Local Anesthetic Delivery Devices

Introduction

• This chapter discusses devices required for the delivery of local anesthetic agents.
• A thorough knowledge of these devices is necessary for appropriate selection and use.
• Practices for safe handling and disposal of the devices will also be discussed.

Devices for Pain Control

• Origin of dental syringe: Harvey Cook
  • Breech-loading
  • Cartridge-type
• First aspirating syringe: Novocol
  • Harpoon-type

Armamentarium

• Mouth mirror
• Recapping/needle disposal devices
• Syringe
• Cotton pliers/hemostat
• Gauze squares
• Cotton swabs
• Needles of appropriate gauge and length
• Cartridges of drugs
• Topical anesthetic agents

Anatomy of a Dental Syringe

• Thumb ring
• Finger grip
• Spring
• Guide bearing
• Piston with attached harpoon
• Syringe barrel
• Needle adaptor

Syringe Types

• Syringes are selected based on technique and clinician preference.
• They include a number of manual and computer-controlled devices.
• Syringes vary in size and design. Clinician preference may be based on hand size.
• Small, Medium, and Large Syringes: Septodont USA has redesigned their syringes to accommodate small, medium, and large hands. Note the graduated sizes of the thumb ring.
• Self-Aspirating Syringes: Self-aspirating syringes do not have harpoons to seat into stoppers.
• Breech-loading Syringe: An example of a breech-loading device (most commonly used today).

Thumb Rings Designs

• Silicone coatings may reduce “slipping” during aspiration procedures and are available on both standard and petite syringes.
• Round thumb rings
• Oval thumb rings. Note the distance from the piston to the upper inside surface of the ring.

Anatomy of a Local Anesthetic Needle

• Needle shaft
• Beveled tip
• Cartridge penetrating end
• Syringe adaptor
• Hub
• Needle cap
• Needle hubs are either metal or plastic, and either prethreaded or self-threading.
• To attach the needle:
  • the cartridge penetrating end is inserted through the cartridge diaphragm;
  • the needle is screwed onto the syringe with firm pressure;
  • once seated, check the bevel orientation.
  • Some needles have dots, arrows, or other markings on their hubs that correspond to the locations of the bevel lumens or openings.

Gauge

• Diameter of the lumen of a needle. The smaller the number, the greater the diameter of the lumen.
• Larger gauge
  • Less deflection
  • Greater accuracy
  • Decreased needle breakage
  • Aspiration easier
  • More reliable
  • 25-gauge preferred
• 100% positive aspirations achieved with 25- gauge needles; 87% positive aspirations with 27-gauge needles; 2% positive aspirations with 30-gauge needles
• 25 gauge should be used when there is a greater risk of positive aspiration: Inferior alveolar, PSA, Mental, incisive nerve block.

Advantages of Larger Gauge Needles

• Less deflection and greater accuracy.
• Less chance of needle breakage.
• Easier and more reliable aspiration.
• No perceptual difference in patient comfort.

Color-Coding

• 25 gauge, red
• 27 gauge, yellow
• 30 gauge, blue

Needle Length

• Long: 1 5/8 inches or 40 mm, average length 32mm from tip to hub
• Short: 1 inch or 25 mm, average length 20mm
• Ultrashort – 30-gauge. Significant differences in length among manufactures

Important Notes

• Never insert a needle up to its hub, as it increases the potential for needle breakage.
• The weakest portion of the needle is at the hub.

Care and Handling

1. Never use on more than one person
2. Change after every 3 to 4 penetrations
3. Cover with protective sheath when not in use
4. Always be aware of the position of an uncapped needle
5. Properly dispose of after use
   1. In Sharps container
   2. Recap with scoop technique or needle holder

• Common Needle Lengths Used in Dentistry
  • Average lengths:
    • Long needles ~32 mm (1½ inches)
    • Short needles ~25 mm (1 inch)
    • Extra-short needles ~12 mm (½ inch)

Needle Deflection

• Traditional