The Use of the PDL Syringe for Inter Osseous Injections
Note: Recently( August 2002 ) Changes have been made to the PDL Intraligamentary Syringe that make it possible to replace internal parts without sending it in to the manufacturer. To see a video of those modifications you can click here. It is about 15 minutes long and includes some other information as well.

Much has been made of the difficulty of administering InterOsseous anesthesia, i.e. the awkwardness of finding the small hole previously drilled with the needle.

I would take this opportunity to remind you of some principles of work simplification most of us learned in dental school.

There are four (actually five) different levels of hand movement. They are:

1. Fifth Degree - movement from the waist(rarely used in dentistry)

2. Fourth Degree - movement that occurs from the shoulder

3. Third Degree - movement that occurs from the elbow

4. Second Degree - movement that occurs from the wrist

5. First Degree - movement that occurs from the fingers only

Any time that we can use First Degree movement we have better control and thus accuracy. Furthermore, with the fourth finger resting on the same arch as the target tooth, if the patient moves the instrument moves with it.

Using a conventional hypodermic type syringe for injections precludes First Degree because we need almost all the fingers to hold onto the syringe and to squeeze the plunger.

Even if we assist this motion with a pistol type syringe we are limited to Third Degree, unless we can rest our wrist on something.

The PDL Intraligamentary Syringe is designed so that it can be held much like a dental handpiece i.e. in a pencil grip (or thumb-palm grip) and apply pressure to the lever with the index finger or thumb, thus making it possible to use a fourth finger rest and thus a First Degree of Motion giving us much greater control.

The unique compound lever action of the PDL makes it possible to exert all the pressure that is necessary to inject against InterOsseous or IntraLigamentary back pressure.

The leverage factor is 18 to 1, i.e. one pound of pressure exerted by the index finger produces 18 pounds on the plunger making it much easier to control the pressure while still maintaining First Degree Motion capability.

Since with InterOsseous anesthesia a contra angle is used to drill a 27 gauge hole in the buccal plate, this is a first degree motion.

While the tissue is still stretched over the hole,

the dental assistant simply removes the contra-angle from the dentist's hand an replaces it with the PDL Intraligamentary Syringe, without the dentist taking his eyes off the 'target.'

Each 'click' of the PDL delivers a metered 1/20cc of fluid.

The syringe can be held in several positions:

• Pencil Grip i.e. actuating the lever with the index finger

• Thumb Palm Forward i.e. actuating the lever with the thumb

• Cross Hand i.e. syringe held between third and fourth fingers

• Thumb Palm Backward i.e. with thumb pointing away from the patien but needle toward

• Modified Fist Grip i.e. holding syringe upright in the fist actuating the lever with third or fourth fingers