Does a motion to amend a statement of claim to assert a new ground of relief arising out of the same facts in a dental malpractice action constitute pleading a new cause of action?

In Denton v. Jones (No. 2) (1976), 1976 CanLII 831 (ON SC), 14 O.R. (2nd) 382, [1976] O.J. No. 2325 (H.C.), Grange J., as he then was, allowed an appeal from a Master’s decision dismissing a motion to amend the statement of claim on the basis of the expiry of a limitation period. The plaintiff sued a dentist for negligence, alleging that the dentist had been retained to extract certain upper teeth but in fact extracted not only those teeth, but all the plaintiff’s lower teeth as well. The claim was brought in negligence, but the amendment sought to add a claim for trespass to the person. Grange J. expressed some doubt as to whether the amendment of the claim to assert an alternative ground of relief arising out of the same facts amounted to pleading a new cause of action. He concluded, however, that there were “special circumstances” – all the necessary facts had been pleaded, there was no need to re-open discoveries and there was no possible prejudice to the defendants, other than the “inevitable prejudice of what might turn out to be the successful plea”: see para. 8.