Avoiding tooth preparation
The use of an implant or multiple implants makes it possible to replace missing teeth without preparing adjacent natural teeth as would be required if a conventional fixed partial denture were placed. There is, however, one type of fixed partial denture that was first introduced as a prosthesis requiring no preparation of the adjacent natural teeth. Unfortunately, the survival rates of resin bonded prostheses has not proven to be exemplary. In fact, the incidence of debonding is substantially higher when the teeth are left intact as opposed to being prepared. Additionally, incisal discoloration of the abutment teeth can occur whether the teeth are prepared or not , thereby creating an esthetic deficit that may limit the use of this type of prosthesis.
Single crowns have a lower incidence of caries than fixed partial dentures. It is reasonable to assume that this difference is related to more food accumulating around fixed partial dentures and some patients not performing oral hygiene procedures at the level required to remove plaque and prevent carious lesions on the abutment teeth. For these patients, placement of an implant and single crown may provide an environment less likely to cause caries in adjacent teeth than if a fixed partial denture were attached to the teeth.
The incidence of periodontal problems surrounding both single crowns and fixed partial dentures is modest. However, it has been determined that single crowns are associated with a lower incidence of periodontal problems than fixed partial dentures.
It seems reasonable to assume that the more demanding oral hygiene procedures required to properly maintain a fixed partial denture could be responsible for some patients performing less than adequate hygiene on a regular basis. Therefore, certain patients may experience a higher level of periodontal health surrounding an implant-retained single crown compared to a conventional fixed partial denture.
When missing teeth are replaced with fixed partial dentures, it is often necessary to place subgingival finish lines on the abutment teeth to achieve adequate length for retention and resistance form, to cover existing restorations, to extend beyond carious or damaged areas of the tooth, and for esthetic reasons so the prosthesis margins are not visible.
While gingival appearance and health can be preserved in the presence of subgingival margins, the literature is replete with studies that identify the potential periodontal challenges associated with subgingival finish lines. Soft tissue trauma can occur during tooth preparation, tissue retraction for the impression, and as a result of the fabrication and use of provisional restorations. The trauma can produce gingival edema, redness, rounding of the gingival margin, recession, loss of the interdental papilla, interference with the normal cervical position of the gingival as an adolescent matures, and the development of granulomatous tissue as a result of trauma from rotary instruments during tooth preparation. The periodontium can also be negatively affected by subgingival margins on the definitive prosthesis. After all, prostheses with subgingival margins are not as ideal as clean, natural teeth when it comes to preserving the biologic environment.
All of the potential problems mentioned above can make the placement of a single implant or multiple implants a desirable treatment modality in the esthetically visible zone of the mouth when compared to conventional fixed restorations with subgingival finish lines.