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Biomedical subjects

S Koka

Publications and source records attributed to S Koka.

At least 19 recordsLinked to original sources
PubMed2006

Cellular toxicity of mineral trioxide aggregate mixed with an alternative delivery vehicle.

OBJECTIVE: Mineral trioxide aggregate (MTA) mixed with water has a short working time, delayed setting, and poor consistency. A preliminary study suggested that substituting KY Jelly as a mixing vehicle improves the working properties of MTA. The present study compared the biocompatibility of white MTA mixed with water or with KY Jelly to that of Fuji II cement and of silver amalgam. STUDY DESIGN: Periodontal ligament (PDL) cells were cultured using standard laboratory procedures. Cells were plated in wells at a density of 10,000 cells/well. The test materials were mixed and eluate placed in contact with the PDL cells. Cell viability was determined by measuring mitochondrial enzyme activity using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenytl)-2H-tetrazolium inner salt assay. Cytotoxicity was also measured in terms of cell lysis using the lactate dehydrogenase assay. The assays were completed in triplicate after time intervals of 24, 48, and 72 h. Mean cell counts were calculated and converted to a percentage of control results. A 2-way analysis of variance and Tukey honestly significant difference post-hoc test were performed to determine statistical significance. RESULTS: Eluate extractions from all materials caused significantly less cell viability and more cell death than control eluate (medium only) at all eluate time points tested. However, at 72 h the MTA/water, MTA/KY, and amalgam eluate extractions led to significantly better cell viability than the Fuji II eluates. However, there was significantly greater cell lysis for all eluates from the tested materials at 72 h than at 24 h. CONCLUSIONS: Within the limitations of this in vitro study, we conclude that MTA/KY, MTA/water, and amalgam have similar biocompatibility regarding effects of their eluates on human PDL cells, and eluates from all 3 materials demonstrate better biocompatibility than eluates derived from a resin-modified glass ionomer cement.

Aluminum Compounds↗
PubMed2002

Regulation of TNF-alpha-induced IL-6 production in MG-63 human osteoblast-like cells.

Tumor necrosis factor-alpha (TNF-alpha) stimulates osteoblast production of interleukin-6 (IL-6), an inflammatory cytokine implicated in osteoclastic bone resorption. Therefore, we tested the hypothesis that TNF-alpha-induced IL-6 production in MG-63 osteosarcoma cells occurs via the p38 mitogen-activated protein kinase (MAPK) pathway. TNF-alpha activated p38 MAPK and stimulated IL-6 secretion by MG-63 cells, and pre-incubation of cells with the p38 MAPK inhibitor abrogated TNF-alpha-dependent IL-6 secretion. Transfection of IL-6 full-length and 5-deletion gene promoter reporter constructs indicated that p38 MAPK activation by TNF-alpha enhanced IL-6 gene expression, and that the p38 MAPK-responsive region resided in the proximal 260-bp segment. Transfection of NFkappaB and C/EBPbeta-sensitive reporter promoter constructs demonstrated that NFkappaB activity was enhanced and that constitutive C/EBPbeta was inhibited by TNF-alpha, with both effects being p38 MAPK-dependent. In conclusion, although p38 MAPK activation by TNF-alpha stimulates IL-6 secretion by MG-63 cells, it has opposing effects on c/EBPbeta and NFkappaB activity.

Analysis of Variance↗
PubMed2001

Ligation of CD40 stimulates the induction of nitric-oxide synthase in microglial cells.

The present study was undertaken to investigate the role of CD40 ligation in the expression of inducible nitric-oxide synthase (iNOS) in mouse BV-2 microglial cells and primary microglia. Ligation of CD40 alone by either cross-linking antibodies against CD40 or a recombinant CD40 ligand (CD154) was unable to induce the production of NO in BV-2 microglial cells. The absence of induction of NO production by CD40 ligation alone even in CD40-overexpressed BV-2 microglial cells suggests that a signal transduced by the ligation of CD40 alone is not sufficient to induce NO production. However, CD40 ligation markedly stimulated interferon-gamma (IFN-gamma)-mediated NO production. Ligation of CD40 in CD40-overexpressed cells further stimulated IFN-gamma-induced production of NO. This stimulation of NO production was accompanied by stimulation of the iNOS protein and mRNA. In addition to BV-2 glial cells, CD40 ligation also stimulated IFN-gamma-mediated NO production in mouse primary microglia and peritoneal macrophages. To understand the mechanism of induction/stimulation of iNOS, we investigated the roles of nuclear factor kappaB (NF-kappaB) and CCAAT/enhancer-binding protein beta (C/EBPbeta), transcription factors responsible for the induction of iNOS. IFN-gamma alone was able to induce the activation of NF-kappaB as well as C/EBPbeta. However, CD40 ligation alone induced the activation of only NF-kappaB but not of C/EBPbeta, suggesting that the activation of NF-kappaB alone by CD40 ligation is not sufficient to induce the expression of iNOS and that the activation of C/EBPbeta is also necessary for the expression of iNOS. Consistently, dominant-negative mutants of p65 (Deltap65) and C/EBPbeta (DeltaC/EBPbeta) inhibited the expression of iNOS in BV-2 microglial cells that were stimulated with the combination of IFN-gamma and CD40 ligand. Stimulation of IFN-gamma-mediated activation of NF-kappaB but not of C/EBPbeta by CD40 ligation suggests that CD40 ligation stimulates the expression of iNOS in IFN-gamma-treated BV-2 microglial cells through the stimulation of NF-kappaB activation. This study illustrates a novel role for CD40 ligation in stimulating the expression of iNOS in microglial cells, which may participate in the pathogenesis of neuroinflammatory diseases.

Animals↗
PubMed2001

The influence of intracrevicular crown margins on gingival health: preliminary findings.

STATEMENT OF PROBLEM: The effect on gingival tissue of various crown materials in combination with different abutment biomaterials should be investigated. PURPOSE: This in vivo study determined the gingival health and subgingival levels of periodontal inflammation-associated bacteria adjacent to various crown and abutment material combinations. MATERIAL AND METHODS: . Patients in the study received 1 of 5 treatments: an all-ceramic crown luted to a natural tooth, a metal-ceramic (titanium) crown luted to natural tooth, a metal-ceramic (high noble alloy) crown luted to natural tooth, an all-ceramic crown luted to a titanium implant abutment, or a metal-ceramic (high noble alloy) crown luted to a titanium implant abutment. Plaque was collected at least 6 months after luting by paper point from the gingival sulcus of each crown and an adjacent unrestored (control) tooth. DNA probe analysis was performed to determine the levels of Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans. In addition, plaque, gingival redness, swelling, and bleeding scores were recorded with use of the California Dental Association scale. Statistical analysis was used to determine the effect of restoration/abutment type on levels of the bacterial species and clinical parameters pertaining to gingival health. RESULTS: None of the sulci sampled contained detectable levels of the 3 bacteria. Plaque levels and gingival redness, swelling, and bleeding scores were low. All treatment groups had similar soft tissue response as measured by gingival redness, swelling, and bleeding. Plaque scores from all-ceramic crown/implant abutment sites were higher than plaque scores from all-ceramic crown/natural tooth sites. However, differences between experimental and control sites within the same treatment group were not observed (P>.05) with any of the 4 clinical measures. CONCLUSION: In patients with suitable oral hygiene, tooth-supported and implant-supported crowns with intracrevicular margins were not predisposed to unfavorable gingival and microbial responses.

Aggregatibacter actinomycetemcomitans↗
PubMed2000

Effects of abutment size and luting cement type on the uniaxial retention force of implant-supported crowns.

STATEMENT OF PROBLEM: The assumption that increasing the diameter of the abutment/crown components will provide greater resistance to crown loosening forces than standard-sized components has not been reported either with clinical trials or in the laboratory. PURPOSE: This study attempted to determine what effect abutment dimension and type of luting agent have on the retention of the prosthetic crown. METHODS AND MATERIAL: Test specimens consisted of standard, wide, and "experimental" CeraOne titanium abutments and matching CeraOne gold cylinders cemented with a zinc phosphate permanent or a zinc oxide eugenol provisional cement. The mean uniaxial force (Newtons) and the load (MPa) required to dislodge the cylinder from the abutment was determined. Statistical analysis of the sample data was performed using a 2-way analysis of variance test (alpha=.05). RESULTS: Mean uniaxial resistance force (Newtons) was significantly greater for zinc phosphate cement than for zinc oxide cement (P <. 001). Abutment size was a significant factor when permanent luting cement is used (P <.001). Retention strength per unit area (MPa) of the wide abutments was lower than the standard size and "experimental" abutments. CONCLUSION: Permanent luting cement produced uniaxial retention forces approximately 3 times greater than provisional cement. The increase in surface area provided by a wide abutment did not result in an improvement in retention strength over the standard abutment.

Analysis of Variance↗
PubMed2000

How to evaluate a diagnostic test.

Tests are used in dentistry to establish, confirm, or reject the clinical impression of a diagnosis. Not all tests are equal in their ability to establish a diagnosis, with some tests demonstrating positive results when no disease is present (false positive) or negative results when disease is present (false negative). Using simple mathematical computations, it is possible to determine the extent to which a test can reliably establish the presence or absence of disease. This article describes the concepts of sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratios through the evaluation of a clinically relevant paper on vital staining for oral carcinoma. This article also describes methods for literature evaluation to determine whether a test conveys meaningful diagnostic information.

Carcinoma↗
PubMed2000

C5a modulation of interleukin-1 beta-induced interleukin-6 production by human osteoblast-like cells.

Periodontal bone resorption is controlled by osteoblast products, including interleukin (IL)-6, which are stimulated by other cytokines and complement components in the pro-inflammatory milieu. This study demonstrated that human osteoblast-like osteosarcoma cells (MG-63) responded to human recombinant (hr) C5a by releasing significant amounts of the bone-resorbing cytokine IL-6. C5a-induced release of IL-6 was enhanced 330% when cells were exposed to IL-1beta prior to C5a challenge at optimal concentrations (1.0 microg/ml C5a, 0.1 ng/ml IL-1beta). Cells simultaneously challenged with these concentrations of C5a and IL-1beta produced a 700% increase in IL-6 release relative to cells challenged with IL-1beta alone. Incubation of IL-1beta-treated cells with anti-human C5a receptor (C5aR) Ab resulted in a 78% suppression of the C5a-induced release of IL-6, but C5aR neutralization did not affect C5a/IL-1beta co-stimulation of IL-6. In addition, neither IL-1beta nor C5a significantly altered the other's cell-surface receptor relative to binding affinity or density. These results indicate that while MG-63 cells express functional C5aRs, the synergistic effect of C5a and IL-1beta on osteoblast IL-6 production is probably controlled by post-receptor signaling events. C5a agonists and antagonist used to alter critical C5a concentrations may present a new point of therapeutic intervention for the treatment of inflammatory bone resorption such as is found in periodontitis.

Alveolar Bone Loss↗
PubMed1999

Qualitative and quantitative determination of dental amalgam restoration volume.

STATEMENT OF PROBLEM: Volume of tooth structure replaced by an existing restoration, as assessed by visual and radiographic examination, is one diagnostic measure used by dental practitioners and dental insurance agencies to determine the relative need to restore a tooth with a full-coverage cast restoration. However, use of these methods has not been validated. PURPOSE: This study compared the volume of a range of dental amalgam restorations placed in typodont teeth, as estimated by dentists, dental students and laypersons, with the actual volume of each restoration. METHODS AND MATERIAL: Sixty subjects (20 dental school faculty, 20 dental students, and 20 clerical staff [laypersons]) participated. After reviewing photographic images of typodont teeth with mesial-occlusal-distal dental amalgam restorations, subjects estimated the volume of each restoration using various restorations on different teeth as a percentage of its tooth's coronal volume. The actual volume of each dental amalgam restoration and that of the coronal portion of the prepared teeth was calculated with a volumetric displacement technique. The single sample 2-sided t test with a.05 level of significance was used to evaluate the null hypothesis (H0 ): The survey participant's estimates of each restoration's percentage volume are the same as the measured volume values versus the alternative hypothesis (H1 ): estimates differed from the measured volume values. One-way analysis of variance was used to determine the significance of any difference between the estimates of the 3 survey test groups. RESULTS: Average volumes reported by all 3 groups were significantly different than the measured volume values (P <.05). Experience and dental training did not significantly affect a participant's ability to evaluate restoration volumes with greater accuracy. Results reported by dentists, dental students, and laypersons were not significantly different (P >.05). CONCLUSIONS: The volume of a restoration is inaccurately assessed by visual and radiographic examination.

Analysis of Variance↗
PubMed1998

Cytotoxicity of root perforation repair materials.

The cytotoxicity of restorative dental materials must be investigated to ensure a safe biological response. The MTS assay, a valid and reliable measure of cell viability based on the mitochondrial activity of cultured cells, was used to evaluate the affects on human periodontal ligament (PDL) cells of two resin-modified glass ionomer cements (R-M GICs) (Fuji Duet and Fuji II LC, GC America, Chicago, IL) and one dental amalgam (Contour, Caulk, York, PA)-all suggested materials for root perforation repair. Twelve 4 x 6 mm cylinders of each material were fabricated and placed in 5 ml of alpha-minimum essential medium supplemented with 100 micrograms/ml of penicillin, 50 micrograms/ml of gentamicin, and 5% fetal bovine serum for 24, 48, and 72 h (n = 3). One hundred microliters of eluate was transferred to triplicate wells containing PDL cells previously plated at a density of 10,000 cells/well in a 96-well plate, and incubated for 24 h at 37 degrees C with 5% carbon dioxide. alpha-Minimum essential medium with supplements provided baseline data. Optical density at 490 nm, directly proportional to the number of viable cells, was determined according to manufacturer instructions. Analysis of variance was used to detect differences between treatments and Tukey's HSD (p < 0.05) to detect for differences between group means. Results demonstrated that both material and time affected cell viability (p < 0.0001), with amalgam eluate significantly inhibitory on cell viability at 24 h, compared with control and the two other tested materials. At 48 and 72 h, all three materials exhibited a similar slightly inhibitory effect on the cell viability. Use of resin-modified glass ionomer cement as a root perforation repair material initially (< 24 h) may result in a more favorable response by PDL cells than the tested dental amalgam.

Adult↗
PubMed1998

Estrogen inhibits interleukin-1beta-induced interleukin-6 production by human osteoblast-like cells.

Estrogen supplements are the primary pharmacologic intervention therapy to prevent and treat loss of bone mass (osteoporosis) in postmenopausal women. Furthermore, at sites of local inflammation near bone, estrogen-deficient women are significantly more susceptible to bone loss than are estrogen-sufficient women. In the present study, we investigate whether estrogen modulates osteoblast (MG-63) production of interleukin-6 (IL-6), an osteoclast recruitment and differentiation of cytokine, in the presence of the proinflammatory cytokine, IL-1beta. Using enzyme-linked immunosorbent assay (ELISA), we demonstrate that IL-1beta significantly enhances IL-6 secretion into culture supernatants in a dose-dependent and time-dependent manner. Using reverse-transcriptase polymerase chain reaction (RT-PCR) and ELISA respectively, we demonstrate further that levels of 17beta-estradiol (active metabolite of estrogen) > or = those found in serum of estrogen-sufficient women inhibit steady-state IL-6 mRNA levels as well as inhibit secretion of IL-6 into culture supernatants. One mechanism by which estrogen therapy preserves bone mass in areas of inflammation may be via inhibition of IL-1beta-stimulated obsteoblast-derived IL-6.

Enzyme-Linked Immunosorbent Assay↗
PubMed1998

Wiropress SL: a multipurpose dental pressure vessel with transparent chamber.

Pneumatic vessels used in dentistry provide a pressurized environment to enhance the outcome of many laboratory procedures. A pressurized environment directs volume loss associated with polymerization shrinkage, minimizes air inclusions in powder/liquid mixtures, raises the boiling point of liquids, and facilitates flow of impression and replication materials, improving surface detail. The following report illustrates the usefulness of a reliable pneumatic vessel during denture base repair resin processing and replication of pattern details.

Acrylic Resins↗
PubMed1997

Periodontal pathogen-related stimulation indicates unique phenotype of primary cultured human fibroblasts from gingiva and periodontal ligament: implications for oral health disease.

STATEMENT OF PROBLEM: The fibroblast is considered an important cellular component in periodontitis because it is the predominant cell type in periodontal connective tissue. PURPOSE: The purpose of this study was to test whether gingival fibroblasts (GF) and periodontal ligament fibroblasts (PDLF) are heterogeneous in their production of inflammatory mediators associated with bone resorption in response to lipopolysaccharides from the gram-negative bacterium Porphyromonas gingivalis. To test this hypothesis, we (1) compared interleukin-6 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide; and (2) compared prostaglandin-E2 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide. MATERIAL AND METHODS: Human periodontal ligament and gingival fibroblasts were cultured from biopsies and exposed to P. gingivalis lipopolysaccharide. Levels of interleukin-6 and prostaglandin-E2 secreted into culture supernatant were measured by enzyme-linked immunosorbent assay and the data analyzed. Gingival fibroblasts secreted similar interleukin-6 and elevated prostaglandin-E2 levels compared with unstimulated cells. Periodontal ligament fibroblasts secreted elevated levels of both mediators compared with unstimulated cells. Secreted levels of interleukin-6 and prostaglandin-E2 by primary gingival and periodontal ligament fibroblast cultures appear to differ when stimulated with a periodontal pathogen-related virulence factor. CONCLUSION: The fibroblast of the periodontal ligament and the fibroblast of the gingiva may represent different phenotypes that play unique roles in tissue responses to implants.

Analysis of Variance↗
PubMed1997

Retention of cemented implant-supported restorations.

PURPOSE: This investigation compared cement failure loads of a gold cylinder luted to a CeraOne titanium abutment (5-mm-high chimney) 24 hours postcementation when either zinc phosphate, Tempbond NE, or Tempbond luting agent was used. MATERIALS AND METHODS: Luting agent (0.01 mL) was applied to the internal aspect of the gold cylinder, and the cylinder was seated with finger pressure followed by a load of 5 kg for 10 minutes. The specimens were stored in 100% humidity at 37 degrees C for 24 hours before a uniaxial tensile force was applied to the gold cylinder by a mechanical testing instrument. A load-displacement chart was plotted and the cement failure load (CFL) calculated in kilograms. CFLs were determined for each luting agent with the access opening for the CeraOne gold screw on the internal of the abutment either unfilled or filled with autopolymerizing resin. RESULTS: A two-way ANOVA and Turkey's HSD revealed that zinc phosphate resulted in significantly higher (p < .05) mean CFLs than Tempbond or Tempbond NE. In general, filling the access opening did not affect mean CFLs for zinc phosphate and Tempbond NE. However, mean CFLs for gold cylinders cemented with Tempbond and a filled access opening were significantly higher than mean CFLs with an unfilled access opening. However, neither the filled nor the unfilled Tempbond group mean CFL was significantly different from either Tempbond NE mean CFL. CONCLUSIONS: Twenty-four hours postcementation, zinc phosphate luting cement significantly enhanced CFLs of a CeraOne gold cylinder luted to a 5-mm CeraOne titanium abutment compared with Tempbond and Tempbond NE. Filling the gold screw access opening of the abutment with autopolymerizing resin only led to higher mean CFLs when Tempbond was used as the luting agent. Filling the access opening had no effect (p > .05) on mean CFLs when Tempbond NE or zinc phosphate was used.

Analysis of Variance↗
PubMed1997

Microwave pressure chamber processing of a denture repair polymer.

Most denture base repairs are made using a chemically activated acrylic resin polymer for reasons of cost and expediency. Heat-activated polymers are not typically used because they require a custom split cast gypsum mold, longer polymerization time, and higher laboratory fees. Repairs made using a chemically activated polymer compared with a heat-activated polymer generally have reduced transverse strength, poorer color stability, increased water sorption, and weak bond strength to existing acrylic resin. A method of utilizing a microwave polymer in a commercially available microwave flask is described. This technique allows denture base repairs to be made with a heat-activated polymer in a manner similar to that of chemically activated repairs.

Acrylic Resins↗
PubMed1996

Intraoral recontouring aid.

This article describes a procedure and a device to expedite the intraoral recontouring of teeth to receive removable partial dentures. This procedure is particularly useful when heights of contour are lowered on posterior teeth and the path of insertion is perpendicular to the plane of occlusion.

Dental Occlusion, Balanced↗
PubMed1996

Factors influencing retention of a CeraOne gold cylinder.

Missing single teeth may be replaced using an endosseous dental implant. The CeraOne system uses a gold alloy cylinder that is cemented to a titanium abutment. This study evaluated the effect of three variables on cement failure loads required to unseat a gold alloy cylinder from its abutment. Two chimney heights (commercially available 3.7 mm and custom fabricated 5.0mm), three luting agents (zinc phosphate, Tempbond NE, and Tempbond), and two luting volumes (0.01 mL and 0.02 mL) were tested. A mechanical testing instrument was used to exert a uniaxial tensile force on the gold cylinders 2 hours after cementation. An analysis of variance and Tukey post hoc test demonstrated that both the choice of luting agent and chimney height affected cement failure loads (P <0.0001). An interactive effect between luting agent and chimney height was observed, with the combination of zinc phosphate and a 5.0 mm abutment-gold alloy cylinder complex resulting in significantly greater retention (P<0.0001). The use of 0.01 mL or 0.02 mL of luting agent resulted in comparable retention values. The results indicate that both chimney height and choice of luting agent may affect retention of a CeraOne gold alloy cylinder. The use of 0.01 mL of luting agent is recommended to minimize expression of excess cement at the restoration-abutment interface.

Analysis of Variance↗