Local anesthetic agents in dentistry
In dentistry, the most commonly used local anesthetic is lidocaine (also called xylocaine or lignocaine), a modern replacement for procaine (also known as novocaine). Its half-life in the body is about 1.5–2 hours. Other local anesthetic agents in current use include articaine (also called septocaine or ubistesin), bupivacaine (a long-acting anesthetic), Prilocaine (also called Citanest), and mepivacaine (also called Carbocaine or Polocaine). A combination of these may be used depending on the situation. Most agents come in two forms: with and without epinephrine (adrenaline) or other vasoconstrictor that allow the agent to last longer. This controls bleeding in the tissue during procedures. Usually the case is classified using the ASA Physical Status Classification System before any anesthesia is given.
Local anaesthesia is deposited at the buccal (cheek) side of the maxillary alveolus which can diffuse through the thin cortical plate of the maxilla, then further into the pulp of the tooth in order to achieve dental anaesthesia effect.
Both regional block and infiltration techniques are considered the first choice injections for anaesthetising the mandibular teeth.
Different techniques are chosen based on different factors:
- Patient age
- Infiltration anaesthesia is a preferable method to anaesthetise deciduous/ primary teeth in children. The method is similar to the maxillary buccal infiltration. Ensure the lip/ cheek is stretched in a lateral and inferior direction instead of superiorly and the needle is then penetrated 45’ with the buccal cortical plate of the bone through the taut tissue of the muccobuccal fold.
- Tooth to be anaesthetised
- Infiltration anaesthesia should be the first choice of method for pulpal and soft tissue anaesthesia of mandibular permanent incisors in adults. Regional block injections are sometimes ineffective due to crossover innervation from the opposite side of inferior alveolar nerve. It is recommended to deposit at least 0.5mL at each buccal and lingual site in the apical region of the tooth of interest. The use of infiltration anaesthesia with 4% articaine with 1:100,000 epinephrine in obtaining pulp anaesthesia of the mandibular permanent first molar is getting more common these days due to its successful formulation.
Regional block techniques
Inferior alveolar and lingual block
The inferior alveolar nerve block is probably one of the most common methods used by dentist to anaesthetise the mandibular teeth in adults. This technique aims to inject the needle and deposit local anaesthetic close the near to the nerve before it enters the mandibular foramen, which locates on the medial aspect of the mandibular ramus. This is to block the nerve transmission in the inferior alveolar nerve before entering into the bone through the mandibular foramen.
It is an alternative anaesthetic injection technique that was first published in 1910. Intraosseous anaesthetic injection involves the deposition of anaesthetic solution directly into the cancellous alveolar bone adjacent to the apex of the root of the tooth to be anaesthetised through a small hole.It also can be use more involved dental procedures such as surgery or endodontic therapy (root canals).
Intraligamentary or periodontal ligament anaesthesia is a technique used primarily for endodontic treatment and to supplement inferior dental blocks where they may have failed. This technique involves ‘the deposition of at least 0.2ml of local anaesthetic solution for each root of the tooth’ diffusing into the marrow spaces surrounding the teeth. Clinicians may adopt this technique due to some benefits such as: no soft tissue anaesthesia, use of a smaller amount of anaesthetic and single tooth anaesthesia however use may be contraindicated due to claims that patients report sharp pain upon administration of interligamentary aesthetic. However the use of a high-pressure syringe and ultra fine needle provide both chemical anaesthesia (by action of anaesthetic agent) and mechanical anaesthesia (by pressure from deposition). Interligamentary anaesthetic may be complicated by poor operator technique where rapid injection and excessive volume is used; this could lead to sensitivity to biting and percussion.
Research has shown that the rate of onset of anaesthesia in the patients was between 15-20 second; this provides an advantage compared to that of inferior alveolar dental block. Other advantages include a decrease in overall trauma in comparison to conventional blocks therefore being an ideal procedure for extractions and endodontic treatment in children.
Inter-pulpal anaesthesia involves the direct placement of anaesthetic agent using a small needle (of 25 or 27 gauge) into the pulp chamber; it is injected under pressure leading to brief yet intense discomfort. This particular technique provides effective pulpal anaesthesia as the pulpal tissue is subject to chemical action by the anaesthetic agent and mechanical stimulus due to the pressure applied. This method is usually adopted when all other techniques have been unsuccessful and must include pre-operative warnings of sharp pain. However it may prove useful for pulpal extirpation or endodontic treatment on any tooth where anaesthesia is difficult to achieve. Nevertheless, due to the patient discomfort associated with this technique it should not be the primary anaesthetic technique used.
Intra-papillary anaesthesia is used as a supplementary technique to infiltrations in order to increase comfort for the patient and is primarily used to replace palatal or lingual infiltrations. This is exceptionally successful in paediatric patients and works to replace or increase comfort for particularly uncomfortable infiltrations such as palatal or lingual infiltrations. The technique involves direct deposition of anaesthetic agent into the papilla with associated tissue blanching at site of injection. The point of penetration should lie in attached gingiva 2mm apical of the papilla
Technology that involves using electric current to block the reception or generation of pain signals; the pain control can be transient.
A jet injection aims to create a release of pressure strong enough to push a liquid medication dose through a small orifice. This is usually done with the help of an energy source which is mechanical. With this, a thin column of fluid is created which has the force to penetrate soft tissues, thus a needle is not required.
· Faster drug absorption at injection site
· Easy to use
· Little/no pain
· Less tissue damage
|Drug name||UK Trade name||Concentration (%)||Maximum dose (mg/kg)|
|Articaine with adrenaline||BartinestTM
|Lidocaine with adrenaline||UtilycaineTM
|Mepivacaine||ScandonestTM||2||1.36 (3 mg per pound), less than 400 mg in adults|
|Prilocaine with Felypressin||CitanestTM||0.5||7|
|Prilocaine Plain||Citanest PlainTM||1||6|
When considering the use of a local anaesthesia there are many factors which should be considered. In terms of contraindications associated with LA there are “absolute” and “relative” contraindications. When something is said to have an “absolute” contraindication this underlines that under no circumstance would that LA be selected to administer to that specific patient as it poses a potential life-threatening risk e.g. allergy. When the LA has a “relative” contraindication the administration of the LA is not preferable and should be avoided, but does not pose a life-threatening risk.
As stated previously local anaesthesia used in dentistry can vary significantly as there are various preparations with a multitude of qualities. Each preparation has slight differences in how the anaesthetic affects the body. This is due to the use of different constituents. Local Anaesthetics which contain adrenaline such as Lidocaine (using 1:80,000 of adrenaline) or Articaine (using 1:100,000 of adrenaline) have a direct effect on the cardiac output by increasing the rate and contraction of the heart itself. Due to these effects, if a patient suffers from unstable angina or severe cardiac dysrhythmia, these preparations are often discouraged as they may predispose to unfavourable side effects. Studies found that both articaine given by infiltration and lidocaine given by inferior block were equally efficient when used for routine dental treatments in pediatric patients, however, articaine injections caused less post-operative pain.
As an alternative, other preparations such as Mepivicaine Hydrochloride or Prilocaine (containing Felypressin) can be used. Prilocaine is especially suitable for a patient who wishes to avoid adrenaline or may have a latex/preservative allergy. The main contraindication of Prilocaine is that it has a short half life and it possesses a mild cytotoxic effect, therefore should be avoided in pregnancy. This cytotoxic effect can influence the uterine tone and interfere with circulation, which can pose detrimental effects on the pregnancy. Mepivicaine Hydrochloride is then considered if Prilocaine is contraindicated. Mepivicaine is the least vasodilatory anesthetic as it has no vasoconstrictors and no preservatives added.
In Relation to the Dose
The dose of local anesthesia is often reduced when a patient has any systemic health implications or habits which may cause an interference. From time to time the local anaesthetic itself should be reduced (therefore reducing the maximum dose). This is particularly done when alcoholism, anaemia (if using Prilocaine), anorexia, bradycardia or GORD is concerned. On other occasions the vasoconstrictor used (often adrenaline) must be reduced when an individual suffers from angina, bradycardia, chronic bronchitis, cardia disarrhythmia, COPD or glaucoma. These include drug abuse, calcium channel blocker containing medications, beta blocker medications or liver disease as this impairs the metabolism.
In Relation to the Technique
The variety of techniques associated when giving a local anaesthetic can affect the success and if done incorrectly lead to a possible fracture of the needle tip. It is extremely rare for the needle to fracture whilst giving an injection intra-orally unless an inadequate technique is adopted. To prevent such an occurrence, especially when performing an inferior alveolar nerve block, it is recommended to not bend the needle, to use the correct needle length and to not insert the needle up to the hub.
Most common local anesthetic procedure
The Inferior alveolar nerve anaesthesia or block or IANB (sometimes termed "inferior dental block", or wrongly referred to as the "mandibular block") probably is anesthetized more often than any other nerve in the body. An injection blocks sensation in the inferior alveolar nerve, which runs from the angle of the mandible down the medial aspect of the mandible, innervating the mandibular teeth, lower lip, chin, and parts of the tongue, which is effective for dental work in the mandibular arch. To anesthetize this nerve, the needle is inserted somewhat posterior to the most distal mandibular molar on one side of the mouth. The lingual nerve is also anesthetized through diffusion of the agent to produce a numb tongue as well as anesthetizing the floor of the mouth tissue, including that around the tongue side or lingual of the teeth.
Several nondental nerves are usually anesthetized during an inferior alveolar block. The mental nerve, which supplies cutaneous innervation to the anterior lip and chin, is a distal branch of the inferior alveolar nerve. When the inferior alveolar nerve is blocked, the mental nerve is blocked also, resulting in a numb lip and chin. Nerves lying near the point where the inferior alveolar nerve enters the mandible often are also anesthetized during inferior alveolar anesthesia, such as affecting hearing (auriculotemporal nerve).
The facial nerve lies some distance from the inferior alveolar nerve within the parotid salivary gland, but in rare cases anesthetic can be injected far enough posteriorly to anesthetize that nerve. The result is a transient facial paralysis, with the injected side of the face having temporary loss of the use of the muscles of facial expression that include the inability to close the eyelid and the drooping of the labial commissure on the affected side for a few hours, which disappears when the anesthesia wears off.
In contrast, the superior alveolar nerves are not usually anesthetized directly because they are difficult to approach with a needle. For this reason, the maxillary arch is usually anesthetized locally for dental work by inserting the needle beneath the oral mucosa surrounding the teeth so as to anesthetize the smaller branches.
Other anesthetics used in dentistry
- Topical anesthetics benzocaine, eugenol, and forms of xylocaine are used topically to numb various areas before injections or other minor procedures.
- Nitrous oxide (N2O), also known as "laughing gas", easily crosses the alveoli of the lung and is dissolved into the passing blood, where it travels to the brain, leaving a dissociated and euphoric feeling in most cases. Nitrous oxide is used in combination with oxygen. Often (especially with children) a sweet-smelling fruity scent similar to an auto scent is used with the gas to inspire deep inhalation.
- General anesthesia drugs such as midazolam, ketamine, propofol and fentanyl are used to put a person in a twilight sleep or render them completely unconscious and unaware of pain. Dentists who have completed a training program in anesthesiology may also administer general IV and inhalation anesthetic agents.
- Nebotamine, a drug with similar effects to ketamine, is injected into the anterior lingual glands blocking action potentials from sending signals to the myelinated nerve. The potency of the anesthetic is directly related to its lipid solubility, since 90% of the nerve cell membrane is composed of lipid.
- Midazolam (Versed), a drug that represses memories of the procedure, is usually given two hours prior to the procedure in combination with Tylenol in general anesthesia so the person will go home with no memories of being in surgery.
- Sevoflurane gas in combination with nitrous oxide and oxygen is often used during general anesthesia followed by the use of isoflurane gas to maintain anesthesia during the procedure. In children sweet fruity scents are often used with the gases to inspire deep inhalation. Scents come in cherry, apple, bubblegum, watermelon, etc...
- Propofol, a drug with similar effects to Sodium Pentathol, is often used through intravenous infusion through an IV during general anesthesia after gasses are initiated.
- Morphine is often used to control pain during the dental surgery under general anesthesia. The morphine is usually administered through IV.
- Ketorolac is often administered through IV to suppress both pain and inflammation while under general anesthesia.
Other drugs used in combination with general anesthesia in dentistry
- Decadron a steroid is often administered through IV to suppress inflammation and swelling resulting during the surgery while under general anesthesia.
- Ondansetron brand named Zofran is often administered to prevent nausea during the surgery which may result from the blood draining into the stomach while under general anesthesia, or it is given after the procedure for postoperative nausea which may result from the anesthesia itself which was administered.
Local anesthesia and the pregnant patient
Provided a dentist performs proper aspiration to avoid intravenous injections, local anesthetics containing epinephrine (adrenaline) are safe to use during pregnancy. lignocaine and prilocaine are assigned a category B ranking by the FDA and are therefore safe for use during pregnancy. Lignocaine and prilocaine are sold as 2% and 4% formulations, respectively. It is therefore safer to use the lignocaine so as to administer a lower concentration of the drug to the pregnant patient.
Mepivicaine, articaine, bupivicaine are given an FDA category C ranking and so should be avoided. Benzocaine, the ingredient of most topical anesthetic formulations, is also ranked as category C and should be avoided. Lignocaine should be used as topical anesthetic instead.
Epinephrine in high doses is harmful to a pregnant woman in that it affects uterine blood flow. However its use in low dose with local anesthetic administration is warranted. The epinephrine causes vasoconstriction which in turn reduces systemic distribution of the anesthetic as well as prolongs its action in addition to decreasing bleeding at the operating site. Lidocaine 2% with 1:100,000 adrenaline is the local anesthetic of choice in the treatment of pregnant women.
Allergy to local anaesthetic
Allergic reactions from local anaesthesia have been reported in some patients. However, this occurrence is rare even in patients who had a past history of adverse reactions to LA.
- E.g. of amide LA: lidocaine, prilocaine, articaine, mepivacaine
- E.g. of ester LA: benzocaine, procaine
Genuine allergic reactions of an amide LA is very uncommon. An ester LA is more possible to result in an allergic reaction because the compound will be broken down to para-aminobenzoic acid (PABA) which is a trigger for allergic reactions. In general dentistry, only topical applications of LA contains esters (benzocaine) when applied onto area before LA is administered.
If one is allergic to an ester LA, then the use of other types of ester LA should be avoided as the breakdown of all esters will produce PABA. However, patients allergic to ester LA will usually not be affected by amide LA because PABA is not produced upon breakdown of amide LA. Unlike ester LA, allergy to an amide LA will not eliminate the use of other types of amide LA.
Some reactions are caused by administration of too much drug, usually because of the route of entry of drug (intravenously) or the quick uptake of drug into the system, or the aftereffect of the vasoconstrictor. Unfavourable reactions to LA can be classified into 3 different groups: psychogenic, allergic, toxic.
Differential Diagnosis & management
- Psychogenic reactions
Unfavourable reactions to LA are commonly be due to a hyperemotional response to a perceived danger within someone’s mind, and it could be demonstrated in several ways. Examples are temporal loss of consciousness, sweating, flush, change in heart rate or blood pressure, panic attack, hyperventilation, of which may be mistaken as allergic reactions.
When treating such patients, treat them with care and take into consideration their anxiety. During treatment if the patients feel faint or experiences a drop in blood pressure, lay them flat and keep their legs elevated in an attempt to restore their blood pressure. Loosen any tight clothing and keep the patients sugary food/drink after they regain consciousness. Reassure the patient.
- Toxic reactions
This may occur when there are large amounts of anaesthetic within their vascular system, which may be due to them receiving repeated LA, intravenous entry of drug, or have underlying systemic conditions that does not metabolize or utilize the drug efficiently. Signs and symptoms mainly involve the nervous system e.g. aggressive behaviour, drowsiness, speech alteration, disorientation etc.
Their symptoms should usually resolve in a few hours, up to 12 hours, as the body will gradually rid the bloodstream of the drug. Assure the patient that their symptoms will improve after a few hours and that such a reaction should not recur, and that there is no need to abstain from that drug hereafter.
Such reactions can be minimized via practicing safe injection methods using an aspirating syringe to prevent injecting in blood vessels, slow administration of drug, and avoid overprescribing LA, keeping in mind the patient’s weight, age and medical history.
Signs & symptoms of allergic reactions to LA
Genuine allergy to LA will manifest either as Type 1 or Type 4 hypersensitivity. Signs and symptoms will vary depending on the type of allergy. Type 1 reactions have a rapid onset of symptoms which include swelling, redness, rashes, itchiness, chest tightness, breathing problems. A Type 4 reaction has a delayed onset of symptoms and is usually localized to the site of injection.
If a genuine allergic reaction to LA should occur, the patient should be treated as an emergency for anaphylaxis, according to the guidelines in the respective areas. For the UK, the section on medical emergencies in dental practice in the “Prescribing in Dental Practice” part in the BNF should be referred to. The patient should be sent immediately to the hospital if their condition worsens.
The individual should undergo further tests to certify their allergy to the LA or for other possible causes of the adverse reaction.
Gate Control Theory in Painless Anaesthesia
The gate control theory explains that pain can be reduced if the touch nerve fibres are stimulated due to non-harmful stimuli.
Advancement in techniques used to deliver local anaesthesia are very important. There are types of local anaesthesia that apply vibrations to the skin while the injection is being placed into the skin. This uses the gate control theory to minimise pain to the patient. The high frequency vibrations coming from the device which is attached to the syringe inhibit the pain sensations coming from the needle. They may interfere with the signals of pain by closing the gate in the brain. The nerve fibres that are stimulated are the Ab fibres using pressure or vibration. Other receptors called meissner’s corpuscles in the deeper tissues and bone also contribute. This closes a ‘neural gate’ This decreases the patient’s feeling of pain.
Methods used by dentist to reduce pain during anaesthesia by using the gate control theory are: Warming of the local anaesthetic cartridge, Stretching the oral mucosa, Gentle rubbing of the extra-oral skin.
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