Differential Scanning Calorimetric Studies of Nickel Titanium Rotary Endodontic Instruments
Brantley, Svec, Iijima, Powers, and Grentzer
Microleakage of Resected MTA
Andelin, Browning, Hsu, Roland, and Torabinejad
The Effect of Sodium Hypochlorite Irrigant Concentration on Tooth Surface Strain
Goldsmith, Gulabivala, and Knowles
Differential Scanning Calorimetric Studies of Nickel Titanium Rotary Endodontic Instruments
W. A. Brantley, T. A. Svec, M. Iijima, J. M. Powers, and T. H. Grentzer
Differential scanning calorimetric (DSC) analyses were performed between - 130° and 100°C on specimens prepared from nickel-titanium (NiTi) rotary endodontic instruments: ProFile (n = 5), Lightspeed (n = 4), and Quantec (n = 3). The ProFile and Light-speed instruments were in the as-received condition, whereas the Quantec instruments were randomly selected from a dental clinic and had unknown history. The DSC plots showed that the ProFile and Light-speed instruments analyzed had the superelastic NiTi property, with an austenite-finish (Af) temperature of approximately 25°C. Differences in DSC plots for the ProFile instruments and the starting wire blanks (n = 2) were attributed to the manufacturing process. The phase transformation behavior when the specimens were heated and cooled between - 130° and 100°C, the temperature ranges for the phase transformations, and the resulting enthalpy changes were similar to those previously reported for nickel-titanium orthodontic wires having super-elastic characteristics or shape memory behavior in the oral environment. The experiments demonstrated that DSC is a powerful tool for materials characterization of these rotary instruments, providing direct information nor readily available from other analytical techniques about the NiTi phases present, which are fundamentally responsible for their clinical behavior.
Microleakage of Resected MTA
Wallis E. Andelin, DDS, David F. Browning, DDS, G-Hong Robert Hsu, DDS, David D. Roland, DDS, and Mahmoud Torabinejad, DMD, MSD, PhD
Forty-six single rooted extracted human teeth were used in this study. After cleaning and shaping, twenty canals were randomly selected for obturation with MTA placed in an orthograde manor (Group 1). Another twenty roots were obturated with gutta-percha and Kerr EWT sealer, using warm vertical compaction (Group 2). The apical 3 mm of each root in both groups were resected at approximately 45 degrees to its long axis. The teeth were aged for 48 h in a humidor. The root-ends of the teeth in Group 2 were then prepared and received MTA as a root-end filling material to a depth of 3 mm. Six roots were used as positive and negative controls. The roots of all teeth were placed in contact with India ink for 48h. The roots were split and examined for dye leakage. There was no discernible leakage in teeth with resected MTA or those with MTA placed as a retrograde root-end filling material. We found no significant difference in dye leakage between resected MTA (Group 1) and non-resected MTA (Group 2.) Based on these results it appears that the resection of set MTA does not affect its sealing ability.
The Effect of Sodium Hypochlorite Irrigant Concentration on Tooth Surface Strain
Michael Goldsmith, FDS, MSc, Kishor Gulabivala, FDS, MSc, and Jonathan C. Knowles, PhD
The effect of root-canal irrigation with different concentrations of sodium hypochlorite (3%, 5.1%, 7.3% NaOCl) on the mechanical properties of teeth was investigated in vitro. Root canals of 13 extracted, human premolars, denuded of enamel, were prepared with nickel-titanium rotary instruments (QuantecTM) to a standard size by using saline irrigation. An electrical strain gauge was bonded to the cervical aspect of each tooth. The 10 experimental teeth were subjected to 5 successive, 30-minute periods of irrigation. The irrigants were used in the following order: (a) saline; (b) 3.0% NaOCl; (c) 5.1% NaOCl; (d) 7.3% NaOCl; (e) saline. Three control teeth were irrigated with saline only for all five periods. After each irrigation, the teeth were cyclically loaded to 110N while the surface strain was measured. Changes in strain of the test teeth after each irrigation regimen followed broadly similar patterns that were different from the control teeth. There was no difference, however, in the strain recorded after irrigation by the different irrigants within the experimental group.