Page 7 - CEREC Q3 | 2014

QUARTER 3 | 2014 | CERECDOCTORS.COM | 5
THE HIERARCHY OF EVIDENCE
So, just what is the best scientific
evidence? According to the ADA policy
statement on EBD, the term “best
evidence” refers to“informationobtained
from randomized controlled clinical
trials, nonrandomized controlled clin-
ical trials, cohort studies, case-control
studies, crossover studies, cross-sectional
studies, case studies or, in the absence
of scientific evidence, the consensus
opinion of experts in the appropriate
fields of research or clinical practice. The
strengthof the evidence follows the order
of the studies or opinions listed above.” 2
The ADA policy statement describes
a hierarchy of evidence for clinical
outcomes indicating that some evidence
is more credible in providing informa-
tion on predictable treatment outcomes.
Notice that the first six items listed for
“best evidence” are various types of
clinical studies, with the most rigorous
type of clinical study being a random-
ized clinical trial. A randomized clinical
trial recruits a significant number of
subjects requiring a similar treatment,
such as a crown on a posterior tooth, and
at random provides each patient either
the test treatment (an all-ceramic crown)
or the control treatment (a gold crown).
The concept of randomization over a
sufficiently large number of subjects
accounts for small variables in each
subject to be equally distributed between
the two groups. Treatment outcomes are
re-evaluated over time to discern differ-
ences in the clinical outcomes. This type
of clinical study design has the strictest
protocol designed to minimize, or at
least control, bias from influencing the
outcome of the study. Randomized clin-
ical trials, and particularly the systematic
reviewofmanyrandomizedclinical trials,
is much more likely to provide unbiased
information on clinical outcomes, and it
has become the best practice standard for
providing scientific evidence.
A cohort or longitudinal clinical study
involves a group of subjects that receive a
specific treatment. The group is followed
over time to evaluate the outcomes
of the treatment. A control group of
subjects is not necessarily included in
this study design. No further interven-
tion is provided after the initial treatment
other than to document the outcomes.
This describes the clinical outcome
of treatment, but does not provide an
internal control for comparison. A case
control study includes subjects based on
specific selection criteria. The subjects
are divided into a control group and
test group. Information is gathered
on the subject groups retrospectively,
comparing the treatments and clinical
outcomes. An example of this type of
study would be to review a significant
number of dental records of patients
who have had endodontic treatment on a
tooth. The two groups of patients might
be those that had a crown to restore
the tooth after endodontic treatment
while the other group had a posterior
composite. The dental records would
be reviewed to document the outcome
of treatment after the restorations were
placed to see if there were differences.
THE SYSTEMATIC REVIEW
The real challenge for a clinician is
to locate and identify good scientific
evidence. Practicing clinicians do not
have the time to devote to exhaus-
tive searches for good evidence. The
benefit of EBD is that systematic
reviews can provide excellent summa-
ries of clinical studies. Systematic
reviews are becoming more prevalent
in dental publications and are gener-
ally published by a group of investi-
gators due to the extensive literature
search that is involved in compiling the
summary. It attempts to review all the
available published evidence to answer
a narrowly focused clinical question.
Another desired approach is to use a
meta-analysis. This is a review that
Lack of evidence
does not mean lack
of effectiveness.
It means it is not
possible to advocate
for a predictable
outcome. This is
commonly the
problem for newer
materials and
techniques —
a lack of clinical
studies to provide
evidence of a
predictable
outcome. And this
poses a problem
for clinicians:
if there is a lack of
scientific evidence,
what should be
used to evaluate
the effectiveness
of a material or
procedure?