RESUMEN
Recent advances in technology have permitted manufacturers to produce endodontic files from NiTi alloy and rotary systems. According to manufacturers, these files maintain original canal shape better than hand files and reduce treatment time. The aim of this study was to compare a new rotary system [Race] with an older one [Profile] in maintaining the original shape of curved canal and the working length as well as the procedural accidents rate. In this experimental study, 40 polyester blocks with curved canals [45], were fabricated and divided into 2 groups. After primary working length determination and staining with methylene blue, photographs were taken. Canal preparation was done with Profile and Race rotary systems according to manufacturers and working length was measured again. Canal staining by eosin was performed and photographs were taken for the second time. The two images were superimposed and changes in canals anatomy in 5 sections were recorded. Data were analyzed by t test with p<0.05 as the limit of significance. There was no significant difference in inner and outer canal walls transportation between 2 groups [P> 0.05]. Changes in working lengths and procedural accidents were similar in the studied groups [P> 0.05]. Based on the results of this study, changes in canal anatomy and working length of simulated severely curved canals as well as procedural accidents rate are similar in two rotary systems and both are suitable for canal preparation. The mean and standard deviation of shear bond strengths [in Mpa unit] of all groups were as follows: One-Step - 19.60 +/- 1.83 One-step +H = 19.72 +/- 2.01 Single Bond-21.44 +/- 3.94 Single Bond +H =18.26 +/- 2.85 Prime and Bond NT-26.51 +/- 5.02 Prime and Bond NT+H -26.98 +/- 5.70 Excite -29.78 +/- 3.85 Excite +H -19.07 +/- 9.94 Analysis of the results revealed that the use of 5.25% sodium hypochlorite for one minute on the surface of demineralized dentin significantly decreased the shear bond strength of Excite and Single Bond [P<0.05]. For Prime and Bond NT and One-Step, shear bond strength increased with this treatment but was not statistically significant [P>0.05]. Based on the results of this study, collagen removal from demineralized dentin surface caused a significant decrease in shear bond strength of alcohol and water/alcohol based bonding systems, while the bonding strength of the acetone based systems was not affected. Therefore, the effect of collagen removal on shear bond strength depends on the bonding system applied and its solvent type
RESUMEN
Various rotary systems are available on the market, therefore selection of a proper instrument for root canal therapy is difficult. The aim of this study was to compare the maintenance of working length and original shape of curved canals and the incidence of procedural errors, using the newly introduced Race and the older Flexmaster rotary systems. In this experimental study, 40 resin blocks with a 45°Curvature were randomly divided into two groups. After determination of the working length and staining with methylen blue, photographs were obtained. All root canals were prepared using Flexmaster and Race rotary systems according to the manufacturers' instructions. The working lengths were determined once more and the prepared canals were stained with Eosin and photographs were taken. Pre- and post-preparation images were superimposed and changes in the canal walls were evaluated. Data were analyzed using Mann-Whitnney and student t-tests. The mean canal transportation [determined from the inner and outer width measurements] was higher for Race as compared to Flexmaster. The mean loss of working length in the Race [0/54mm] and Flexmaster groups [0/59 mm] was similar. The incidence of zips and elbows was%20 and%35 in the Race and Flexmaster groups, respectively. Based on the results of this study, Race instruments produce more changes in the anatomy of severely curved simulated root canals, as compared to Flexmaster instruments