Effect of pre-flaring and file size on the accuracy of two electronic apex locators

Objective: This ex vivo study evaluated the effect of pre-flaring and file size on the accuracy of the Root ZX and Novapex electronic apex locators (EALs). Material and methods: The actual working length (WL) was set 1 mm short of the apical foramen in the palatal root canals of 24 extracted maxillary molars. The teeth were embedded in an alginate mold, and two examiners performed the electronic measurements using #10, #15, and #20 K-files. The files were inserted into the root canals until the "0.0" or "APEX" signals were observed on the LED or display screens for the Novapex and Root ZX, respectively, retracting to the 1.0 mark. The measurements were repeated after the pre-flaring using the S1 and SX Pro-Taper instruments. Two measurements were performed for each condition and the means were used. Intra-class correlation coefficients (ICCs) were calculated to verify the intra-and inter-examiner agreement. The mean differences between the WL and electronic length values were analyzed by the three-way ANOVA test (p<0.05). Results: ICCs were high (>0.8) and the results demonstrated a similar accuracy for both EALs (p>0.05). Statistically significant accurate measurements were verified in the pre-flared canals, except for the Novapex using a #20 K-file. Conclusions: The tested EALs showed acceptable accuracy, whereas the pre-flaring procedure revealed a more significant effect than the used file size.

A NEO-KALECKIAN MODEL OF PROFIT SHARING, CAPACITY UTILIZATION AND ECONOMIC GROWTH

This paper sets forth a Neo-Kaleckian model of capacity utilization and growth with distribution featuring a profit-sharing arrangement. While a given proportion of firms compensate workers with only a base wage, the remaining proportion do so with a base wage and a share of profits. Consistent with the empirical evidence, workers hired by profit-sharing firms have a higher productivity than their counterparts in base-wage firms. While a higher profit-sharing coefficient raises capacity utilization and growth irrespective of the distribution of compensation strategies across firms, a higher frequency of profit-sharing firms does likewise only if the profit-sharing coefficient is sufficiently high.

Influence of apical foramen lateral opening and file size on cemental canal instrumentation

Since instrumentation of the apical foramen has been suggested for cleaning and disinfection of the cemental canal, selection of the file size and position of the apical foramen have challenging steps. This study analyzed the influence of apical foramen lateral opening and file size can exert on cemental canal instrumentation. Thirty-four human maxillary central incisors were divided in two groups: Group 1 (n=17), without flaring, and Group 2 (n=17), with flaring with LA Axxess burs. K-files of increasing diameters were progressively inserted into the canal until binding at the apical foramen was achieved and tips were visible and bonded with ethyl cyanoacrylate adhesive. Roots/files set were cross-sectioned 5 mm from the apex. Apices were examined by scanning electron microscopy at ×140 and digital images were captured. Data were analyzed statistically by Student’s t test and Fisher’s exact test at 5% significance level. SEM micrographs showed that 19 (56%) apical foramina emerged laterally to the root apex, whereas 15 (44%) coincided with it. Significantly more difficulty to reach the apical foramen was noted in Group 2. Results suggest that the larger the foraminal file size, the more difficult the apical foramen instrumentation may be in laterally emerged cemental canals.

Influence of cervical preflaring on determination of apical file size in the palatal roots of maxillary molars

PURPOSE: The aim of this study was to investigate the influence of cervical preflaring in determining the initial apical file (IAF) in the palatal roots of maxillary molars, and to determine the morphologic shape of the canal 1 mm short of the apex. METHODS: After preparing standard access cavities the group 1 received the IAF without cervical preflaring (WCP). In groups 2 to 5, preflaring was performed with Gates-Glidden (GG), Anatomic Endodontics Technology (AET), GT Rotary Files (GT) and LA Axxes (LA), respectively. Each canal was sized using manual K-files, starting with size 08 files, and making passive movements until the WL was reached. File sizes were increased until a binding sensation was felt at the WL. The IAF area and the area of the root canal were measured to verify the percentage occupied by the IAF inside the canal in each sample by SEM. The morphologic shape of the root canal was classified as circular, oval or flattened. Statistical analysis was performed by ANOVA/Tukey test (P < 0.05). RESULTS: The decreasing percentages occupied by the IAF inside the canal were: LA>GT=AET>GG>WCP. The morphologic shape was predominantly oval. CONCLUSION: The type of cervical preflaring used interferes in the determination of IAF.