Local Anesthesia in Dentistry

GDC Learning Outcomes

• Appropriate dental, oral, craniofacial, and general anatomy knowledge must be described and applied to patient management.
• Relevant and appropriate physiology must be described and applied to patient management.
• Properties of relevant medicines and therapeutic agents must be described and discussed in their application to patient management.
• Patient anxiety and pain are managed through communication, reassurance, and behavioral techniques.
• Patient pain is managed through the appropriate use of analgesia.

Aims and Objectives

• Deliver safe and effective local anesthesia to patients.
• Describe and identify related oral anatomy and nerve supplies.
• Relate how to safely deliver infiltrations and IDBs.
• Investigate the legal framework for LA delivery in dentistry.
• Highlight the potential complications of LA delivery.

Action Potential

• The sodium-potassium pump actively moves Na+ and K+ ions across the nerve cell membrane to restore balance.
• Membrane potential returns to approximately -70mV.
• Resting potential is high in Na+ extracellularly and low in K+ intracellularly.
• Resting potential measures -70mV.
• Depolarization opens the activation gates on most Na+ channels, while the K+ channels remain closed which makes the membrane positive.
• The inactivation gates on most Na+ channels close blocking Na+ influx, whilst the activation gates on most K+ channels open, permitting K+ which makes the inside of the cell negative again.

LA Agents

• LA agents set up a chemical roadblock between the source of the impulse and the brain.
• LA agent acts in two ways:
• Binding to specific receptors in the sodium channels in the nerve cell membrane, which blocks the inward movement of Na+ ions during the conduction of an impulse.
• Causing non-specific expansion of the nerve cell membrane causing physical obstruction of the Na+ channels.
• This means that no action potential is generated, so no impulse is conducted to the brain.

Trigeminal Nerve Revision

• The Trigeminal nerve includes the ophthalmic branch V1, the maxillary branch V2, and the mandibular branch V3.

Patient Preparation

• Legal: a valid prescription is present.
• Medical history: any contraindications assessed, if the patient has taken their medication, and any previous reactions to LA assessed.
• Food: if the patient has eaten as usual to prevent a vasovagal attack.
• Explain: the sensation and the procedure with appropriate language to reassure the patient.
• Patient: address anxiety and phobias with distraction techniques and maintain a calm atmosphere.
• Operator: optimal positioning and visibility achieved to use LA equipment.

Pain Threshold

• Factors such as anxiety, previous experience, culture, age, psychological makeup, physical environment, and emotional state can affect a patient's pain threshold.
• The Gate Control theory includes hypnosis, distraction, calm atmosphere, and alternative stimulus.

Anasthetising Nerves

• Key nerves to anaesthetise for dental procedures include:
• Maxillary nerve.
• Posterior superior alveolar nerve.
• Middle superior alveolar nerve.
• Anterior superior alveolar nerve.
• Pterygopalatine nerves anatomy includes
• Incisive foramen
• Nasopalatine nerve
• Greater palatine artery and nerve (hard palate)
• Greater Palatine foramen
• Palatine bone (horizontal plate)
• Lesser palatine foramina
• Posterior nasal spine
• Vomer
• Choanae
• Pterygoid process (medial plate)
• Lesser palatine artery and nerve (soft palate)
• Pterygoid process (lateral plate)
• Position the patient supine, comfortable and well supported, at the correct height for the operator, with light directed into the sulcus area.

Buccal Infiltration Technique

• Dry the mucosa and apply topical anesthetic agent on a cotton wool roll and leave for 2-3 minutes before the injection.
• Estimate the position of the apex of the tooth and pull the surface mucosa taut.
• Insert the needle through the mucosa at 25 degrees to the bone, aiming for the apex of the tooth and keeping roughly parallel to the long axis of the tooth.
• Smoothly allow the needle to glide through the taut mucosa.
• Avoid contacting bone; if contacted withdraw 1-2mm.
• Needle should be bevel to bone.
• Aspirate, especially if injecting around upper second/third molars.
• Check cartridge.
• Deliver solution gently and low until 0.5ml - 1ml of solution per site for infiltrations for perio work or 2.2ml of solution for restorations is delivered.
• Very little pressure should be required on the plunger.
• Withdraw needle smoothly.
• Make the needle safe.
• Pulpal analgesia should be established within 2-5 minutes.
• Soft tissue analgesia should take 1-2 minutes.
• Particular care is required for labial aspect of upper incisors - VERY SENSITIVE (use lots of topical and inject very slowly).
• The labial aspect of lower incisors is the attachment of mentalis and depressor labii inferioris muscles.

Supplementary Injections

• Supplemental injections such as palatal infiltrations, lingual infiltrations, and intrapapillary injections can be very useful.

Palatal Infiltration Technique

• Topical application/pressure on area first, then infiltrate the palatal mucosa of the appropriate tooth.
• Inject at 90 degrees to the mucosa at about 1-1.5cm from the gingival margin, halfway between gingival margin and midline of palate.
• There will be Considerable resistance, and then deposit 0.2 ml of solution.
• Palatal infiltration is for: deep restorations, subgingival PMPR (Professional Mechanical Plaque Removal), and extractions of deciduous maxillary dentition.

Intrapapillary Injection

• Intrapapillary injections are useful for achieving palatal analgesia in children and nervous patients;
• Direct the needle at right angles to the interdental papilla.
• Insert needle into the center of the papilla at the level of attachment to periosteum.
• Deposit 0.25ml of solution, and then check the palatal mucosa has blanched.

Inferior Dental Block (IDB)

• Innervation of the mandible includes: the long buccal nerve, the mental nerve, the inferior dental/alveolar nerve, the mylohyoid nerve, and the lingual nerve.
• Basic anatomy of the mandible includes: the condylar process, the coronoid process, the submandibular fossa, the sublingual fossa, the alveolar process, the mental foramen, the mental protuberance (chin), the body, the retromolar fossa, the mandibular foramen, and the ramus.

Pterygomandibular Space

• The pterygomandibular space includes the parotid salivary gland, sphenomandibular ligament, medial pterygoid muscle, facial nerve, lingual nerve, inferior alveolar nerve, pterygomandibular raphe, medial surface of ramus of mandible, coronoid notch of mandible and masseter muscle.
• The facial nerve can be blocked if the analgesic solution is deposited outside the pterygomandibular space in the deep lobe of the parotid gland, causing paralysis of the facial muscles and temporary facial palsy.

IDB Techniques

• The patient can be supine or upright; if large tongue or obese patient, try upright position.
• You need good lighting and it is ideal to use topical analgesia.
• The patient's mouth should be wide open to allow good visualization of the anatomical landmarks.
• Choose a long needle of size 35 mm, 27 gauge.
• Use finger or thumb to locate the retromolar fossa.
• Identify pterygomandibular raphe: with finger or thumb and look for "crease" in mucosa between 1 and 2, where the point of entry is +
• Position barrel of syringe over contra-lateral premolars.
• Insert needle smoothly and slowly into the pterygomandibular space, aiming for the mandibular foramen at a depth of 2.0-2.5 cm.
• Do not insert the full needle -5mm of needle must ALWAYS be visible.
• If mandibular bone is contacted, withdraw needle 1 mm and aspirate
• If blood present upon aspiration, withdraw from the needle 1 or 2 mm
• Aspirate again.
• If no blood, continue with injection.
• If positive again, reposition, and repeat aspiration, making sure the tip of the needle is not in a vein, then slowly deliver the anaesthetic solution.
• Withdraw needle quickly and smoothly and re-sheath needle to make it safe
• Have the patient sit up for a rinse.
• The IDB makes the half of the tongue and alveolar on one side numb.
• Bone struck too soon: withdraw, swing needle round to midline, advance for 7 mm, swing back to the original position, and proceed.
• Electric shock sensation in tongue or lip means lingual nerve or mandibular nerve respectively touched by needle; you must withdraw 1-2mm from mandibular nerve.

Incisive and Mental Block

• Useful if you want anesthesia of several anterior teeth (incisors, canine, and first premolar).
• Aim for the mental foramen, which is between the apices of first and second premolar.
• The incisive and mental block procedure is: to check the position of mental foramen on radiograph (if one is available), position the patient ideally supine, or with good lighting, apply a topical LA, ask patient to open wide; unsheathe needle (30 gauge short).
• Place tip of the needle in reflection of buccal sulcus between root apices of LL4 and LL5, aspirate- if not positive, slowly inject at least 1ml solution, and then withdraw needle and re-sheath safely.
• Can may provide unreliable anesthesia and need a lingual infiltration.

Needle Stick Injury

Safety guidance before contact with the patient:

• No transfer of infection can occur if the needle has not contacted the patient.
• Double lock cover on the needle.
• Remove gloves, wash with soap, and dress wound if necessary.
• Inform your senior tutor on clinic.
• Get a new syringe/needle/cartridge and holder and new gloves.
• Note no additional reporting needs to happen.

Safety Post Patient Contact

Safety guidance after contact with the patient:

• Potential transfer of infection from patient to operator from the needle
• Add a double lock cover to needle.
• Remove gloves and WASH the wound under running water or rinse mucous membranes appropriately.
• Report to your senior tutor on clinic.
• Check the medical history to confirm if there's a known blood-borne virus.
• Contact Occupational Health or A&E (out of hours) for advice.
• Take a patient blood sample.
• Leave an accurate record in notes and create a Datix incident report.

Legal Framework

• LA is a Prescription Only Medicine (POM) .
• A written prescription for each specific agent from a recognised prescriber- a dentist.
• The Human Medicines Regulations 2012 details a patient group directive (PGD) – gives legal framework that allows registered health professionals – including Dental Hygienists and Therapists to administer specified medicines without the need for a prescription.
• As of 26 June 2024, an amendment to the Human Medicines Regulations made it possible for dental hygienists and therapists to supply and administer certain prescription-only medicines (POMs) under exemptions, without the need for a prescription from a dentist or a patient group direction (PGD); training must still be had.
• The changes do not give any prescribing powers to hygienists or therapists, or amend the POM status of the listed medicines.
• It is integral to provide a valid prescription for LA that includes: the type of LA e.g. lidocaine or articaine, the route of administration e.g. infiltration or IDB, the dosage e.g. one cartridges or 2.2ml etc, and the date to ensure the prescription is in date for each course of tx.

Post Operative

• Never leave the patient alone after injection as a reaction may occur at any time, including faint or anaphylaxis.
• Duration of Anaesthesia usually, is a few hours, therefore:
• Avoid hot food/drinks and biting lips/cheeks.
• Refrain from poking/prodding area with finger/tongue.
• Do not smoke for the duration of the LA.

Documentation

• A dated signed entry must be made on the patient's record every time LA is given, including the:
• Type of LA agent and vasoconstrictor.
• Amount of solution administered.
• Site of injection.
• Any unusual effects.
• Batch number and expiry date of LA cartridge.
• Post operative instructions given verbally POIV.
• E.g. LA - 2ml lidocaine 2% with epinephrine 1: 80,000, buccal infiltration UL7, UL4, UL2 BN: B296663 ED: 01/24 POIGV.

Complications

• Unwanted effects may occur as a result of injecting: an inappropriate solution, too much solution, or into the wrong site.
• Complications can be either local or general.

Local Complications

• Failure to go numb in which case you must avoid overdosing and get advice
• Bleeding into the tissues following puncture of the blood vessel.
• Haematoma formation which may cause pain or trismus.
• Skin blanching due to vasospasm of artery.
• At point of injection.
• Trismus.
• Visual disturbances.
• Local complications are Prolonged impairment of sensation, with serious complication 1 in 14,000 IDBs cause permanent injury that means one must seek help immediately, facial paralysis (IDB), needle breakage, and post anesthetic reactivation of herpes simplex virus.

General Complications

• Psychogenic
• Toxicity of LA agent
• Overdose
• Reduced tolerance
• Intravascular adrenaline
• Allergy- anaphylaxis
• Drug interactions

Bleeding Risk

• ID blocks and lingual infiltrations may be contraindicated or used with caution depending on bleeding risk.
• Risk relates to the act of injection, not the LA agent and is applicable to patients with:
• Genetic bleeding disorders such as hemophilia.
• Those taking anticoagulants or antiplatelet drugs such as warfarin and clopidogrel.
• Alcoholics (reduced liver function).
• Patients with liver disease.

Failure of Anaesthesia

• Too long a delay before commencing treatment.
• Too little solution administered.
• Intravascular injection (aspirate).
• Inaccurate placement of needle point (IDBs).
• Anatomical variations.
• Incorrect choice of technique.
• Anxiety/fear/negative experience.
• Poor storage of LA (too hot/ in sunlight).
• Never inject into an area of inflammation/infection.
• Inject mesial and distal to the area.