LATERAL PERFORATION
General Rule
Imagine a horizontal line along the gingival margins of the teeth and a vertical line through the interdental papilla. A point about 2mm apical to where these lines meet is usually a suitable site for a lateral perforation.

VERTICAL PERFORATION
General Rule
Edentulous areas may be treated, if preferred, by choosing a site on the alveolar crest (where the cortical plate is thinnest) to provide a vertical perforation rather than a lateral perforation.

Site selection in the mandible

(a) Inject distal rather than mesial, where possible, because a smaller dose suffices.
In most cases, a mesial injection will provide adequate anesthesia, but in a small number it will not.

(b) Avoid perforating between the lower central incisors (because good cancellous spaces are not present in this area).

(c) Avoid the mental foramen area. Preferably, a site between the bicuspids should be avoided, even though a perforation at a distance of 2mm from the gingival margin would usually be well clear of the mental foramen.

Site selection in the maxilla

(a) Avoid perforating between the upper central incisors (because good cancellous spaces are not present in this area).

(b) Avoid perforating into the maxillary sinus. Penetrating the maxillary sinus would not cause permanent damage but local anesthesia would not be achieved.