Dental Nerve Supply, Local Anaesthesia, and Clinical Management
The Nerve Supply Relevant to Local Anaesthetic in Dentistry
The Trigeminal Nerve (CN V):
The Trigeminal Nerve (Cranial Nerve V) is crucial for dentistry, responsible for sensation and motor functions in the head and face.
It has three main branches:
Ophthalmic (V_{1}): Primarily sensory.
Maxillary (V_{2}): Primarily sensory.
Mandibular (V_{3}): Both sensory and motor.
Nerve Supply of the Mandible:
Mandibular Branch (V_{3}):
Enters through the Mandibular Foramen and is protected by the Lingula.
It gives rise to the:
Lingual Nerve: Supplies sensation to the lingual gingiva only (specifically teeth 8-1 on the lower arch) and the tongue.
Inferior Alveolar Nerve (IDN): Supplies sensation to all lower teeth. It branches into the Mental Nerve.
Long Buccal Nerve: Supplies sensation to the buccal gingiva only (specifically teeth 6, 7, 8 on the lower arch).
Mental Nerve: Branches off from the IDN through the Mental Foramen, which is located at the apices of the premolars. It supplies sensation to the lower lip, buccal mucosa, and the chin.
Nerve Supply of the Maxilla:
Maxillary Nerve (V_{2}):
Posterior Superior Alveolar (PSA) Nerve: Supplies the upper molars (excluding the mesiobuccal root of the first molar in some cases) and buccal gingiva in that region.
Middle Superior Alveolar (MSA) Nerve: Supplies the premolars and sometimes the mesiobuccal root of the first molar, as well as the buccal gingiva.
Anterior Superior Alveolar (ASA) Nerve: Supplies the incisors and canines, and the associated labial gingiva.
Nasopalatine Nerve: Enters through the Incisive Foramen. It supplies sensation to the palatal mucosa of the anterior maxilla, specifically from canine to canine.
Greater Palatine Nerve: Enters through the Greater Palatine Foramen. It supplies sensation to the soft palate and the palatal gingiva from the premolar region posteriorly.
Local Anaesthetic (LA) in Dentistry:
The oral cavity has an excellent nerve supply, meaning pain receptors can be extremely unpleasant during dental procedures.
LA is essential for carrying out most dental treatments.
Definition:
"Anaesthesia" is defined as "LOSS OF ALL SENSATION."
In dentistry, LA typically achieves LOSS OF PAIN ONLY. Patients remain conscious and can still feel pressure or vibration.
Therefore, the term LOCAL ANALGESIA more accurately describes the effect achieved in conscious dental patients.
Mechanism of Action:
The body's sensations are transmitted as electrical impulses along sensory neurons (nerve cells) to the brain.
LA works by blocking these electrical transmissions from the source of stimulation (e.g., the tooth or surrounding tissues).
This prevents painful information from reaching the brain, ensuring the patient feels no unpleasant or painful stimuli, even while being conscious and aware of the treatment.
Local Anaesthetic Solutions – Components:
There are five key components in a local anaesthetic cartridge:
Anaesthetic Agent:
This is the primary compound responsible for blocking electrical nerve transmission to the brain, preventing the sensation of pain and temperature changes.
Common examples include Lidocaine, Articaine, Prilocaine, and Mepivacaine.
Sterile Water:
Acts as a carrying solution, making up the bulk of the cartridge contents.
Buffering Agent:
Maintains the contents at a neutral pH (neither acidic nor alkaline) to prevent irritation of soft tissues upon injection.
Preservative:
Extends the shelf life of the product.
Vasoconstrictor:
Present in some LA solutions to prolong the action of anaesthesia.
It works by constricting (closing) blood vessels in the injection area, preventing the anaesthetic solution from being carried away too quickly by the bloodstream.
Vasoconstrictors and Contraindications:
Adrenaline (Epinephrine):
The most common vasoconstrictor used in LA.
It is a potent cardiac stimulant, which increases the rate and depth of the patient's heartbeat.
Used as an emergency drug for conditions like anaphylaxis, where blood pressure drops severely.
Contraindications: Cannot be safely used in some medical conditions due to its systemic effects:
High Blood Pressure
Heart Disease
Overactive Thyroid Gland (increases metabolic rate).
Adrenaline Content Ratios:
Typically 1:80,000 (e.g., Lignospan).
Can be 1:100,000 (e.g., Articaine) or sometimes 1:200,000 (e.g., Prilocaine).
Alternative Vasoconstrictors:
For patients with compromised medical histories (e.g., high BP, heart disease, overactive thyroid), plain LA (no vasoconstrictor) or LA with an alternative vasoconstrictor like Felypressin or Octapressin (found in Citanest) should be used.
Disadvantage of Plain LA: Analgesic action wears off more quickly, and there is an increased risk of haemorrhage during surgical procedures.
Felypressin/Octapressin Contraindication: Should not be given to pregnant patients as Felypressin is a potent drug used to induce labor due to its contractive action on uterine muscles.
Drug Classification and Disposal:
The anaesthetic agent and any vasoconstrictor are classified as drugs.
Their safe disposal is subject to strict regulations.
Managing Patient Anxiety: "The Jag" (Needle Fear):
Role of the Dental Nurse in Patient Support:
Discuss with the patient prior to treatment.
Discuss and confirm with the operator, ensuring shared understanding of patient needs.
Maintain positive body language.
Engage in encouraging chat.
Offer to hold the patient's hand.
Provide reassuring comments like "almost done, well done!" and offer praise.
Local Anaesthetic Delivery: Equipment and Techniques:
Patient Comfort:
Topical Anaesthetics:
Available as gels, creams, or sprays (e.g., Xylonor gel, Topex Topical Anaesthetic Gel).
Used to anaesthetize the surface of the mucous membrane.
Typically applied before injecting the local anaesthetic to reduce the discomfort of the needle stick.
The effect is temporary, and normal sensation returns within a few hours.
Greatly improves patient comfort and reduces anxiety related to dental treatments.
Administration Techniques:
Four main methods of administering LA in dentistry:
Infiltration: Direct injection into the tissue near the tooth.
Nerve Block: Injection near a main nerve trunk, anaesthetizing a larger area.
Intra-ligamentary: Injection directly into the periodontal ligament.
Intra-osseous: Injection directly into the bone.
Local Anaesthetic Equipment:
Syringes:
Various designs, including side-loading, breach-loading, and self-aspirating types.
Most are metallic and autoclavable.
Disposable syringes are available but are a costlier option.
Syringe Components (e.g., Aspirating Syringe):
Thumb Ring: Used by the operator to 'draw back' (aspirate) to check for blood in the cartridge.
Harpoon (Part D): Engages the rubber bung of the cartridge. By pulling back on the thumb ring, the harpoon creates negative pressure for aspiration. If blood appears, the needle has penetrated a blood vessel; the needle must be removed, realigned, and re-aspirated before continuing delivery.
Self-Aspirating Syringe (e.g., T-bar type): The operator presses firmly to push the rubber bung for delivery. Releasing pressure on the T-bar allows for aspiration in this type of syringe.
Intraligamentary Syringe: Designed for injectin into the periodontal ligament, often featuring a lever for precise pressure delivery.
Dental Needles:
Gauge: The larger the gauge number, the smaller the internal diameter of the needle (e.g., 30G is smaller than 27G).
Color-coded hubs and boxes for easy identification.
Pre-threaded plastic hub fits securely onto the syringe.
Siliconized cannula provides smooth penetration and minimal discomfort.
Red Dot indicator identifies the needle bevel position before uncapping, aiding injection accuracy and reducing stick risk.
Common Sizes:
Short Needle: 30G; typically used for maxillary delivery (infiltration, buccally or palatally).
Long Needle: 27G; typically used for mandibular delivery, especially for Inferior Dental Nerve (IDN) blocks (requires 6-10 mm penetration).
Sharps Bin:
Must be placed next to the operator on the worktop for immediate and safe disposal of needles and cartridges.
Warning: Do not fill above the designated line.
Administering LA: Clinical Considerations:
Aspiration: Essential to ensure the needle has not entered a blood vessel.
If blood is present in the cartridge: Stop immediately, alter the position of the needle slightly, deliver another tiny quantity of LA, aspirate again. If no blood, proceed with delivery.
Syringe Safety: Safety Plus Syringes (e.g., Ultra Safety Plus) are designed with protective sheaths and handles to minimize needlestick injuries.
Pre-operative Advice to Patients:
Patient information about the procedure and what to expect.
Post-operative Instructions to Patients After Receiving LA:
Sensation Loss: Inform patients that sensation will be lost for several hours.
Eating/Drinking: Advise against eating or drinking until sensation returns to prevent biting or burning themselves.
Restorations: Avoid chewing directly on newly restored teeth (e.g., amalgam) to prevent damage.
Paraesthesia: Explain that a tingling sensation indicates the anaesthetic is wearing off.
Post-Injection Tenderness: Note that IDN blocks may cause localized tenderness for about a day; intraligamentary injections may cause tenderness in surrounding gingivae.
Potential Complications of LA Administration:
Too Rapid Injection: Excessive pressure can tear tissues, leading to localized irritation and post-operative pain.
Too Large Injected Volume: Injecting more than necessary can tear tissues, especially in the palate.
Injection into Infected Area: Avoid injecting directly into an infected area; a nerve block is preferable to infiltration in such cases.
Trismus: Stiff opening of the jaw after an IDN Block, usually for a couple of days, and resolves without treatment.
Laceration of the Nerve: Can occur in nerve blocks due to damage to the nerve sheath or the nerve itself, causing prolonged anaesthesia and local irritation.
Laceration of an Artery or Vein: Arteries are rarely damaged due to tough walls. A punctured vein causes immediate localized swelling that subsides spontaneously.
Laceration of the Periosteum: Due to rough manipulation of the needle, resulting in post-operative pain in the area.
Bleeding at Injection Site: Stops spontaneously; more common when no vasoconstrictor is used.
Dental Procedures and Corresponding Nerve Blocks:
Extraction of an Upper Permanent Central Incisor:
Superior Anterior Alveolar Nerve
Nasopalatine Nerve
(Area anaesthetized: Lower eyelid, lateral aspect of the nose, and upper lip)
Extraction of an Upper Permanent First Premolar:
Middle Superior Alveolar Nerve
Greater Palatine Nerve
Surgical Removal of an Upper Third Permanent Molar:
Posterior Superior Alveolar Nerve
Greater Palatine Nerve
Extraction of a Lower Permanent Central Incisor:
Either an Inferior Dental Nerve Block
Or buccal and lingual infiltration injections.
Extraction of a Lower Right First Molar:
Inferior Dental Nerve Block
Lingual Nerve
Long Buccal Nerve
Specific Nerve Anaesthetization Examples:
Posterior Superior Alveolar Nerve: Upper 6 (distal), 7, 8 and buccal gingiva.
Long Buccal Nerve: Gingiva only for lower 6, 7, 8.
Maxillary Palatal Aspect - Greater Palatine Nerve: Palatal gingiva only for upper 4, 5, 6, 7, 8.
Mandibular Inferior Dental Nerve: All lower teeth, buccal gingiva for lower 5, 4, 3, 2, 1, lower lip, and chin.
Nurse Safety After Injection:
Needlestick Injury Risk: The used needle is a significant source of cross-infection due to contamination with blood.
Re-sheathing: Re-sheathing the needle is the most common cause of needlestick injury to dental staff.
NEVER re-cap a needle using both hands.
Recommended Method: The One-Hand Scoop Technique. The needle sheath should be placed in a device to hold it firmly and upright. The syringe is then held by its back end, and the needle is re-sheathed using one hand, keeping fingers away from the dirty needle. This procedure should be performed by the dentist.
Safety Syringes: Ultra Safety Plus systems integrate a protective sheath that covers the needle upon withdrawal, designed to lower the risk of injury.
Inoculation Injury Protocol (If a Needlestick Occurs):
Treat every patient as high risk.
Immediate Action:
STOP IMMEDIATELY.
Remove the glove and place it in the clinical waste bin.
Squeeze the sharps injury area immediately to encourage bleeding under a running tap.
Run the area under tap water while squeezing.
Dry the area and apply a waterproof dressing.
Reporting and Follow-up:
Inform the dentist/practice manager immediately.
Record the incident in the accident book.
Check the patient's medical history (age, high/low risk).
Contact the local occupational health department for advice and provide all required information.
The occupational health nurse will determine if a blood test (for the injured staff member and potentially the patient) is required.
Practice Policies:
Every practice maintains its own policies regarding sterilization and disinfection.
Basic principles must always be adhered to, including:
Hand washing
Personal Protective Equipment (PPE)
Cleaning of the surgery using zoning principles
Cleaning of equipment and instruments
Clinical waste management
Resources like the Scottish Dental Clinical Effectiveness Programme (SDCEP) provide guidelines.