Though uncommon, OVC crowns can come off if the surface of the tooth is not prepared properly, the incorrect bonding technique is used or surface contamination occured prior to bonding.
Yes. You can reattach the OVC if the patient still has it with them.
For rebonding an OVC use a conventional dental crown cement.
Rhondium Dental Labs only recommends high strength dual-cure bonding with products, such as Optibond FL or Panavia V5 when bonding the original OVC. However, if you have experienced any bonding issues with the OVC, we recommend that you reassess your bonding techniques.
To bush up on your bonding techniques please read the following: https://www.dentalproductsreport.com/article/5-things-you-need-know-about-adhesives?page=0,1