During the preparation of the 48 canals, no instruments separated, and only one FlexMaster and one K-Flexofile permanently deformed.
The scores for the debris and the smear layer are detailed in Tables 2 and 3. Completely cleaned root canals were not found with any of the two instruments. On average, more effective cleaning was observed in the coronal and the middle thirds of the canals (Fig. 1).
In general, the use of K-Flexofiles resulted in significantly less debris (P < 0.001) (Fig. 2) and less smear layer (P < 0.05) compared to the canal preparation with Flex-Master instruments (Tables 2 and 3); these differences were not significant in the apical third.
Figure 1. Canal wall after preparation with FlexMaster rotary nickel-titanium instruments.Instrumentation results.
(a) Clean canal wall with only very small debris particles in the middle portion of the prepared canal (score1, original magnification 40x).
(b) Apical portion of the canal: Complete or nearly complete covering of the canal wall by debris after preparation (score 5, original magnification 80x).
Table 3. Summary of scores for smear layer.
*The number of canal areas evaluated as scores 1-5 (n=24 teeth per group).Three canal areas (coronal, middle and apical thirds) have been evaluated per tooth, thus resulting in a total of 72 canal areas per group. Score1indicates the best and score 5 the worst result.
Figure 2. Clean surface in the apical third of a curved root canal after manual instrumentation using K-Flexofiles in a reaming working motion (score1, original magnification 40x).
Figure 3. Straightening of the curved canals after preparation with the two different instruments (n=24 canals in each group): Combined box-and-whisker, and dot plot, each dot represents a reading of the difference between canal curvature prior to and after instrumentation.
Table 4. Mean preparation time and SD, and mean changes of working distance and SD in the two different instruments.
Table 5. Mean degree of straightening of curved canals (8) and SD after canal preparation in the two different instruments.
* n= 24 canals in each group.
The mean time taken to prepare the canals with the two types of instruments is shown in Table 4. There were no statistically significant differences between the two instruments (P=0.666).
All the canals remained patent following instrumentation, thus, none of the canals were blocked with dentine. With both types of instruments, one canal showed overextension of preparation, whereas a loss of working distance was found in two canals prepared with FlexMaster and three canals enlarged with K-Flexofiles. The mean changes of working length that occurred with the different instruments are listed in Table 4. The differences between the two instrument types were not statistically significant (P=0.797).
The mean straightening of the curved canals is shown in Table 5. The use of FlexMaster instruments resulted in significantly less straightening during instrumentation (P < 0.0001) compared to the K-Flexofiles (Fig. 3).