Measuring oral health literacy: a scoping review of existing tools

This article presents findings from a scoping review of tools used to measure oral health literacy. Interest in this topic, as a domain of health literacy, and a determinant of health, has been growing since the late 1990s. In 2010, the United States Department of Health and Human Services released their 10-year national objectives for improving the health of all Americans [1]. In this document, the scale of oral health disparities, and the significant burden of oral disease were outlined. Oral health literacy was identified as key to promoting oral health and preventing oral health disease. Drawing on broader understandings of health literacy, oral health literacy was defined as the ‘degree to which individuals have the capacity to obtain, process and understand basic oral health information and services needed to make appropriate health decisions’.

Internationally, interest in oral health literacy is driven by oral health disparities, particularly for disadvantaged groups, with conditions such as dental caries and periodontal disease contributing substantially to the global burden of disease [2‐5]. In Australia $7.5bn was spent on dental services in 2009–10, with 61% of this being direct out-of-pocket costs followed by 14% from health insurance funds. Australian Government contributions accounted for the remaining 25% [6]. The economic costs associated with poor oral health are well-documented [7, 8] and the association between oral health, and general health and wellbeing have been noted in numerous studies, with poor oral health impacting on quality of life across the lifespan [2, 7, 9]. Oral health extends beyond dental disease, with a healthy mouth central to the capacity to eat, talk and lead meaningful lives free of disease, pain or embarrassment [3, 10].

The importance of oral health beyond dental care is reflected in the WHO Global Oral Health Program, which is predicated on disease prevention and health promotion. Priority action areas of the WHO are directed at improving oral health literacy to drive increased knowledge and health-promoting behaviours [2] Authors argue that people who have poor levels of oral health literacy have poor dental health knowledge, increased dental visits and severity of oral health disease [11‐13]. In the United States, the National Institute of Dental and Craniofacial Research (NIDCR) lobbied strongly for a focus on oral health literacy, arguing that poor oral health literacy is widespread and a causal factor in disparities in the oral health status between groups with high levels of oral health literacy and those without [3].

A scoping review was undertaken to identify what tools or instruments currently exist that measure oral health literacy across a range of different population groups. Scoping reviews are useful to map, collate and summarise existing literature on a topic and can assist researchers to identify the nature and extent of the current research evidence. Unlike systematic reviews, the focus of a scoping review is not on the assessment of the quality of the research [37] rather, the approach supports identification of a broader range of literature, including all types of study designs [38]. The work of Arksey and O’Malley [38] provides a useful methodological framework for scoping reviews. For this study, we adopted their five-stage approach: identifying the research question; identifying relevant studies; study selection; charting the data; and collating, summarising and reporting results.

As outlined in Tables 2 and 3, the scoping review identified several oral health literacy tools that have been used since 2007. The most frequently used are those based on the Rapid Estimate of Adult Literacy in Medicine (REALM) developed by Davis and colleagues in 1993 [32]. Adaptations to measure oral health literacy include REALD 99 [43], REALD-30 [44‐46], REALM-D [46, 48], and most recently, REALMD-20 [48]. The REALD tools are essentially word recognition tests that consist of dental terms from the American Dental Association Glossary of Common Dental Terminology and patient education materials [44‐48]. The tools have reportedly shown to be valid and reliable in measuring word recognition. Adding 69 new words to REALD-30, thereby creating REALD-99, did not improve results sufficiently to justify extending the list of dental words [43]. Gironda and colleagues [49] developed a shortened version, REALMD-20, for clinicians to detect limited medical/dental health literacy in patients attending for treatment in dental/medical clinics. The authors acknowledge that the tool is useful for measuring the reading ability of patients and whilst not an effective measure of comprehensive health literacy, it does provide clinicians with a useful tool to use as a screening instrument.

The other popular oral health literacy tool identified in the review is based on the Test of Functional Health Literacy in Adults (ToFHLA) [33], a widely used measure of health literacy. This instrument, the Test of Functional Health Literacy in Dentistry (ToFHLiD), was developed by Gong and colleagues [50] and consists of a 68-item reading comprehension section and a 12-item numeracy section. Initial validation of ToFHLiD showed a low internal reliability but a strong convergent validity since the ToFHLiD scores were highly correlated to the REALD-99 scores. In addition, ToFHLiD showed a moderate ability to discriminate between dental and medical literacy. Despite these limitations it is often used in conjunction with other tools designed to measure oral health literacy levels (see Table 3).

In more recent years a variety of other oral health literacy measurements tools have been developed. The Oral Health Literacy Instrument (OHLI) was developed by Sabbahi et al. [11] for use with adult dental patients. This tool (like the ToFHLA) contains both reading comprehension and numeracy sections. The reading comprehension is a 38 item test with words omitted from one passage on dental caries and another on periodontal disease. The numeracy section has 19 items to test comprehension of directions for taking common prescriptions associated with dental treatment, post extraction instructions and dental appointments. Sabahhi and colleagues added an oral health knowledge test to the tool that was designed to evaluate the patients’ general dental knowledge to be used as a predictor of functional health literacy. The knowledge test consists of seven pictures depicting 17 labelled items such as perioral and intra-oral structures, oral diseases and conditions, dental fillings, a dental prosthesis, and different oral hygiene aids. To complete this test patients were asked to match the pictures to the words. Used with a sample of 100 patients it was shown to be a valid and reliable instrument when compared to other OHL tools. The authors acknowledge that the OHLI measures the patient’s ability to perform oral health literacy-related tasks that require reading, comprehension and numeracy skills and whilst it provides a useful estimate of these abilities it does not capture the full complement of literacy skills. The authors conclude that more work is needed to investigate the instrument’s predictive validity and sensitivity to change using oral health outcomes with population groups known to be at high risk of low functional oral health literacy [11].

In 2010, Macek [51] and colleagues used a combination of the REALM, the Short Test of Functional Health Literacy in Adults (Short-TOFHLA) and later a new survey they developed to explore conceptual oral health knowledge [52]. These were administered to 100 adults in Baltimore. The respondents were also asked about socio-demographics, dental health, and utilization of dental services. Psychometric analysis was used to identify a subset of oral health knowledge questions from the new survey instrument. The resulting Comprehensive Measure of Oral Health Knowledge (CMOHK) was categorized into three levels of knowledge (poor, fair, good). This preliminary study yielded a new measure of oral health conceptual knowledge, available for use in future oral health literacy studies.

Similarly many researchers interested in exploring oral health literacy with low income populations have utlised the REALD-30 and oral hygiene behaviours to investigate the association of female caregivers’ oral health literacy with their knowledge, behaviours and the reported oral health status of their young children [13, 45, 51‐56] . The sample for these studies were drawn exclusively from those enrolled in the Women’s Infants and Children’s (WIC) supplemental nutrition program in North Carolina.

Few tools had been adapted for specific populations or cultural groupings. The Hong Kong Rapid Estimate of Adult Literacy in Dentistry (HKREALD-30) [57, 58], the Hong Kong Oral Health Literacy Assessment Task for Paediatric Dentistry (HKOHLAT-P) [56, 58‐60], and the Oral Health Literacy Assessment-Spanish (OHLA-S) [54] are exceptions. Other tools have been adapted for use with specific cultural groups [34, 54‐66]. A recent study by Parker and Jamieson [34] used REALD-30 and oral health literacy-related outcome associations to calculate risk indicators for poor self-reported oral health among rural-dwelling Indigenous Australians. This study aimed to determine the relationship between oral health literacy, as assessed by REALD-30 and oral health literacy-related outcomes. The researchers identified individuals’ oral health knowledge, oral health self-care and utilisation of dental services, to determine if these factors (often measured in existing tests of oral health literacy) are risk indicators for seven domains of poor self-reported oral health. Parker and Jamieson acknowledge the shortcomings of REALD-30 particularly that it measures word recognition only, with no test of comprehension or functional oral health literacy. The authors initially included questions from the TOFHLiD, as an attempt to measure broader aspects of oral health literacy, including reading comprehension and numerical ability but these were removed after trialling with the Indigenous reference group, members of which identified a potential lack of acceptance within their community. The researchers note that some participants felt uncomfortable with the instrument, feeling like they were being “tested” and “judged” [34]. The findings of this study confirmed that those with poorer oral health literacy, as measured by REALD-30, had poorer oral health knowledge and engaged in more harmful oral health behaviours.

Seeking to develop a reliable, valid and culturally appropriate instrument to assess oral health literacy among vulnerable groups, Jones et al developed the Health Literacy in Dentistry scale (HeLD). Using the Health Literacy Measurement Scale (HeLMS) as a foundation, a number of theoretical constructs were included which assume “a person’s ability to seek, understand and use oral health information is important in being able to access and benefit from oral health care services” [63]. The HeLD has eight domains which mirror those used in the HeLMS. The HeLD accounts for the multidimensional nature of oral health literacy and encompasses the domains of communication, access, receptivity, understanding, utilisation, support and economic barriers which have all been shown to impact on oral health status. The results of a HeLD pilot with 209 Indigenous adults highlight the potential for using the instrument across a variety of health care settings whilst “still allowing reliable international comparisons to be made” [63:6]. The researchers state that results of studies utilising this tool will be of interest to all those working on OHL measurement with both marginalised and mainstream groups [63].

Sistani and colleagues [64‐66] developed and pilot tested an Oral Health Literacy Adults Questionnaire (OHL-AQ) which they state is valid and reliable. The OHL-AQ comprises four sections: reading comprehension, numeracy, listening, and decision-making. This tool was developed to address limitations of existing oral health literacy instruments, including their length, lack of generalizability across populations, and their focus on measuring either the ability of a person to read specific dental health vocabularies or the ability to read and comprehend oral health information and calculate numbers. Their aim was to develop a generic oral health literacy instrument for adults that included measures of listening and appropriate decision making. They argue that the OHL-AQ is a valid and reliable instrument for the functional assessment of adults’ oral health literacy in community or population-based studies and because it is short and easy to use, could be used in clinical or research settings to improve oral health-related literacy skills and dentist–patient communication. The authors conclude that adding two new measures (listening and decision-making) improves the performance and quality of the existing instruments. They highlight that future research should include a larger population, in order to demonstrate the determinants of oral health literacy, particularly amongst those with limited general literacy skills.

The most widely used oral health literacy measurement tools are based on either the REALM or the TOFHLA. Findings from this scoping exercise confirm our findings from preliminary scans that the majority of tools are heavily biased towards word recognition, numeracy and reading skills, rather than what this means in terms of health behaviours and service utilisation. More recent developments have attempted to incorporate other aspects considered important, including decision making and possibly service navigation. The incorporation of these aspects should increase the validity of these tools as a measure of oral health literacy in its broader sense incorporating communicative/interactional and critical levels however formal validation work is required. In addition further work is required to develop tools adapted for specific populations tested to ensure acceptability and cultural competence. Lastly tools that are developed should be able to be used to determine risk and/or be sensitive enough to measure changes resulting from interventions.