Este estudo comparou aresistência à torção de duas marcasde instrumentos de níquel-titânio acionados à motor indicados para remoção de material obturador durante o retratamento endodôntico,Mtwo#15 e#25 eProTaperUniversal D2e D3, os quaisnforam submetidos aum testede torção nosentido horário de rotação.Os dois parâmetrosavaliados foram torquemáximo e deflexão angular máxima suportados até a fratura. Em relação à deflexão angulara rupturadiminuiuna seguinte ordem: instrumentos Mtwo#15, Mtwo#25, Pro-TaperD2, e ProTaperD3.Quanto aosvalores de torquemáximo,os resultados revelarama seguinte ordem decrescente:Pro-TaperD2, Mtwo#25, ProTaperD3 e Mtwo#15.Amicroscopia eletrônicade varredurarevelou queocorreudeformação plásticado eixohelicoidaldos instrumentosfraturados e as superfícies dessas fraturas tinham caracteristicas do tipodúctil.Concluiu-se que os instrumentostestadosapresentaram comportamentotorsionaldiferentes, dependendo doparâmetro avaliado.
Palavras chaves: Deflexão angular. Instrumentos endodônticos. Retratamento endodôntico. Torque máximo. Fratura torsional.

This study compared the torsional resistance of two brands of rotary nickel-titanium (NiTi) instrumentsindicated for endodontic retreatment. Mtwo retreatment instruments #15 and #25 and ProTaper Universal retreatment instruments D2 and D3 were subjected to a torsional assay in clockwise rotation. The two parameters evaluated were maximum torque and angular deflection at failure. Fractured instruments had their fractured surfaces and helical shafts examined by scanning electron microscopy.The results indicated that the angular deflection at fracture decreased in the following order: Mtwo retreatment file #15 ,Mtwo retreatment file #25, Pro-Taper Universal retreatment file D2 , ProTaper Universal retreatment file D3. As for the maximum torque values, the results revealed the following descending order: Pro-Taper Universal file D2,Mtwo retreatment file #25,ProTaper Universal file D3 andMtwo retreatment file #15. Scanning electron microscopic analysis revealed that plastic deformation occurred along the helical shaft of the fractured instruments. Fractured surfaces were of the ductile type. The instruments tested showed different torsional behavior depending on the parameter evaluated.
Keywords: Angular deflection. Endodontic instruments. Endodontic retreatment. Maximum torque.Torsional fracture. Ver menos