Effect of the smear layer on a pulp proximity-indicating instrument.

The purpose of the study was to determine the effect of removing or modifying the smear layer on the indication provided by the Prepometer pulp proximity-indicating instrument. Third molars were prepared to produce flat surfaces in the coronal dentine, and control Prepometer LED readings were made. Group E was treated with 18% EDTA and Group T with Tubulicid. Prepometer readings were repeated. Dentine was removed in 0.5 mm increments, and readings repeated until a red LED appeared, indicating a danger of pulp exposure. Distances to the pulp were measured. t test, Wilcoxon signed ranks test (WSR) and ordinal regression (OR) analysis were performed, together with SEM examination. There were significant differences between both test groups and their untreated controls. OR showed that a red LED appeared further from the pulp with EDTA treatment than with no treatment. A red LED appeared closer to the pulp with Tubulicid treatment than with no treatment. SEM showed smear removal in Group E and occlusion of tubules in Group T. Prepometer performance was significantly influenced by treatment with EDTA and Tubulicid. Practitioners would be required to learn to interpret the display of the Prepometer instrument in the context of the tooth under treatment and the surface condition of the cut dentine.