Sometimes fillings can be made indirectly from a dental lab but taking a measurement of the cavity and procuring a readymade filling that is then fixed with dental cement onto the tooth. This is usually done for teeth with very large cavities and is not a usual procedure. Inlays can be made from metal, composite or ceramic.
Onlays are similar to half caps and are more conservative of tooth structure. They are given in teeth after root canals when a full cap is not desired.