This study described the occurrence of OHRQoL in a general population birth cohort of dentate 32-year olds born in New Zealand. It has found strong associations between OHRQoL and measures representing clinical oral health, with an apparent sex-based difference in the manifestation of some of those associations. Other factors most associated with ‘impacts’ include SES, usual reason for visiting a dentist, having already acquired dental caries experience, and having already lost teeth. These associations with oral health status and risk indicators of oral diseases suggest that the OHRQoL measures are valid and support their use in oral health surveys to augment the traditional dental public health clinical measures which count teeth, as in the DMFT, or tooth sites, when using the Community Periodontal Index of Treatment Needs (CPITN). This traditional approach is not, however, without its drawbacks, in particular, the DMFT, CPITN, and other clinical indices neglect the fact that the level of treatment (if any) carried out is influenced by the patient’s perceived needs and ability or willingness to pay. Incorporating self-reported measures that address these needs will provide a complementary perspective that will be far more effective than simply counting decayed teeth.
In the current study, 23% of 32-year-old dentate subjects reported that their oral condition had negatively impacted upon them in some way fairly often or very often over the preceding 4 weeks, thereby affecting their quality of life. Most participants, however, reported only one or two problems during the previous month. Does a proportion of almost one in four individuals represent a high prevalence? In other words, how do the OHRQoL estimates from the Dunedin cohort compare with those from other populations? When the Dunedin OHIP data were compared with estimates for dentate adults in the UK and Australia (10
), the prevalence of impacts was significantly greater in New Zealand (23.4%) than in either of those countries (18.2% and 15.9% respectively; ). When the extent and severity scores were compared, the New Zealand estimates were similar to those from Australia, but they were higher than those from the UK. These findings were consistent across different OHIP dimensions, and among males and females. Females in Australia and New Zealand appear to experience more ‘severe’ impacts of oral disorders on everyday life (represented by higher OHIP-14 mean scores) than males. However, it should be noted that the age distributions of the UK and Australian samples differed from that of the New Zealand sample: the median age in the former averaged around 40 years (10
), whereas the Dunedin study participants were all aged 32 years. Thus, differences may be partly explained by differences in sampling strategies and/or participation rates. In the Dunedin study, an entire cohort was followed for 32 years (with a very high participation rate), while the data from the UK and Australia were derived from representative probability samples that had lower participation rates of 72% and 64.6%, respectively. There is the possibility that the participants in the Dunedin study are more aware than most of their oral health as a result of the regular follow-ups that are part of the study, but comparisons of the Dunedin Study members with people of the same age in the nationally representative New Zealand Health and National Nutrition Surveys found little evidence that the repeated assessments in the Dunedin Study had significantly altered the study members’ health (24
). It is therefore possible that nonresponse bias may have led to an underestimation of the true prevalence in the Australian and UK studies, while the Dunedin study members’ regular follow-up visits may have had little or no effect.
International comparisons of prevalence, extent and severity of overall impacts and selected dimensions among dentate adults
Nevertheless, in general population samples, it is expected that relatively few people are handicapped or frequently experience the more severe dimensions of disability. OHIP data from a national survey in Germany revealed a prevalence of frequent impairment (response categories ‘fairly often’ or ‘very often’) of less than or equal to 6% for all items, while the previous-month prevalence of any impairment ranged from 13% to 46% across all items, with higher prevalence observed for people wearing removable dentures or complete dentures than those without dentures (25
). Similarly, prevalence estimates were low using the Norwegian version of the Oral Impacts on Daily Performance (OIDP) instrument in a representative sample of Norwegian adults (26
): 18% reported at least one oral impact during the past 6 months. As with the OHIP-14, the OIDP (27
) has items which only consider the negative impact of oral health on quality of life (28
In this study, only 7% of dentate adults experienced pain associated with their teeth, mouth, or dentures fairly/very often in the previous 4 weeks. Approximately 11% said they had an unsatisfactory diet or had to interrupt meals (physical disability), and one in 10 reported a psychological effect of their oral state (in the sense that they felt conscious or tense about their teeth). Coincidently, physical pain and physical disability were the dimensions of the OHIP that contributed most to variations in the sex- and age-category distributions of subjective impacts between adults in the UK and Australia (10
). It is noteworthy that the national norms for the OHIP-14 differed dramatically from age–sex norm values previously presented for the 16-item United Kingdom Oral-health- related Quality of Life Measure (OHRQoL-UK; 29) primarily because of differences in the underlying concepts and dimensions of the two instruments (28
). Using the OHRQoL-UK, 75% of respondents perceived their oral health as affecting their life quality, either in a negative or positive way (or both), but age, social class, and the number of retained teeth accounted for substantial variation in OHRQoL-UK scores. Furthermore, Slade et al. (10
) included only those impacts reported ‘fairly often’ or ‘very often’ in the previous year, while McGrath and Bedi (29
) included all categories, regardless of their frequency. This difference in instruments might very well explain the different levels of impact found across the two studies. We adopted the more restrictive definition of prevalence of adverse impacts, as chronic or repeated impacts are most likely to be considered as a public health problem.
The present study has several strengths. Foremost among these is that the Dunedin study used both clinical indicators of oral health status and a multi-item OHRQoL scale. Clinical indicators of oral health status were significantly related to the measure of OHRQoL in stratified analyses by sex and SES. The effects of clinical oral health status on OHRQoL persisted after controlling for sex, SES, and dental visiting in the multivariate analyses. We believe that when oral health is evaluated using true endpoints such as tooth loss, or more clinically relevant cut-points for severity of dental caries and periodontitis, poor OHRQoL parallels poor oral health, when estimated using clinical measures of disease.
Consistent with the findings of other studies, we found that women perceive their oral health as having a greater impact on their quality of life than men (15
), and this was despite the Dunedin study women having fewer missing teeth or untreated decayed surfaces, and less periodontal attachment loss than men. They were also more likely to be preventive dental visitors. Moreover, women who were defined as cases of periodontal disease had a threefold greater risk of frequent oral impacts than females who were not cases. Sex differences in OHRQoL cannot be solely explained by poor oral health status; to further understand differences in OHRQoL between men and women, the different lifecourse influences for each sex must be considered (17
There were also socioeconomic differences, with the impact of dental caries and self-rated oral health (and change in oral health) on OHRQoL differing between the high/medium-SES and low-SES groups. The reasons why socioeconomic circumstances are associated with oral health and OHRQoL are poorly understood and may go beyond the simple explanation of material deprivation. For example, in a recent French study (30
), 63% of economically disadvantaged 35–44-year olds (who were eligible for publicly funded health insurance coverage for dental care) reported poor oral health and 79% perceived a need for care as measured by the General Oral Health Assessment Index (GOHAI) (31
). While the GOHAI score was correlated with the number of decayed and missing teeth, it was unrelated to oral health behavior, as less than half (48%) of the sample had visited a dentist during the previous 12 months. This finding signals that access to care by itself
will not improve oral health and OHRQoL in low SES groups.
It has been suggested that psychosocial factors are important in understanding pathways between socioeconomic position, oral health status and OHRQoL (32
). A recent study using self-report data obtained from a representative Australian adult sample revealed that those with high scores for a sense of control, social support and life satisfaction reported that oral conditions disrupted their quality of life less often, while those with higher OHIP-14 scores had significantly higher levels of stress in relation to their oral health (33
). A national oral health study of Finnish adults arrived at similar conclusions with respect to psychosocial factors and OHRQoL (34
). The Finnish study found that people with a strong or moderate sense of coherence (SOC) had significantly fewer problems attributed to oral conditions (OHIP) than those with a weak SOC. The SOC was also associated with all of the subscales of the OHIP, and the association was most evident with the psychological discomfort, psychological disability and handicap subscales. Most importantly, rehabilitative dental treatment offered to indigent adults in San Francisco improved OHRQoL and employment (35
). As 57% of the cohort was either homeless or provisionally housed, the loss to follow-up of participants was high (35%), yet those welfare recipients who completed their dental treatment program were twice as likely to achieve a more favorable employment outcome and improved quality of life.
It is important to acknowledge that the current study was unable to determine whether clinical oral health status, self-rated oral health, dental visiting behavior, sex, or SES had a direct causal association with the OHIP scores because we have had to treat it as a cross-sectional study, as the OHIP-14 measure was first used when the cohort was at age 32 years; thus, it is not possible to establish the temporal sequence of these events at this time. Using the OHIP-14 in subsequent data collection phases with the Dunedin cohort should enable examination of the nature of the association between SES, oral health, and OHRQoL using a lifecourse approach.
In summary, OHIP-14 scores in this New Zealand birth cohort were significantly associated with oral health status after controlling for sex, SES, and use of dental services. These findings indicate that self-reported OHRQoL measures have a future in population-based surveys, not as a substitute for the oral examination, but as an adjunct to identifying the conditions with the most potential to compromise patient well-being and quality of life. From a dental public health services perspective, there is merit in using OHRQoL instruments in combination with traditional measures, particularly when planning public health services for those most in need of oral health promotion interventions or community-based oral health strategies. When healthcare resources are scarce, findings from such patient-based outcome measures can be used to ensure that funding and/or services are directed at those conditions most likely to have a negative effect on OHRQoL of specific populations.