Incomplete numbness usually comes from inflamed tissue, anatomical nerve variation or high anxiety. In most cases it can be solved.
"Anaesthetic does not work on me" is rarely a fixed personal trait. Incomplete numbness usually has a technical or biological explanation: inflamed tissue at the site, anatomical variation in the nerve, or a high level of anxiety.
Why inflammation reduces the effect
Local anaesthetics need a particular acid-base balance to cross the nerve membrane. Inflamed tissue is more acidic, so less of the drug is in the form that can get in. Blood flow is also increased, carrying the drug away faster, and inflamed nerve fibres fire more readily. Together these mean the same dose achieves less.
The practical lesson: delaying treatment until an abscess develops makes numbing harder. Coming early makes the appointment easier.
Anatomical reasons
Lower molars are the hardest region to numb, because the jawbone is dense and the drug cannot diffuse to the root. A block injection is used near the nerve, and the nerve's course varies between individuals. Some people also have accessory nerve supply. In those cases the dentist changes technique: a supplementary block, an injection into the ligament, or an intra-tooth approach.
Other contributing factors
- High anxiety, which raises pain perception so that pressure can be read as pain.
- Arriving hungry or short of sleep, which lowers the pain threshold.
- Not waiting long enough for a block to take effect.
- Recent high-dose painkillers or certain regular medications; share your medication list.
- Alcohol and some chronic conditions that alter pain perception.
What you can do
Tell your dentist beforehand if numbing has been difficult in the past. That single sentence lets them plan a different technique from the start. During treatment, raise your hand rather than enduring discomfort, because tension and anxiety amplify what you feel.
After the appointment
Numbness usually lasts a few hours. Avoid hot drinks and take care not to bite your lip or cheek. This is especially important for children, who need reminding.
Difficulty numbing does not mean treatment cannot be done. Where a dental abscess is present, drainage may come first. See our pages on root canal treatment and emergency tooth extraction.
