Objectives This study aimed to evaluate and compare the efficacy of the S1 reciprocating system and the D-Race retreatment rotary system for filling material removal and the apical extrusion of debris. Materials and Methods Sixty-four freshly extracted maxillary canines were shaped with size 10 and size 15 K-files, instrumented using ProTaper Gold under irrigation with 2.5% sodium hypochlorite (NaOCl), obturated according to the principle of thermo-mechanical condensation with gutta-percha and zinc oxide eugenol sealer, and allowed to set for 3 weeks at 37°C. Subsequently, the teeth were divided into a control group ( n = 4), the D-Race rotary instrument group ( n = 30), and the S1 reciprocating instrument group ( n = 30). After classical retreatment, the canals were subjected to a complementary approach with the XP-Endo Shaper. Desocclusol was used as a solvent, and irrigation with 2.5% NaOCl was performed. Each group was divided into subgroups according to the timing of radiographic readings. The images were imported into a software program to measure the remaining filling material, the apical extrusion, and the root canal space. The data were statistically analyzed using the Z-test and JASP graphics software. Results No significant differences were found between the D-Race and S1 groups for primary retreatment; however, using a complementary cleaning method increased the removal of remnant filling ( p < 0.05). Conclusions Classical removal of canal filling material may not be sufficient for root canal disinfection, although a complementary finishing approach improved the results. Nevertheless, all systems left some debris and caused apical extrusion.

A successful endodontic treatment depends on a comprehensive knowledge of the morphology of canal and its variations, an appropriate access cavity, cleaning and shaping, and adequate root canal filling. Lack of knowledge in this regard and missing a root canal are among the most common causes of failure of root canal treatments. Most previous studies on maxillary molars have reported that they usually have three roots and four canals since an extra canal is often found in the mesiobuccal root. Other anatomical variations, such as an extra C-shaped canal, have also been reported in distobuccal and palatal roots. Thus, because of having a more complex anatomy compared to other teeth, maxillary molars have the highest rate of endodontic failure. Several studies have assessed the morphology of root canal anatomy in different populations using different techniques such as sectioning, root canal clearing, association of a dental operating microscope and ultrasonic tips, periapical radiography, and computed tomography scanning. Recently, CBCT was suggested to three-dimensionally explore the root canal details before an endodontic treatment. The purpose of this chapter was to highlight the importance of having a thorough knowledge about the root canal morphology of the permanent first and second maxillary molar.

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