Assessing oral health-related quality of life in general dental practice in Scotland: validation of the OHIP-14

Abstract – Objectives: To validate the Oral Health Impact Profile (OHIP)-14 in a sample of patients attending general dental practice. Methods: Patients with pathology-free impacted wisdom teeth were recruited from six general dental practices in Tayside, Scotland, and followed for a year to assess the development of problems related to impaction. The OHIP-14 was completed at baseline and at 1-year follow-up, and analysed using three different scoring methods: a summary score, a weighted and standardized score and the total number of problems reported. Instrument reliability was measured by assessing internal consistency and test–retest reliability. Construct validity was assessed using a number of variables. Linear regression was then used to model the relationship between OHIP-14 and all significantly correlated variables. Responsiveness was measured using the standardized response mean (SRM). Adjusted R2s and SRMs were calculated for each of the three scoring methods. Estimates for the differences between adjusted R2s and the differences between SRMs were obtained with 95% confidence intervals. Results: A total of 278 and 169 patients completed the questionnaire at baseline and follow-up, respectively. Reliability – Cronbach's coefficients ranged from 0.30 to 0.75. Alpha coefficients for all 14 items were 0.88 and 0.87 for baseline and follow-up, respectively. Test–retest coefficients ranged from 0.72 to 0.78. Validity – OHIP-14 scores were significantly correlated with number of teeth, education, main activity, the use of mouthwash, frequency of seeing a dentist, the reason for the last dental appointment, smoking, alcohol intake, pain and symptoms. Adjusted R2s ranged from 0.123 to 0.202 and there were no statistically significant differences between those for the three different scoring methods. Responsiveness – The SRMs ranged from 0.37 to 0.56 and there was a statistically significant difference between the summary scores method and the total number of problems method for symptomatic patients. Conclusions: The OHIP-14 is a valid and reliable measure of oral health-related quality of life in general dental practice and is responsive to third molar clinical change. The summary score method demonstrated performance as good as, or better than, the other methods studied. There is an increasing recognition that oral disorders can have a significant impact on physical, social and psychological well-being. This has resulted in a greater clinical focus on quality of life improvement as a major, if not a primary outcome of dental care, and has led to the development of a number of instruments that aim to measure dental outcomes in terms of the impact of changes in oral health on quality of life. Among these, the short form of the Oral Health Impact Profile (OHIP), is emerging as a powerful tool in the assessment of Oral Health-Related Quality of Life (OHRQoL). The short form version (OHIP-14) consists of 14 items organized in seven sub-scales, which address aspects of oral health that may compromise someone's physical, psychological and social well-being (1). The original 49-item OHIP was developed by Locker and Slade (2) and based on Locker's conceptual model of oral health (3) and includes seven domains namely: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. Since its development, the OHIP-14 has been preferred to the OHIP-49 by a number of researchers due to its practicality. A considerable body of evidence now exists on the validity and reliability of the OHIP-14 in a number of hospital settings and dental conditions, including surgical removal of impacted molars (4), elderly partially edentulous and complete edentulous patients seeking dental rehabilitation (5), and oral lichen planus (6). Three different scoring methods have been reported in studies using the OHIP-14: a summary OHIP-14 score (which is expressed as the sum of the seven raw sub-scale scores on a scale from 0 to 4 where a high score signifies worse OHRQoL); a weighted and standardized summary score (where weights are attributed to every question within the domain); and the total number of problems reported (i.e. occasionally, often, or very often with a possible range of 0–14 problems) (1, 7). Only one study has specifically assessed the validity of the OHIP-14 in a UK context (8). Robinson et al. found that the OHIP-14 (using the summary score) demonstrated superior validity to another oral health-related quality of life measure, the Oral Impacts on Daily Performance (OIDP), when used in a dental hospital setting. However, the authors did not assess instrument reliability and responsiveness. There have not been, to date, reports on the validation of the OHIP-14 on a UK-based sample of patients attending general dental practice. The OHIP-14 was used in the 1998 UK Adult Dental Health Survey, which sampled over 5000 members of the general UK population (9). This study provided good indirect evidence for the validity of the OHIP-14 in general dental practice, but general populations are not necessarily representative of general dental practice attenders. In addition, no rigorous formal validation of the OHIP-14 was reported in the UK Adult Dental Health Survey, and only one scoring method (the total number of reported problems) was used. Convincing evidence for the validity and reliability of the OHIP-14 in general dental patients is essential if the instrument is to be used to measure OHRQoL in primary care research and practice in the UK. Responsiveness, or the ability of a health status measurement tool to detect clinically important changes over time is a critical requirement of an outcome measure (10) (and indeed, the OHIP-14 was originally intended to assess long-term effects on OHRQoL). To date, little evidence exists for the responsiveness of OHIP-14 to clinical change over time. Recently Locker et al. (11) assessed the responsiveness of the OHIP-14 over a 1-month period in a dental care programme for the elderly using several formal statistical methods. They concluded that in this context the OHIP-14 was able to detect modest change in OHRQoL and that relatively large samples would be required to detect minimally important clinical differences (defined as five-point scale). The Scottish Molar Actuarial Life Table Project (The Scottish MALT Project) is a longitudinal observational study looking at the natural history of lower impacted wisdom teeth. Patients with pathology-free impacted third molars were recruited from general dental practices in Tayside, Scotland and were followed for a year to assess clinical pathological changes and development of symptoms associated with impaction. Despite the publication of several studies and guidelines (12–14) on the management of impacted wisdom teeth, controversy still exists over whether retained asymptomatic impacted lower wisdom teeth will remain symptom-free. Also, these guidelines state that not all previously asymptomatic teeth that develop symptoms should be removed, but no assessment has been reported of the impact that the retention of impacted third molars will have on OHRQOL. The design of the Scottish MALT study provided the perfect opportunity to assess for the first time not only the validity and reliability of the OHIP-14 in a primary care setting but also whether or not this measure is responsive to changes in the clinical status of impacted wisdom teeth over a 1-year period.