Streptococcus mutans biofilm transient viscoelastic fluid behaviour during high-velocity microsprays.

Using high-speed imaging we assessed Streptococcus mutans biofilm-fluid interactions during exposure to a 60-ms microspray burst with a maximum exit velocity of 51m/s. S. mutans UA159 biofilms were grown for 72h on 10mm-length glass slides pre-conditioned with porcine gastric mucin. Biofilm stiffness was measured by performing uniaxial-compression tests. We developed an in-vitro interproximal model which allowed the parallel insertion of two biofilm-colonized slides separated by a distance of 1mm and enabled high-speed imaging of the removal process at the surface. S. mutans biofilms were exposed to either a water microspray or an air-only microburst. High-speed videos provided further insight into the mechanical behaviour of biofilms as complex liquids and into high-shear fluid-biofilm interaction. We documented biofilms extremely transient fluid behaviour when exposed to the high-velocity microsprays. The presence of time-dependent recoil and residual deformation confirmed the pivotal role of viscoelasticity in biofilm removal. The air-only microburst was effective enough to remove some of the biofilm but created a smaller clearance zone underlying the importance of water and the air-water interface of drops moving over the solid surface in the removal process. Confocal and COMSTAT analysis showed the high-velocity water microspray caused up to a 99.9% reduction in biofilm thickness, biomass and area coverage, within the impact area.

High-Velocity Microsprays Enhance Antimicrobial Activity in Streptococcus mutans Biofilms.

Streptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm's complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. The authors assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-d-old S. mutans biofilms. Biofilms were exposed to a 90° or 30° impact, first using a 1-µm tracer bead solution (109 beads/mL) and, second, a 0.2% chlorhexidine (CHX) or 0.085% cetylpyridinium chloride (CPC) solution. For comparison, a 30-s diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth into the biofilm. Assessment of antimicrobial penetration was determined by calculating the killing depth detected by live/dead viability staining. The authors first demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared with diffusion and mouthwashing exposures. Next, these experiments revealed that the microspray yielded better antimicrobial penetration evidenced by deeper killing inside the biofilm and a wider killing zone around the zone of clearance than diffusion alone. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 20% more bacteria killing (for both CHX and CPC) than the 90° impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver microparticles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm-burst interface might have enhanced bead and antimicrobial delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents' delivery inside biofilm in those protected areas where some biofilm might remain.

Hippocampal dysfunction during aging II: deficits on the radial-arm maze.

Middle-aged and aged rats received dorsal hippocampal lesions before performance was evaluated on the radial-arm maze. The maze task contained simultaneous spatial working memory and visually cued reference memory components. Both middle-aged and aged rats that received lesions committed more errors of both types than sham-operated rats. Moreover, an age-related deficit was found for working and reference memory errors. After 14 sessions of training, a probe session revealed that: (a) middle-aged sham rats relied on spatial cues, (b) middle-aged lesioned rats employed the visual cues at the ends of the maze arms, (c) aged sham rats relied predominately on spatial information, (d) aged lesioned rats could not use spatial information or the visual cues at the ends of the maze arms. The additive effect of lesion and age suggests continued reliance on the hippocampus despite age-related deficits in its functioning. These data are suggestive of reduction in flexible cue utilization during aging, resulting paradoxically in more dependence on the hippocampus for aged rats than younger animals.

Hippocampal dysfunction during aging I: deficits in memory consolidation.

Numerous ablation studies indicate a critical role for the hippocampal system in establishing or consolidating certain types of memory. Normal aging manifests by selective neurobiological changes in the hippocampal formation and on performance of tasks that require a functional hippocampus, including retention of contextual fear conditioning. To determine if impairments in the consolidation process contribute to memory dysfunction in aging, middle-aged and aged rats were fear conditioned and subsequently received dorsal hippocampal lesions or sham surgery after a 1, 7, 14, or 28-day interval. During retention tests, middle-aged rats exhibited a temporally graded retrograde amnesia of contextual fear conditioning, whereas aged rats manifested contextual memory impairments at all intervals. We postulate that the lack of consolidation in aged animals relates to previous findings of age-related changes in neuroanatomy and neurophysiological plasticity. The present findings suggest that impaired hippocampal consolidation contributes to age-related learning and memory deficits.

Relationship between gap width and recurrent dental caries beneath occlusal margins of amalgam restorations.

This study examines the relationship between gap width and the presence of recurrent dental caries subjacent to occlusal margins of amalgam restorations. The study population consisted of 35 adult patients of the university's dental clinic who were having occlusal amalgam restorations removed solely because of defective margins. In this group, an impression was made recording the width of a clinically detected gap between the amalgam restoration and the adjacent enamel cavosurface. Of this study population, 20 teeth with recurrent caries were identified from 18 subjects after restoration removal. Upon removal of the restoration, the presence and location of recurrent dental caries associated with a margin was noted. The mean gap widths of recurrent carious sites and non-carious sites were compared in the same tooth. A difference of 187 microns was found between the mean gap width of the recurrent caries sites and the non-carious sites, with the recurrent caries gaps being wider. A paired t-test based on the differences was calculated (P < 0.0001). The results suggest that there is a direct association between gap width and recurrent caries in occlusal margins of amalgam restorations.

Surface roughness of opalescent porcelains after polishing.

Intraoral porcelain polishing is an important consideration in many restorative and esthetic procedures. Several porcelain polishing systems as well as improved ceramics are now commercially available. This study evaluated the efficacy of eight different intraoral polishing techniques on three opalescent porcelains. The surface roughness (Ra) of the opalescent porcelains were measured before and after the polishing procedures with a profilometer. These results were then compared to self-glazed and overglazed control groups. Five of the techniques tested produced surfaces smoother than glazing. The use of a 30-fluted carbide bur before diamond polishing paste produced the smoothest surfaces.

Disinfection and sterilization of composite polishing instruments.

PURPOSE: To evaluate the efficacy of several methods of sterilization and disinfection on two different types of composite finishing and polishing instruments. MATERIALS AND METHODS: The instruments consisted of a proprietary light-cured resin cup impregnated with an abrasive and a silicon dioxide-impregnated rubber cup. Chemical and physical methods included treatment with iodophor, synthetic phenol, glutaraldehyde, microwaving, autoclaving, and chemiclaving. RESULTS: Glutaraldehyde (Vital Defense-S) was an effective disinfectant; however, other chemical (cold) disinfectants overall, were not reliable. Autoclaving, chemiclaving, and microwaving all provided to be effective means of sterilization.

Long-term impact of discontinued or reduced calcineurin inhibitor in patients with chronic allograft nephropathy.

BACKGROUND: Chronic allograft nephropathy is the major cause of progressive renal failure in renal transplant recipients. It has no definitive treatment. METHODS: One hundred eighteen renal transplant recipients with declining kidney function and biopsy-proven chronic allograft nephropathy had their cyclosporine or tacrolimus dose reduced or discontinued with either the addition or continuation of mycophenolate mofetil and low-dose steroids at a mean of 853.3 days post-transplantation. Their renal function was modeled before and after this intervention by two methods: A least-square regression was used to assess the decay of renal function after the intervention and to compare that with the slope pre-intervention, whereas a hinge regression line method was used to assess the correlation of the intervention with the inflection point and the impact of the intervention on the decay of renal function. Mean follow-up was 651.0 days after the intervention. Serum creatinine at the time of intervention was 2.8 +/- 0.9 mg/dL in the reduced dose cyclosporine (N = 67) and reduced dose tacrolimus (N = 33) groups, and was 2.7 +/- 0.7 mg/dL in the group with discontinued calcineurin inhibitor (N = 18). RESULTS: Using the least-square method, 91.7% of the no calcineurin inhibitor group, 51.6% of the reduced dose cyclosporine group, and 59.3% of the reduced dose tacrolimus group had improved or lack of deterioration in slope after the intervention. Using the hinge regression line method, there was a statistically significant correlation of the inflection point with the intervention (P = 0.001). Moreover, there was a similar relationship with stabilized or improved graft function observed with the hinge regression line method and the least-square method, as 72.2% of the calcineurin inhibitor withdrawal group, 54.4% of reduced-dose cyclosporine group, and 40% of the reduced-dose tacrolimus group had improved the slope of decay of renal function or lack of deterioration after the inflection point. The difference between the calcineurin inhibitor withdrawal group and the reduced-dose cyclosporine/tacrolimus groups on the decay in renal function was significant (P = 0.038) with the least-square method and nearly significant (P = 0.056) using the hinge regression line method. CONCLUSION: This intervention was safe, well tolerated, and associated with a minimal risk of acute rejection. We conclude that the reduction and possible withdrawal of calcineurin inhibitors may be necessary to slow the rate of loss of renal function in patients with chronic allograft nephropathy and deteriorating renal function.