Author : Satish B. Alapati
Publisher :
ISBN 13 :
Total Pages : 62 pages
Book Rating : 4.:/5 (71 download)
Book Synopsis An Investigation of Phase Transformation Mechanisms for Nickel-titanium Rotary Endodontic Instruments by : Satish B. Alapati
Download or read book An Investigation of Phase Transformation Mechanisms for Nickel-titanium Rotary Endodontic Instruments written by Satish B. Alapati and published by . This book was released on 2006 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Nickel-titanium rotary instruments based upon the intermetallic compound NiTi have gained considerable popularity among endodontists because the very low elastic modulus of NiTi enables these instruments to readily negotiate curved root canals during endodontic therapy with a slow-speed handpiece. However, concern about in vivo separation (fracture) of nickel-titanium instruments during treatment is still a major challenge confronting every manufacturer and endodontist, since this often happens without prior warning signs from permanent deformation. NiTi exists in two major microstructural phases: austenite, and martensite. Transformations between these NiTi phases occur rapidly by twinning on the atomic level and are reversible for stresses below the onset of permanent deformation. An intermediate R-phase is also sometimes observed for the transformation between austenite and martensite. The nickel-titanium rotary instruments are intentionally manufactured in the superelastic condition having the fully austenitic structure, which provides the capability of accommodating extensive elastic strain without fracture under clinical conditions associated with conventional root canal therapy. The overall objective of this study was to gain new insight into the microstructural phases in commercial NiTi rotary instruments and their transformations, which would be of scientific importance for development of new instruments with improved clinical performance. The phases present were identified by Micro-XRD (micro-x-ray diffraction) and TMDSC (temperature-modulated differential scanning calorimetry), using clinically popular ProFile GT and ProTaper nickel-titanium rotary instruments, which have two different cross-sectional designs. Instruments were analyzed in the as-received condition, after clinical use, and following elevated-temperature heat treatments. The first null hypothesis was that microstructural phases and phase transformations do not have an impact on clinical performance and instrument failure. The second null hypothesis was that appropriate heat treatments previously used for orthodontic wires would not result in beneficial changes in microstructural phases that may significantly affect the clinical life of these instruments. Based upon the present research and complimentary previous studies by this investigator, both null hypotheses were rejected. Information obtained from this research should aid future development of improved instruments with reduced likelihood of failure during clinical use.