Sometimes if the cavity is big then the filling material does not hold and keeps on coming out and each time more tooth material has to be cut to do the filling. This can expose the tooth and tooth can become infected. To avoid this, it is always advisable to go for cap in such cases. So if the dentist has advised you for cap, it is better you go for it to save the tooth. For more info on dental caps/crowns you can browse the following link in our website... http://www.identalhub.com/articlecategory-dental-crowns-72.aspx