OBJECTIVES: To evaluate the mechanical properties and metallurgical characteristics of the M3 Rotary and M3 Pro Gold files (United Dental). MATERIALS AND METHODS: One hundred and sixty new M3 Rotary and M3 Pro Gold files (sizes 20/0.04 and 25/0.04) were used. Torque and angle of rotation at failure (n = 20) were measured according to ISO 3630-1. Cyclic fatigue resistance was tested by measuring the number of cycles to failure in an artificial stainless steel canal (60° angle of curvature and a 5-mm radius). The metallurgical characteristics were investigated by differential scanning calorimetry. Data were analyzed using analysis of variance and the Student-Newman-Keuls test. RESULTS: Comparing the same size of the 2 different instruments, cyclic fatigue resistance was significantly higher in the M3 Pro Gold files than in the M3 Rotary files (p < 0.001). No significant difference was observed between the files in the maximum torque load, while a significantly higher angular rotation to fracture was observed for M3 Pro Gold (p < 0.05). In the DSC analysis, the M3 Pro Gold files showed one prominent peak on the heating curve and 2 prominent peaks on the cooling curve. In contrast, the M3 Rotary files showed 1 small peak on the heating curve and 1 small peak on the cooling curve. CONCLUSIONS: The M3 Pro Gold files showed greater flexibility and angular rotation than the M3 Rotary files, without decrement of their torque resistance. The superior flexibility of M3 Pro Gold files can be attributed to their martensite phase.
Calorimetry, Differential Scanning ; Fatigue* ; Heating ; Hot Temperature ; Pliability ; Stainless Steel ; Torque

Severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) causes COVID-19 that has been spreading worldwide since December 2019. Viral entry into cells requires expression of both angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) on the surface of the host cell. The male reproductive system, including the prostate, was supposed to be a potential target for SARS-CoV-2 since the presence of ACE and TMPRS2 receptors. This paper investigated for the first time the presence of SARS-CoV-2 mRNA in the prostatic tissue of a patient with active infection. In addition, we searched for the virus in the prostate of five patients after their recovery from COVID-19. The SARS-CoV-2 RNA was not detected in any of the prostate tissues tested even during the acute phase of infection. As case series have limitations, causality cannot be excluded and sporadic evidence of prostatic tissue invasion by SARS-CoV-2 may be detectable.