Psychometric characteristics of the Croatian and the Serbian versions of the oral health impact profile for edentulous subjects, with a pilot study on the dimensionality

Oral health-related quality of life (OHRQoL), as a part of general health and well-being, has become very important in dental epidemiological and clinical studies that measure the extent of teeth loss and the impact of dental intervention (1, 2, 3, 4). A recent study identified 20 Dental Patient-Reported Outcome Measure (dPROM) Questionnaires with multiple items in the English language (5). Some of them were aimed at a specific population, such as the young (6), elderly (7), disease-specific (8, 9) or edentulous population (10). Unidimensional questionnaires were developed to measure one specific dimension of OHRQoL, such as the Orofacial Esthetic Scale (11) or the Chewing Function Questionnaire (12). However, the Oral Health Impact Profile (OHIP), a multidimensional questionnaire, has been one of the most frequently used dPROMs. The original version, with 49 items grouped into seven theoretical domains (functional limitation, physical pain, physical limitation, psychological discomfort, social limitation, and disability (handicap)), has been translated into more than 30 languages and culturally adapted (13). Recent studies reported the existence of only four major dimensions for the OHIP-49 questionnaire, i.e., Oral Function, Orofacial Pain, Orofacial Appearance and Psychosocial Impact (14, 15, 16). The short 14-item OHIP questionnaire was developed soon after the original one (17) and adapted worldwide to reduce the time required and the number of incomplete answers. Owing to the floor effect, it was not sensitive enough for status measurement and treatment improvements in edentulous subjects (10). The 19-item OHIP-EDENT questionnaire has therefore been developed and adapted in several different cultural environments (10, 18, 19, 20).

The OHIP-49 and the OHIP-14 questionnaires have already been validated in Slovenia, while in Serbia only the OHIP-14 has been validated (21, 22, 23). The OHIP-EDENT has not yet been translated or psychometrically validated either in Croatia or Serbia. The aim was to develop Croatian and Serbian versions of the OHIP-EDENT, validate them in a target population, and perform a pilot study of the dimensionality of the questionnaires. The hypothesis was that both versions would show good reliability, validity and responsiveness.

Each questionnaire needs to be validated before it can be used in different cultures. This is due to differences in language, education, amenities, culture, social or economic factors, which are especially important in a disease-specific population (30, 31, 32, 33). The need existed in Croatia and Serbia for a disease-specific questionnaire for edentulous subjects. Cross-cultural adaptation of the original OHIP-EDENT instrument was therefore performed (10). Both versions used the original five-point Likert scale instead of the three-point scale of the Brazilian questionnaires (20, 24, 37). Schools in Croatia and Serbia use a five-point scale, so the participants have already become accustomed to it. The higher summary score obtained among Croatian participants was attributed to the longer period of being edentulous and consequent alveolar ridge atrophy, especially in the mandible, which resulted in reduced denture stability (34, 35, 36).

Cronbach’s coefficient alpha for internal consistency was calculated to compare the results with other studies. It was higher in Croatia than in Serbia. It was higher than in the Portuguese (20, 24, 37), Japanese (18) and Nepalese OHIP-EDENT questionnaires (38). However, it was lower than in the Chinese version (19). Cronbach’s alpha coefficient in Serbia was similar to the Portuguese (20, 24, 37) and Japanese (18) versions. The differences between counties can be explained by differences in sampling strategy, duration of edentulism and cultural environments. However, both alpha coefficients were >0.7. When the alpha coefficient is close to one, redundant questions may exist. This was not found in this study. Cronbach’s alpha coefficient was not calculated for each of the originally proposed seven domains. A recent study on the dimensionality of the 49-item OHIP recommended that one summary score should be used in research using the shortened OHIP versions due to high correlations between factors and the small number of indicators for some dimensions (16). As Cronbach’s alpha coefficient has recently been criticised (39), another measure for internal consistency, i.e. Guttman’s Split-Half coefficient, was also calculated in this study. This revealed that the internal consistency of both questionnaires was good.

The test-retest reliability was also calculated for the summary scores. It was considered that a 15-day period between the two administrations of the questionnaire would be long enough for the participants not to remember the questions, but short enough to prevent changes to oral health. The high ICC values confirmed satisfactory test-retest reliability for the both instruments.

As already mentioned, an EFA was conducted for the purposes of a pilot analysis of the latent structure of the OHIP-EDENT questionnaire. The KMO measure, together with the significance of the Bartlett’s Test of Sphericity, confirmed that the data was appropriate for the EFA. All items had adequate loadings, indicating a strong relationship with their factors. The EFA extracted four factors (dimensions) from both questionnaires, similar to the Brazilian study by Souza et al. (24). Another study from Brazil extracted and confirmed three factors: “Physical Impact”, “Psychological Impact” and “Social Impact” (36). Five factors were found in the Chinese and Nepalese versions (18, 33). The four factors extracted in this study could not be interpreted in a clear manner. According to the content of the items, the dimensions could be: Function, Pain, Comfort and Psychosocial Impact. Due to a lack of questions related to orofacial aesthetics in the OHIP-EDENT questionnaire, the four extracted factors are not in line with the recent four-dimensional oral health model derived from the OHIP-49 questionnaires (2, 5, 14, 15, 16, 40, 41, 42, 43). The confirmatory factor analysis (CFA) was not performed in this study because a new sample was needed for the CFA in both Croatia and Serbia. It is possible that the deletion of some factors with cross-loadings or the insertion of some additional questions related to orofacial aesthetics would have led to a different pattern of factor loadings and groupings.

In the CFA study on the dimensionality of the OHRQoL using the 49-item OHIP, some items had been omitted because they had no salient loadings on one of the four proposed dimensions (16). Moreover, the study in question recommended that condition-specific versions, such as the OHIP-aesthetic and the OHIP-EDENT questionnaires (which was adapted in the present study), be used with one summary score, supported by the OHIP’s strong general factor (16). This was done in the present study. When fixed to one factor, the OHIP-EDENT-CRO explained 42.51% of the variance (total variance was 66.6%), and the OHIP-EDENT-SRB explained 30.66% of the variance (total variance was 59.34%).

The confirmatory factor analysis (CFA) was not performed in this study because a new sample in each country must be collected if an adequate CFA is to be performed. The CFA will be the object of further research to yield a better insight into the dimensionality of the OHIP-EDENT questionnaire and the item groupings. An attempt to adapt the OHIP-EDENT to fit into the newly 4-D concept of the OHRQoL through the addition of some items and the deletion of others may also be studied.

The convergent validity of the OHIP-EDENT-CRO and the OHIP-EDENT-SRB was confirmed by significant negative Spearman’s rank correlation coefficients between the summary scores and one question in which participants rated their dentures (which represented a measure of the same construct).

One important characteristic of the questionnaire is its sensitivity to changes elicited by treatment, which has been proved in many studies (44, 45). In Croatia and Serbia, CD therapy is covered by health insurance. However, dental implant costs must be paid by the patient. Two-implant supported overdenture has become a minimum standard of mandibular edentulism therapy (47) and, recently, four mini-implants for edentulous patients with slim mandibular ridges (48). We predicted that dental implants would improve OHRQoL in edentulous patients. The cost of implants in Croatia was covered by a research grant. As expected, both treatments increased OHRQoL and significantly reduced the OHIP-EDENT summary scores. After treatment, the summary scores reached almost equal values in both countries. However, a higher effect size was observed in Croatian participants due to their worse baseline oral health, probably resulting from a longer period of edentulism. The results are in line with other studies (35, 48). The Serbian participants had to pay dental implant costs and therefore might have had higher expectations.

Limitations of this study are the inclusion of participants with different edentulism durations and the relatively small sample size (which allowed only a pilot study to be conducted on the dimensionality). Further research should be directed towards performing the CFA on new samples from each country and towards the possible exclusion or inclusion of some new items in the OHIP-EDENT questionnaire (2, 4, 13, 14, 15).

The OHIP-EDENT-CRO and the OHIP-EDENT-SRB questionnaires demonstrated satisfactory internal consistency, validity and responsiveness. Further dimensionality will be the subject of future studies.