Investment strength as a function of time and temperature

OBJECTIVES

The purpose of this investigation was to evaluate and compare the compressive strength characteristics of selected investments and to determine if these change as a function of time and temperature after mixing.

METHODS

Two phosphate-bonded investments and one gypsum-bonded investment were selected and 288 cylindrical specimens were fabricated (n = 9). Baseline compressive strength values were determined for each material at room temperature and compressive strength measurements were made for all materials at 700 degrees C, and at 872 degrees C only for phosphate-bonded investments. Each material was tested at 2, 6, 12, and 24 h after mixing. Specimens were heated at 15 degrees C/min and heat soaked for 5 min in a burnout oven at the applicable testing temperature. They were transferred to a preheated chamber on an Instron testing machine and subjected to a compressive load at a crosshead speed of 2 mm/min until failure. The resulting strength data are presented in MN/m2.

RESULTS

The gypsum-bonded investment did not exhibit marked differences in strength as a function of either time or temperature. The phosphate-bonded investments, on the other hand, demonstrated considerable changes in compressive strength and differed in compressive strength characteristics at 700 degrees C and 872 degrees C respectively.

CONCLUSIONS

At elevated temperatures, all materials approximated peak strength 2 h after initial mixing. At room temperature, the phosphate-bonded investments in this study were not significantly stronger than the gypsum-bonded investment material. However, they exhibited increased compressive strength as a function of time and temperature that was considerably higher than that exhibited by the gypsum-bonded investments.

An evaluation of bond strengths of denture repair resins by a torsional method

Chemical cure resin materials are generally used in the repair of dentures. Different repair resins used may yield different results. The bond strength of three autopolymerizing resins were evaluated using a torsional test method. The results showed that Palapress and Caulk resins had a higher repair strength than Rapid Repair resin.

Five-year performance of high-copper content amalgam restorations in a multiclinical trial of a posterior composite

PURPOSE

This paper reports the 5-year performance of the restorations of the high-copper content dental amalgam alloys included in the worldwide programme of clinical trials of Occlusin, including unique data on wear.

METHODS

The methods employed are common to those previously reported for the multiclinical evaluation of Occlusin. Analysis of the data is limited to simple statistical procedures.

RESULTS

The findings lend support to existing knowledge concerning the favourable performance of restorations of high-copper content dental amalgam alloys, notably in relation to restorations in moderate- to large-sized Class II preparations in permanent molar teeth. Analysis of the data sheds new light on the influences of variables, including type of tooth restored, size and class of restoration and the presence or absence of occlusal contact(s) on performance.

CONCLUSION

Conclusions are drawn regarding ways in which protocols for future evaluations of the type reported should be expanded, and, together with suggestions for further work, it is concluded that this paper is a timely reminder of the value of existing dental amalgam alloys.

A 14-year clinical assessment of 12 amalgam alloys

After 14 years, 40 patients from an in vitro/in vivo study of 12 amalgam alloys were evaluated. All these patients had been attending private practitioners over the past 10 years, and the clinical evaluation revealed that 320 restorations were intact and 47 (12.8%) had been lost. The majority (75.0%) of the lost restorations were lost to crown placement or the replacement with another amalgam restoration. The six high-copper alloys exhibited better clinical performance, in both loss rate and fracture at the margins, than did traditional low-copper materials. Fracture at the margins was a better predictor of the loss of a restoration than were mechanical properties.

An investigation into the incidence of voids in indirect composite inlays formed using different packing techniques

An investigation is described into the incidence of voids in indirect composite inlays formed using different packing techniques and different composite systems. From the results it was found that packing inlays under a 6 bar air pressure prior to light curing produced significantly fewer voids than layering or bulk packing techniques.

Five-year findings of a multiclinical trial for a posterior composite

This paper reports the 5-year findings of a multiclinical (n = 11) trial of a posterior composite restorative. The overall findings, based on data collected from 649 (68 per cent) of the 958 restorations originally included in the study, indicate that the material evaluated satisfies established clinical requirements for posterior composites over periods of up to 5 years. Deviations in the reporting of certain elements of the data appear to have been related to local variations in method.

A 5-year study comparing a posterior composite resin and an amalgam

Eighty class I and class II light-cured posterior composite resin restorations were compared with 43 class I and class II amalgam restorations during a 5-year period after placement. The results of this clinical study showed that both materials were satisfactory during the time period and that the only significant statistical differences are a poorer marginal integrity for the amalgam and a greater wear rate for the composite resin.

Mechanical properties of metal-ceramic alloys at high temperature

Four alloys used for the construction of porcelain-fused-to-metal restorations were tested at high temperatures (1000 degrees C) so that loss of properties could be ascertained. In addition, thin flat plates of metal (30 x 11 x 1 mm) with a 9-mm recess and a metal thickness of 0.35 mm were processed for porcelain application and distortion measured at 15 points along the surface prior to and following each firing cycle. Yield and ultimate tensile strengths and elongation were determined on specimens at room temperature and at 1000 degrees C. None of the alloys tested showed a great amount of distortion during the various firing cycles, yet they showed increased change with each successive heating. The greatest distortion occurred with Jelenko "O" alloy. When the mechanical properties were compared, there was a marked loss of both yield and ultimate strength values for each alloy (Jelenko "O"-Y.S., 95.64%, U.T.S., 96.22%; Olympia--Y.S., 95.08%, U.T.S., 96.76%; Tempo--Y.S., 91.23%, U.T.S., 93.46%; Biobond II--Y.S., 83.72%, U.T.S., 86.21%). Percent elongation increased by 272% with Biobond II and 370% with Jelenko "O", whereas Tempo and Olympia increased by 120 and 155%. It is apparent that the palladium-based alloy and the nickel-chromium-based alloy have higher mechanical properties at the temperature where porcelain will be applied.

13-year clinical assessment of 10 amalgam alloys

The first commercial high-copper amalgam was developed in the mid-1960's. In 1975, a study to evaluate in vivo/in vitro performance of nine of these new alloys was initiated at Indiana University. These nine high-copper amalgams plus a traditional amalgam were tested for four laboratory properties and their gamma-2 content, and were clinically assessed for fracture at the margins. Originally, 60 restorations of each material were placed in patients and then recalled at six, 12, and 24 months. Recently, 13 years post-operatively, approximately one-third of the original patients were located. These patients were given a clinical exam, and photographs were taken of their restorations. From these recall data, the mean loss of all restorations at 13 years was 11.3%. The alloys Cupralloy, Tytin, and Dispersalloy had the lowest loss rates. The evaluation of the fracture at the margins (ridit means) indicates that there are five groups of alloys with some overlap between groups. The alloys Cupralloy, Indiloy, Dispersalloy, and Phasealloy exhibited the least fracture at the margins. The gamma-2-containing alloys--Optaloy II, Micro II, Velvalloy, and Aristaloy CR--showed the greatest rate of fracture at the margins. A correlation matrix of the ridit means at different years, the loss of restorations at 13 years, and the mechanical properties indicate that the early (one- and two-year) fracture at the margins predicts the 13-year results. Mechanical properties, however, do not predict the clinical performance of the materials at 13 years.

A 12-year clinical evaluation of two composite resins

Two composite resin materials were clinically evaluated after 12 years in vivo. Although the Class III restorations did not have the benefit of acid etching and bevels, all 32 restorations in the nine patients who were located were intact, and none needed to be replaced. Stain was the most prominent problem, both at the margins and on the surface of the restorations. Neither wear or marginal integrity appeared to be a problem.

Fluoride distribution in teeth using a silicate model

The fluoride determinations were done on enamel biopsies taken before and after restoration of extracted teeth with silicate cement. Two sites, one near the restoration and one 3 mm or more away from the restoration, were assayed. No difference was noted in pre- and post-restoration biopsies when teeth were restored with a fluoride-free silicate. Post-restoration biopsies at sites near and away from the restoration were significantly higher in fluoride as compared to pre-restoration biopsies when the teeth were restored with a fluoride-containing silicate.

Social class and ethnicity effects on clinical judgments

To resolve conflict between earlier studies finding contradictory recommendations on need for professional help of middle- vs lower-class persons given normal, neurotic, and psychotic behavior descriptions, and to explore ethnicity effects, 92 students (70 Anglo, 22 Chicano) rated fictitious biographical vignettes. A pro-middle-class bias was found consistent with Routh and King's study but inconsistent with that by Schofield and Oakes. Also contrary to the latter, treatment recommendations agreed with ratings. Ethnicity bias appeared, since Anglos recommended Chicanos more often for involuntary hospitalization. Inconsistency between the two earlier studies results from a methodological variation, discussed in this study.

A comparison of pin-retained amalgam and composite resin cores

The 24 hour tensile loads required to separate the core material and dentin produced the following results: 1. No statistical difference was found between the tensile strength of retained amalgam and composite resin core materials. 2. Generally, no statistical difference was found between the retentive ability of three and four pins. 3. No statistical difference was found between the retentive ability of regular pins and minim pins if three or more pins were employed. 4. As the number of regular pins was increased beyond three, and when four minim pins were used, there was a very significant increase in dentin fracture.

Influence of certain manipulative variables on the static creep of amalgam

The effects of trituration time on the creep of eight commercial dental amalgams was determined. The data show that trituration time does influence the creep of amalgam, but its magnitude varies from one alloy to another. The condensing procedure also influences creep.

An evaluation of silicophosphate as an orthodontic cement

In a laboratory and clinical evluation, when used for the cementation of orthodontic bands, a zinc silicophosphate cement has proved to be comparable to zinc phosphate cement in its bond strength to enamel. This was demonstrated in laboratory tests by higher values being required to break the mechanical bond and in the clinical study by the slightly smaller percentage of bands which became loose during orthodontic treatment. In both the laboratory and clinical studies it was found that silicophosphate remained attached to the enamel in higher percentages after a band had become loose. It also was found that the remaining cement was often quite difficult to remove from the enamel. Probably the greatest advantage of using silicophosphate is that no decalcification of enamel was found under bands which had become loose during orthodontic treatment. This may be attributable to the higher bond strength and/or the presence of fluoride in the cement. Further clinical studies of this nature appear warranted.

Addition of fluoride to pit and fissure sealants--a feasibility study

The data obtained in this in vitro study indicate that contact with pit and fissure sealants to which NaF has been added in amounts ranging from 2 to 5% substantially increases the fluoride content of the enamel and reduces its solubility in acid. The properties of the materials do not seem to be impaired by the addition of fluoride in these amounts. It thus appears that this approach to providing a backup anticariogenic mechanism may, indeed, be feasible. However, further investigation must be done to confirm the anticariogenic effect and to establish the most efficacious means of fluoride incorporation in the materials.

In vitro wear response of composite resin, amalgam, and enamel

A two-body, wear-testing method was developed and the test results were used for comparing and ranking the rate of wear for an amalgam, an experimental composite resin, and a commercial composite resin. The ranking of wear found by this method was the same as that shown by clinical research for the rate of wear of amalgam and commercial composite resin.

Effects of restorative materials on plaque composition

Analysis of certain components of plaque grown at margins of restorations shows variation in composition with time. Stability occurs within one year in vivo. Comparable plaque grows on all materials tested with the exception of silicates. Fluorides within silicates apparently cause the difference in this plaque composition.

Effect of fluoride-containing zinc oxide-eugenol cements on solubility of enamel

The solubility of intact enamel surface was reduced by contact with zinc oxide-eugenol formulations to which sodium fluoride or stannous fluoride was added. The magnitude of the reduction was comparable to that incurred in enamel in contact with silicate cement. No change in solubility was observed when fluoridefree zinc oxide-eugenol cements were used.

Party switching, authoritarianism, and dogmatism in the 1964 election

Postulating that primary group identification is stronger than ideology, it was predicted that there would be no differences on the California F Scale or the Rokeach Dogmatism Scale between supporters of Goldwater and Johnson or a great amount of party switching and that those who switched would have higher mean scores on both scales than those who did not switch on the grounds that ideology must be intense to overcome primary group loyalty. All hypotheses were confirmed.

Direct pH determination of setting cements. 2. The effects of prolonged storage time, powder/liquid ratio, temperature, and dentin

SYNOPSIS IN INTERLINGUA

DETERMINATION DIRECTE DEL pH DE CEMENTOS IN PRISA.-Le resultatos del presente studio indica que le pH se stabilisava verso le fin de 48 horas. A generalmente parlar, plus basse proportiones de pulvere a liquido reduceva le lecturas initial de pH, durante que mixturas spisse exerceva un effecto minus pronunciate super le augmento del pH. Le duo mixturas plus spisse de cementos a phosphato de zinc, a silico-phosphato, e a cupro Typo II esseva proxime a pH 7, durante que cementos de silicato e a cupro Typo I, quando mixte in le mesme proportiones, esseva approximativemente 5,5 al fin de 1 mense. Augmentos del temperatura e contacto con structuras dental haheva solo modestissime influentias super le augmento del pH de varie cementos.

Direct pH determinations of setting cements. I. A test method and the effects of storage time and media

SYNOPSIS IN INTERLINGUA

DETERMINATIONES DIRECTE DEL PH DE CEMENTOS IN PROCESSO DE PRISA.—In general, le massa interne del cementos esseva minus acide que le superficie externe. Le pH de omne le cementos montava in le curso del tempore. Inter le materiales investigate, cementos a phosphato de zinc e a argento e phosptiato de zinc habeva le plus rapide augmentos, Le plus acide del materiales investigate esseva le cementos a cupro rubie e a cupro nigre. Le pH del cementos a silicate jaceva inter illo del eementoa a cupro e illo del cementos a phosphato de silicium. Esseva trovate un relation directe inter le pH de silicatos e le proportion de liquido a pulvere: quanta plus sgisse le mixtura, tanto plus alte le pH.