Effect of treatment concentration on lipopolysaccharide affinity for two alloys

In vitro study of structural and mechanical properties of latex and non-latex intermaxillary orthodontic elastics

PURPOSE

We evaluated bacterial endotoxin adhesion, superficial micromorphology and mechanical properties of latex and non-latex intermaxillary orthodontic elastics.

METHODS

To quantify the adhered bacterial endotoxin, elastics were divided into 5 groups: experimental (n = 12) latex and non-latex elastics, previously contaminated by an endotoxin solution, negative control (n = 6) latex and non-latex elastics without contamination, and positive control (n = 6) stainless steel specimens (metallic replicas), contaminated by an endotoxin solution. In parallel, the structural micromorphology (n = 6) and surface roughness of latex and non-latex intermaxillary orthodontic elastics were assessed using confocal laser microscopy. Force degradation (g) and deformation of the internal diameter change (mm) were also evaluated. Structural micromorphology, surface roughness (µm), force degradation (g) and internal diameter (mm) change were evaluated at time 0 and after 24 and 72 h in a deformation test. Data were analyzed by the Shapiro-Wilk, Kruskal-Wallis, Dunn, ANOVA and Bonferroni tests (α = 5%).

RESULTS

Endotoxin adhered similarly to both types of elastics with scores of 3 (> 1.0 EU/mL). The surface microstructure of both types of elastics showed irregularities and porosities at all times. Initially, the latex elastics had a higher surface roughness (p < 0.001) than the non-latex ones. After 24 h loading, surface roughness of the latex elastics was significantly reduced (p < 0.001), while after 72 h, the values were similar for both types (p > 0.05). The non-latex elastics had significantly higher force generation values (p < 0.05) at 0, 24 and 72 h compared with the latex elastics, although there was a significant reduction (p < 0.001) in force over time for both elastics. Despite similar initial values, non-latex elastics had a significantly larger internal diameter (p < 0.001) after the loading periods of 24 and 72 h compared with the latex elastics.

CONCLUSION

Both elastics showed high affinity with endotoxin and microstructural irregularities of their surface. The non-latex elastics generated higher force values but demonstrated greater deformation of the internal diameter after loading.

Effects of lipopolysaccharides on the corrosion behavior of Ni-Cr and Co-Cr alloys

STATEMENT OF PROBLEM

Lipopolysaccharides (LPS) are constituents of gingival crevicular fluid and may affect the base metal alloys used in metal ceramic crowns. The role of LPS in base metal alloys is currently unknown.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of gram-negative bacterial LPS on the electrochemical behavior of Ni-Cr and Co-Cr alloys.

MATERIAL AND METHODS

Alloy specimens were divided into 4 groups according to Escherichia coli LPS concentration (0, 0.15, 15, and 150 μg/mL) in acidic saliva (pH 5). Open circuit potential (OCP) and potentiodynamic polarization behavior were examined using a computer-controlled potentiostat. Metal ions released from the 2 alloys were measured by immersion in LPS-free solution and 150 μg/mL LPS solution and analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Data were evaluated using 1-way ANOVA (α=.05).

RESULTS

Compared with control groups, medium LPS concentration (15 μg/mL) accelerated Ni-Cr alloy corrosion (P<.05), whereas high LPS concentration (150 μg/mL) accelerated Co-Cr alloy corrosion (P<.05), as determined by OCP, corrosion current density, and polarization resistance parameters. After immersion in high LPS concentrations (150 μg/mL), a slight increase in Ni ion release (P >.05) was observed for the Ni-Cr alloy, while a more significant Co ion release (P<.05) was observed for the Co-Cr alloy.

CONCLUSIONS

LPS negatively affected the electrochemical behavior of both the Ni-Cr and Co-Cr alloys.

Biocompatibility of dental casting alloys

Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

Effect of a metal alloy fuel catalyst on bacterial growth

Many microorganisms have been demonstrated to utilize petroleum fuel products to fulfill their nutritional requirement for carbon. As a result, the ability of these microbes to degrade fuel has both a deleterious affect as well as beneficial applications. This study focused on the undesired ability of bacteria to grow on fuel and the potential for some metal alloys to inhibit this biodegradation. The objective of this study was to review the pattern of growth of two reference strains of petroleum-degrading bacteria, Pseudomonas oleovorans and Rhodococcus rhodocrous, in a specific hydrocarbon environment in the presence of a commercially available alloy. The alloy formulated and supplied by Advanced Power Systems International Inc. (APSI) is sold for fuel reformulation and other purposes. The components of the alloy used in the study were antimony, tin, lead, and mercury formulated as pellets. Surface characterization also showed the presence of tin oxide and lead amalgam phases. Hydrocarbon used for the study was primarily 87-octane gasoline. The growth of the bacteria in the water and mineral-supplemented gasoline mixture over 6-8 weeks was monitored by the viable plate count method. While an initial increase in bacteria occurred in the first week, overall bacterial growth was found to be suppressed in the presence of the alloy. Results also indicate that the alloy surface characteristics that convey the catalytic activity may also contribute to the observed antibacterial activity.

Effect of pH on endotoxin affinity for metal-ceramic alloys

STATEMENT OF PROBLEM

Crevicular pH may modify bacterial endotoxin affinity for high-noble metal-ceramic alloys.

PURPOSE

Porphyromonas gingivalis lipopolysaccharide (LPS) affinity for 3 metal-ceramic alloys at 3 different pH levels was compared in vitro by measuring adsorption to and release from the alloy surface.

MATERIAL AND METHODS

Metallographically polished disks were fabricated from Pd-Ag-Sn, Au-Pd-Ag-Sn-In, and Au-Pd-In-Ga alloys. Clean disks were placed individually into 1 mL at pH 6.5, 7.0, or 7.5 phosphate-buffered saline solution containing 0.9 endotoxin units per square millimeter tritiated LPS (n = 3 disks per alloy-pH group). The disks were incubated for 24 hours at 37 degrees C before being transferred to LPS-free buffer and incubated, again for 24 hours at 37 degrees C, to evaluate elution. This transfer continued at 24-hour intervals up to 96 hours total elution incubation. Lipopolysaccharide adsorption to and elution from disks was determined through liquid scintillation spectrometry. Adsorption data were evaluated with a 2-way analysis of variance (alpha=.05) and the post hoc Tukey honestly significant difference test.

RESULTS

Lipopolysaccharide adsorption values ranged from 0.48 +/- 0.04 EU/mm(2) for the Au-Pd-Ag-Sn-In alloy at pH 7.5 to 0.75 +/- 0.04 EU/mm(2) for the Pd-Ag-Sn alloy at pH 6.5. Alloy type (P=.0001) and environmental pH (P=.0001) significantly influenced adsorption. Adsorption to the Pd-Ag-Sn and Au-Pd-In-Ga alloys at pH 6.5, 7.0, and 7.5 were similar and decreased with increasing pH. In contrast, adsorption to the Au-Pd-Ag-Sn-In alloy was significantly less than to other alloys at pH 6.5 but did not differ at other pH levels. Lipopolysaccharide release from the alloy surface could not be detected.

CONCLUSION

P. gingivalis LPS affinity for metal-ceramic alloys was modified by environmental pH. The degree of LPS adsorption depended on the composition and surface chemistry of each alloy.

In vitro TNF-α release from THP-1 monocytes in response to dental casting alloys exposed to lipopolysaccharide

STATEMENT OF PROBLEM

Studies have found that lipopolysaccharide (LPS) attaches to and is eluted from dental alloys, but the biologic effects of LPS are not known.

PURPOSE

This study evaluated the ability of dental casting alloys pre-exposed to LPS to activate human monocytes with and without subsequent elution of the LPS.

MATERIAL AND METHODS

Eight types of casting alloys (n = 6 specimens per type) were exposed to LPS (Escherichia coli @ 100 micrograms/mL) for 24 hours. Controls were not exposed to LPS. Teflon (Tf) (+/- LPS) served as the material control. Treated alloys were transferred to THP-1 human monocytes for 24 hours or placed into phosphate-buffered saline (PBS) solution for 120 hours before monocyte exposure. Monocyte activation was assessed by tumor necrosis factor alpha (TNF-alpha) secretion into the medium. Alloys without LPS, with LPS but without PBS elution, and with LPS and elution were compared with ANOVA and Turkey intervals (alpha=.05).

RESULTS

Specimens without LPS exposure but with elution caused no detectable TNF-alpha secretion from monocytes. Specimens without elution into PBS caused low-to-moderate TNF-alpha secretion, indicating a possible false-positive result from the alloy conditioning solution used. After LPS exposure but no elution, high levels of TNF-alpha were found. When alloys were eluted for 120 hours after LPS exposure, there was no detectable TNF-alpha released.

CONCLUSION

In this in vitro system as in past studies, LPS appeared to adhere to and elute from the alloys. Monocytes were activated initially but not after elution into PBS for 120 hours. Alloy conditioning solutions may also have an artifactual effect on cytokine release.

Periodontal tissue responses after insertion of artificial crowns and fixed partial dentures

PURPOSE

The purpose of this review was, first, to critically evaluate published evidence on the effects of artificial crowns and fixed partial dentures (FPDs) on adjacent periodontal tissue health, and second to synthesize this evidence into meaningful summaries. Restoration qualities that contribute to inflammatory responses were identified based on strength of evidence, and variables that should be controlled in future investigations were outlined. Such information is necessary to accurately predict the prognosis of periodontal tissues adjacent to crowns or FPDs.

METHODS

Clinical trial and epidemiologic evidence published in English was collected. The effects of crowns or FPDs on gingival inflammation, probing depths, and bone loss were evaluated based on accuracy of measurement, reliability of measurement, and/or appropriateness of data analysis.

RESULTS

Crowns and FPDs increased the incidence of advanced gingival inflammation adjacent to restorations, particularly if restorations had intracrevicular finish line placement, poor marginal adaptation, or rough surfaces. However, because of the limitation in the accuracy and reliability of probing depth measurements, reports of greater mean probing depths of crowned teeth, which tended to be less than 1 mm greater than control teeth, should be questioned. Finally, crowns and FPDs in general did not accelerate the rate of adjacent bone loss.

CONCLUSION

Clinically deficient restorations, as well as clinically acceptable restorations, can contribute to gingival inflammation. However, with the limitations of the applied methods of measurement, current evidence has not shown an increased attachment loss adjacent to crowns or FPDs. Future trials should document periodontal health before therapy and periodically after restoration insertion so that each tooth serves as its own control. In future studies, the periodontal disease history of the patient, the influence of the restoration on plaque formation, and the composition of the crevicular microflora must be recorded.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.

Endotoxin affinity for orthodontic brackets

Endotoxin, cell envelope lipopolysaccharide produced by gram-negative bacteria can activate an immune response through a variety of pathways. In addition, it can stimulate bone resorption and reduce the periodontal tissue's healing capacity. Previous studies have documented the affinity of lipopolysaccharide for restorative materials. This study evaluated the affinity of lipopolysaccharide for commercially available orthodontic brackets. Stainless steel, ceramic, plastic, and "gold" brackets were exposed to 10 EU/mm2radiolabeled Porphyromonas gingivalis or Escherichia coli lipolpoysaccharide in water and incubated for 24 hours at 37 degrees C. Brackets were then transferred to fresh lipopolysaccharide-free water and incubated for 24 hours at 37 degrees C to evaluate elution. This elution transfer was continued up to 96 hours total incubation. Lipopolysaccharide adherence and elution levels were calculated after treatment, and elution solutions were evaluated through liquid scintillation spectrometry. Mean initial lipopolysaccharide adherence ranged from 2.42 +/- 0.26 EU/mm2(E. coli, plastic) to 6.75 +/- 0.34 EU/mm2 (P. gingivalis, stainless steel). P. gingivalis lipopolysaccharide adherence was significantly greater than E. coli lipopolysaccharide adherence for all bracket types. Moreover, for each lipopolysaccharide type, stainless steel brackets exhibited significantly greater lipopolysaccharide adherence. Regarding elution, only the P. gingivalis lipopolysaccharide-exposed ceramic and plastic brackets at 24 hours and the stainless steel and ceramic brackets at 48 hours eluted measurable lipopolysaccharide. Results from this study demonstrate that P. gingivalis and E. coli LPS exhibit a high affinity for orthodontic brackets. In vivo, this affinity could affect the concentration of LPS in the gingival sulcus, thereby contributing to inflammation in tissues adjacent to the brackets.

Dental materials citations: Part A, January to June 1997

OBJECTIVE

A search was conducted in biomedical journals published from January 1997 to June 1997 to identify all dental materials publications and sort them into major categories.

METHODS

Tables of contents for 79 journals for the period of January to June, 1997 were inspected and divided into 17 categories. Citations were analyzed by both frequency in journals and in categories, as well as compared to frequencies for previous years.

RESULTS

A total of 445 citations were detected in 79 journals for the period January 1997 to June 1997. Certain journals (n = 19) demonstrated a higher citation frequency (> or = 10 citations for 6 months) and represented 77.8% of all citations. The greatest number of citations continued to involve bonding (n = 97), resin-based restorative materials (composites; glass ionomers) (n = 95), prosthodontic materials (n = 51), and pulp protection/luting materials (n = 48). Frequencies by category were very similar to those for the last four years.

SIGNIFICANCE

The compiled literature citations provide a supplement for researchers and academicians seeking information in existing electronic databases.