Selection of Needles for Dentistry

1. There are two types of needles used in dentistry: 27 and 30 gauge
2. The former has brown or yellow cap, whereas the latter has blue cap
3. For local anesthesia, 27 gauge is usually used for lower jaw, whereas 30 for upper, why?
4. The former is longer than the latter
5. To produce profound (deep) numbness (anesthesia) for the lower jaw, we need to reach nerve trunk in deep area (so called block anesthesia). In the upper jaw, the nerves are pretty evenly distributed and superficially located.  The bone is pretty porous.  A few drops of anesthetic (so-called infiltration anesthesia) can produce profound anesthesia for upper tooth if dropped near the root tip
6. Why bother to use short needle for upper jaw?  Short needle looks less intimating to patients, particularly younger ones.  Upper jaw is closer to the eyes than lower one.  More important is that short needle has smaller diameter, creating less pain than long needle
7. Why does short needle have large gauge (30 vs. 27)?
8. In fact gauge refers to the inner diameter of the needle in an invert proportion.  Which is bigger (in value) now, 1/27 vs. 1/30?
9. General rule is that 27 gauge is used for lower jaw, whereas 30 for upper
10. Exceptions for upper: if upper third molar or canine is highly impacted, we may end up needing to use longer needle (which gauge, 27 vs. 30?).  For large procedure such as sinus graft, block anesthesia is required? Which needle is needed (27 vs. 30)?
11. Exception for lower: child and petit (small, tiny) women or men; implant (see below).  We do have extra short needle with white and blue cap for child upper jaw
12. There is a big nerve inside the mandible, called inferior alveolar nerve.  Long needle is used to block the nerve to produce profound anesthesia.  The latter is needed for all of dental procedure except implant placement.  Short needle is used to give local infiltration anesthesia, which is less profound.  If drill or osteotome is close to the nerve, the patient will tell us.  After taking X-ray to confirm the depth of drill or osteotome, long needle may be used to produce profound anesthesia.  Damage to the nerve during implant placement is a big complication.  We should do everything to prevent it and at the same time to place as big and long implant as possible.  It is good to tell the patient the situation in advance.  He or she will be pleased to know that
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Xin Wei, DDS, PhD, MS 1st edition 07/19/2011, last revision 07/19/2011