Rebecca L. Taylor

Colonization and penetration of denture soft lining materials by Candida albicans

OBJECTIVES Colonization of denture soft lining materials by Candida albicans can result in clinical problems, and deterioration of the material. This study aimed to monitor this interaction by comparing the short-term adhesion of C. albicans to six denture lining materials and to monitor any longer term penetration of material by the yeast. METHODS Denture lining materials (Molloplast B, Flexor, Permaflex, Luci-soft, Eversoft and Ufi Gel hard C) were processed against glass slides or dental stone. Adhesion of yeast to surfaces was monitored after one hour incubation (37 degrees C) of standardized (2.8 x 10(6) cfu/ml) washed cell suspension with test materials. Attached cells stained with acridine orange were counted microscopically. Penetration of yeast into materials bonded onto acrylic after six weeks incubation (culture medium was replaced weekly) was observed through sections stained using acridine orange. Hyphal and yeast penetration was estimated (qualitatively and quantitatively, respectively) for three levels of the liner (subsurface, central section and adjacent to lining-acrylic junction). RESULTS None of the materials produced a zone of inhibition when compared with the nystatin control. There was no significant difference (p>0.5) in cell numbers on any of the smooth surfaces. Significantly, (p<0.001) higher numbers of cells were observed on roughened surfaces. Both hyphal and yeast forms were observed when penetration was monitored. Penetration was greatest into Ufi Gel hard C (no hyphae observed), but not at the acrylic-liner junction and least into Eversoft. SIGNIFICANCE Different denture lining materials exhibit different properties in terms of susceptibility to yeast penetration, although the initial attachment is comparable. Smoother surfaces retain fewer cells. The selection of appropriate materials for a given function, and their fabrication may affect performance.

Disinfection procedures: their effect on the dimensional accuracy and surface quality of irreversible hydrocolloid impression materials and gypsum casts.

OBJECTIVES This study primarily investigated the effect of disinfection procedures (Perform and sodium hypochlorite) on the dimensional accuracy and surface quality of four irreversible hydrocolloid impression materials and the resultant gypsum casts. The antibacterial efficacy of the procedures was also studied. METHODS Dimensional accuracy was determined from the mean percentage deviation of six measurements taken from casts made from disinfected impressions compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance. Surface quality was determined using a stainless steel test block in accordance with ISO 1563. RESULTS The dimensional accuracy of the impression materials tested were of a comparable standard following disinfection. The surface quality of casts taken from Blueprint Cremix impressions were unaffected by the disinfection procedures. The remaining impression materials studied showed greater surface deterioration on casts following disinfection with sodium hypochlorite than immersion in Perform. All disinfection procedures selected proved appropriate for antibacterial purposes. SIGNIFICANCE Individual analysis of impression materials is required to determine their suitability to a given disinfection protocol.

Retention of oral microorganisms on cobalt-chromium alloy and dental acrylic resin with different surface finishes

STATEMENT OF PROBLEM The effect of surface finish of dental materials on the subsequent contamination by microorganisms. PURPOSE This study compared the retention of Streptococcus oralis, Actinomyces viscosus, and Candida albicans on polished, sandblasted (fine and coarse) and electrobrightened cobalt-chromium alloy and dental acrylic resin to assess in vitro the effect of such techniques on prosthesis contamination. MATERIAL AND METHODS Standardized cell suspensions were incubated with test materials for 1 hour at 37 degrees C, after which retained cells were counted by using image analysis (percentage area of a microscopic field covered by cells). RESULTS Retention of bacterial cells was substantial (S oralis 12% to 20% and A viscosus 9% to 16%) irrespective of surface finish. Maximal retention was observed on cobalt-chromium alloy that had undergone fine sandblasting and electrobrightening (P < .01). For C albicans, an increase in surface roughness (0.15 to 3.53 microns) resulted in an increase in retention (3% to 9%). CONCLUSION Cell size and the type of roughening significantly affected the retention of microorganisms on surfaces. Electrobrightening of cobalt-chromium alloy did not reduce the surface roughness or subsequent cell attachment.

Modulation of bacterial adhesion to hydrogel contact lenses by albumin

Purpose. The purpose of this investigation was to measure the abilities of Pseudomonas aeruginosa and Staphylococcus epidermidis strains to adhere to two hydrogel lens materials and measure the effect of a protein-coated surface on the number of adhered bacteria. Methods. Proteins absorbed to contact lenses during sleep were extracted, subjected to sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), and probed for the presence of albumin. Bacterial adhesion was measured by counting bacteria adherent to contact lenses coated in vitro in increasing concentrations of albumin, examining the ability of albumin in solution to prevent adhesion to albumin-coated lenses, and examining the topography of bacterial adhesion by electron microscopy. Results. Albumin adsorbed to lenses during overnight wear. In vitro studies demonstrated that Polymacon lenses adsorbed more albumin than Etafilcon A lenses. In general, the numbers of adherent bacteria increased with increasing concentration of albumin. Bacteria adhered in higher numbers to Polymacon lenses than Etafilcon A (p<0.05). P. aeruginosa showed an increased adhesion as the amount of albumin on Etafilcon A lenses increased. There was a decrease in numbers of bacteria adhering per milligram of albumin as the level of albumin increased on Polymacon lenses. Cells tended to adhere to “deposits” on albumin-coated lenses. Discussion. Albumin adsorbed onto the surface of contact lenses modulated the ability of P. aeruginosa and S. epidermidis to adhere. P. aeruginosa is commonly associated with contact lens-associated microbial keratitis, where bacterial adhesion to contact lenses is believed to be an important first step in the pathogenesis of the disease.

Bacterial adhesion to inert thermoplastic surfaces

The adhesion of four bacterial species, two strains of each, to four hydrophobic thermoplastics was observed. Image analysis of adherent cells stained with acridine orange provided a rapid, direct and objective means of measuring adhesion to clear, translucent and opaque surfaces by calculating the percentage area of a microscopic field covered by cells (percentage coverage). There was a highly significant correlation (P>0.05) between percentage coverage value and adherent cell count (obtained manually) for both rods and cocci. Bacterial adhesion to thermoplastics appeared to be strain specific and was not related to polymer composition. Highest percentage coverage values were obtained using hydrophobic bacteria, and lowest using hydrophilic bacteria. There was no relationship between the origin of the organisms (culture collections or isolates from biomaterial-associated infections) and their ability to adhere, after cultivation in brain heart infusion broth. Many factors influence this ability: an awareness of all experimental variables is essential.

A review of facial protective equipment use in sport and the impact on injury incidence

Sporting activities have an inherent risk of facial injury from traumatic impacts from fellow competitors, projectiles, and collisions with posts or the ground. This retrospective review systematically describes the interplay between the type of sport (including the level at which specific sports are played), the sex of the players and their musculoskeletal characteristics, the technology behind the materials used, the protective devices commonly used, the anatomical site, and the regularity of incidence of fractures. We describe how variations in sporting activities induce different orofacial fracture patterns, and critically consider the methods used to test protective headgear against more contemporary techniques. Facial injuries can have a profound psychological effect on those injured, can take a long time to heal, and have been known to end promising careers. Use of properly fitted protective head or facial equipment could reduce the number of facial fractures commonly seen in sports. We recommend that individual sports should have full risk assessments, and that mandatory standards should be agreed about protective devices that would be appropriate.

Effect of element concentration on nickel release from dental alloys using a novel ion beam method

OBJECTIVES Nickel chromium is widely used as a restorative material in dentistry but its biocompatibility is of concern as there are reports of patients suffering adverse effects caused by exposure to nickel-based restorations. The aim of this work was to quantify the amount of nickel released into solution from commercially available nickel-based alloys with varying compositions and to identify the potential use of thin films in further understanding the role of chromium in reducing nickel release. METHODS Six commercially available nickel-based alloys were cast using the lost wax technique. Nickel chromium thin films were deposited onto silicon substrates by ion beam assisted physical vapor deposition. Both types of alloys were immersed into solution representative of saliva at pH 5 for 7 days. The amount of nickel released into solution was quantified by graphite-furnace atomic absorption spectrophotometry. RESULTS The amount of nickel released from commercially available cast alloys did not correspond to the amount of nickel within the alloy. The total amount of chromium and molybdenum within the alloys proved to be of greater influence. Increasing the amount of chromium in the thin film alloys reduced the amount of nickel released but this was not linear. SIGNIFICANCE Differences in the composition of commercial cast alloys highlighted the importance of other elements within the alloy on reducing the amount of nickel released. The use of thin film alloys can be useful in further understanding how the composition of an alloy can affect the amount of nickel released.

The effect of resin/crosslinker ratio on the mechanical properties and fungal deterioration of a maxillofacial silicone elastomer

Variation of the crosslinker/resin ratio of a room temperature condensation cure maxillofacial silicone elastomer has caused considerable changes in the mechanical properties and deterioration by Candida albicans. Increasing the crosslinker/resin ratio caused a decrease in the tensile strength and stiffness of the elastomer. However, tear strength appeared to show an optimum value at the recommended crosslinker/resin ratio. These effects were due to the low molar mass silicone polymer that acts as a carrier for the actual crosslinking additive. The general decrease in mechanical properties was accompanied by an increase in the hexane extractables content and an increase in the Si–H content of the elastomer. The unbound polymer (extractable material) content of the elastomer was found to influence the colonization of the material by C. albicans. An increase in the unbound polymer content corresponded to an increasing number of hyphae and blastospores observed penetrating into the elastomer. The data obtained in this study have significant implications concerning the degree of control of elastomer formulation and the deterioration of maxillofacial appliances.

Comments on the routine testing of water samples for Legionella sp.

Water samples analysed for Legionella sp. by a commercial company were studied over a 6 month period. Samples yielding legionella were re-examined to determine the efficiency of heat or acid pre-treatment in isolating legionella compared to untreated specimens. In addition, more than one colony of each colony type were tested serologically to determine whether serotypes in addition to those originally identified were present. Significantly (P < 0.01) higher legionella colony numbers were found on the heat pre-treatment plates than on the acid pre-treatment plates. Legionellae were identified from only the untreated plate in 5.1% of positive water samples; in these instances the concentrations of legionellae tended to be low. Six out of 18 positive samples were found to contain more than one serogroup of Legionella pneumophila when more than one colony of each colony type was tested. It is recommended that the procedures used in legionella screening be rationalised to facilitate maximum detection without excessive workload.

The effect of model inclination during fabrication on mouthguard calliper-measured and CT scan-assessed thickness.

AIM Excessive material thinning has been observed in the production of custom-made mouthguards in a number of studies, due to production anomalies that may lead to such thinning. This study investigated thinning material patterns of custom-made mouthguards when the anterior angulation of dental model was increased during the thermoforming process. MATERIALS AND METHODS A total of 60 samples of mouthguard blanks were thermoformed on identical maxillary models under four anterior inclination conditions (n = 4 × 15): control 0, 15, 30 and 45°. Each mouthguard sample was measured, using an electronic calliper gauge at three anatomical points (anterior labial sulcus, posterior occlusion and posterior lingual). Mouthguards were then CT scanned to give a visual representation of the surface thickness. RESULTS Data showed a significant difference (P < 0.005) in the anterior mouthguard thickness between the four levels of anterior inclination, with the 45° inclination producing the thickest mouthguards, increasing the mean anterior thickness by 75% (2.8 mm, SD: 0.16) from the model on a flat plane (1.6 mm, SD: 0.34). Anterior model inclination of 30 and 45° inclinations increased consistencies between the thickest and thinnest mouthguards in the anterior region of these sample groups. CONCLUSION This study highlights the importance of standardizing the thermoforming process, as this has a significant effect on the quality and material distribution of the resultant product. In particular, greater model inclination is advised as this optimizes the thickness of the anterior sulcus of the mouthguard which may be more prominently at risk from sport-related impact.