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CROWN- AND BRIDGE-WORK. 185

the space where tlie roots liave been renioNcd—lia\e neither
collars nor posts. Jn constrncting these teeth, the matter
of cleanliness should cs])eciall_\' be considered; where it is
admissible to allow them to come in contact with the gum-
tissue (as in the anterior part of the mouth), only the cer-
vical porcelain tips should touch. The metallic backing
and solder should recede, leaving self-cleansing spaces.
Limitations.— l^\:)r the support of bridge-dentures strong,
healthy roots are required, and the width of the space to be
spanned must be go\-erned by the size and strength of these
Fig. 160.

points of anchorage. Whether a full upper or lower den-
ture can be supported by four points of attachment depends
upon the relative smallness of the jaw, the size and strength
of the roots and teeth, and the occlusion, the operator always
being governed by the condition of individual cases. For
instance : One strong central root will support two teeth,
that is, the crown and either the adjoining central or lateral.
Two central roots will support the four incisors. Two
strong cuspid roots alone, or with the aid of a central root,
will support the six anterior teeth. A cuspid root and a
strong, healthy second or third molar on the same side will
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