In this study, extracted human maxillary premolars were used which may not represent the rest of human tooth anatomy due to the oval cross section. However, teeth with combination of all canal anatomy based on Vertucci’s classification were divided into three matching groups of teeth with identical canal anatomy. Teeth were kept in 100% humidity at the room temperature throughout the study.
The percentage of void volumes were used to avoid discrepancies between the different sizes of root canal space within different teeth.
The combination of gutta-percha and/or sealer was considered a root filling matter. Should this be considered important, a different threshold higher than that of GP applied to the root filling data sets would allow the area of sealer only to be identified, and this could be subtracted from the root filled area to give the area filled in with gutta-percha only. However, this study did not aim to separate one from the other as this has limited clinical implication.
TubliSeal® EWT (Kerr Corporation) was used to avoid the effects of the rapidly setting cement, especially with heat, on the formation of voids within the filled canals.
The ISO GP points were used in CLC technique because the PTU matching GP point (Dentsply Maillefer) would first not match the apical stop size, and second interfere with the spreader penetration coronally. One might argue that this could contribute to the TVV detected in the CLC technique as smaller GP points were used at the start of filling the canal space. However, voids in the CLC group were mainly found at the canal periphery not between the GP points i.e the use of multiple GP points rather than single matching GP point had no or limited effect on the TVVs detected.
The streak shape of these voids Fig. 2 suggests that these could have resulted when the accessory GP points failed to fill the whole space created by the finger spreader. Voids between the GP points, on the other hand, could have been filled with sealer and the software was not able to differentiate between the GP and the sealer. This could also be explained by the machine inability to detect those spaces between GP point due to the beam hardening artefact.
Figure 2 streak-like void in a CLC sample
In the CWC group, “barrel-like” voids were detected between the apically condensed GP and the back-filled GP (Fig. 3). These can be due to the sealer setting too quickly, the inappropriate choice of pluggers for condensation after the apical plug placement or extruder tip not reaching the binding point due to setting sealer or insufficient vertical pressure after heat application to the apically fitted master GP point.
Figure 3 barrel-like void in a CWC sample
In the SC group, sleeve-like voids (Fig. 4) were detected along the GP point which can extend and straddle across the whole canal length. These can be attributed to insufficient amount of sealer despite that the operator used sealer in abundance with this technique to overcome the mismatch between the conic PTU GP points and the oval cross section of the canal anatomy. This could also be due to the inappropriate choice of GP point size. Hence, it would be sensible to avoid the use of conic GP point to fill canals with oval cross section.
Figure 4: sleeve-like void in a SC sample
Quantitative study of voids obturated root canals
Percentage of the total void volumes in three filling techniques
As the method of calculating TVVs in the present study is different to previous studies, it is not possible to compare the value of the void volume with others. Nevertheless, our results agree with previous studies that none of the three obturation techniques could produce a void free obturation.19 There was a trend that CLC produced more void than CWC (0.75% and 0.55% respectively; p ≤ 0.05), corresponding to the results of Asheibi, Qualtrough 20 who found 2.40% and 1.04% voids for CLC and CWC techniques respectively. However, Somma, Cretella 21, using AH Plus as a sealer, showed that CWC and SC had similar void volumes (1.82% and 1.63% respectively). This is contrary to the present study which found that CWC had significantly less residual void volume than SC (0.55% and 1.86% respectively). Moinzadeh, Zerbst 19 also had contradictory results that SC was a better obturation technique than CLC with void volumes of 3.095% and 0.445% for each technique respectively. It is not clear whether this difference is due to the difference in the sealer used, or the method used in calculating void volumes.
Regarding absolute values in general, the TVV in the present study appears to be lower than those recorded previously. For example, Naseri, Kangarlou 22 reported that of the percentage void volume in CWC and CLC were 15.2% and 19.6% respectively, compared to 0.55% and 0.75% respectively in the present study. This could be down to the choice of imaging threshold. Hence, it is essential that researchers using Micro-CT to measure void volume should have a consensus of a unified and universal method to avoid subjective use of threshold value so that direct comparison can be made in the future, though differences in resolution will always affect the ability to detect very small voids.