Root canal treated teeth need strength

The standard/rule of thumb answer is: crown. After a tooth is hollowed out to clean out the affected nerve, the tooth is weaker and likely to fracture. Covering up completely is best.

If the access hole is small, sometimes nothing is needed, but the lower front teeth are so small that small holes are still very large (by proportion).  If the access was from the front of the tooth, a veneer might work.

So truly, the best person to ask is a dentist that is right there looking at the situation.