**3. Results**

The mean and standard deviations of fracture resistance among the investigated groups are presented in Table 1.


SD. Standard deviation, LC. Cold lateral compaction, SC. Single cone, GP. Gutta Percha.

The Kolmogorov–Smirnov test displayed normal distribution of data. Specimens of group 1 (positive control) displayed the highest fracture resistance (946.61 ± 166.465 N); however, the lowest fracture strength was demonstrated by the specimens in group 2 (negative control) (433.31 ± 129.350 N). ANOVA revealed that fracture strengths among study groups were statistically significant (*p* ≤ 0.05).

Individual comparisons among all the investigated groups established that group 2 displayed significantly lower fracture strength among all experimental groups. Group 1 (positive control) showed higher fracture strength than groups 2 (*p* < 0.01) and 5 (*p* = 0.0); however, it was comparable to groups 3 (*p* > 0.05), 4 (*p* = 0.10) and 6 (*p* = 0.33), respectively. Specimens treated with AH plus using different obturation techniques (group 3 and 4) showed comparable outcomes (*p* = 0.99). Similarly, specimens treated with TotalFill BC sealer with different obturation techniques showed statistically similar outcomes (*p* = 0.77). It was also observed that specimens in groups 3, 4, 5 and 6 demonstrated comparable outcomes of fracture strength (*p* > 0.05) (Table 2).


**Table 2.** Statistical comparison of root fracture resistance among study groups (Tukey's post hoc test).

LC. Cold lateral compaction, SC. Single cone, GP. Gutta Percha.

### **4. Discussion**

The present study was based on the hypothesis that there will be no difference in fracture resistance of root canals obturated with TotalFill BC Sealer and AH Plus sealer. It was also hypothesized that there will be no difference in fracture resistance when two different obturation techniques, i.e., lateral condensation and the single cone technique were used. Thus, the postulated hypothesis was accepted as experimental groups in which root canals were obturated using different sealers (TotalFill sealer and AH Plus sealer) and different techniques (lateral condensation technique and Single Cone technique) showed comparable fracture resistance outcomes. A multitude of reasons are responsible for such outcomes, including the adhesive properties of the sealer, bioactivity of sealers, instrument type and instrumentation methods, and root dentin anatomy.

In the present study, in order to avoid inter-operator variability, a single operator performed all procedures including root canal preparation, irrigation and obturation. Similarly, for root canal preparation, the crown down technique was adopted as it allows debris to be expelled from the canal orifice [19]. Moreover, further standardization was achieved by using AH Plus sealer, which is considered as a gold standard root canal sealer in dentistry [20].

A sealer is conceived as a joint created between radicular dentin and the root filling material [13]. Adhesion between an endodontic sealer and root dentin serves two important purposes [21]. Primarily, the root canal sealer gives a superior seal, which prevents coronal and apical leakage [22]. Secondly, it inhibits filling material displacement during restorative procedures. In the present study, it was found that the mean value of fracture loads of the positive control (433.31 ± 129.350 N) was significantly lower than all other groups tested. The above findings can be associated with loss of radicular dentin thickness (RDT) and moisture due to canal instrumentation and the reinforcement effect by both sealers [23,24].

It was also established that positive control specimens, in which no canal instrumentation performed displayed a fracture strength comparable to group 3 (AH plus sealer + Lateral condensation technique) (733.71 ± 232.572 N), group 4 (AH plus sealer + Single Cone technique) (752.77 ± 120.587 N), and group 6 (TotalFill sealer + Single Cone technique) (797.46 ± 204.557 N). There are various justifications that are accredited to such an outcome. AH Plus sealer, being epoxy resin-based, unveils some desired proprieties, i.e., adhesion by forming a covalent bond between the open epoxide ring and exposed amino acids in the collagen [25]. Moreover, AH Plus possesses an excellent penetration ability into the surface micro-irregularities due its creeping property, which results in increased

fracture strength [11,26]. This finding is in line with the results of the earlier stated studies by Sagsen et al. and Topçuo ˇ glu et al., which suggested that obturation with AH plus root ˇ canal sealers are able to resist the fracture load equivalent to the sound tooth structure in which no canal preparation and filling was performed [3,16]. Similarly, the comparable fracture resistance demonstrated by the BC sealer in group 6 specimens to the positive control group can be explained by its property to produce hydroxyapatite, which leads to increased chemical bonding of sealer to the canal dentinal walls [11,27]. In addition, the presence of small "nanoparticles" and their ability to penetrate deeply into isthmuses, accessory canals and canal irregularities also justifies the higher fracture strength of Total-Fill sealer [5,28]. This finding is in accordance with the outcomes of several studies that proposed that BC-based sealers were able to increase the fracture resistance comparable to that of the intact tooth [29,30].

On the other hand, it was also found that root filling with the lateral condensation technique and Total fill root canal sealer is able to increase the fracture strength of the specimens but is not comparable to the un-instrumented sound tooth. Similar results were noted in the study conducted by Saw and Messer [31]. This finding can be explained by the fact that the finger spreader used for the lateral condensation technique generates stress on the canal wall that may weaken the tooth resulting in less fracture resistance [32]. Spreader design and applied forces are suggested as the contributing factors to the appearance of vertical root fractures during lateral compaction [31]. Moreover, the comparable fracture resistance among all the groups, which were sealed using TotalFill sealer and AH Plus sealer, further suggested that the difference in fracture load may be due to the difference in methodologies used [33]. Sagsen et al. and Mohammed & Al-Zaka. in their studies ˇ revealed that difference in fracture strength among different sealer groups was due to variation in the technique opted for obturation [11,16].

The present in vitro study presented some inherent limitations. The diameter of the root was not standardized in the present study, which has a potential influence on the fracture resistance of the tooth. Moreover, the impact of canal shape cannot be overlooked as more tapered canals results in more dentin removal from the canal resulting in weakening of the specimens. Furthermore, the amount of dentinal tubules present in each specimen also influences the outcomes of root fracture resistance. As the present study was an in vitro experiment, more clinical-based studies should be conducted to validate the findings of the present study for clinical applications.

#### **5. Conclusions**

The use of TotalFill-BC sealer showed similar vertical root fracture resistance reinforcing effect as AH plus sealer in root canal treated teeth. Use of total fill-BC and AH Plus sealer in root canal treatment showed vertical root fracture resistance comparable to untreated natural teeth. Use of different obturation techniques (Single cone and lateral condensation technique) in the presence of sealers (AH plus and TotalFill) did not show a significant influence on vertical root fracture resistance.

**Author Contributions:** Conceptualization, M.F.A., K.H.A., F.A.A., A.M.A. and A.S.A.; methodology, M.F.A., F.A.A., K.H.A. and F.V.; validation, F.V., A.M.A. and T.A.; formal analysis, A.S.A., A.M.A., A.A.A. and K.H.A.; investigation, M.F.A., A.A.A. and F.V.; resources, T.A. and A.A.A.; data curation, F.V., K.H.A., O.M.A., A.A.A. and F.A.A.; writing—original draft preparation, F.V.; writing—review and editing, T.A. and F.V.; supervision, F.V., A.S.A., O.M.A. and A.M.A.; funding acquisition, T.A.; surgical assistance and data collection, revisions, A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors are grateful to the Researchers supporting project at King Saud University for funding through Researchers supporting project No. (RSP-2019-44).

**Institutional Review Board Statement:** This study was submitted, reviewed, and approved by, Specialist Dental practice and Research Centre, Riyadh, Saudi Arabia (UDCRC/009-20). The ethical standards of the 1964 Helsinki declaration and national and/or institutional research committee

were strictly followed while performing all the procedures. Additional information on the study was provided verbally by the study investigator or in a written format.

**Informed Consent Statement:** Consent was taken from individuals at teeth extraction.

**Data Availability Statement:** The data is available on contact from the corresponding author.

**Acknowledgments:** The authors are grateful to the Researchers supporting project at King Saud University for funding through Researchers supporting project No. (RSP-2019-44).

**Conflicts of Interest:** The authors declare no conflict of interest.
