Artificial posterior teeth offer maximum opportunity for balanced occlusion development, when their cuspal angulation is:
Anatomic Teeth
It is defined as, “Teeth which have prominent pointed or rounded cusps on the masticating surfaces and which are designed to occlude with the teeth of the opposing denture or natural dentition” - GPT. Anatomic teeth have a 33° cusp angle. Cusp angle can be defined as, “the angle made by the slopes of the cusp with a perpendicular line bisecting the cusp, measured mesiodistally or buccolingually”
Semi-anatomic Teeth
These teeth have cusp angles ranging between 0o and 30o. The cusp angles are usually around 20o. They are also called modified anatomic teeth.
Non-anatomic or 0° or cuspless 
Teeth Non-anatomical teeth are defined as, “Artificial teeth with occlusal surfaces which are not anatomically formed but which are designed to improve the function of mastication” - GPT. Cuspless teeth are defined as, “They are teeth designed without cuspal prominences on the occlusal surfaces” - GPT. Zero degree teeth are defined as,“Artificial posterior teeth having no cusp angles in relation to the horizontal occlusal surfaces” - GPT.
Key Concept:
Anatomic teeth with cuspal angulation of 33 degrees, allows for optimum balancing of complete  dentures.
Ref: Textbook of prosthodontics by Nallaswamy Ed 2nd  Pg 8
22 degrees
20 degrees
30 degrees
33 degrees