In intraoral radiograph, patient radiation is decreased by
all except:
High speed film
Intensifying screens
Lead apron
Decreasing kVp
Kilovoltage:
The optimal operating potential of dental X-ray units is between 60 and 70 kVp (ADA 2012).
Although image diagnosis may be improved slightly with increased image contrast (low kVp) images, the patient dose is reduced with higher kVp exposures. Most intraoral machines use 60 to 70 kVp. The availability of constant-potential (fully rectified), high-frequency or direct current (DC) dental X-ray units have made possible the production of radiographs with lower kilovoltage and at reduced levels of radiation. The surface exposure required to produce a comparable radiographic density using a constant-potential unit is approximately 25% less than that of a conventional self-rectified unit operating at the same kilovoltage. At the present time, several manufacturers produce DC units.
Thus, in intraoral radiograph, patient radiation is not decreased by decreasing kVp.
 Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 36