The Cost of Instrument Retrieval on the Root Integrity

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

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).

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).

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.