Psychometric properties of the Albanian version of chewing-function questionnaire CFQ-ALB

A sample of 205 subjects, aged from 19 to 86 years participated in this study. The study was approved by the Ethics Committee of the University Dentistry Clinical Center of Kosovo. Informed consent was obtained from each subject participating in this study. The sample was divided into four groups. Group A comprised of randomly selected employees of Raiffeisen Bank in Prishtina, with natural teeth (NT, n = 36). Group B comprised of dental students with natural teeth (NT, n = 61), who were examined by a specialist of prosthodontics; the examination results indicated that none of the dental students required dental treatment. Group C a convenience sample comprised prosthodontics patients (n = 57) who already had prosthetic restorations that were not older than one year, and they were satisfied with them. Twenty-seven of them had fixed partial dentures (FPD) (C1; n = 27) and thirty had removable dentures (RD) (C2; n = 30). Group D included prosthodontics patients (D; n = 51) asking for prosthodontic treatment. Specialist of prosthodontics assessed that 31 patients (D1) needed FPD and 20 patients needed RD (D2). Groups C and D were selected at the Department of Prosthodontics, Dental School, Faculty of Medicine, University of Prishtina and Private Dental Clinic GS, Prishtina in Kosovo. Both prosthodontic sample groups (C,D) were interviewed, whereas the two first sample groups (A,B) with natural teeth self-administered the CFQ questionnaire and were supervised by three dentists. For each question, subjects were asked how frequently they have experienced chewing difficulties, using ordered coded pseudo continuous response categories; 0 = never, 1 = hardly ever, 2 = occasionally, 3 = fairly, 4 = very often or extreme difficulties. Zero indicates the absence of any chewing difficulties and higher scores indicate more impaired chewing function. Ten items of CFQ can sum up to give a CFQ summary score, with lower scores representing satisfaction with their chewing function and higher scores representing impaired chewing function. Besides the CFQ questionnaire, the subjects also answered another question related to their general satisfactions with chewing, using a 5-point Likert scale that ranged from 5 (excellent) to 1 (unsatisfactory).

The original version of the CFQ was translated from the English language into Albanian according to the accepted techniques, already used in earlier validation studies of Oral Health Related to Quality of Life [5, 25, 26]. The original edition which contained 10 items was translated into the Albanian language by a qualified and experienced translator who possesses excellent knowledge of dental terminology and interpretation. Furthermore, two other dentists with excellent proficiency in English were also involved for the translation of several terms. After being translated, the CFQ-ALB was edited by three other dentists, (Dental School, Faculty of Medicine, University of Prishtina), with an excellent knowledge of both Albanian and English language. The translation was done individually and then the last version was incorporated into the final version. Further, the final version was back-translated into English by another qualified freelance translator, in collaboration with two other Kosovar dentists with excellent knowledge of English. The final version translated back to English was evaluated independently by a professor from the Dental School, University of Zagreb, with an excellent proficiency of English and also by a native English language speaker. There were no significant differences between the back translated and the original questionnaire. Considering that there were no dissimilarities in the implication of the items which were observed, the final translation was considered to be adequate for its further use. To test the clarity of the CFQ items in the Albanian language, a pilot study was performed with 20 prosthodontic patients (age 25 to 59 years). Patients were asked whether they had any difficulties understanding and answering the items of the questionnaire. All items were understood clearly, without any difficulties.

Validity was investigated by evaluating construct, convergent and discriminat validity [30]. All subjects were included. Exploratory factor analysis (EFA) was used to assess the factor structure of the CFQ-ALB. The factor extraction criterion was eigen value more than 1. An item is considered to have loaded onto a factor when the factor loading exceeded 0.30. Due to the small number of participants, we did not perform a confirmatory factor analysis. The Bartlett’s test of sphericity, scree plot, and the Kaiser-Mayer-Olkin (KMO) test were used [31, 32]. Convergent validity was determined by Spearman’s rank correlation between self-reported general satisfaction with chewing’ and the CFQ summary scores. Discriminant validity was evaluated using one-way analysis of variance and Sheffe post-hoc tests, by determining whether patients with natural teeth (A, B), fixed partial dentures (C1, D1) and removable dentures (C2, D2) significantly different from one another. The natural teeth group (A,B) was expected to have lower CFQ summary scores in comparison to fixed partial denture group (C1, D1) and the removable denture group (C2, D2).

Responsiveness was tested on fifty-one prosthodontic patients with a treatment need [33]. They completed the questionnaire twice; prior to the treatment and a month after they had received new dentures. One month period was considered acceptable for the patients to adapt to their new prosthodontic restorations. Responsiveness was tested using the paired t-test and by calculating the standardized response mean and the effect size [34]. According to Cohen, the effect size >0.80 is considered large, 0.50 moderate and the effect size < 0.20 is considered small. Satisfactory changes, i.e. improvement of the chewing ability after receiving new prosthodontic restoration was expected. The standardized effect size was computed as following: (baseline score of CFQ - after treatment score)/standard deviation of the baseline CFQ score [35].

The corrected item-total correlation, part of the internal consistency of the CFQ in the Albanian language ranged from 0.646 to 0.924 (Table 2). The highest coefficients were obtained for two items “Have you had any difficulty chewing apples/raw carrots or foods of similar consistency?” and “Have you had any difficulties chewing biscuits, crackers, tea biscuits or foods of similar consistency?” and the lowest coefficient was obtained for the item “Have you noticed food catching or food remaining stuck in your teeth or dentures during or after meals?”. If items were deleted one by one, the Cronbach’s alpha would not increase and it ranged between 0.968 and 0.971 (Table 2). The highest correlation was found between “Have you had any difficulties chewing biscuits, crackers, tea biscuits or foods of similar consistency?” and “Have you had any difficulty chewing fresh bread, doughnuts or foods of similar consistency?” The weakest correlation was found between items “Have you noticed food catching or food remaining stuck in your teeth or dentures during or after meals?” and “Have you had any difficulty chewing bacon/smoked ham/baked or fried firm meat or foods of similar consistency?” (Table 3). The obtained results suggest good internal consistency for the CFQ-ALB. The Cronbach’s alpha coefficients for the overall sample, as well as for each group are shown in Table 4. The Cronbach’s alpha coefficient calculated for all subjects was 0.974 and the Inter-item correlation - IIC was 0.792. For the prosthodontic patients in need of treatment (D1, D2), Cronbach’s alpha coefficient was 0.946 and the IIC was 0.634. For the prosthodontic patients (C1, C2) Cronbach’s alpha coefficient was 0.968 and the IIC was 0.761, and for the natural teeth (Sample A, B) the Cronbach’s alpha coefficient was 0.912 and the IIC 0.534. These results confirmed excellent internal consistency. Results of intraclass correlation coefficients are presented in Table 5. Test-retest reliability was supported.

The results of the factor analysis for CFQ is given in Table 2. Exploratory factor analysis revealed one-factor structure on the basis of eingenvalue >1 and accounted for the 81.711 % of the variance (Scree plot; Fig. 1). The one-dimensional model results are considered acceptable corresponding to other published studies [24, 36]. Convergent validity was established by the strong relationship between the self-reported general satisfaction with chewing score and the CFQ-ALB summary score, as well as by statistically significant relationship between general satisfaction with chewing function and each item of the instrument (Table 6). The results of discriminant validity are presented in Table 7. Statistically significant differences between all sample groups was observed for each question, as well as for the CFQ summary score (p < 0.01). The lowest scores pertaining to each individual question and the CFQ summary score in the NT samples (A,B), followed by the FPD (C1,D1) with the highest scores in the RD (C2,D2).

The responsiveness was confirmed by the significant difference between the baseline summary scores and the after treatment scores (Table 8). The mean change between the baseline and the after treatment summary scores was 15.57 (SD = 2.49) (p < 0.001, Table 8). The effect size for the CFQ-ALB summary score was 2.03.