The license of any dentist or dental hygienist in this state shall be subject to restriction, suspension or revocation, as hereinafter provided, in case of inability of the licensee to practice dentistry or dental hygiene with reasonable skill or safety to patients by reason of one or more of the following:
Mental illness;
Physical illness, including, but not limited to, deterioration through the aging process, or loss of motor skill;
Excessive use or abuse of drugs, including alcohol.