Comparison of edge chipping resistance of PFM and veneered zirconia specimens.

OBJECTIVES: To investigate the chipping resistance of veneered zirconia specimens and compare it to the chipping resistance of porcelain fused to metal (PFM) specimens. METHODS: Veneered zirconia and PFM bar specimens were prepared in clinically relevant thicknesses. The specimen edges were chipped with different magnitude forces, producing chips of various sizes. The range of sizes included small chips that did not penetrate all the way through the veneers to the substrates, and also chips that were very large and reached the zirconia or metal substrates. The relationship between force magnitude and chip size (edge distance) was graphed. The resulting curves were compared for the veneered zirconia and PFM specimens. Knoop hardness vs. force graphs for the veneers and substrates were also obtained. RESULTS: The zirconia and PFM veneer chipping data followed a power law (coefficient of determination, R(2)>0.93) as expected from the literature. The curves overlapped within the combined data scatter, indicating similar resistance to chipping. The chips made in both types of specimens detached and did not penetrate into the substrate when they reached the veneer/substrate intersections. The hardness-load curves for the veneers and substrates all exhibited an indentation size effect (ISE) at low loads. The Knoop hardness values with uncertainties of +/-one standard deviation at 4N loads for the metal, zirconia, and the metal and zirconia veneers are: (2.02+/-0.08, 12.01+/-0.39, 4.24+/-0.16 and 4.36+/-0.02GPa), respectively, with no statistically significant difference between the veneers (Tukey pairwise comparison at 0.95 family confidence). SIGNIFICANCE: This work indicates that a similar resistance to chipping might be expected for veneered zirconia and PFM restorations, in spite of the large difference in substrate hardness. Differences in susceptibility to chip spalling were not detected, but the chips in both specimen types detached off the sides in a similar manner instead of extending into the substrates.

Three-body wear of dental resin composites reinforced with silica-fused whiskers.

OBJECTIVE: Recent studies used silica-fused whiskers to increase the strength and toughness of resin composites. This study investigated the three-body wear of whisker composites. It was hypothesized that the whisker composites would be more wear resistant than composites reinforced with fine glass particles, and the whisker-to-silica filler ratio would significantly affect wear. METHODS: Silica particles were mixed with silicon nitride whiskers at seven different whisker/(whisker + silica) mass fractions (%): 0, 16.7, 33.3, 50, 66.7, 83.3, and 100. Each mixture was heated at 800 degrees C to fuse the silica particles onto the whiskers. Each powder was then silanized and incorporated into a dental resin to make the wear specimens. A four-station wear machine was used with specimens immersed in a slurry containing polymethyl methacrylate beads, and a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. RESULTS: Whisker-to-silica ratio had significant effects (one-way ANOVA; p < 0.001) on wear. After 4 x 10(5) wear cycles, the whisker composite at whisker/(whisker + silica) of 16.7% had a wear scar diameter (mean +/- sd; n = 6) of (643 +/- 39) microm and a wear depth of (82 +/- 19) microm, significantly less than a wear scar diameter of (1184 +/- 34) microm and a wear depth of (173 +/- 15) microm of a commercial prosthetic composite reinforced with fine glass particles (Tukey's multiple comparison). SEM examination revealed that, instead of whiskers protruding from the worn surface, the whiskers were worn with the composite surface, resulting in relatively smooth wear surfaces. SIGNIFICANCE: Silica-fused whisker reinforcement produced dental resin composites that exhibited high resistance to wear with smooth wear surfaces. These properties, together with the strength and fracture toughness being twice those of current glass particle-reinforced composites, may help extend the use of resin composite to large stress-bearing posterior restorations.

Eccrine porocarcinoma of the eyelid treated with Mohs micrographic surgery.

BACKGROUND: Eccrine porocarcinoma (EPC) is a rare malignant tumor of the eccrine sweat glands. The lesions are reported to occur most commonly on the lower extremity with variable prognosis. OBJECTIVE: To discuss the clinical and histologic features and the prognosis of EPC. METHODS: We report a 71-year-old man who presented with an asymptomatic lesion on his lower eyelid that had been present for 6 weeks. RESULTS: The 4 x 4-mm lesion was removed in two stages using the Mohs micrographic surgery fresh-tissue technique. The histopathologic diagnosis was primary EPC. CONCLUSION: EPCs most commonly occur on the lower extremity. This case is interesting because the lesion was located on the lower eyelid.

Treatment of squamous cell carcinoma with intralesional 5-Fluorouracil.

BACKGROUND: 5-Fluorouracil (5-FU) has been used topically and intralesionally to treat lesions related to squamous cell carcinoma (SCC) such as actinic keratosis, Bowen's disease, and keratoacanthoma. OBJECTIVE: We sought to determine whether intralesional 5-FU might be effective in treating a patient with SCC. METHODS: A patient with SCC at the junction of the right alar crease and right nasolabial fold was treated with eight weekly injections of 5-FU, with doses ranging from 0.8 to 2.4 mL. RESULTS: A repeat biopsy after the eighth treatment showed total clearance of the cancer, and the patient has remained free of recurrence during a 5-month follow-up period. CONCLUSION: This modality may provide patients with SCC in cosmetically important locations or in areas that require complex surgery the advantage of a nonsurgical cure.