03 July 2019

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Metal-free implant-supported restorations: modern solutions for single tooth applications

Massimo Gagliani

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In many areas of restorative dentistry, metal-free materials offer an alternative to metal-based restorations while ensuring high levels of biocompatibility and esthetics. Rapidly evolving CAD/CAM technology has significantly expanded the range of materials available, providing access to materials classes and their combinations not previously available within conventional manufacturing, such as zirconia ceramics and hybrid ceramics. Mechanical properties over the decades have changed the clinical long-term success but it is still very much dependent on an appropriate indication and proper material selection These two review article provides an up-to-date overview of the possibilities and limitations of metal-free implant-supported single-tooth restorations.

Resultant treatment concepts are presented and evaluated based on clinical examples. Actually, metal free implant abutments, firstly proposed as alumina ceramics, have been substituted by partially stabilized zirconia; among them can be distinguished prefabricated abutments, cast-on/pressable abutments, and CAD/CAM abutments. Prefabricated abutments are available in various sizes, shapes, and angulations. One-piece ceramic CAD/CAM abutments without an adhesive base are fabricated from monoblocks, like titanium abutments. Today, semi-finished zirconia blanks are the raw material almost exclusively used for this purpose; the interface between the implant and abutment will already have been created during the industrial manufacturing process. The external geometry of the abutment is custom-milled from the blank based on the design data or wax-up. In some cases, a certain amount of modification using, for example, matching sintering ceramics can still be performed.

To summarize, the current solutions are: Hybrid abutment with separate crown part and  Hybrid abutment crowns.

• Hybrid abutment with separate crown part 
  To avoid direct contact between the extremely hard zirconia of the abutment (Vickers hardness: approx. 1,200) and the sensitive titanium structures of the implant (Vickers hardness: approx. 384), alternative concepts were quickly developed that facilitated titanium-to-titanium interfaces without having to relinquish the option of using a ceramic abutment. Monolithic crowns made of lithium (di)silicate or zirconia frameworks with a sintered lithium (di)silicate veneer appear to be suitable as definitive superstructures cemented on titanium or zirconia hybrid-abutments. These materials appear to have a failure mode that protects the implant, as their strength is lower than that of monolithic zirconia
• Hybrid abutment crowns
  The introduction of prefabricated lithium disilicate blanks with an industrially prefabricated connection geometry for titanium adhesive bases has revolutionized the fabrication of metal-free implant-supported single crowns for almost all implant systems. In principle, a hybrid abutment crown can also be produced in a conventional workflow. Prefabricated titanium bases from various manufacturers are available for this purpose, whose height can be reduced if specific guidelines are followed. This second opportunity might simplify the total workflows giving to the clinician the most practical and suitable solution in single tooth implant reconstructions. 

For additional informations: 
Metal-free implant-supported single-tooth restorations. Part I: Abutment and cemented crowns.