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PubMed1990

Measurement of absorbed doses near metal and dental material interfaces irradiated by x- and gamma-ray therapy beams.

Soft-tissue damage adjacent to dental restorations is a deleterious side effect of radiation therapy which is associated with low-energy electron scatter from dental materials of high electron density. This study was designed to investigate the enhancement of dose to soft tissue (or water) close to high electron-density materials and to measure the detailed lateral and depth-dose profiles in soft-tissue-simulating polymer adjacent to planar interfaces of several higher atomic-number materials: 18-carat gold dental casting alloy; Ag-Hg dental amalgam alloy; Ni-Cr dental casting alloy; and natural human tooth structure. Interleaved stacks of calibrated thin radiochromic dosimeter films and tissue-simulating polymer were used for these measurements. Assemblies of these polymer-dosimeter stacks on both sides of the dental materials were irradiated in one fixed direction by collimated 60Co gamma-ray or 10 MV x-ray beams directed perpendicularly to the material interfaces. In another test, designed to simulate more closely therapeutic treatment conditions, a phantom constructed on both sides of a row of restored and unrestored whole teeth (restoration materials: gold alloy crown; Ni-Cr alloy crown; Ag-Hg mesial-occlusal-distal (MOD) amalgam filling; unrestored tooth) was irradiated in one fixed direction by the collimated photon beams. Results indicate that the dose-enhancement in 'tissue' is as great as a factor of 2 on the backscatter side adjacent to gold and a factor of 1.2 adjacent to tooth tissue, but is insignificant on the forward-scatter side because of the predominant effect of attenuation by the high-density, high atomic-number absorbing material.

Chromium Alloys↗

PubMed2004

Exposure to methylmercury in non-fish-eating people in Sweden.

The extensive use of fish meal as a source of protein for poultry and swine may lead to additional exposure to methylmercury (MeHg). We determined the concentration of MeHg and inorganic mercury (I-Hg) in blood and total mercury (T-Hg) in hair in 27 persons (9 men and 18 women, 20-58 years of age) who stated that they had consumed no fish for a period of 2 years or more. The participants answered a food frequency questionnaire and reported their number of dental amalgam fillings. The MeHg concentrations in blood (median, 0.10 microg/L; range, 0.0-1.0 microg/L) were very low and did not constitute a concern for health effects. We also analyzed selenium (Se) in serum. The median concentration was 76 microg/L (range, 53-103 microg/L), which is in agreement with previous studies of the Swedish general population, indicating that the Se status of non-fish-eating individuals is not substantially lower than that of people who include fish in their diet. We found a significant association (P=0.002) between the number of dental amalgam fillings and the I-Hg concentration in blood (median, 0.09 microg/L; range, 0.03-0.57 microg/L). The T-Hg in hair (median, 0.06 mg/kg; range, 0.04-0.32 mg/kg) was significantly associated (R2=0.89; P<0.001) with the MeHg in blood, but not with the I-Hg in blood. Therefore, the T-Hg in hair seems to reflect MeHg exposure and not I-Hg exposure even in persons with no intake of fish.

Adult↗

PubMed1982

Analysis of dental materials as an aid to identification in aircraft accidents.

The failure to achieve positive identification of aircrew following an aircraft accident need not prevent a full autopsy and toxicological examination to ascertain possible medical factors involved in the accident. Energy-dispersive electron microprobe analysis provides morphological, qualitative, and accurate quantitative analysis of the composition of dental amalgam. Wet chemical analysis can be used to determine the elemental composition of crowns, bridges and partial dentures. Unfilled resin can be analyzed by infrared spectroscopy. Detailed analysis of filled composite restorative resins has not yet been achieved in the "as-set" condition to permit discrimination between manufacturers' products. Future work will involve filler studies and pyrolysis of the composite resins by thermogravimetric analysis to determine percentage weight loss when the sample examined is subjected to a controlled heating regime. With these available techniques, corroborative evidence achieved from the scientific study of materials can augment standard forensic dental results to obtain a positive identification.

Accidents, Aviation↗

PubMed1990

Normal pituitary hormone response to thyrotrophin releasing hormone in dental personnel exposed to mercury.

Basal serum levels of TSH, PRL, T3, T4, cortisol, glucose and calcium were determined in a group of dental personnel (n = 11) exposed to mercury vapour from dental amalgam, and in an occupationally unexposed control group (n = 9). The TSH and PRL responses after injection of 25 micrograms TRH were also analysed. There were no significant group differences in basal hormone levels or in TRH responses. The findings do not indicate a negative influence on the pituitary function at the present low grade, chronic mercury exposure.

Adult↗

PubMed1992

Microstructures of admixed amalgams produced from Pd-containing dispersants.

Blended Pd-containing dental amalgams were developed by substituting Pd for up to 20 w/o Ag or Cu in the Ag-Cu eutectic alloy. Melted ingots were lathe-comminuted to a particle size distribution of 1-45 microns. Alloy blends were created from two parts of a traditional amalgam and one part of experimental Ag-Cu-Pd particles. Amalgams with from 0.42 to 1.67 w/o Pd were fabricated by trituration of alloys and mercury at a Hg/alloy ratio of 1:1 with a mechanical triturator at 5000 rpm for 10 s and hand-condensed. XRD studies of these amalgams revealed the suppression of eta' (Cu6Sn5) phase with Pd addition and no gamma 2 (Sn8Hg) phase found. At 3.3 w/o Pd, the eta' (Cu6Sn5) concentration of the amalgam was below the detection limit of the instrumentation (1%). SEM micrographs revealed that reaction zones around eutectic particles decreased with increased Pd concentration.

Dental Amalgam↗

PubMed1992

Use of self-curing composite resins to facilitate amalgam repair.

Resin cements, which have been shown to adhere to various metal alloys, were investigated as possible repair adhesives for dental amalgam. Test bars of repaired amalgam, formed by condensing new alloy against previously set alloy with or without the use of "adhesive" resins, were subjected to three-point bending measurements of transverse fracture strength. The results indicated that application of adhesive resin did not improve the breaking strength of the repaired specimens from that of specimens prepared without the use of such resins. The breaking strength of all repaired specimens was approximately 15% of the transverse fracture strength of the original intact amalgam bars. Scanning electron microscopy revealed that there was an intermixing of fresh amalgam and unset interfacial resin, which led to mechanical bonding of these materials, but there was no evidence of adhesion of the resin to the previously set amalgam.

Acrylic Resins↗

PubMedDate not supplied

The influence of a packable resin composite, conventional resin composite and amalgam on molar cuspal stiffness.

Packable resin composites may offer improved properties and clinical performance over conventional resin composites or dental amalgam. This in vitro study examined the cuspal stiffness of molars restored with a packable resin composite, a conventional posterior microfilled resin composite and amalgam. Forty-eight intact caries-free human third molars were distributed into four treatment groups (n=12) so that the mean cross-sectional areas of all groups were equal. Standardized MOD cavity preparations were made and specimens restored using one of four restorative materials: (1) a spherical particle amalgam (Tytin); (2) Tytin amalgam with a dentin adhesive liner (OptiBond Solo); (3) a conventional microfilled posterior resin composite (Heliomolar); (4) a packable posterior resin composite (Prodigy Posterior). Cuspal stiffness was measured using a Bionix 200 biomaterials testing machine (MTS). Specimens were loaded vertically to 300 N at a crosshead speed of 1.0 mm/minute. Stiffness was measured at 10 intervals: (1) prior to cavity preparation (intact); (2) following cavity preparation, but before restoration; (3) seven days after restoration; then (4) 1, 2, 3, 4, 5, 6 and 12 months after restoration. All specimens were stored at 37 degrees C in deionized water throughout the study and thermocycled (5 degrees/55 degrees C; 2000 cycles) monthly for 12 months. Repeated Measures ANOVA revealed significant differences among treatment groups over time (p<0.0001). Cavity preparation reduced cuspal stiffness by more than 60%. At 12 months, the cuspal stiffness of restored teeth was, on average, 58% that of intact specimens. Neither the packable nor the conventional resin composite increased cuspal stiffness over that of amalgam.

Acrylic Resins↗

PubMed2000

Considerations in measuring the electrical potentials of metallic restorations in vivo.

Many variables are believed to affect the accurate measuring of metallic restoration electrical potentials. This study examined the effects of intra- versus extra-oral location of the reference electrode, the type of metallic probe used to make contact with the restoration, and scratching and brushing of the restoration surface. Dental amalgam restorations were measured in 40 human subjects. Results showed that only the location of the reference electrode affected the central tendency of the potential. The study discusses the significance of some experimental variables in the accurate measuring of metallic potentials and the need to consider individual subject differences when statistically analysing for the central tendency of a sample.

Adult↗

PubMed2001

Elimination of mercury from amalgam in rats.

The aim of this study was to measure the urinary mercury excretion in rats exposed to amalgam over a two months period. Animals were either exposed to mercury from 4 dental amalgams or fed the diet containing powdered amalgams. The results showed significantly higher mercury amount in urine of both exposed groups than in control. Even two months after the amalgam had been placed in rats teeth, the amount of mercury in the urine remained 4-5 times higher than in control, and 4 times higher than in rats exposed to diet containing powdered amalgam. The elevated urinary Hg amount was accompanied by an increased level of total protein in urine. In the same exposure period the excretion of total protein in urine of rats with amalgam fillings was 2 times higher than in control and 1.5 times higher than in rats exposed to amalgam through diet. Concentrations of mercury in the sera of all groups were below the detection limit of the method. The results show that amount of mercury and protein in the urine of rats were related to the mercury release from dental malgam.

Animals↗

PubMed1985

Wear patterns of composite restorative resins in vivo; observations by scanning electron microscopy.

In this study, the wear pattern of seven commercial composite resins, one experimental composite and one dental amalgam were investigated. These materials were separately inserted in a separation preparation cavity of the patient's mouth. After clinical service for 3, 9 and 12 months the specimens were taken out and observed by scanning electron microscopy (SEM). It was found that the softer resin matrix wore away first while the inorganic filler particles showed no signs of abrasive wear, whereafter filler particles were loosened once there was no support of the resin matrix around them.

Composite Resins↗

PubMed1977

The influence of some manipulative factors on creep.

The effects of a number of factors on creep in dental amalgam was investigated. The factors studied were the delayed time between mixing and packing, the packing technique, the alloy system and the annealing or ageing of specimens at 37 degrees C for one and 190 days. The delayed time and the alloy system factors as well as an interaction between them had a significant influence on the one day annealed specimens. The alloy system in the 190 days annealed specimen was the only factor to affect creep.

Dental Amalgam↗

PubMed1989

Relationship between oral symptoms, salivary function, smoking habits and general health in patients with complaints related to dental restorative materials.

Eighty consecutive patients, referred to the Department of Prosthetic Dentistry, Public Dental Service, Stockholm, for examination of complaints related to dental restorative materials or for supposed adverse effects from mercury released from dental amalgams were investigated. Clinical examination as well as battery of laboratory tests were performed. Statistical correlations were found between subjective and objective oral symptoms and lowered pH-values in stimulated saliva (p less than 0.001) as well as between objective oral symptoms only and lowered pH-values in stimulated saliva (p less than 0.001), which indicate salivary tests to be a useful tool when examining this type of patients.

Adult↗

PubMed1986

Periodontal attachment responses to surgical injury in the cat. Removal of buccal bone with and without placement of foreign body at ligament periphery.

Recently, PDL progenitor cells were claimed essential for the establishment of new connective tissue attachment to root surface. To further test new periodontal attachment after surgical injury, portions of the buccal alveolar plate were removed from the canines of 4 cats. Removal of bone was carried out with or without removal of the underlying PDL, and in half of the experimental sites, dental amalgam was placed at ligament periphery. Tissue blocks were prepared for routine histologic evaluation (H & E) and specific collagen stains (Mallory Trichrome and Mallory PATH). Exfoliation of amalgam was noted in 6 experimental sites during the healing period. At all sites, plaque accumulation and marginal gingivitis were observed before sacrifice. Histologic observation demonstrated limited new connective tissue attachment to root surfaces at PDL periphery where bone, PDL and cementum had been removed. Where PDL was retained, connective tissue attachment was present which appeared to be the result of fiber interdigitation between root-inserted fiber ends and gingival wound edge fibers. "Blockage" of PDL cell migration by amalgam could not be well controlled. However, the placement of amalgam seems to have interfered with new connective tissue attachment and/or cementogenesis. In 5 specimens, root resorption had progressed into dentin. At these sites, collagen tufts appeared to arise from dentin. These tufts were in intimate contact with zones of dense inflammatory cellular infiltrate and connective tissue elements. We suggest that this observation may be a further tissue response to injury, namely: root resorption with the unmasking of dentinal collagen, which may finally lead to fiber interdigitation.

Alveolar Process↗

PubMed1984

Unexpected inorganic elements in oral lesions: results of X-ray energy spectroscopy (XES) on particulate matter in paraffin sections.

X-ray energy spectroscopy (XES) of all particulate matter found by light microscopy in histological sections of 222 oral lesions revealed a much wider range of elements than expected from dental amalgam. Subsequent XES of a variety of endodontic materials, impression materials and toothpastes indicated possible sources for virtually all elements identified in the histopathological lesions. The range of materials identified is tabulated; histopathological lesions and probable source substances are correlated; light microscopic pointers to the elemental nature of particulate matter in sections are indicated--titanium and bismuth have characteristic appearances; possible implications of local implantation and large scale ingestion of such substances are discussed.

Barium Sulfate↗

PubMed1998

Dental materials: 1996 literature review.

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. 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, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

Dental Alloys↗

PubMed1991

Dental materials and magnetic resonance imaging.

Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face and jaw. In this work, we assessed the MRI appearances of dental prosthetic materials in vitro, including precious alloys, nonprecious alloys, ceramic prostheses, dental amalgam, and composite materials. For in vivo studies, these materials were placed in the patient's mouth. Nonprecious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. The in vivo study showed the anatomical zones that were most affected on MRI scans. The size of these zones produced by the presence of nonprecious alloys is influenced by the volume of the prosthesis and is related to the scanning sequence used.

Adult↗

PubMed2000

Resin-based composites and compomers in primary molars.

Resin-based composite resins and polyacid-modified resin-based composites (compomers) have become popular for the restoration of primary anterior and posterior teeth. In some European countries, resin-based composites or glass-ionomers are the materials of choice for primary teeth because of the controversy over dental amalgam and its alleged adverse health effects resulting from the release of mercury, although a clear correlation between amalgam restorations and health has not been determined. Another reason for the worldwide increased use of resin-based composites and glass-ionomers in pediatric dentistry could be attributed to the growing demand from parents to provide esthetic restorations to their children. More conservative preparations can be performed maintaining more tooth structure because of the adhesive properties of the composites and compomers. The most conservative treatment planning and meticulous care in the placement of the resin-based composites and compomers would produce long-term satisfactory results. These restorations should be placed in patients with low-to-moderate caries risk, and after placement the restorations should be monitored carefully to avoid complications mainly produced by recurrent caries and wear.

Adhesives↗

PubMed2001

Shear strengths of a gallium alloy bonded to human enamel following nine different surface treatments.

OBJECTIVE: Gallium and indium-containing alloys have demonstrated an ability to wet and bond to many types of materials including enamel. The purpose of this study was to evaluate and compare the bond strengths of a gallium-and-indium-containing alloy and a dental amalgam to human enamel surfaces. METHOD: A flat enamel bonding surface was created by slicing recently extracted human molars with a 180-grit diamond wheel. Cylinders of amalgam or a gallium-indium alloy were bonded to the as-cut surfaces or to as-cut surfaces that had been pumiced, air-abraded or acid-etched for various times. Before testing, samples were stored under different conditions (100% humidity, immersed in water, thermocycled). The shear-bond strength was determined using a crosshead speed of 0.1 mm x min(-1). Sample size was 10. Data was subjected to ANOVA and a post-hoc Tukey's test. RESULTS: The bond strength of amalgam to enamel was zero. The bond strength of the gallium-indium alloy ranged between 6.5 MPa (10s etch with 10% phosphoric acid) and 4.2 MPa (pumiced enamel). Acid-etching significantly increased the bond strength (P>0.0001) The bond strength was not significantly affected by the type of mechanical surface preparation, storage conditions, thermocycling, etching times or acid concentrations. SIGNIFICANCE: Bonding, particularly chemical bonding, suggests a greater potential for better wetting and therefore better sealing of a cavity. Since microleakage of restorations is one of the principal causes of restoration failure, materials that can bond may in turn posses enhanced resistance to microleakage and ultimately, resistance to restoration failure. The gallium-indium alloy evaluated in this study may be such an alloy.

Acid Etching, Dental↗