Cross-cultural validation of a short form of the Oral Health Impact Profile for temporomandibular disorders.

Objectives: We set out to develop and validate an Italian version of the Oral Health Impact Profile Questionnaire (OHIP) that is appropriate for use in temporomandibular disorders (TMD).

Methods: At first, we had the questionnaire translated from English into Italian by three bilingual individuals whose mother tongue was Italian and thus had three different versions of the questionnaire. These were translated back into English by a native English speaker and the version closest to the original English OHIP was selected. The validation of a questionnaire generally involves the study of the psychometric properties of the instrument: its validity and reliability. Before studying these properties, we assessed the factorial structure of the questionnaire.

Results: The number of eigenvalues >1, computed by exploratory factor analysis, was seven. The percentage of cumulative variability explained by a model with six dimensions is 66, whereas that explained by a model with seven dimensions is 70. Therefore, considering that the increment of explained variability due to the seventh dimension is low (3.68%) and that the seventh eigenvalue is very close to 1, we considered a six-factor model capable of explaining the factorial structure of the data. Content analysis suggested eliminating the item 'Felt Self-conscious', as most of the subjects did not understand its meaning. Spearman correlation coefficients showed an association between the scores of all the different subscales and the variable for pain. All the coefficients were significantly different from 0 (P < 0.05). Cronbach's alpha value, always >0.70, showed quite a good reliability for each of the six subscales.

Conclusions: These results reveal a reasonable degree of cross-cultural consistency between the two versions of the OHIP, and thus indicate that our Italian version is valid.