3dimensional information in IOPAs can be taken by:
Image in a X-ray is a dimensional information. To exactly locate the position of an object a three dimensional information is necessary. To obtain this 2 methods can be used

examining two films projected at right angles to each other.
examining  two films projected at different angles called as CLARK Rule (or) Buccal object rule (or) Tube shift metro or LOB rule.
Examining 2 films projected at right angle to each other
Examining 2 films projected at different angles
CLARK rule
All of the above