My daughter transitioned by putting milk only in bottles at nap time and bed time and used sippy cups for milk at other times, juice and water. At that age the baby only needs approximately 24 oz. of milk. The kids hadn't had juice in bottles. She started the juices in the sippy cups while they were still using bottles for milk.
Her attitude was a matter of fact this is the way it is now. Milk in bottles, juice and water in sippy cups. They could carry the sippy cups around with them but not the bottles which added to the kids preference for sippy cups. "It's sippy cup time. Do you want juice or water." She then gradually reduced the number of bottles until they were only getting a bottle at bedtime and milk also in sippy cups. When they had several teeth she switched to giving them a sippy cup with water at bedtime.
It was a gradual process over several months. I would hesitate stopping cold turkey at 20 months. That bottle provides more than nutrition. It's calming and provides comfort.
Her pediatrician said that sucking on a bottle just long enough to empty it is not what causes misalignment of teeth. It's having the bottle in their mouth for long periods of time and sucking on a pacifier all day long.
We are all born with a need to suck. I agee with some professionals who say that not having sucked long enough as a child is part of the reason that people smoke. I've also seen middle schoolers walking around with teen sized pacifiers. There is no proof but I wonder if having a need for oral gratification isn't caused in part by having the bottle taken away too soon, before the baby has satisfied their need to suck and get comfort from that sucking.
I'd add that the baby isn't ready to let go of the bottle until they learn some other way of comforting themselves and soothing themselves to sleep. For my grandkids they transitioned into holding a specific stuffed animal without having the bottle too.
I think that if a baby cries for hours when he's without a bottle then he's not ready to let go of the bottle. It's another one of those tricky lines when making a decision.