Effect of surface conditioning methods on the bond strength of luting cement to ceramics

OBJECTIVES: This study evaluated the effect of three different surface conditioning methods on the bond strength of a Bis-GMA based luting cement to six commercial dental ceramics. METHODS: Six disc shaped ceramic specimens (glass ceramics, glass infiltrated alumina, glass infiltrated zirconium dioxide reinforced alumina) were used for each test group yielding a total number of 216 specimens. The specimens in each group were randomly assigned to one of the each following treatment conditions: (1) hydrofluoric acid etching, (2) airborne particle abrasion, (3) tribochemical silica coating. The resin composite luting cement was bonded to the conditioned and silanized ceramics using polyethylene molds. All specimens were tested at dry and thermocycled (6.000, 5-55 degrees C, 30 s) conditions. The shear bond strength of luting cement to ceramics was measured in a universal testing machine (1 mm/min). RESULTS: In dry conditions, acid etched glass ceramics exhibited significantly higher results (26.4-29.4 MPa) than those of glass infiltrated alumina ceramics (5.3-18.1 MPa) or zirconium dioxide (8.1 MPa) (ANOVA, P<0.001). Silica coating with silanization increased the bond strength significantly for high-alumina ceramics (8.5-21.8 MPa) and glass infiltrated zirconium dioxide ceramic (17.4 MPa) compared to that of airborne particle abrasion (ANOVA, P<0.001). Thermocycling decreased the bond strengths significantly after all of the conditioning methods tested. SIGNIFICANCE: Bond strengths of the luting cement tested on the dental ceramics following surface conditioning methods varied in accordance with the ceramic types. Hydrofluoric acid gel was effective mostly on the ceramics having glassy matrix in their structures. Roughening the ceramic surfaces with air particle abrasion provided higher bond strengths for high-alumina ceramics and the values increased more significantly after silica coating/silanization.     

Damage mechanics and load failure of fiber-reinforced composite fixed partial dentures

OBJECTIVES: Damage mechanics has been defined as the study of the initiation (initial failure) and accumulation of damage to and including rupture (final failure). This study was designed to evaluate the effect of increasing fiber-reinforced composite (FRC) substructure within a standardized fixed partial denture (FPD) model on the failure performance, in terms of damage mechanics. METHODS: The two FRC restorative systems, Targis/Vectris (TV) (Ivoclar Vivadent) and EverStick (ES) (Stick Tech with Gradia, GC Corp.), were used to restore the molar FPD model (1.5 mm axial and 2.0 mm occlusal reduction). Templates were used to standardize substructure designs with 0, 18, 43, and 66% cross-sectional FRC volume fraction (V(FRC)) of fiber substructure. Specimens (n = 5) were homogenized at 29 points and stored for 1 week at 37 degrees C in distilled water. Specimens were luted with calcium hydroxide, then statically loaded until failure. Initial failure (IF), final failure (FF) and the mode of failure were recorded. RESULTS: The lowest mean load to initial failure was 530 N (TV 18%) and the highest was 1208 N (ES 66%). Linear regression analysis calculated the Pearson's correlation coefficient (r) for the interactions between V(FRC) and IF (ES: r = 0.7879, TV: r = 0.6184), V(FRC) and FF (ES: r = 0.912, TV: r = 0.8152), and between IF and FF (ES: r = 0.892, TV: r = 0.7237). Unreinforced specimens universally fractured instantaneously. SIGNIFICANCE: The highest loads to initial and final failure were yielded by specimens with the highest cross-sectional V(FRC).     

The synthesis and localization of alternatively spliced fibronectin EIIIB in resting and thrombin-treated megakaryocytes

There are several species of alternatively spliced fibronectin (FN). One of these, FN EIIIB, is primarily present in embryonic and in proliferating and migrating cells and is believed to be important for cell maturation. We have studied the synthesis, localization, and secretion of this FN isoform in isolated guinea pig megakaryocytes, nonmegakaryocytic bone marrow cells, and platelets. There was 7.5 times more general FN in megakaryocytes than in nonmegakaryocytic cells based on the analysis of equivalent amounts of protein. FN EIIIB was detected by Western blotting in megakaryocytes but not in nonmegakaryocytic cells present in bone marrow. Neither megakaryocytes nor platelets secreted FN EIIIB, while megakaryocytes secreted 25.3% +/- 4.6% general FN and platelets secreted about 61% general FN in response to thrombin. Analysis of immunostained cells by confocal microscopy revealed that FN EIIIB had been redistributed to the surface of megakaryocytes in response to thrombin. Synthesis was studied by metabolic labeling, and megakaryocytes were shown to synthesize FN and FN EIIIB. Thus, megakaryocytes and platelets are among a small number of adult cells and tissues that synthesize and contain FN EIIIB. The expression of FN EIIIB on the megakaryocyte surface may influence migration and maturation.     

The bond strength of light-curing composite resin to finally polymerized and aged glass fiber-reinforced composite substrate

OBJECTIVE: This study examines the shear bond strength of visible light-curing composite resin (VCR) to aged glass fiber-reinforced composite (FRC) substrate with multi-phase polymer matrix. METHODS: Linear polymethyl methacrylate and dimethacrylate monomer preimpregnated unidirectional glass fiber reinforcement was used as an adhesion substrate for low-viscosity diacrylate veneering composite resin and restorative composite resin. A total of 60 test specimens were divided into three groups according to the brand and the use of an intermediate monomer resin (IMR). The used IMRs were either BisGMA-HEMA-resin, BisGMA-TEGDMA resin or the controls were left without the IMR treatment. Dry- and water-stored FRC-substrates were used for adhering the VCR with or without the IMR. The shear bond strength of the VCR to the substrate was measured for dry and thermocycled specimens and the results were analyzed with multi-variate ANOVA. RESULTS: The highest mean shear bond strength (23.9 +/- 4.8 MPa) was achieved with FRC/BisGMA-HEMA/VCR combination when the FRC substrate was water stored and the test specimen was thermocycled. FRC/BisGMA-TEGDMA/VCR combination resulted in 15.7 +/- 6.0 MPa with the water-stored FRC substrate and after thermocycling of the test specimens. The lowest shear bond strength (1.0 +/- 0.5 MPa) was obtained with FRC/VCR combination with water-stored substrate and after thermocycling of the test specimens. Significant differences were found between the mean values of three groups according to the use of IMR (p<0.001). The storage conditions of the FRC substrate were related to brand of the IMR or the composite (p<0.001). High mean values of the shear bond strength after thermocycling fatigue were related to the type of IMR (p<0.001). SIGNIFICANCE: The results suggest that the IMRs used in this study greatly influence the mean shear bond strength values when the test specimens are thermocycled.     

VIRAL ENCEPHALITIS PRESENTING AS CATATONIC SCHIZOPHRENIA (A Case Report)

A rare case of viral encephalitis in an 18 year old recruit who presented with signs of catatonic schizophrenia is reported.KEY WORDS: Viral encephalitis, Catatonic schizophrenia     

ROLE OF EPIDURAL MEDICATION IN LUMBOSCIATIC SYNDROME

Role of epidural medication through caudal route was studied in 109 patients having lumbago with or without sciatica to highlight the value of this mode of treatment which relieved symptoms in more than 70% of cases without hospitalisation and without being off work for long periods as in usual methods of conservative treatment.KEY WORDS: Epidural medication, Backache, Lumbago, Sciatica