Phosphate-bonded Investment Research Articles

Influence of heating rate in thermal expansion of dental phosphate‐bonded investment material

The thermal expansion of a phosphate-bonded investment material was tested when three heating rates were used during the heating procedure. One of them was too low, one too high, and the third, in the middle. The examination was done through the fit of 12 MOD inlays and 12 full crowns in steel master dies. From the results it can be concluded that rates that are too fast must be avoided in the heating procedure, because they reduce the thermal expansion of the phosphate-bonded investment material and thus produce castings with limited fit.

リン酸塩系埋没材硬化時の発熱挙動とその影響 : 第 2 報温度変化と硬化特性との関連

In order to examine the effects of the exothermic behavior of phosphate-bonded investment on dental casting, the setting characteristics were analyzed referring the temperature changes in the previous report. Setting time and expansion were measured for six commercially available phosphatebonded investments. The larger setting time and slower setting expansion were generally observed in the material showing slower and smaller exothermic temperature rise. It was also found that the setting had already initiated before the temperature reached the softening or melting temperature of waxes. The materials used were classified into three groups by the time the peak temperature, 60 to 80℃ appeared : before the start of setting expansion, during expansion, and around the finish of expansion.

Application of gypsum-bonded investment containing niobium carbide on casting of alloy for metal-ceramic restoration

Experimental gypsum-bonded investments containing 0.5-5.0 wt% NbC were prepared by mechanical mixing of each powder. Setting and thermal expansion measurement, compressive strength and casting accuracy for Ni-Cr alloy for metal-ceramic restoration were investigated. Analysis of NbC during heating was carried out by X-ray diffraction, TG-DTA and SEM. NbC was oxidized to Nb2O5 with a volume change between 300-600 degrees C, as in the following equation: 2NbC + 4 1/2O2----Nb2O5 + 2CO2 The theoretical volume of 1/2Nb2O5 calculated from the lattice constants according to JCPDS file was approximately 4 times larger than that of NbC. The experimental investments of 70 wt% cristobalite and 30 wt% gypsum containing 2.0, 3.0 and 5.0 wt% NbC showed large thermal expansion of 7.0, 10.0 and 13.0% respectively. The investment containing 2.0 wt% NbC showed nearly the same casting accuracy for Ni-Cr alloys for metal-ceramic restoration as the commercial phosphate-bonded investment.

Porosity determination of cast investment by a wax-infiltration technique

A reproducible method of determining the porosity (pore volume) of cast investment materials is described. This procedure, requiring no highly specialized equipment, involved the infiltration of a test sample with paraffin wax and the weighing of the wax-infiltrated sample in both air and water. Pore-volume wax is then extracted with chloroform and the sample reweighed. The difference in weight is used to calculate the porosity of the investment material. Pore-volume data thus obtained are comparable to those resulting from standard techniques and far more sophisticated (and expensive) instrumentation. The porosities of hand-mixed samples of gypsum-bonded, phosphate-bonded and silica-bonded investments were 53·9 per cent, 36·9 per cent and 31·4 per cent and those of the vacuum-mixed samples were 52·5 per cent, 31·3 per cent and 26·9 per cent, respectively. The results show that gypsum-bonded investments were more porous than phosphate-bonded investments while silica-bonded investments were the least porous. Hand-mixed samples appeared to have greater porosity than vacuum-mixed samples.

リン酸塩系埋没材硬化時の発熱挙動とその影響 : 第 1 報 硬化時の温度変化

リン酸塩系埋没材硬化時の発熱挙動とその影響 : 第 1 報 硬化時の温度変化

Setting expansion of investment and accuracy of castings

Setting expansion of 4 phosphate-bonded investments was measured under 3 different conditions: a hygroscopic condition, a condition using a ring lined with a wet liner and a condition using a ring lined with a dry liner. Accuracy of castings of a Ni−Cr alloy made in each of the 4 investments in rings lined with a wet liner was measured. One investment exhibited negative potential for hygroscopic expansion. Expansion of all investments in wet-lined rings was not significantly different from their expansion under the hygroscopic condition. There was no significant difference in setting expansion between the investments when a wet liner was used. Significant differences in accuracy existed between castings produced in the different investments using a wet liner. The correlation between the setting expansion of the investments using a wet liner and the accuracy of castings produced using a wet liner was not high and was not significant. Comparison between investments with regard to their ability to produce accurate castings in terms of mould expansion by measurement of setting expansion is of no value.

Measurement Technique of Setting Expansion of Phosphate-Bonded Investment for Lost-Wax Casting

Several measurement techniques were investigated on the setting expansion of a phosphate-bonded investment for lost-wax casting. Measuring the vertical expansion of a cylindrical investment molded in a vessel which was internally lined with an appropriate buffer material, gave a high expansion value. The friction or restriction by the vessel wall accompanied by the progress of the expansion, influenced the expansion value. In the case of measuring the expansion with a differential transformer, an expansion suppressing effect was generated by the load from the sliding-tip of the differential transformer. However, the load was reduced by modification of the differential transformer, which has enabled us to obtain values nearly equal to those by a non-contact type LASER displacement measuring apparatus.

Mechanical studies on cast clasps by a superelastic Ni-Ti alloy. Part 3. Fitness of cast clasps

The purpose of this study is to investigate the influence of setting expansion and thermal expansion of the phosphate-bonded investment on the fitness of cast claspsfabricated by a superelastic Ni-Ti alloy. Investment models were made from the columnar stainless-steel model supposed the abutment tooth the various dilusion colloidal silica solutions.Cast clasps were fabricated using by using a superelastic Ni-Ti alloy, then dimensional changes at the tip and mid-point of clasp arm between before and after fitness of cast clasps to the stainless-steel model were measured by the using of a profile projector. In addition, setting expansion and thermal expansion of investments were measured.Results were as follows:(1) Setting expansion increased with the increase of the concentration of colloidal silca solution, however thermal expansion kept constant.(2) Cast clasps fabrcated by using the investment model with 1.6% of setting expansion and 1.0% of thermal expansion showed the best fitness.

The Influence of the Addition of CaO on the Thermal Expansion of Phosphate-bonded Investment

The Influence of the Addition of CaO on the Thermal Expansion of Phosphate-bonded Investment

Delayed hygroscopic expansion of phosphate-bonded investments

Delayed hygroscopic expansion is caused by immersion of investments after their nominal final set. Its magnitude was established in a previous paper (1) for gypsum bonded investments. In the present investigation high values of delayed hygroscopic expansion were also found for phosphate-bonded investments. In addition, experimental conditions intentionally introduced (liquid concentrations for spatulation and immersion times) caused significant differences upon the measured values of expansion. Such variations if not adequately controlled by the dental laboratory technician can cause severe casting misfits.

The burn-in and devitrification of calcium phosphate crystalline ceramic crowns

Calcium phosphate crystalline ceramics (hereafter referred to as CPCC) is a glass ceramic and the so-called castable ceramic crown. Therefore, taking up CPCC as a material to be casted, adopting phosphate-bonded investment or cristobalite investment as a casting mold, with mold temperature of 400, 500, 600 and 700°C, and using centrifugal casting or air pressure casting as a casting method, 10 specimens were made respectively to the 16 different casting conditions, so that the occurrence of burn-in and devitrification could be studied. Further, the effect of devitrification on crystalization was also studied.The following results were obtained.(1) In case of adopting phosphate-bonded investment, the occurence rate of burn-in became higher as the casting temperature increased. Concering the casting methods, the burn-in occurrence rate was higher for air pressure casting than for centrifugal casting.(2) When cristobalite investment was used, the occurrence rate of burn-in was higher for air pressure casting, while as for the mold temperature, the occurrence rate was maximum at 600°C, but conversely decreased at 700°C, roughening on the casted surface became prominent.(3) The lower the mold temperature was, the lower the occurrence rate of devitrification was and the crystalline size became smaller.(4) Crystals precipitated by devitrification became responsible for deformed crystal structure in the subsuquent crystallization.

Restraining factors affecting setting expansion of phosphate-bonded investments.

The effects of several factors on the setting expansion of a phosphate-bonded investment used in a steel casting ring were studied. The results show that the setting expansion under the conditions analyzed can be characterized only as a most unreliable means to partly compensate for the solid thermal contraction of casting alloys in a precision-requiring technique.

Non-restraining factors affecting setting expansion of phosphate-bonded investments.

Only a few studies on the setting expansion of phosphate-bonded investments have been published. In the present work the effect on the non-restrained setting expansion of mixing time, mixing liquid, mixing device, and volume mixed was investigated for selected brands of this type of investment. It was found that all variables studied may greatly affect the setting expansion, and that the use of the special liquid delivered by the manufacturers in most cases causes an unacceptably high expansion. A modification of the brands studied appears necessary before they can be employed in a precision-requiring technique.

Mold-reaction Products with Phosphate-bonded Investment in Ni-Cr Alloys containing Mn, Si and Al

Mold-reaction Products with Phosphate-bonded Investment in Ni-Cr Alloys containing Mn, Si and Al

Thermal expansion of dental casting alloys and phosphate-bonded investments.

Thermal expansion of dental casting alloys and phosphate-bonded investments.

リン酸塩系埋没材の硬化膨張:第2報 結合材量および基材粒度の影響

リン酸塩系埋没材の硬化膨張:第2報 結合材量および基材粒度の影響

Incidence of bubbles on samples cast in a phosphate-bonded investment

P hosphate-bonded investments are widely used to produce castings of high-fusing alloys for both ceramometal and all-metal dental restorations. These investments are generally stronger, more refractory, and can be manipulated for a greater degree of mold expansion than gypsum-bonded investments. The investments are primarily composed of 75% to 90% silica refractory in the form of quartz or cristobalite, which is initially bound together by magnesium and ammonium magnesium phosphate formed by reaction of magnesium oxide with monoammonium phosphate in water. High temperature burnout results in loss of water, crystallization, recrystallization of magnesium phosphates and formation of silicophosphate glasses, which give the mold high strength at casting temperatures.“’ An unfortunate sideeffect of the initial setting reaction is the liberation of gas (presumably ammonia) bubbles, which often adhere to the surface of the wax pattern and result in positively cast nodules on the surface of the casting (Fig. 1). Such nodules interfere with the fit of the casting and must be removed before the casting is clinically serviceable. This is time-consuming and troublesome for the dental technician and may compromise the fit of the casting if excessive internal grinding is required. It was the purpose of this study to examine the effect of a number of investing variables on the incidence of bubbles cast to wax patterns invested in a phosphatebonded investment. The following investing variables were examined. 1. Liquid/powder ratios 2. Mixing time under vacuum 3. Low speed (hand) vs. high speed (machine) mixing 4. Special liquid/water ratios for a fixed total L/P ratio 5. Use of a debubblizer

Effect of addition of micro-capsules to the disintegration of phosphate-bonded investment

Effect of addition of micro-capsules to the disintegration of phosphate-bonded investment

リン酸塩系埋没材の膨張と鋳造精度 : (第1報)リン酸塩系埋没材の膨張変化

リン酸塩系埋没材の膨張と鋳造精度 : (第1報)リン酸塩系埋没材の膨張変化

Expansion of the Phosphate-bonded Investment and Preciseness of the Casting : Part 2 Effects on Dimensional Accuracy and Fit of Ni-Cr Alloy Castings

Expansion of the Phosphate-bonded Investment and Preciseness of the Casting : Part 2 Effects on Dimensional Accuracy and Fit of Ni-Cr Alloy Castings