Successful prosthetic retention needs to be stable, durable, meet occlusal requirements, support healthy hard and soft tissues and provide excellent esthetics, especially in the esthetic zone. Until recently neither cement nor screw retention were believed to meet all of these criteria. However, new clinical data suggest that—when it comes to hard and soft tissue response—screw retention is a superior option.
Hard tissue response associated with screw retention is comparable or better than that associated with cement retention. In a pooled analysis of single-tooth restorations in the esthetic zone, the use of a cement-retained vs. a screw-retained provisional crown was associated with significantly higher marginal peri-implant bone loss at ≥1-year follow-up (Slagter, 2014). However, a clinically irrelevant difference at 4 years and no difference at 10 years have been reported in another study (Vigolo, 2012).
Soft tissue analysis using a modified plaque index and a sulcus bleeding index reveals that peri-implant soft tissues respond more favorably to screw-retained crowns when compared with cement-retained crowns. One possible underlying reason for this result is excess cement, which in this study has been indicated to account for over 80% of peri-implantitis cases (Wilson, 2009).
Fewer complications with screw-retained restorations
A systematic review shows that screw-retained solutions exhibit significantly lower technical and biological complication rates per 100 life years (Wittneben, 2014):
- Cement retention was associated with a 9x increase in loss of retention and almost 4x more frequent abutment loosening (both P<0.01).
- Fracture or chipping occurred more commonly (3.5 times) with screw retention (P=0.02).
- Event rates for loss of the access hole cover and screw loosening were 0.81 and 1.76 per 100 life years, respectively.
Lower failure rates with two-piece screw-retained restorations
Overall, the difference in survival between cement-retained vs. screw-retained restorations is very small. However, estimated failure rates associated with two-piece screw retention are significantly lower than for cement retention (P=0.00).
In view of recent data tying cement retention to an increased likelihood of peri-implantitis, the current consensus statement (Wismeijer, 2014) has limited the recommended use of cement to the following situations:
- For short-span prostheses with margins at or above tissue level (in order to simplify fabrication procedures).
- To enhance esthetics when the screw access passes transocclusally or vestibularly, or in cases of malposition of the implant.
- When an intact occlusal surface is desirable.
- To reduce initial treatment costs.
Excess cement should be avoided
Wadhwani and Piñeyro surveyed over 400 dentists, finding that many of them place up to 20 times more cement than is required to secure the crown, while others fail to use the required minimum amount. Such overload means up to 95% of the placed cement is extruded at the restorative margin. This margin is frequently found below the gum, making cement removal on implant-supported restorations virtually impossible.