This study revealed how having, caring for and having preserved natural teeth in general improved the quality of life of frail older people through a sense of achievement, pride, a sense of control, intactness, oral function, comfort and appearance. We identified a not previously documented response, especially by severely frail people with chronic pain, that involved clinging to an intact body part (natural teeth) as a means to preserve self-worth, in particular through pride, a sense of control, and a sense of intactness. This is also the first study to indicate how particular frailty aspects (chronic pain and impaired fine motor skills) and the degree of frailty modify the relation between QoL and having natural teeth.
Both quantitative studies [25, 26, 30, 42, 43] and qualitative studies [28, 29] have identified the positive contribution of natural teeth to QoL, but only MacEntee and his collaborators  have addressed this contribution in some detail. Their observations largely correspond with ours, but, as natural teeth were not the focus of their research, they did not provide a comprehensive analytical context and identify specific factors that reflect the value of having natural teeth, or identify the positive effect of natural teeth on self-worth and personal identity, as we did.
Strengths and limitations of the study
One of the strengths of our study is that its design enabled differentiation between participants with different levels and characteristics of frailty. Hence we were able to compare responses between people of different degrees of frailty and with different frailty characteristics, even though comparisons based on frailty characteristics did not reveal obvious differences other than those related to chronic pain and impaired fine motor skills.
By focusing on natural teeth and its contribution to QoL in 38 lengthy interviews, we were able to cover the subject in more depth than previous studies that focused on oral health in general. Moreover, by explicitly asking what constituted QoL for the respondent before asking about the contribution of natural teeth to QoL, we could explore the value of natural teeth to QoL domains that were deemed important by the participant.
Apart from chronic pain and loss of fine motor skills, loss of cognitive function is probably another strong, frailty-related, influence on oral health related QoL , but our interviews were limited to elders who were cognitively alert. Nor did we include edentulous people because we were primarily interested in the value of natural teeth to QoL of frail elders. However, older people without natural teeth could add insight to the value of having natural teeth by comparing their experiences before and after tooth loss, an experience that is generally but not always unpleasant [28, 31, 33]. We looked at coping and adaptation, which we expected to be the most relevant personal aspects in relation to our study aims, but not at other personal traits like neuroticism, extraversion, and openness, which may  or may not  influence dental perceptions. Likewise, in our analysis, we did not account for socio-economic status (SES), even though there is evidence that higher SES has a positive influence on OHrQoL [46, 47].
The influence of cultural background could not be comprehensively evaluated, since our study included only two people from non-European heritage, which was due to the lack of non-European dentulous elderly who live in assisted living homes or frequent daycare centers in East-Netherlands.
Meaning of the study: possible explanations and implications for research
The impact of achievement and pride, intactness and sense of control in relation to having natural teeth seemed to be the most obvious for severely frail, institutionalized people. This impact can be understood with help of social comparison theory  and a theoretical model from educational psychology: The internal/ external frame of reference model . According to this model, students base their self concepts on two simultaneous sets of comparisons. The internal comparison (or “frame of reference”) includes an individual student’s appraisal of competence in one academic area compared to his or her competence in other academic areas. The external comparison is the student’s appraisal of his or her competence in that academic area relative to the perceived ability of peers, following social comparison theory.
Likewise, our participants, by attributing value to having natural teeth, compared their oral status both externally with their peers and internally to other health areas e.g. their own mental health or motor abilities. For the most severely frail dentulous elderly, both external and internal comparisons are likely to contribute more to a concept of self in a positive way , than for slightly frail or non-frail dentulous elderly. The severely frail, especially if they are institutionalized, are more often surrounded by other severely frail people, who are more likely to be toothless than less frail or non-frail elders . Hence, when severely frail dentulous elders compare themselves to their, mostly edentulous, peers (external comparison), they feel more special since they are one of the very few who still have natural teeth.
Making an internal comparison, people value their dental status in comparison to other health areas. Dentulous frail older people realize that their teeth have remained in relatively good condition while other parts of their body have declined. When the decline in other health areas is more severe, the contrast with healthy teeth is even greater, and teeth can contribute even more significantly to self-worth.
In contrast, the experiences of increasing frailty can help prepare people to cope and accept tooth loss, which corresponds with current beliefs about coping resources and declining health [17, 52].
This study revealed the contribution of having natural teeth to a positive body-image, not only through dental appearance, but also through intactness and normal functioning, all of which aspects are integrated in the body-image concept as described by Carver . Donnelly  indicated how oral impairments could negatively affect the body image of elderly people and consequently decrease self-esteem. She warned that elderly, living in a society where the emphasis is on youth and beauty, may become increasingly concerned about their dental appearance and feel inadequate when they do not have white and straight teeth. Most of our participants, however, did not mind that their teeth were a bit yellow and misaligned. They were more concerned about keeping their own teeth, since artificial teeth made them ‘feel like a different person.’ This association between natural teeth and identity (of which body image is a ‘central aspect’ ) at old age, may become more important to OHrQoL as people age and become more frail, than the mere aesthetic aspects of teeth. Most consulted literature indeed supports the idea of decreasing emphasis on physical attractiveness in relation to QoL as people age [56–59], while the experience of bodily decline appears to “urge old people to redefine their identity” . However, further research in the area of oral health is required to test our hypothesis.
The way natural teeth can contribute to a more positive body image and self-worth, cannot be measured by existing OHrQoL instruments. More in general, and to our surprise, body image assessment has not been integrated into the oral health related QoL literature, and has only recently become a topic in health related QoL literature [61–64], despite consistent observations that changes in physical appearance, function, and body integrity are crucial to the experience of health and illness . It may therefore be useful, when researching the OHrQoL of frail elderly, to supplement commonly used OHrQoL instruments like OHIP and GOHAI with questions that target the influence of oral health on body-image and self-worth, e.g. “Do you think that your teeth positively contribute to (a) how others perceive you; (b) how you perceive yourself.”
Implications for the health sector, health care staff and the dental profession
We found that the severely frail people were less able and less prepared to take good care of their teeth, despite the value they attributed to having natural teeth. There seems to be a turning point where frail people abandon oral care, and our participants indicated that this occurred when they experienced other more disturbing discomforts or pain. At the same time, our results show that even the most severely frail generally wish to keep their natural teeth and benefit from keeping them. Both the health care and public health sector should become aware of the QoL benefits of preservation of natural teeth even for severely frail people. We recommend the dental profession and health care staff to adopt a patient-centered approach through identifying individual oral health needs and wishes of frail dentulous elderly and translating these into a tailor made care plan. In identifying those needs, health care staff needs to be alert to care behavior and the general oral condition. Several of our participants had unclean teeth and simply wanted to be reminded about or help with brushing their teeth or with dental visits, so enhancing their QoL may not require that much effort. However, the required effort needs to be facilitated by the health care and public health sector through allocation of appropriate resources. Only then, the type of requested oral health care, including assistance with daily oral care and arrangement of dental visits, can be better geared to preserve teeth and sustain QoL of frail older people, than is currently the case.