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EXCLUSION OF MOISTURE IO7

of the pressure, it returns to its original shape, without

tearing or buckling, it is fit for use. It may be cut into
triangujar, oblong or square form. Cutting into triangular
form is economical, this form being cut from pieces 6 to 9
inches wide. If the oblong form is used for anterior teeth, it

should be about 3K to 4 in. in length, from its upper to its
lower border. For molars the dam should be cut into square
form and measure at least 5 inches from upper to lower border;
while the size and shape for bicuspids should be intermediate
between that for the anteriors and the molars. It should
always be cut large enough to cover the upper lip and chin,

but should not interfere with the nostrils.
For operations on the six anteriors, at least two teeth
mesial and two distal to the tooth to be operated upon should
be included. For the bicuspids of either side, include one

or more of the molars and as far forward as the lateral, while
for molar operations, make the application to include the
bicuspids and at least one, or better two teeth distal to the
one operated upon.
The following conditions regulate the width of space

between the holes:
1. The space between the teeth (wide inter-proximal

spaces, wide spaces between the holes),
2. The height of the gum festoon (large festoons or re-

ceded gums, large spaces),
3. The weight of the dam (light weight, large spaces),
4. The size of the teeth (large teeth, large spaces).
The average space should be from 2 to 4 mm. The size
of the tooth will largely regulate the size of the hole to be cut.
Before and after removal of the dam, the following general

rules should be observed:
I. Remove calculus and glutinous deposits and douche
the teeth with warm water before applying the dam.