ORTHODONTIC APPLIANCES
OSSICLE
O
orthodontic appliances Fixed or re-
movable devices, commonly known as
braces, worn to correct
malocclusion,
or
to reposition overcrowded or
buck
teeth.
Usually fitted during childhood and
adolescence, they move teeth using
sustained gentle pressure. A fixed appli-
ance has brackets attached to the teeth
through which an arch wire is threaded
and tightened to exert pressure. These
are usually kept in place for about a year,
after which time a retainer plate may be
needed to hold the teeth in place until
tooth and jaw growth has finished.
Removable appliances, consisting of a
plastic plate with
attachments
that
anchor over the back teeth, are used
when only one or a few teeth need cor-
recting. They apply force by means of
springs, wire bows, screws, or rubber
bands fitted to the plate.
orthodontics A
branch
of
dentistry
concerned with preventing and treating
malocclusion.
The procedures are usually
performed while teeth are developing
and still relatively manoeuvrable, but
can also be of benefit in adulthood.
An orthodontist may first make mod-
els of the teeth (see
impression, dental
)
and take
X-rays
of the head and jaws.
Certain teeth, often premolars, may be
extracted to make room for the remain-
ing teeth. Poorly positioned teeth are
then moved by gentle pressure exerted
by
orthodontic appliances.
orthognathic surgery An operation to
correct deformity of the jaw and the
severe
malocclusion
that is invariably
associated with it. The bones of the jaw
are repositioned under general anaesthe-
sia, and often require splinting (see
splinting, dental
) until they heal.
orthopaedics The branch of surgery con-
cerned with disorders of the
bones
and
joints
and their associated
muscles
,
ten-
dons
, and
ligaments
. Procedures include
setting broken bones and applying casts;
treating
dislocations,
slipped
discs,
arthritis, and back problems; treating
bone tumours and birth defects of the
skeleton; and repairing or replacing hip,
knee, or finger joints.
orthopnoea Difficulty in breathing when
lying flat. Orthopnoea is a symptom of
heart failure
and
pulmonary oedema
,
and also occurs with
asthma
and chronic
obstructive pulmonary disease (see
pul-
monary disease, chronic obstructive
).
orthoptics Techniques used mainly in
children to measure and evaluate
squint
,
including eye exercises, assessment of
monocular and binocular vision, and
measures to combat
amblyopia
.
orthotics Use of appliances to support
or correct weakened or deformed joints.
os An anatomical term for a bone; also
refers to an opening in the body, as in
the cervical os (entrance to the
uterus
).
Osgood-Schlatter disease Painful en-
largement and tenderness of the tibial
tuberosity (the bony prominence of the
tibia
), which occurs most commonly in
boys aged between 10 and 14. It results
from excessive, repetitive pulling of the
quadriceps muscle
, due to repeated exer-
cise. The disorder often clears up without
treatment; severe pain may require
physiotherapy
or immobilization of the
knee in a plaster
cast.
osmosis The passage of a solvent from a
weaker solution to a more concentrated
one through a semipermeable membrane.
All body cells are surrounded by such
membranes, which allow water, salts, sim-
ple sugars (such as
glucose
), and
amino
acids
(but not proteins) to pass through.
Therefore, osmosis plays an important
part in regulating the distribution of water
and other substances in body tissues.
ossicle A small bone, especially any of the
3 tiny bones in the middle
ear
(malleus,
incus, and stapes) that conduct sound
from the eardrum to the inner ear.
OSSICLE
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