Environmental decontamination of a hospital isolation room using high-intensity narrow-spectrum light.

The performance of a new decontamination technology, referred to as 'high-intensity narrow-spectrum light environmental decontamination system' (HINS-light EDS) was evaluated by a series of three studies carried out in a hospital isolation room used to treat burns patients. The ceiling-mounted HINS-light EDS emits high-intensity 405nm light which, although bactericidal, is harmless to patients and staff thereby permitting continuous environmental disinfection throughout the day. Performance efficacy was assessed by contact agar plate sampling and enumeration of staphylococcal bacteria on environmental surfaces within the room before, during and after HINS-light EDS treatment. When the room was unoccupied, use of HINS-light EDS resulted in ∼90% reduction of surface bacterial levels and when the room was occupied by an MRSA-infected burns patient, reductions between 56% and 86% were achieved, with the highest reduction (86%) measured following an extended period of HINS-light EDS operation. In an on/off intervention study, surface bacterial levels were reduced by 62% by HINS-light EDS treatment and returned to normal contamination levels two days after the system was switched off. These reductions of staphylococci, including Staphylococcus aureus and meticillin-resistant S. aureus, by HINS-light EDS treatment were greater than the reductions achieved by normal infection control and cleaning activities alone. The findings provide strong evidence that HINS-light EDS, used as a supplementary procedure, can make a significant contribution to bacterial decontamination in clinical environments.

The role of oxygen in the visible-light inactivation of Staphylococcus aureus.

Exposure to visible-light causes the photoinactivation of certain bacteria by a process that is believed to involve the photo-stimulation of endogenous intracellular porphyrins. Studies with some bacterial species have reported that this process is oxygen-dependent. This study examines the role of oxygen in the visible-light inactivation of Staphylococcus aureus. Suspensions of S. aureus were exposed to broadband visible-light under both oxygen depletion and oxygen enhancement conditions to determine whether these environmental modifications had any effect on the staphylococcal inactivation rate. Oxygen enhancement was achieved by flowing oxygen over the surface of the bacterial sample during light inactivation and results demonstrated an increased rate of staphylococcal inactivation, with approximately 3.5 times less specific dose being required for inactivation compared to that for a non-enhanced control. Oxygen depletion, achieved through the addition of oxygen scavengers to the S. aureus suspension, further demonstrated the essential role of oxygen in the light inactivation process, with significantly reduced staphylococcal inactivation being observed in the presence of oxygen scavengers. The results of the present study demonstrate that the presence of oxygen is important for the visible-light inactivation of S. aureus, thus providing supporting evidence that the nature of the mechanism occurring within the visible-light-exposed staphylococci is photodynamic inactivation through the photo-excitation of intracellular porphyrins.

Pulsed ultra-violet inactivation spectrum of Escherichia coli.

Inactivation of Escherichia coli is examined using ultra-violet (UV) radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV content. The flashlamp provides high-energy UV output using a small number of short-duration pulses (30 micros). The flashlamp is used with a monochromator to investigate the wavelength sensitivity of E. coli to inactivation by the pulsed UV light. Using 8 nm wide pulses of UV radiation, the most efficient inactivation is found to occur at around 270 nm and no inactivation is observed above 300 nm. A pyroelectric detector allows the energy dose to be determined at each wavelength, and a peak value for E. coli population reduction of 0.43 log per mJ/cm(2) is measured at 270 nm. The results are compared with the published data available for continuous UV light sources.

Dentin bonding agents and resin cements--current status.

Contemporary restorative dentistry is a rapidly evolving science which challenges the progressive clinician with a plethora of "new and improved" products. Sound product choices should be couched in the prudent consideration of well conducted in vitro and in vivo product research. This review shall list the most recent product developments in dentin bonding agents (fifth generation agents), resin-containing dental cements and the newest generation of dental cements i.e., resin-ionomer dental cements.

Stress distribution in the single-unit osseointegrated dental implant: finite element analyses of axial and off-axial loading.

Occlusal overload may contribute to the extensive crestal bone loss often noted around late-failure dental implants. A particularly high risk of traumatic overload occurs with the posterior single-unit implant restoration because the restoration itself is usually wider than the implant, creating the potential for a cantilever effect with high bending moments. The objective of this study was to evaluate the simulated effects of axial and off-axial vertical loads on stress gradients at the implant/bone interface of a single-unit osseointegrated root-form endosseous dental implant. A two-dimensional finite element model was generated. A 490-N load was applied at 0, 2, 4, and 6 mm from the vertical axis of the implant. Off-axis loading resulted in greatly increased compressive stresses within the crestal cortical bone on the side to which the load was applied and similarly increased tensile stresses on the side opposite the load. These stresses increased considerably with each mm increase off axis of the applied load. These data suggest that off-axis loading of single-unit implant restorations provides a significant contribution to increased stresses at the implant/cortical bone interface. The distance off axis at which the load is applied is also significant.

Restoration of endodontically treated teeth with posts and cores.

This article is a review of the current technique and materials used in the restoration of endodontically treated teeth with post and core materials and procedures. It is intended to aid clinicians in making selections which are appropriate to their individual practices through the evaluation of relevant literature about the restoration of endodontically treated teeth.

Effect of brushing with sonic and counterrotational toothbrushes on the bond strength of full veneer crowns.

STATEMENT OF PROBLEM: Earlier studies on orthodontic brackets have shown a loss of bond strength after a sonic toothbrush was used. PURPOSE: This in vitro study evaluated the difference in bond strength of single complete veneer crowns after being subjected to the equivalent of 2 years of brushing with sonic and counterrotational toothbrushes. MATERIAL AND METHODS: Complete gold crowns were fabricated with a conventional indirect technique for 30 extracted, intact, prepared human premolar teeth. Castings were then luted to the teeth with glass ionomer cement. Teeth were randomly divided into 3 groups of 10 teeth each, 1 group to be brushed with Sonicare sonic toothbrush, 1 group to be brushed with Interplak counterrotational mechanical toothbrush, and 1 group as the control. Groups 1 and 2 were then brushed for the equivalent of 2 years per tooth. A uniform force of 50 g for the sonic toothbrush and 120 g for the counterrotational toothbrush was used. Control specimens were not brushed. Brush heads and sample teeth in contact with the toothbrush were kept moist at all times. Tensile dislodgment force was determined with an Instron universal testing machine. RESULTS: The castings brushed with a sonic toothbrush required a mean of 43.22 kg (+/- 11.16) force to remove the crowns from the teeth, whereas the counterrotational group required a mean of 42.87 kg (+/- 10.42) and the control group a mean of 42.12 kg (+/- 6.61). Analysis of variance on the force data indicated no differences among the 3 groups in the force needed to remove the castings (F[2,24] = 0.031, P = .97). CONCLUSION: This in vitro study demonstrated no significant differences between groups in the amount of tensile dislodgment force required to remove cemented full veneer crowns from prepared teeth after brushing for the equivalent of 2 years time with a sonic toothbrush or a counterrotational toothbrush.

Defining predoctoral prosthodontic curriculum: a workshop sponsored by the American College of Prosthodontists and the prosthodontic forum.

Prosthodontic educators participated in a workshop held at The American College of Prosthodontists annual session in Kansas City, MO, in October 1996. Their goal was to review elements of the predoctoral prosthodontic curriculum to establish a consensus on the levels of expected skill and knowledge. Skill components were designated at the competency and exposure levels, while knowledge components were designated at the understanding and familiarity levels. The workshop recommendations were distributed to American and Canadian dental schools and the communities of interest for comments in January 1997. The workshop recommendations were reviewed and finalized at the American Association of Dental Schools annual meeting in Orlando, FL, in March 1997. The recommendations may be used by dental educators to prioritize curricular elements in relation to limited time dedicated to the prosthodontic curriculum. Outcomes assessment methods will be needed to ensure competency in the new dentist.

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry.

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever.

Modifications in the design and fabrication of mandibular osseointegrated fixed prostheses frameworks.

This article presents the advantages of design modifications and fabrication techniques for mandibular osseointegrated fixed prostheses. These design features provide definite mechanical advantages and access for oral hygiene maintenance. A review of implant surface properties is presented that affect bacterial plaque and food debris adherence. The suggested design involves a lingual contour of the cast alloy suprastructure to yield an environment for reduced plaque and debris accumulation. The right angle cross-section ensures strength and increased stress distribution in structurally compromised areas when compared with conventional implant framework designs.

Characterization and use of an optical fiber interferometer for measurement of the electric wind.

An optical fiber interferometer of the Mach-Zehnder type has proved to be a convenient and accurate method for measuring the electric wind in the active region of a corona discharge. The technique relies on the cooling effect of the wind on a small heated region of one arm of the interferometer, which has been remotely heated with an infrared CO(2) laser beam. Wind speeds of up to 5.5 m s(-1) have been measured near the generation region, and by the use of a mesh electrode, the wind has been detected on the axis up to 0.5 m away from the gap. A number of characterization experiments that show the interferometer to be a useful diagnostic tool in the quantitative analysis of the CO(2) laser beam have also been carried out, and good agreement between experimental results and theoretical calculations based on a simple heat-power balance equation for the fiber exists.

Esthetic and biomechanical considerations in reconstructions using dental implants.

The single-tooth implant-supported restoration can provide an outstanding service to many patients. It requires an understanding of the biomechanical principles involved and attention to the many details involved with the diagnosis and treatment planning for these restorations. The clinician should realize that this restorative approach is contraindicated in many circumstances. As Peter K. Thomas said, "Spend more time planning than doing and doing becomes easier."

Effects of laboratory disinfecting agents on color stability of denture acrylic resins.

This study determined the effects of chemical disinfecting agents on denture acrylic resins. Tested resins included the products CH Lucitone, Triad VLC, and Truliner. The disinfecting agents were sodium hypochlorite, Exspor, Cidex, and Wescodyne-D. Acrylic resin samples were placed in the various disinfecting agents and then evaluated for color changes at time intervals ranging from 15 minutes to 72 hours. No observable color change of any acrylic resin was seen before 2 hours. Both 1% sodium hypochlorite and 2% Cidex disinfectants produced the least discoloration of the acrylic resins, and Wescodyne-D disinfectant produced the most acrylic resin discoloration. Truliner resin discolored more than Triad VLC resin, and both underwent more color change than CH Lucitone resin. If manufacturers' recommended disinfecting times are followed, clinical and laboratory disinfection of acrylic resin dentures should cause no observable color change.

Comparison of exothermic release during polymerization of four materials used to fabricate interim restorations.

Four materials commonly used to make resin crown and fixed partial denture interim restorations (poly)methylmethacrylate, vinyl ethylmethacrylate, visible-light activated resin, and a Bis-acryl composite resin) were studied to evaluate their heat-producing capabilities. All four materials, despite manufacturers' claims, created a rise in temperature during polymerization. Poly(methylmethacrylate)'s temperature increases were significantly higher than those of the other three materials and visible-light activated resin had temperature increases that were significantly lower than those of the other three products. Dentists must be aware of all potential heat-producing sources to minimize thermal injury to the hard and soft tissues of the oral cavity during the fabrication of interim crowns and fixed partial dentures.

Solubility of zinc oxide-eugenol and calcium hydroxide cements in simulated dentinal fluid.

The solubility of four dental cement bases was measured in simulated dentinal fluid and distilled water to evaluate the relevancy of the American Dental Association solubility test for cement bases in contact with vital dentine. A simulated dentinal fluid was formulated utilizing glucose, distilled water, and sterile human plasma. Cement-base samples were immersed in either distilled water or simulated dentinal fluid at 37 degrees C in a shaker water-bath for 1, 2, or 3 months. Weight loss values were compared utilizing a three-way analysis of variance. Zinc oxide-eugenol cements were significantly more soluble in simulated dentinal fluid than distilled water, while the calcium hydroxide cement bases were significantly more soluble in distilled water than simulated dentinal fluid.

Effects of sodium hypochlorite on denture base metals during immersion for short-term sterilization.

The effects on Vitallium and Ticonium alloys immersed in different concentrations of sodium hypochlorite for various immersion times are described. The results of this investigation demonstrate that samples of these metals soaked in 2% sodium hypochlorite for at least 5 minutes or in 5.25% sodium hypochlorite for a minimum of 3 minutes were sterilized and not tarnished or corroded. Although Vitallium alloy was more resistant than Ticonium alloy to the deleterious effects of sodium hypochlorite, either metal can be safely immersed for sterilization purposes under the guidelines presented. Therefore, an effective and economical method for sterilizing removable partial denture frameworks made of chrome-cobalt or chrome-nickel alloys is attainable through the proper use of household bleach.

Masking power of dental opaque porcelains.

A technique was developed to qualify the masking power of undiluted opaque dental porcelain by dilution of opaque powder with a clear glaze powder and by extrapolation of quantitative data gathered by reflectance spectrophotometry. Quantification of reflectance data was made on dilute opaque porcelains using the scattering and absorption coefficients in the Kubelka-Munk equation. Qualitative comparisons of undiluted opaque porcelains were made from quantitative data gathered from diluted opaque porcelains.

Versatile polarization interferometer.

A new form of polarizing interferometer has been assembled from six calcite-glass prisms and two halfwave plates. The interferometer has the large shear and long beam path capabilities needed for the examination of large objects and is capable of providing a stable interference pattern even when the two ends of the interferometer are supported independently. Lenses can be conveniently added to the system either to facilitate alignment or to extend its useful length.