msa and asa (infraorbital) nerve blocks

still needs ASA

what is unique about the middle superior alveolar nerve?

it is absent in about 72% of people and is present in only about 28%

when absent, its areas are usually supplied by the ASA nerve

when is an MSA nerve block indicated?

when the ASA block fails to anesthetize teeth distal to the canine

treating both mx premolars

the mb root of the mx first molar still has sensation after a PSA block

what are areas anesthetized by the MSA block?

pulps of: first premolar, second premolar, MB root of the mx first molar

+buccal bone and buccal periodontium over these teeth

what are the contraindications for an MSA block?

infection or inflammation is present at the injection site

remember that if the MSA nerve is absent, the ASA block will be needed

advantages and disadvantages of the MSA block

advantages: fewer injections, less anesthetic required

disadvantages: none listed

alternatives to the MSA block

supraperiosteal infiltration

PDL injection

IO injection

ASA block when appropriate

MSA technique

27-gauge short or long

insertion: height of the mucobuccal fold above the second premolar

target: mx bone above the apex of the second premolar

landmark: mucobuccal fold over the second premolar

what complication may occur with a MSA block?

rarely, a hematoma may form

management: apply pressure with sterile gauze for at least 60 seconds

what is the ASA nerve block?

anesthetizes the anterior maxillary teeth

often called infraorbital, but this is INCORRECT. The infraorbital nerve itself supplies soft tissues, while the ASA branch supplies the teeth.

which nerves are anesthetized by the ASA block?

the anterior superior alveolar nerve

middle superior alveolar nerve (when present)

infraorbital nerve branches: inferior palpebral, lateral nasal, superior labial

what areas are anesthetized by the ASA block?

pulps of: central incisor, lateral incisor, canine

in about 72% of patients, also: premolars, MB root of first molar

also anesthetizes: buccal bone and periodontium, lower eyelid, lateral nose, upper lip

hen is an ASA block indicated?

when multiple anterior maxillary teeth require treatment

ex: scaling and root planing from canine to canine on one side

when is an ASA block contraindicated?

when only one or two teeth require treatment

localized hemostasis is needed

in these cases, use a supraperiosteal injection

advantages of the ASA block

easy technique, safe, requires fewer injections, uses less anesthetic

disadvantages of the ASA block

psychological: fear of damaging patient’s eye

infraorbital landmarks can occassionally be difficult to locate

ASA technique

needle: 25-27 gauge long, (27 gauge short may be used for children)

insertion: height of the mucobuccal fold over the first premolar

target: infraorbital foramen

landmarks: mucobuccal fold, infraorbital notch, infraorbital foramen

patient and operator positioning for ASA block

operator: 10 o’clock position

patient: preferably supine, neck extended slightly

(improves access to the infraorbital foramen)

what complication can occur with an ASA block?

rarely, a hematoma beneath the lower eyelid

management: apply pressure over the infraorbital foramen for 2-3 minutes

a patient requires treatment on teeth #6-8. which injection would you choose?

ASA block

a patient requires treatment on teeth #4 and #5 only. which injection is preferred?

usually: supraperiosteal infiltrations (high success and technically simple)

if multiple premolars require anesthesia or an ASA block has failed to anesthetize the premolars: an ASA block may be used

• you cannot determine beforehand whether the MSA nerve is present. If the ASA block fails to anesthetize the premolars, that suggests the patient likely has a separate MSA nerve

a patient needs SRP on teeth #7-9. is one right ASA block enough?

no. a right ASA block anesthetizes only the right anterior teeth (#7 and #8)

bc the ASA block is unilateral, tooth #9 requires additional anesthesia, such as a left supraperiosteal injection (or a left ASA block if more anterior teeth are involved)