The pulpal effects of electrosurgery involving unrestored enamel, cementum, calcium hydroxide-copal varnish-based restorations and unbased restorations were evaluated in extracted human teeth and posterior teeth of cynomolgus monkeys. Electrosurgery for all studies was performed with a fully rectified filtered unit under conditions of normal clinical usage. Studies in extracted human teeth measured the voltage potential generated between a reference probe in apical pulp tissue and an activated electrosurgery electrode placed on enamel, cementum, based restorations, and unbased restorations. Placement of a base reduced but did not prevent passage of electrosurgical current, and no measurable potential was associated with activated electrode contact on cementum or enamel. Studies in three cynomolgus monkeys included electrosurgery of based and unbased cervical silver amalgam restorations, electrosurgery of unrestored enamel, restored teeth not subjected to electrosurgery and teeth that were neither restored nor subjected to electrosurgery. Electrosurgery of restored teeth, regardless of the presence of a base, consistently resulted in pulpal damage characterized by an altered dentin matrix, necrosis adjacent to the cavity preparation, and a transition zone between necrotic and apparently vital pulp tissue. By 8 weeks following electrosurgery, the majority of specimens showed replacement of the odontoblastic layer and adjacent pulp tissue by dense connective tissue with areas of irregular calcification.