Topical Anesthesia

Topical anesthesia is used to obtund the discomfort associated with the insertion of the needle into the mucosal membrane. The usefulness of topical anesthesia has been debated. For instance, the taste of the anesthetic, the period during which the patient anticipates the needle, and the establishment of a conditioned patient response from the needle immediately following the application of topical anesthetic have been considered to be detrimental factors. However, the operator’s effectiveness in interacting with children to distract them and increase their suggestibility about managing their own anxieties may supersede the disadvantages of topical anesthesia. Therefore we recommend the use of a benzocaine topical anesthetic that tastes good and is available in an easy-to-control gel. The best results behaviorally and physiologically occur when the gel is used sparingly and applied to a very dry mucosal surface for at least 2 minutes.

A small amount of topical anesthetic should be applied with a cotton-tipped applicator to a mucosa that has been adequately dried and isolated with a 2 × 2 inch cotton gauze pad (Figure 28-1). The time required for the topical anesthetic to reach its full effectiveness may vary from 30 seconds to 5 minutes. Although a toxic response to topical anesthesia is rare, application of an excessive amount should be avoided.¹

General Considerations for Local Anesthesia

The mechanism of action of local anesthetics has been further elucidated in recent years. As described in Chapter 7 the evidence supports the notion that local anesthetics penetrate neurons, attach to intraneural receptor sites, and mediate configurable changes of sodium receptors in the neuronal membrane that subsequently block sodium channels. The net result is inhibition of neuronal excitability, which reduces the likelihood of action potential transmission. Therefore local anesthetics alter the reactivity of neural membranes to propagated action potentials that may be generated in tissues distal to the anesthetic block. Action potentials that enter an area of adequately anesthetized nervous tissue are blocked and fail to transmit information to the central nervous system (CNS).²

The efficacy of local anesthesia depends on the concentration of the anesthetic on a segment of the nerve. Beyond a fixed amount of local anesthetic necessary for blockage of neuronal impulses, any excess is wasteful and potentially dangerous. Failure to obtain anesthesia is most likely due either to operator error in depositing the solution sufficiently close to the nerve or to anatomic aberrations (e.g., accessory innervation).

Local infection and inflammation can modify the normal local physiology of tissue by causing the release of neuroactive substances (e.g., histamine, leukotrienes, kinins, and prostaglandins) and by lowering the pH. These changes reduce the lipid solubility of the anesthetic and interfere with its ability to penetrate the nervous tissue. Blocking the nerve at a more proximal site distant from the infected area may be a viable alternative. Antibiotic administration over a few days may reduce the extent of infection and permit definitive treatment under local anesthesia that would otherwise be impossible.

Local anesthesia may be obtained anatomically by one of three means:

Local anesthetics used in dentistry are classified as esters or amides. Amides are used more frequently because of their reduced allergenic characteristics and greater potency at lower concentrations. The concentration of the different agents varies, and care must be taken to prevent overdose (Table 28-1). As an example, two full cartridges (carpules) of 2% lidocaine (Xylocaine) without vasoconstrictor may be easily tolerated by an adult, but the same amount exceeds the maximal allowable dosage (2 mg/lb body weight) for a 20-pound child. Great care must be taken when a 4% concentration of a local anesthetic (e.g., articaine) is used with children because the amount of local anesthetic is twice that of a 2% solution.

Local anesthetic cartridges (1.8 ml or 1.7 ml) also contain preservatives, organic salts, and sometimes vasoconstrictors. The preservatives (e.g., methylparaben) may be a source of allergic reactions. Concern about rubber products in local anesthetic cartridges as a source of allergic reactions has not been supported by any studies or case reports.³ The vasoconstrictors (e.g., epinephrine) are used to constrict blood vessels, counteract the vasodilatory effects of the local anesthetic, and prolong the duration of the anesthetic.

Operator Technique

Communicating at a level appropriate to the child’s development is necessary in a pediatric dentistry practice. The dentist may have to modify his or her wording to accommodate the level of the child’s understanding when discussing the injection. For instance, the child may be told that the tooth will be “going to sleep” after a “little pinch” is felt near his tooth. The dentist should not deny that the injection might hurt because this denial may cause the child to lose trust in the dentist and confidence about the procedure. The dentist should minimize but not reinforce the child’s anxieties and fears about the “pinch.”

The discomfort of the injection may be lessened by counterirritation, distraction, and a slow rate of administration. Counterirritation is the application of vibratory stimuli (e.g., rapid displacement of loose alveolar tissue) or of moderate pressure (e.g., with a cotton-tipped applicator) to the area adjacent to the site of injection. These stimuli have a physical and psychological basis for modifying noxious input. Distraction can be accomplished by continuing a constant monologue with the child and by maintaining his or her attention away from the syringe. The operator should always aspirate (i.e., gently pull back on the plunger of the dental syringe to cause negative pressure and aspiration of blood into the carpule if the needle is in the blood vessel) and alter the depth of the needle if necessary before slowly injecting the anesthetic. The deposition of a single carpule should take at least 1 minute. Rapid injections tend to be more painful because of rapid tissue expansion. They also potentiate the possibility of a toxic reaction if the solution is inadvertently deposited in a blood vessel.

The role of the dental assistant is important during transfer of the syringe and in anticipation of patient movement. During the transfer of the syringe from the assistant to the dentist, the child’s eyes tend to follow the dentist’s. The eyes of the dentist should be focused on the face of the patient (Figure 28-2). The hand of the dentist that is to receive the syringe is extended close to the head or body of the child. The body of the syringe is placed between the index and middle finger, with the ring of the plunger slipped over the dentist’s thumb by the assistant. The plastic sheath protecting the needle is then removed by the assistant. The dentist’s peripheral vision guides the syringe to the mouth in a slow, smooth movement.

Reflexive movements of the child’s head and body should be anticipated.⁴ The head can be stabilized by being held firmly but gently between the body and arm or hand of the dentist. The assistant passively extends his or her arm across the child’s chest so that potential arm and body movements can be intercepted. The area of soft tissue that is to receive the injection is reflected by the free hand of the dentist. The hand can also be used to block the vision of the child as the syringe approaches the mouth. Once tissue penetration by the needle has occurred, the needle should not be retracted in response to the child’s reactions. Otherwise, the child’s behavior may deteriorate significantly if he or she anticipates reinjection. Use of finger rests is strongly advocated.

A short (20 mm) or long (32 mm), 27- or 30-gauge needle may be used for most intraoral injections in children, including mandibular blocks. There apparently is little difference in discomfort level between the 25-gauge and 30-gauge needles for inferior alveolar injections; thus the 27-gauge needle would seem less likely to break or bend during injections and is preferred.⁵ An extrashort (10 mm), 30-gauge needle is appropriate for maxillary anterior injections.

Because of the concern for inadvertent needle sticks, retractable needle delivery systems are becoming popular and in some cases required in hospital settings. Injection delivery systems now have needles covered by a needle sheath and a retractable cover preventing needlesticks associated with resheathing needles after injection.

Maxillary Primary and Permanent Molar Anesthesia

The innervation of maxillary primary and permanent molars arises from the posterior superior alveolar nerve (permanent molars) and middle superior alveolar nerve (mesiobuccal root of the first permanent molar, primary molars, and premolars).

In anesthetizing the maxillary primary molars or permanent premolars, the needle should penetrate the mucobuccal fold and be inserted to a depth that approximates that of the apices of the buccal roots of the teeth (Figure 28-3). The solution should be deposited adjacent to the bone. The maxillary permanent molars may be anesthetized with a posterior superior alveolar nerve block or by local infiltration.

Maxillary Primary and Permanent Incisor and Canine Anesthesia

The innervation of maxillary primary and permanent incisors and canines is by the anterosuperior alveolar branch of the maxillary nerve. Labial infiltration commonly is used to anesthetize the primary anterior teeth. The needle is inserted in the mucobuccal fold to a depth that approximates that of the apices of the buccal roots of the teeth (Figure 28-4). Rapid deposition of the solution in this area is contraindicated because it produces discomfort during rapid expansion of the tissue. The innervation of the anterior teeth may arise from the opposite side of the midline. Thus it may be necessary to deposit some solution adjacent to the apex of the contralateral central incisor.

Infraorbital block injection is an excellent technique that may be used in place of local infiltration of the anterior teeth. All ipsilateral anterior maxillary teeth are anesthetized by this block. The needle is inserted anywhere in the mucobuccal fold from the lateral incisor to the first primary molar and is advanced next to bone to a depth that approximates the infraorbital foramen. The foramen is readily palpated as a notch on the infraorbital rim of the bony orbit. The solution is deposited slowly only after an aspiration procedure.

Palatal Tissue Anesthesia

The tissues of the hard palate are innervated by the anterior palatine and nasal palatine nerves. Surgical procedures involving palatal tissues usually require a nasal palatine nerve block (Figure 28-5) or anterior palatine anesthesia (Figure 28-6). These nerve blocks are painful, and care should be taken to prepare the child adequately. These injections are not usually required for normal restorative procedures unless the procedure involves palatal tissue. However, if it is anticipated that the rubber dam clamp will impinge on the palatal tissue, a drop of anesthetic solution should be deposited into the marginal tissue adjacent to the lingual aspect of the tooth. Blanching of the tissue will be observed.

Mandibular Tooth Anesthesia

The inferior alveolar nerve innervates the mandibular primary and permanent teeth. This nerve enters the mandibular foramen on the lingual aspect of the mandible. The position of the foramen changes by remodeling more superiorly from the occlusal plane as the child matures into adulthood. The foramen is at or slightly above the occlusal plane during the period of the primary dentition./>