Introduction

Population aging has shifted attention from the absence of disease toward the preservation of functional ability, psychological well-being, social participation, and quality of life in later life [1]. Within this broader perspective, oral health is increasingly understood as more than the presence or absence of dental disease. Contemporary frameworks conceptualize oral health as a multidimensional domain encompassing physical, psychological, and social functioning [2,3]. Oral health-related quality of life (OHRQoL) captures the perceived effects of oral conditions on everyday functioning, comfort, emotional well-being, and social participation, thereby complementing traditional clinical indicators [4,5].

Oral difficulties may affect chewing, speaking, smiling, facial expression, and confidence in interpersonal situations. Previous research has associated poorer oral health or OHRQoL with functional decline, depressive symptoms, psychological distress, shame, reduced resilience, lower self-care engagement, and social withdrawal among older adults [6-11]. Taken together, this evidence establishes the psychosocial relevance of OHRQoL without implying that oral health alone determines these broader outcomes.

Sleep represents another multidimensional component of healthy aging and is shaped by interacting biological, psychological, and social factors [12,13]. Sleep disturbances are common in later life and have been associated with chronic health conditions, emotional distress, cognitive difficulties, and reduced quality of life [14,15]. Daytime napping is also frequent among older adults and may reflect age-related, behavioral, compensatory, or broader health-related processes [16]. Its interpretation therefore requires caution, particularly when information on nap duration, timing, intentionality, and underlying reasons for napping is unavailable. Emotional loneliness, defined as the perceived absence of close emotional attachment and relational security, has consistently been associated with poorer subjective sleep outcomes [17-20]. Beyond its association with sleep, loneliness has also been linked to cognitive decline and an increased risk of dementia in later life, underscoring its importance as a broader adverse health concern among older adults [19]. These findings provide a rationale for examining emotional loneliness alongside OHRQoL and sleep indicators.

Dream recall frequency represents a narrower and less well-established aspect of sleep-related experience. Previous research has examined dream activity in relation to emotional and cognitive processes [21,22], while the frequency of dream recall has been shown to vary according to individual, attentional, and contextual factors [23,24]. It was included in the present study as an exploratory subjective nocturnal variable rather than as an outcome for which a direct oral-health mechanism was hypothesized. We examined whether the associations of OHRQoL with broader sleep-related and psychosocial experiences extended to this additional domain. No direct causal pathway from OHRQoL to dream recall was assumed. Moreover, recall frequency does not capture dream content, emotional tone, vividness, or the broader experience of dreaming.

Although OHRQoL has been linked to psychological and social well-being, and substantial research has examined sleep in older adults, emotional loneliness, subjective sleep indicators, and dream recall frequency have rarely been studied together in relation to oral health. Guided by the biopsychosocial model [25] and the literature reviewed above, the following theory-guided hypotheses were examined: (H1) better OHRQoL would be associated with lower emotional loneliness; (H2) better OHRQoL would be associated with greater sleep sufficiency, better subjective sleep quality, and less frequent daytime napping; (H3) greater emotional loneliness would be associated with poorer subjective sleep quality and lower sleep sufficiency; and (H4) OHRQoL would remain positively associated with sleep quality after adjustment for age, gender, and emotional loneliness. Because evidence concerning OHRQoL and dream recall was limited and no direct explanatory mechanism was specified, analyses involving dream recall frequency were treated as exploratory rather than hypothesis-testing. These hypotheses were theory-guided but were not preregistered and should therefore not be interpreted as strictly confirmatory.