Reproducibility of an index for recording the alignment of individual teeth

In order that relationships between dental irregularities and the caries and periodontal status of individual teeth can be examined, the STRAIT index (standardized technique for recording the alignment of individual teeth) was developed. Tooth position scores representing vertical relationship, rotation, mesio-distal inclination, displacement and radial relationship are recorded using three- or five-category scales. Contact point scores representing bucco-lingual and mesio-distal relationships are measured directly. These characteristics are recorded for each tooth in the dentition, together with overjet and overbite measures for maxillary incisors and canines. Repeat measurement of 50 sets of models was undertaken by two examiners in order to assess intra-and interreproducibility of the index. A formula for adjusted agreement was employed for analysis of the categorized variables, and reproducibility was typically 80 per cent or better. Analysis of the reproducibility of the continuous variables was based on calculation of root mean square values of the difference between data sets and t-tests. In the main, intra- and interreproducibility was within 0.5 mm. These levels of accuracy meet the requirements of the index and it has since been used in an investigation of 1000 subjects.