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Biomedical subjects

D B Mahler

Publications and source records attributed to D B Mahler.

At least 37 records · Page 2Linked to original sources
PubMed1987

Effect of time at 37 degrees C on the creep and metallurgical characteristics of amalgam.

When aged at 37 degrees C for six months, dental amalgam exhibits a marked decrease in the property of creep. The objective of this study was to investigate the relationship between this decrease in creep and selected metallurgical characteristics. The formation of beta 1 (Ag-Hg), the grain size of gamma 1 (Ag-Hg), and the composition of gamma 1 were chosen for investigation. Creep was determined according to ADA Specification test No. 1, beta 1 was measured by x-ray diffraction, and gamma 1 grain size and gamma 1 composition were determined by electron-probe microanalysis. The results showed that the decrease in creep was related to beta 1 formation and not to changes in either gamma 1 grain size or gamma 1 composition.

Chemical Phenomena↗
PubMed1986

Modulus of elasticity in bending of composites and amalgams.

In this study, the modulus of elasticity in bending (a measure of rigidity) and transverse strength (a measure of edge strength) were determined for composites and amalgams. the results were as follows. The modulus of elasticity of microfilled composites is approximately one-third that of the macrofiller-containing composites. Composites containing a relatively coarse-sized macrofiller have a higher elastic modulus than those containing a finer macrofiller. The transverse strength of microfilled composites is approximately one half that of the macrofiller-containing composite, which, in turn, is close in value to the transverse strength of amalgam. High-copper amalgams are substantially more rigid than the traditional low-copper amalgams, but do not show large differences among themselves. The transverse strength among various amalgams does not appear to be related to amalgam type but does correlate to final Hg content. The modulus of elasticity of composites most likely to be used in posterior teeth is approximately one third of the modulus of elasticity of amalgam; that is, amalgams are three times more rigid.

Composite Resins↗
PubMed1986

Standardizing evaluations of the clinical marginal fracture of amalgam.

In this study, we investigated both inter-examiner and intra-examiner differences in the evaluation of the marginal fracture characteristics of dental amalgam restorations. Evaluations were made by matching intra-oral photographs of the occlusal surfaces of clinical restorations to a reference set of clinical photographs illustrating increasing amounts of marginal fracture. Four amalgam alloys and five examiners provided the data base. Differences in marginal fracture indices were found among examiners and between evaluation times for the same examiners. However, these differences were reduced significantly after application of a standardization procedure.

Dental Alloys↗
PubMed1984

Microprobe analysis of three high-copper amalgams.

Three single-composition, high-copper amalgams were analyzed for the composition of their before- and after-reaction phases. The method used was electron probe microanalysis. The results may be summarized as follows: All alloys consist essentially of Ag3Sn (gamma), Cu3Sn (epsilon), and, in some cases, Ag4Sn (beta). When the original alloy contains higher amounts of Cu, more Cu is found in solution in the Ag3Sn (gamma) and Ag4Sn (beta) phases. The reaction phases in amalgams made from these alloys consist essentially of Ag22Sn Hg27(gamma 1) and Cu6Sn5 (eta'), with no detectable Sn8Hg (gamma 2). When In is present, it is found principally in the Ag3Sn (gamma) and Ag22Sn Hg27(gamma 1) phases, and both the gamma and gamma 1 phases are of different composition than that for the other alloys. When Pd is present, it is found principally in the Cu3Sn (epsilon), Cu6Sn5 (eta'), and Ag22Sn Hg27(gamma 1) phases.

Chemical Phenomena↗
PubMed1984

Factors affecting the marginal leakage of amalgam.

On the basis of reports of an increased incidence of postoperative sensitivity associated with the use of a particular spherical amalgam alloy, an investigation of in vitro marginal leakage was initiated. An air pressure test was applied to simulated Class I restorations made from this alloy and a control alloy. Factors such as mix plasticity, condensation force, and condensation technique also were examined. The results showed that the spherical alloy in question had a greater tendency for marginal leakage than the control alloy. For both alloys studied, the following factors are important in reducing marginal leakage: increased plasticity of the mix; increased condensation force; condensation of each increment directly along or against cavity walls in overlapping thrusts; and burnishing the amalgam after condensation. Although it is not known what percentage of postoperative sensitivity is caused by leakage of amalgam restorations, the results of this study indicate that leakage can be minimized by using optimum amalgam manipulative procedures and that a reduced incidence of postoperative sensitivity is likely to result.

Chemical Phenomena↗
PubMed1981

Effect of age on the creep of a high-copper amalgam.

A previous study of the effect of final Hg content on the static creep of a single-composition high-Cu amalgam alloy showed a sudden increase or jump in creep at a specific Hg content, and the presence of the Sn-Hg phase (gamma 2) at final Hg contents subsequent to this creep jump. This observation is consistent with the less-than-optimum clinical performance reported for this alloy. A repetition of these tests conducted on test specimens 3 months and 6 months of age showed the creep jump to shift to higher Hg contents. However, even at 6 months of age, the final Hg content to be expected in clinical restorations was still positioned after the initiation of the creep jump where a small amount of gamma 2 is known to be present.

Chemical Phenomena↗
PubMed1980

Clinical assessments of dental amalgam restorations.

In assessing the performance of amalgam restorations in most clinical studies, the significant factor to evaluate is marginal fracture. The clinical relevance of marginal fracture is reflected in its relationship to the presence of secondary caries. Furthermore, whereas most other failures can be avoided by proper operator technique, marginal fracture is an inherent deficiency of amalgam restorations. Although the extent of marginal fracture can be influenced by many factors, the nature of the alloy has been found to play a major role. However, for a properly conducted study, other factors which include the operator, patient and tooth type should be acknowledged in the research design. To evaluate marginal fracture in clinical studies, the occlusal photograph--visual assessment technique is a most sensitive method and the scoring of test restorations according to a standard set of photographs has several significant advantages.

Dental Alloys↗
PubMed1979

The influence of final mercury content on the characteristics of a high-copper amalgam.

In this study, specimens of a high-copper amalgam, prepared at different final Hg contents, were examined in several different experiments. The results showed that as the Hg content is increased, a point is reached beyond which creep and the amount of Sn in gamma1 exhibit a sudden increase. As the Hg content is increased further, gamma2 can be detected. These phenomena can be explained by the hypothesis that insufficient Cu is present at higher Hg contents to combine with Sn to form Cu6Sn5.

Chemical Phenomena↗
PubMed1979

Behavior of three high-Cu amalgams.

Amalgams made from three single-composition high-Cu alloys of the same nominal composition were investigated for differences in creep behavior. The curves of creep vs. final Hg content for all three alloys showed a sudden creep increase (jump) at approximately 46% final Hg content. Previous studies have shown this creep jump to be associated with the initiation of the Sn--Hg phase (gamma 2). The anticipated final Hg content in clinical restorations for two of these alloys is below the creep jump and gamma 2 would not be expected. On the other hand, the clinical Hg content for the third alloy was above its creep jump and gamma 2 would be expected. The effect on clinical behavior of this finding require further investigation.

Chemical Phenomena↗
PubMed1979

The effect of time on the marginal fracture behaviour of amalgam.

In this study the effect of time on the marginal fracture behaviour of amalgam was determined. Six alloys in clinical service for up to 6 years were used as a data base and occlusal photographs were categorized according to a standard set of photographs depicting varying degrees of marginal fracture. The standard set of photographs was assigned a linear numerical scale, and the index of extent of fracture was considered to be an arithmetic mean based on this linear scale. An observed patient effect and unequal sample size were considered in the determination of both the mean and variance. The results of applying these procedures to the data of this study showed that marginal fracture increased with time for all alloys; that the relative ranking of alloys did not change with time; and that, with certain limitations, early time evaluations can predict long-term behaviour.

Dental Alloys↗
PubMed1979

Clinical performance of a gold-containing amalgam.

In this study, the clinical performance (marginal fracture) of a gold-containing amalgam was compared to five traditional gamma 2-containing amalgams and one non-gamma 2 amalgam. The results showed that the performance of this gold-containing amalgam was bettered by the non-gamma 2 amalgam and four of the five gamma 2-containing amalgams. A microprobe evaluation of a five-year-old clinical restoration made from this alloy revealed an unusual corrosion pattern.

Chemical Phenomena↗
PubMed1979

The effect of the operator on the clinical performance of amalgam.

In this study, the effect of the operator on the clinical performance of amalgam was examined by evaluating the marginal fracture characteristics of four alloys placed by four operators. The results were as follows: --Marginal fracture was influenced by the operator. Therefore, careful attention should be given to the cavity design and the placement technique. --The interaction between operators and alloys was such that, for the worst alloy, there was no difference caused by the operators; for the intermediate alloys, there were large differences caused by the operators; and for the best alloy (a non-gamma 2 system), there was almost no difference caused by the operators. --The difference in marginal fracture characteristics among alloys was greater than the difference attributed to operators. --It appears that all practitioners should use non-gamma 2 amalgams because such amalgams perform better clinically and are less susceptible to variations in operators.

Clinical Competence↗