Novel methods reveal that parallelism contributes to the functional vertical slot dimension in ceramic and metal brackets

Abstract

To validate a novel method for measuring the clinically relevant bracket slot and use these methods to test the hypothesis that various metal injection molded (MIM) and esthetic ceramic injection molded (CIM) brackets have a bracket slot accuracy within 1 mil (0.001") of their reported slot dimension. A Nikon iNEXIV-VMA-2520 laser microscope was used to measure slots of six series of CIM brackets and two series of MIM brackets via a vision measuring system of 256 gray levels to capture each edge of the slot, largely taking out human subjectivity. This system had a maximum permissible error of 2 + 8 L/1000 μm with a point resolution of 0.1 μm and was estimated to be more accurate than previous methods by a factor of 10. The video image for each bracket was autofocused by a blinded operator, and 40 point-to-line measurements were calculated along the clinical slot and averaged. Vertical slot dimension varied from series to series and within the series of brackets. Three of six CIM and two of three MIM brackets had a statistically significant mean slot size 0.001 inches larger than reported. The reported precision of these CIM brackets, as determined from standard deviation, varied from series to series. A novel system that incorporates parallelism into analysis of vertical bracket slot dimension was described. When the entire clinically relevant slot was considered, MIM and CIM brackets had similar precision but were significantly oversized, with contribution from a nonparallel, likely diverging, vertical slot dimension.