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Biomedical subjects

James L Borke

Publications and source records attributed to James L Borke.

11 recordsLinked to original sources
PubMed2007

Infiltration/evaporation-induced shrinkage of demineralized dentin by solvated model adhesives.

During dentin bonding, solvated adhesive comonomers are applied to water-saturated decalcified dentin matrices. When alcohol-solvated hydrophilic or hydrophobic methacrylate monomers are applied, they chemically remove water and cause matrix shrinkage during comonomer infiltration. Evaporation of solvent induces further shrinkage. The purpose of this work was to compare the shrinkage of water-saturated dentin matrices infiltrated with ethanol- or methanol-solvated 2-hydroxyethyl methacrylate (HEMA), 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane (BisGMA), or triethyleneglycol dimethacrylate (TEGDMA) at 90/10, 70/30, 50/50, and 30/70 mass fraction % alcohol/monomer before and after evaporation of alcohol. Thin (ca 0.2 mm) disks of human mid-coronal dentin were demineralized and placed in a well beneath the contact probe of a linear variable differential transformer (LVDT). The height of the matrix was measured before and after random application of one of the twelve alcohol/monomer mixtures. Matrix height was measured during infiltration and during solvent evaporation. Between trials, residual monomer was extracted using ethanol. These studies were repeated on specimens in which 100% alcohol was used to substitute for water in the matrix. Both studies revealed that matrices shrink 30-50% but that pretreatment of matrices with alcohol prevents BisGMA phase separations from occurring. Wet bonding with ethanol instead of water permits infiltration of relatively hydrophobic alcohol/monomers.

Adhesives↗
PubMed2006

Net expansion of dried demineralized dentin matrix produced by monomer/alcohol saturation and solvent evaporation.

The purpose of this work was to determine if nonaqueous methacrylate monomer/alcohol mixtures could expand dried collapsed demineralized dentin matrix. Thin disks (ca. 200 microm) of human dentin were demineralized and placed in wells beneath contact probes of linear variable differential transformers. The probes were placed on water-saturated expanded matrices to record the shrinkage associated with drying. Monomer mixtures containing hydroxyethyl methacrylate, 2,2-bis[4-(2-hydroxy-3 methacryloyloxy)propoxyphenyl] propane, or triethyleneglycol dimethacrylate were mixed with methanol or ethanol at alcohol/monomer mass fraction % of 90/10, 70/30, 50/50, or 30/70. They were randomly applied to the dried matrices to determine the rate and magnitude of expansion; then shrinkage was recorded during evaporation of the alcohols. The results indicated that matrix expansion was positively correlated with the Hoy's solubility parameters for hydrogen bonding forces (delta(h)) of the monomer/solvent mixtures (p < 0.001). Expansions were more rapid with methanol-containing than with ethanol-containing monomer mixtures. For the test solutions, triethyleneglycol dimethacrylate-containing mixtures produced the slowest rate of matrix expansion and hydroxyethyl methacrylate-containing mixtures the most rapid expansion. When the solvents were evaporated, the matrix shrank in proportion to the solvent content and the delta(h) of the monomer-solvent mixtures. The results indicate that expansion of dried, collapsed dentin matrices requires that the delta(h) of the mixtures be larger than 17 (J/cm(3))(1/2). The greater the delta(h) of the monomer solutions, the greater the rate and extent of expansion.

Alcohols↗
PubMed2005

Fractal analysis of the PDL-bone interface and implications for orthodontic tooth movement.

BACKGROUND: The periodontal ligament (PDL) is a soft tissue interposed between the tooth and the alveolar bone. It is responsible for transmission of forces in vivo; this promotes bone remodeling. The purpose our study was to use fractal analysis to quantify the complex morphology of the PDL-bone interface. METHODS: We used Scion Image (Scion Corp, Frederick, Md) and Benoit fractal analysis (Tru Soft International, St. Petersburg, Fla) programs to calculate the fractal dimension of the PDL-bone interface in rats via the box-counting method. Rats in the experimental groups received an initial force of 0.1N or 0.5N with customized springs for 6 hours. RESULTS: Our studies showed an increase in normal fractal dimension at the root apices of the rats' maxillary molars. We also found evidence that the fractal dimension varies along the entire root length from the apex to the cementoenamel junction. CONCLUSIONS: Mechanical loading might lead to an increase in fractal dimension at the PDL-bone interface apart from mechanisms of bone cell directed remodeling. These changes in fractal dimension are proportional to loading and could provide a new parameter for force determination in orthodontic tooth movement.

Alveolar Process↗
PubMed2004

Brief synopsis of cranial sutures: optimization by adaptation.

This article reviews the form and function of cranial sutures across the temporal and spatial scales. The temporal scale spans 530 million years, from ostracoderms to contemporary humans. The spatial scale spans eight orders of magnitude, from the macroarchitectural level (the entire cranium), through the mesoarchitectural (the local/regional bone-suture-bone complex) and microarchitectural levels (tissues and cells), to the nanoarchitectural level (molecules within and outside the cells). A mechanomorphologic loop, or cycle, exists. The mechanical strain experienced by the sutures eventually alters the morphology of the sutures. In turn, these morphological changes affect the strain distribution within and around the sutures. At the microarchitectural level, the responses of bone and sutural cells to environmental perturbations depend on the content (what that perturbation is), the context (the other coexisting extrinsic and intrinsic factors), and the history of the perturbation (how often and for how long).

Animals↗
PubMed2004

An evaluation of the origin of trabecular bone patterns using visual and digital image analysis.

OBJECTIVE: The purpose of this research project was to investigate the origin of the anatomical structures interpreted as trabecula bone on dental radiographic images. STUDY DESIGN: Mandible sections were cut sagitally into halves. Trabecular bone was removed from each section in 4 stages. Following each stage, standardized radiographs were made, using CDR direct digital equipment. Trabecular bone in the resulting digital images was measured with 4 methods: (1) mean gray level; (2) the fractal dimension of the basic images; and, following morphological image processing, (3) counting the number of trabecular ends, intercepts, and segments (EIS) and (4) performing fractal analyses of the skeletonized images. Additionally, human visual interpretation of the collected images was conducted through a written examination. Repeated measures analysis of variance (ANOVA) was used to test for changes in measurements attributable to bone removal. RESULTS: Repeated measures ANOVA indicated that the use of gray levels, fractal dimension, and morphologic operations quantifying using EIS or fractal analysis had similar performance and resulted in significant changes in measurements following bone removal ( P < .05). Visual differences were not always apparent between each stage of bone reduction. Radiometric and morphologic analysis showed measurable differences between stages. CONCLUSIONS: These results imply that the inner trabecula, the junctional trabecula, and the actual cortical housing all contribute to some extent to the radiograph, although changes in the radiographic architecture are not always clinically detectible.

Absorptiometry, Photon↗
PubMed2003

Tension-induced reduction in connexin 43 expression in cranial sutures is linked to transcriptional regulation by TBX2.

Cranial sutures produce bone at precisely the right rate and time to maintain homeostasis. Connexin 43 (CX43), a protein important for communication in bone, is downregulated during cell proliferation and is released from suppression or upregulated during differentiation. Our previous studies have shown that binding sites for the transcription regulatory protein TBX2 are located in the promoter sequence, upstream of the Cx43 gene. We have shown that TBX2 binding suppresses Cx43 expression. The current study uses transgenic mice in which the TBX2 promoter has been spliced upstream of the coding sequence for green fluorescent protein (GFP). This study shows upregulation of TBX2 after stretching. RNA from stretched and unstretched sutures was used for GeneChip and Western analysis. The results show an increase in Tbx2 and a decrease in Cx43 gene and protein expression with stretch. Our findings support a model of strain-regulated bone formation with feedback inhibition that maintains sutural patency during development.

Animals↗
PubMed2003

Negative transcriptional regulation of connexin 43 by Tbx2 in rat immature coronal sutures and ROS 17/2.8 cells in culture.

BACKGROUND: Tbx2 is a member of the T-box family of transcriptional regulatory genes with an extensive but not yet fully understood role in embryonic development. This study explores the potential role of Tbx2 in calvarial morphogenesis. OBJECTIVES: To explore the hypothesis that Tbx2 has a negative regulatory effect on the expression of connexin 43 (Cx43), a protein necessary for cell-to-cell communication; document the presence of Tbx2 protein in the developing cranial sutures; and determine the spatial pattern of expression of this developmentally regulated transcription factor in calvariae. DESIGN: The osteoblast-like cell line ROS 17/2.8 was stably transfected with sense or antisense Tbx2. Immunohistochemistry and Western blotting was used to study Tbx2 and Cx43 expression in these cells and sections of embedded developing coronal sutures. RESULTS: The ROS 17/2.8 cells transfected with antisense Tbx2 showed a decrease in expression of Tbx2 protein and an increase in expression of endogenous Cx43. The reverse is seen with sense-transfected cells. Both of these proteins are expressed in rat developing coronal sutures. The pattern of Tbx2 expression in the developing was also reciprocal to the pattern of Cx43 expression. Tbx2 protein is concentrated in the center of the sutural blastema, an area devoid of Cx43 protein localization. Conversely, Tbx2 protein expression is low in the periphery of the sutures, in which there is high Cx43 protein expression. CONCLUSIONS: Taken together, these studies suggest that Tbx2 protein is a negative regulator of Cx43 expression at the transcriptional level in cranial sutures in vivo.

Animals↗
PubMed2003

Digital image analysis of cadaver mandibular trabecular bone patterns.

BACKGROUND: The purpose of this study was to investigate the source of radiographic trabecular patterns by removing trabecular bone in four sequential steps from six cadaver mandible sections, radiographing the sections after each removal, and using four digital-image analysis methods to quantify any resulting changes to the radiographs. METHODS: Mandible sections were cut sagittally into halves. Trabecular bone was removed from each section in four stages. Following each stage, standardized radiographs were taken, using direct digital equipment. Trabecular bone in the resulting digital images was measured with four methods. Mean gray level values (method 1) and cumulative percent histograms (method 2) were calculated from the raw data. Morphological image processing was used to skeletonize the trabecular structure, which was quantified by counting the number of trabecular ends and segments in the skeletonized images (method 3) and performing fractal analyses of the skeletonized images (method 4). Repeated measures analysis of variance (ANOVA) was used to test for changes in measurements attributable to bone removal. RESULTS: Repeated measures ANOVA indicated that the use of gray levels, cumulative percent histograms, and morphologic operators resulted in highly significant changes in measurements following bone removal (P < 0.01). Ends and segments demonstrated similar performance, with changes highly significant over time (P < 0.01). Fractal analysis also resulted in highly significant changes over time (P < 0.01). CONCLUSIONS: The analyses performed in this study demonstrated consistent image differences following the four steps of bone removal. These differences appeared whether light, cancellous bone or heavier endosteal bone was removed. These findings indicate that trabecular and endosteal bone combine to form the structure that most dentists identify as trabeculae on intraoral radiographs.

Analysis of Variance↗
PubMed2002

Taurine in submandibular gland of the rat: effect of muscarinic drugs.

Taurine exerts a number of actions in mammalian cells, including regulation of ion transport and osmoregulation. The production and secretion of saliva involve transepithelial ion transport, thereby making the plasma-like primary saliva hypotonic before secretion. Therefore, it is plausible to suggest modulation of salivary taurine by muscarinic agents that affect salivary gland function. One of the objectives of this study was to determine tissue content and localization of taurine in the submandibular gland of the rat. Further, we determined whether treatment with muscarinic drugs that either increase (e.g., pilocarpine) or decrease (e.g., propantheline) saliva secretion affects the submandibular gland taurine content. The results indicate that the submandibular gland contains an appreciable amount of taurine (8.9 +/- 0.3 micromoles/g wet wt). Further, acute treatment of the rats with either of the muscarinic drugs did not significantly affect tissue taurine content compared to the control group. By contrast, chronic treatment with propantheline, but not pilocarpine, reduced the tissue content of taurine compared to the control rats (p<0.05). Utilizing light microscopic immunohistochemical techniques, intense immunoreactivity was found primarily in the striated ducts of the submandibular gland. Neither pilocarpine nor propantheline treatment led to differential distribution of immunoreactivity in this tissue. In conclusion, the submandibular gland contains an appreciable amount of taurine, primarily in the striated ducts, that can be decreased by chronic muscarinic receptor blockade.

Animals↗
PubMedDate not supplied

Chemoprevention of oral cancer by green tea.

Green tea has been a popular beverage for many centuries. Only recently, however, has the anti-cancer power of green tea constituents been unveiled. Green tea polyphenols are found to induce apoptosis (programmed cell death) in many types of tumor cells, including oral cancer cells. However, mechanisms that enable normal cells to evade the apoptotic effect still are not understood. In this study, cell growth and invasion assays combined with apoptosis assays were used to examine the effects of green tea extracts, green tea polyphenols, and the most potent green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), on normal human keratinocytes and oral carcinoma cells. The results showed that green tea and its constituents selectively induce apoptosis only in oral carcinoma cells, while EGCG was able to inhibit the growth and invasion of oral carcinoma cells. These differential responses to green tea and its constituents between normal and malignant cells were correlated with the induction of p57, a cell cycle regulator. These data suggest that the chemopreventive effects of green tea polyphenols may involve a p57 mediated survival pathway in normal epithelial cells, while oral carcinoma cells undergo an apoptotic pathway. Therefore, regular consumption of green tea could be beneficial in the prevention of oral cancer.

Antineoplastic Agents, Phytogenic↗