The triangle of safety: a modified posterior superior alveolar injection technique based on the anatomy of the PSA artery

Gen Dent. Nov-Dec 2002;50(6):554-7; quiz 558-9.


The posterior superior alveolar (PSA) injection technique is commonly used to anesthetize soft and hard tissues of the posterior maxilla. As with all injections, complications arise, including hematoma formation secondary to needle-induced vascular trauma. In an attempt to develop a hemorrhage-free PSA injection technique, 361 infratemporal dissections were completed on human cadaver specimens. Three distribution patterns were identified for the external branch of the PSA artery. Regardless of distribution pattern, an anatomical Triangle of Safety was found superior to the maxillary second molar that was free of neurovascular tissues in more than 99% of individuals. Injection into this area appears to meet anesthetic needs while reducing the risk of hematoma formation. The combination of this anatomical triangle with newer anesthetic agents and computerized delivery systems holds promise for continued improvement of the PSA injection technique.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Alveolar Process / anatomy & histology
  • Alveolar Process / blood supply*
  • Anesthesia, Dental / instrumentation
  • Anesthesia, Dental / methods*
  • Anesthesia, Local / instrumentation
  • Anesthesia, Local / methods*
  • Cadaver
  • Facial Muscles / blood supply
  • Female
  • Hematoma / prevention & control
  • Hemorrhage / prevention & control
  • Humans
  • Injections / instrumentation
  • Injections / methods
  • Male
  • Maxilla / anatomy & histology
  • Maxilla / blood supply*
  • Middle Aged
  • Molar / blood supply
  • Needles / adverse effects
  • Orbit / blood supply