MJ did not wear wigs, nor hair pieces, after the Pepsi accident in 1984, thanks to Dr. Steven Hoefflin.
That doctor performed revolutionary laser surgery on his scalp after the accident with immediate positive results.
Here is what the doctor revealed back then:
“…We were able to cover the area using his own hair, he did not need any implants or transplants … The operation was very important to him, to have a full head of hair without the necessity of wigs or other hair coverings…” (Dr. Steven Hoefflin, April 1984)
Also, on the ‘BAD’ album cover MJ did not wear any wigs/hair pieces, either.
His use of wigs started from mid 90’s onwards, when you can easily spot the differences of his hair’s length from one music video to another which were released between very short periods.
From 00’s onwards, he began to wear wigs more extensively when they became a permanent accessory of his look.