‘2. Credit. An eligible dentist determined to be eligible before January 1, 2011 is allowed a credit for each taxable year, not to exceed $15,000, against the taxes due under this Part. For dentists determined to be eligible on or after January 1, 2011, an eligible dentist is allowed a credit for each taxable year, not to exceed $12,000, against the taxes due under this Part. The credit may be claimed in the first year that the eligible dentist meets the conditions of eligibility for at least 6 months and each of the 4 subsequent years. The credit is not refundable.’