Reliability and Failure Modes of a Hybrid Ceramic Abutment Prototype

Purpose

A ceramic and metal abutment prototype was fatigue tested to determine the probability of survival at various loads.

Materials and Methods

Lithium disilicate CAD‐milled abutments (n = 24) were cemented to titanium sleeve inserts and then screw attached to titanium fixtures. The assembly was then embedded at a 30° angle in polymethylmethacrylate. Each (n = 24) was restored with a resin‐cemented machined lithium disilicate all‐ceramic central incisor crown. Single load (lingual‐incisal contact) to failure was determined for three specimens. Fatigue testing (n = 21) was conducted employing the step‐stress method with lingual mouth motion loading. Failures were recorded, and reliability calculations were performed using proprietary software. Probability Weibull curves were calculated with 90% confidence bounds. Fracture modes were classified with a stereomicroscope, and representative samples imaged with scanning electron microscopy.

Results

Fatigue results indicated that the limiting factor in the current design is the fatigue strength of the abutment screw, where screw fracture often leads to failure of the abutment metal sleeve and/or cracking in the implant fixture. Reliability for completion of a mission at 200 N load for 50K cycles was 0.38 (0.52% to 0.25 90% CI) and for 100K cycles was only 0.12 (0.26 to 0.05)—only 12% predicted to survive. These results are similar to those from previous studies on metal to metal abutment/fixture systems where screw failure is a limitation. No ceramic crown or ceramic abutment initiated fractures occurred, supporting the research hypothesis. The limiting factor in performance was the screw failure in the metal‐to‐metal connection between the prototyped abutment and the fixture, indicating that this configuration should function clinically with no abutment ceramic complications.

Conclusion

The combined ceramic with titanium sleeve abutment prototype performance was limited by the fatigue degradation of the abutment screw. In fatigue, no ceramic crown or ceramic abutment components failed, supporting the research hypothesis with a reliability similar to that of all‐metal abutment fixture systems. A lithium disilcate abutment with a Ti alloy sleeve in combination with an all‐ceramic crown should be expected to function clinically in a satisfactory manner.     

Individual Lithium Disilicate Crowns in a Full‐Arch,Implant‐Supported Rehabilitation: A Clinical Report

This clinical report presents the clinical outcome of a maxillary full‐arch implant‐supported fixed rehabilitation with lithium disilicate reinforced glass ceramic monolithic crowns opposing a mandibular metal‐acrylic implant‐supported fixed rehabilitation in a 62‐year‐old woman. Eight implants were successfully placed (four maxillary, four mandibular), and no complications occurred in the postoperative or maintenance periods. Six months after delivery, the maxillary and mandibular prostheses were found to be clinically, biologically, and mechanically stable, and the patient was satisfied with the esthetics and her ability to function. Although the present indications for the use of lithium disilicate are still restricted to tooth‐borne restorations, it is possible to successfully rehabilitate edentulous patients through implant‐supported fixed prostheses using lithium disilicate reinforced glass ceramic monolithic crowns.     

Fracture resistance of computer‐aided design/computer‐aided manufacturing‐generated composite resin‐based molar crowns

The aim of this study was to investigate whether different fabrication processes, such as the computer‐aided design/computer‐aided manufacturing (CAD/CAM) system or the manual build‐up technique, affect the fracture resistance of composite resin‐based crowns. Lava Ultimate (LU), Estenia C&B (EC&B), and lithium disilicate glass‐ceramic IPS e.max press (EMP) were used. Four types of molar crowns were fabricated: CAD/CAM‐generated composite resin‐based crowns (LU crowns); manually built‐up monolayer composite resin‐based crowns (EC&B‐monolayer crowns); manually built‐up layered composite resin‐based crowns (EC&B‐layered crowns); and EMP crowns. Each type of crown was cemented to dies and the fracture resistance was tested. EC&B‐layered crowns showed significantly lower fracture resistance compared with LU and EMP crowns, although there was no significant difference in flexural strength or fracture toughness between LU and EC&B materials. Micro‐computed tomography and fractographic analysis showed that decreased strength probably resulted from internal voids in the EC&B‐layered crowns introduced by the layering process. There was no significant difference in fracture resistance among LU, EC&B‐monolayer, and EMP crowns. Both types of composite resin‐based crowns showed fracture loads of >2000 N, which is higher than the molar bite force. Therefore, CAD/CAM‐generated crowns, without internal defects, may be applied to molar regions with sufficient fracture resistance.