How to prevent subgingival margins by the use of a new resin temporary cement
How a new cement from VOCO can avoid problems in partial coverage restorations.
One of the biggest reasons dentists avoid partial coverage restorations like onlays and veneers is problems related to how to temporize or provisionalize preparations without mechanical retention or axial walls. A new cement from VOCO, Bifix Temp, could be a great help in overcoming this obstacle.
Crown preparation with subgingival margins are part of the history and fabric of dentistry. Crowns are often preferred to partial coverage restorations because of their perceived simplicity. Many times it’s just because crowns are easier to temporize!
With the proper use of new materials like Bifix Temp (VOCO) and supra-gingival adhesive restorative techniques, crowns with subgingival margins should be the exception, and not the rule. Utilizing supra-gingival, minimally invasive adhesive restorative techniques, to intentionally keep restorative margins supra-gingival, can render traditional mechanically retained restorations like full crowns virtually obsolete. The greatest benefit adhesive dentistry can bring to a patient is periodontal health, in addition to many other attributes, as well as making dentistry easier and more predictable.
Disadvantages of axial walls and mechanical retention
The lack of trust in adhesion, the perceived need for mechanical retention and the need for an axial wall with minimum heights of 3 to 4 mm, often leads to placing the margins subgingivally, as we frequently run out of tooth structure after occlusal reduction and caries removal, especially on short teeth like second molars. Reitemeier concluded in a clinical research study that subgingival crown margins double the chance of periodontal bleeding upon probing. It is well known that calculus and root surface roughness have a very damaging effect on our patients periodontal health and we are swift to eradicate such periodontal enemies. Nevertheless it is at least as damaging, if not more, to have overhangs, open margins, or any subgingival restorative margin, it is permanent tartar.1,2 Additionally axial wall preparation has the significant negative side effect of allowing the diamond rotary cutting instruments close proximity to the pulp, thus increasing the temperature and irritating the pulp.3,4
Preventing subgingival margins
The location of the restorative margins should not be left to luck. Using a supra-gingival protocol, like the five principles of supra-gingival restorative dentistry, helps prevent or minimize subgingival restorative margins. The second principle is to avoid, boxes, axial wall reduction or any other mechanical feature which is counterproductive to staying supra-gingival or to adhesive dentistry. Following this principle means that even after caries removal, old restoration removal and occlusal reduction we end up with a tooth that is flat just above the gum (Fig. 1). No effort will be made to create axial walls, boxes or any retentive feature, as any of this would lead to subgingival margins and would be counterproductive. We must trust in adhesion. In fact unretentive flat preparations are better suited for adhesive dentistry (Fig. 2). They are mechanically better, easier to cement and to prepare. One large problem with unretentive preparations is how to retain temporaries or provisional restorations.
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