INTRODUCTION:

Pain prevention in pediatric dentistry is crucial for a child in achieving positive experience during the dental visit, building trust and cooperation and making future visits enjoyable. One of the main methods to prevent pain is the administration of local anesthesia. ^[1,2]

Local anesthesia is the temporary loss of sensation including pain in one part of the body produced by a topically-applied or injected agent without depressing the level of consciousness. Local anesthetics act within the neural fibers to inhibit the ionic influx of sodium for neuron impulse. ^[3,4]

The pediatric dental professional should be aware of proper dosage (based on weight) to minimize the chance of toxicity and the prolonged duration of anesthesia, which can lead to accidental lip, tongue, or soft tissue trauma. ^[5]Knowledge of gross and neuroanatomy of the head and neck allows for proper placement of the anesthetic solution and helps minimize complications. Familiarity with the patient’s medical history is mandatory to decrease the risk of aggravating a medical condition while rendering dental care. Medical consultation should be obtained as and when needed. ^[4,5]

How Local Anesthetics Work:

The primary action of local anesthetics in producing a conduction block is to decrease the permeability of ion channels to sodium ions (Na+). Local anesthetics selectively inhibit the peak permeability of sodium, whose value is normally about five to six times greater than the minimum necessary for impulse conduction (e.g., there is a safety factor for conduction of 5× to 6×). ^[4]

Local anesthetics reduce this safety factor, decreasing both the rate of rise of the action potential and its conduction velocity. When the safety factor falls below unity, conduction fails and nerve block occurs. Local anesthetics produce a very slight, virtually insignificant decrease in potassium (K+) conductance through the nerve membrane. Calcium ions (Ca++), which exist in bound form within the cell membrane, are thought to exert a regulatory role on the movement of sodium ions across the nerve membrane. Release of bound calcium ions from the ion channel receptor site may be the primary factor responsible for increased sodium permeability of the nerve membrane. This represents the first step in nerve membrane depolarization. Local anesthetic molecules may act through competitive antagonism with calcium for some site on the nerve membrane. ^[4]

Local Anesthetic agents available:

Numerous local anesthetic agents are available to relieve pain during the dental procedure. The most commonly used local anesthetics for pediatric dentistry are the amide type agents. Lidocaine hydrochloride (HCl) 2% with 1:100,000 epinephrine is preferred because of their low allergenic characteristics and their greater potency at lower concentrations. ^[7]Vasoconstrictors are used to constrict blood vessels, counteract the vasodilatory effects of the local anesthetic, prolong its duration, reduce systemic absorption and toxicity, and provide a bloodless field for surgical procedures.^[7,8]The use of the vasoconstrictor will allow the maximum total dose of the anesthetic agent to be increased by nearly 40%. ^[9,10] Many agents have been employed as vasoconstrictors with local anesthetics. But none has proved to be as clinically effective as epinephrine.^[9]

However epinephrine is contraindicated in patients with hyperthyroidism. The dose should be kept to a minimum in patients receiving tricylic antidepressants since dysrhythmias may occur. ^[5]Levonordefrin and norepinephrine are absolutely contraindicated in these patients. Patients with significant cardiovascular disease, thyroid dysfunction, diabetes, or sulfitesensitivity and those receiving monoamine oxidase inhibitors, tricyclic antidepressants, or phenothiazines may require a medical consultation to determine the need for a local anesthetic without vasoconstrictor. ^[5,11]

A long-acting local anesthetic (ie, bupivacaine) is not recommended for the child or the physically or mentally disabled patient due to its prolonged effect, which increases the risk of soft tissue injury. Claims have been made that articaine can diffuse through hard and soft tissue from a buccal infiltration to provide lingual or palatal soft tissue anesthesia. ^[4]

Dose Calculation

Local amide anesthetics available for dental usage include lidocaine, mepivacaine, articaine, prilocaine, and bupivacaine (Table 1). Absolute contraindications for local anesthetics include a documented local anesthetic allergy. ^[11] True allergy to an amide is exceedingly rare. Allergy to one amide does not rule out the use of another amide, but allergy to one ester rules out use of another ester.^[12] A bisulfate preservative is used in local anesthetics containing epinephrine. For patients having an allergy to bisulfates, use of a local anesthetic without a vasoconstrictor is indicated. ^[11]

The maximum dose of lidocaine and mepivacaine, without vasoconstrictors, recommended for children is 4.4 mg/kg body weight (Table 2), and 7 mg/kg body weight for lidocaine with vasoconstrictors. ^[4,13] (Table 2)

So, for a child weighing 25 kg, the maximum permissible dosage of LA is 7 × 25 = 175 mg of LA.

As lidocaine is generally available as 2% solution, this is 2 gm in 100 ml of solution or 100 ml of solution will have 2 gm of LA.

1 ml of solution has 2/ 100 =0.02 gm or 20 mg of LA 1.8 ml of solution (1 cartridge) will have – 20 × 1.8 = 36 mg of LA

If a total of 175 mg can be safely administered to a child weighing 25 kg, it means 175/36 = 4.8 or 5 Cartridges of Lidocaine with adrenaline (1.8 ml of solution) can be safely administered.

Table : 1 – Injectable Local Anesthetics ^[5]

Anesthetic

Maxillary Infiltration

(Duration in Minutes)

Mandibular block

(Duration in Minutes)

Maximum Dosage

Maximum Total Dose

Pulp

Soft Tissue

Pulp

Soft Tissue

(mg/kg)

(mg/lb)

(mg)

Lidocaine

2% Plain

2% + 1:50,000 epinephrine

2% + 1:1,00,000 epinephrine

170

5-10

190

4.4

2.0

300

Mepivacaine

3% Plain

2% + 1:1,00,000 epineprine

2% + 1:20,000 levonordefrin

170

130

165

190

185

4.4

2.0

300

Articaine

4% + 1:1,00,000 epinephrine

4% + 1:2,00,000 epinephrine

190

180

230

240

7.0

3.2

500

Prilocaine

4% Plain

4% + 1:2,00,000 epinephrine

105

140

190

220

6.0

2.7

400

Bupivacaine

0.5% +1:2,00,000 epinephrine

340

240

440

1.3

0.6

Table 2: Maximum Dose – Lidocaine Without Adrenaline ^[30]

Patient Weight (kg/lb)	mg	No. of cartidges
10/23	44	1.2
15/34.5	66	1.8
20/46	88	2.4
25/57.5	100	2.7
30/69	132	3.6
40/92	176	4.8
50/115	220	6.1
60/138	264	7.3
70/161	300	8.3

Rule of 10:

Administering a painless inferior alveolar nerve block for a preschooler is one of the most difficult task for a dentist. There has been discussions whether to give a local infiltration or an inferior alveolar nerve block to anesthetize the mandibular primary molars. Rule of 10 is a better approach to determine which injection is appropriate. ^[14] The primary tooth to be anesthetized is assigned a number from 1 to 5 according to its location in the dental arch (central incisor = 1, second molar = 5). This number is added to the age of the child (in years), and if the number is 10 or less, then an infiltration is more appropriate; if greater than 10, then an inferior alveolar nerve block is likely to be more effective. This simple approach works well in most cases. The only instance where the rule would be contraindicated is where quadrant dentistry involving pulp treatment of both first and second molar. In this case local infiltration may not provide a sufficient depth of pulpal analgesia and a mandibular block would be preferred.

Topical Anesthesia:

The primary goal in applying a topical anesthetic agent is to minimize discomfort caused during administration of local anesthesia. It is effective on surface tissues (up to two to three mm in depth) to reduce painful needle penetration of the oral mucosa. ^[3,4] Topical anesthetic agents are available in gel, liquid, ointment, patch, and aerosol forms.

The onset duration of lidocaine is 3-5 minutes. A recent study which compared the efficacy of commonly used topical anesthetics demonstrated the superiority of 5% EMLA cream (eutectic mixture of local anesthesia containing lidocaine and prilocaine) over all other topical anesthetic agents. The topical anesthetic benzocaine is manufactured in concentrations up to 20%; lidocaine is available as a solution or ointment up to 5% and as a spray up to 10% concentration. Localized allergic reactions, however, may occur after prolonged or repeated use. Topical lidocaine has an exceptionally low incidence of allergic reactions but is absorbed systemically and can combine with an injected amide. ^[15]

Complications of Local Anesthesia:

There are numerous potential complications associated with the administration of local anesthetics. These complications may be separated into those that occur locally in the region of injection and those that are systemic.

The Local Complications include: ^[4]

1. Needle breakage

2. Prolonged anesthesia or paraesthesia

3. Facial nerve paralysis

4. Trismus

5. Soft tissue injury

6. Hematoma

7. Pain on injection

8. Burning on injection

9. Infection

10. Edema

11. Sloughing of tissues

12. Postanesthetic intraoral lesions

The systemic complications include: ^[13]

1. Toxicity due to overdose

2. Allergy

3. Idiosyncrasy

4. Syncope

5. Drug interaction

6. Serum hepatitis

7. Occupational dermatitis

8. Respiratory arrest

9. Cardiac arrest

10. Hyperventilation

Recommendations to reduce local anesthetic complications: ^[5]

1. Clinicians who utilize any type of local anesthetic in a pediatric dental patient should have appropriate training, skills, availability of proper facilities, personnel, and equipment to manage any reasonably foreseeable emergency.

2. Care should be taken to ensure proper needle placement during the intraoral administration of local anesthetics. Clinicians should aspirate before every injection and inject slowly.

3. Following an injection, the doctor, hygienist, or assistant should remain with the patient while the anesthetic begins to take effect.

4. Residual soft tissue anesthesia should be minimized in pediatric and special health care needs patients to decrease risk of self-inflicted postoperative injuries.

5. Clinicians should advise patients and their care-givers regarding behavioral precautions (eg, do not bite or suck on lip/cheek, do not ingest hot sub-stances) and the possibility of soft tissue trauma while anesthesia persists. Placing a cotton roll in the mucobuccal fold may help prevent injury, and lubricating the lips with petroleum jelly helps prevent drying.

Failures in Local Anesthesia:

Numerous factors contribute to the failure of local anesthesia. These may be related either to the patient or the operator.

Operator‑dependent factors are:

i) Poor choice of local anesthetic solution

ii) Improper technique

Patient‑dependent factors are:

i) Anatomical variations

ii) Presence of infection

iii) Psychogenic factors (severe anxiety may influence pain perception). ^[16,17]

Local Anesthesia and Infection:

If a local anesthetic is injected into an area of infection, its onset will be delayed or even prevented. The inflammatory process in an area of infection lowers the pH of the extracellular tissue from its normal value (7.4) to 5 or lower. This low pH inhibits anesthetic action because little of the free base form of the anesthetic is allowed to cross into the nerve sheath to prevent conduction of nerve impulses. Inserting a needle into an active site of infection could also lead to a possible spread of the infection. ^[13]

Newer Techniques in Local Anesthesia:

The traditional aspirating syringe is still the most common method by which local anesthetics are administered. Newer techniques have been developed that can help the dentist administer the local anesthetic with minimum injection pain and adverse effects.

Computer Controlled Local Anesthetic Delivery system (CCLADS):

In the mid‑1990s, work began on the development of local anesthetic delivery systems that incorporated computer technology to control the rate of flow of the anesthetic solution through the needle. This concept is now called computer‑controlled local anesthetic delivery (CCLAD). ^[18] The first of these CCLAD devices, the Wand™ (Milestone Scientific, Inc., Livingston, N.J.), was introduced in 1997. Subsequent versions from same manufacturers were named Wand Plus and then CompuDent™, the current designation.

Wand/ CompuDent System:

The Wand system enables the operator to accurately manipulate needle placement with fingertip accuracy and deliver the LA with a foot‑activated control. It consists of a disposable handpiece component and a computer control unit. The handpiece is an ultralight pen‑like handle which is linked to a conventional anesthetic cartridge with plastic micro tubing. A growing number of clinical trials in medicine also demonstrate measurable benefits of CCLAD technology. ^[19,20]

Comfort control syringe

The Comfort Control Syringe has two main components: A base unit and a syringe. Several functions of the unit‑ most importantly injection and aspiration‑ can be controlled directly from the syringe, possibly making its use easier to master for practitioners accustomed to the traditional manual syringe. The Comfort Control Syringe has five pre‑programmed speeds for different injection techniques and can be used for all injection techniques. ^[21] A comparison between the traditional dental syringe and the Comfort Control Syringe revealed no meaningful differences in ease of administration, injection pain and efficacy, and acceptance by patients.^[22]

Jet Injectors

This technique is based on the principle of using a mechanical energy source to create a release of pressure sufficient to push a dose of liquid medication through a very small orifice, creating a thin column of fluid with enough force that it can penetrate soft tissue into the subcutaneous tissue without a needle. Jet injectors are believed to offer advantages over traditional needle injectors by being fast and easy to use, with little or no pain, less tissue damage, and faster drug absorption at the injection site.^[23] Studies in adults and children have concluded that traditional infiltration was more effective, acceptable, and preferred, compared with the needleless injection. ^[24]

Vibrotactile Devices:

Inui and colleagues ^[25] have shown, however, that pain reduction due to non‑noxious touch or vibration can result from tactile‑induced pain inhibition within the cerebral cortex itself and that the inhibition occurs without any contribution at the spinal level, including descending inhibitory actions on spinal neurons.

VibraJect

It is a small battery‑operated attachment that snaps on to the standard dental syringe which delivers a high‑frequency vibration to the needle that is strong enough for the patient to feel.^[23] Researches evaluating the effectiveness of VibraJect, have shown mixed results. Nanitsos et al.,^[26]and Blair ^[27] have recommended the use of VibraJect for painless injection. In contrast, Yoshikawa et al.,^[28]found no significant pain reduction when VibraJect was applied with a conventional dental syringe.

DentalVibe

This is a cordless, rechargeable, hand held device that delivers soothing, pulsed, percussive micro‑oscillations to the site where an injection is being administered. Its U‑shaped vibrating tip attached to a microprocessor ‑controlled Vibra‑Pulse motor gently stimulates the sensory receptors at the injection site, effectively closing the neural pain gate, blocking the painful sensation of injections. It also lights the injection area and has an attachment to retract the lip or cheek.^[29]

Accupal

The Accupal (Hot Springs, AR, USA) is a cordless device that uses both vibration and pressure to precondition the oral mucosa. Accupal provides pressure and vibrates the injection site 360° proximal to the needle penetration, which shuts the “pain gate,” according to the manufacturer. After placing the device at the injection site and applying moderate pressure, the unit light up the area and begins to vibrate. The needle is placed through a hole in the head of the disposable tip, which is attached to the motor. ^[29]

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Received on 24.05.2019 Modified on 28.06.2019

Research J. Pharm. and Tech 2019; 12(8): 4066-4070.

DOI: 10.5958/0974-360X.2019.00700.5