Residual Dentin Thickness in Maxillary Premolars Prepared with ProTaper-Rotary Instruments

Methods: Fourteen extracted, untreated maxillary premolars with two root canals were embedded in cold-curing resin in a muffle device. The embedded teeth were horizontally sectioned at the level of the furcation, immediately coronal to the canal divergence. The mesio-distal and the bucco-palatinal axes of each root were carefully marked and the dentin thickness was measured with a microscope in the mesial, distal, buccal and palatinal directions extending from the lumen of the root canal to the outer surfaces. The distance between the buccal and the palatinal root canal, along the bucco-palatinal axis, at the level of the furcation, as well as the surface of the buccal and the palatinal root canal were measured. The sections were reassembled in the muffle and the root canals were prepared to the working length with ProTaper rotary instruments according to the manufacturer's instructions, up to the Finishing file No 3 (ISO 30). The slices were then removed from the muffle system and the residual dentin thickness, as well as the surfaces of the root canals were recorded for the same distances as described above. Statistical analysis by two-way analysis of variance with repeated measures was performed.

Results: There was a statistically significant difference between the residual dentin thickness before and after the instrumentation in all directions (P<0.0001). However, the decrease in the dentin thickness was similar in all directions.

Conclusions: ProTaper rotary instruments prepare safely the coronal part of root canals of maxillary premolars.