Several studies have shown a correlation between apical microleakage rates and marginal gaps between the filling materials and dentinal walls of the root canals [27, 28]. The rationale of our study was to test the ability of the SCC with CaSi sealer to achieve a comparable marginal adaptation to MTA and Biodentine apical plugs which might add another simple and feasible treatment modality for management of immature permanent teeth.
In the present study, SEM analysis showed a statistically significant difference between the SCC with CaSi sealer and the other groups. Therefore, the null hypothesis was rejected.
Chloroform dip technique was chosen to customize the master cone in the current study because chloroform was reported by Wennberg et al. [29] to have the strongest dissolving or softening activity for gutta percha points compared to other alternatives and evaporates quickly which makes it suitable for chairside procedures.
It has been reported in many studies that CaSi sealers are biocompatible with antimicrobial properties and are bioactive which can stimulate hard tissue formation [30]. Accordingly, their biocompatibility can make them suitable to be used in cases of immature apices in which unintended extrusion of material might happen. Additionally, they exhibit advantageous penetration of the dentinal tubules which provides an increased contact surface between the filling material and dentinal walls [31] and can also form a chemical bond to dentin, resulting in an improved sealing ability [32]. A novel CaSi sealer (NeoSEALER Flo, Avalon biomed) was used in the current study as it has been reported to have a high push out bond strength in the apical third [33] and according to the manufacturer, it is bioactive, promotes hydroxyapatite formation, resin free, non-staining, biocompatible and has superior handling properties.
Extracted maxillary anterior human teeth (central and lateral incisors) were chosen in this study due to their relatively uniform canals with less variations in their root canal anatomy and 3 mm were sectioned apically to exclude curvature, lateral canals which helped in standardization of the specimens. In addition, they are the most affected teeth with pulp necrosis and immature apices due to trauma [34].
Open apex teeth models were prepared in a similar way to that used by Lertmalapong et al [21] but a Peeso reamer size 3 was used in our study in a retrograde direction, instead of size 4 used in the mentioned study, to standardize apical diameter to 1.1mm. This diameter was chosen because it is large enough to be difficult to achieve a good seal with the conventional obturation method resembling stage 9 in Nolla’s classification [35] of tooth development.
Clinical environment was simulated by placing the prepared roots in moist floral arrangement. This was beneficial in providing hydration to the roots which was needed for the setting of the calcium silicate materials used and limiting the filling materials extrusion from the apex. Moreover, a collagen sponge was placed apically against which the filling materials were packed, minimizing their iatrogenic extrusion.
In the current study, the smear layer removal was done using 10 ml of 17% EDTA followed by 10 ml of 5.25% NaOCl with a final flush of sterile saline to avoid the adverse effects of EDTA as it can disrupt the hydration of calcium silicates decreasing their hardness and biocompatibility due to calcium chelation [30]. Moreover, the canals were left moist by using 3 paper points only to allow setting of the used materials which require hydration to set as it was shown in a previous study that slightly moist canal walls resulted in the highest push out bond strength for the tested CaSi sealer [36].
Although there is controversy related to the proper thickness of the apical plug used for apexification of immature permanent teeth, many researchers have agreed that 5 mm thickness could be adequate to provide a good apical seal [37], which was applied in our study.
It is important to mention that although the three tested groups in the current study showed good obturation quality in both mesiodistal and buccolingual digital radiographs, SEM analysis revealed marginal gaps. SEM analysis was chosen as a method of evaluating marginal adaptation of the filling materials tested due to its high resolution, enhanced interface magnification, and superior depth of field [38]. The maximum gap between the filling material and the dentinal walls of the root canal was measured in each specimen as a mean of 8 measurements circumferentially to be more accurate as the gaps are assessed throughout the whole perimeter of the root canal.
The results of our study differ from a study by Hamdan et al [39] who concluded that there was no difference in leakage resistance between a customized gutta percha cone with BioRoot sealer and MTA apical plug in immature permanent teeth as they both showed unsatisfactory apical seal and nearly all specimens showed dye penetration. This contradiction may be due to different methodology and testing tools in which dye penetration test was used in the mentioned study to assess the microleakage. However, dye penetration test was avoided in our study because it has been reported to have questionable reliability, reproducibility and clinical relevance [40].
A possible reason for the maximum marginal gaps found in the SCC with CaSi sealer group is that two materials are used in obturation unlike MTA or Biodentine which are packed and condensed as one obturation material and provided good apical seal and smaller marginal gaps.
The marginal gaps were larger at 3 mm from the apex than at 1 mm in the SCC with CaSi group, although there was no significant difference statistically, this may be due to insufficient softening of the customized cone in which only the most apical 2mm were dipped in chloroform for one second following a technique used in a previous study by Van Zyl et al [15] but this might not be enough to take a proper impression of the large canals in the current study especially at 3mm from the apex noting that the previous study was done on mature teeth with smaller root canals and apices.
Biodentine apical plug showed the best marginal adaptation in the current study with the least mean gap at its interface with the dentinal walls, followed by MTA with no significant difference between them. This is in line with the results obtained by de Sá et al[19] who concluded that there was no significant difference between the marginal adaptation of MTA and Biodentine to dentinal walls when used as apical plugs in simulated immature teeth and is also in agreement with Bani et al.[9] who used fluid filtration technique and concluded that the sealing ability of Biodentine and MTA were similar at any apical plug thickness. Moreover, Abbas et al.[41] showed that both materials had the same sealing ability using bacterial leakage method of assessment. However, in a study by Refaei et al [42], Biodentine resulted in significantly less microleakage than ProRoot MTA when used as orthograde apical plug in immature permanent teeth.
Interestingly, the marginal adaptation of both Biodentine and MTA at 3 mm from the apex was significantly better than at 1 mm. This could be explained by the better packing of the material against the previously placed layers at 3mm than against the less firm collagen sponge in the first layer placed at 1mm from the apex.
It is worth mentioning that the current study has some limitations. First, one method of assessment was used to test the sealing ability of the used materials, however, it is suggested to combine two or more methods of microleakage assessment to give more reliable results [43]. Second, the study is limited to the straight canals of maxillary anterior teeth in which the placement of apical plugs is easier and more predictable than in curved canals or those with difficult clinical accessibility.
Based on the results of the current study, it is recommended to further evaluate the customized gutta percha cone technique using other types of solvents such as orange oil, eucalyptol, or using heat, customizing gutta percha cone with longer dipping time or dipping a larger area in the solvent. Furthermore, other types of CaSi sealers or a resin sealer could be tested with the customized gutta percha cone. Finally, the apical sealing ability of a SCC with CaSi sealer and warm vertical compaction should also be evaluated.