In Johnny Tremain, what happened to cause Johnny to change his position in the Lapham house ? What role did Dove play in this event?

Johnny Tremain had been the most valuable apprentice at the Laphams house and shop.  After his hand is crippled in a terrible accident, he is no longer able to work at silversmithing, and loses his position as the leader of the others.

The accident that crippled Johnny was intentionally caused.  Dove, a lazy dolt of a boy, is jealous of Johnny, who is so much more capable and willing as a worker and an artisan.  Unwilling to work harder to improve himself, Dove chooses to improve his situation by bringing Johnny down.  One Sunday, when Johnny, Dove, Dusty, and Mrs. Lapham are working feverishly to finish a very important job for the illustrious Mr. John Hancock, Johnny asks for a crucible, and Dove, knowing that it will not stand the heat of the furnace, hands him one with a crack in it.  Dove thinks "it (will) just about serve Johnny Tremain right - after the insufferable way he (has) been bossing everybody - if the crucible (gives) way and the hot silver...spill(s) all over the top of the furnace", making Johnny "look like a fool".  Sure enough, the crucible collapses, and when Johnny jumps towards the silver that is "running over the top of the furnace like spilled milk", he somehow slips, and his right hand comes down on the scalding metal, covering it "from wrist to fingertips".

Mrs. Lapham does not want her husband to know that they had been working on the Sabbath, so instead of going for the doctor, she fetches the midwife, Gran' Hopper.  Gran' Hopper is very skilled in midwifery and in treating children's diseases, but she is unfamiliar with how to handle an injury like Johnny's.  She allows the hand to "draw together" as it heals, and Johnny is left crippled, his thumb and palm grown together.  With such a handicap as this, Johnny is useless as a silversmith, and loses his place of prominence at the Lapham house (Chapter 4).