Measuring irregularity index: Comparing study cast caliper method with 2D dimensional ImageJ photogrammetry and 3D STL image measurement

Abstract

Purpose: Irregularity accounts for interproximal contact point displacements and can be measured using a variety of techniques. The aim of this study was to evaluate the validity and reliability of three methods in relation to the “gold standard” of manual caliper measurements of plaster study casts. Materials and Methods: Six mandibular study casts representing varying degrees of anterior crowding were measured by the same observer using four methods over the course of 5 weeks. Validity was statistically assessed with single sample statistical testing by the cast, method, and week (or combinations) and reliability was tested using intraclass reliability coefficient. Results: The three noncaliper techniques demonstrated validity (P > 0.05) when the caliper method mean was used as the set value, but the three noncaliper methods produced means that were significantly greater when mean differences among techniques were compared to hypothetical zero. However, none of the differences were clinically significant (>0.5 mm). High reliability (reproducibility) was demonstrated (P > 0.05) with both aggregated and nonaggregated mean differences. Conclusions: Reliability of measuring irregularity index with any of the four methods tested was high, but the validity of techniques compared to the “gold standard” method of manual caliper measurements of plaster study casts should continue to be questioned. Differences among the techniques were not clinically significant or important.