Failure analysis of eleven Gates Glidden drills that fractured intraorally during post space preparation. A retrieval analysis study
Abstract The purpose of this study was to determine the failure mechanism of clinically failed Gates Glidden (GG) drills. Eleven retrieved GG drills (sizes #1 to #3) which fractured during root canal preparation were collected and the fracture location was recorded based on macroscopic observation. All fracture surfaces were investigated by a SEM. Then the fractured parts were embedded in acrylic resin and after metallographic preparation, the microstructure and elemental composition was evaluated by SEM and EDS. The Vickers hardness (HV) of all specimens was also determined. Macroscopic examination and SEM analysis showed that the drills failed near the hand piece end by torsional fatigue with fatigue cracks initiating at several locations around the circumference and propagating toward the center. Final fracture followed by a tensile overloading at the central region of cross section. Microstructural analysis, hardness measurements and EDS show that the drills are made of a martensitic stainless steel like AISI 440C. Based on the findings of this study, clinicians should expect fatigue fracture of GG drills that have small size during root canal preparation. Selection of a more fatigue resistant stainless steel alloy and enhancing the instrument design might reduce the incidence of quasi-cleavage fracture on GG drills.
Torsional and metallurgical properties of rotary endodontic instruments. 2. Stainless steel Gates Glidden drills.
A laboratory study was performed on stainless steel Gates Glidden drills to determine their torsional and metallurgical properties. Samples of #1 to #6 drills from the two manufacturers that distribute these instruments in the United States were tested in incremental and continuous clockwise torsional loading by using a digital torque meter. The values of mean torque at fracture obtained with these tests generally showed no statistically significant differences for the same drill size and a given manufacturer. However, it was not possible to completely evaluate drill sizes #5 and #6 because the torsional moments developed during testing exceeded the capacity of the test instrument. Scanning electron microscope examination confirmed the occurrence of ductile torsional fracture processes, which were evident from visual observation of the instruments after fracture. This study is part of a continuing investigation to establish standards for all rotary endodontic instruments.
Student occupational exposure incidence: perception versus reality.
Reports of clinical injuries made to a dental school Office of Occupational Health and Safety at the time of their occurrence were compared to self-reports on a survey for dental students in five classes at various times over their educational careers. The majority of injuries were from needlesticks and mishaps with hand instruments. Underreporting at the time of injury was approximately one-third in the first clinical year and one-half in the final clinical year of the three-year program. Students reported a greater perceived likelihood of injury later in their education than at the beginning but a decreased fear of such injuries. Female students reported more needlesticks and a greater fear of injury than did male students. It is hypothesized that a personal interpretation of the meaning of clinical injuries influences reporting behavior.