First, always check the carpule for cracks or
suspended articles floating in the solution. If you find
any, discard the carpule and notify the dental and
dental supply to ensure other batches of anesthetic are
usable. Disinfect the rubber diaphragm on the carpule
before loading it in the syringe. Do not touch the
rubber diaphragm after you disinfect it. Placing the
carpule end in the aspirating syringe is fairly easy. Use
the following steps:
Use the thumb ring to pull the plunger back
against the syringe body.
Place the cartridge into the barrel of the syringe
with the rubber stopper end in first, positioned toward
Break the seal on the needle container and
remove only a small portion of the plastic needle cover.
Insert the needle into the syringe and screw the
hub onto the syringe.
ring with your other hand.
Engage the harpoon into the rubber stopper of the
cartridge by holding the body portion of the syringe
with one hand while lightly tapping the end of the thumb
Do not tap the thumb ring with too much force;
this might cause the glass carpule to shatter.
Make a quarter turn with the thumb ring to
ensure that the harpoon is firmly engaged in the
rubber stopper. If it is, the thumb ring will rotate
back to its original position.
Force a small, but visible amount of
anesthesia through the needle to expel air.
Loosen the needle cap, but keep the plastic
needle covering in place until you pass the syringe to
the dentist to guard against possible contamination.
The plastic needle cover must be removed to
check the syringe's operation and during the
Passing and Receiving the Syringe
The dentist will be ready to administer the local
anesthetic after the topical anesthetic is applied. The
assistant passes the syringe with the needle cover in
place. Hold the barrel of the syringe in your hand.
Place the thumb ring of the syringe over the dentist's
thumb and the finger grip between the dentist's index
and middle fingers. While you are still holding the
syringe by the barrel, use the other hand to remove the
After the dentist gives the injection, carefully
remove the syringe by grasping the barrel and lifting
the syringe out of the dentist's hand. Remember to
exercise extreme caution when grasping the barrel of
the syringe because the needle is exposed and
contaminated. DO NOT attempt to recap the needle
while the syringe is in the dentist's hand. If it is
necessary to recap the needle, it must be done using
some type of mechanical device or the one-handed
scoop technique discussed in Volume I, Chapter 9,
Disassembling the Aspirating Syringe
After the patient is dismissed, the syringe must be
disassembled safely. It is vitally important to prevent
needle sticks from the contaminated needle. It is
advisable to first remove the carpule with the needle
remaining in place.
This provides an air vent to
prevent the glass carpule from shattering. To unload
the carpule, pull the piston rod back as far as possible to
disengage the harpoon from the rubber stopper without
pulling the stopper from the carpule. The carpule can
then be easily removed from the syringe. Remove the
used needle and dispose of it into a puncture-resistant
container according to established infection control
IRRIGATION AND ASPIRATION
Immediately after the dentist administers the local
anesthesia, you will irrigate and aspirate the injection
site. This is necessary because the anesthetic solution
produces a bitter taste in the patient's mouth.
Additionally, you are required to irrigate and aspirate
(drawn by suction) often throughout the treatment
procedure to maintain a clean treatment site.
The dentist expects you, as the dental assistant, to
irrigate the oral cavity when necessary. By applying
water or saline solutions to the treatment site in the oral
cavity, small tooth particles, dried blood, and other
debris are flushed from the area and removed by
aspiration. Handpieces with water spray systems
provide some irrigation, but additional irrigation is
always necessary. At times, the dentist may decide not
to use the water spray system on the handpiece for a
particular procedure. During routine operative
procedures, you will use the three-way syringe on the