Assessing an electronic device for determining dentine thickness during tooth-preparation

When preparing teeth for restorations, dentists must rely largely on experience to determine pulp proximity. The Prepometer (Hager-Werken, Duisburg, Germany) is an instrument that purports to indicate dentine thickness by incrementally displaying a 10-LED green/amber/red continuum. Objectives: To determine whether extracted teeth could be used to test the instrument in vitro, and to assess its accuracy and reliability in determining dentine thickness. Methods: Occlusal surfaces of extracted third molars were reduced to a flat plane just beneath the enamel fissures. Diagonal quartering axes were scribed and reference points marked at the intersection and 2.5mm peripheral to it. Three instrument readings were made at each of the 5 points and averaged. Abrasives were used to remove ±0.5mm of dentine normal to the cut surface (the precise reduction being measured) and further readings made. Reduction and measurements were repeated until the instrument displayed LEDs 9 or10 (red) at all 5 points. The teeth were sectioned across each diagonal in turn, and the surface to pulp distance measured at each reference point using a measuring microscope. These distances were reconstituted by adding the thickness of each reduction, then paired with their corresponding LED scores, preparatory to statistical analysis using ordinal regression. Results: Analysis of 275 data pairs permitted construction of a highly significant predictor-model (p<0.01); the point of equal probability (p=0.414) at the red/amber LED boundary coinciding with an overburden value of 2.4mm. Conclusion: The instrument reliably predicted dentine thickness in this extracted-tooth model. The 2.4mm thickness that triggered a red LED was more conservative than the 1.4mm cited by the manufacturer as the minimum safe distance from the pulp.