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Biomedical subjects

R I Holland

Publications and source records attributed to R I Holland.

At least 19 recordsLinked to original sources
PubMed1992

Corrosion testing by potentiodynamic polarization in various electrolytes.

The effect of different electrolytes on the results from potentiodynamic polarization corrosion testing was studied for nine different dental alloys. In general, the difference in the results was greater between certain alloys using the same electrolyte than between the electrolytes with the same alloy. However, there were some differences between the electrolytes, most pronounced when testing dental amalgams. The electrolyte consisting of 1% NaCl seemed to offer the most corrosive environment. Darvell's and Fusayama's solutions were much less corrosive, at least for dental amalgam specimens. With regard to the ranking by corrosion sensitivity of the amalgams, only the results obtained by using Fusayama's solution were consistent with the clinical experience of the materials.

Analysis of Variance↗
PubMed1991

Use of potentiodynamic polarization technique for corrosion testing of dental alloys.

The number and in particular the diversity in types and composition of alloys used in dentistry are increasing, thus enhancing the need for predictive corrosion testing. No corrosion test is generally accepted as being both applicable to and relevant for all dental alloys. However, some methods have gained a certain recognition, and among these are the potentiodynamic polarization techniques. The purpose of the present work was to study the application, the reproducibility and the influence of some methodological variables on the results of potentiodynamic polarization corrosion testing. Embedded specimens of 18 different dental alloys, representing all major types, were subjected to anodic polarization scan within the potential range of -700 mV to 1000 mV (SCE). Artificial saliva, with and without organic compounds, and sodium sulfide solution were used as electrolytes. The results were processed on a microcomputer using locally developed software. The curves of current density versus potential showed fair reproducibility, with great differences between some of the alloys, showing a clear relationship to nobility or passivity of the alloy. There were marked differences between the results obtained in artificial saliva and in sodium sulfide solution, while addition of organic components to the artificial saliva only had a minor effect. The potentiodynamic polarization corrosion test supplies detailed information such as anodic charge, and open circuit, rupture, and passivation potential. Furthermore, it indicates the passive range and sensitivity to pitting corrosion. These are all useful when evaluating the corrosion properties of a dental alloy. An analysis of variance of the results in this study showed that possible differences between the alloys were clearly detectable with this method. However, for alloys releasing non-ionic products during corrosion/degradation, the method may be inappropriate. It is thus concluded that the method appears applicable as an in vitro corrosion test for most dental alloys, with the possible exception of amalgams.

Analysis of Variance↗
PubMed1990

Effect of placement of amalgam restorations on urinary mercury concentration.

Dental amalgam emits mercury, especially during setting. In addition, the preparation of the amalgam and its compaction into the cavity involve unbound metallic mercury or create a waste product with free metallic mercury. The present study was performed to explore whether emission of mercury in these situations would measurably influence the individual urinary mercury concentration of dental patients as a result of a single-session treatment with dental amalgam restorations. Informed consent was obtained from the patients of nine children about to be treated with amalgam restorations as part of their regular dental care. The children delivered a total of five morning urine samples before, during, and after the treatment period. No effect on the urine mercury concentration was found during the treatment period. Conclusively, one single session of amalgam treatment did not per se represent a mercury exposure of sufficient quantity to be detectable in a longitudinal, individual study.

Adolescent↗
PubMed1989

Studies in oral galvanism: mercury and copper levels in urine, blood and saliva in submerged electrically cutting divers.

The aim of the study was to analyse the concentration levels of mercury and copper in urine, blood/blood plasma and saliva in relation to intra-oral electrical activity. Five Swedish Navy divers took part in the study in order to determine whether working submerged with electrical cutting equipment produced changes in the presence and level of oral galvanism and whether this posed a serious occupational health risk. The investigation concluded that the risk of seriously increased intra-oral electrical activity during welding or cutting activities was small. Development of the study is suggested, with long-term sampling of urine and blood samples of divers supported.

Adult↗
PubMed1987

Correlation between amalgam restorations and mercury concentrations in urine.

The creatinine-adjusted urinary concentration of mercury in 73 schoolchildren with a mean age of 12 years was determined. In addition, the number of amalgam restorations and their size, prevalence of allergy, and days absent from school due to illness were recorded for each individual. A significant positive correlation (r = 0.55) was found between urine Hg and extent of amalgam restorations, but no correlation existed between urine Hg and allergy or between urine Hg and absence from school due to illness. Neither could any correlation be found between extent of amalgam restorations and either allergy or absence from school.

Child↗
PubMed1987

Electrical activity in dental amalgam of submerged divers during welding.

Divers performing underwater manual metal arc welding/cutting (UMMA) have complained about a metallic taste phenomenon. In several dives with voluntary leakage in their diving suits, potential alterations in dental amalgam were registered when they performed UMMA. Polarization resistance values were obtained for the test amalgam cylinders used and the diver's dental restorations. These values, along with the recorded potential values of the amalgam test cylinders and of the diver's dental restorations, enabled us to calculate the depolarizing current, using the law of Ohm. The current depolarizing the amalgam test cylinder did not differ significantly from the mean intermetallic currents between the dental restorations. The clinical effect of intraoral currents when performing UMMA welding should be regarded as small, whereas considerably higher currents should not be ruled out in an intense cutting situation.

Adult↗
PubMed1986

Porosity in posterior composite resins.

The percent pore area and the mean pore size were measured in specimens made of nine brands of composite resin restorative materials. The overall percent porosity ranged from 0.01 to 4.5%. The specimens for the study were prepared in two ways; by condensation or by pressure. Most of the materials, including all those chemically activated, showed more porosity in the condensed than in the pressure specimens. Reversed results emerged for two of the materials, and for another two, the specimens were similar in this respect. The mean pore sizes were smaller in the condensed than in the pressure specimens. Neither mean pore size nor total amount of porosities could be correlated to the curing method of the materials.

Composite Resins↗
PubMed1986

Influence of submerged electrical welding/cutting on dental amalgam in Swedish divers.

Professional commercial divers working with electrical cutting and welding sometimes experience a metallic taste phenomenon. An enquéte study among divers showed no influence of different equipment on the occurrence of such metallic taste, but it seems to occur less frequently in low salinity water. It has been suggested that this metallic taste phenomenon is due to increased corrosion rate of dental restorations, especially of amalgam. Experimental results recording the potential of amalgam specimens placed in the oral cavity of divers during welding, showed influence on the potential, and thus probably on the corrosion rate, during welding only when the diver came into direct contact with the water, e.g. through leakage in the suit.

Adult↗
PubMed1985

Strength and creep of dental amalgam: the effects of deviation from recommended preparation procedure.

The effects of deviations from recommended preparation procedures on the compressive strength, modulus of elasticity, plastic deformation, toughness, and creep of four commercial amalgam alloys have been investigated. Deviations included changes in trituration time, mercury/alloy ratio, and condensation pressure. With regard to both compressive strength and creep, there were great differences in the susceptibility of different amalgam alloys to variations in manipulation. One conventional alloy showed almost no variation in compressive strength as a result of the deviations from the recommended preparation procedure. This material also showed much greater plastic deformation and fracture toughness than the other materials, making it less brittle and probably more resistant to bending forces. Dispersalloy exhibited both increased and decreased strength as a result of the deviations, while ANA 2000 and Revalloy only showed decreased strength. Some of the alterations for ANA 2000 and Revalloy resulted in a decrease in strength below an acceptable clinical level. Regarding the modulus of elasticity, only the conventional alloys were affected by the alterations in the preparation procedure. However, for the plastic deformation, the results were reversed; only the high-copper alloys were affected. The toughness of the specimens was decreased for all the alloys with the exception of one, which was insensitive to changes in the preparation procedure as far as compressive strength was concerned. One of the high-copper alloys showed the least change in creep relative to deviations in preparation procedures. Lowered condensation pressure increased the creep value for all the amalgams; and for the conventional alloys a lowered mercury/alloy ratio also resulted in increased creep.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1985

Influence of variations in preparation of dental amalgam on dimensional stability and porosities.

The susceptibility of amalgam to deviations in the preparation procedure produced an overall trend for both the setting dimensional stability and the number of porosities. The dimensional stability of ANA 2000 was the least affected by the deviations, while ANA 68 exhibited low susceptibility to the deviations when porosities are concerned. Lowered condensation pressure usually increased both the setting expansion and the number of porosities, and vice versa. Dispersalloy exhibited an increased number of porosities with both higher and lower condensation pressure. Except for ANA 2000, undertrituration caused increased expansion and porosities, while overtrituration resulted in increased contraction but minor effects on porosities. Lower mercury/alloy ratio increased the setting expansion and the number of porosities, while the response to a higher ratio was relatively small with the exception of a markedly increased setting expansion for ANA 68.

Chemical Phenomena↗
PubMed1985

Electrochemical potentials of amalgam restorations in vivo.

The potentials of 407 amalgam restorations have been determined in vivo. The measurements were performed with very high impedance equipment, and relative to a Ag/AgCl reference electrode. The readings varied from -23 mV to -595 mV, with 90% of the readings confined to within -127 mV to -431 mV and a mean value of -226.1 mV. Of the restorations, 394 were measured twice, and no significant difference could be found between the first and the second reading. During the study, eight new restorations were inserted. Their potentials varied from -180 mV to -565 mV, with a mean of -339.4 mV, which was significantly lower than that of the older restorations.

Adult↗