Effect of large instrument use on shaping ability and debris extrusion of rotary and reciprocating systems.

AIM: The aim of the present study was to evaluate the effect of large instrument use on the shaping ability and apical debris extrusion of rotary and reciprocating systems in oval-shaped root canals. METHODS: Forty-five mandibular premolars, with an 18-mm long, oval-shaped single canal, and apical diameter ranging from 300 to 350 µm, were separated into three groups (n=15), according to the system used: ProTaper Universal group, F5 (0.50/0.05); ProTaper Next (PTN group), X5 (0.50/0.06); and Reciproc (RC group), R50 (0.50/0.05). Cone-beam computed tomography was performed before and after preparation to analyze apical transportation (AT), centering ability (CA), and change in root canal diameter (CRCD). For evaluating apical debris extrusion, the roots were coupled to pre-weighed glass receptacles to collect the extruded debris during preparation. RESULTS: All systems promoted AT and apical debris extrusion; the latter was higher for the PTN group (P<.05). No system presented perfect CA. The RC group demonstrated the largest CRCD (P<.05). CONCLUSIONS: As consequences of their use, the large instruments promoted undesirable AT and debris extrusion, irrespective of the system used to perform root canal preparation. Moreover, no system was able to remain perfectly centralized within the root canal.

Comparison of cyclic fatigue and torsional resistance in reciprocating single-file systems and continuous rotary instrumentation systems.

As compared with continuous rotary systems, reciprocating motion is believed to increase the fatigue resistance of NiTi instruments. We compared the cyclic fatigue and torsional resistance of reciprocating single-file systems and continuous rotary instrumentation systems in simulated root canals. Eighty instruments from the ProTaper Universal, WaveOne, MTwo, and Reciproc systems (n = 20) were submitted to dynamic bending testing in stainless-steel simulated curved canals. Axial displacement of the simulated canals was performed with half of the instruments (n = 10), with back-and-forth movements in a range of 1.5 mm. Time until fracture was recorded, and the number of cycles until instrument fracture was calculated. Cyclic fatigue resistance was greater for reciprocating systems than for rotary systems (P < 0.05). Instruments from the Reciproc and WaveOne systems significantly differed only when axial displacement occurred (P < 0.05). Instruments of the ProTaper Universal and MTwo systems did not significantly differ (P > 0.05). Cyclic fatigue and torsional resistance were greater for reciprocating systems than for continuous rotary systems, irrespective of axial displacement.

Influence of artificial accelerated ageing on the colour stability of paints used for ocular prosthesis iris painting.

OBJECTIVES: To evaluate the colour stability of paints used for ocular prosthesis iris painting submitted for accelerated artificial ageing (AAA). MATERIALS AND METHODS: Forty specimens of acrylic resin for sclera (16 × 2 mm) were made and separated into eight groups (n = 10) according to the type of paint (gouache, GP; oil, OP; acrylic AP; and composite resin for characterisation, CR) and the colours used (blue/brown). After drying (72 h), a new layer of colourless acrylic resin was applied and the initial colour readout was performed (Spectrophotometer PCB 6807). New colour readouts were performed after AAA, and ΔE was calculated. RESULTS: Statistical analysis (two-way anova-Bonferroni, p < 0.05) demonstrated that the brown colour showed lower ΔE means in comparison with the blue colour, with statistically significant difference for AP only. Blue colour showed no statistically significant difference with regard to the type of paint used. Brown AP showed lower ΔE than the other groups, with significant difference for OP and GP. GP showed greater alteration in ΔE for the brown colour, being statistically similar only to OP. CONCLUSIONS: Only the AP group for brown pigment shows clinically acceptable values for colour stability after AAA.