Anesthetics in Dentistry

The most widely used drugs in dentistry today are local anesthetics. When using local anesthetics, dentists make their choices to achieve profound anesthesia based on body weight of the patient and duration of a dental procedure. A dentist also makes a decision whether it is necessary to use a vasoconstrictor.

Beneficial effects of adding vasoconstrictor are:
  • Decreasing the amount of anesthetic agent used
  • Prolong action of anesthesia
  • Minimizing blood loss during dental surgery
Knowledge of the toxicology and pharmacology of anesthetic agents will maximize the safety of local anesthetic injections. It is always wise to weigh the risks of anesthetic agents and a vasoconstrictor against the benefits for each patient before using anesthetic injection.

DentalVibe Injection Comfort System,
DentalVibe Injection Comfort System,
DentalVibe Injection Comfort System,
New study:
According to a study by the Department of Pediatric Dentistry, Tufts University School of Dental Medicine, the DentalVibe, a handheld device delivers a pulse to block the brain from pain sensation.  When using in conjunction with dental injection, results in a significant reduction of pain in an adolescent.

Standard local anesthetic agents used in dentistry:

Lidocaine Hydrochloride (Xylocaine) with Epinephrine - the most common local anesthetic of the amide type used in dentistry for nerve blocking and infiltration technique.

The active ingredient in Xylocaine is Lidocaine Hydrochloride 20 mg/ml.  The inactive ingredient is Sodium Chloride 6mg/ml.

The active ingredient in epinephrine is Epinephrine Bitartrate 0.01 mg/ml. Inactive ingredients are Sodium Chloride 6 mg/ml, Sodium Metabisulfite 0.5mg/ml, Citric Acid 0.2 mg/ml.

Preparation in 1.8 ml per cartridge:
  • Lidocaine HCl 2%
  • Lidocaine HCl 2% with 1: 100,000 (0.01 mg/ml) Epinephrine
  • Lidocaine HCl 2% with 1: 50,000 (0.02 mg/ml) Epinephrine
Dosage and Administration
For local dental procedures: the dosage of Xylocaine (lidocaine HCl) Injection depends on:
  • The physical status of the patient
  • The anesthetized location
  • The vascularity of the oral tissues at the anesthetized location
  • The technique of administration
Palatal injection before extraction of the permanent maxillary tooth is not necessary according to a study reported in Indian J. Dental 2011.

Inject the least volume of anesthetic solution that yields effective local anesthesia. Observation time for any adverse reaction should be allowed between injections.

In most routine dental procedures, 2% Lidocaine HCl with epinephrine 1:100,000 is a drug of choice. However, when greater anesthesia depth and more pronounced hemostasis is necessary, the preferred dose is a 2% Lidocaine HCl with 1:50,000 epinephrine concentration, provided that the patient does not have heart problems.

In adults, an initial dose is 1½-2½ cartridges (1.0-5.0 mL) of 2% Lidocaine HCl with either epinephrine 1:50,000 or 1:100,000 is sufficient to achieve local anesthesia needed.  An anesthetics action wears off within eight hours.

Avoid injections into the same site over the prolonged period due to the restriction of blood flow influenced by vasoconstrictor agents. Reduction of blood flow may lead to delayed healing, edema, and tissue necrosis at the injection site.

Maximum dose in adult
  • Lidocaine HCl without epinephrine - do not exceed 2 mg/lb (4.5 mg/kg) of body weight or 300 mg
  • Lidocaine HCl with epinephrine - do not exceed 3.2 mg/lb (7 mg/kg) of body weight or 500 mg
Treatment for children age 2-17 based on body weights in Lbs:
  • Calculated according to Clark's rule:
Child's dose = adult dose X (child's weight in pounds ÷ 150)


  • Calculated according to Young's rule:
Child's dose = adult dose x [child's age ÷ (child's age+12 )]

The safety and effectiveness of Lidocaine depend upon;
  • Proper dosage
  • Correct technique
  • Adequate precautions
  • Readiness for emergencies
To avoid high plasma levels and serious adverse effects; use the lowest effective dosage. Repeated dose may cause slow accumulation of the drug or its metabolites in the blood. Tolerance to elevated Lidocaine blood levels varies with each patient. For example, patients with a severe hepatic disease, are at greater risk of developing toxic plasma concentrations due to their inability to metabolize local anesthetics.

Note: The U.S Food and Drug Administration (FDA) warns the use of oral viscous lidocaine 2% solution at the gums in infants and children during pain derived from tooth eruption. Accidentally ingestion or overdose of lidocaine in children and infants may result in hospitalization or death. 

Articaine (Astracaine) is a short-acting amide type of local anesthetic with a rapid metabolism.  It is useful as a nerve block or infiltration with fast onset. For this reason, Articaine is a drug of choice when it is necessary to repeat the anesthesia.

Preparations:

Articaine HCL 4% with Epinephrine 1:100,000, e.g.,
  • Septocaine with Epinephrine 1:100,000
  • Articadent with Epinephrine 1:100,000
  • Zorcaine
Articaine HCL 4% with Epinephrine 1:200,000 is the preferred injection for most routine dental procedure, e.g.,
  • Septocaine with Epinephrine 1:200,000
  • Articadent  with Epinephrine 1:200,000
According to a clinical study from Faculty of Dentistry, Tehran, Iran published in International Endodontic Journal: In comparison between administering lidocaine 2% and articaine 4% for buccal infiltration after inferior nerve block in mandibular. The researchers found articaine provided better successful rate than lidocaine.

Adult dose for Articaine is 3.2 mg/lb (7 mg/kg)
Prilocaine (Citanest) is a local anesthetic of the amide type, dispensed in 1.7 mL cartridges. Prilocaine onset time, when used for an inferior nerve block, is less than 3 minutes with anesthesia duration of approximately 3 hours.

Preparations:
Citanest Plain Dental Injection 4% without Epinephrine
Citanest Forte Dental Injection 4% with Epinephrine 1:200,000

Composition
Citanest Plain: Prilocaine HCl 40 mg/ml
Citanest Forte: Prilocaine HCl 40 mg/ml, Epinephrine (as the bitartrate) 0.005 mg/ml, Sodium Metabisulfite 0.5 mg/ml

Metabisulfite in Citanest Forte may cause allergic reactions including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible patients.

The local anesthetic action of Prilocaine: stabilizing the neuronal membrane and preventing the initiation and transmission of nerve impulses, results in local anesthesia.

Onset time
Infiltration injection with Citanest Plain or Citanest Forte, onset time is less than 2 minutes. Citanest Plain provides an anesthesia of 10 minutes.  It is, therefore, used in short procedures in the maxillary anterior teeth. For extended treatment, use Citanest Forte.

An inferior alveolar nerve block with Citanest Plain or Citanest Forte, onset time is less than three minutes. Citanest Forte provides operating anesthesia of approximately 3 hours; Citanest Plain provides operating anesthesia of 2½ hours.

Adult dosage: maximum dosage is 4 mg/lb (8.0 mg/kg), and not to exceed 400 mg.

Mepivacaine (Carbocaine, Polocaine) is a local anesthetic of the amide type:

Preparations:
Mepivacaine HCl 3%
Mepivacaine HCl 2% with levonordefrin (vasoconstrictor) 1:20,000

Levonordefrin is a vasoconstrictor similar to epinephrine, but less potent in raising blood pressure, and as a vasoconstrictor. Use Levonordefrin with caution in patient with a history of:
  • Heart disease
  • Diabetes
  • Thyroid problem
  • Hypertension
Compositions
Mepivacaine HCl 3%: Mepivacaine HCl 30 mg, Sodium Chloride 6 mg, water 1 ml
Mepivacaine HCl 2%: Mepivacaine HCl 20 mg, Sodium Chloride 4 mg, Potassium Metabisulfite 1.2 mg, Edetate Disodium 0.25 mg, Sodium Hydroxide q.s. ad pH; Hydrochloric Acid 0.5 mg, water 1 ml

The onset time: 30 seconds to 2 minutes in the upper jaw, 1 to 4 minutes in the lower jaw

Anesthesia duration:  Mepivacaine HCl 3% will provide operating anesthesia of 20 minutes in the upper jaw and 40 minutes in the lower jaw.

Mepivacaine HCl 2% with Levonordefrin 1:20,000 provides operating anesthesia of 1 hour to 2.5 hours in the upper jaw and 2.5 hours to 5.5 hours in the lower jaw.

Dosage: 1 cartridge 1.7 ml (34 mg of Mepivacaine HCl 2%, 51 mg of Mepivacaine HCl 3%) for infiltration and block injection is sufficient.

Maximum dose in adult:
  • Mepivacaine HCl 3% is 3 mg/lb, should not exceed 270 mg
  • Mepivacaine HCl 2% with Levonordefrin (vasoconstrictor) 1:20,000is 3 mg/lb, should not exceed 180 mg

Caution:

1. All local anesthetics are capable of producing methemoglobinemia. Patients taking drug-induced Methemoglobinemia are at greater risk for developing Methemoglobinemia, e.g.:
  • Sulfonamides
  • Benzocaine
  • Nitroglycerin
  • Acetaminophen
  • Acetanilid
  • Chloroquine
  • Dapsone
  • Naphthalene
  • Nitrates and Nitrites
  • Nitrofurantoin
  • Nitroprusside
  • Pamaquine
  • Aniline dyes
  • Phenobarbital
  • Para-Aminosalicylic Acid
  • Phenacetin
  • Phenytoin
  • Primaquine
  • Quinine

Methemoglobinemia is a condition where a large amount of methemoglobin presents in the blood.  Methemoglobin is a conversion form of hemoglobin, which does not carry oxygen, results in a bluish discoloration of the lips, mucous membrane, skin, and nail beds.  Other symptoms include weakness, breathing difficulty and may include dizziness in severe cases. The quantity of Methemoglobin in the circulation signifies the severity of symptoms from Methemoglobinemia.

2. Nerve injuries
The two most frequently injured are Inferior alveolar nerve and lingual nerve. It occurs during wisdom teeth extraction, the placement of the dental implant and root canal therapy. If the nerve is traumatized, the patient will feel a sudden onset of pain radiating to the ear.

The duration of the sensory impairment varies widely, depending on the severity of the injury to the nerve. However, nerve tissue can slowly heal itself within six months; any residual sensory deficits beyond that point are assumed to be permanent.
Symptoms of injuries to the inferior alveolar and lingual nerves are:
  1. Numbness in the lips, gums and chin area
  2. A tingling sensation in the lips, chin, and gums
  3. Drooling
  4. Speech impairment
Occasionally, the trigeminal nerve is injured, results in trigeminal neuralgia that causes pain in the forehead, jaws, lips, nose, and the eyes.

3. Intravascular penetration
Occasionally, during lower local anesthetic administration, the needle inadvertently enters a small blood vessel (intravascular) causing the local anesthetic agent to go directly into the bloodstream. If an anesthetic agent includes vasoconstrictor, patient often experiences high blood pressure, nausea, rapid pulse, and seizure. The injection should be made slowly to avoid intravascular injection.   Always, begin with aspiration.

4. Use vasoconstrictor solution in local anesthetic cautiously.  Avoid using vasoconstrictor in patients with a history of hypertension, impaired cardiovascular function, heart disease.

5. Use of sedative: if the sedative is prescribed to reduce patient's apprehension, reduce anesthetic doses.

6. Use local anesthetic with caution in an area involving inflammation or sepsis

7. After injection, patients should be warned of the possibility of biting trauma to the tongue and cheek during the loss of sensation.

Adverse reactions following the administration of local anesthetics often involved the central nervous system and the cardiovascular system

Causes:
  • Dose-related - excessive dosage results in high blood level
  • Rapid absorption
  • Unintended intravascular injection, the incidence can be reduced by performing aspiration before each injection
  • Hypersensitivity to one of the ingredients
  • Patients have little tolerance 
  • Technique used by the dentists
  • Physical condition of the patients
  •  Injury to the nerve during the injection
Symptoms:
  • Central Nervous System
    • Excitation 
    • Depression
    • Nervousness
    • Dizziness
    • Blurred or double vision
    • Tremors
    • Vomiting, 
    • Twitching
    • Drowsiness
    • Convulsions
    • Confusion
    • Unconsciousness
    • Respiratory depression
    • Cardiac arrest

  • Cardiovascular System:
    • Hypotension
    • Bradycardia
    • Cardiac arrest 
    • Sweating
    • Fainted feeling
    • Pulse changes
    • Cerebral hypoxia
    • Seizure.

  • Allergic reaction - characterized by anaphylactic reaction, urticaria, edema, cutaneous lesion

  • Paresthesia, a result of nerve injury
Drug interactions
Avoid administering local anesthetic (with or without epinephrine) to patients taking:
  • Monoamine oxidase inhibitors
  • Tricyclic anti-depressants
  • Phenothiazines
These types of drugs may cause severe and persistent hypertension or cerebrovascular accident.

Prevention is the best management of anesthetic emergencies:

Careful monitoring of respiratory and cardiovascular vital signs and the patient's state of consciousness following each injection.  At the first sign of change, administer oxygen. Endotracheal intubation may be necessary to maintain a patient airway.

Convulsion management consists of maintaining patient's airway, deliver oxygen by mask. 
The clinicians should be familiar with these anticonvulsant drugs before using local anesthetics. Supportive treatment of circulatory depression may require administration of intravenous fluids and, when appropriate, a vasopressor (e.g., Ephedrine).

Cardiovascular depression -  management consists of changing the patient's position in the recumbent position and ventilate with oxygen. The patient may be required an intravenous fluid and, when appropriate, a vasoactive drugs (e.g., Ephedrine or Methoxamine), administered intravenously.

Both convulsion and cardiovascular depression, if not treated immediately or correctly, can cause acidosis, hypoxia, bradycardia, arrhythmia, and cardiac arrest. If cardiac arrest occurs, initiates cardiopulmonary resuscitation.

If Methemoglobinemia occurs (the appearance of cyanosis 2-4 hours following anesthetic injection), administers Methylene blue to reverse the condition.