The Reverse Margin™ System consists of a specifically designed abutment and co-functioning crown that systematically prioritizes the installation sequence to optimize results. A custom healing abutment is also offered to facilitate the contouring of the transgingival tissues in preparation for the Reverse Margin™ abutment.
To reduce complications and improve outcomes, the priority is to optimize the implant / abutment connection. The abutment is installed without the prosthesis attached, thereby minimizing the influence of proximal contacts on the prosthesis. Of course, an appropriately shaped transgingival opening facilitates the installation of the abutment. Optimal fit of implant parts can be achieved more effectively without the prosthesis in place, because the PDE Dragon is removed from this step.
The margin of the Reverse Margin™ abutment margin can be positioned up to 1 mm subgingivaly. Whenever possible the margin should be placed at or above the gingival margin. Dr. Svoboda aims for ½ mm below the gingiva for best results. He rarely places this margin more than 1 mm below the gingiva. It is simply rarely necessary. If the zirconia hybrid abutment is selected for the abutment, it will be shade matched to the crown and provides an esthetic foundation to support the crown. The hybrid abutment involves a zirconia shape that is cemented upon a BioHorizons titanium base. Where esthetics is not a consideration, the solid titanium base does not depend on the patency of the cement bond between the Reverse Margin™ zirconia shape and the titanium base. If there is an unfortunate separation of the prosthesis-abutment complex from the titanium base, it is not usually very difficult to refurbish the complex for re-installation.
To complete the installation, the crown is cemented over the abutment. The Reverse Margin™ Crown is designed with a unique external vent around the margin circumference and adequate cement space on both sides of the crown margin. This facilitates passive seating of the crown, the escape of excess cement and easy removal of excess cement from on top of the margin.
The inflected margin of the abutment and unique cement space allows the crown to be somewhat self-centering during installation. This makes adjustment of contacts much easier. It also minimizes the risk of open margins and eliminates the problem of overhanging margins. Ensuring a proper fit of the crown also reduces adjustments related to hyperocclusion. Once the contacts have been adjusted there are no tissues to resist seating of the prosthesis as the abutment has moved the gingiva out of the way of the crown. This allows the dentist to seat the crown with minimal force and a lot less stress. Reducing poor margins reduces remakes that can be frustrating for both the dentist and the patient.
Retrievability – The Reverse Margin™ Abutment and Crown are retrievable by accessing the screw through the occlusal surface of the crown. The access point can be marked. Pink or white Teflon is used to protect and easily identify the screw. The abutment-prosthesis complex usually does not need to be removed in order to tighten or replace a screw. Loose screws are an uncommon event, because the implant-abutment fit has been optimized on installation day!
The term Prosthesis Dimensional Error (PDE) describes the culmination of all the errors involved in making the prosthesis. There is abundant research describing PDE over the span of the last 30 years. What is in short supply is information about how to deal with it in a safe way. Dr. Svoboda has done that.
For screwed-in prosthetics, PDE can cause open and tight contacts, hyperocclusion and misfit of implant parts, like the implant-abutment misfit and/or the abutment prosthesis misfit. Misfits, even when using cut and solder procedures to reduce them, can range from 95 to 232 micrometers. Misfits can render implant connections unstable and open them to penetration and growth of billions of oral pathogens in the subgingival environment. This can result in chronic inflammation and disease, commonly referred to as peri-implant disease. The negative health consequences of this disease may follow that already attributed to periodontitis. Not good for the peri-implant environment for sure!
For cemented-in prosthetics, PDE can cause open and tight contacts, hyperocclusion, open overhanging and overextended margins and residual subgingival cement. Ill-fitting margins and submarginal cement can accommodate billions of oral pathogens. Not good for the peri-implant environment for sure!
The term Tissue Effects (TE), coined by Dr. Svoboda, describes the result of the dynamic interaction between the base of the abutment and/or prosthesis during their installation and the hard, soft and fluids tissues adjacent to them. There are two main groups of TE. Dr. Svoboda coined the terms Resistance to Displacement and the Gingival Effects to name them.
Resistance to Displacement (RTD) refers to how tissues like gingiva, alveolar bone, bone graft granules and adjacent teeth or their replacements can impede the fit of implant parts and prosthetics from seating properly.
For screwed-in prosthetics, RTD can interfere with the proper fit of implant parts. This can prevent the parts from connecting optimally and rendering them less stable than intended and provides a breeding environment for oral pathogens. Poor contacts and hyperocclusion can result as well.
For cemented-in prosthetics, RDT can exacerbate the problem of submarginal cement as well as cause open and offset prosthesis margins and hyperocclusion. In addition, the Gingival Effects can, themselves, be responsible for large amounts of residual subgingival cement. As the prosthesis is pressed into place onto a margin, the gingiva can form a seal with the base of the prosthesis and trap the cement in the sulcus. As the dentist continues to press the prosthesis into place, the trapped cement, plus the excess cement still exiting from under the prosthesis is pressurized and can thus be projected deep into the subgingival spaces. The GE are very important to understand and to prevent.
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