Lessons learnt from the construction and implementation of a prospective ventral hernia database.

PURPOSE: The New England VA Hernia Registry was created in 2011 to prospectively collect relevant details of ventral hernia repairs, with the intention to assess and improve long term outcomes. The goal of this study is to assess registry compliance. METHODS: All ventral hernia operations performed in five VA hospitals between 2011-2022 were obtained. We assessed compliance at the hospital and surgeon level. RESULTS: 3,516 cases were performed. Overall compliance with registry entry was 37.5%, ranging from 10.8% to 67.2% across hospitals. At the hospital level, there was a negative correlation between average yearly hernia volume per surgeon and registry compliance (r2 = 0.53). Surgeon compliance varied within hospitals and over time. CONCLUSION: Registry compliance was low and highly variable. Lack of interest, incentives, oversight, and surgeon turnover are possible factors for noncompliance. Building a registry with these factors in mind, providing timely feedback, and conducting frequent audits may improve compliance.

Maspin: synthesis by human cornea and regulation of in vitro stromal cell adhesion to extracellular matrix.

PURPOSE: Maspin, a tumor-suppressor protein that regulates cell migration, invasion, and adhesion, is synthesized by many normal epithelial cells, but downregulated in invasive epithelial tumor cells. The purpose of this study was to determine whether cells in the normal human cornea express maspin and whether maspin affects corneal stromal cell adhesion to extracellular matrix molecules. METHODS: Maspin expression was analyzed by immunodot blot, Western blot, and RT-PCR analyses in cells obtained directly from human corneas in situ. Maspin protein and mRNA were also studied in primary and passaged cultures of corneal stromal cells using Western blot analysis, RT-PCR, and immunofluorescence microscopy. Maspin cDNA was cloned and sequenced from human corneal epithelial cells and expressed in a yeast system. The recombinant maspin was used to study attachment of cultured human corneal stromal cells to extracellular matrices. RESULTS: Maspin mRNA and micromolar amounts of the protein were found in all three layers of the human cornea in situ, including the stroma. Maspin was also detected in primary and first-passage corneal stromal cells, but its expression was downregulated in subsequent passages. Late-passage stromal cells, which did not produce maspin, responded to exogenous recombinant maspin as measured by increased cell adhesion not only to fibronectin, similar to mammary gland tumor epithelial cells, but also to type I collagen, type IV collagen, and laminin. CONCLUSIONS: The corneal stromal cell is the first nonepithelial cell type shown to synthesize maspin. Loss of maspin expression in late-passage corneal stromal cells in culture and their biological response to exogenous maspin suggests a role for maspin on the stromal cells in the cornea. Maspin may function within the cornea to regulate cell adhesion to extracellular matrix molecules and perhaps to regulate the migration of activated fibroblasts during corneal stromal wound healing.

Mechanical properties of glass-only porcelains prepared by the use of two feldspathic frits with different thermal properties.

Low- and non-leucite-containing commercial porcelains with low firing temperatures have become popular. However, improving the strength of glass porcelains is difficult. The purpose of this study was to determine if dispersed glass particles could be used as a reinforcing agent for an all-glass porcelain. We produced 3 feldspathic glasses (high-fusing, medium-fusing, low-fusing) by melting powders consisting of potassium-feldspar and 0, 5, or 20 mass% Na2O, respectively. For high-fusing, medium-fusing, and low-fusing feldspathic glasses, the deformation temperatures were 945 degrees C, 647 degrees C, and 518 degrees C, and the thermal expansion coefficient values were 8.6 x 10(-6)/degrees C, 10.3 x 10(-6)/degrees C, and 13.4 x 10(-6)/degrees C between 25 degrees C and the glass-transition temperature, respectively. The high-fusing-glass (or medium-fusing-glass) powders were mixed with low-fusing-glass powders before being fired into test specimens. The mean flexural strength and fracture toughness (K1C) of 3 single-glass porcelains ranged from 57 to 63 MPa and from 0.68 to 0.73 MPa m(1/2), respectively, presenting no significant differences in one-way ANOVA. However, the flexural strength of 50% high-fusing-glass + 50% low-fusing-glass porcelain was 114 MPa (p < 0.05) and K1C was 1.2 MPa m(1/2) (p < 0.05). Microcracks were observed with a back-scattered scanning electron microscope and were associated with the high- (or medium-) fusing glass particles, suggesting residual stress in the low-fusing-glass matrix due to a coefficient of thermal expansion mismatch between the dispersed glass particles and the matrix glass. The dispersing glass particles appeared to act as a reinforcing agent for strengthening a glassy porcelain.

Regulation of nitric oxide synthase 2 in rabbit corneal cells.

PURPOSE: The purpose of these studies was to investigate the role of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), and transforming growth factor-beta (TGF-beta) in the regulation of inducible nitric oxide synthase (NOS2) activity in rabbit corneal cells. METHODS: Rabbit corneal epithelial, stromal, and endothelial cells were grown in culture and treated with cytokines and growth factors, alone or in combination. NOS activity was measured at times up to 72 hours after treatment by assaying the culture medium for nitrite using the Griess reaction. Cell lysates were analyzed by Western blot analysis for NOS2 protein. RNA was isolated and amplified with NOS1-, NOS2-, and NOS3-specific primers by RT-PCR. RESULTS: NOS2 expression was induced by combined cytokine treatment from nondetectable levels to abundant levels in low passage (<4) stromal cells and to low levels in corneal endothelial cells but not in corneal epithelial cells. In the absence of IFN-gamma, little or no nitrite accumulation was induced by TNF-alpha, IL-1beta, or lipopolysaccharide (LPS) treatment. The inductive effects of IFN-gamma were antagonized in a dose-dependent manner by the myxoma virus rabbit IFN-gamma receptor homolog, M-T7. rRaIFN-gamma, in combination with IL-1beta and TNF-alpha, induced the appearance of NOS2 mRNA within 24 hours but detectable nitrite did not accumulate in large amounts (>10 microM) until after 24 hours postinduction. NOS2 was identified as a 130 kDa protein on Western blot analysis using monoclonal antibody against murine NOS2. TGF-beta(1) and beta(2) inhibited the accumulation of cytokine-induced nitrite in a dose-dependent manner while not significantly reducing the steady state level of NOS2 mRNA. The activity of the induced NOS was inhibited by 1400W, a NOS2-selective inhibitor, but not 7-nitroindazole, a NOS1-selective inhibitor. CONCLUSIONS: In cultured corneal stromal cells, NOS2 expression was upregulated by IFN-gamma in combination with IL-1beta and TNF-alpha but not by any of these cytokines alone, while TGF-beta downregulated the activity. Cultures of corneal epithelial cells could not be induced to express NOS2, yet cultures of endothelial cells produced low amounts of NO in response to cytokines. The NOS1 and NOS3 isoforms were not detected in any of these corneal cells.

Interferon coordinately inhibits the disruption of PML-positive ND10 and immediate-early gene expression by herpes simplex virus.

Interferons (IFNs) are important components of the innate immune response, limiting herpes simplex virus (HSV) infection. In recombinant HSV-infected cells, IFN inhibited expression of beta-galactosidase from the immediate-early gene, ICP4, promoter. The extent of inhibition was dependent on IFN dose, IFN type, cell type, and multiplicity of infection (moi). IFN inhibited gene transcription, leading to a complete block in ICP4 promoter-driven gene expression in 90% of cells. The same IFN treatments resulted in an increase in the size and number of nuclear domain 10 (ND10) structures that stained positive by immunofluorescence for the promyelocytic leukemia (PML) protein. In cultures infected at low moi with a recombinant HSV producing ICP4 as a fusion protein with green fluorescence protein, the appearance of green fluorescence in the nucleus coincided with loss of PML-positive ND10 in the same nucleus, even in the rare ICP4-expressing IFN-treated cells. IFN-dependent inhibition was nearly complete when the immediate-early promoter was in the viral genome but was minimal when the promoter was stably integrated into the cellular genome. These data reveal that IFN can completely block viral gene expression in infected cells and that enhancement of the ND10 structure, which is the site of initiation of HSV replication, correlates with the block in viral gene expression.

Cellular adaptation to down-regulated iron transport into lymphoid leukaemic cells: effects on the expression of the gene for ribonucleotide reductase.

Ribonucleotide reductase is an iron-containing enzyme that is essential for DNA synthesis. Whereas previous studies have used various iron chelators to examine the relationship between cellular iron metabolism and ribonucleotide reductase activity in cells, they have not elucidated the relationship between iron transport into cells and the expression of the gene for ribonucleotide reductase. To investigate this, we examined ribonucleotide reductase mRNA, protein and enzyme activity in a novel line of CCRF-CEM cells (DFe-T cells) that display an approx. 60% decrease in their uptake of iron compared with the parental wild-type cell line. We found that DFe-T cells displayed an approx. 40% decrease in ribonucleotide reductase specific enzyme activity relative to wild-type cells without a change in their proliferation. Kinetic analysis of CDP reductase activity revealed an approx. 60% decrease in V(max) in DFe-T cells without a change in K(m). Despite the decrease in enzyme activity, the mRNA and protein for the R1 and R2 subunits of ribonucleotide reductase in DFe-T cells were similar to those of wild-type cells. ESR spectroscopy studies revealed that DFe-T cells had a 22% decrease in the tyrosyl free radical of the R2 subunit, suggesting that a larger amount of R2 protein was present as functionally inactive apo-R2 in these cells. Our studies indicate that ribonucleotide reductase activity in CCRF-CEM cells can be down-regulated by more than 50% in response to down-regulated iron transport without an adverse effect on cell proliferation. Furthermore, our studies suggest a regulatory link between ribonucleotide reductase activity and iron transport into these cells.

Strengthening mechanisms of current dental porcelains.

Dental porcelains have a high glass content, which provides the translucency necessary for esthetic restorations. Because glasses are brittle, they fail under tension or bending by the propagation of preexisting flaws (e.g., scratches, porosities). Several approaches that are based on impeding the propagation of flaws have been used to strengthen dental porcelains, including bonding to metals, adding microcrystalline phases, and surface treatments (i.e., polishing, ion exchange, hydration). Through these methods, porcelain systems are used routinely for all-ceramic anterior restorations; however, porcelain-fused-to-metal restorations remain the most reliable for posterior applications.

Synergistic anti-varicella-zoster virus activity of interferon-alpha 2a and acyclovir in corneal cells.

Human corneal stromal (HCS) cells in cultures established from donor corneas can serve as host cells for replication of varicella-zoster virus (VZV). Comparative infectious centers assays suggest that HCS cells are more restrictive hosts than MRC-5 cells, a line of human embryonic lung fibroblasts, commonly used for VZV isolation. VZV propagated in MRC-5 cells was infectious for both MRC-5 and HCS cells, but titers in HCS were one fifth of those in MRC-5 cells. Inhibition of VZV replication in HCS cells by acyclovir (ACV), recombinant human interferon-alpha 2a (IFN-alpha 2a), or the combination of these two antivirals was detected by both an infectious centers-plaque-reduction assay and an ELISA method using monoclonal anti-VZV antibody. In the infectious centers-plaque-reduction assay combinations of ACV with IFN-alpha 2a showed synergistic anti-VZV activity. VZV protein synthesis, as detected by the ELISA, was a less sensitive measure of the antiviral effects producing an ED50 value of 50 microM for ACV, five to ten times the ED50 determined in the plaque reduction assay. In the ELISA, high titers of IFN-alpha 2a (2000 IU/ml) decreased virus antigen expression only slightly, while combinations of ACV and IFN-alpha 2a were synergistic in their detected anti-VZV activity. These data document the replication of VZV in HCS cells and demonstrate that VZV is sensitive to the synergistic antiviral action of combinations of IFN-alpha 2a and ACV.

Fracture strength of glass infiltrated-magnesia core porcelain.

PURPOSE: This study determined the fracture strength of magnesia-core porcelain after using a glass infiltration firing technique. MATERIALS AND METHODS: Eighty refractory dies were replicated from a stainless steel master die milled to the dimensions of a maxillary premolar that had been prepared for a porcelain crown. The core porcelain was applied to the refractory dies using traditional condensation methods, and then formed into standardized copings using a centrifugal sculpturing device. The copings were vacuum-fired from 593 degrees C to 1 of 8 high temperatures. Five copings per temperature were then coated with a glass-infiltrate and ground back to a standard thickness. The finished copings were bonded to a duplicate die with an adhesive resin luting system and placed in an Instron testing machine and loaded to fracture. RESULTS: Analysis of variance and Student-Newman-Keuls tests demonstrated significant differences among treatments and temperatures (P < 0.05). A significant increase in fracture strength was observed after glass infiltration of the magnesia-core porcelain. Sintering the copings to 871 degrees C or 899 degrees C prior to glass infiltration gave the highest fracture load values. CONCLUSION: Glass infiltration significantly increased the fracture strength of the magnesia-core porcelain.

Investigation of two mercury vapor collection techniques.

OBJECTIVES: The purpose of this investigation was to develop and test two in vitro mercury vapor collection techniques: a closed bottle technique (CB) and an intraoral flow (IOF) technique. METHODS: Amalgam samples were prepared in acrylic first molars (#30) with standardized Class I preparations. In the CB technique, samples were placed in either a 25, 100 or 500 ml bottle (n = 5). Vapor was analyzed with the Jerome M-411 using a syringe method over a 7 day period. In the IOF technique an impression of the lower right quadrant of a Typodont was taken with PVS impression material leaving a 5 mm space over #30. Samples were analyzed with the Jerome M-411 connected to the impression tray via tygon tubing at the buccal surface. Average mercury vapor release rates and standard deviations were calculated for each method. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05). RESULTS: Both techniques indicated mercury vapor release was dependent on volume. The largest bottle, 500 ml, yielded a significantly greater (p < or = 0.00) amount of mercury vapor within the CB systems. In the IOF technique, the addition of air flow over the restoration demonstrated a significant increase (p < or = 0.05) in mercury vapor released compared to the sealed IOF technique. SIGNIFICANCE: A method for mercury vapor analysis was developed for possible intraoral application. The IOF method with direct air flow removes possible saturation effects found in a CB system, while limiting external variables, which may contribute to errors associated with in vivo measurements.

Effects of palladium addition on emission of mercury vapor from dental amalgam.

OBJECTIVES: The purpose of this investigation was to test the hypothesis that palladium causes a reduction in mercury emission when added to dental amalgam during condensation. METHODS: Mercury vapor release was measured in a closed bottle system and an Intraoral Flow device(IOF). Conventional amalgam restorations were modified by addition of various palladium pellets. 1.57 mm diameter palladium pellets with different porosities were fabricated. These pellets were then placed in amalgam restoration using typical condensation and carving procedures. The samples were stored in a closed bottle and mercury measurements were taken from the bottles at 30 min, 1, 3, 5, 24 and 48 h and 7 days after trituration using a Jerome 411 Mercury Vapor Analyzer (Arizona Instrument Corp., Jerome, AZ). The palladium pellets identified as the most effective in mercury vapor reduction were further tested in an IOF device. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05). RESULTS: The palladium containing amalgams when tested in the closed bottle system yielded significantly lower (p < 0.05) mercury vapor release than the controls. Pellets fabricated with the highest porosity yielded the greatest reduction in overall mercury vapor release. In the IOF device the overall amount of mercury vapor released from the palladium containing amalgams was also significantly less than the control (p < 0.05). SIGNIFICANCE: Mercury vapor emission from dental amalgam was greatly reduced by adding palladium pellets to amalgam during condensation. These techniques require only slight modifications of the standard operative procedures.

Tissue-specific accumulation of latency-associated transcripts in herpes virus-infected rabbits.

PURPOSE: Herpes simplex virus (HSV) DNA persists in the corneas of patients and animals with a history of herpetic keratitis. The purpose of this study was to detect viral transcripts in the corneas of latently infected rabbits with a history of herpetic keratitis to determine whether the viral DNA represents latent virus, characterized by the restricted transcription of HSV genes and accumulation of the stable latency-associated transcripts (LATs), as occurs in neurons. METHODS: Rabbits were injected in the subalveolar mucosa with HSV strain RE. After 30 days, corneas were infected by intrastromal injection of HSV. Corneal disease was evaluated, and 7 to 378 days after infection, the rabbits were killed. DNA and RNA were isolated from corneas and trigeminal ganglia and amplified by PCR using gene-specific primers. RESULTS: Herpetic keratitis developed in all rabbits. All corneas of these immune rabbits contained viral DNA as many as 120 days after infection and then the frequency decreased over the next 260 days. Overall, viral DNA was detected in all ganglia and in 57% of corneas. All latently infected ganglia but no corneas contained LATs. Transcripts of the early viral gene for thymidine kinase were detected in 23 of 30 ganglia and 10 of 17 corneas. Transcripts for the late viral glycoprotein C were not detected in either tissue. CONCLUSIONS: These data document that after HSV keratitis, viral DNA persists in corneas in the absence of stable LATs and with restricted expression of other viral genes.

Combined effects of interferon-alpha and acyclovir on herpes simplex virus type 1 DNA polymerase and alkaline DNase.

Treatment of cells with combinations of human interferon-alpha (IFN-alpha) and the nucleoside analog, acyclovir (ACV), leads to the synergistic inhibition of herpes simplex virus type 1 (HSV-1) replication. We have examined the effect of these agents on the replication of HSV-1 DNA and the synthesis of early viral enzymes to understand the mechanism(s) responsible for this synergistic activity. Combination treatment with 100 IU/ml IFN-alpha and 5 microM ACV led to HSV-1 DNA levels more than 8-fold lower than in cells treated with ACV alone, while IFN-alpha treatment alone had no detectable effect on viral DNA synthesis. Steady state levels of DNA polymerase were reduced approximately 50% by IFN-alpha and 25% by ACV, but combination treatment did not decrease enzyme levels to an extent greater than the sum of these effects. In contrast, the activity of another early viral enzyme, alkaline DNase, was reduced less than 20% by IFN-alpha alone or combination treatment and was unaffected by ACV treatment. No decrease in the level of mRNA encoding either enzyme was detected in IFN-alpha-treated cells although ACV treatment reduced polymerase mRNA levels. These studies suggest that the synergistic anti-HSV activities of IFN-alpha with ACV could be mediated, in part, through some post-transcriptional mechanism induced by IFN-alpha treatment, leading to the reduction in production of viral early enzymes, especially DNA polymerase.

The effects of interferon-alpha and acyclovir on herpes simplex virus type-1 ribonucleotide reductase.

Herpes simplex virus-type 1 (HSV-1) encodes both the small (UL40) and large (UL39) subunits of the enzyme, ribonucleotide reductase. Treatment of HSV-1-infected cells with interferon-alpha (IFN-alpha) reduced the levels of both enzyme subunits. Reduced steady state levels of the large subunit were demonstrated by immunoblot using polyclonal antibody specific for the viral enzyme. Reduction in the amount of small subunit was shown by a reduction in the electron spin resonance signal derived from the iron-containing tyrosyl free-radical present in this subunit. Treatment of cells with 100 IU/ml of IFN-alpha decreased levels of both subunits resulting in a reduction in enzyme activity as measured by conversion of CDP to dCDP. The decrease in the amount of the large subunit was not due to a reduction in the level of its mRNA. The combination of IFN-alpha and ACV treatment of human cornea stromal cells did not result in a further reduction in amounts of ribonucleotide reductase relative to that detected with IFN-alpha alone. The IFN-alpha-induced reduction in ribonucleotide reductase activity is the likely cause of decreased levels of dGTP which we have previously demonstrated in IFN-alpha-treated, infected cells.

The comparative anti-herpes simplex virus effects of human interferons.

The mechanism(s) of anti-herpes simplex virus (HSV) activity of interferons (IFNs) have not been clearly identified. We have tested natural and recombinant human IFN-alpha, IFN-beta, and IFN-gamma preparations for their relative anti-HSV activity in human corneal and Vero monkey kidney cells. The relative anti-HSV activities in corneal cells were IFN-beta > rIFN-gamma > IFN-alpha (lymphoblastoid) > rIFN-beta2a = rIFN-alphaA/D. IFN-beta at 100 IU/ml reduced virus yield by 59+/-24%. The relative anti-HSV activity in Vero cells was rIFN-gamma > IFN-beta = IFN-alpha (lymphoblastoid) > rIFN-alphaA/D > rIFN-alpha2a. IFN-gamma at 100 IU/ml reduced virus yields by 90+/-4%. Reducing the multiplicity of infection significantly increased the apparent antiviral activity of all IFNs. The antiviral activity of IFNs could be detected by 4 h after treatment of Vero cells but not until 8 h in corneal cells. Western blot analysis showed that none of the IFNs detectably reduced the levels of immediate-early HSV protein, ICP4, but some reduced ICP0 levels early during infection, the extent and duration of the reduction varying with both IFN and cell type. The greatest effects on viral protein levels were detected in IFN-y-treated Vero cells. These data indicated that the targets of the anti-HSV activities of IFNs can vary with both IFN and cell type.

Cerium oxide as a silver decolorizer in dental porcelains.

OBJECTIVES: Silver-base alloys are known to produce an esthetically unpleasant yellow-green tint in the dental porcelain when making PFM restorations. Cerium oxide is used in dental porcelains to simulate the natural fluorescence found in human dental enamel, and has also been used in the glass industry as a decolorizer. The purpose of this study was to determine the effect of CeO2 additions on the resistance of dental porcelain to staining from silver contamination. METHODS: Five batches of porcelain were prepared according to Weinstein et al. (1962) with 0.00, 0.05, 0.10, 0.15 and 0.20 wt% additions of CeO2. To determine the resistance of these porcelains to silver staining, 0.10 wt% additions of the silver oxides were triturated into the prepared CeO2 porcelains prior to sample fabrication. This procedure provided a more quantitative method of staining than firing directly on silver alloys. Silver oxide was added in two valence states as Ag2O and AgO to test for any possible effects on staining. Samples were pressed into a 17 mm diameter mold, and fired to 960 degrees C under vacuum. Three additional samples were prepared from the non-cerium porcelain frit to produce a non-stained control group. Color measurements were made with a spectrophotometer on the ten experimental groups and the control group. The CIE L*a*b* color difference, delta E*, was calculated between the control and the experimental groups. RESULTS: There was a significant decrease in the silver staining of dental porcelains when CeO2 additions of 0.10 wt% or greater were used. SIGNIFICANCE: Cerium oxide additions in the range of 0.10 to 0.20 wt% caused a three-fold reduction in the staining of dental porcelain samples which had been doped with 0.10 wt% of AgO or Ag2O.

Depth-resolved Raman microprobe examination of a commercial dental porcelain exposed to a simulated oral environment.

OBJECTIVES: The specific aims were investigation of the chemical transformations into the interior of a commercial dental porcelain upon exposure to a simulated oral environment and identification of structural alterations that contribute to the strengthening of the porcelain. METHODS: Samples of a commercial dental porcelain, Duceram LFC, were exposed to refluxing dilute acetic acid for 0, 1, 5, 10, and 72 h to simulate exposure to the oral environment. The control and refluxed samples were examined using a depth-resolved Raman microprobe system covering the low (0-2550 cm-1) and high (2000-4000 cm-1) frequency ranges. Spectra were processed using exploratory factor analysis. Significant factors were retained, accounting for 99.999% of the variance. RESULTS: The porcelain was found to be significantly depolymerized prior to acid-refluxing. Exposure to water and to acid resulted in the formation of a better-ordered region near the surface. In that region, three intermingled zones of chainlike metaborate and pyroborate, of boroxol rings, and of a mixture of borate and silicate tetrahedra were identified. The borate/silicate factor was dependent on refluxing time. Hydroxyl groups were detected in all of the samples, but no changes to the hydroxyl environment were noted until after 10 or more hours of refluxing. Then, molecular water and isolated hydroxyls/SiOH were detected. After 72 h, an additional unassigned factor around 2800-2950 cm-1 was noted. SIGNIFICANCE: Acid refluxing causes generation of ordered boron-containing species near the surface of the porcelain.

Stress induced phase transformation of a cesium stabilized leucite porcelain and associated properties.

OBJECTIVES: The addition of CS2O to dental porcelains might provide a means for controlling the thermal expansion and toughness of feldspathic porcelains. The purpose of this investigation was to determine for a leucite porcelain the effect of CS2O content upon its coefficient of thermal expansion (alpha), toughness, hardness, and content of low (tetragonal) leucite and high (cubic) leucite. METHODS: In order to determine the amount of low leucite in the specimens, an x-ray calibration curve for low leucite and an internal standard of copper was obtained using quantitative x-ray diffraction techniques. Utilizing a stress induced phase transformation between low and high leucite, an x-ray intensity conversion ratio (r) was determined for high leucite so that the calibration curve for low leucite could be used to determine the amount of high leucite present in the experimental porcelains. Specimens were prepared with various amounts of CS2O (0.0, 0.5, 1.0, 1.5, 2.0 mol%) so that, except for the as-received porcelain (A), all had the same thermal history. Specimens were tested for content of low and high leucite, hardness (Vickers), toughness (indentation-strength method), and coefficient of thermal expansion (alpha) over two temperature ranges (30-500 degrees C and 30-640 degrees C). Fractured surfaces were examined with a scanning electron microscope (SEM). For each property, specimen groups were compared for statistical differences. These comparisons were statistically analyzed using analysis of variance (ANOVA) and Fisher's protected least significant differences (PLSD). RESULTS: Quantitative x-ray examination of abraded and heat-treated specimens demonstrated that a stress induced phase transformation occurred which could be reversed by heat treatment. The conversion ratio was determined as r = 1.93 +/- 0.29. The addition of CS2O lowered the wt% of low leucite from 63 +/- 6% to 0% and increased the amount of high leucite from 0% to 62 +/- 5%. ANOVA showed that the addition of CS2O had a significant effect on alpha (p < 0.0001), hardness (p < 0.005), and toughness (p < 0.0001). CS2O significantly (PLSD) lowered the alpha (p < 0.0001), hardness (p < 0.01), and toughness (p < 0.0001) of a high-content leucite porcelain. SIGNIFICANCE: A stress induced phase transformation of high leucite to low leucite was demonstrated and, as a consequence, suggested the potential for phase transformation toughening. The alpha of a leucite porcelain could be controlled by stabilizing high (cubic) leucite to room temperature with the fraction of high leucite dependent upon the amount of CS2O added. A method was developed to determine the amount of high leucite present in a porcelain.

Color distribution of three regions of extracted human teeth.

OBJECTIVES: Knowledge of human tooth color and its distribution are critical to the understanding of shade matching in esthetic dentistry. The color of human teeth shows a gradation from the gingival to the incisal region. There have been many reports in the literature on the distribution of color in teeth, but not in the CIE 1976 L*a*b* system. This study was conducted to determine the color distribution in three regions in a sample of human teeth and express the results in Munsell notation, CIE 1976 L*a*b* and CIE delta E* color differences. The hypothesis of this research was that it is possible to detect significant differences in the color parameters of the three distinct regions in teeth. METHODS: All of the teeth used in this study were extracted, cleaned and stored in artificial saliva. Prior to measurement, the teeth were removed from the solution and mounted in a holder to ensure consistent measurements. Spectral data were collected using a GE recording spectrophotometer, CIE chromaticity coordinates calculated using CIE illuminant C and 1931 observer data, and conversions made to L*, a*, b* and Munsell notation. The results were analyzed by ANOVA and Scheffé's multiple comparisons test. RESULTS: The mean L*, a*, b*s were 72.6, 1.5, 18.4 for gingival, 72.4, 1.2, 16.2 for middle, and 71.4, 0.9, 12.8 for incisal. Average Munsell parameters were 1.2 Y 7.1/2.7 for gingival, 1.3 Y 7.1/2.4 for middle, and 1.4 Y 7.0/1.9 for incisal. The mean CIE delta E* between the gingival and incisal regions of the 95 teeth showed a clinically significant difference of 8.2. SIGNIFICANCE: The distribution of color was identified for three regions of the tooth. A statistical analysis determined that there are statistically significant color differences between the regions, and these differences are also clinically significant. This information is beneficial when esthetic restorations are required.