Quality of life, health-related quality of life and oral health-related quality of life
Quality of life (QoL) research has gained increasing attention in medicine and dentistry in recent years, undergoing a quantum shift. Where it was once regarded as a secondary outcome, occasionally useful to complement biologic and clinical markers of disease, QoL issues are now at the forefront of public health policy . Quality of life can be defined as an individual’s perception of his/her position in life, in the context of the culture and value systems in which he/she lives and in relation to his/her expectations, goals and concerns . In 2003, Allen noted that “there appears to be an association between health and quality of life, which is not clearly defined, and the term health related quality of life is used to describe this association” . Although the term health-related quality of life has no strict definition, there is consensus that it is a multidimensional construct capturing people’s perceptions about factors that are important in their everyday lives .
Oral health-related quality of life (OHRQoL) is a part of health-related quality of life that focuses on oral health and orofacial concerns. It describes the way in which oral health affects a person’s ability to function, psychological status, social factors and pain or discomfort . Therefore, the OHRQoL attempts to represent the subjective side of oral health. Not surprisingly, as with health-related quality of life, the term OHRQoL has no strict definition . However, it is generally agreed that it is also a multidimensional concept. The definitions for OHRQoL that are available vary from simple to more rigorous. One example of a simple definition is the one provided by the U.S. Surgeon General’s report on oral health, which defines OHRQoL as “a multidimensional construct that reflects (among other things) people’s comfort when eating, sleeping, and engaging in social interaction; their self-esteem; and their satisfaction with respect to their oral health” .
Concepts of oral health
Traditional methods to measure oral health are based on clinical standards. As in medicine, clinical dental indicators and indices of disease are used as an inverse measure of oral health in dentistry. These indices provide a quantitative method for measuring, scoring and analysing dental conditions in individuals and groups. An index describes the status of individuals or groups with respect to the condition to be measured. For example, the gingival index  and periodontal index  are used to describe periodontal diseases, and the DMFT index (number of decayed, missing and filled teeth) is used to describe a person’s dental caries experience . However, as important as these objective measures are, they only reflect the endpoint of the disease processes . They also focus on the mouth rather than the person and give no indication of their impact on an individual’s daily life and general health .
The limitations of this paradigm of oral health have been recognised, principally that this model only deals with disease . Thus, Locker developed a conceptual framework for measuring oral health status that is based on the World Health Organization classification of impairment, disability and handicap and attempts to capture all possible functional and psychosocial outcomes of oral disorders . In this model, disease can lead to impairment, which may then lead to a functional limitation or pain/discomfort, either physical or psychological. Either of these outcomes may lead to physical, psychological or social disability, which is defined by Locker as any limitation in or lack of ability to perform activities of daily living. As a final consequence, handicap can occur. It is characterised by social disadvantage, e.g. social isolation. Functional limitation may also lead directly to handicap .
Measuring oral health-related quality of life
OHRQoL can be measured using a questionnaire approach. Results can serve as an outcome measure; they allow insight into how a patient’s oral health affects his/her well-being and quality of life at a given point in time . Multiple-item questionnaires are the most widely used method to assess OHRQoL. Researchers have developed several quality of life instruments specific to oral health, and the number continues to grow rapidly to comply with the demand for more specific measures .
Slade and Spencer developed the Oral Health Impact Profile (OHIP), which differs from other measures in that it is based on both Locker’s conceptual framework as well as input from dental patients with a variety of oral conditions . The OHIP is the most widely used instrument in studies evaluating OHRQoL. The questionnaire attempts to measure the effects of both the frequency and the severity of oral problems on functional and psychosocial well-being. The OHIP has 49 items that are grouped into seven subscales: functional limitation, pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. For each OHIP item, the patient is asked how frequently he/she experienced the impact of that item during last month. Responses concerning item impact are given using an ordinal rating scale (0 = never, 1 = hardly ever, 2 = occasionally, 3 = fairly often, 4 = very often). The summary score (sum of item responses resulting in a range of 0–4 × 49 = 0–196) represents a “problem index” that characterises the OHRQoL. A “0” summary score indicates the absence of any problems, higher OHIP scores represent more impaired OHRQoL, and a summary score of “196” indicates that all problems are experienced very often. The patient’s score can be evaluated by comparison to a table of standard values representative of different populations.
The OHIP is a technically sophisticated OHRQoL instrument that is widely used internationally [12, 13]. Several language versions already exist (e.g. Spanish , Swedish , Chinese , German  and Hungarian ) and initial evidence for the instrument’s cross-cultural equivalence is available [14–18]. The questionnaire has been applied several times, including in patients with temporomandibular disorders [19, 20], xerostomia , burning mouth syndrome , tooth agenesis  and HIV infection [24, 25]. Clinical trials have also used the OHIP to evaluate implant-supported prostheses [26, 27] and steroidal therapy for oral lichen planus . However, regarding the condition of dentine hypersensitivity (DHS) and OHRQoL (and especially the OHIP), the literature is limited.
DHS and its influence on oral health-related quality of life
DHS is an oral complaint frequently reported in clinical dental practice. It is characterised by a short and sharp pain that occurs in the presence of thermal, chemical, evaporative, tactile or osmotic stimuli, ceases after their removal and cannot be explained as arising from any other form of dental defect or pathology [29, 30]. From the relatively few studies that have been concerned with the prevalence of DHS, it can be concluded that it is a frequent condition . Depending on the patient group and the study design, prevalences of 4–57 % up to 60–98 % have been reported [32, 33]. In a national survey in Germany, 39 % of middle-aged adults reported problems with hypersensitive teeth . Pain is the major symptom of the condition. The degree of discomfort depends on the individual’s pain perception and pain tolerance, as well as emotional and physical factors. Whereas many affected individuals do not seek treatment to desensitise their teeth because they do not perceive DHS to be a severe oral health problem , studies have indicated that a substantial segment of patients (10–25 %) do seek treatment, complaining of different causes of discomfort, such as pain while consuming hot or cold foods and beverages (coffee, ice cream), during toothbrushing or sometimes even while breathing [36, 37]. From the perspective of the patients, these symptoms and problems are highly relevant. The restrictions on everyday activities can have an important effect on their overall quality of life . However, relatively little research on DHS has been reported.