Cross-cultural adaptation procedures are a critical component of the validation process of an instrument to assess OHRQoL and several guidelines can be found for this purpose [32
]. In the present study, the translation process from English to Spanish was straightforward and the comparison between the original OHIP questionnaire and the back translated English version did not reveal conceptual content differences. The equivalent words needed for translation of the questions were not difficult to find, and the grammar structure of the sentences was not difficult to build during the translation process, possibly owing to the fact that English and Spanish share a common Latin background.
Previous studies have shown a low frequency of oral health impacts for young populations such as the present [23
]. Moreover, there are drawbacks of using ordinal scales for questionnaire responses, which may make the scale not only instrument-specific, but also sample- and item-specific [46
]. To best of our knowledge, there are no studies addressing this issue on adolescents, but the results of a study on the assessment of changes in the quality of life using OHIP on adults [5
] suggest that the differences found between groups may be consistent, regardless of the use of dichotomous or ordinal scoring systems. We therefore considered it best for the purpose of the present study to dichotomize the response options for each question into 'Yes' or 'No'. We realize that this approach departs from the common use of Likert-like scales ranging from 'never' to 'very often' in many OHIP studies. This, and the fact that the use of the Oral Health Impact Profile among adolescents has consistently considered only the 14-item versions of the OHIP, and rather different recall periods [23
], makes direct comparisons between studies rather difficult. We are not aware of studies of the effect of different types of response scales on estimates of validity and consistency for the same study group, but the estimates will almost certainly differ.
The interpretation of the study results should also consider the different recall periods used in different studies. To the best of our knowledge, this is the first study considering a lifetime recall period for the administration of the questionnaire among adolescents. The impact of the use of different recall periods has not been addressed in young populations. In a recent study, John et al., [50
] applied a German version of OHIP on adults using 3 different recall periods (lifetime, 1 year, 1 month) and found better consistency for the shortest recall period, and a lower impact of oral health for the lifetime recall period.
The mean score values in this study suggest a relatively low impact of oral health in the population studied, similar to the impact reported previously by Soe et al. among Myanmar adolescents with low levels of dental disease [23
], and considerably lower than the oral health impact reported in studies comprising minority adolescent populations with higher oral disease burden [49
] and adult populations [51
Our finding that 8 items related to eating impairment, use of prostheses, general health, and inability to function were rather infrequent in this adolescent population, indicates that a number of items from the original OHIP representing severe impairment may be irrelevant for adolescents who have only experienced minor oral disease. Our observations suggest that the highest impacts concern some items from the domains representing 'physical pain'; 'functional limitation' and 'psychological discomfort' in this young adolescent population. This is in agreement with the observations by Broder et al. [49
] among minority adolescents, and our findings on 'physical pain' and 'psychological discomfort' also agree with the observations by Ferreira et al. [47
] in Brazilian schoolchildren, thus suggesting that some dimensions from these domains of OHRQoL frequently affect adolescents.
Construct validity of the OHIP-Sp
The OHIP-Sp exhibited adequate convergent validity, in agreement with studies conducted using other versions of the Oral Health Impact Profile among adolescents [23
A potential limitation of this study to assess discriminative validity is the lack of inclusion of a common pain-related dental health outcome such as caries, which could be a better oral health outcome to distinguish between groups of adolescents with known differences in dental health. The oral health outcomes used in this study are usually considered in studies among adults [53
] but not in studies conducted among adolescents [23
], in which the occurrence of tooth loss and periodontal disease is expected to be low. Nevertheless, the results of the assessment of discriminative validity using Mann Whitney statistics suggest that OHIP-Sp is suitable to distinguish between groups with and without oral conditions such as clinical attachment loss and tooth loss among adolescents. The area under the ROC curves for the four outcomes tested are not impressive and challenge the application of statistical testing for the assessment of discriminative validity.
The ROC curve areas for different severity levels of clinical attachment loss and increasing extent of tooth loss demonstrated that OHIP-Sp is suitable to discriminate subjects with increasing severity and/or extent of these dental outcomes.
Internal consistency of the OHIP-Sp
The values for internal consistency estimated with Cronbach's alpha relate to OHIP scores obtained for an specific study group rather than to the instrument itself [55
]. This means that the numerical size of Cronbach's alpha is significantly influenced by the degree of disease variation in the study group used to test the instrument. The Cronbach's alpha coefficients for internal consistency found in this study were slightly lower than those observed by Broder et al., [49
] for disadvantaged adolescents, and similar to those obtained by Soe et al., [23
] for Myanmar adolescents with low oral disease experience. The population in which the OHIP-Sp was tested represents one of the most demanding situations for the instrument. Our observation that OHIP-Sp did in fact capture oral health impacts when used in a young population with a low periodontal disease burden and very limited tooth loss testifies to the usefulness of the instrument. While it may be noted that the recommendation of Cronbach's alpha > 0.70 for sufficient internal consistency [42
] was reached only for one of the domains and for the total summary score, it is also clear that most other domains were approaching this limit. Moreover, higher estimates for internal consistency are likely to be found if the instrument is applied to (older) study groups with more disease experience.
Clearly, further studies of the properties of OHIP-Sp should include testing of the questionnaire in older populations and in populations with a higher disease burden/disease variation; as well as the inclusion of caries as a dental outcome. Additional aspects of the instrument that should be assessed are the use of test-retest reliability exercises to evaluate the stability of the test; and the assessment of the responsiveness of OHIP-Sp to changes in oral health conditions.