restoration are able to resist the normal forces of mastication regardless of loss of tooth
structure caused by caries and cavity preparation. Retention form is a form that tends to
prevent dislodgment of the restoration and is characterized by lock, dovetails, and
undercuts. This step may also be accomplished with a small round bur, inverted cone
bur, or tapered fissure bur. Convenience form will be accomplished at this time to obtain
access for removing the remaining decay and to facilitate placement of the restorative
(2) High speed procedures. Use of high speed cutting instruments reduces
cutting time, increases operator control of the instrument (no tendency to bind, wedge, or
hop), lessens patient apprehension, and reduces operator strain and fatigue.
(a) Control of heat. The main clinical problem in restorative dentistry is
the heat generated during the cutting of the tooth. Temperatures high enough to damage
the pulp can be developed at any speed, but, because elevated temperatures develop
more rapidly at higher speeds, greater care and attention must be given to heat control.
Operating at speeds up to 4,000 rpm and applying moderate force may be done without
generating too much heat, but at greater speeds, coolants must be used. Streams of
water, air, or mixture of air and water are used as coolants. Air is effective only in the
lower ranges of high speeds. For higher speeds, a spray or stream of water must be
used. In addition to lowering the temperature in the field of operation, the coolant carries
away debris produced by the cutting operations of the bur and helps prevent clogging of
the bur's cutting surface. Instruments so cleaned cut more rapidly and last longer. A
number of devices have been developed for delivering the coolant to the cutting site by
the handpiece. These may be attached to or built into the handpiece. The dental officer
may prefer not to use such a device or one may not be available. In this case, the dental
specialist must apply the coolant with a hand-held water syringe.
(b) High-speed hand pieces. Hand pieces designed to operate at
speeds up to 8,000 rpm will not operate satisfactorily at higher speeds. Increased speed,
therefore, has required greater precision in manufacture and replacement of sleeve-type
bearings with ball, roller, or needle bearings. Care of the handpiece, which was always
important, has become even more critical.
(c) High velocity evacuation. Since high-speed handpieces require a
continual flow of water for cooling during cavity preparation, there is a need for more
efficient removal of water from the oral cavity than is possible with the saliva ejector. One
method employs a suction apparatus that uses a vacuum pump to remove large volumes
of saliva, water, and debris through a tube and mouthpiece of large diameter. Thus, high
velocity suction can be achieved with little suction pressure. A number of mouthpieces
have been designed for different operations in different locations of the mouth. The
mouthpiece of this instrument functions best when handled by the chair assistant.
Advantages of this system are that it relieves tension of the patient by keeping fluids out
of his throat and relieving the need to use the cuspidor, helps to keep the operating field
dry and the mirror clean, and saves time by eliminating rinsing.