Cutting ability of a KiS 2D tip with varying powers and loads

Aim To correlate the vibrations of a retro tip under a range of loads and generator powers with its cutting ability. Methodology A scanning laser vibrometer was used to measure the maximum vibration displacement amplitude of a KiS 2D tip (Obtura Spartan, USA) under loads of 10-50 g (10 g increments). Loads were applied by contacting the tip against a polished root dentine surface (1200 grit) and were measured using a load cell (RDP Electronics, UK). A calibrated scale was placed over the power dial of the generator (Piezon Master 400; EMS, Switzerland) which enabled incremental power settings (1-5) to be selected between minimum and quarter power of the total generator output. Ten repeat scans were made for each load and generator power combination. The retro tip was then used to create cavities in polished dentine surfaces. The tip was operated using the same experimental conditions as described above (five power settings, 10-50 g loads). For each condition, the tip was contacted against surfaces for 5 s and used to make 10 repeat cavities. Cavities were scanned with a 3D laser profilometer (TaiCaan, UK), enabling the maximum width and length of the cavity to be measured. The same generator and handpiece were used throughout the experiment. Results Load significantly reduced tip vibration displacement amplitude at 30-50 g (P <0.0001) when compared with 10 and 20 g. Conversely, it was found that loads of 30-50 g led to either no significant difference (P = 0.242) or even significant increases (P <0.02) in the length and width of the cavities produced when compared with those obtained at 10 and 20 g. Profile views of the cavities, obtained through laser profilometry, suggest that greater loads may cause chipping of the dentine near the surface. Conclusions It is clinically recommended that low loads are exerted on tips to reduce the incidence of fracture. This recommendation is supported by this work which showed that, at loads greater than 20 g, tip vibration displacement amplitude was significantly reduced. Although the length and width of the cavities produced increased at greater loads, it is suggested that the instrument breaks up dentine distant to the periphery of the instrument with a chipping action, potentially causing the instrument to be less precise.