Dental Syringe Mechanism and Types

Dental Syringe

• Dental syringes are the standard of care due to their ability to aspirate blood if the needle tip is intravascular.
• The armamentarium includes 4 parts: syringe, needle, cartridge, and preparation.
• Syringe parts include thumb ring, finger grip, piston rod, barrel, harpoon, and threaded tip

Parts of a Dental Syringe

• Threaded fitting for the needle
• Slit for inspecting the tubular vial
• Coupling for the plunger of the tubular vial
• Barrel
• Finger grip
• Plunger
• Handle

Self-Aspirating Uses

• The elasticity of the rubber diaphragm in the anesthetic cartridge allows for multiple aspirations easily.

Aspirating Syringe

• The needle adaptor is sometimes inadvertently discarded with the disposable needle.
• The harpoon is a sharp tip on the piston that penetrates the thick silicone rubber stopper at the cartridge's other end.

Pressure Syringes

• Used for PDL (intraligamentary) injections.

Additional Syringe Types

• Second generation PDL Syringes
• Jet Syringes: needle-less injection, forces liquids through small openings (jets) at very high pressure, penetrates skin and mucous membrane
• Syrijet is the most popular jet syringe, holds 1.8ml cartridges of local anesthetic.

Safety Syringe

• Some dental safety syringes come with autoclavable plungers and disposable self-contained injection units.
• All dental safety syringes are single use items.

2-Dental Needles

• Components include bevel, shank, hub, syringe adaptor, and cartridge penetration end.

Parts of a Needle

• Bevel
• Shaft
• Gauge number
• Hub

Needles Divided by Length

• Dental needles are available in long, short, and ultrashort lengths.
• The most common are long and short.
• Lengths may vary by manufacturer, long needles are generally 32mm (1.5in) and short 20mm (1.0in).
• Long needles are for mandibular blocks (20-25mm penetration depth).

Needle Breaking & Placement

• Needles can break at the hub easily.
• If broken, and less than 5mm of it is exposed, it's difficult to retrieve.
• Long needles are usually preferred for the anterior superior alveolar (ASA)/infraorbital injections.
• Short needles are preferred for posterior superior alveolar (PSA) injections, supraperiosteal injections, and tissue infiltrations.

Needle Gauge

• Needle gauge refers to the diameter of the lumen(hollow tunnel).
• Common gauges include 25, 27, and 30.
• Larger number equates to thinner and smaller gauge.
• 25 and 27 gauge are most common.

Needle Gauge Recommendations

• 25-gauge needles are recommended for injections with high risk of positive aspiration and significant depth of penetration.
• 27-gauge needles are restricted to injections with minimal depth of penetration and positive aspiration risk.
• 30-gauge is not typically used for deeper injection.

Bevel Correct Position

• The bevel should be oriented towards the bone during injections close to the periosteum.
• This reduces trauma and increases patient comfort.

Dental Cartridge (Carpuke)

• A glass cylinder containing local anesthetic solution.
• Parts include cylindrical glass tube, stopper, aluminum cup, diaphragm.
• Glass cartridges should not be autoclaved.