Pediatric  Dental  Health

• Dental local anesthetics fall into two groups: amides and esters. The names are derived from the type of chemical link between the two ends (aromatic and base) of the local anesthetic molecule.
• The majority of local anesthetics used today, including lidocaine, are tertiary amines.
• All local anesthetics are amphipatic. That is, they have both lipophilic and hydrophilic characteristics - usually at opposite ends of the anesthetic molecule. The lipophilic end of the molecule is attracted to lipids, and the hydrophilic end is attracted to water.
  
  HOW DOES A LOCAL ANESTHETIC WORK?
• Local anesthetics create a chemical roadblock between the source of the pain or stimulation – and the brain.
• The function of a nerve is to carry messages from one part of the body to another. These messages are in the form of electrical signals called action potentials.
• Local anesthetics block the operation of a specialized gate, called the sodium channel. When the sodium channel of a nerve is blocked, nerve signals cannot be transmitted.
• The only site at which the local anesthetic molecules have access to the nerve membrane is at the nodes of Ranvier, where there is an abundance of sodium channels. The interruption of a nerve signal in a myelinated nerve (dental nerve) occurs when nerve depolarization (the nerve signal) is blocked at 3 consecutive nodes of Ranvier – a length of about 8 to 10 mm.
• A vasocontrictor (which constricts blood vessels) is usually added to local anesthetic solution to prolong the duration of anesthetic action. The vasoconstrictor, such as epinephrine, works by slowing the removal of the anesthetic from the vicinity of the nerve.
• The potency of a local anesthetic is directly related to its lipid solubility, since 90% of the nerve cell membrane is composed of lipid.
• The more acidic the local anesthetic solution is, the slower the onset of action, however. In addition, the more closely the equilibrium pH (the pKa) for a given anesthetic approximates physiologic pH, the more rapid the onset of anesthetic action.
• Finally, the better the local anesthetic molecule binds to the protein in the sodium channel of the nerve, the longer the anesthetic will be effective.
  
  WHY DON’T SOME CHILDREN GET NUMB?
• An imperfect injection technique is the most common cause of problems with getting numb.
• Another common cause of problems is that local anesthetics do not work well in an acidic environment - such as an inflamed or abscessed area. It is therefore sometimes useful to control a dental infection with antibiotics before a local anesthetic can be successfully used.
• All other factors being equal, the single most important determinant of local anesthetic potency is its lipid solubility, however.
  
  HOW IS A LOCAL ANESTHETIC ADMINISTERED?
• An important requirement for administering a local anesthetic is for the dentist to be familiar with the manner in which the teeth are innervated.
• Second, the dentist should use the smallest possible dose which achieves adequate anesthesia. The maximum dose for lidocaine injection in children is 4.5 mg/kg per appointment. The dose of local anesthetic should be adjusted downward when children are sedated, however.
• When anesthetizing in the maxillary arch, the dentist should recall that the permanent first molar’s mesiobuccal root is innervated by fibers from the middle superior alveolar nerve branch, while the remaining roots are innervated by the posterior superior alveolar nerve branch. This means that at least two injections are required for anesthetizing this tooth.
• The primary maxillary second molar is innervated by both the posterior superior alveolar nerve and the middle superior alveolar nerve branches.
• Dentists should remember that the greater palatine nerve has accessory nerve fibers that innervate the palatal roots of the upper primary and permanent molars.
• In the mandibular arch, the only guaranteed way to accomplish profound pulpal anesthesia is to perform an inferior alveolar nerve block. Primary incisors, however, can be anesthetized using supraperiostial injections – which anesthetizes branches of the incisive nerve.
  
  ARE LOCAL ANESTHETICS SAFE FOR CHILDREN?
• When administered correctly, local anesthetics are safe for children.
• Since the 1960’s, dentists have begun using an aspirating syringe, which has a small internal harpoon that engages the rubber stopper of the local anesthetic carpule. This technique enables dentists to aspirate for blood, and see if the needle has inadvertently entered a blood vessel - before injecting the anesthetic solution.
• Local anesthetics have a low margin of safety between the effective dose and the toxic dose. The lethal dose for many local anesthetics is only 3 times that of the effective dose.
• Deaths following local anesthetic administration are almost always a result of overdosage. The maximum safe dose of lidocaine for a child is 4.5 mg/kg per dental appointment.
• Bupivicaine (Marcaine) is an amide local anesthetic with a high toxic potential, and should not be used in children. The duration of anesthesia with bupivicaine can be as long as 24 hours.
• Lidocaine is less toxic than many other local anesthetics, because its interactions with the cardiac sodium channel are “fast in – fast out,” whereas a local anesthetic such as bupivicaine is "fast in – slow out.”
• The cardiac dysrhythmias caused by bupivicaine overdose are difficult to treat, because the plasma concentration which causes convulsions is close to that which causes cardiovascular collapse. Thus, there is no advance warning of an impending cardiovascular collapse.
• When sedating a child, the local anesthetic dose should be lowered to decrease the risk of toxicity and complications.
• Finally, in a neonate, repeated doses of an amide local anesthetic such as lidocaine, puts the newborn at greater risk for toxicity than an older child. The reason for this problem is that the P-540 enzyme system, in the liver, is poorly developed at birth.
  
  MANAGEMENT OF LOCAL ANESTHETIC COMPLICATIONS:
• Step One: prevent complications by being prepared. Know your patient. The treating clinican must always obtain a current medical history of the patient before initiating any treatment.. The dentist should be certified in Basic Life Support, and be familiar with either Pediatric Advanced Life Support or Advanced Cardiac Life Support. The doctor should have proper resuscitation equipment on hand in case of an emergency.
• Step Two: immediately stop the dental procedure, and activate the EMS system.
• Step Three: evaluate and recognize the signs and symptoms of a local anesthetic emergency. In a lidocaine overdose emergency, the patient will initially complain of lightheadedness, tinnitus (ringing in the ears), numbness around the mouth, a metallic taste, and double vision. With higher toxic doses of lidocaine, tremors will develop and eventually coalesce into a grand mal seizure. CNS (central nervous sytem) depression may lead to respiratory arrest. It is essential to monitor blood pressure and vital signs during an emergency so that an accurate diagnosis of the problem can be made.
• Step Four: secure and protect the patient’s airway.
• Step Five: provide 100% oxygen via a nasal mask, or assist breathing with a resuscitation bag – if necessary.
• Step Six: ensure adequate blood circulation. Begin CPR if necessary.
• Step Seven: if a seizure occurs, protect the patient from self-injury. It is not necessary to put anything into the patient’s mouth – as long as the airway remains open. Seizure activity may be controlled with 5-10 mg IV Valium. Avoid giving Dilantin during a seizure because it may worsen the toxic effects of a lidocaine overdose.
  
  WHAT CAUSES LOCAL ANESTHETIC COMPLICATIONS?
• Deaths following local anesthetic administration are almost always the result of an overdose. The maximum safe dose of lidocaine for a child is 4.5 mg/kg per dental appointment. For example: a 35 lb child should never receive more than 2 carpules of 2% lidocaine during a dental appointment.
• Adverse reactions to local anesthetics occur primarily in the CNS and cardiovascular system, because these tissues are also composed of excitable membranes.
• If a local anesthetic (with epinephrine) is accidentally injected into a blood vessel or a very vascular area, the patient is likely to experience flushing of the skin, tachycardia (very fast heat rate), and nausea. The hypertension (increased blood pressure) and tachycardia is due to the epinephrine in the anesthetic. Constant blood pressure monitoring is therefore essential for diagnosing the nature of the anesthetic emergency.
• Most reactions reported by patients as “allergies” are actually caused by an intravascular (blood vessel) injection with local anesthetic - or from the uptake of epinephrine from the anesthetic solution.
• No more than 1 percent of reactions to local anesthetics are true allergies. The most common cause of a true allergic reaction to a local anesthetic is sensitivity to the preservative in the anesthetic solution. Methylparaben and bisulfites are widely-used preservatives, and may be the offending agents in a true allergy to local anesthetic. For patient who are sensitive to these preservative, the dentist should consider using a mepivicaine preparation which contains no methylparaben.
• When a topical local anesthetic (benzocaine) is used, the metabolite PABA (para-aminobenzoic acid) may also be responsible for a true allergic reaction in some people.
• Allergic hypersensitivity reactions demonstrate a variety of symptoms, ranging from a mild rash to anaphylactic shock.
• Finally, both benzocaine and prilocaine produce metabolites which can cause methemoglobinemia. These metabolites cause the oxidation of the ferric form of hemoglobin to the ferrous form.
  
  TIPS FOR CLINICIANS:
• Apply topical anesthetic to the injection site(s) for one minute prior to giving the injection.
• Consider using a small mouth prop during the injection procedure. This will help provide access and visibility, prevent injury, and will help direct the needle to the correct injection site.
• Don’t let the child see the needle.
• Use the Explain-Practice-Do technique for giving local anesthetic to children. Tell the child what he/she will feel during the procedure. Stress the importance of holding still during the administration of local anesthetic.
• Make sure that you or your assistant will be able to control any of the child’s sudden head or hand movements during the injection.
• Be gentle when administering local anesthetic to a child. Give the injection very slowly to avoid discomfort.
• Aspirate frequently to avoid injecting into a blood vessel. Use an aspirating-type syringe which has a tiny harpoon that engages the rubber stopper of the anesthetic carpule.
• Use the smallest and shortest needle which will do the job.
• Use the smallest dose of local anesthetic which will achieve adequate anesthesia. The dentist should consider the child’s weight and medical history in determining the correct dose of local anesthetic. Never give more than 4.5 mg/kg of lidocaine per dental appointment.
• Remember that the mandibular foramen in a child is located slightly below the plane of occlusion. In addition, the foramen is located more anterior than in adults – due to the narrow anterioposterior width of a child’s mandible.
• If an upper primary or permanent molar is not “getting numb,” try giving a greater palatine nerve injection. In children, it is usually adequate to infiltrate under pressure into the gingival sulcus of the troublesome upper molar.
• The long buccal nerve will sometimes innervate the lower primary or permanent molars, especially when placing a rubber dam clamp. This nerve passes lateral to the body of the mandible, and should be anesthetized slightly buccal to the last tooth being treated.
• The mylohyoid nerve sometimes gives accessory innervation to the lower teeth. A submucosal deposition of anesthetic at the medial surface of the mandible, at its junction with the floor of the mouth, will usually stop the problem.
• Remember to warn the child not to bite the “numb” cheek or lips. Give the warning during the dental appointment as well at the end of the appointment.
  
  A case report in the Journal of the American Dental Association describes complications caused by a local anesthetic injection. A 33 year-old patient received an inferior alveolar nerve block at her dentist’s office. Within one minute of the injection, the facial skin, intraoral structures, and eye were adversely affected on the left side. Presumably, the epinephrine in the local anesthetic was injected into the inferior alveolar artery, traversed backward into the internal maxillary artery, and affected the whole left side of the face. Within 45 minutes of the injection, however, all unusual findings dissipated.
  
  Webber B, Orlansky H, Lipton C, Stevens M: Complications of an intra-arterial injection from an inferior alveolar nerve block. JADA. Dec 2001; Vol 132:1702-1704.
  
  
  

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