Errors and Discrepancies in Measurement of Tooth Size

¹ Department of Orthodontics, School of Dentistry, University of Michigan, Ann Arbor, Michigan

This investigation of experimental errors and discrepancies involved in the measurement of the mesiodistal tooth diameter on plaster casts included nine comparisons. These consisted of consideration of differences between first and second measurements, differences between measures made by two investigators, differences between measures made with dividers and with sliding calipers, differences between two sets of replicate casts, differences in measuring maxilla versus mandible and left versus right, differences between tooth types, differences between measures made on casts and in the mouth, and differences between measures made on soaped and unsoaped casts. The mean differences and their variabilities were studied.

Of the nine comparisons, four showed only experimental errors. These were comparisons between two investigators, between two sets of replicate casts, between maxillary and mandibular measures, and between left and right sides.

Certain teeth, such as maxillary molars and lateral incisors and mandibular cuspids, were found to be more difficult to measure for morphologic reasons.

To some extent, the more an investigator measures, the more accurately he does so. Also, the differences between measurements made by two investigators can usually be shown to be statistically significant, although these differences are of small magnitude.

The remaining three comparisons showed systematic differences: measurements made with dividers were approximately 0.1 mm. larger, on the average, than measurements made with sliding calipers; measurements made intraorally of maxillary teeth averaged almost 0.1 mm. smaller than those made on plaster casts of the same teeth; and measurements made of soaped casts were systematically larger, though very slightly so, than measures made on unsoaped casts.

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