Every subscription contract made by a dental service plan corporation shall provide for the payment of dental services for a period of twelve (12) months from the date of issue of the subscription certificate. The contract may provide that it shall be subject to renewal from year to year unless there has been one (1) month's prior written notice of termination by the dental service plan corporation. A subscriber shall forfeit membership upon failure to renew the contract, or upon voluntary resignation. During the first contract year, the contract may provide that the inception coverage may be deferred for not more than two (2) months from date of issue of the contract, and may exclude treatment of dental ills existing at the inception of the contract.