What Exactly Are 'Open Margins' when Comes to Dental Restorations?

Whenever there is a space or gap between the edge of a crown or veneer and unprepared tooth structure, that's an open margin. Open margins are a problem when plaque (which is mostly bacteria) gets into this space. This can cause decay (also known as caries) to occur around or under the restoration. There should be a smooth transition and seal between a restoration and the surrounding tooth, without any gaps, spaces, grooves or rough areas. A gap between a restoration and the gum is not necessarily an open margin. A restoration that ends short of the gums can be o.k as long as the edges are closed, meaning no gaps are present.

In general throughout dentistry an open margin is a space between the natural tooth and whatever man made restoration is in the tooth. An open margin will eventually cause a restoration to fail due to bacteria being able to get in and under causing decay.

An open margin is the space between the dental restoration and the tooth.  Having an open margin can cause issue with the restoration and can lead to the decay.  You should have it fixed

The term "open margins" is used by dentists when the edge of a restoration is not sealed against the tooth structure.  This can allow bacteria and even mold to seep in under the veneer usually seen as black or gray areas, and under a crown can go undetected until the bacteria reach the nerve and cause the tooth to abcess.  How can it happen?  When the dentist has prepared the tooth for the restoration, a putty or digital impression is taken to fabricate the restoration.  Inaccuracies in the impression can cause the restoration to have a slight miss-fit.  A restoration that seals the tooth but stops short of the gums is NOT a case of open margins.  Such restorations usually have a better fit because the ceramic artist making the restoration can clearly see the tooth preparation margins.

An open margin is a space between where the dental restorative material (crown, filling, etc.) meets the remaining tooth structure.  This can allow bacteria to congregate and create a cavity in the area which then can spread under and around the restoration.