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
Asja ČELEBIĆ
1*
, Ivica STANČIĆ
2
, Ines KOVAČIĆ
1
, Aleksandra POPOVAC
2
,  
Jolanda TOPIĆ
3
, Ketij MEHULIĆ
1
, Sašo ELENČEVSKI
4
, Sanja PERŠIĆ
1
1
University of Zagreb, School of Dental Medicine, Department of Removable Prosthodontics, 
Gunduličeva 5, 10000 Zagreb, Croatia
2
University of Beograd, School of Dentistry, Department of Prosthodontics, Serbia
3
Private Dental Office, Makarska, Croatia
4
University of Skopje, Faculty of Dentistry, Department of Prosthodontics, North Macedonia  
Received: May 25, 2020
Accepted: Nov 24, 2020 
Original scientific article
*Corresponding author: Tel. + 385 91 50 36 459; E-mail: celebic@sfzg.hr
10.2478/sjph-2021-0009 Zdr Varst. 2021;60(1):55-64
55
PSIHOMETRIČNE LASTNOSTI HRVAŠKE IN SRBSKE RAZLIČICE 
VPRAŠALNIKA ZA OCENO KAKOVOSTI ŽIVLJENJA V POVEZAVI Z 
ORALNIM ZDRAVJEM (OHRQOL) ZA BREZZOBO POPULACIJO
Čelebić A, Stančić I, Kovačić I, Popovac A, Topić J, Mehulić K, Elenčevski S, Peršić S. 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. Zdr Varst. 2021;60(1):55-64. doi: 10.2478/sjph-2021-0009.
ABSTRACT
Keywords: 
OHIP-EDENT, 
questionnaire, 
adaptation, 
reliability, validity, 
responsiveness, EFA, 
Croatia, Serbia
IZVLEČEK
Ključne besede: 
OHIP-EDENT, 
vprašalnik, 
prilagoditev, 
zanesljivost, veljavnost, 
odzivnost, EFA, 
Hrvaška, Srbija
Introduction: The aim was to adapt the Croatian and the Serbian versions of the Oral Health Impact Profile for the 
edentulous population (OHIP-EDENT-CRO and OHIP-EDENT-SRB).
Methods: The translation and cross-cultural adaptation were carried out in accordance with accepted international 
standards. A total of 95 and 177 removable denture wearers were recruited in Croatia and Serbia respectively. 
The reliability was evaluated by calculating Cronbach’s alpha coefficient and by test-retest (30 participants in 
each country). The concurrent validity was determined by calculating the Spearman’s rank coefficient between 
the OHIP-EDENT summary scores and one question related to removable denture satisfaction. Construct validity 
was determined by exploratory factor analysis (EFA). Responsiveness was determined by comparison of the 
OHIP-EDENT summary scores before and after dental implant placement to support mandibular overdentures (23 
patients in Croatia, 21 in Serbia).
Results: Cronbach’s alpha coefficient was 0.92 in Croatia and 0.87 in Serbia. The intraclass correlation coefficient 
was 0.98 in Croatia and 0.94 in Serbia. In Croatia the Spearman’s correlation coefficient was -0.71 (p<0.001) and in 
Serbia -0.74 (p<0.001). Both confirmed concurrent validity. Construct validity was tested by EFA, which extracted 
four factors in each country, accounting for 66.59% of the variance in Croatia and 59.33% in Serbia. Responsiveness 
was confirmed in both countries by a significant OHIP-EDENT summary score reduction and a high standardised 
effect size (3.9 in Croatia, 1.53 in Serbia).
Conclusion: The results prove that both instruments, the OHIP-EDENT-CRO and the OHIP-EDENT-SRB, have very 
good psychometric properties for assessing OHRQoL in the edentulous population.
Uvod: Namen raziskave je določiti psihometrične lastnosti hrvaške in srbske različice vprašalnika za oceno 
kakovosti življenja v zvezi z oralnim zdravjem (OHRQoL), to je »Oral Health Impact Profile« za brezzobo populacijo 
(OHIP-EDENT-CRO in OHIP-EDENT-SRB).
Metode: Prevod in medkulturno prilagajanje sta bila izvedena v skladu s sprejetimi mednarodnimi standardi. Na 
Hrvaškem in v Srbiji je bilo vključenih 95 oziroma 177 udeležencev s snemno zobno protezo. Zanesljivost smo ocenili 
z izračunom Cronbachovega koeficienta alfa in s ponovnim testom, ki je vključeval 30 udeležencev v vsaki državi. 
Sočasna veljavnost je bila določena z izračunom Spearmanovega koeficienta ranga med zbirnimi ocenami OHIP-
EDENT in enim vprašanjem v zvezi z zadovoljstvom s snemno protezo. Veljavnost konstrukta je bila določena z 
eksplorativno faktorsko analizo (EFA). Odzivnost je bila določena s primerjavo zbirnih rezultatov OHIP-EDENT pred 
namestitvijo zobnega vsadka za podporo mandibularne delne proteze in po njej (23 hrvaških in 21 srbskih pacientov).
Rezultati: Cronbachov koeficient alfa je na Hrvaškem in v Srbiji znašal 0,92 oziroma 0,87. Intraklasni korelacijski 
koeficient je znašal 0,98 za hrvaško in 0,94 za srbsko različico. Za hrvaško različico je Spearmanov koeficient 
korelacije znašal –0,71 (p < 0,001), za srbsko pa –0,74 (p < 0,001) in pri obeh je bila potrjena sočasna veljavnost. 
Veljavnost konstrukta je bila preizkušena z EFA, ki je v vsaki jezikovni različici določila štiri dejavnike. Ti 
pojasnjujejo 66,59 % variance pri hrvaškem in 59,33 % variance pri srbskem vprašalniku. Odzivnost je bila v obeh 
državah potrjena z znatnim zmanjšanjem skupnega rezultata OHIP-EDENT in z visoko vrednostjo standardizirane 
velikosti učinka (3,9 na Hrvaškem; 1,53 v Srbiji).
Zaključek: Rezultati dokazujejo, da imata oba instrumenta, OHIP-EDENT-CRO in OHIP-EDENT-SRB, zelo dobre 
psihometrične lastnosti za oceno OHRQoL pri brezzobi populaciji.
© Nacionalni inštitut za javno zdravje, Slovenija. 

1 INTRODUCTION
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 (1–4). 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 (14–16). 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, 18–20).
The OHIP-49 and the OHIP-14 questionnaires have already 
been validated in Slovenia, while in Serbia only the OHIP-
14 has been validated (21–23). 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.
 
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56
2 MATERIAL AND METHODS 
2.1 Participants
A sample of 95 participants was recruited at the School 
of Dental Medicine, University of Zagreb, Croatia. A 
sample of 177 participants was recruited at the Faculty 
of Dental Medicine, University of Belgrade, Serbia. The 
criterion for inclusion was the wearing of maxillary and 
mandibular removable dentures for at least six months 
prior to the research. This was to ensure full adaptation. 
In Croatia, 83 participants had complete dentures (CD) 
in both jaws, while 12 had one complete and one partial 
removable denture. In Serbia, all participants were CD 
wearers. Subjects who reported a history of mental 
disorders in anamnestic data were excluded. The sample 
size was determined using a strategy similar to that used 
in other studies (19, 24). A minimum of 95 participants 
was required. Participants answered questions from the 
OHIP-EDENT questionnaire by rating the frequency of a 
particular problem experienced during the previous week 
(25). The responses were rated on a Likert-type scale (0 
– never, 1 – hardly ever, 2 – occasionally, 3 – fairly often, 
4 – very often), where “zero” represented the absence of 
problems while higher scores represented more problems 
and worse oral health. The research has been conducted 
in accordance with the Declaration of Helsinki. Written 
informed consents were obtained from each participant. 
The study was approved by the ethics committees of the 
Croatian (approval no 05-PA-26-6/2015) and Serbian dental 
schools (approval no 36/18).
2.2 Translation
The OHIP-EDENT was translated using the accepted 
standard of the forward-backward process (26). The 
original and back-translated versions were compared 
by two specialists in prosthodontics with fluency in 
the English language, together with one native English 
language speaker in both countries. The preliminary 
versions were additionally pilot-tested in ten CD wearers 
to check understanding and clarity of the items. The 
OHIP-EDENT-CRO and the OHIP-EDENT-SRB questions are 
shown in Figure 1.

10.2478/sjph-2021-0009 Zdr Varst. 2021;60(1):55-64
57
2.4 Validity
Concurrent validity assessed the degree to which the OHIP-
EDENT summary scores correlated with another measure 
of the same construct at the same time. The association 
between the OHIP-EDENT summary score and a simple 
question, “Please rate your satisfaction with dentures”, 
was assessed in both countries. Satisfaction with the 
existing dentures was rated from 1 to 5 (1 represented the 
worst and 5 the best score). It was assumed that patients 
who rated their dentures with higher scores would 
have lower OHIP-EDENT summary scores. Spearman’s 
correlation coefficient was calculated.
Construct validity was assessed using exploratory factor 
analysis (EFA) to identify interrelationships and groupings 
among items in the OHIP-EDENT-CRO and the OHIP-EDENT-
SRB. Before performing EFA, the Kaiser-Meyer-Olkin (KMO) 
measure of sampling adequacy and Bartlett’s Test of 
Sphericity were conducted. KMO values above 0.6 and a 
Bartlett’s Test of Sphericity significance of <0.0001 were 
considered adequate for the performance of EFA. The main 
factors were extracted using the Principal Component 
Analysis, and varimax rotation was performed. A minimum 
eigenvalue of 1 was assigned as the factor extraction 
criterion. Item loadings ≥0.4 were considered sufficient 
(27). 
2.5 Responsiveness
Responsiveness is defined as the ability of the measure to 
evaluate changes after therapy in patients over time (28). 
We had two samples: 21 CD wearers in Serbia and 23 CD 
wearers in Croatia. In Serbia, 21 CD wearers received two 
standard-size implants in the mandible in approximate 
sites of previous canines. After osseointegration (three 
months), the implants were loaded. The Locator system 
was used and the abutments were screwed at 35 Ncm. 
Metal housings were mounted using a self-curing acrylic 
resin into the existing mandibular dentures, which were 
relined and adjusted when necessary. A sample of 23 CD 
wearers was recruited in Croatia. All participants had slim 
alveolar ridges (≤4 mm) in the mandible. They therefore 
received four slim ball-type mini dental implants (MDIs) 
in the interforaminal region. Early loading protocol was 
used. Metal housings with “o-rings” were attached into 
the existing mandibular CDs using a self-curing resin. The 
dentures were relined when necessary. The participants 
completed the questionnaire twice: before the implant 
placement and one month after the implants had been 
loaded and the dentures adjusted. The standardised 
effect size was calculated using the equation: Mean 
(baseline OHIP-EDENT score – follow-up OHIP-EDENT)/
Standard deviation of the baseline OHIP-EDENT score (29).
  
Figure 1. Translation of the original English language OHIP-
EDENT into the Croatian and Serbian languages.
2.3 Reliability
Two types of reliability were assessed: internal consistency 
and test-retest reliability. The internal consistency was 
assessed by calculating Cronbach’s alpha coefficient, 
which captures the extent of agreement between all 
possible subsets of questions. Guttman’s “Split-Half” 
coefficient was also calculated. A value of >0.7 was 
considered acceptable.  
The test-retest reliability was assessed in 30 participants 
willing to make a recall visit in each country. They were 
not provided with any treatment between the two 
administrations of the questionnaire. The prediction was 
that OHRQoL would not change during a 15-day treatment-
free period. The test-retest reliability was assessed by 
intraclass correlation coefficients (ICC) of the OHIP-EDENT 
summary scores, based on the one-way repeated-measure 
analysis of variance (ANOVA) from the repeated tests.

3 RESULTS
3.1 Participants
A sample of 95 participants was recruited in Croatia 
and 177 participants in Serbia. Sampling strategies, 
together with the participants’ age and demographic 
characteristics, are presented in Table 1.
10.2478/sjph-2021-0009 Zdr Varst. 2021;60(1):55-64
58
Croatia 
 
 
 
 
 
 
Serbia
OHIP-EDENT-CRO
Participants
OHIP-EDENT-SRB
Participants
Table 1.
Table 2.
Sampling strategy and participants’ demographic data.
Cronbach’s alpha coefficient, average inter-item correlation, mean and summary scores with standard deviations, and 
Guttman’s Split-Half Coefficients of the OHIP-EDENT-CRO and the OHIP-EDENT-SRB; n=number of participants. 
M=mean value; SD=standard deviation
SD=standard deviation
Removable 
denture 
wearers 
Removable 
denture 
wearers
Removable 
denture 
wearers
Complete 
denture 
wearers 
Complete 
denture 
wearers
Complete 
denture 
wearers
Internal 
consistency, 
Concurrent 
validity
Test-retest 
reliability 
Responsiveness 
 
Internal 
consistency, 
Concurrent 
validity
Test-retest 
reliability 
Responsiveness
 
0.92
0.87
69.08±9.2 
 
 
71.8±10.2 
 
66.6±10.2 
 
63.8±11.5 
 
 
65.3±10.3 
 
63.8±10.5
 
30.21
19.51
7.6±7.9 
 
 
7.6±6.6 
 
7.6±5.9 
 
3.5±7.6 
 
 
3.8±6.6 
 
3.5±5.6
 
0.83
0.74
Convenience 
 
 
Consecutive
 
 
Convenience 
 
Convenience 
 
 
Consecutive 
 
Convenience
95
177
95 (65%) 
 
 
30 (60%) 
 
23 (61%) 
 
90 (51%) 
 
 
30 (40%) 
 
21 (43%)
 
0.39
0.25
51–93 
 
 
52–91 
 
51–93 
 
35–90 
 
 
43–90 
 
42–79
 
15.95
7.60
1–30 
 
 
1–30 
 
2–28 
 
1–21 
 
 
1–18 
 
1–14
Country
Questionnaire
Sample Research 
purpose
Cronbach’s α
Mean age 
(years)
M±SD
Mean Summary 
Score
Duration of 
edentulism
(M±SD)
Guttman’s Split-
Half Coefficient
Sampling
n
n
(% women)
Average inter-
item correlation
Age range 
(years)
SD (Mean 
Summary Score)
Range of 
edentulism 
(years)
3.2 Reliability
3.2.1 Internal consistency
Cronbach’s alpha coefficients, average inter-item 
correlations, mean and summary scores with standard 
deviations of the OHIP-EDENT questionnaires, as well as 
Guttman’s Split-Half coefficients, are presented in Table 
2. In Croatia, higher Cronbach’s alpha and Guttman’s Split-
Half Coefficients were obtained, as well as higher mean 
item score and mean summary score (Table 2). 
Table 3 presents mean scores of each item with standard 
deviations, corrected item-total correlation, Cronbach’s 
alpha when one item was deleted, and factor loadings 
(EFA) of both questionnaires. All item-total correlations 
were above 0.20. Even if one item was deleted, Cronbach’s 
alpha coefficient remained higher than 0.7.

Difficulty chewing
Food catching
Dentures not fitting
Painful aching
Uncomfortable to eat
Sore spots
Uncomfortable dentures
Worried
Self-conscious
Avoid eating
Unable to eat
Interrupt meals
Upset
Embarrassed
Avoid going out
Less tolerant
Irritable with others
Unable to enjoy company
Life less satisfying
Table 3. Mean item scores, standard deviations, corrected item-total correlations, Cronbach’s alpha coefficients when the item was 
deleted, and factor loadings of the OHIP-EDENT-CRO and the OHIP-EDENT-SRB; SD=standard deviation.
SD=standard deviation
0.75
0.70
0.52
0.63
0.56
0.40
0.44
0.60
0.69
0.39
0.58
0.42
0.67
0.69
0.69
0.66
0.61
0.70
0.64
0.56
0.50
0.60
0.69
0.61
0.68
0.69
0.65
0.62
0.62
0.71
0.73
0.78
0.77
0.71
0.71
0.64
0.73
0.66
0.65
0.63
0.64
0.58
0.55
0.57
0.62
0.94
0.83
0.53
0.48
0.43
0.97
1.18
1.00
0.21
0.82
0.75
1.07
1.24
1.24
1.46
1.12
1.39
1.22
1.45
1.50
1.62
1.41
1.37
1.33
1.54
1.35
1.21
.84
.95
1.12
1.26
1.17
0.92
0.55
0.44
1.25
0.64
0.71
1.39
2.68
1.15
1.07
0.16
1.59
1.62
0.83
0.03
0.56
0.90
1.93
2.60
1.84
2.43
.99
2.32
1.67
2.16
2.03
1.94
2.06
1.72
1.35
1.91
1.51
0.87
0.45
0.58
0.71
1.07
0.84
0.87
0.87
0.86
0.86
0.87
0.86
0.85
0.86
0.86
0.86
0.86
0.85
0.86
0.85
0.87
0.86
0.85
0.86
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.91
0.91
0.92
0.92
0.92
0.92
0.92
0.50
0.23
0.28
0.37
0.46
0.24
0.42
0.68
0.37
0.46
0.44
0.34
0.63
0.61
0.72
0.21
0.56
0.68
0.58
0.57
0.49
0.48
0.45
0.64
0.56
0.63
0.69
0.51
0.72
0.62
0.65
0.79
0.74
0.56
0.57
0.52
0.51
0.61
Questionnaire OHIP-EDENT-CRO OHIP-EDENT-SRB
Factor 
loadings
Factor 
loadings
SD SD Mean Mean Cronbach’s 
alpha if item 
deleted
Cronbach’s 
alpha if item 
deleted
Corrected 
item–Total 
correlation
Corrected 
item–Total 
correlation
3.2.2 Test-retest reliability
Thirty CD wearers in each country answered the same 
questions of the OHIP-EDENT twice, without any 
treatment between the two administrations. The results 
are presented in Table 4. The ICC values were high in both 
countries (0.99 and 0.97 in Croatia and Serbia respectively).
OHIP-EDENT-CRO
Complete denture wearers (n=30)
OHIP-EDENT-SRB
Complete denture wearers (n=30)
Table 4. Test-retest reliability measured by intraclass correlation coefficients (ICC) for the OHIP-CRO-EDENT and the OHIP-SRB-
EDENT); n=number of participants. 
ICC=intraclass correlation coefficient
 
0.99
0.97
 
-0.37
-1.0
 
0.98–0.99
0.93–0.98
 
-1.42–0.69
-2.01–0.70
0.48 NS
0.11 NS
Questionnaire ICC Mean 
difference
95% confidence 
interval of the ICC
95% confidence interval 
of the difference
P
3.3 Validity
3.3.1 Concurrent validity
The concurrent validity was confirmed by a significant 
negative Spearman’s correlation coefficient between the 
OHIP-EDENT summary scores and one question in which 
participants rated satisfaction with their dentures. In 
Croatia the coefficient was -0.71 (P<0.001) and in Serbia 
-0.74 (P<0.001).    
10.2478/sjph-2021-0009 Zdr Varst. 2021;60(1):55-64
59

1
2
3
4
Difficulty chewing
Food catching
Dentures not fitting
Painful aching
Uncomfortable to eat
Sore spots
Uncomfortable dentures
Worried
Self-conscious
Avoid eating
Unable to eat
Table 5.
Table 6.
Factors with eigenvalue >1.0 before and after varimax rotation (Croatian OHIP-EDENT and Serbian OHIP-EDENT 
questionnaires).
Factor loadings after varimax rotation of the OHIP-EDENT-CRO and the OHIP-EDENT-SRB.
20.41
17.78
15.93
12.47
 
0.81
0.31
0.72
0.13
0.21
0.32
0.27
0.42
24.98
16.94
9.33
8.08
 
0.11
-0.15
0.64
-0.12
0.52
42.51
11.04
7.08
5.96
0.61
0.35
0.15
0.13
0.54
0.33
0.28
0.67
0.72
0.50
30.66
14.33
7.90
6.44
0.83
0.52
0.71
0.71
0.58
0.44
0.15
0.38
0.26
3.88
3.38
3.03
2.37
0.41
0.61
0.75
0.47
0.76
0.33
0.47
0.69
4.75
3.22
1.77
1.54
 
0.83
0.47
0.35
0.21
0.45
0.21
0.11
0.40
8.08
2.10
1.35
1.13
0.13
0.13
0.10
0.20
0.16
0.21
0.28
0.23
5.83
2.72
1.50
1.23
0.20
0.25
0.19
0.73
0.52
0.41
0.29
Factor
Factor
OHIP-EDENT-CRO
OHIP-EDENT-CRO
OHIP-EDENT-SRB
OHIP-EDENT-SRB
Unrotated
Component
Rotated
Eigenvalue
3
Eigenvalue
3
Eigenvalue
1
Eigenvalue
1
% of variance
4
% of variance
4
% of variance
2
% of variance
2
3.3.2 Construct validity 
The KMO measure 0.871 and Bartlett’s Test of Sphericity 
1,021.58 (df=171, P<0.001) in Croatia and the KMO measure 
0.85 and Bartlett’s Test of Sphericity 1,348.96 (df=171, 
P<0.001) in Serbia demonstrated sufficient values and 
significant correlations enabling the performance of EFA. 
All factor loadings of the OHIP-EDENT-SRB questionnaire 
were >0.4 (except one, which was 0.39). All factor 
loadings of the OHIP-EDENT-CRO were >0.5 (Table 3). In 
both questionnaires, four factors (dimensions or domains) 
with eigenvalues >1 were extracted. Table 5 shows the 
eigenvalues and percentages of variance of non-rotated 
and rotated matrices. The OHIP-EDENT-CRO explains 
66.65% and the OHIP-EDENT-SRB 59.35% of the variance. 
When fixed to one factor, the OHIP-EDENT CRO explained 
42.51% of variance, while the OHIP-EDENT-SRB explained 
30.66%. In non-rotated matrices, most of the items tended 
to concentrate on the first factor, while the rotated matrix 
presented more even distribution (Table 5). 
Factor loadings after rotation are presented in Table 6. 
Unrotated
Component
Rotated
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60

Interrupt meals
Upset
Embarrassed
Avoid going out
Less tolerant
Irritable with others
Unable to enjoy company
Life less satisfying
0.70
0.19
0.13
0.26
0.19
0.21
0.16
0.14
-0.11
-0.76
-0.29
-0.21
0.16
0.19
0.70
0.64
0.26
0.16
0.33
0.60
0.20
0.18
0.12
0.10
0.25
0.30
0.19
0.26
0.23
-0.15
-0.13
0.19
0.40
0.14
-0.13
0.38
0.41
0.57
0.79
0.76
0.74
0.84
0.71
0.19
0.80
0.81
0.76
0.22
0.60
0.80
0.77
Factor OHIP-EDENT-CRO OHIP-EDENT-SRB
Component
3 3 1 1 4 4 2 2
Component
3.4 Responsiveness
Responsiveness of the Croatian and Serbian versions of the 
19-item OHIP was tested in CD wearers before and after 
dental implant placement in the mandible. The results are 
presented in Figure 2. Significant improvement of OHRQoL 
was achieved in both countries, as expected (t=20.9 in 
Croatia; t=5.05 in Serbia; p<0.001). The standardised 
effect size was high for both countries. However, it was 
higher in Croatia (3.9 in Croatia, 1.53 in Serbia).
Figure 2. Mean baseline and after-treatment scores of the 
Croatian and Serbian 19-item Oral Health Impact 
Profiles (before and after implant-supported 
overdenture treatment in the mandible).
 *Croatian participants (n=23) received four mini dental 
implants; ** Serbian participants (n=21) received two 
standard-sized implants 
4 DISCUSSION
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 (30–33). 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 (34–36). 
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 
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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–
16, 40–43). 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, 13–15). 
5 CONCLUSION
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.
CONFLICTS OF INTEREST
The authors declare no conflicts of interest. 
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62

FUNDING
The study was financed by the Croatian Science Foundation 
(Grant no 1218) and the Ministry of Education and Science 
of Serbia. 
ETHICAL APPROVAL 
Received from the Schools of Dental Medicine in Zagreb 
(approval no 05-PA-26-6/2015) and Belgrade (approval no 
36/18).
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