When a nerve has been exposed on a baby tooth, that usually means that there was a sizable cavity. Since baby teeth are so small, large cavities can make it difficult to retain fillings for any length of time. Therefore, it is best to place crowns over those type of teeth. Since baby teeth will be coming out in a few years, it is best to not put an expensive porcelain crown on it. The recommended procedure is to place a crown made of stainless steel.
These crowns come pre-formed so they do not have to be custom made. They come in various sizes. The dentist will remove the outer layer of the tooth, then try on different sizes until one is found that fits. The stainless steel is thin enough that it can be modified with special pliers if needed to get a better fit. The crown is then cemented into place with the same cement used for adult crowns. Although this technique is not ideal for long term, it works well in the interim for baby teeth and keeps the costs down significantly.