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702 ORTHODONTIA AS AN OPERATIVE PROCEDURE.
root. The result is an enlarged socket in which the tooth never again
becomes rigid.
Permanent enlargement of the alveoli may occur also from not
retaining teeth fixedly in their new position but allowing them to move
back and forth. The action of the osteoblasts in forming new bone is
thus interfered with so much as to absolutely prevent it, and the result
is an enlarged alveolus.
Injury to the Enamel (Caries).—This may occur from too long
retention of either regulating or retaining appliances in contact with
the teeth.
Bands that are to be retained more than a few weeks should be
cemented upon the teeth and carefully watched, as a loose band will
surely result in a softening of the enamel under
Fig. 619.
it, sometimes even to the extent of forming a
cavity.
Retaining appliances should be so constructed
that no flat or broad surfaces remain in contact
Round and flat contacts
in regulating fixtures. with the teeth. A round wire is as efficacious
as a flat bar, and the tooth under it is easily kept clean, as the point
of contact is so small. (See Fig. 619.)

Appliances, Materials, Methods, and Forces Employed.
Definitions.—To prevent repetitions a few appliances and materials
will be briefly described.
Rubber Band.—A section cut from French rubber tubing from
of an inch in diameter and from g\ to i of an inch wide. (See
i to i
Fig. 620.) These lose their elasticity by remaining stretched, and should
be changed at least twice a week.

Fig. 020. Fig. 621.

Bicuspid. Molar.
Rubber tubing for bauds. Adjustable bands (Angle).
Gauge.—In indicating the thickness of plate and size of wire the
number referred to is that of B. & S. gauge, c. g. wire No. 20, plate
No. 27, etc.
Tube or Tubing.—Made of a strip of platinum-gold or German
silver No. 27 to No. 32 gauge and \ of an inch or less wide, drawn
through successive holes in a draw-plate until a tube is formed and
reduced to the desired size. (See Fig. 628.) To make a tube to fit any