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The combination prosthesis: A digitally designed retrievable cement- and screw-retained implant-supported prosthesis.

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The combination prosthesis: a digitally designed retrievable cement- and screw-retained implant-supported prosthesis

Introduction

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.

Technique

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.

Discussion

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.

Conclusion

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.

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