It's possible to have different dental issues, completely unrelated to each other, that both require treatment at the same time. When you're due to have braces fitted by an orthodontist, it can come as an unpleasant surprise when your dentist tells you that you have other issues to address, such as a deteriorated tooth in urgent need of a dental crown.
No Need to Wait
Your first thought might be to wait until after your braces have been removed before having a dental crown fitted. This may not be wise. Dental crowns and orthodontic work can be very compatible, and delaying a crown risks further deterioration of the tooth, especially considering that you may be wearing your braces for the better part of a year and a half (and possibly longer). There's also the fact that braces must apply light pressure to teeth in order to reposition them. If a tooth has significantly deteriorated to the point that a crown is necessary, it may not be able to withstand this pressure without the reinforcement offered by the crown bonded over the tooth.
An Unaffected Root Structure
Crowns are bonded to a tooth with dental cement, but the tooth's root structure is unaffected by the addition of the crown. The margin of the crown is in a subgingival position, meaning it's within the gum tissues at the base of the tooth and should not be visible (unless you're experiencing gum recession, often caused by periodontal disease). Because the tooth's root structure is intact (and presumably healthy), the tooth (crown and all) can be repositioned with orthodontic work in exactly the same manner as a tooth without a crown.
Specific Techniques and Materials
An orthodontist will largely treat a dental crown just as they would any other teeth, but there will be a few specific considerations. These are particularly relevant when you're to receive traditional metal or ceramic braces, which require a bracket to be bonded to each tooth. Because the crown means that the surface of the tooth is now ceramic (as opposed to natural dental enamel), your orthodontist will use a bonding agent designed for porcelain. When your braces are removed, this specialist bonding agent means that the bracket can easily be removed without damaging the porcelain surface of your crown.
Fortunately, crowns are one of the types of dental restoration that are completely compatible with orthodontic work, meaning you don't need to prioritize one over the other. Reach out to a dentist for more information about dental crowns.