Absence notes - Determining justifiable absence

I have heard of a doctor's note, but never a dentist's note. Can you explain to me what types of sick notes are valid?

When an employee is off sick and claiming to be 'incapable of work' then it is necessary, for the administration of statutory sick pay, that they provide medical evidence that enables the employer to certify incapacity for periods of absence; self-certification can be accepted normally for up to six days of absence, while a doctor's note is likely to be needed for seven days or more. Commonly, someone who has been a hospital in-patient will be certified by the ward sister.

Whether or not you