This study evaluates the OHIDL transition scale’s longitudinal validity and reliability. The results show that the transition scale is sensitive to change over time and possesses good longitudinal validity and reliability. After receiving dental treatment, older adults perceived fewer oral health problems and positive changes in oral health impacts on daily living.
Considering the subjectivity of quality of life assessment, people may refer to various internal reference systems when they answer the same question. Because individuals’ circumstances may change with time, the basis on which the individuals make a QoL judgment may also change [44]. Response shift refers to a change in the meaning of one's evaluation of a construct as a result of a change in one's internal standards of measurement, a change in one's values, or a change in one's definition of the construct [45]. Individuals who are coping with an illness may value health states differently throughout the course of the disease or treatment. QoL measures currently used in clinical research are not designed to account for response shifts but assuming that people would respond consistently on the measurement scales and that scales are directly comparable across individuals and over time [46]. Considering the response shift, assessing change in OHRQoL with prospective measurements, such as change score, may cause biases to estimate the treatment effect. As a result, conventional prospective assessments of change based on self-reports may overestimate or underestimate the intervention or the effect of illness [47, 48].
This study tried to evaluate the change in OHRQoL through a transition scale retrospectively. When people talk about a situation to be “better” or “worse”, the meaning may also differ from person to person. Being better is not only reflected in changes in the state of the disorder (resolution) but could be an adjustment of life to work around the disorder (readjustment) or an adaptation to living with the disorder (redefinition) [49]. Thus, people may respond differently over time, not only because their quality of life has changed due to disorder or treatment but also because they may have changed their views on what quality of life means to them. This consideration is important for assessing treatment outcomes, as changes in quality of life may reflect response shift, treatment effects, or a complex combination of the two. When the transition scale is used as the outcome measurement to retrospectively evaluate the change in OHRQoL as an evaluation of the effectiveness of a certain treatment, it is necessary to interpret the results with caution and not to exaggerate or underestimate the treatment effect. Study design with control groups and incorporating the objective clinical indicators would be needed [50]. Besides, some researchers suggest adding qualitative questions following the transition questions, such as asking "why do you report being <better, worse or about the same>?" to further explore the reasons for answering and identify the root causes of the changes [51].
In this study, the global rating of change in perceived oral health impacts was used to compare the transition scale's longitudinal validity and the change score. It was considered an indicator and served as an anchor for the overall change in OHRQoL. Compared to the change score, the transition scale had better agreement with the global rating’s change categories, as higher positive correlations with the global rating were found. However, the relationships with global rating were not that obvious for the change score. The transition scale also had larger diversity among different global rating categories, indicating higher sensitivity than the change score in terms of detecting change.
When the OHIDL change score is zero, there is no change in OHRQoL or the change cannot be reflected due to the ceiling/floor effect. In this study, 13% of the participants reported having perceived no oral health impacts on their daily lives at baseline, and 31% of the participants reported low oral health impacts with an intensity score of less than 5. For participants with low impact at baseline, the OHIDL transition score showed positive change after treatment, while the change score detected no difference. After treatment, deterioration in oral health impacts was detected by using the change score for the participants who reported no impact before dental treatment. This observation may be explained by the ceiling/floor effect, which is viewed as the change score’s methodological flaw. The improvement cannot be captured by the change score when individuals already reported the lowest possible value of impacts at the baseline. In this situation, OHRQoL is only “allowed” to remain stable or deteriorate over time. In contrast, employing the transition score allows an individual to report improvement after receiving dental treatments regardless of the status of the perceived impact before treatment [10].
Interpreting the change data would be more confident with the transition scale as it includes the individual’s subjective valuation. It would solve the difficulty of what degree of change is necessary to be considered meaningful. Post-OHIP has been developed to use the transition scale to assess change in OHRQoL and assess the effectiveness of prosthodontic treatment [32, 33]. Post-OHIP consisted of 14 items, and the responses were recorded into three categories: “better”, “equal” and “worse”. Compared with post-OHIP, the change in OHRQoL in the OHIDL transition scale was evaluated in a 7-point Likert scale in this study. Considerable variation was found among “a little improvement”, “moderate improvement” and “a great improvement” suggesting it is more sensitive in quantifying the magnitude of change.
The effectiveness of dental treatment can be measured through different indicators, e.g., reduction in oral health problems, improvement in OHRQoL or satisfaction with treatment. In this study, participants who reported fewer oral health problems at baseline had higher transition scores at the follow-up, indicating the dental treatments’ positive effects. However, after dental treatment, a high proportion of participants were still reporting food catching (72.7%) and missing teeth (40.3%), which was only slightly lower than those found at baseline, indicating potential treatment needs. Many of the low-income study participants received dental treatment funded by the Comprehensive Social Security Assistance (CSSA) provided by the Hong Kong SAR government. The treatment plans were restricted by the limited funding regardless of the treatment need. As a result, these older adults usually chose to receive simple dental treatments, such as scaling, filling and extraction that could be covered by the CSSA and to avoid paying the high costs of advanced dental treatments out of their own pockets. Alternatively, some participants may choose to leave these oral health problems unsolved, possibly because the problems were not severe enough to affect OHRQoL. The findings highlight dental neglect among Hong Kong older adults, which is widespread and associated with socio-demographic factors and OHRQoL [52]. People can live with chronic oral health problems without seeking any dental treatment. The dental neglect continues until the accumulative eating function impairment can no longer be coped with, i.e., the problems are severe enough to affect OHRQoL. A previous study found that adults in Hong Kong were more prepared for tooth loss than adults in the UK [53]. This may be because they have developed a set of strategies to cope with various life stresses and strains [54]. Another possible reason is that the emotional effects of tooth loss are not marked among older adults in Hong Kong [55]. The negative oral health impacts can be minimized through psychological adjustments, such as changes in expectations, lifestyles and living environment, and using dental devices [56].
Around two-thirds of the participants in this study were satisfied with the dental treatment they received. A significantly higher transition score was only observed among patients who felt very satisfied with the treatment received. The treatment satisfaction indicators and change in OHRQoL imply different measurement outcomes, which can dramatically change the conclusion of the treatment effectiveness. Patients may not be satisfied with the received treatment even if there is an improvement in OHRQoL, although these two factors tend to be significantly associated with one another [57]. Treatment satisfaction can also be influenced by many factors, e.g., the quality of health care, access, and treatment cost [58]. Despite the high level of treatment satisfaction, the perceived change in OHRQoL after dental treatment was low, with over 50% of the study participants reporting no change on each item. The low perceived oral health impacts at baseline may be one reason for this. Items in the “Social” domain showed the smallest change, consistent with previous studies that Chinese older adults reported a low level of social impacts [36,37,38]. It is not surprising to find the social domain showed the smallest change after the study participants received dental treatment. Another reason is that the common treatments the participants in this study received were relatively simple procedures, and only a few participants received prosthodontic or other advanced treatments. This finding is expected in Hong Kong older adults, mainly because of the expensive cost of comprehensive dental treatment.
Findings in this study highlight the effectiveness of endodontic treatment in improving the OHRQoL of older adults, and likely, the teeth that required endodontic treatment were heavily broken down and painful. The success of this treatment removed the pain and restored function, which had significantly improved the OHRQoL. Note that the treatments were not mutually exclusive, i.e., older adults who received advanced treatment may also have received some simple treatments. Thus, the more significant improvement as observed in these older adults may be attributed to the combined treatment effect. Since more than half of the participants had received multiple treatments, the interaction effect existed between individual treatment items. The co-existence of multiple treatments may confound each type of dental treatment’s effectiveness. However, limited by the sample size, it was not practical or feasible to explore all the combinations in this study. Future studies should be conducted to investigate the effectiveness of specific dental treatment in improving OHRQoL using the OHIDL in a controlled setting.
This study has several limitations. First, the study participants were recruited from four dental clinics run by NGO, it was a convenience sample and might not be representative. Second, the small number of study participants who had received complex dental treatment may affect the accuracy of the study results. A deliberate study design with a larger sample size and including older adults with more diverse socio-demographic backgrounds from a representative sample is demanded in future study. Third, this study was also limited by the repeated interviews for the test–retest reliability which were carried out right after the follow-up interview, instead of after some time, e.g., several days or a week later. Since the follow-up data were collected in individual home visits, it would be disturbing to approach the participants one more time. Although the test–retest information could also be collected through other ways, such as telephone interview, there could be a risk of bias because of the change in the mode of administration. Because of time constraints and being burdensome for the older adults to repeat answering all the items in the OHIDL transition scale, only five items were randomly selected (different items were selected in the different repeated interviews) for duplication during the follow-up evaluation. Although the test–retest reliability was evaluated for each item only instead of the whole scale, it is believed the result still supports the reliability of OHIDL. Future studies may consider carrying out the duplication with a longer time interval. However, caution needs to be taken when choosing the time interval because OHRQoL is a dynamic concept, and respondents’ perceptions can quickly change based on their expectations and experience [59].