Dental Local Anesthesia

Local Anesthesia

• Local anesthesia is the loss of sensation in a circumscribed area of the body caused by a depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.

Properties of a Local Anesthetic

• Should not be irritating to the tissue it is applied to.
• Systemic toxicity should be low.
• Must be effective regardless of whether it is injected into the tissue or applied locally to mucous membranes.
• Time of onset of anesthesia should be as short as possible.
• Duration of action must be long enough to permit completion of the procedure yet not so long as to require an extended recovery.
• Should not cause any permanent alteration of nerve structure.

Composition of a Local Anesthesia Agent

• Local anesthetic (e.g. lidocaine hydrochloride).
• Vasoconstrictor (e.g. epinephrine).
• Preservative for vasoconstrictor (e.g. sodium bisulfite).
• Isotonic solution (e.g. sodium chloride).
• Preservative (e.g. methylparaben).
• Sterile water to make up the rest of the volume.

Commonly Used Local Anesthetics

• 2% lidocaine with 1:100,000 epinephrine (most commonly used).
• 4% articaine with 1:100,000 epinephrine.
• 0.5% bupivacaine with 1:200,000 epinephrine (long acting).
• 3% mepivacaine with 1:20,000 levonordefrin.

Local Anesthetic Overdose

• Develops when the blood level of the drug in a target organ (e.g. brain) becomes excessive.
• Can cause central nervous system (CNS) and cardiovascular system (CVS) depression.
• Reactions can range from mild tremor to tonic-clonic convulsions (CNS) and from a slight decrease in blood pressure and cardiac output to cardiac arrest (CVS).
• Maximum recommended doses (MRD’s) of all drugs administered by injection should be calculated by body weight and should not be exceeded.

Classification of Local Anesthetics

• Based on chemical structure: ester group (e.g. cocaine, benzocaine, procaine, tetracaine) and amide group (e.g. lidocaine, mepivacaine, prilocaine, etidocaine, bupivacaine).
• Based on duration of action: short acting (e.g. procaine), intermediate acting (e.g. lidocaine), and long acting (e.g. bupivacaine).

Complications of Local Anesthesia

• Local complications: hematomas, infection, trismus, nerve damage by the needle, needle breakage in soft tissues, and masticatory trauma.
• Systemic complications: allergic reaction, cardiovascular and central nervous system dysfunction.
• Management of soft tissue trauma involves reassuring the patient, allowing time for the anesthetic effects to diminish, and coating the involved area with lubricant.

Anesthesia for the Maxillary Tissues

• Posterior superior alveolar nerve block: innervates the posterior maxillary deciduous molars.
• Middle superior alveolar nerve block: innervates the premolars and the mesiobuccal root of the 1st permanent teeth.
• Maximillary anterior region block: infiltration in the apical region of the anterior teeth provides satisfactory anesthesia in most cases.
• Infraorbital nerve block: the infraorbital foramen in a 3-year-old is about 5 mm above the vestibular depth.
• Palatal infiltration: anesthetic agent is injected into the depth of rugae as they contain less sensory endings.
• Nasopalatine nerve block: nasopalatine nerve innervates the maxillary anterior teeth.
• Greater palatine nerve block: greater palatine nerve innervates the maxillary posterior teeth in the palatal aspect.

Anesthesia for the Mandibular Tissues

• Inferior alveolar nerve block: for anesthetizing the molars and premolars.
• Factors to be considered: the mandibular foramen is located near the posterior border of the ramus in children.
• Technique: the needle is penetrated into the pterygomandibular space and the solution is deposited close to the mandibular foramen.
• Lingual nerve block: the needle has to be withdrawn and solution deposited half the distance from the inferior alveolar foramen.
• Buccal nerve block: can be anesthetized by infiltration in the buccal sulcus distal to the permanent teeth.
• Mental nerve block: anesthetizes the anterior teeth and premolar.