Despite being in clinical use for more than a century, local anesthetics (LA) continue to surprise researchers and clinicians alike.
It is defined as a loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves(Stanley F Malamed,1980).
The 1st chemical local anesthetic came with discovery of cocaine in 1860 by Albert Nieman, but its anesthetic property was not realized until in 1862 when Schraff noted its local effect on tongue. William Halsted Steward carried out the 1st recorded inferior dental nerve block using cocaine in 1884.Modern chemical LA agents came of age when Alfren Einhorn achieved esterification of the base alcohol with benzoic acid to synthesize procaine in 1904-1905. Lofgren succeeded in synthesizing Lidocaine from a series of aniline derivatives in 1943. Bupivacaine became the longest acting amide LA in 1980’s to be followed by Rupivacaine in mid 1990.
On the basis of myelinated and non myelinated, diameter and velocity, nrebe fibres have been classified into different categories
| CHARACTERSTICS | A alpha | A beta | A gamma | A delta | C | |
| MYLEIN | +++ | ++ | ++ | ++ | + | - |
| DIAMETER(µm) | 12 to 20 | 5 to 12 | 5 to 12 | 1 to 4 | 1 to 3 | 0.5 to 1 |
| CONDUCTION VELOCITY(m/sec) | 70 to 120 | |||||
| ONSET TIME | 6 | |||||
| FUNCTION | Motor muscle propiception | Touch , pressure propioception | Touch, motor propioception | Pain, temperature ,pressure propioception | Preganglionic autonomic( sympathetic)activity | Pain,temperature ,pressue, itchpst ganglionic sympathetic |
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Esters of Benzoic acid (ESTER GROUP) It includes Butacaine , Cocaine, Ethyl Amino Benzoate, Benzocaine, Piperocaine, Tetracaine
Esters of paraamino benzoic acid: Chloroprocaine, Procaine, Propoxycaine.
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Injectable:
A) Low potency, short duration: Procaine, Chloroprocaine
B) Intermediate potency & duration: Lidocaine, Prilocaine.
C) High potency & longduration: Bupivacaine, Tetracaine.
Electrical potential theory
Acetycholine theory
Interference with nerve metabolism
Reversible coagulation theory
Plasma membrane expansion theory
Calcium gate theory
Specific receptor theory (most accepted): According to this theory the LA agent acts by binding to specific receptors that are present on the sodium channel. The action of the drug has been stated to be direct & involves the binding of the agent to the specific receptor & prevents the entry of sodium into the cell.
Adminstration of agent is nonirritating
Little or no allergenicity
A rapid onset & adequate duration
Anesthesia is completely reversible.
Minimal systemic toxicity.
Anesthesia is selective to nociception pathway
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Extraction of teeth.
Alveoloplasty and alveolectomy.
Incision and drainage of abcesses.
Cavity preparation especially in deep painful cavities.
Pulp procedures like pulpotomy and pulpectomy.
Periodontal surgery and gingival surgery.
Cyst enucleation or marsupialization
Removal of residual infection, small neoplastic growths and salivary stones etc.
Sore spots as a result of denture get relieved
Treatment of trismus and trigeminal neuralgia
In patients who shows gagging especially during placement of film.
For anesthesia of oral cavity and jaw bones for routine surgical procedures like treatment of fractures etc.
Fearful and apprehensive patients who refuse for injection.
Allergy to local anaesthetic solution.
Acute infection.
Mentally retarded and unco-operative children or very young children.
Anatomic anomalies.
Hyperthyroidism, Liver disorders, Renal disorders, Cardiac problems, Diabetes mellitus.
Internal hemorrhage.
Major oral surgical procedure
Caused by anesthetic solution.
2.Caused by vasoconstrictor drugs
3. Local reactions
4. Complications attributed to needle insertion
Sign and symptoms
Central Nervous System: All LA produces a sequence of stimulation followed by depression. Lidocaine toxicity may commence at concentrations >5 μg/mL, but convulsive seizures
generally require concentrations >8 μg/mL.
Cardiovascular Reactions: These are cardiac depressants but no significant effects are seen at conventional doses. Bupivacaine is relatively more cardiotoxic & can produce ventricular tachycardia. Lidocaine has little effect on contractility b& conductivity & is used as an antiarrythmic agent.
Blood vessels: Cause fall in blood pressure. This is primarily due to sympathetic blockade, but high doses do cause direct relaxation of arteriolar smooth muscles.
Methemoglobinemia: A metabolite of prilocaine,
Peripheral Nerve Paresthesia: Articaine is associated with fivefold higher incidence of paresthesia compared with lidocaine. There can be damage to inferior nerve or lingual nerve.
Allergic Reaction: The amide local anesthetics appear to have an extremely little immunogenic and therefore low rate of allergic reactions.
Reaction to Anesthetic Formulations contaning a Sulfite Antioxidant: Allergic reactions like urticaria, bronchospasm & anaphylaxis. The use of local anesthetic without vasoconstrictors is a possible alternative with these patients.
For prolong action of local anesthetic solution and to reduce its toxicity, vasoconstrictors have been added but its addition lead to contraindication of local anesthetic solution in various patients like in cardiac patients especially those suffering from refractory dysrhythmias, angina pectoris, postmyocardial infarction (6months) and uncontrolled hypertension. Other contraindications to vasoconstrictors are endocrine disorders such as hyperthyroidism, hyperfunction of the medullary adrenal (pheochromocytoma) and uncontrolled diabetes mellitus.
Infections caused by contaminated solutions are rare because of high standard of asepsis practiced by manufacturers.
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Sign and Symptoms
Pallor, Nausea, Vomiting, Patient may feel strange or different, Unconsciousness, Bradycardia and Hypotension
Stop the dental procedure.
Lower the chair back and elevate the legs of the patient.
If patient is conscious, instruct him to take deep breath.
Check patients BP, pulse rate and color.
Ensure adequate oxygenation and CVS stability.
Common and mainly occurs after inferior alveolar nerve block.
Causes: Trauma to muscle during insertion, Infection (local), Hemorrhage.
Treatment
Mild: Slight exercises coupled with application of moist warm compresses for 15-20 min. /h, Mild analgesics, Physiotherapy consist of opening closing and side to side movement 5-10 min. every 3-4 hrs.
Severe: Add centrally acting muscle relaxant
Most commonly occur due to carelessness of dentist.
Prevention: Use Sharp needle, No multiple traumas, Needle insertion should be Atraumatic and slow, LA should be forced into the tissue slowly.
Most annoying and depressing complication of anesthesia.
Prevention : Do not force needle against resistance, Do not change the direction of the needle while embedded in tissue, Do not use needle of too fine a gauge, Do not use resterilized needle & Inform the patient before inserting the needle
It is associated with posterior superior alveolar nerve block and infraorbital nerve block. Occurs because of improper technique.
Treatment
Subsequent: Do not apply heat to the area for 6 to 8 hours after the incident. Application of ice to the region immediately and reassure the patient.
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(a) Sprays: Sprays are useful because of their rapidity of action.The active ingredient is 10% lignocaine hydrochloride in a water miscible base, which is expelled in small quantities from an aerosol container. The onset time of anesthesia is approximately 1 min & the duration about 10 min.
(b) Ointments & Jelly: Ointments containing 5% lignocaine hydrochloride can be used for a similar purpose, but it takes 3-4 min to produce surface anesthesia. It is occasionally used to produce surface anesthesia prior to incision of fluctuant abscesses.
(c) EMLA (Eutectic Mixture of Local Anesthetics ) : EMLA cream (composed of lidocaine 2.5% & prilocaine 2.5%) is an emulsion in which the oil phase is a eutectic mixture of lidocaine & prilocaine in 1:1. Usually anesthetic solutions work on abraded skin but it provides anesthesia to intact skin
Indication: In pediatrics, Vein puncture, Suture removal, Split thickness skin graft , Pulpal anesthesia and Needle phobic patients
Contraindications : Patients with congenital/ idiopathic methemoglobinemia, Infants under the age of 12 months and Patients allergic to local anesthesia
2. Local Infiltration: In this, local nerve endings in the area of surgery are flooded with local anesthetic solution, rendering them insensitive to pain or preventing them from becoming stimulated & creating an impulse. Incision is then made into the same area in which the local anesthetic has been deposited.
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7. Supraperiostal Injection: For obtaining pulpal anesthesia in maxillary anterior teeth when treatment is limited to one or two teeth.
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9. Greater or Anterior Palatine Nerve Block :Nerves anesthetized: Greater palatine nerve. Region anesthetized: Posterior portion of hard palate & its overlying soft tissues anteriorly till 1st premolar.
10. Infraorbital Nerve Block
Nerves anesthetized : Anterior superior alveolar nerve, Middle superior alveolar nerve, Infraorbital nerve , Inferior palpebral branch, Lateral nasal branch Supeior labial branch
Regions anesthetized: Maxillary central incisors upto maxillary premolars, MB root of 1st molar & buccal investing tissues.
11. Nasopalatine Nerve Block
Nerves anesthetized: Nasopalatine nerves bilaterally.
Regions anesthetized: Anterior portion of hard palate from 1st premolar to 1st premolar.
12. Maxillary Nerve Block
Nerves Anesthetized: Maxillary nerve & its branches.
Area anesthetized: Maxillary teeth, overlying bone & mucosa on the affected side, Hard & soft palate , Upper lip, cheeks, side of the nose & lower eyelid.
1. Supraperiostal (Infiltration): recommended for limited treatment protocols
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1. Mental & Incisive Nerve Block
Nerves anesthetized: Mental & incisive nerves.
Regions anesthetized: Lower lip, Mucosa anterior to mental foramen, teeth anterior to second premolar.
2. Classical Inferior Alveolar Nerve Block
Nerves anesthetized: Inferior alveolar, incisive, mental & lingual nerve.
Regions anesthetized: Mandibular teeth & buccal soft tissues anterior to 1st molar & anterior 2/3rd of tongue & floor of the mouth.
3. Closed Mouth Approach (Vazirani-Akinosi Block)
Nerves
4. Gow-Gates Nerve Block: It is an intraoral mandibular nerve block given at neck of condyle & provides hard & soft tissue anesthesia of mandible upto the midline. Mandibular nerve & its branches are blocked including its auriculotemporal subdivision.
Preanesthetic evaluation should be done before administering any anesthetic drug. It is done to secure pertinent information to evaluate and not to diagnose or treat the patient for any medical problem. It is done to determine the following:
Patients general and psychological condition.
Need for medical consultation.
History of any previous unpleasant esthetic experience.
Specific drug sensitivity of the patient.
The need for premedication or intraoperative sedation.
The time to be allotted for procedure.
The technique or method to be used.
Choice of an anesthetic solution.
The need and quantity of vasoconstrictor.
On first visit patients pulse rate and blood pressure should be taken. Brief medical history should be taken. It involves:
CVS Status
Any respiratory difficulties, nervous system disorder, metabolic deficiencies, endocrine imbalance, hematological pathologies & iatrogenic conditions
Presence of allergy, patient’s size and age, emotional or psychological problems.
Medications the patient may be taking
Consultation with patient physician taken when indicated.
Procedure should be planned to fit the individual patient condition.
If patient is anxious he should be moderately premedicated or sedated during appointment.
He should be given short appointment to prevent undue tiring.
Least possible amount of anesthesia should be used.
Vasoconstrictors, although not contraindicated, should be kept at a minimum dose or eliminated if necessary.
Patient may be given oxygen by nasal cannula during procedure.
Prophylaxis with appropriate antibiotics should be given if indicated
Precautions
Treatment should be given in afternoon.
Preoperative medications such as adhesives, hypnotics and narcotics should be used with extreme caution as they interfere with cough reflex and depress ventilation.
Bronchodialators, nebulizers and expectorants can be given preoperatively.
Choice of local anesthetic or vasoconstrictor is not of utmost importance provided there are no other complicating pathologies.
Oxygen can be given by nasal cannula if required during dental procedure.
(1) Diabetes Precautions
. Severity of diabetes.
Evaluate the patient treatment whether diabetes is controlled by diet/hypoglycemic agents/insulin.
Patient controlling diabetes by diet pose no problem.
Patient on insulin should be treated between 9.00 am – 12pm because as a result of food and insulin intake, it is during these hours that they are best able to tolerate stressful situations.
(2) Hypothyroidism
These patients do not metabolize drug as well as the normal individual therefore doses of vasoconstrictors in drug should be kept minimum because of relative CVS conditions.
(3) Hyperthyroidism
Physician consultation
Well premedication/sedation
Vasoconstrictor should be reduced.
Local anesthetics can be safely used when treating pregnant & postpartum patients if careful guidelines are followed . Because teratogenic risks are highest in the first trimester, the 2nd trimester is usually the period chosen for routine dental care. Lidocaine is least associated with medical complications.
1. Administer LA away from the area of inflammation: It helps in preventing the spread of infection to uninvolved regions. It also provides adequate pain control because of presence of more normal tissue condition. Regional nerve block anesthesia is the major factor in pain control for pulpally involved teeth.
2. Deposit a larger volume into the region : It will provide a greater no. of uncharged base molecule to diffuse through the nerve sheath to give satisfactory nerve block. Some patients respond unfavorably to instrumentation of their root canal, even when canals are debrided thoroughly.
Solution : Infiltration, Intrapulpal anesthesia & Topical anesthesia: Can apply a small amount of topical anesthetic ointment onto the file or reamer prior to inserting it into the canal.