The results of the analysis of the photographs of the canal cross-section and their buccal and lingual extensions are detailed in Table 1. In the unprepared segments of the buccal extensions, Lightspeed and ProFile.04with 15% obtained a worse result than Quantec SC with 13.3%. Concerning the unprepared segments of the lingual extensions, the following ranking resulted: Lightspeed (28.3%), ProFile.04(25%) and Quantec SC (13.3%).
Superimposition of the photographs of the cross-sections of the pre- and postoperative root canal shapes showed that all three systems left uninstrumented areas in many cases. Only 10 (Lightspeed), 19 (Quantec SC) and 21 (ProFile .04) specimens out of 60 per group showed no contact between the pre- and postoperative root canal outlines, indicating limited circumferential instrumentation of the root canal wall (Table 2).The best results were recorded in the apical third. Overall Lightspeed demonstrated 46 of 60 specimens showing 0- 25% contact between pre- and postoperative diameter, followed by ProFile .04 (45 specimens) and Quantec SC (39 specimens). No statistically significant differences could be found between the instruments (Kruskal- Wallis test: apical, P = 0.4157; middle, P = 0.6885; coronal, P = 0.0727).
Table 1. Prepared and unprepared areas of canals in the buccal and lingual extensions of oval canals by instrument.Root canal cleanliness.
Table 2. Contact between pre- and postoperative cross-section.
Table 3. Assessment of root canal cleanliness (buccal and lingual extensions are combined).
Following longitudinal splitting of the 60 root segments per group, the buccal and lingual specimens were analysed for cleanliness of the buccal and lingual extensions using the SEM. Some specimens could not be evaluated because of technical difficulties. The results of the SEM analysis of the root canal walls are shown in Table 3.
Generally, the root canals showed no homogeneous appearance. Some specimens (ProFile .04, 30 out of 114 (26.3%); Quantec SC, 27 out of 120 (22.5%) and Lightspeed, 25 out of 115 (21.7%)) showed completely clean walls without any remaining debris (score 1). Most canals received a score 2 (Quantec SC, 38 (31.7%); ProFile .04, 33 (27.5%) and Lightspeed, 31 (25.8%)). A total of 67 of 349 evaluated specimens (19.2%) root canal segments remained unprepared. No statistically significant differences between the three systems were found for remaining debris in the apical, middle and coronal segments respectively (Kruskal-Wallis test: buccal extensions - apical, P = 0.3963; middle, P = 0.5521; coronal, P = 0.5666; lingual extensions - apical, P = 0.4595; middle, P = 0.5710; coronal, P = 0.9353).
Lightspeed preparation resulted in 12 out of 115 (10.4%) surfaces without smear layer (score 1), ProFile .04 in eight out of 114 (7.0%) and Quantec SC in seven out of 120 (5.8%). A high number of specimens within each group were rated score 3 (ProFile .04, 40.3%; Quantec SC, 36.7%; Lightspeed, 29.6%). Unprepared root canal walls were detected in 67 of 349 (19.2%) evaluated specimens with most of them in the Lightspeed group (27 of 115, 23.5%). ProFile .04 preparation resulted only in 22 out of 114 (19.3%), Quantec SC in 18 out of 120 (15.0%) specimens with completely unprepared extensions. Differences between the systems were not significant (Kruskal-Wallis test: buccal extensions - apical, P = 0.3312; middle, P = 0.4052; coronal, P = 0.8013; lingual extensions - apical, P = 0.4321; middle, P = 0.4546; coronal, P = 0.4254). Procedural errors.
ProFile .04 preparation proved to be a safe technique with no instrument fracture, perforation, apical block age and cases with loss of working length. With the Lightspeed system, two fractures (sizes 35 and 42.5) occurred, but both instruments could be removed from the canals. No perforation, apical blockage and case of loss of working length were observed. With the Quantec SC system, two apical blockages occurred after preparation with the second instrument. Working time.
Measurement of working time, not including time for instrument changes and irrigation, resulted in a median of 195.7 s for ProFile .04 instrumentation (10 instruments), 206.9 s for Quantec SC (10 instruments) and 208 s for the Lightspeed system(20 instruments).Differences between the systems were not significant (Kruskal- Wallis-test: P = 0.4534). Including time for irrigation, the root canal preparation resulted in the following median working times (Lightspeed, 338.9 s; Quantec SC, 272.4 s; ProFile.04, 261.2 s).