Why'd the expert dentist's girlfriend leave him? He was in and out before she felt a thing. Judging from the family photos hanging on the walls of Kenneth Wong's Polk Street office, this exquisite dentist hasn't had to pay such penance for his talent. But his good-humored, sympathetic chairside manner, combined with his incomparable skill in filling cavities without causing pain, puts him among the dental elite. He has the ability to make patients feel at peace, even when he's holding a screeching drill. His sensitivity is such that he remembers the content of bantering dental-chair conversations from months and years past, and he can clean the rotted contours of a cavity without so much as glancing off a nerve. What's more, he does his own tooth cleanings, a rarity, and a gift to any patient who's been brutalized by a learning-on-the-job assistant.