Every dentist licensed in Illinois to practice dentistry, and who is reputable and in good standing, shall be eligible to become a participating dentist in the dental service plan corporation operating in the geographic area in which he resides or practices, under such terms and conditions as are imposed on other participating dentists under similar circumstances. A dental service plan corporation shall impose no restrictions on the dentists who treat its subscribers as to methods of diagnosis or treatment. The private dentist-patient relationship shall be maintained, and a subscriber shall at all times have free choice of any dentist who is a participating dentist in the corporation and who agrees to accept a particular beneficiary as a patient.
     Except as otherwise provided in Section 15 of this Act, no person shall offer to the public any dental service plan or otherwise engage in the business of a dental service plan corporation without having first received a charter from the Director.