There's very little margin for error with dental implants. If their dimensions aren't precise, the implant might not be successful. Fortunately, this very rarely happens. When it does happen, it feels as though the porcelain crown (the prosthetic tooth) that finishes the implant process doesn't quite fit as well as it should. What can cause this?
It could be that there was a manufacturing error with the porcelain crown, even though this is extremely unlikely. It could also be that the implant itself (the titanium bolt inserted into your jaw) has shifted from its projected position during osseointegration (which is when the implant fuses to the surrounding tissue). This can lead to the final placement of the porcelain crown feeling as though it doesn't quite correspond to the empty space where it was placed.
A New Feeling
It's possible that there's nothing wrong with your dental implant, and any feeling of irregularity with it is just the fact that its presence in your mouth is new. This can be especially noticeable when the dental socket has been empty for an extended length of time before the implant was installed. A short wait and see period can be helpful, because any feeling of strangeness might rapidly subside. Still, if the implant continues to feel as though it doesn't quite fit, you should schedule an appointment with the dentist.
Even though the implant and its crown might be functional as a tooth, even the slightest imbalance can cause dental problems in the future. Your teeth require an even bite, and when the crown is misaligned, the distribution of your bite pressure can be uneven, leading to accelerated wear and tear on your other teeth. An uneven bite pressure can also become uncomfortable. If there was any error with the implant, what can a dentist actually do?
Modifications and Replacement
Porcelain dental crowns can receive a minor modification, but this is all. If they're reshaped too much, they can lose their structural integrity, and are unable to function as a tooth replacement. Still, when only a minor modification is needed, your dentist will perform this work (sometimes requiring the crown to be temporarily removed). When it's determined that the crown requires more significant reshaping, it will be removed and replaced with a new crown, with precise dimensions that will avoid a repeat of your problem.
In summary, if it feels like your new porcelain crown doesn't quite fit, wait and see. If the feeling persists, see your dentist for a thorough inspection.