Effect of universal testing machine crosshead speed on the shear bond strength and bonding failure mode of composite resin to enamel and dentin

An investigation was conducted to determine if testing machine crosshead speed influenced shear bond strength (SBS) or the failure mode of composite bonded to enamel and dentin. Composite cylinders were bonded to 50 enamel and 50 dentin surfaces and thermocycled. Groups of 10 samples were debonded at speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. Data were examined with analysis of variance and post-hoc testing. Failure modes were determined using 10x magnification. With enamel, no significant differences in SBS existed, and cohesive vs. adhesive failure modes were similar for all groups. With dentin, the 0.5, 1.0, and 5.0 mm/min samples had significantly higher SBS than the 0.1 and 10.0 mm/min samples (p < 0.05). No other differences in SBS were found. Samples tested at 0.5 mm/min demonstrated strikingly better cohesive vs. adhesive results than all other groups. SBS and cohesive vs. adhesive failures achieved with dentin bonding were significantly affected by crosshead speed.     

Gingival seal of deep Class II direct and indirect composite restorations

PURPOSE: To evaluate in vitro the gingival microleakage of Class II direct and indirect composite restorations with cervical margins 0.5 mm apical to the cemento-enamel junction (CEJ). METHODS: Mesial-occusal (MO) preparations of similar size were made in 10 homologous pairs of caries-free extracted human third molars. One specimen for each pair was prepared for a direct composite restoration and the other for an indirect composite restoration. Direct preparations were restored per manufacturer's instructions. Indirect preparations were impressed, and composite restorations were fabricated and cemented with a dual-cure cement. A total-etch technique was used for all restorations. Restorations were finished, polished, stored for 1 week in distilled water at 37 degrees C, thermocycled (5 degrees-55 degrees C x 1000), sealed with fingernail polish (leaving a 1.5 mm open periphery adjacent to the gingival margin), and placed in 0.5% basic fuchsin dye for 24 hours. Teeth were sectioned longitudinally (mesio-distally) within the restoration in two cuts and the four resulting surfaces (two inner cut surfaces, two outer cut surfaces) were evaluated for dye penetration with a x10 stereoscope using a scale of 0 (no penetration) to 4 (dye penetration involving more than half the axial wall). RESULTS: All 20 specimens had at least one score of three (dye penetration involving less than half of the axial wall) or four. Statistical analysis (Wilcoxon paired-sample test) disclosed a significant decrease in the indirect composite microleakage scores for the two outer cuts (P = 0.006, P = 0.002). No significant differences in microleakage scores were found between materials for the inner cut surfaces of the specimens. Overall, the results of die penetration showed no statistical difference between Class II direct and indirect composite restorations for microleakage.     

Lipid-mediated resistance of Gram-negative bacteria against various pore-forming antimicrobial peptides

Lipopolysaccharides (LPSs) play a dual role as target and as effector molecules. The knowledge of the LPS-induced activation of human immune cells is increasing; however, surprisingly, much less effort seems to be directed towards the understanding of the mechanisms leading to the killing of the bacterial organisms, which eventually results in the release of LPS from the bacterial surface into the blood circulation. We demonstrate mechanisms of interaction of peptides of the innate immune system (e.g. defensins and cathelicidins) as well as of externally administered antibiotics (e.g. Polymyxin B) with Gram-negative bacteria. The main focus is directed on data derived from electrical measurements on a reconstitution system of the outer membrane as an asymmetric bilayer composed on one side of LPS and on the other of phospholipids. All these antimicrobial peptides (AMPs) are membrane-active and induce the permeabilization of the reconstituted membranes by the formation of lesions. We found that differences in the activity of the AMPs against various sensitive and resistant Gram-negative bacteria can be explained solely by variations in the chemical structure of LPS, e.g. in the composition of the sugar head group. A reduction of the net negative charge of LPS is responsible for a reduced interaction with the polycationic AMPs and thus for resistance. A most important side effect of positively charged AMPs is the neutralization of the negatively charged LPS released from the bacterial surface as a consequence of AMP-induced killing.     

A differential diagnosis in chronic lower abdominal pain

INTRODUCTIONSpigelian hernias represent 0.12–2.4% of all abdominal wall hernias. Its diagnosis is elusive and requires a high level of conjecture given the disease rarity, vague associated abdominal complaints and frequent lack of consistent physical findings.PRESENTATION OF CASEA 60-year-old woman presented with a history of chronic pain in the left lower side of the abdomen. The patient was treated for several diseases with no relief of symptoms. Abdominal ultrasound showed a Spigelian hernia in the lower left abdomen and surgery was scheduled for treatment.DISCUSSIONA SH is generally an inter-parietal hernia, meaning that the pre-peritoneal fat and the hernia sac penetrate the trasnversus abdominis and internal oblique muscles but remain behind the external oblique aponeurosis. In most of the patients the lack of clinical signs demands radiological investigation. That's the importance of the high grade of suspicious of the disease during the physical exam. The surgical repair is necessary due to the high risk of incarceration-related complications which can occur in up to 21% of cases.CONCLUSIONIt's important to think in the Spigelian hernia as cause of lower abdominal pain to prompt indicate surgical repair and provide the patient's symptom relief. Also the type of repair is dependent on the surgeon's choice and also the means available in each center.     

Resin penetration through submicrometer hiatus structures: a SEM and CLSM study

The purpose of this study was to confirm the existence of submicrometer hiatus structures and to examine the degree of resin penetration through these formations. Dentin disks 2.0 mm in thickness were sectioned from 48 human molars with the use of a microtome saw. Three different fifth-generation (total-etch, combined primer/resin) dentin adhesive systems were used to bond a light-cured, resin-based composite to the dentin disks (n = 16 each group). Bonded disks from the three groups were then sectioned. Half of each group was examined with the use of a scanning electron microscope (SEM) (n = 8), and the other half with the use of a confocal laser scanning microscope (CLSM) (n = 8). The frequency of submicrometer hiatus formation was recorded and documented with associated imaging techniques. Resin penetration within submicrometer hiati were observed in 41.7% (10/24) of SEM specimens and 83.3% (20/24) of CLSM specimens. The location and size of these structures were found to be quite uniform. Submicrometer hiati approximated 200 microm in each of the three dentin bonding systems examined. Resin penetration through submicrometer hiati does not appear to be an artifact of desiccation. These structures were clearly identified within the hybrid layer of each dentin adhesive system used in this study.     

Effect of four intermediate layer treatments on microleakage of Class II composite restorations

This in vitro study examines the marginal sealing ability of four different intermediate materials applied before placement of a condensable composite. Class II preparations were made with gingival margins placed 1.0 mm apical to the cementoenamel junction of 60 extracted teeth, randomly assigned to five groups of 12. Following restoration, teeth were thermocycled, soaked in 0.5% basic fuchsin, and sectioned longitudinally. The resin-modified glass ionomer cement demonstrated significantly less microleakage than the use of a dentin bonding agent alone or in combination with flowable composite, flowable compomer, or autoploymerizing composite (p < 0.05, Dunn's test). This study supports the use of the glass ionomer open sandwich technique in deep Class II direct composite restorations.     

Effect of three root canal sealers on the retentive strength of endodontic posts luted with a resin cement

AIM: This investigation examined what effect three different sealers had on retention of endodontic posts (Parapost) luted with a resin cement (Panavia 21 OP). METHODOLOGY: Sixty-four single-rooted teeth were decoronated, filed, cleaned, and shaped with a size 5 Gates-Glidden drill and 0.12 taper G.T. rotary instrumentation (Dentsply/Tulsa Dental). Teeth were then divided into four groups of 16 each. Group 1 was not obturated, and served as a control. The other three groups were obturated with gutta-percha using a different sealer for each group. Group 2 used a eugenol containing sealer (Kerr Pulp Canal Sealer), group 3 a resin sealer (AH-26), and group 4 a calcium hydroxide sealer (Sealapex). After 1 week's storage at 100% humidity, 10-mm deep post spaces were prepared with a size 6 Gates-Glidden drill, and size 5 Paraposts were cemented. Following 48 h of storage, samples were mounted in a PVC pipe with acrylic, and the posts were removed vertically using a universal testing machine at 1 mm min-, with data recorded in kilograms. RESULTS: The mean values of force required to remove the posts were: group 1 = 61.80, SD = 16.21; group 2 = 43.14, SD = 14.66; group 3 = 48.54, SD = 17.84; group 4 = 53.52, SD = 18.77. Using anova and Bonferroni tests, group 1 demonstrated significantly greater mean retention strength values than group 2, but no other significant differences existed between groups. CONCLUSION: The chemical formulation of root canal sealers did not significantly affect the retention of endodontic posts luted with resin cement.