Yes. Although you may only be seeing them for specific treatment you are initiating a “doctor-patient” relationship.  As such, you owe a duty of beneficence to the patient, meaning a duty to promote the patient’s welfare. The ADA describes this as: “The competent and timely delivery of dental care within the bounds of clinical circumstances presented by the patient, with due consideration being given to the needs, desires and values of the patient.”
If you recognize findings that you reasonably believe may be adverse to the patient’s dental health and may or may not require immediate attention but, if not acted upon, may worsen over time and possibly result in an adverse patient outcome, you should advise the patient and document your records accordingly.
You may also consider documenting the fact the patient is presenting only for specific treatment therefore a complete and thorough exam may not be completed.  Another consideration is including language in the informed consent form that the treatment is limited to the specific treatment. However, again, if you notice something during the treatment, it would be best to address the issue with the patient and/or refer the patient accordingly.