Dental Handpiece Force Transducer for Measuring Cutting Force

Objective:  To determine if a dental handpiece modified to act as a force transducer can measure cutting forces of natural tooth structure.  Methods: A Midwest Quiet Air handpiece (Midwest Dental Supply) had four strain gauges (120 Ohm, Vishay MicroMeasurements Group) bonded onto four machined sections on the handpiece neck (top, bottom, right, left).  Gauges on opposite sides connected to form two half-bridge circuits that connected to a two-channel amplifier (Type 2100, Vishay MicroMeasurements Group).  Each amplifier channel linked to a LabJack U12 data acquisition device (LabJack Corporation).  Data points were collected every 0.003 seconds with 12-bit resolution.  The handpiece transducer was calibrated in four directions (right, left, up, down) at intervals of 0.5N from 0.5N to 5N.  Three sets of natural teeth were cut using the handpiece transducer: teeth mounted in dental stone (n=4); teeth with enamel removed mounted in stone (n=4), and teeth mounted in Express STD (3M Dental Products) (n=3).  Teeth were scanned before and after cutting using the University of Minnesota contact profiler.  Volume of material removed was calculated using AnSur software (Copyright Regents University of Minnesota).  Statistical comparisons used an unpaired t-test.  Results: Calibration curve linear regressions had an r²=0.99.  Mean cutting force in N (SD): enamel in stone 1.23 (0.41); Enamel in Express 0.72 (0.13); Dentin in stone 0.72 (0.20).  The force to cut enamel in stone is significantly greater than that to cut dentin (p=0.0004) and enamel in Express (p=0.0003).  Cutting rate in mm³/second (SD): Enamel in stone 0.093 (0.040); Enamel in Express 0.134 (0.058); Dentin in stone 0.325 (0.126).  Enamel cutting rates were not significantly different (p=0.25); they were different from that of dentin (p=0.0004).  Conclusions: A handpiece modified to be a force transducer can measure cutting forces for enamel and dentin, and it can distinguish between cutting enamel and dentin.