Types of Local Anesthetics and Their Metabolism

Local Anesthetics

• There are two general types of local anesthetic formulations: Esters (e.g., procaine, benzocaine, tetracaine) and Amides (e.g., lidocaine, mepivacaine, prilocaine, articaine).
• Ester Group: Hydrolyzed in the plasma by the enzymes pseudocholinesterase.
• Amide Group: Primary site of biotransformation is in the liver, and excretion is from the kidney.

Successful Local Anesthesia

• Dependent on:
  • Communication with the child
  • Good topical anesthesia, allowing adequate time for it to act
  • Slow injection of warm solution

Topical Anesthesia

• Reduces discomfort associated with the insertion of the needle before the injection of the local anesthetic.
• Active agent is present in greater concentration in topical preparations than in local anesthetic solutions.
• Uptake from the mucosa is rapid.
• Various anesthetic agents have been used in topical anesthetic preparations, including:
  • Ethyl aminobenzoate
  • Butacaine sulfate
  • Cocaine
  • Dyclonine
  • Lidocaine
  • Tetracaine
• Most commonly employed agents are lidocaine (lignocaine) and benzocaine.
• Ethyl aminobenzoate (benzocaine) liquid, ointment, or gel preparations are probably best suited for topical anesthesia in dentistry.
• Topical anesthetics are available in:
  • Gel
  • Liquid
  • Ointment
  • Pressurized spray forms

Jet Injectors

• Belong in a category somewhere between topical anesthesia and local anesthesia.
• Allow anesthesia of the surface to a depth of over 1cm without the use of a needle.
• Deliver a jet of solution through the tissue under high pressure.
• Used in:
  • Children with bleeding diatheses
  • Jet injection has been used both as the sole means of achieving LA and prior to conventional techniques
  • This method of anesthesia has been used alone and in combination with sedation to allow the pain-free extraction of primary teeth
• Disadvantages:
  • Expensive equipment is required
  • Soft tissue damage can be produced if a careless technique is employed
  • The specialized syringes can be frightening to children because of both their appearance and the sound produced during anesthetic delivery
  • The unpleasant taste of the anesthetic solution, which can accompany the use of this technique

Local Anesthesia Armamentarium

• The Syringe
• The Needle
• The Cartridge
• Other Armamentarium:
  • Topical Anesthetic (strongly recommended)
  • Ointments, gels, pastes, sprays
  • Applicator sticks
  • Cotton gauze

Syringe Components

• Needle adapter
• Piston with harpoon
• Syringe barrel
• Finger grip
• Thumb ring

Needles

• A short (20mm) or long (32mm) 27 or 30 gauge needle may be used for most intra-oral injections in children.
• An extrashort (10mm) 30 gauge needle has been suggested for maxillary anterior injection.
• Long needles are frequently suggested for inferior dental block anesthesia.
• For most injections, the bevel of the needle is oriented toward bone.

Local Anesthesia (LA)

• Maximum Recommended Doses: 4.4 mg/kg body weight
• Dose Calculation:
  • 2% lidocaine = 20 mg/ ml
  • 1 carpule = 1.8ml
  • Amount of LA in 1 carpule = 20X 1.8 = 36mg/carpule
• Example: 20 Kg child can tolerate a maximum dose of 2% lidocaine with vasoconstrictor of LA = 4.4 X 20 = 88 mg = 2.4 carpules

Infection and Local Anesthesia

• If a local anesthetic is injected into an area of infection, its onset will be delayed or even prevented.

Sedation and Local Anesthesia

• As local anesthetics and sedative agents both depress the CNS, it is recommended that the dose of local anesthesia be adjusted downward when sedating children.
• The dosage of local anesthetic does not need to be altered if nitrous oxide/oxygen analgesia/anxiolysis is administered alone.
• For patients undergoing general anesthesia, the anesthesia care provider must be made aware of concomitant use of a local anesthetic containing epinephrine as epinephrine can produce dysrhythmias when used with halogenated hydrocarbons (e.g., halothane).

Types of Injection Procedures

• 1. Nerve block: depositing the LA solution within close proximity to a main nerve trunk.
• 2. Field block: depositing the LA solution in proximity to the larger nerve branches.
• 3. Local infiltration: small terminal nerve endings are anesthetized.

Techniques

• Patient Position:
  • Sitting upright can increase the chance of fainting, whilst at the other extreme (fully supine) the child may feel ill at ease.
  • The upper body should be around 30° to the vertical.

Infiltration Anesthesia

• Maxillary buccal infiltrations
• Infiltration anesthesia is the method of choice in the maxilla.
• The infiltration of 0.5–1.0mL of local anesthetic is sufficient for pulpal anesthesia of most teeth in children.
• The objective is to deposit LA solution as close as possible to the apex of the tooth of interest (supra-periostelly).
• Landmark: insertion 45° to the long access of the tooth.

Areas Anesthetized

• 1. Pulp and root area of the tooth
• 2. Buccal periosteum
• 3. Connective tissue (buccally)
• 4. Mucous membrane (buccally)

Techniques

• Assuming that the proper materials and equipment have been chosen, the following technique can be used to reduce the discomfort of buccal infiltration injections in the maxilla posterior to the canine:
  1. Dry the mucosa and apply a topical anesthetic for 1 to 2 minutes.
  2. Wipe off excess topical anesthetic.
  3. Stretch the mucosa.
  4. Distract the patient (stretching the mucosa and gentle pressure on the lip between finger and thumb can achieve this).
  5. Insert the needle—if bone is contacted, withdraw slightly.
  6. Aspirate; if positive, reposition the needle without withdrawing from the mucosa and when negative proceed.
  7. Inject 0.5–1.0 mL supra-periosteally very slowly (15–30 seconds or via a computerized system).

Palatal Anesthesia

• Anesthesia of the palatal tissues can be one of the more exquisitely painful procedures performed in dentistry.
• Indication: palatal anesthesia for a single anterior tooth removal.
• Techniques:
  • Deposit anesthetic solution in the attached palatal gingiva adjacent to the tooth to be removed.
  • Nasopalatine nerve block: will anesthetize the palatal tissues of the six anterior teeth.

Nasopalatine Nerve Block

• Painful technique (deposition of the anesthetic solution in advance of the needle).
• The path of insertion of the needle is alongside the incisive papilla, just posterior to the central incisors.
• The needle is directed upward into the incisive canal.
• In case of canine, inject a small amount of anesthetic adjacent to the lingual aspect of the canine to anesthetize overlapping branches of the greater palatine nerve.
• If it is observed that the patient does not have profound anesthesia of anterior teeth during the operative procedures with the supra-periosteal technique, a nasopalatine injection is advisable.