Measuring failure of orthodontic treatment: a comparison of outcome indicators

To compare treatment failure rates on a sample of completed and discontinued orthodontic treatment cases as measured by PAR, IOTN and ICON to determine whether the use of a sole index would suffice.

All patients completing or discontinuing orthodontic treatment in the hospital orthodontic departments in the Northern Region during two calendar months were identified and pre and post-treatment models were analysed. PAR scores, IOTN (DHC and AC) and ICON were recorded.

One-hundred-and-forty-five cases were identified and 15 had incomplete records on the day of analysis. The final sample was therefore 130. The overall treatment discontinuation rate of these 130 patients was 24.6%. The treatment failure rate with respect to occlusal improvement varied from 3.1% when measured by PAR and 10.0% using ICON. With respect to residual need it varied from 0.77 to 20.1% with respect to IOTN depending on the criteria examined. The residual treatment need with respect to ICON was 17.2%.

Different occlusal indices give differing failure rates when used on the same patients with ICON being the most critical index. We felt that ICON was the most valid with respect to identifying treatment failure. Its use would enable international comparison of results.