PubMed · 3456373
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W R Hume, O F Makinson. 1986. Microwave sterilization.. https://doi.org/10.14219/jada.archive.1986.0331
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OBJECTIVE: We sought to compare digital images with radiographs for the perceived clarity of small endodontic file tips at 2 different working lengths, as well as for the visualization of periapical bone lesions. STUDY DESIGN: Standardized conventional radiographic and phosphor-plate digital images were taken of 20 extracted permanent mandibular molars with 06 K-files placed in the distal root canal either 2 mm short or flush with the apical foramen. Similar images were obtained from mandibles with teeth that demonstrated large (n = 10) or small (n = 10) periapical lesions. Four evaluators ranked the clarity of the digital image with that of the radiograph. Results were analyzed by using the 2-sided sign test, ordinal logistic regression, and the kappa test. RESULTS: The perceived clarity of an endodontic file tip, at any position, and of a small or large periapical lesion was significantly (P < .01) less on all digital images compared with conventional films. CONCLUSION: Evaluator ratings indicated that the perceived clarity of fine endodontic files and periapical lesions was significantly less with phosphor-plate digital images than with conventional radiographs.
It has been shown that rotary nickel-titanium files cannot be used indefinitely. Researchers and clinicians have not been able to agree on how many times a file can be used before being discarded, except if a file has fractured or become visibly distorted. This study used ISO size 20 files of 0.04 taper in the curved canals of extracted mandibular molars. The canals had been previously instrumented to an ISO size 15 with stainless steel hand files. The irrigant used during rotary and hand instrumentation was Glyde. The rotary files were closely examined with scanning electron microscopy before use to detect any defects. They were then reexamined after each of five uses to document deterioration. An electric handpiece was configured to rotate at 150 rpm and secured to the testing device, which also held the extracted tooth. The testing device controlled the load at 8 N, the depth of penetration for each canal and the rate of penetration (12 mm/min). Used instruments demonstrated surface fatigue wear and cracking. Torsional moment at failure was determined on a torsiometer for used and new instruments. Data (n = 10) were analyzed by analysis of variance. The torsional moment for used and new instruments was not affected by use (p = 0.25).
AIM: The aim of this study was to compare canal preparations completed with Hedstrom and K-files of ISO size 15 - 40, made of nickel-titanium (Ni-Ti) and stainless steel (SS). METHODOLOGY: Eighty simulated canals with 200 and 30 degrees C curvatures were prepared using the step-back technique and quarter turn/pull instrument manipulation. Middle and apical level canal sections were taken using computed tomography. RESULTS: No significant difference was found between any of the file types at either level with respect to canal curvature (20 degrees or 30 degrees). At the middle level, the stainless steel files caused more enlargement toward the inner part, compared to nickel-titanium files. At the apical level, nickel-titanium canal files caused more enlargement toward the inner part, whereas more outward enlargement was caused by stainless steel instruments. No significant difference could be observed at the middle level (P > 0.05) related to the enlargement toward the outer side of the canal curvature. Transportation at both levels was significantly less (P < 0.001) for the Ni-Ti files than the SS ones. Centring ratios of the file types at the middle level were low, but not significantly different (P > 0.05), whereas at the apical level the centring ratios were significantly higher for the Ni-Ti files (P < 0.001). CONCLUSIONS: Ni-Ti instruments produced preparations with adequate enlargement, less transportation, and a better centring ratio.