calculus, dental
A hard, crust-like deposit, also called
tartar, found on the crowns and roots
of the teeth. Calculus forms when m in-
eral salts in saliva are deposited in
a coating of mucus and
debris that forms on the teeth.
There are two types of dental calculus.
Supragingival calculus is a yellowish or
deposit that forms above the
gum margin, on the crowns of teeth in
areas close to the openings of
ducts. Subgingival calculus forms
below the gum margin, is more evenly
distributed around all the teeth, and is
brown or black.
Both types of calculus are hard and
are therefore difficult to remove; the
subgingival variety may be more diffi-
cult to remove because of its location
and degree of calcification.
The toxins present in calculus can lead
to gum inflammation (see
) ,
w hich may progress to destruction of
the supporting tissues (see
Calculus should be removed on a regu-
lar basis by professional
attention to
oral hygiene
may reduce the
recurrence o f dental calculus.
calculus, urinary tract
A stone in the kidneys, ureters, or blad-
der that is formed from crystallized
substances in the urine.
Kidney and ureteral stones
Most stones
that form in the kidneys and ureters are
composed o f calcium oxalate or other
salts crystallized from the urine. These
stones may be associated w ith a diet
that is
rich in oxalates
(w hich are
found, for example, in leafy vegetables
and tea); high levels o f
in the
blood due to
activity o f the parathyroid glands); or
chronic dehydration.
Other types o f kidney or ureteral
stone are associated w ith
and cer-
tain cancers. Stones that develop
these locations due to chronic
tract infection
termed “infective” .
Kidney stones that fill the entire net-
work o f urine-collecting ducts at the
top o f the ureter are called “staghorn”
calculi, due to their shape.
Bladder stones
In developing countries,
bladder stones usually occur as a result
o f dietary deficiencies. In developed
countries, they are usually caused by an
obstruction to urine flow from
bladder and/or a longstanding urinary
tract infection. The composition o f the
stones is related to the acidity or alka-
linity o f the urine.
The most common symptom o f a stone
in the kidney or ureter is
renal colic
a severe pain in the back, under the
ribs, that often spreads into the groin.
This pain may be accompanied by nau-
sea and vomiting. There may also be
(blood in the urine). A blad-
der stone usually causes difficulty in
passing urine.
Investigation o f a suspected calculus
usually starts with microscopic exami-
nation o f the urine, w hich may reveal
red blood cells and the presence of
crystals. The degree o f acidity or alka-
linity o f the urine may reflect the type
o f stone involved. The site o f a stone
can usually be confirmed by intraven-
Some stones, particularly
those containing calcium, are visible on
a plain abdominal X-ray.
Renal colic is treated w ith bed rest
and an
analgesic drug
(painkiller). With
an adequate fluid intake, small stones
are usually passed in the urine without
causing problems. The first line o f treat-
ment for larger stones in the urinary
tract is often
a procedure that
uses ultrasonic waves or shock waves to
stones. Alternatively,
can be used to crush and
remove stones in the bladder and lower
ureter. In some cases, surgery may be
needed to remove the stones.
calendar method
A method of
also called
the rhythm method, based on abstain-
ing from sexual intercourse around the
Calculi form in the urinary tract when
certain substances in the urine become
overly concentrated. The substances
form crystals, which grow into stones.
Some stones may be associated with
recurrent episodes of
urinary tract
Symptoms vary according to
the site of the stone. Small stones may
be passed in the urine and cause no
symptoms. Some stones, however, may
lodge in a ureter, causing
renal colic
sudden, severe pain in the small of the
back that moves towards the groin) and
haematuria (blood in the urine). In the
bladder, stones may settle over the
outlet, which can cause difficulty in
passing urine, a poor flow rate, and
dribbling. Any obstruction to urine flow
may result in rapid kidney damage and
acute, severe infection
S p i n e
B l a d d e r
s t o n e
P e lv is
X-ray of a bladder stone
A large bladder stone, such as the one that
can be clearly seen in this X-ray, can make the
passing of urine both difficult and painful.
S m a l l e r
k i d n e y
s t o n e
C a ly c e s
S t a g h o r n
c a l c u l u s
Staghorn calculus
Here, a staghorn calculus has filled the entire
pelvis and calyces ofthe kidney, producing a
cast ofthem. A smaller stone has formed in
the medulla (central area).
P e lv is o f
k i d n e y
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