Patient had an old amalgam filling. Amalgam has metal content which, as a metal, can expand and contract over time. This movement can press against the remaining tooth structure, which if thin, can crack off. This is precisely what happen in his case. His treatment options consisted of an onlay or crown (made in the lab) or bonding done directly in the office. He elected for the bonding, which is a direct and more economical way to replace tooth structure and make the tooth whole again.