Purpose: The concept of the minimal important difference (MID) of an oral health-related quality of life (OHRQoL) questionnaire has been proposed to refer to the smallest OHRQoL score difference considered to be clinically important in oral health. This study determined the MID for the 49-item Oral Health Impact Profile (OHIP) in prosthodontic patients. This could serve as a patient-based approach to define clinical significance for prosthodontic interventions.
Materials and methods: A consecutive sample of 224 adult patients completed the OHIP questionnaires twice before treatment was performed and 4 to 6 weeks after prosthodontic treatment was finished. At follow-up patients were asked about their overall impression of the treatment (global transition; answer categories "improved a lot,""improved a little,""stayed the same,""worsened a little," and "worsened a lot").
Results: The median of baseline and follow-up differences in OHIP (change scores) was computed for subjects (N = 47) reporting a "little improvement." This figure was considered the MID for the OHIP, and it was found to be 6 OHIP units (95% confidence interval: 2 to 9).
Conclusion: The MID of the OHIP is an important benchmark to assess individual and group treatment effects in prosthodontics and could be used to approach what is clinically significant in terms of patient-based outcomes.