The objective of this study was to investigate the preventive
effect of oral hygiene on pneumonia and respiratory tract
infection, focusing on elderly people in hospitals and nursing
homes, by systematically reviewing effect estimates and
methodological quality of randomized controlled trials
(RCTs) and to provide an overview of additional clinical
studies in this area. Literature searches were conducted in
the Medline database, the Cochrane library databases, and
by hand-searching reference lists. Included publications
were analyzed for intervention (or topic) studied, main
conclusions, strength of evidence, and study design. RCTs
were further analyzed for effect magnitudes and methodological
details. Absolute risk reductions (ARRs) and numbers
needed to treat (NNTs) were calculated. Fifteen
publications fulfilled the inclusion criteria. There was a
wide variation in the design and quality of the studies included.
The RCTs revealed positive preventive effects of
oral hygiene on pneumonia and respiratory tract infection
in hospitalized elderly people and elderly nursing home
residents, with ARRs from 6.6% to 11.7% and NNTs from
8.6 to 15.3 individuals. The non-RCTstudies contributed to
inconclusive evidence on the association and correlation
between oral hygiene and pneumonia or respiratory tract
infection in elderly people. Mechanical oral hygiene has a
preventive effect on mortality from pneumonia, and nonfatal
pneumonia in hospitalized elderly people and elderly
nursing home residents. Approximately one in 10 cases of
death from pneumonia in elderly nursing home residents
may be prevented by improving oral hygiene. Future research
in this area should be focused on high-quality RCTs
with appropriate sample size calculations. J Am Geriatr Soc
56:2124–2130, 2008.
Health-care associated (hospital-acquired, or nosocomial)
pneumonia occurs in patients in intensive
care units and institutionalized individuals, such as nursing
home residents.1 Pneumonia is a common infection in elderly
people and the most common cause of mortality from
nosocomial infection in elderly patients, with a mortality
rate of up to 25%.1,2 Bacterial species that normally do not
colonize the oropharynx frequently cause health care–
associated pneumonia, and the oral cavity has been suggested
as an important reservoir for these respiratory
pathogens.1 Elderly patients in nursing homes often have
poor oral health due to difficulties in maintaining a sufficient
level of personal oral hygiene and difficulties in accessing
professional dental care.3 Hence, a relationship
between poor oral hygiene and bacterial pneumonia or
lower respiratory tract infections has been suggested in the
literature.4–6 A plausible mechanism of health care–associated
pneumonia could be aspiration of oral pathogens into
the lungs.7 Clinical trials have sought to determine whether
oral care reduces the incidence of pneumonia, respiratory
tract infections, and mortality in pneumonia in elderly people,
and a relatively recent systematic review concluded that
better oral hygiene and frequent professional oral care reduce
the progression or occurrence of respiratory tract diseases
in high-risk elderly people living in nursing homes and
intensive care units.8 This study was initiated to further
elucidate and systematically summarize the effect estimates
and the methodological quality of available randomized
controlled trials (RCTs) linking oral hygiene status to pneumonia
and respiratory tract infections in elderly people and
to provide an overview of additional clinical studies in this
area.
METHODS
Literature Searches
Literature searches were conducted in the MEDLINE database
(April 2007–November 2007), focusing on combinations
of search terms: ‘‘dental health’’[All Fields], ‘‘muscle
strength’’[All Fields], ‘‘respiratory capacity’’[All Fields],
‘‘survival’’[All Fields], ‘‘pneumonia’’[All Fields], ‘‘all cause
mortality’’[All Fields], ‘‘periodontitis’’[All Fields], and ‘‘periodontium’’[
All Fields]). Additional literature searches
were conducted in the Cochrane Central Register of Controlled
Trials and the National Health Service Economic
Evaluation Database (November 2007) using the Medical
Subject Headings descriptor ‘‘Dental Care for Aged,’’ search
function: ‘‘explode all trees.’’ A list of names of known authors
in this research area was also used in the searches
(kindly provided by Dr. P. Ha¨ma¨ la¨inen, Jyva¨skyla¨ University,
Jyva¨skyla¨ , Finland). The literature searches were limited
to publication years 1996 to 2007 and to studies
conducted in humans only. Additional studies were located
by scrutinizing the reference lists of obtained publications
and the doctoral thesis by Ha¨ma¨ la¨inen.9 The predetermined
inclusion criteria were clinical studies, focusing on RCTs,
linking oral hygiene to health care–associated pneumonia
or respiratory tract infection in elderly people (_65, although
not an absolute limit). Publications in Dutch, English,
German, and any of the Nordic languages (Danish,
Finnish, Icelandic, Norwegian, Swedish) were included.
Publications about authority opinions and reports of expert
committees were excluded, as were studies on subjects with
mechanical ventilation or tube feeding. After the literature
searches were completed, no additional publications were
included.
Strength of Evidence
All publications were scrutinized for study design and ordered
according to the hierarchical strength of evidence,
from the strongest level (type-1 evidence) to the weakest
(type-5) evidence, in accordance with the principles of evidence-
based medicine (EBM).10 Systematic reviews of
RCTs were considered to be type-1 evidence; RCTs, type-
2; and studies with a nonrandomized design, type-3. Type-4
evidence, as presented previously,10 was not used in this
study, because it is intended for well-designed nonrandomized
studies from different research groups on a specific
topic. Thus, all nonrandomized studies were grouped together
on the type-3 level, with the exception of descriptive
studies that were assigned the lowest (type-5) level of
evidence.10
Methodological Assessments
All studies fulfilling the predetermined inclusion criteria
were scrutinized for country of origin, intervention (or
topic) studied, journal of publication, main conclusions,
publication year, strength of evidence, and study design.
The quality of RCTs was assessed using a validated scale
that includes three items directly related to the validity of an
RCT, described in detail elsewhere.11 Briefly, the adequacy
of reporting random allocation, double-blinding, and withdrawals
and dropouts were rated, giving a total score of 0 to
5 points (0–2 points5poorer quality, 3–5 points5higher
quality).11 Also, for RCTs a definition of pneumonia or
respiratory tract infection, as well as the presence of a
power calculation were assessed. Although, one of the authors
(PS) was experienced in conducting quality assessments
of RCTs, two of the authors (EN, PS) completed all
assessments.
Data Extraction and Analyses
Data extraction from RCTs was focused on the outcome
frequency in the control group (control event rate, CER%)
and in the experiment group (experiment event rate,
EER%)1 and sample size in the control group and in the
test group(s). For parallel group RCTs, the frequency of
pneumonia, or lower respiratory tract infection, in the control
group (CER%) and in the experiment group (EER%),
were used to calculate the absolute risk reductions (ARRs;
ARR5CER%_EER%), and numbers needed to treat
(NNTs) were calculated with 95% confidence intervals
(CIs) using standard formulas (95% CI5ARR _ 1.96 _
standard error).12,13 The NNT values (95% CIs for NNTs)
were obtained as reciprocals of ARR (NNT5100/ARR), as
previously described.12 To ensure the consistency of the
assessments throughout the study, two authors (EN, PS)
performed the data extraction independently, and any
disagreements were solved in consensus meetings. Pooling
data from individual studies (meta-analysis) was not
deemed suitable because of heterogeneous study designs,
quality of reporting methodological aspects, and trial
conduct.
To provide an overview of additional clinical studies in
this research area, the non-RCT studies that were identified
in the literature were scrutinized for the authors’ main conclusion(
s).
RESULTS
Literature Searches
The Medline literature searches resulted in 191 eligible
publications that were scrutinized for predetermined inclusion
and exclusion criteria of this study. In addition, 137
studies were identified by hand-searching reference lists of
the publications obtained. Fifteen publications fulfilled the
inclusion criteria and remained throughout the assessments
(Table 1). The studies included were published during 1996
to 2006, in 10 scientific journals and originated from six
countries (Table 1).
Methodological Assessments of RCTs
One systematic review (type-1 evidence) and five RCT publications
(type-2 evidence) were identified (Table 1), although
two of the RCT reports covered the same trial (i.e.,
duplicate publication) (Table 1). Methodological quality
assessment of the RCTs revealed that one of the RCTs contained
an appropriate methodology of double-blinding, and
an adequate method of random allocation was given in
three RCT publications (Table 2). Moreover, three of five
RCT reports gave a complete reporting of withdrawals and
dropouts (Table 2). High-quality scores (3 to 5 points
on the Jadad scale) were assigned for three RCT reports
(Table 2). A power calculation was not reported in any of
the RCTs, whereas a definition of the studied endpoint
(pneumonia or respiratory tract infection) was given in four
of five trial reports (Table 2). In total, three of the RCTs (one
duplicate publication) were parallel group trials, and one
had a cross-over design (Table 2).
Effect Estimates in RCTs
In the parallel-group RCT publications (n54), two of
which covered the