While taking bitewing radiograph, what should be the angulation to avoid overlapping of the cusps on the occlusal surface?
Bitewing or interproximal radiographs include the crowns of the maxillary and mandibular teeth and the alveolar crest on the same film. The beam is angulated +7 to +10 degree vertically to preclude overlap of the cusps on the occlusal surface.
Vertical angulation: 
The aiming cylinder is positioned about +10 degrees to project the beam parallel with the occlusal plane (occlusal dentinoenamel junction). This orientation minimizes overlapping of the opposing cusps onto the occlusal surface and thus improves the probability of detecting early occlusal lesions at the dentinoenamel junction.
Ref: White and Pharoah's Oral Radiology,Principles and Interpretation 8TH EDITION
20 degrees
5 degrees
10 degrees
15 degrees