The combination prosthesis: a digitally designed retrievable cement- and screw-retained implant-supported prosthesis
screw-retained prostheses have the advantage of being easily retrievable. However, the presence of occlusal access channels compromises their esthetics, ceramic strength, and occlusion. Cement-retained prostheses are easier to fabricate, offer easier delivery in the posterior area of the mouth, and have higher potential for passive fit. A major limitation of cement-retained implant restorations is the difficulty in removing the excess cement. Residual cement remnants have been associated with peri-implantitis.
Nissan et al in a clinical study reported that the combination of cement- and screw-retained implant prosthesis improves the survival rates of these prostheses and lowers the cost of maintenance without increasing the risk for ceramic fracture or screw loosening.
1. Inspect the peri-implant soft tissue for any sign of soft tissue pathosis. Evaluate periapical radiographs to ensure osseointegration.
2. Make complete-arch definitive impressions of the patient’ s maxillary and mandibular arches with poly(vinyl siloxane) impression (PVS) material (Genie VPS; Sultan Healthcare). Make an interocclusal record with PVS occlusal registration material (Exabite II NSD; GC America Inc).
3. Place a scanning abutment on the implant analog and scan the impressions (D700; 3Shape). Simulate the definitive prosthesis design with the provided software. Design 2 separate milled titanium abutments and a cementable zirconia superstructure prosthesis (Fig. 1 ).
4. Mill the titanium abutments from a titanium blank (Inclusive Custom Titanium Abutments Blanks; Glidewell Laboratories) and the cementable superstructure prosthesis with occlusal access channels from a zirconia blank (BruxZir Milling Blank; Glidewell Laboratories) by using a milling machine (TS150 Milling Solution; IOS Technologies).
5. Place the milled titanium abutments intraorally. Seal the occlusal access channels with low-viscosity PVS impression material (Exafast NDS; GC America, Inc) (Fig. 3 A).
6. Position the prosthesis over the abutments (Fig. 3 B). Evaluate the interproximal contacts, prosthesis fit, occlusion, esthetics, and accessibility for oral hygiene.
7. Place resin cement (RelyX Luting Plus Cement; 3M ESPE) in the prosthesis and secure the prosthesis over the abutments. Apply pressure and allow sufficient time for the cement to polymerize (Fig. 4 ).
8. Clean the excess cement from the occlusal access channels and remove the prosthesis (Fig. 5 A). The prosthesis has now been converted into a screw-retained prosthesis. Remove the excess cement from the cervical area of the prosthesis (Fig. 5 B).
9. Insert the combination prosthesis intraorally. Tighten the abutments according to the manufacturer’ s recommendations. Confirm occlusion and proximal contacts. Place a cotton pellet and composite resin (Filtek Supreme Ultra; 3M ESPE) to seal the occlusal access channels.
Rajan and Gunaseelan introduced the concept of fabricating a combination screw- and cement-retained prosthesis. The concept was first applied for a single implant-supported crown where a metal-ceramic crown was cemented on a cast custom abutment. Uludag and Celik and Uludag et al described the concept of a combination prosthesis for multiunit implant restorations where a fixed metal-ceramic partial denture was cemented on multiple cast custom abutments.
The proposed technique offers an alternative method of fabricating a cement- and screw-retained combination prosthesis by implementing digital technology. Long term human studies are needed to validate the use of the described technique on a routine clinical basis. The proposed technique offers an alternative method of fabricating a cement- and screw-retained combination prosthesis by implementing digital technology. Long term human studies are needed to validate the use ofhe described technique on a routine clinical basis.