This propensity score matching, multicenter, cross-sectional study explored the effects of various prosthetic treatments for KCIPE on oral hypofunction, subjective frailty symptoms, and oral health-related QOL among dental clinic outpatients. Compared with the RPD group, the ISFP group exhibited superior oral function, fewer subjective symptoms, and better oral health-related QOL, revealing how prosthetic methods affect these parameters.
The choice of ISFP or RPD for a patient with KCIPE is based on that patient's oral status, living situation, general condition, economic status, and personal preferences (3). To our knowledge, this study is the first to provide clear evidence concerning the therapeutic efficacies of ISFP and RPD in patients with KCIPE.
The present results are highly accurate because we specified the defect types and explored the effects of prosthetic methods on those defects. The multicenter design ensured a large sample size and avoided bias. Although the cross-sectional nature of the study precluded random assignment and may have introduced confounding factors, propensity score matching enabled estimation of causal effects by adjusting for biases that could influence the findings.
Sample sizes after propensity score matching vary among studies because of population-related differences in propensity scores. Prior to study completion, we could not predict the sample size after propensity score matching. However, after propensity score matching, we performed sample size analysis using G* Power software (version 3.1.9.4); we assumed that the mean difference in QOL score between ISFP and RPD groups would be 0.82, based on previous findings (8). The analysis revealed that the minimum sample size was N = 42 [alpha, 0.05; beta, 0.05 (95% power)], indicating that our sample sizes were sufficient.
Factors affecting post-treatment oral function (e.g., masticatory function and occlusal force) include clinical difficulty. In the treatment of partially edentulous patients, Prosthetic treatment difficulty indices developed by the Japan Prosthodontic Society indicate that, among partially edentulous patients, it is most difficult to treat patients with KCIPE who display premolar and molar defects (28). In the present study, we did not specify the defect size. The participants were patients who had been fitted with a dental prosthesis for ≥ 1 year and had undergone regular maintenance treatment without problems. Therefore, we suspect that pre-treatment clinical difficulty levels were randomized via propensity score matching. However, confounding bias cannot be excluded with respect to factors that were not regarded as covariates when calculating propensity scores. Additionally, the present study did not include participants with substantial impairment concerning physical function or oral function, which may limit the generalizability of the findings.
To our knowledge, few clinical studies have compared ISFP wearers and RPD wearers (5–8). Akagawa et al. used electromyography to examine chewing function during RPD wear and ISFP wear in patients with Kennedy Class II partially edentulous mandibles; they found that ISFP wearers had greater masticatory muscle activity and better masticatory function, compared with RPD wearers (5). Kapur et al., Kuboki et al., Furuyama et al., and Kurosaki et al. reported that ISFP wearers had better oral health-related QOL than RPD wearers in studies of patient-oriented outcomes (6–9). Yamazaki et al. observed earlier loss of adjacent teeth to intended edentulous space in RPD wearers than in ISFP wearers (10, 11). However, these studies were limited to patients with Kennedy Class II partially edentulous arches or patients with unspecified defect status, limiting their generalizability to the selection of optimal prosthetic treatments for KCIPE. In the present study, seven types of oral function were comprehensively evaluated in patients with KCIPE; the results showed that odds ratios for oral hypofunction in the RPD group were 2.06 (compared with the NT group) and 4.67 (compared with the ISFP group). Although the comparison groups were not identical, these results suggest that ISFPs are effective for the prevention of oral decline in patients with KCIPE.
Aspects of oral function, such as the number of remaining teeth and chewing ability, are associated with oral health-related QOL (29–31). Therefore, oral health maintenance is essential for improving oral health-related QOL. In the present study, comprehensive assessments of oral function revealed that RPD group had significantly worse results concerning multiple aspects of oral function compared with the other groups; it also had significantly lower oral health-related QOL. Kodama et al. investigated the relationship between oral hypofunction and oral health-related QOL in community residents aged ≥ 65 years (32); they found that oral health-related QOL decreased as the number of functional impairments increased, consistent with the present results.
In previous cohort studies involving community residents, the incidences of oral hypofunction ranged from 42.7–62.9% (21, 33–35). Hatanaka et al. reported that the incidence of oral hypofunction was 63.4% among older outpatients in a university hospital (36). Ozaki et al. reported that the incidence of oral hypofunction was 89.8% among older people requiring nursing care (37). In the present study, the RPD group had the highest incidence of oral hypofunction (28%); this value is considerably lower than the values in previous reports. These findings suggest that the incidence of oral hypofunction varies according to the characteristics of the study population. The low incidence of oral hypofunction in the present study may be attributed to the patients’ regular management at dental clinics, as well as the exclusion of patients undergoing dental treatment or displaying substantial functional decline.
Oral frailty reportedly involves slight declines in oral function, such as decreased tongue movement, food spillage, and mild choking (20). Kugiyama et al. reported that oral frailty was a risk factor for physical frailty and death in a longitudinal study of community-dwelling older adults (15). There is evidence that oral frailty and oral hypofunction have many overlapping aspects and cannot be easily distinguished (20). To our knowledge, no previous study used questionnaires to assess subjective symptoms of oral hypofunction. In the present study, we used an existing questionnaire (24) to investigate subjective symptoms of physical and oral frailty. This questionnaire was previously used by Hihara et al., who reported that oral frailty tended to increase with age in a population of 1214 individuals (24). Our analysis involved propensity score matching to adjust for age differences among groups; thus, we could not assess the relationship between age and subjective symptoms of frailty. However, our results indicated that scores concerning subjective symptoms of frailty and oral health-related QOL were similar to the incidence of oral hypofunction. These results highlight the importance of regular management and maintenance of oral function, with attention to subjective symptoms of frailty and oral health-related QOL; such efforts can facilitate early detection of oral hypofunction.