Faculty Bibliography

This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth-motion fatigue. The dimensions of a mandibular first molar were imported into computer-aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900 degrees C to 25 degrees C. Crowns were fabricated and mouth-motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue

PURPOSE: The aim of this research was to evaluate the fatigue behavior and reliability of monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate and hand-layer-veneered zirconia all-ceramic crowns. MATERIALS AND METHODS: A CAD-based mandibular molar crown preparation, fabricated using rapid prototyping, served as the master die. Fully anatomically shaped monolithic lithium disilicate crowns (IPS e.max CAD, n = 19) and hand-layer-veneered zirconia-based crowns (IPS e.max ZirCAD/Ceram, n = 21) were designed and milled using a CAD/CAM system. Crowns were cemented on aged dentinlike composite dies with resin cement. Crowns were exposed to mouth-motion fatigue by sliding a WC-indenter (r = 3.18 mm) 0.7 mm lingually down the distobuccal cusp using three different step-stress profiles until failure occurred. Failure was designated as a large chip or fracture through the crown. If no failures occurred at high loads (> 900 N), the test method was changed to staircase r ratio fatigue. Stress level probability curves and reliability were calculated. RESULTS: Hand-layer-veneered zirconia crowns revealed veneer chipping and had a reliability of < 0.01 (0.03 to 0.00, two-sided 90% confidence bounds) for a mission of 100,000 cycles and a 200-N load. None of the fully anatomically shaped CAD/CAM-fabricated monolithic lithium disilicate crowns failed during step-stress mouth-motion fatigue (180,000 cycles, 900 N). CAD/CAM lithium disilicate crowns also survived r ratio fatigue (1,000,000 cycles, 100 to 1,000 N). There appears to be a threshold for damage/bulk fracture for the lithium disilicate ceramic in the range of 1,100 to 1,200 N. CONCLUSION: Based on present fatigue findings, the application of CAD/CAM lithium disilicate ceramic in a monolithic/fully anatomical configuration resulted in fatigue-resistant crowns, whereas hand-layer-veneered zirconia crowns revealed a high susceptibility to mouth-motion cyclic loading with early veneer failures

OBJECT/OBJECTIVE:The authors describe their experience in a series of cases of intraneural ganglia within the hip and pelvic regions, and explain the mechanism of formation and propagation of this pathological entity. METHODS:Five patients with 6 intraneural ganglia are presented. Four patients presented with symptomatic intraneural ganglia in the buttock and pelvis affecting the sciatic and lumbosacral plexus elements. An asymptomatic cyst affecting the opposite sciatic nerve was found on MR imaging in 1 patient. The fifth patient, previously reported on by another group, had an obturator intraneural ganglion that the authors reinterpreted. RESULTS:All 5 intraneural ganglia affecting the sciatic and lumbosacral plexus elements were found to have a joint connection to the posteromedial aspect of the hip joint; the obturator intraneural cyst had a joint connection to the anteromedial aspect of the hip joint. In all cases, initial review of the MR images led to their misinterpretation. CONCLUSIONS:To the authors' knowledge, these are the first cases of intraneural ganglia demonstrated to have a connection to the hip joint. This finding at a rare site provides further evidence for the unifying articular (synovial) theory for the formation of intraneural ganglia and reveals a shared mechanism for their propagation. Furthermore, understanding the pathogenesis of these lesions provides insight into their successful treatment and their recurrence.

OBJECTIVE:Using the sequential inflation of 2 sphygmomanometers, Lewis et al. (Heart 16:1-32, 1931) concluded that compressive neuropathy was secondary to ischemia of the compressed nerve segment. Despite subsequent animal studies demonstrating that compressive lesions are more likely the result of mechanical nerve deformation, disagreement remains as to the etiology of rapidly reversible compressive neuropathy. Our hypothesis is that, during the classic sphygmomanometer experiments, the areas of nerve compression at the cuff margins overlapped, so that a region of transient nerve deformation persisted during the second cuff inflation. If true, the original results by Lewis et al. would be consistent with a mechanical pathogenesis. METHODS:In our study, 6 patients underwent sequential upper extremity dual-sphygmomanometer inflation with serial assessment by grip-dynamometer and 2-point discrimination. The order of cuff inflation, as well as the distance between cuffs, was varied. Mean grip force and 2-point discrimination values were statistically compared between conditions. RESULTS:Patients with overlapping cuffs maintained their neurological deficits, whereas those with separated cuffs experienced an improvement in both grip force (P = 0.02) and 2-point discrimination (P < 0.001) when cuff inflation was switched. CONCLUSION/CONCLUSIONS:Rapidly reversible compressive neuropathy seems to be secondary to mechanical nerve deformation at the margins of the compressive force rather than the result of ischemia of the compressed nerve segment. Overlap of the mechanically deformed nerve segments likely explains why neurological deficits persisted despite sequential cuff inflation in the classic experiments by Lewis et al.

Angiotensin-converting enzyme (ACE) inhibitors have been extensively used for the treatment of patients with cardiovascular disease, but several concerns have been raised about their efficacy in African American (AA) patients with heart failure, hypertension, and left ventricular hypertrophy. In this study the authors assessed the effect of ACE inhibitors on total and cardiovascular mortality in high-risk AA patients with angiographically proven coronary artery disease (CAD). This was a retrospective analysis of 810 AA men who underwent diagnostic coronary angiography between 1995 and 2003. All patients had demonstrable CAD and had undergone a complete ischemic workup. Follow-up was from 3 to 10 years. ACE inhibitors were administered to 237 patients, while the remaining 537 patients were not taking ACE inhibitors. Patients taking ACE inhibitors had significantly more comorbidities (hypertension, diabetes, left ventricular hypertrophy, heart failure, severe CAD) at baseline, compared with patients not taking ACE inhibitors (P<.05 for all comorbidities). Despite the unfavorable baseline profile, patients taking ACE inhibitors had significantly lower mortality from CAD during follow-up than patients who were not taking ACE inhibitors (P=.006). Stroke mortality rates were similar in both groups. Cox regression analysis showed an 80% higher relative risk in patients not receiving ACE inhibitors. These data indicate a substantial benefit from ACE inhibitor therapy in high-risk AA patients with CAD.