Measuring OHRQoL in children by means of questionnaires is associated with several challenges because the children's abilities to read, think in abstract terms and their age-related ability to understand the concepts used in the questionnaire should be taken into account [5,6]. Bearing in mind these challenges, the Child Perceptions Questionnaire (CPQ) was developed to measure the OHRQoL among children between the ages of 8 and 10 years (CPQ_8–10) and between the ages of 11 and 14 years (CPQ_11–14) [7,8]. The CPQ includes four domain subscales of oral symptoms, functional limitations, emotional well-being and social well-being.

The CPQ_8–10 and CPQ_11–14 have been shown to enjoy sufficient convergent validity, i.e. the self-reported health status correlates with the overall CPQ scores [7,8]. Three studies [8-10] demonstrated that the CPQ_11–14 could be used to discriminate between groups with known different physical dental health status, but another study challenged this finding [11]. The CPQ_8–10 seemed to have less discriminatory power than the CPQ_11–14 [7]. The internal consistency of the CPQ_8–10 and the CPQ_11–14 has been estimated as sufficient, with Chronbach's alpha ranging from 0.81 to 0.91 [7,9,12].

The translation procedure from English into Danish raised several issues for consideration. In the original, English wording of the questions, only the first question on each page contained the full wording of the question (viz. "How often have you ....."). After the first question, the next questions were shortened versions, i.e. the opening phrase "How often have you" was left out. In the Danish translation, the opening line was repeated in all questions to exclude any doubt about the wording of the questions, even if the addition of the wording raised some concern about the length of the questions. A number of questions caused problems during the translation process, for example "How often have you had a hard time biting or chewing food like apples, corn on the cob...", because "corn on the cob" only recently became a widespread dish in Denmark. Although some of the questions contained built-in problems like in the above example, we found that all of the questions could be used in the Danish context [14,16]. In addition, Swedish colleagues engaged in similar translation problems were consulted before deciding on the final versions. Furthermore, we considered the domains of oral-health-related-quality of life identified by Jokovic et al. as well ad their names to be relevant and understandable for Danish children.

Children with more than 2 missing items were excluded from further analysis. There were only few instances of non-response and no specific pattern of non-response could be ascertained. The effect of the absence of responses was therefore considered to be minor.

Like the majority of Danish children, all of the included children were pupils of public schools and therefore most likely representative of the Danish child population.

The study showed that the overall CPQ scores correlated well with the global assessment of the influence of dental health on everyday life. This is in agreement with previous studies on the CPQ questionnaire [7,8]. However, for the CPQ_8–10, the correlation between the global assessment of the influence of the dental health on everyday life and the CPQ scores was low for the symptom scores and high for the scores on social well-being. This contrasted with the findings by Jokovic et al [7]. One possible explanation is that 8-to-10-year-olds are familiar with oral symptoms, among others due to loose primary teeth, and these symptoms may have less impact on their everyday life than similar symptoms in the older group. In the daily clinical situation, dental health carers will, most likely, be concerned about oral symptoms when they evaluate the patient's oral health, but, as demonstrated, this is not necessarily the most important component of the OHRQoL among the 8-to-10-year-olds. This finding underlines the value of considering broader aspects of the dental health in children than only the physical ones.

Three of the CPQ_11–14 domain scores did not correlate with the self-reported assessment of oral health. A possible explanation is that the 11–14 year-olds consider their teeth to be healthy if caries-free, while the CPQ_11–14 questions explore emotional and social aspects which may dominate in the minds of the 11–14-year-olds. Furthermore, the CPQ scores did not increase with decreasing self-reported oral health from the answer category "Excellent" to the answer category "Very good", which may simply be so because it can be semantically difficult to distinguish between "Very good" and "Excellent".

In agreement with the majority of previous studies, the CPQ allowed us to discriminate between groups with known differences in dental health [8-10]. A remarkable, high CPQ_11–14 score was observed among children with fixed orthodontic appliances and, in contrast to another study [8], the CPQ scores of orthodontic patients exceeded those of the cleft lip and palate patients. We may have obtained this result because our inclusion criteria restricted orthodontic patients to subjects with newly inserted fixed appliances. As shown in previous studies, pain and discomfort are most pronounced during the first period after insertion of the appliances [17-19]. Furthermore, Sergl et al. showed that patients with fixed appliances experience more discomfort than patients with removable appliances [17]. Surprisingly, children with cleft lip and palate reported CPQ-scores similar to those reported by healthy children. This finding disagreed with previous studies comparing CPQ-scores among children with cleft lip and palate and healthy children [8] and the observation may question the discriminative validity of the instrument. Another possible explanation is that cleft lip and palate is a chronic disorder which allows the children time to adapt to their situation.

Even though quality of life is a subjective perception, parents are frequently used as informants on children's health. However, previous studies have shown less than optimal agreement between parents' and children's rating of OHRQoL [20]. It is therefore essential to be able to measure self-reported OHRQoL in children.