The platform is showing! Prosthetic management of implants placed too far coronally

[drsushant]

A dentist placing an implant aims to do so with the final restoration in mind. Prosthetically driven implant placement requires respect of anatomical landmarks in all three dimensions. In the apical-coronal dimension, the implant platform will be located 2 mm below the adjacent tooth’s cementoenamel junction. This would leave 3 mm of soft tissue from the platform to the free gingival margin of the final restoration, under ideal circumstances.

One potential complication that faces restorative dentists is when an implant has been placed too shallow. Fewer than 3 mm of “running room” exist for the restorative dentist to fabricate the final restoration. There are two scenarios:

1. The implant platform is 1 to 2 mm subgingival.
2. The implant platform is equigingival or supragingival.

In the first scenario, the implant (circular cross-section) must be transformed into a tooth (triangular or rhomboidal cross-section) more abruptly. This can lead to additional stresses being placed on the gingiva as it expands to accommodate the emergence profile of the restoration. Alternatively, there may be no emergence profile at all and, instead, a 90-degree shift (Fig. 1). This shift acts like a full ridge lap or modified ridge lap, depending upon the design. The difficulty of hygienic procedures around ridge lap surfaces is well known.

Fig. 1: A 90-degree shift creating a modified ridge lap.

In the second scenario, the platform is clearly visible to the eye and presents a significant esthetic challenge. When this situation is encountered in nonesthetic areas, the clinician may choose to leave the metal exposed in the final restoration. However, when dealing with the esthetic zone, two popular techniques are used to compensate for equigingival or supragingival platforms.

One option is to prepare the platform with a high-speed handpiece and copious irrigation. The restorative margins are brought subgingivally while leaving the internal platform-abutment interface intact. An impression coping is inserted and retraction cord is placed to permit adequate capture of the margin in impression material. A cementable implant crown is fabricated by the laboratory and delivered.

There are several concerns with this approach. The titanium implant is difficult to prepare intraorally. Even with copious irrigation, significant heat will be generated that may damage the bone-implant interface. The dentist must worry about the sparks and debris created upon preparation as well as collateral soft-tissue damage. Extreme care must be used not to alter the internal platform-abutment interface; any alteration will interfere with the precise and passive fit of machined components. Subgingival cement must also be meticulously removed during insertion.

This author’s preferred treatment modality is to create a flange of porcelain that covers any exposed implant surface (Figs. 2 through 6). The major disadvantage is that the dentist has traded an esthetic problem for a hygienic one. The porcelain flange acts like a full ridge lap and requires diligent home care to dislodge plaque and food debris from accumulating.

The porcelain flange may extend subgingivally if there is any depth of tissue around the platform. Alternatively, the flange may extend supragingivally along the facial contour of the ridge. Both scenarios present the hygienic problems of a full ridge lap.

        

[drsushant]

 

Fig. 2: An implant in site No. 4 was placed with its platform at the level of the gingiva on the facial. The cover screw extends supragingivally.





Fig. 3: The implant restoration at the bisque bake stage. A full ridge lap has been created on the facial.





Fig. 4: The try-in of the restoration at the bisque bake stage reveals inadequate coverage of the platform at the mesial-facial line angle. Additional porcelain will be added.




Fig. 5: The final restoration shows the full extent of porcelain that must be added to conceal the implant platform.





Fig. 6: The final restoration in place. Although the porcelain flange creates a minor esthetic discrepancy by making the tooth appear longer than the adjacent teeth, it is a superior choice to leaving the metal of the implant platform exposed.

 

        

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