The Cost of Instrument Retrieval on the Root Integrity.

Aim: To evaluate dentine loss in mesial canals of mandibular molars following instrument fragment retrieval using two techniques.

Methodology: Ten mesial roots of mandibular molars with Type II configuration were selected and scanned in a micro-computed tomography (CT) device. After canal preparation, a 3-mm fragment of a size 35/0.04 rotary instrument was intentionally fractured in the middle third of each mesial canal. In each tooth, one mesial canal was randomly assigned to either ultrasonic retrieval (n = 10) or the combined ultrasonic/lasso technique (n = 10). Removal time was recorded, and pre- and post-retrieval scans were registered to assess changes in dentine thickness, dentine volume, canal volume and cross-sectional area. Data were analysed using Student's t-test, Mann-Whitney U test, Chi-square and Fisher's Exact tests (α = 0.05).

Results: All fragments were successfully retrieved. Ultrasonic removal was faster than the combined technique (p = 0.023) but resulted in greater dentine thickness reduction (p = 0.029). No significant differences were observed in canal area increase between groups (p = 0.698). After instrument retrieval, canal volume increased by 23.8%, while dentine volume decreased by 2.2%. Both techniques led to significant reductions in thick dentine regions and increases in thinner regions after preparation and retrieval (p < 0.001), with no significant differences between groups (p > 0.05).

Conclusions: Both techniques were effective in retrieving fractured instruments and resulted in similar increases in canal area and volume, as well as comparable proportions of cross-sections exhibiting minimal dentine thickness below 0.5 mm. However, while ultrasonic removal was faster, it caused a greater percentage reduction of dentine thickness compared to the combined ultrasonic/lasso technique.