Effect of Intracanal Irrigants on Coronal Fracture Resistance of Endodontically Treated Teeth Undergoing Combined Bleaching Protocol: An In Vitro Study

Irrigation plays a critical role in endodontic treatment. Various single and combined irrigants and irrigation protocols are available. The aim of this study was to evaluate the effect of some common irrigation protocols on the coronal fracture resistance of endodontically treated teeth undergoing bleaching. After preparation of access cavities in 120 maxillary premolars, the teeth were divided into five groups (n=24) based on the irrigation protocol; G1:2.5% sodium hypochlorite (NaOCl), G2: 2% chlorhexidine (CHX), G3: NaOCl+CHX, G4: NaOCl+ethylenediaminetetraacetic acid (EDTA), G5: NaOCl+EDTA+CHX. Each group was subdivided into 2 subgroups of A: non-bleached (NB) and B: bleached (B). In subgroup B, the teeth underwent in-office and at-home bleaching techniques using 38% hydrogen peroxide and 20% carbamide peroxide gels for 3 weeks. The teeth were restored with composite resin, thermocycled, incubated for 24 hours, and underwent fracture resistance tests. Data were analyzed with one-way analysis of variance (ANOVA) and t-test (α=0.05). T-test showed significant differences between every two corresponding groups (P<0.0001). In subgroup A, the minimum fracture resistance was recorded in G1. Also, G2 specimens exhibited a significantly higher fracture resistance compared to G1, G4, and G5. In subgroup B, G2 specimens exhibited a significantly higher fracture resistance compared to G1 and G4 that were irrigated using NaOCl and NaOCl+EDTA. It can be concluded that irrigation protocols can affect the coronal fracture resistance of bleached endodontically treated teeth, and specific irrigation protocols can be recommended for teeth undergoing bleaching. Key words: Root Canal Irrigants; Fracture; Endodontically-Treated Teeth; Tooth Bleaching Agents