Discussion
Avoiding deep subgingival restorative margins may be the best way to prevent retained cement that results in a destructive inflammatory process. Recognizing the predisposing factors that can lead to excessive retained cement is the best method of prevention. Radiographs taken after the crown is cemented may identify retained cement before destructive pathologic processes occur. Another method of prevention can be accomplished by the implant surgeon through precise site preparation and implant positioning. It is recommended that a clinical protocol should include a reduced amount of cement, cement with thinner film thickness, and cementation technique utilizing an abutment analog. Another recommendation would be to incorporate petroleum jelly in the cement to facilitate easier removal of cemented crowns and cement clean-up. Finally, the use of custom abutments that allow for shallow marginal placement with a more physiologic contour will assist the restorative dentist in cement removal.
There have been a few articles in the literature that describe techniques for limiting excess cement. One common theme in these technique articles is to limit the amount of cement in the restoration by a trial run with a "practice abutment" ( through ). Another technique described by Wolfart and coworkers limited the quantity of cement by only filling the occlusal half of the crown with cement before delivery. The potential concern with these techniques is delivering an inadequate amount of cement for retention. A recent study by Santosa and colleagues showed that while this was a concern with temporary cement, it was less of a concern when a permanent resin-modified glass-ionomer (RMGI) cement was used.
Other articles have described a technique in which a venting hole is fabricated on either the occlusal or lingual aspect of the permanent restoration. The disadvantage of this technique is the additional laboratory work involved and the necessity of filling the access hole after permanent cementation.
The limitations of these articles are that, with the exception of the in vitro study by Santosa and colleagues, they are technique articles without any clinical evaluation of their effectiveness. Thus, while using a venting or practice abutment cementation technique makes sense intuitively, it is difficult for a clinician to make an evidence-based decision on how to properly cement implant restorations.
Research on the type of cement that should be used for implant restorations has focused more on retentive strength, and whether that is desirable or not. Some studies have advocated a less-retentive cement to allow retrievability of the restoration. Very few studies have looked at which cements might be more likely to result in retained cement after delivery of the restoration. Agar and coworkers found that resin cements were more difficult to remove in a simulated subgingival environment. A recent survey of cementation protocols for implant restorations in US dental schools found that RMGI luting agents were the most commonly used. However, the authors suggested that the choice seemed to be based more on convenience and familiarity with that particular cement rather than a literature-based decision.
Various articles have discussed the film thickness of various luting agents. The thicker the luting agent, the greater the risk of poor marginal adaptation of the crown margin to the abutment. Wadhwani and colleagues investigated the radiographic density of eight different cements used for implant prostheses. They concluded that some of the cements commonly used for the cementation of implant-supported prostheses have poor radiodensity and may not be detectable after radiographic examination.
Once the restoration has been cemented, the clinician will try to detect and remove any excess cement. Most clinicians will attempt to do this clinically by exploring subgingivally with an instrument. Agar and coworkers discussed avoiding metal scalers and explorers because of the potential for scratching of the abutment or implant surface. They advocated the use of plastic instruments.
Maintenance of the dental implant restoration should be accomplished on a periodic basis. Office protocol should include visual inspection of soft tissues for color changes around the implant restorations, checking for bleeding on probing, and yearly or biyearly radiographic evaluation as well as monitoring of occlusal forces. Comparison of serial yearly radiographs may demonstrate crestal bone level changes, which can be a result of bacterial infection, retained cement, or occlusal overload. Follow-up of the final restoration at a 1- to 2-month time period would also allow for the evaluation of possible retained cement by monitoring the gingival response to the restoration or detection on a radiograph. Color changes of marginal gingiva, bleeding upon light probing with plastic probes, or evidence of suppuration may alert the clinician to the possibility of retained excess cement. Wilson demonstrated that suppuration or continued bleeding on probing around the gingival margins of implant restorations had an 81% correlation to the presence of excess cement. The shared maintenance responsibility between the restorative dentist and the implant surgeon must include clinical gingival inspection, radiographic comparison, monitoring occlusal forces to prevent occlusal overload issues, and considering pathologic changes from retained excess cement.
Conclusion
The destructive nature of retained excess cement has been reported in the literature and, unfortunately, is a frequent problem that requires recognition and management. Predisposing factors that can lead to retained excess cement have been reviewed and office protocol strategies have been discussed. Early recognition is advantageous to prevent destructive changes to the peri-implant soft and hard tissues. Ideally, establishing an office protocol of abutment design, cementation technique, and reassessment procedures would be beneficial in preventing or minimizing the problem. Evidence of retained cement issues on dental implants have been demonstrated in the case reports.
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