Jonathan L. Ferencz

All-ceramic systems: Laboratory and clinical performance

Several all-ceramic systems have been developed in dentistry to meet the increased expectations of patients and dentists for highly aesthetic, biocompatible, and long-lasting restorations. However, early bulk fractures or chippings have led the research community to investigate the mechanical performance of the all-ceramic systems. This overview explores the current knowledge of monolithic and bilayer dental all-ceramic systems, addressing composition and processing mechanisms, laboratory and clinical performance, and possible future trends for all-ceramic materials.

Reliability of Metalloceramic and Zirconia-based Ceramic Crowns

Despite the increasing utilization of all-ceramic crown systems, their mechanical performance relative to that of metal ceramic restorations (MCR) has yet to be determined. This investigation tested the hypothesis that MCR present higher reliability over two Y-TZP all-ceramic crown systems under mouth-motion fatigue conditions. A CAD-based tooth preparation with the average dimensions of a mandibular first molar was used as a master die to fabricate all restorations. One 0.5-mm Pd-Ag and two Y-TZP system cores were veneered with 1.5 mm porcelain. Crowns were cemented onto aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Mouth-motion fatigue was performed, and use level probability Weibull curves were determined. Failure modes of all systems included chipping or fracture of the porcelain veneer initiating at the indentation site. Fatigue was an acceleration factor for all-ceramic systems, but not for the MCR system. The latter presented significantly higher reliability under mouth-motion cyclic mechanical testing.

Reliability of Reduced-thickness and Thinly Veneered Lithium Disilicate Crowns

The present investigation hypothesized that the reliability of reduced-thickness monolithic lithium disilicate crowns is high relative to that of veneered zirconia (Y-TZP) and comparable with that of metal ceramic (MCR) systems. CAD/CAM first mandibular molar full-crown preparations were produced with uniform thicknesses of either 1.0-mm or 2.0-mm occlusal and axial reduction, then replicated in composite for standard crown dies. Monolithic 1.0-mm (MON) and 2.0-mm CAD/CAM lithium disilicate crowns, the latter with a buccal thin veneer (BTV) of 0.5 mm, were fabricated and then sliding-contact-fatigued (step-stress method) until failure or suspension (n = 18/group). Crack evolution was followed, and fractography of post mortem specimens was performed and compared with that of clinical specimens. Use level probability Weibull calculation (use load = 1,200 N) showed interval overlaps between MON and BTV. There was no significant difference between the Weibull characteristic failure loads of MON and BTV (1,535 N [90% CI 1,354–1,740] and 1,609 N [90% CI 1,512–1,712], respectively), which were significantly higher than that of Y-TZP (370 N [90% CI 322–427]) and comparable with that of MCR (1,304 N [90% CI 1,203–1,414]), validating the study hypothesis.

Maintaining and enhancing gingival architecture in fixed prosthodontics

The long-term success of fixed prosthodontic restorations is greatly dependent upon the health and stability of the surrounding periodontal structures. This article deals with the interrelationship between fixed prosthodontic procedures and the stability and health of the periodontium. The commonly encountered problem of alterations in gingival architecture is examined in relation to tooth preparation as well as soft tissue preparation. In addition, the ability of the provisional restoration to guide soft tissue form is discussed as well as the role of the final restoration in providing long-term tissue maintenance. Key factors such as margin placement, tissue damage during tooth preparation, the role of the provisional restoration, tissue injury during impression procedures, crown contour, pontic design, and embrasure design are covered in detail.

Tensile strength analysis of midpontic soldering

A total of 120 three-unit fixed partial dentures were made by using a latex mold to produce uniform wax patterns. Four groups were used to compare the tensile strength of connectors with interproximal solder, midpontic vertical solder, midpontic diagonal solder, and a control of one-piece castings. Three different metals were tested and the tensile load required to fracture the samples as well as the fracture sites were recorded. The following was found: Soldering the interproximal connector area produced the weakest solder joints, regardless of metal tested, at p less than .001. There was no significant difference in the fracture loads between midpontic vertical soldering and midpontic diagonal soldering with all three metals at p less than .01. There was no significant difference in fracture loads between midpontic soldering and unit casting with all three metals at p less than .01. The extreme variations in fracture loads when soldering nickel-chrome-beryllium confirms the technique sensitivity of presoldering this alloy.