to English. The review reveals marked differences between the results obtained in static and dynamic tests, and also, the results for the same instruments assessed either under static or dynamic experimental conditions are widely inconsistent. Between the lowest and the highest value for one and the same pathfinding instrument was a factor of about 123 when cyclic fatigue was assessed either under static or dynamic experimental conditions. Moreover, standard deviations of up to 30% have been reported. Environmental temperature has a 500% impact on the lifetime of instruments. In conclusion, fatigue resistance tests conducted under room temperature should be regarded as having little meaning and the scientific and clinical benefits of fatigue resistance tests are very limited. These data should be provided by the manufacturer of the instruments.

Influence of the Pecking Motion Frequency on the Cyclic Fatigue Resistance of Endodontic Rotary Files

“…Hülsmann et al (2019) reported similar findings to ours and highlighted the differences between static and dynamic cyclic fatigue tests [30]. Nevertheless, only 12% of published cyclic fatigue studies have used a dynamic fatigue device [30]. Most studies that have compared static and dynamic cyclic fatigue studies have concluded that the time to fracture of endodontic rotary instruments submitted to dynamic cyclic fatigue studies was approximately 20-40% higher than that found in static cyclic fatigue studies [26,[31][32][33][34][35].…”

“…Ray et al (2007) also performed dynamic cyclic fatigue studies with standardized axial movement, and they concluded that the pecking motion increased the lifespan of the endodontic rotary instruments submitted to cyclic fatigue compared with the results obtained from static cyclic fatigue studies [29]. Hülsmann et al (2019) reported similar findings to ours and highlighted the differences between static and dynamic cyclic fatigue tests [30]. Nevertheless, only 12% of published cyclic fatigue studies have used a dynamic fatigue device [30].…”

“…The higher β values observed for the group with 30 movements/min for all three variables reveal more predictable behavior of the failure of the endodontic rotary instruments in this study group, and the lower η values found in the groups with 60 and 120 movements/min for all three variables indicate a lower cyclic fatigue resistance of the endodontic rotary instruments in these study groups. The location of the crystal structure transformation is changed in the endodontic rotary instrument during the pecking motion, which increases the cyclic fatigue resistance [30].…”

Shaping Ability, Cyclic Fatigue Resistance and Fractographic Analysis of Hybrid and Reciprocating Nickel Titanium Endodontic Instruments

“…It has been concluded that cyclic fatigue resistance of the NiTi endodontic instruments highly depends on the alloy, cross-sectional design and the manufacturing method [28,29]. The extensive testing of the cyclic fatigue of newly developed instruments has a significant clinical importance [4].…”

Research that matters: studies on fatigue of rotary and reciprocating NiTi root canal instruments

“…In a previous editorial, it was suggested that it should be the responsibility of the manufacturers to provide relevant data (Hülsmann ). Secondly, as demonstrated in a review paper in this issue of the IEJ (Hülsmann et al ), the results from studies on cyclic fatigue – static or dynamic in nature – vary considerably. There are differences up to more than 100% between dynamic and static tests, and even the results between static tests differ significantly.…”