42 Clinical evidence and Science Pre-treatment of bonding surface, restorative possibilities as hybrid abutment or hybrid abutment-crown Nowadays, the use of titanium bases in combination with CAD/CAM technologies is a common treatment option for single tooth restorations. The benefits of screw-retained restorations are less cement excess, possibility of individualized emergence profiles, and stable metallic implant-abutment connections. Additionally, the digital workflow allows for efficient treatment protocols with reduced visits and costs and an excellent aesthetic outcome. In a pre-clinical test setup, a research group from the University of Geneva investigated the stability of restorations with CONELOG® titanium bases. The testing specimens were artificially aged by means of thermocycling and mechanical loading in a chewing simulator. Afterwards, the retention forces between the crowns and abutment were tested by using a pull-off test or the samples were loaded until fracture. Pitta et al. (2021) evaluated the effect of different sand-blasting particle sizes while pretreating the bonding surface of the titanium bases before cementation with crowns made from lithium disilicate (19). Airborne particle abrasion demonstrably increased the retention forces and stability between titanium bases and crowns compared to untreated surfaces. The use of 50 µm Al2O3 showed the most stable connections and could be recommended by the team. Two further studies by Pitta et al. (2019 and 2021) evaluated the stability of different crown materials and the use of meso-abutments bonded to titanium bases. In the first study customized zirconia meso-abutments bonded to titanium bases were restored with different crown materials: lithium disilicate, zirconia, and polymer-infiltrated ceramic network (PICN) (20). The control group consisted of a customized titanium abutment with a lithium disilicate crown. After thermomechanical testing, no failures were observed in any group. The static failure test revealed a statistically significant higher bending moment in the zirconia group. But all tested combinations reached values that would withstand the oral loading during biting. The study team attested very good stability to all crown materials tested in combination with hybrid abutments. The second study examined monolithic lithium disilicate abutment-crown, zirconia abutment-crown, or polymer-infiltrated ceramic network (PICN) abutment-crown directly bonded to titanium bases (21). Additionally, a group with lithium disilicate abutment-crown bonded to a customized titanium abutment was tested. After aging, the two groups with lithium disilicate abutment-crowns revealed no fractures and less complications (e.g., loosening) than the other group. The authors recommended to use monolithic lithium disilicate abutment-crowns due to their good mechanical and bonding outcomes in case of a hybrid abutment-crown complex. KEY TAKE OUTS: HANDLING OF TITANIUM BASES In order to achieve good retention between the crown or a meso-abutment with the titanium base pre-treatment of the bonding surface with sandblasting (50 µm Al2O3) demonstrably increases the stability. Titanium bases can then be restored with lithium disilicate, zirconia, and PICN that withstand the oral loading during biting. Titanium bases PROSTHETIC RESTORATIONS: SCIENTIFICALLY BASED TREATMENT OPTIONS
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