How often to dental professionals miss oral cancer lesion?

No one is perfect: Can't say it is impossible, but unknown how often these are missed. Some lesions are very early, and/or very subtle, and/or in locations that are not easily examined. As such, they might be more easily missed. Hygienists, dentists (of all specialties) are trained to examine the mouth to look for early and subtle signs of cancer, as well as the more obvious lesions.

Oral cancer: Every dentist is trained to check for any suspicious oral lesion and a regular visit to your dmd should reassure to detect any possible missed small lesions.