Risks of inlays and onlays include:
Inlay and onlay tooth preparation can weaken the tooth structure and make permanent changes to the tooth underneath the restoration.
Placing inlays and onlays can temporarily cause gum and tooth sensitivity.
The tooth underneath the restoration might end up needing a root canal down the line.
If the inlay/onlay cement seal weakens, a cavity may form where the restoration meets the tooth.
The porcelain may chip.