Value of total filtration for 70 kVp is
2.1 mm
2.3 mm
1.5 mm
2.5 mm
Total filtration is the sum of the inherent and added filtration. Governmental regulations require the total filtration in the path of a dental x-ray beam to be equal to the equivalent of 1.5 mm of aluminum for a machine operating at up to 70 kVp and 2.5 mm of aluminum for machines operating at higher voltages.
Oral Radiology, Principles and Interpretation / Stuart C. White, Michael J. Pharoah - 7th ed - pg - 10,11