Informed Consent to Treatment

Canadian law recognizes the fundamental right of every mentally capable person to accept or refuse health care regardless of its risks or benefits. It is also acknowledged that, without sufficient information about proposed treatment, a patient cannot make an educated choice, rendering this right of self-determination effectively meaningless.

Dentists and other health practitioners are sometimes confused about how much and what kind of information must be provided in order to ensure patients are able to make fully informed health care decisions. The following describes the basic principles of the law of informed consent to treatment in Ontario.

The duty to disclose

The foundations of the Canadian common law of informed consent were established in 1980 when the Supreme Court of Canada held that health practitioners have a pre-treatment duty to answer a patient’s questions and to disclose information that a reasonable person in the patient’s position would want to know before consenting.

The particulars of this duty are now codified in Ontario’s Health Care Consent Act, 1996 (HCCA). Specifically, subsections 11(2) and (3) of the HCCA state that, in addition to having their questions answered, patients are entitled to be informed about:

  1. the nature of the treatment;
  2. the expected benefits of the treatment;
  3. the material risks of the treatment;
  4. the material side effects of the treatment;
  5. alternative courses of action;
  6. the likely consequences of not having the treatment.

RCDSO also requires its members to discuss the direct and ancillary costs of treatment with patients as part of the disclosure process.

Material risks

It is worth noting that patients need not be advised of every risk associated with proposed treatment for consent to be informed, only material ones. As a general rule, risks are considered material if they occur frequently, even if the consequences are minor (e.g. temporary pain or numbness), or if the consequences are significant, even if they occur rarely (e.g. paralysis or death). That said, because patients are less likely to accept risks associated with unnecessary procedures, even less consequential risks may have to be disclosed in order to obtain a patient’s fully informed consent to elective treatment.

Materiality may also depend on a patient’s unique circumstances: a concert flautist would likely be more concerned about the possibility of even transient oral paresthesia than the average patient, creating a heightened onus of disclosure for the treating dentist.

While treatment providers cannot know every detail of their patients’ lives, the scope of the duty to warn in any particular case is determined by what the health professional did know or would have learned about the patient in the ordinary course of taking a history.

In addition, a health care provider cannot be wilfully blind to indicia that a specific patient may have reason to be concerned about a risk that might not otherwise be considered material.


In the regulatory context, an inquiry into a patient complaint of absence of informed consent focuses on whether the health practitioner met standards of disclosure and record-keeping.

But a breach of the standard of care is only one of the elements that must be proved for a health care provider to be held civilly liable for malpractice. To succeed in an action for negligence, the patient/plaintiff must also demonstrate on a balance of probability that the defendant’s wrongdoing caused his or her injuries.

Where the claim is based on an alleged failure to warn, the plaintiff must persuade the court that the risk that manifested itself was material and knowing about it would have led a reasonable person in his or her position to decline the treatment. If, out of necessity or by choice, a reasonable patient would have consented to the procedure despite its risks, the breach of the duty to warn caused no harm.

This is not to say that a practitioner who wrongly caused a known risk of a procedure to materialize cannot be held liable for a patient’s losses, since the acceptance of material risks does not equate to a waiver of liability for negligent treatment.

Evidence of consent

A signed consent form is one piece of evidence that information was disclosed to and discussed with a patient and the patient agreed to treatment. However, obtaining consent is not a single event, but rather a process that occurs over time. And since a legal action for alleged absence of informed consent can be brought years after the treatment was completed, health professionals should supplement written consent forms with clear documentation of each consent discussion in their patients’ charts.