This study demonstrated that individuals' perception of chewing ability is substantially related to oral health-related quality of life in partially dentate patients. More specifically, higher chewing function scores were associated with lower OHIP-J14 summary scores, reflecting that better perceived chewing ability is associated with better OHRQoL. This correlation has been observed previously among older nonpatient populations. Using the Oral Impacts on Daily Performance instrument, Kida et al.  showed that older adults in nonpatient populations with reduced posterior occlusion were four times more likely to have problems with chewing all food, and twice as likely to report any impairment of daily performance, than their counterparts with intact posterior dentition. Brennan et al.  also reported a significant association between chewing ability and OHRQoL as measured by OHIP-14 in a population-based sample (random sample, n = 879, age range 45-54). Oral conditions such as infected or sore gums, loose teeth, toothache pain, and fewer functional tooth units have been reported to be associated with onset of chewing difficulty . Our results are in line with this study, because our participants were sampled at a prosthodontic clinic where a majority of them had oral health problems related to tooth loss or dentures. Therefore, based on evidence from different settings and populations, chewing ability seems to have a consistently significant impact on OHRQoL.
It was expected that chewing ability would be related to specific oral health impacts that are directly related to eating, such as "uncomfortable to eat any foods," "diet has been unsatisfactory," and "had to interrupt meals." In our study, the chewing function score was indeed significantly correlated with these three OHIP items, and we observed the highest correlations between chewing function scores and OHIP items for these items, except for a similarly high correlation observed for the item "trouble pronouncing any words." However, the chewing function score was also significantly correlated with all other OHIP items, including psychological dimensions such as "difficult to relax" and "been a bit embarrassed." This finding suggests that chewing difficulty has the potential to have direct or indirect (i.e., because of the correlation with other oral problems) impacts on psychological and social dimensions of oral health. It has been suggested that such effects may be mediated through limitation of food choice and enjoyment of meals and diet .
The number of teeth as the major physical characteristic of oral health has previously been reported to impact both chewing ability and OHRQoL in prosthodontic patients . However, in the current study, when correlations between perceived chewing ability and OHRQoL were separately calculated for two populations of participants based on the number of teeth, the correlation between both constructs basically remained unchanged. This result suggests that correlation between perceived chewing ability and OHRQoL is not due to the number of teeth a patient has - a finding which is consistent with the study by Brennan et al. . However, when calculated in groups of patients with different denture status, correlations differed more. The findings are exploratory because of the small number of subjects in the groups and the number of analyses performed.
Interestingly, the correlation between perceived chewing ability and OHRQoL did not change much across the two age strata we examined, although age has been associated with chewing ability  and OHRQoL [31, 32] in previous studies. On the other hand, we observed that the correlation between both constructs was different in men and women and in two categories of years of schooling, with the male patients and those patients with higher years of schooling having the stronger correlations. Although the reasons for these differences were not further explored in the present study, these findings suggest that nonclinical characteristics influence how patients' perceived impaired chewing ability is related to overall perceived oral health, as measured with the concept of oral health-related quality of life.