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For a detailed and accurate answer, please consult the WREB Candidate Guide
http://www.wreb.org/dental/dentalPDFs/2Operative06.pdf
On pages 14 and 15 of this section (pages 30 and 31 of the overall guide), the Scoring Criteria Rating Scale gives you details for the three categories of Outline & Extension, Internal Form, and Operative Environment. If you meet those with a score of 3 or better, you should have no difficulty with the exam.
Having sat in as an official observer for a recent WREB exam, I can assure you that the Candidate Guide is an excellent resource for the clinical exam.
Good luck!