Influence of apical preparation size and final irrigation protocol on the debridement of oval root canals

This study assessed the influence of apical preparation size and final irrigation protocol on the debridement of the apical third of oval root canals of mandibular molars. Seventy-seven distal roots were divided into 7 groups (n = 11): Control: without instrumentation or irrigation; Group 30CI: ProTaper Next (up to size 30; PTN) + conventional irrigation (CI); Group 30UAI: PTN + ultrasonically activated irrigation (UAI); Group 30XPF: PTN + XP-endo Finisher (XPF); Group 40CI: PTN + ProDesign Logic (up to size 40; PDL) + CI; Group 40UAI: PTN + PDL + UAI; and Group 40XPF: PTN + PDL + XPF. The total volume of irrigating solutions used per root canal in all the experimental groups was 33 mL of 2.5% sodium hypochlorite (NaOCl) and 6 mL of 17% ethylenediaminetetraacetic acid (EDTA). After specimen processing and histological analysis under a digital microscope (100x), the percentages of untouched canal walls (UCW) and remaining debris (RD) were assessed using Image J software. A descriptive and exploratory analysis was conducted, indicating that the data failed to meet the assumptions of an analysis of variance. Therefore, generalized linear models were used to assess the effects of the different instrumentation and irrigation protocols, as well as the interaction among them, on the percentage of UCW and RD. No significant difference was found among the irrigation protocols regarding the percentage of UCW, irrespective of apical preparation size (p>0.05). However, UCW and RD were significantly lower in groups 40CI, 40UAI and 40XPF than in groups 30CI, 30UAI and 30XPF (p<0.05). The percentage of RD was significantly lower in the UAI and XPF groups than in the CI groups, irrespective of apical preparation size (p<0.05). The difference between preparation sizes 30 and 40, with respect to RD, was higher when CI was used (p<0.05). In conclusion, instrumentation up to apical preparation size 40 resulted in lower percentages of UCW and RD than up to apical preparation size 30. Use of UAI or XPF resulted in lower percentages of RD than CI.