from the contact area, to avoid damage to the adjacent tooth. The bur should be
angled away from the vertical so that a shoulder is not created at the gingival margin.
The same bur may be used for the whole preparation, although it can be quicker to use
a larger diamond for the next stage, which is to reduce the occlusal surface to allow
1.5-2 mm of space between the prepared tooth and its opposite number.
Many authorities advocate doing no more preparation than this but it takes little
further time to reduce the buccal and lingual surfaces sufficiently to remove any
undercuts above the gingival margin. Any sharp line angles are rounded off to avoid
interferences that might prevent the crown seating.
The mesial and distal preparation might seem rather radical in comparison to that
required when a cast crown is constructed for a permanent tooth, but the principles of
retention and resistance of the two types of crown are different. A cast crown is
retained by friction between the walls of the prepared tooth and the internal surface of
the crown. It is, therefore, important to have near parallel walls of adequate height. A
stainless-steel metal crown is retained by contact between the margins of the crown
and the undercut portion of the tooth below the gingiva. The shape of the preparation
above the gingiva is relatively unimportant and difficulty in fitting these crowns is
most often because of under-preparation. However, it is most important that a
shoulder is not formed at the gingival margin as this would make the seating of a
well-adapted crown impossible.
Try the crown on and check to feel that it is within the gingival crevice (361HFig. 8.13 (c))
by probing. If it rests on the gingival crevice then crimp in with some pliers. Again
seat the crown. If it is over-extended, cut down in that area with a stone or scissors
and smooth off before retrying. Check contacts with adjacent teeth and finally polish
the margins with a stone or rubber wheel. Wash and dry the tooth before cementation
with a glass ionomer cement. Seat the crown from lingual to buccal pressing down
firmly (362HFig. 8.13 (d)). Remove excess cement when set with a probe and dental floss
(363HFig. 8.13 (e)), before removing rubber dam and checking the occlusion. Although not
proven statistically beneficial, some operators favour making small holes in the
approximal surfaces of the stainless-steel crown, to confer the benefits of fluoride
release from the glass ionomer cement to the adjacent teeth (364HFig. 8.13 (f)).
365HFigure 8.14 (a)-(d) shows how the restoration of heavily carious primary molars with
stainless-steel crowns has maintained arch space and allowed permanent premolars to
erupt into ideal occlusion.
Success rates of stainless-steel crown restoration
Over the last 20-30 years authors have consistently recorded and reported higher
success rates for stainless-steel crowns as compared with other restorations in primary
molars. In a recently published meta-analysis, it was clear that stainless-steel crowns
were by far the most durable restorations for primary molars, and the most remarkable
fact was that once placed they seldom needed replacing.
366H
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