Effect of Lubricant Viscosity on Separated Instrument Retrieval Time and Dentine Preservation in Root Canal Curvatures: An In Vitro Study

This study aimed to evaluate the effect of silicone oils with varying viscosities (100, 350 and 1000 cSt) and 17% Ethylenediaminetetraacetic acid (EDTA) (1.8 cSt) on the efficiency of removing separated instruments using an ultrasonic device from the curved regions of mesio-buccal canals in mandibular first and second molars. Forty-eight mesio-buccal canals of mandibular first and second molars with curvatures ranging from 15 to 30 degrees were prepared and simulated with separated instruments. Nickel-titanium (Ni-Ti) 25-4% rotary files, measuring 3-4 mm in length, were intentionally fractured within the curvature region of the canals. The samples were randomly divided into four groups (n = 12) based on the lubricant used: EDTA and silicone oils with viscosities of 100, 350 and 1000 cSt at 25°C. Primary outcomes were retrieval time and dentine loss from the canal's inner wall, measured via Cone Beam Computed Tomography (CBCT). Secondary outcomes included the coronal exposure of separated instruments to initiate bodily movement and the accuracy of CBCT versus periapical radiography in measuring fractured file length. Data were analysed using the Shapiro-Wilk test for normality, one-way ANOVA and the Kruskal-Wallis test at a significance level of 0.05. The experimental conditions were homogeneous between groups, with no significant differences in canal curvature (p = 0.907), ultrasonic preparation time (p = 0.632), or actual SI length (p = 0.082). The results showed no significant differences among the groups regarding SI retrieval time (p = 0.797), dentine loss (p = 0.653), or coronal SI exposure (p = 0.653). CBCT measurements demonstrated significantly greater accuracy in determining fractured file length compared to periapical radiography (p < 0.001). Within the limitations of this in vitro study, the findings suggest that silicone oils, regardless of their viscosity, did not provide additional benefits over EDTA in reducing retrieval time or preserving dentine in the mesio-buccal canals of mandibular molars. However, CBCT proved more accurate than periapical radiography in measuring SI length. Despite the lack of significant effects of silicone oils with higher viscosity, EDTA remains clinically preferred due to its inherent chelating properties. Further research is needed to confirm or refute these findings.