In vitro evaluation of a measurement method to analyze the interdental, mesially directed force

In order to evaluate interdental forces as a benchmark for mesial drift, a measurement technique was tested and evaluated on a human specimen. The measurement technique is based on the principle that a mesially directed horizontal force (FH) within a complete dental arch has an effect on interdental friction at the points of contact. The dynamic force (FZ), needed to pull out a defined metal strip from the interdental space is equal to the interdental frictional force (FR). Assuming unmodified approximal surfaces and unchanged tooth mobility in a complete dental arch, relative modifications of the interdental frictional force level provide a way of measuring horizontal force fluctuations. The validity of this measurement technique was measured by applying mesially directed forces of 1 to 5 N to the distal surface of the 2nd molar in a human specimen. The frictional forces measured increased in proportion to the distally applied force. The mesially directed force on the 2nd molar was transmitted in the dental arch anteriorly up to the incisor region and resulted in an increase of frictional forces. The reproducibility of this measurement technique was tested by quantitative analysis of potential measurement errors in the human specimen. The effect on interdental force measurement of the speed at which the metal strip is pulled was evaluated in a range of 50 to 500 mm/min. At the maximum pulling speed of 500 mm/min, a maximum scatter of 8% was recorded. Dependency of the dynamic force on direction of pull was measurable only when the metal strip was angled at more than 15 degrees. Experimental tests on the human specimen confirmed that the measurement technique presented here is sufficiently valid and reproducible for clinical long-term studies of interdental forces.