Final answer:
The teeth most vulnerable to perforation due to slight deviations from proper bur angulation after mandibular incisors are maxillary first premolars.
Step-by-step explanation:
The teeth that are easiest to perforate by slight mesial or distal deviation from proper angulation of a bur are mandibular incisors and maxillary first premolars. After the four fang-like cuspids (or canines) that flank the incisors, the next in line are the premolars. These teeth have a flatter shape with two rounded cusps, which make them less sturdy against improper drilling angles compared to the robust and larger molars. The molars have several pointed cusps that are designed to crush food, making them inherently stronger and more resistant to drilling deviations. The incisors are the sharp front teeth, while the canines have a pointed edge for tearing up food. These teeth are more susceptible to perforation because of their shape and location.