Technique Comparison for Efficient Orthodontic Tooth Measurements Using Digital Models

Objectives: Digital models have been shown to be an acceptable substitute to stone casts for tooth measurements. No studies have been done to determine what measurement technique(s) should be used. This would help to standardize how digital models are measured, increase intra- and inter-examiner reliability and reproducibility, and increase efficiency of measurement. The purpose of this study was to determine the best technique for measuring mesial-distal tooth widths on digital models.

Methods: The mesial-distal tooth widths were measured (first molar to first molar, maxillary and mandibular) on 32 stone casts and corresponding digital models (emodels, GeoDigm, Chanhassen, MN). The casts were each measured with a digital caliper to the nearest 0.1mm. The digital models were measured using five different techniques: occlusal aspect; occlusal aspect zooming in on each individual tooth; facial aspect rotating as needed; facial aspect from three standard positions (R buccal, facial, and L buccal); qualitatively rotating the model in any plane the measurer sees fit. Measurements were repeated three times at least a week apart. The operator time needed to complete each set of measurements was recorded.

Results: Measuring from the occlusal resulted in the fewest teeth (4) with measurements statistically different (p<0.05) than the stone casts, and neither the Bolton 12 nor the Bolton 6 measurements were statistically different. It also, on average, took the second least amount of time to measure (2:03) using the occlusal method. Qualitatively rotating the model resulted in the greatest amount of teeth with statistically different measurements (16) and took the longest time to measure (5:34).

Conclusions: Measurement of tooth width on digital models from the occlusal aspect was the best combination of speed of measurement and minimal variation from the stone casts.