Nanoindentation for NiTi Instruments Modified by Plasma Immersion Ion Implantation
U.-M. LI, Cardinal Tien Hospital, Taipei, Taiwan, W.-H. CHANG, Show-Chwan Memory Hospital, Changhua, Taiwan, S. ALAPATI, Medical University of South Carolina, Charleston, USA, M. IIJIMA, Health Sciences University of Hokkaido, Japan, W.A. BRANTLEY, The Ohio State University, College of Dentistry, Columbus, USA, and C.-P. LIN, National Taiwan University, Taipei, Taiwan | Although
NiTi rotary endodontic instruments have widespread use, there is need for
improved clinical performance. Purpose: Utilize nanoindenter to
investigate surface hardness and elastic modulus for NiTi instruments modified
by a new Plasma Immersion Ion Implantation (PIII) technique. Methods: Three
as-received ProTaper F2 rotary instruments (Dentsply/Maillefer) were cross-sectioned
by low-speed saw, with surfaces polished through 0.05 ľm alumina. Two specimens
were treated (Institute of Nuclear Energy Research, Taiwan) at 20 kV target
voltage and incident nitrogen ion dose of 5x1017 cm2 for
1 hour (group I) and 2 hours (group II); the third instrument served as the control.
Resin-mounted specimens were placed in the nanoindenter (MTS Systems
Corporation), and all tests were performed within 500 nm depth. Means of
hardness or elastic modulus of experimental instruments were compared (ANOVA,
Tukey) to the control instrument for 16 measurements. Results: Instruments
had thin TiN surface layers after PIII treatment. Surface hardness and elastic
modulus of the experimental groups were significantly increased compared to the
control group. Mean values of both properties for PIII-treated instruments
decreased gradually from the surface to the NiTi matrix with increased nanoindenter
displacement. Maximum hardness values were 7.11 and 7.37 GPa, which occurred at
12 and 18 nm depth for groups I and II instruments, respectively. Mean hardness
was 3.69 GPa for the NiTi matrix. Both groups of PIII instruments had increased
hardness within 120 nm from the surface. Maximum elastic modulus values were
102.8 and 103.6 GPa for groups I and II instruments, respectively, and occurred
at 3 nm depth. Mean elastic modulus was 59.8 GPa for the NiTi matrix. Both PIII
groups had increased elastic modulus within 60 nm from the surface. Conclusions:
PIII is a promising surface modification technique to improve surface hardness
and elastic modulus of NiTi instruments.
| Seq #190 - Cast Titanium and Wrought Alloys of Titanium, including Ni-Ti 2:00 PM-3:15 PM, Friday, July 4, 2008 Metro Toronto Convention Centre Exhibit Hall D-E |
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