The middle superior alveolar (MSA) nerve is present in only about 28% of the population. These nerves and their terminal branches are anesthetized with this specific injection. However, when the ASA nerve block fails to provide pulpal anesthesia distal to the maxillary canine, the MSA block is indicated. The areas that are anesthetized are the pulps of the maxillary first and second premolars and the mesiobuccal root of the first molar. The buccal periodontal tissues and bone over these teeth are also anesthetized. The success rate of the MSA nerve block is high.
Proper technique:
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25 or 27-gauge short needle is recommended
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Area of insertion: height of mucobuccal fold above the maxillary second premolar
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Target area: maxillary bone above the apex of the maxillary second premolar
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Landmarks
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Mucobuccal fold​ above the maxillary second premolar
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Orientation of the bevel: toward bone
Procedures:
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Correct patient & clinician positioning
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Right MSA, right-handed clinician sit at 10:00 facing patient / left-handed clinician sit at 2:00 facing patient
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Left MSA, right-handed clinician sit at 8:00 or 9:00 facing patient / left-handed clinician sit at 3:00 or 4:00 facing patient​
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Prepare tissue at the injection site
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Dry with gauze or blow air with air/water syringe​
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Apply topical anesthetic for minimum of 1 minute
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Stretch the patient's upper lip to make tissues taut and to gain visibility
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Insert needle into height of mucobuccal fold over second premolar with the bevel facing bone
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Penetrate the mucous membrane and slowly advance the needle until its tip is located well above the apex of the second premolar (about 1/4 length of needle)
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Aspirate
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Slowly deposit 0.9-1.2mL of anesthetic solution (1/2 to 2/3 cartridge) approximately 30-40 seconds
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Slowly withdraw needle and safely recap
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Wait 3-5 minutes before starting dental procedure​
