The taper of cast post preparation measured using innovative image processing technique

<p>Abstract</p> <p>Background</p> <p>No documentation in the literature about taper of cast posts. This study was conducted to measure the degree of cast posts taper, and to evaluate its suitability based on the anatomy aspects of the common candidate teeth for post reconstruction.</p> <p>Methods</p> <p>Working casts for cast posts, prepared using Gates Glidden drills, were collected. Impressions of post spaces were made using polyvinyl siloxan putty/wash technique. Digital camera with a 10' high quality lens was used for capturing two digital images for each impression; one in the Facio-Lingual (FL) and the other in the Mesio-Distal (MD) directions. Automated image processing program was developed to measure the degree of canal taper. Data were analyzed using Statistical Package for Social Sciences software and One way Analysis of Variance.</p> <p>Results</p> <p>Eighty four dies for cast posts were collected: 16 for each maxillary anterior teeth subgroup, and 18 for each maxillary and mandibular premolar subgroup. Mean of total taper for all preparations was 10.7 degree. There were no statistical differences among the total taper of all groups (P = .256) or between the MD and FL taper for each subgroup. Mean FL taper for the maxillary first premolars was lower significantly (P = .003) than the maxillary FL taper of the second premolars. FL taper was higher than the MD taper in all teeth except the maxillary first premolars.</p> <p>Conclusions</p> <p>Taper produced did not reflect the differences among the anatomy of teeth. While this technique deemed satisfactory in the maxillary anterior teeth, the same could not be said for the maxillary first premolars. Careful attention to the root anatomy is mandatory.</p

Defects in ProTaper S1 instruments after clinical use: Fractographic examination

Aim: To investigate the mode of failure of a brand of nickel-titanium instruments separated during clinical use, by detailed examination of the fracture surface. Methodology: A total of 122 ProTaper S1 instruments were discarded from an endodontic clinic at a stomatological school in China over a period of 17 months; 28 had fractured. These fractured instruments were ultrasonically cleaned, autoclaved and then examined under a scanning electron microscope. From the lateral view the fracture was classified into 'torsional' or 'flexural'. The specimens were then re-mounted and the presence of characteristics of shear failure and fatigue striations was recorded under high-power view of the fracture surface. The difference in the mean lengths of fractured segment between the shear and fatigue groups was compared using Student's t-test. Results: Twenty-seven separated instruments were available for analysis. Under low-power magnification, only two fell into the category of 'torsional' failure when examined laterally; the others appeared to be 'flexural'. Close examination of the fracture surface revealed the presence of fatigue striations in 18 specimens. Nine instruments (including the two putative 'torsional' failures above) fell into the shear fracture group, in which fatigue striations were absent or characteristics of shear failure of the material were found. The mean length of fractured segments resulting from fatigue failure (4.3 ± 1.9 mm) was significantly greater than that for shear failure (2.5 ± 0.8 mm) (P < 0.001, two-sample t-test). Conclusions: Examination of the fracture surface at high magnification is essential to reveal features that may indicate the possible origin of cracks and the mode of material failure. Macroscopic or lateral examination of separated instruments would fail to reveal the true mechanism of failure. Fatigue seems to be an important reason for the separation of rotary instruments during clinical use. © 2005 International Endodontic Journal.link_to_subscribed_fulltex

Comparison of defects in ProTaper hand-operated and engine-driven instruments after clinical use

Aim: To compare the type of defects and mode of material failure of engine-driven and hand-operated ProTaper instruments after clinical use. Methodology: A total of 401 hand-operated and 325 engine-driven ProTaper instruments were discarded from an endodontic clinic over 17 months. Those that had fractured were examined for plastic deformation in lateral view and remounted for fractographical examination in scanning electron microscope. The mode of fracture was classified as 'fatigue' or 'shear' failure. The lengths of fractured segments in both instruments were recorded. Any distortion in hand instrument was noted. Data were analysed using chi-square, Fisher's exact or Student's t-test, where appropriate. Results: Approximately 14% of all discarded hand-operated instruments and 14% of engine-driven instruments were fractured. About 62% of hand instruments failed because of shear fracture, compared with approximately 66% of engine-driven instruments as a result of fatigue (P < 0.05). Approximately 16% of hand instruments were affected by shear, and either remained intact or was fractured, compared with 5% of engine-driven instruments (P < 0.05). The length of the broken fragment was significantly shorter in hand versus engine-driven group (P < 0.05). Approximately 7% of hand instruments were discarded intact but distorted (rarely for engine-driven instruments); all were in the form of unscrewing of the flutes. The location of defects in hand Finishing instruments was significantly closer to the tip than that for Shaping instruments (P < 0.05). Conclusions: Under the conditions of this study (possibly high usage), the failure mode of ProTaper engine-driven and hand-operated instruments appeared to be different, with shear failure being more prevalent in the latter. © 2007 International Endodontic Journal.link_to_subscribed_fulltex