For patients with penicillin allergy, which antibiotics are most commonly rx'd for dental procedures such as root canal or wisdom tooth extraction?

Several options: Reasonable choices would be cephalexin, clindamycin, azithromycin, and erythromycin, maybe sometimes a tetracycline (doxycycline and others). I can't say which of these might be most commonly used; probably it varies widely between different dentists. (Leaving aside whether an antibiotic really is needed just because of these procedures, which seems questionable.)

Dental work.: Check with your dentist for his/her preference, but you’d be OK with Clindamycin, Azithromycin or Erythromycin, to name a few.