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Background
F
or many years, it was thought that any missing
tooth should be replaced,1
although numerous
clinicians and researchers questioned
this opinion. Arnd Käyser was the first to coin
the term “shortened dental arch” (SDA) to describe
the concept of acceptable oral function with
partial dentition.2
Through a number of clinical
studies, he and his co-workers came to the conclusion
that many people could function without a
full complement of teeth and that not all missing
teeth require replacement.2–6 For many people, a
functional dentition consists of as little as opposing
anterior and premolar teeth.1
In terms of
a minimum number of teeth that patients need,
Käyser and colleagues suggested that, in addition
to anterior teeth, most people require at least 4 occlusal
units of posterior teeth (1 pair of opposing,
occluding premolars would be 1 occlusal unit, a
pair of occluding molars would represent 2 occlusal
units).2
People with asymmetrical tooth loss noticed a change in chewing function when they
had fewer than 6 units (Figs. 1 and 2).2
The Effect of a Shortened Dental Arch on
Oral Function
In general, studies comparing people with a
full complement of teeth with those with SDAs
have not demonstrated significant differences in
ability to chew.1
Among patients with the minimum
recommended number of occlusal units, the
insertion of a removable partial denture does not
significantly improve oral function.3
According to
some studies, the more teeth missing beyond the
minimum, the more difficulty a person will have
chewing.1
In addition, those without molar support have
not been shown to have a higher incidence of the
signs and symptoms of temporomandibular disorders.5
Similarly, SDA has not been associated with
significant discomfort, distress or occlusal wear.1
Although it seems that most people can function
acceptably with an SDA, this is not true
for everyone: 7% to 20% of people with an SDA
have reported that their chewing ability is hindered
or that they had to change food preparation
practices.1
An SDA may also be associated with greater
tooth migration and interdental spacing among
patients younger than 40 years, although the migration
was deemed small and clinically insignificant.1
An SDA may also be associated with greater
overeruption of teeth, although only 2% of such
patients reported that it hindered their oral function.1
People with SDA have been found to have
more mobile teeth and lower alveolar bone levels.
The combination of increased occlusal loading
and existing periodontal disease probably represents
a risk factor for further loss of teeth in these
people. Patients with SDA probably also represent
a high-risk group in terms of periodontal disease.
Additional longitudinal studies have been recommended
to study this relationship.1
Shortened Dental Arch Options in Dental
Practice
The SDA concept is increasingly accepted, although
in some areas, it is not widely put into
practice.1
For dentists who provide services to patients
with limited financial resources or patients
who do not wish to acquire a prosthesis, the evidence
provides a measure of reassurance that “no
treatment” can be a sound option. Considering the
implications of informed consent and the evidence
collected by Käyser and others, it is prudent to
ensure that treatment planning for all partially
edentulous patients includes a discussion of the
option of not replacing missing teeth and the pros
and cons of this choice. For many patients, there may be no need to replace missing teeth, unless
they are unhappy with their ability to chew or
their appearance (Figs. 3 and 4). For patients with
4 or more occlusal units who do not feel they can
chew as well as they wish, replacements can still be
fabricated (Fig. 5).
The SDA concept is based on the notion that
patients have an adaptive capacity to function with
missing teeth. This capacity clearly varies, and not
all patients will feel they have optimum function
with the same number of teeth. Future research
will most likely improve our understanding of this
clinically relevant subject.