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C R Lehner

Publications and source records attributed to C R Lehner.

14 recordsLinked to original sources
PubMed1992

All-ceramic crowns.

Despite the good appearance and biocompatibility of dental porcelains, failures are still of considerable concern because of some limited properties common to all-ceramic crown systems. As in the years before, pertinent scientific articles published between November 1990 and December 1991 focused on strengthening mechanisms and compared fracture toughness for different ceramic systems by using various test methods. Some evaluated the clinical implications thereon for seating and loading crowns and measured wear against different ceramic surface conditions. Recently introduced with pleasing aesthetic qualities, IPS-Empress (Ivoclar, Schaan, Liechtenstein), a new European leucite-reinforced glass-ceramic, has finally drawn attention in some journals and has been reviewed with promising in vitro test results. Using a simple press-molding technique, well-fitting crowns, inlays, and veneers can be fabricated without an additional ceramming procedure. Again, only long-term clinical trials will validate achievements compared with other all-ceramic systems and with well-established metal ceramics.

Aluminum Oxide↗
PubMed1991

SEM and energy dispersive X-ray surface analysis of the interfacial region of selected porcelain-metal systems.

Comparative bond strength data of Ceramco and Vita opaque and body porcelains when fired to high noble, medium noble, and base metal porcelain-fused-to-metal alloys were recently published. In the present study SEM and energy dispersive X-ray (EDX) microanalyses were undertaken--using the same specimens after debonding--to relate the bond strengths reported for 12 different porcelain-metal composites to morphology and chemistry at fracture sites. SEM examination revealed intimate contact between the different porcelains and the metal oxide substrates. On Olympia, a medium noble alloy, bubbles trapped in porcelain at or near fracture sites appeared to decrease the potential interaction. Area scan semiquantitative EDX analysis of the interfacial fracture sites detected high concentrations of metal oxides thought to be essential for a successful chemical bond. Multi-spot surface spectroscopy on similar traces of porcelain residuals revealed significant differences in the amount of particular back scattering activity. Further examination with cross sectional quantitative EDX analysis is suggested for a more precise characterization of element concentration within all components of the porcelain-metal interface.

Dental Alloys↗
PubMedDate not supplied

Variable reduced metal support for collarless metal ceramic crowns: a new model for strength evaluation.

A newly designed specimen allowed strength testing of simulated collarless metal ceramic crowns. The design provided precision replication of specimens having ceramic veneers that were completely supported by metal or that were extended 1 and 2 mm beyond the metal support. Twelve specimens of each design were loaded to failure at angles of 90, 45, and 6 degrees. Specimens with unsupported extensions approximated the compressive strength of those with complete framework support (means of 291.6 MPa, 320.2 MPa, and 335.9 MPa, respectively, for 1 mm, 2 mm, and 0 mm of porcelain extension) when tested at 90 degrees. However, for corresponding porcelain lengths, mean resistance to fracture at an angle of 45 degrees was 7.3, 11, and 5.8 times smaller, and at an angle of 6 degrees, 45, 60, and 25 times smaller. The differences were highly significant (P < .001). These results suggest that collarless metal ceramic crowns having up to 2 mm of unsupported porcelain could resist the same axial pressure as those restorations with complete metal support, provided a 90-degree shoulder tooth preparation is used.

Analysis of Variance↗