Received: 22 October 2019
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Revised: 30 April 2020
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Accepted: 8 June 2020
DOI: 10.1111/joor.13040
SUPPLEMENT PAPER
Foundations of oral health-related quality of life
Mike T. John
Department of Diagnostic and Biological
Sciences, School of Dentistry, University of
Minnesota, Minneapolis, Minnesota, USA
Abstract
Oral health-related quality of life (OHRQOL) is the component of health-related quality of life that relates to the effects of oral diseases and dental interventions on pa-
Correspondence
Mike T. John, Department of Diagnostic and
Biological Sciences, School of Dentistry,
University of Minnesota, 7-536 Moos Tower,
515 Delaware Street SE, Minneapolis, MN
55455.
Email: mtjohn@umn.edu
tients. This article describes why OHRQOL is important and how it is measured. The
conceptual basis for OHRQOL is discussed. A four-dimensional structure consisting
of Oral Function, Orofacial Pain, Orofacial Appearance and Psychosocial Impact as the
OHRQOL dimensions has emerged as psychometrically sound and clinically intuitive.
Consequently, when the impact of oral diseases or the effects of dental interventions
Funding information
National Institute of Dental and Craniofacial
Research of the National Institutes of
Health, USA, Grant/Award Number:
Grant/Award Number: R01DE022331,
R01DE028059
are measured, four dimension scores capturing these attributes need to be used.
KEYWORDS
assessment, dental patient-reported outcome measures, dental patient-reported outcomes,
dimensions, oral function, oral health-related quality of life, orofacial appearance, orofacial
pain, psychosocial impact
1 | W H AT I S O R A L H E A LTH - R E L ATE D
Q UA LIT Y O F LI FE ?
are represented by the concept oral health-related quality of life
(OHRQOL). OHRQOL can simply be understood as the component
of HRQOL that relates to the effects of oral diseases and dental in-
What makes life worth living is described by the term quality of life
terventions on patients.
(QOL). It includes several components. Safety or environment are
obvious examples, but health is also an important component. The
World Health Organization (WHO) has defined health as “a state of
complete physical, mental and social well-being and not merely the
2 | W H Y I S O R A L H E A LTH - R E L ATE D
Q UA LIT Y O F LI FE I M P O RTA NT ?
absence of disease or infirmity,”1 emphasising a bio-psycho-social
model of health and illness.
As the reduction and elimination of the effect of oral diseases on the
Health-related quality of life (HRQOL), the component of QOL
patient is the goal of oral health care, in a patient-centred approach,
that is related to health, is grounded on this definition of health.
the concept OHRQOL, which captures these effects, becomes the
HRQOL is, like the larger concept QOL, also multidimensional. It en-
primary target for dental interventions. They should decrease pa-
compasses physical, mental and social components. While several
tient suffering, or, in other words, improve OHRQOL. It seems ob-
definitions for HRQOL have been proposed, there is broad agree-
vious that an intervention's outcomes should be perceived by the
ment that HRQOL represents the effect of a medical condition and/
patient as beneficial. OHRQOL is not only important for an individ-
2
or its consequent therapy upon a patient. The patient's perceived
ual patient but is also the major indicator for dental public health.
health status is not a deterministic reflection of the physical health
Two major categories of outcomes can be differentiated for oral
situation, rather it is shaped by individual factors (eg personality
diseases, oral disease-oriented outcomes, such as pocket depth or
characteristics), environmental factors (eg physical but also societal
range of mandibular motion, and patient-oriented or patient-re-
environment such as family, friends and coworkers).
3
ported outcomes (PROs), in this case, more specifically dental
Oral health is a part of general health and it is affected by oral
patient-reported outcomes (dPROs).4 Oral disease-oriented out-
diseases. They are a large, frequent and often chronic group of dis-
comes indirectly influence the patient through their relationship
eases.4 They have specific impacts on patients, and these impacts
with dPROs. While only both outcome categories together offer a
J Oral Rehabil. 2020;00:1–5.
wileyonlinelibrary.com/journal/joor
© 2020 John Wiley & Sons Ltd
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JOHN
complete oral health characterisation, only dPROs directly represent
used benchmark to decide whether OHRQOL changes are clinically
the patient-perceived impact. Consequently, dPROs are fundamen-
relevant.
tal for evidence-based dentistry, 5 essential to increase research effi-
The impact of oral diseases has a time dimension, and conse-
cacy and to reduce research waste by addressing questions relevant
quently, a timeframe needs to accompany the questions. It makes a
to clinicians and patients6 and necessary for value-based oral health
difference for patients whether they had an oral health impact often
7
care, a concept relating outcomes to costs. OHRQOL is the most
during the last year or often during the last day. The recall or ref-
important dPRO.
erence period for OHRQOL items depends on the purpose of the
assessment; however, most instruments intend to assess the effects
3 | H OW I S O R A L H E A LTH - R E L ATE D
Q UA LIT Y O F LI FE M E A S U R E D?
of dental interventions and this purpose requires short reference
periods. Dental interventions often change oral health problems
rapidly, for example extraction of a painful tooth relieves the patient
of his/her pain quickly. Therefore, to capture the interventions’ ef-
Dental patient-reported outcome measures (dPROMs) assess dPROs.
fects, short reference periods such as “past 7 days” are preferred
While oral disease-oriented outcomes are objective and clinician-as-
compared to longer periods such as “past month” or “past year.”8
sessed, dPROs in general and OHRQOL in particular are subjective
and patient-reported. As a mental image, OHRQOL is not directly
observed. It cannot be directly measured like the length of an object
could be measured by a ruler. Instead, OHRQOL is assessed by its
indicators. Typically, to assess OHRQOL, patients are asked several
4 | W H AT I S TH E CO N C E P T UA L BA S I S
FO R O R A L H E A LTH - R E L ATE D Q UA LIT Y O F
LI FE ?
questions about how they are impacted by oral diseases. Proxy respondents are needed for some individuals, for example small chil-
Because OHRQOL is a concept, a mental image, it needs a concep-
dren who are not able to answer the questions themselves. The item
tual model. Wikipedia describes a conceptual model as “a represen-
responses are coded numerically, for example a 0 for “oral health
tation of a system, made of the composition of concepts which are
problem absent” or 1 for “oral health problem present.” If not only
used to help people know, understand, or simulate a subject the
the presence of the problem but the level of the impact is of interest,
model represents. It is also a set of concepts.” 9
typically the frequency or the intensity of the impacts is assessed,
Most OHRQOL instruments are grounded on Locker's model10
for example using 5 points ranging from 0 “impact did not occur” to
of oral health that is based on a model of the WHO’s International
4 “impact occurred very frequently.” Finally, the responses to several
Classification of Impairments, Disabilities, and Handicaps from
or all questions in a questionnaire are combined into a dPROM score.
1980.11 However, this model is not valid anymore. Since 2001, the
Dimension scores (the characterisation of an OHRQOL component)
WHO’s International Classification of Functioning, Disability and
and total scores (the characterising of the entire OHRQOL con-
Health (ICF) is the international standard to describe and measure
struct) exist. These scores characterise the patient's standing in the
health and disability.3 This situation, that the underlying model used
spectrum of the target attribute. How many scores a questionnaire
to develop the instrument is not valid anymore, challenges the cur-
has is determined by its dimensionality and whether all questions are
rent validity of existing OHRQOL instruments when these instru-
combined into a total score or not.
ments intend to measure OHRQOL dimensions.
OHRQOL is a positive concept because more of the attribute
OHRQOL is considered better than less of the attribute. However,
it is often operationalised as a deviation from the ideal situation
of being oral disease-free. Therefore, most OHRQOL scores are a
“problem” index, that is, higher instrument scores represent more
5 | WHY ARE DIMENSIONS OF OR AL
H E A LTH - R E L ATE D Q UA LIT Y O F LI FE S O
I M P O RTA NT ?
oral health impacts. The impact of oral diseases is characterised by
a spectrum with 0 (no disease impact) and the instrument's high-
Many concepts are broad and often smaller concepts reside within
est score (maximum disease impact.) Whether a particular score is
a larger concept. The larger concept has dimensions. Dimensionality
high or low is not so easy to interpret because scores have an ar-
is a psychometric property that refers to the number and nature of
bitrary metric. Therefore, scores need a frame of reference. Single
underlying attributes reflected in the questionnaire's items.12 The
scores, for example, can be compared with a score distribution in
dimensionality is of fundamental importance for a multidimensional
a reference population. Often this is the general population, allow-
construct.13 For OHRQOL, it determines what the construct is and
ing an assessment of how a particular patient's suffering compares
how many scores an OHRQOL instrument needs to have.
with general population subjects. Interpretation of score changes,
While there was broad agreement that OHRQOL is a multidi-
induced by treatment for example, is often done by internal, that
mensional attribute,14 it was until recently that studies disagreed
is statistically derived, criteria such as ratios of score magnitude to
about how many dimensions exist and what these dimensions are.
score distribution, or external criteria, representing known health ef-
Many studies investigated dimensionality of OHRQOL instruments.
fects of the patient. The minimal important difference is a frequently
A selection is presented here that used the Oral Health Impact
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JOHN
3
Profile (OHIP),15 the most widely used instrument, to characterise
In 2014, in Brazilian post-partum women admitted to a Public
the diversity of methodological approaches and the findings to de-
Maternity Hospital and older urban community-based individuals, an
termine OHRQOL dimensionality.
EFA followed by a CFA found that OHRQOL measured by OHIP-14 is
The OHIP was developed based on WHO’s International
Classification of Impairments, Disabilities, and Handicaps from 1980
and experts assigned 49 items to seven factors based on Locker's
a single construct.22
The variability of the findings mentioned above can be explained
by three major methodological factors:
model of oral health.10 In 2005, in a clinical setting investigating Italian
temporomandibular disorder (TMD) patients with OHIP-49,16 an ex-
• What set of indicators is used to capture the concept OHRQOL?
ploratory factor analysis (EFA) found six factors, but factors were not
named. In 2007, in Turkish patients with Behcet's disease and recurrent
A larger set of indicators that is representative of patients’ oral
aphthous stomatitis with the 14-item OHIP version, an EFA found three
health impact is better suited than a smaller set of selected indica-
factors. These dimensions were called Physical Symptoms, Psychosocial
tors. Among several available instruments to investigate the dimen-
Symptoms and Psychological Symptoms.17 In 2008, in a population-based
sionality of OHRQOL, the 49-item Oral Health Impact Profile15 is a
setting with Canadian older adults using the 49-item OHIP, a struc-
very well-suited set of indicators.
tural equation modelling analysis rejected OHIP’s 7-domains structure.
A 6-dimensional structure was explored.18 A similar analytic approach
• What group of subjects is used to capture oral disease impact?
in British adults using OHIP-14 provided support for five factors
(Functional Limitation, Pain, Discomfort, Disability and Handicap).19 In
Oral disease impact differs from disease to disease. To be rep-
2010, in a community-based setting of healthy Spanish workers using
resentative of oral disease impact, patients should be affected by
both OHIP-14 and Oral Impact on Daily Performance,20 an EFA study
several common oral diseases. Tooth loss is dentistry's major phys-
followed by a confirmatory factor analysis (CFA) found three dimen-
ical, disease-oriented outcome. It is caused by caries, periodontitis,
21
trauma and several behavioural and environmental non-carious
sions (Functional Limitation, Pain-Discomfort and Psychosocial Impacts).
TA B L E 1
Dimensions of oral health-related quality of life - Important research steps
Research step
Short description of rationale, methods and findings
1. Initial finding
The 4 OHRQOL dimensions Oral Function, Orofacial Pain, Orofacial Appearance and Psychosocial Impact were initially
found in a large random sample of the adult German general population using exploratory factor analysis. 27
2. Define principles for
a systematic study of
OHRQOL dimensions
An appropriate set of OHRQOL indicators and a large sample of typical dental patients are necessary to identify
OHRQOL dimensions.
A systematic collection of data best suited to investigate OHRQOL dimensionality in adults identified 35 studies,
including about 10 000 prosthodontic patients and general population subjects from six countries with OHIP-49
data. These data were included in the Dimensions of OHRQOL (DOQ) Project. 23
3. OHRQOL
dimensions—
Exploratory analyses
Using the DOQ Project's Learning Sample, an exploratory factor analysis in 5146 subjects was conducted. The factor
analysis found a four-factor solution and the factors were named Oral Function, Orofacial Pain, Orofacial Appearance
and Psychosocial Impact. 28
4. OHRQOL
dimensions—
Confirmatory analyses
Using the DOQ Project's Validation Sample, a confirmatory factor analysis in an independent sample of 4993
subjects was performed. The four-factor model was deemed best in terms of strong item loadings, model fit
(RMSEA = 0.05, CFI = 0.99) and interpretability. 29
5. OHRQOL
dimensions—Validation
Four OHRQOL dimensions can occur in 16 combinations, that is, sets of dimensions, and all these combinations are
expected to occur based on clinical expertise. Agreement between occurrence of the 16 combinations in empirical
data with predictions of how OHRQOL impact should manifests itself in patients and general population subjects
provides an essential clinical validation of the dimensions.
In DOQ Project participants, all expected 16 combinations of OHRQOL dimensions were observed and agreed with
expectations.30
6. Generalisation: From
OHIP-derived OHRQOL
dimensions to OHRQOL
dimensions in general
All OHRQOL instruments should fit the four OHRQOL dimensions. All questions from two widely used OHRQOL
instruments, the OIDP20 and the GOHAI,31 as well as culturally specific OHIP items should fit clinicians’ predictions
about the items’ dimensional OHRQOL impact.
In 267 international prosthodontic patients, OHRQOL items fit the predictions of clinicians where OHRQOL impact
can be expected, providing evidence for the generalisability of OHIP-derived dimensions to other OHRQOL
instruments.32
7. Generalisation: From
OHRQOL dimensions to
dimensions for generic
multi-item dPROMs—
(exploratory analyses)
Researchers created dental patient-reported outcome measures (dPROMs) to capture what is important to patients.
Among the multi-item dPROMs that measure the effect of oral disease and dental interventions, two types of
instruments, oral disease-generic (applicable to all oral diseases) and oral disease-specific (applicable to a particular
disease) instruments can be differentiated.
A systematic review collecting all generic multi-item dPROMs showed that the identified 53 dPROMs assessed only
four general attributes, the four dimensions of OHRQOL.33
4
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JOHN
processes that lead to tooth substance loss. Therefore, prosthodon-
ORCID
tic patients can be considered “typical” dental patients because they
Mike T. John
https://orcid.org/0000-0002-5169-7691
suffer from tooth loss and have often received dental interventions
such as fillings, root canal treatments and extractions. 23
• What methods are used to identify the dimensions?
Methods can range from experts using qualitative methods24
to quantitative methods such as exploratory17 or confirmatory factor analyses, 22 statistical methods that aim to describe variability
among observed, correlated variables in terms of a smaller number
of unobserved variables called factors. To determine the number of
these factors, investigators need to make decisions regarding several methodological factors that can influence the results. 25 Finally,
naming the factor is, of course, subjective.
6 | W H AT A R E TH E FO U R D I M E N S I O N S
O F O R A L H E A LTH - R E L ATE D Q UA LIT Y O F
LI FE ?
A psychometrically sound and clinically intuitive 4-dimensional
OHRQOL structure, consisting of Oral Function, Orofacial Pain,
Orofacial Appearance and Psychosocial Impact, emerged in a series of
studies (Table 1).
7 | CO N C LU S I O N S
Oral health-related quality of life is the most important dPRO, and
it is a notable contributor to health-related quality of life. To make
OHRQOL measurable, instruments (questionnaires) capture the patient-perceived impact, and instrument scores are used to express
patient suffering as a number. Of fundamental importance is that
OHRQOL is not a homogenous attribute but consists of dimensions.
A four-dimensional structure of OHRQOL has emerged as psychometrically sound and clinically intuitive. Oral Function, Orofacial
Pain, Orofacial Appearance and Psychosocial Impact are the dimensions of oral health-related quality of life and they are the reasons
why dental patients seek care. 26 Consequently, when the impact of
oral diseases or the effects of dental interventions are measured,
four dimension scores capturing these attributes need to be used
because they describe what matters to dental patients.
AC K N OW L E D G M E N T S
The research reported in this publication was supported by the
National Institute of Dental and Craniofacial Research of the National
Institutes of Health, USA, under the Award Numbers R01DE022331
and R01DE028059.
PEER REVIEW
The peer review history for this article is available at https://publo​
ns.com/publo​n/10.1111/joor.13040.
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How to cite this article: John MT. Foundations of oral
health-related quality of life. J Oral Rehabil. 2020;00:1–5.
https://doi.org/10.1111/joor.13040