Clinical review required: Local anaesthetic choice and dose must be individualised. Allergy, pregnancy, medicines, heart disease, liver function, age and the planned procedure can change the safest approach.

What is local anaesthesia?

Local anaesthesia temporarily blocks nerve signals from a defined area so dental treatment can be performed without sharp procedural pain while the patient remains awake. It does not treat anxiety and does not necessarily remove pressure, movement or vibration. The dentist selects the drug, concentration, vasoconstrictor, injection site and volume according to anatomy, health and treatment duration.

How dental local anaesthetics work

Local anaesthetic molecules enter nearby nerves and reduce sodium-channel activity, interrupting propagation of pain signals. Onset depends on drug properties, tissue pH, injection accuracy and nerve anatomy. Inflamed acidic tissue can make anaesthesia less predictable. Numbness wears off as medicine is redistributed and metabolised; duration varies between soft tissue and the tooth itself.

Infiltration and nerve block

An infiltration places solution near small terminal nerve branches, commonly beside an upper tooth. A nerve block deposits it near a larger nerve before it branches, such as an inferior alveolar block for lower molars. Supplemental intraligamentary, intraosseous or intrapulpal techniques may be considered when conventional methods are insufficient. Each has different anatomy and risk.

Common medicines

Lidocaine has a long clinical history and is a common reference drug. Articaine, mepivacaine, prilocaine and bupivacaine are used in selected settings. Comparative evidence suggests articaine can provide higher anaesthetic success in some routine applications, but no agent is best for every patient. Duration, concentration, vasoconstrictor, medical history and local licensing guide selection.

Why adrenaline may be included

Epinephrine, also called adrenaline, constricts local blood vessels, slowing anaesthetic removal, prolonging effect and reducing bleeding. Temporary palpitations or tremor can follow intravascular exposure or sensitivity. Cardiovascular disease does not automatically prohibit vasoconstrictor, but dose and technique may need adjustment. Levonordefrin or felypressin is used in some formulations and countries.

Pre-injection assessment

The dentist reviews allergies, previous reactions, weight when relevant, pregnancy, cardiovascular disease, liver or kidney impairment, methemoglobinemia risk and current medicines. A history of fainting, racing heart or prolonged numbness should be described precisely; many reported "allergies" are anxiety, vasovagal episodes or adrenaline effects rather than immune allergy.

How the injection is made more comfortable

Topical anaesthetic can reduce needle-puncture pain at some oral sites but is less reliable for deeper solution deposition. Drying tissue, using a sharp appropriate needle, stable hand support, slow deposition, distraction and clear communication can help. Warming or buffering solutions has supportive evidence in some settings, but effects vary. No technique can guarantee that every injection is sensation-free.

What should be felt?

A brief pinch, pressure or mild burning can occur. The patient should not be forced through severe pain. A stop signal allows pauses. During treatment, pressure and vibration may remain, but sharp, electric or escalating pain warrants reassessment and additional anaesthesia or a different technique. Silence should never be interpreted as adequate numbness.

Testing before treatment

Lip or cheek numbness confirms soft-tissue effect but does not always prove pulpal anaesthesia. The dentist may test cold, probing or another stimulus appropriate to the procedure. For an inflamed lower molar, profound lip numbness can coexist with a responsive pulp. Treatment should begin only when the relevant tissue is adequately anaesthetised.

Why anaesthesia sometimes fails

Causes include anatomical variation, inaccurate deposition, inflammation, accessory innervation, insufficient time, inadequate dose or an intravascular placement that removes medicine from the target. Severe irreversible pulpitis is particularly challenging. Anxiety can amplify perception but should not be used to dismiss real pain. Repeating the same ineffective injection indefinitely is not a plan.

Supplemental techniques

A different block, buccal infiltration, periodontal-ligament injection, intraosseous access or direct intrapulpal administration may be used according to diagnosis. Some techniques act rapidly but have shorter duration or specific risks. Sedation can reduce anxiety but does not replace local pain control. General anaesthesia is rarely the first response to a technically solvable local anaesthesia problem.

Maximum dose and cumulative exposure

Safe limits depend on drug, concentration, vasoconstrictor, body size and health. All cartridges and topical agents must be included in the calculation. Maximum recommended dose is a ceiling, not a target. Long multi-quadrant sessions may require staging to avoid excessive cumulative exposure and to maintain predictable postoperative function.

Common temporary effects

Numb lip, tongue or cheek, altered speech, difficulty judging temperature and mild injection-site tenderness are common. Children and some adults may bite or burn numb tissue. Avoid chewing until control returns and follow instructions about hot drinks. Rarely, bruising, restricted opening or transient nerve symptoms occur.

Important complications

Vasovagal fainting or anxiety-related symptoms.
Intravascular injection with palpitations, dizziness or toxicity.
Haematoma, infection or needle injury.
Temporary facial-nerve weakness after misplaced block.
Prolonged altered sensation or nerve injury.
Allergic reaction, which is uncommon with amide agents.
Local anaesthetic systemic toxicity from excessive or intravascular dose.

Signs of systemic toxicity

Early features can include circumoral tingling, metallic taste, tinnitus, agitation, slurred speech or dizziness, progressing in severe cases to seizures or cardiovascular collapse. Clinics must calculate doses, aspirate and inject carefully, monitor the patient and maintain emergency protocols. Sudden concerning symptoms require immediate cessation and medical management.

Pregnancy and breastfeeding

Necessary dental treatment and appropriate local anaesthesia can often be provided during pregnancy. Timing, agent and vasoconstrictor are selected with obstetric context and the urgency of infection or pain. Untreated disease also carries risk. Breastfeeding interruption is not routinely required for many commonly used local anaesthetics, but individual medicines and health circumstances should be checked.

Children

Paediatric dose is calculated carefully and all sources counted. Behaviour guidance and topical anaesthetic can support the injection. Long soft-tissue numbness increases lip-biting risk, so caregivers need clear supervision instructions. Devices marketed as needle-free may still create pressure or tissue injury and do not remove the need for dose control.

After the appointment

Protect numb tissues, avoid testing them with biting, and wait before hot food or drink. Contact the clinic if numbness lasts substantially beyond the advised interval, weakness persists, swelling increases or severe pain develops. A numb area that is gradually shrinking is different from new or worsening neurological symptoms.

Treatment abroad

Ask which agent and vasoconstrictor will be used, who calculates the total dose and how failed anaesthesia is managed. Extensive same-day dentistry may involve many cartridges. Keep a treatment and medicine record, especially if another clinician will manage complications after travel.

Aspiration and slow deposition

Before depositing near a vascular area, the clinician may aspirate to check whether the needle tip is in a blood vessel. A negative result does not remove all risk, so incremental slow injection and observation remain important. Sudden palpitations can reflect intravascular vasoconstrictor, anxiety or both. The team pauses, checks the patient and records the event rather than assuming it is harmless.

Inflamed teeth and irreversible pulpitis

Inflammation changes nerve excitability and local tissue conditions, making conventional blocks less reliable. Evidence-based management may combine a primary block with buccal infiltration or another supplemental technique and appropriate preoperative analgesic planning. Repeated painful access attempts are not a diagnostic test. If profound anaesthesia cannot be achieved safely, treatment can be staged or referred.

Nerve injury and altered sensation

Persistent tingling, numbness, burning or altered taste after an injection is uncommon but deserves documentation and follow-up. Causes can include needle trauma, bleeding, inflammation, surgery or chemical irritation; association does not prove a single mechanism. Early examination maps the area and function. Worsening symptoms, motor weakness or additional neurological signs need prompt specialist assessment.

Local anaesthetic and infected tissue

Injecting directly into acutely infected acidic tissue can be painful and less effective. A regional block placed away from infection may work better. Drainage or urgent operative care may still be required; antibiotics alone do not reliably anaesthetise or cure a local source. Spreading infection, fever, swallowing difficulty or airway symptoms require urgent escalation.

Record keeping

The clinical record should identify the product, concentration, vasoconstrictor, cartridge volume, total dose, sites, technique and patient response. Unusual reactions and instructions are recorded for future visits. Accurate data help distinguish true drug sensitivity from a technique-related or anxiety event and prevent cumulative dosing errors during long appointments.

Questions to ask

Which tissues need to be numb?
Which medicine and vasoconstrictor are planned?
How will you confirm pulpal anaesthesia?
What is the plan if I still feel sharp pain?
How long should numbness last?
Which symptoms require urgent contact?

Frequently asked questions

Is articaine always stronger than lidocaine?

No. Evidence supports high success in many uses, but anatomy, technique, procedure and patient factors determine the best choice.

Can I be allergic to dental anaesthetic?

True allergy to modern amide local anaesthetics is uncommon. A detailed reaction history and specialist testing may be needed.

Why is my lip numb but my tooth hurts?

Soft-tissue numbness does not always equal pulpal anaesthesia, especially in an inflamed lower molar.

Can sedation replace the injection?

No. Sedation manages anxiety and awareness; most operative dentistry still requires local anaesthesia.

Sources and clinical review references

Editorial review note: Evidence reviewed 22 July 2026. Named clinician and local medicines review are required before indexation.

Local Anaesthesia