Efficiency of ultrasonic retrieval for separated instruments within the middle third of root canals using modified staging platform: a comparative in-vitro study.

AIM: This study aimed to compare the efficiency of ultrasonic retrieval using a Modified Staging Platform (MSP) versus a Conventional Staging Platform (CSP) for 3, 5, and 7 mm separated NiTi instrument fragments in moderately curved mesiobuccal canals of mandibular molars, by assessing retrieval time, success rate, and vertical root fracture resistance, with loop intervention for unretrieved fragments. METHODOLOGY: Seventy-seven extracted mandibular first molars were prepared and allocated randomly into 2 main groups (CSP, MSP; n = 33 each) and one control group (n = 11). Each main group was subdivided into 3 subgroups (n = 11) according to separated fragment-length (3, 5, 7 mm). NiTi rotary instruments were separated in mesiobuccal canals, and retrieval was attempted under dental operating microscope (DOM) using CSP or MSP corresponding to the allocated group. Retrieval time and success rate (maximum 45 min) were recorded for each case. Failed samples underwent loop retrieval (15 min). Following retrieval procedures, mesial roots were sectioned and decoronated to a standardized root length (15 mm), for vertical fracture testing using a universal testing machine. Nonparametric tests (Mann–Whitney U and Kruskal–Wallis with Dunn post hoc) were applied (α = 0.05).

RESULTS

For 3 mm fragments, MSP yielded significantly shorter ultrasonic retrieval time than CSP (p < 0.001). For 5 mm fragments, CSP was faster than MSP (p = 0.002). Neither technique retrieved 7 mm fragments ultrasonically. Loop retrieval succeeded in 90.9% of 7 mm fragments for CSP but failed for MSP (p < 0.001). Both retrieval methods showed significantly lower fracture resistance than controls (p < 0.001); no significant difference in fracture resistance was found between MSP and CSP groups.

CONCLUSION

MSP was more time-efficient than CSP for short (3 mm) fragments, whereas CSP performed better for 5 mm fragments and permitted successful loop-assisted removal of long (7 mm) fragments. Both techniques significantly reduced vertical root fracture resistance relative to intact controls.