Rematitan Plus Research Articles

A quality assessment of titanium castings produced in an experimental short-heating-cycle investment

The aim of this study was to evaluate the quality of casting produced in an experimental short-term heating-cycle investment. Thus, reaction layer and castability of titanium casting using an experimental spinel-based investment (VR) with short heating cycle were compared with the commercial short-heating-cycle spinel-based investment Trinell (TR), the silica-phosphate-based investment Rematitan Plus (RP), and the conventional spinel-based investment Rematitan Ultra (RU). VR has polymeric fibers added to inorganic particles. Reaction layer assessments were carried out using Vickers hardness and elemental analysis using dispersive X-ray microanalysis (EDX). Mesh patterns were used for castability test, and powder characterization was made by scanning electron microscopy (SEM). Hardness evaluation showed no difference among the investments between 100 and 200 µm. The most important contaminant element for VR, TR, and RU was oxygen. Higher levels of mold filling were found for TR, VR, and RU compared with that obtained with RP. The quality of castings, characterized by means of the assessments of reaction layer and castability, made from the VR was similar to the commercial investments TR and RU but superior to the RP.

Improvement to the marginal coping fit of commercially pure titanium cast in phosphate-bonded investment by using a simple pattern coating technique

Coatings of zirconite, Y(2)O(3) or ZrO(2) on wax patterns before investing in phosphate-bonded investments have been recommended to reduce the reaction layer in titanium castings, but they are not easily obtainable. Spinel-based investments are relatively stable with molten titanium and could be used as coatings to improve the quality of castings made with those investments. The purpose of this study was to evaluate the effect of pattern coating with a commercial spinel-based investment before investing in 1 of 3 phosphate-bonded inves tments on the marginal coping fit and surface roughness of commercially pure titanium castings. Ten square acrylic resin patterns (12 × 12 × 2 mm) per group were invested in the phosphate-bonded investments Rematitan Plus (RP), Rema Exakt (RE), and Castorit Super C (CA) with or without a coating of the spinel-based investment, Rematitan Ultra (RU). After casting, the specimens were cleaned and the surface roughness was measured with a profilometer. Copings for dental implants with conical abutment were invested, eliminated, and cast as previously described. The copings were cleaned and misfit was measured with a profile projector (n=10). For both tests, the difference between the mean value of RU only and each value of the phosphate-bonded investment was calculated, and the data were analyzed by 2-way ANOVA and Tukey's HSD test (α=.05). In addition, the investment roughness was measured in bar specimens (30 × 10 × 10 mm), and the data (n=10) were analyzed by 1-way ANOVA and Tukey's HSD post hoc test (α=.05). Two-way ANOVA for casting surface roughness was significant because of the investment, the coating technique, and the interaction between variables. One-way ANOVA was performed to prove the interaction term, and Tukey's post hoc test showed that RP with coating had the lowest mean, while RP had the highest. CA with coating was not different from RP with coating or CA without coating. RE with coating was similar to CA, while RE was different from all groups. For coping marginal fit, the 2-way ANOVA was significant for the investment, the coating technique, and the interaction between variables. The interaction was analyzed by1-way ANOVA and Tukey's HSD test that showed no significant difference among the coated groups, which had better marginal fit than the groups without coating. Among the groups without coating, CA had significant lower marginal misfit than RP, while RE was not different from CA and RP. For the investment surface roughness, the 1-way ANOVA was significant. CA and RU were smoother than RE and RP (P<.001). The coating technique improved the quality of castings fabricated with phosphate-bonded investments.

The surface roughness analysis of the titanium casting founding by a new titanium casting investment material

To investigate the surface roughness property of the titanium castings cast in a new investment for titanium casting. Six wax patterns (20 mm × 20 mm × 0.5 mm) were invested using two investments: three in a new titanium investment material and three in the control material (Rematitan Plus). Six titanium specimens were obtained by conventional casting. After casting, surface roughness of the specimens were evaluated with a surface profilometer. The surface roughness of the specimens cast in new titanium investment material was (1.72 ± 0.08) µm, which was much smaller than that from Rematitan Plus [(1.91 ± 0.15) µm, P < 0.05]. The surfaces of titanium cast using these two investment materials are both smooth enough to fulfill the demand of the titanium precision-casting for prosthodontic clinical use.

Effect of different investments and mold temperatures on titanium mechanical properties

The aim of the present study was to evaluate commercially pure titanium (CP Ti) casting quality when a specific to titanium and a conventional phosphate bonded investments were used under different mold temperatures. For this, the evaluated parameters were surface roughness, bending strength, Vickers microhardness, casting quality by radiographies and microstructure of CP Ti. Wax patterns (28 mm × 3 mm × 1 mm) were invested using two phosphate bonded investments: Rematitan Plus (REM), specific to titanium, and Castorit Super C (CAS), a conventional investment, fired and cooled until reaching two mold temperatures: 430 °C (430) and room temperature (RT). Specimens were cast from CP Ti by plasma. After casting, specimens were radiographically examined and submitted to Vickers microhardness, roughness and bending strength evaluation. Microstructure was analyzed in the center and at the surface of specimen. Qualitative analysis of radiographs showed that specimens which were cast using CAS-RT presented more casting porosities while the specimens which were cast with REM-430 did not present any casting porosity. No significant difference was noted among the groups in the surface roughness and Vickers microhardness data, but the bending strength of the specimens cast using CAS was greater than REM groups. The microstructure of the specimens of the different groups was similar, presenting a feather-like aspect. Casting porosities found in the specimens cast using conventional investments (CAS) and lower mold temperatures would limit their use, even mechanical properties were similar than in specimens cast using specific to titanium investment (REM) at temperatures recommended by the manufacturer.

The influence of short-heating-cycle investments on the quality of commercially pure titanium castings

A new short-cycle, spinel-based investment was developed to minimize the long heating cycle generally required for conventional investments for titanium castings, but the quality of castings made using this material has yet to be evaluated. The purpose of this study was to compare the Vickers hardness, castability, surface roughness, in vitro marginal misfit, and internal porosity of castings made using silica phosphate-based and spinel-based investments. The specimens were commercially pure titanium cast using silica phosphate-based investment, Rematitan Plus (RP), and spinel-based investments, Rematitan Ultra (RU) or short-heat-cycle Trinell (TR). Disc-shaped patterns (6 × 3 mm) were cast, and Vickers hardness was measured at the surface, and 50, 100, 150, and 200 μm beneath the surface (n=10). Microstructure was analyzed by optical microscopy (×100). Mesh patterns (14 × 14 × 0.5 mm) were used for castability testing (n=10). Surface roughness (Ra) was measured on disc-shaped patterns (13 × 3 mm) with a profilometer (n=8). Wax copings were cast, screwed to implant abutments, and the marginal misfit was measured using image analysis software (n=10). Internal porosity of the copings was evaluated by density comparisons (n=10). Hardness data were analyzed by 2-way ANOVA and the Tukey HSD test. Castability, surface roughness, and marginal misfit were analyzed by 1-way ANOVA and the Tukey HSD test, and internal porosity by Kruskal-Wallis and Student-Newman-Keuls tests (α=.05). RP had the highest hardness values at the surface and 50 μm beneath, but the hardness values of TR, RU, and RP were statistically equivalent at 100, 150, and 200 μm. Significant differences were seen when comparing RU and TR with RP for castability (P<.001), surface roughness (P<.001), and marginal misfit (P<.001). No significant differences were seen for internal porosity. The quality of castings made from the new investment, TR, was similar to the quality of those made using the conventional spinel-based investment, RU, and superior to those made using RP.

The Effect of Coating Patterns with Spinel-Based Investment on the Castability and Porosity of Titanium Cast into Three Phosphate-Bonded Investments

This study evaluated the effect of pattern coating with spinel-based investment Rematitan Ultra (RU) on the castability and internal porosity of commercially pure (CP) titanium invested into phosphate-bonded investments. The apparent porosity of the investment was also measured. Square patterns (15 × 15 × 0.3 mm(3)) were either coated with RU, or not and invested into the phosphate-bonded investments: Rematitan Plus (RP), Rema Exakt (RE), Castorit Super C (CA), and RU (control group). The castings were made in an Ar-arc vacuum-pressure machine. The castability area (mm(2) ) was measured by an image-analysis system (n = 10). For internal porosity, the casting (12 × 12 × 2 mm(3) ) was studied by the X-ray method, and the projected porous area percentage was measured by an image-analysis system (n = 10). The apparent porosity of the investment (n = 10) was measured in accordance with the ASTM C373-88 standard. Analysis of variance (One-way ANOVA) of castability was significant, and the Tukey test indicated that RU had the highest mean but the investing technique with coating increased the castability for all phosphate-bonded investments. The analysis of the internal porosity of the cast by the nonparametric test demonstrated that the RP, RE, and CA with coating and RP without coating did not differ from the control group (RU), while the CA and RE casts without coating were more porous. The one-way ANOVA of apparent porosity of the investment was significant, and the Tukey test showed that the means of RU (36.10%) and CA (37.22%) were higher than those of RP (25.91%) and RE (26.02%). Pattern coating with spinel-based material prior to phosphate-bonded investments can influence the castability and the internal porosity of CP Ti.

Effect of phosphate-bonded investments on titanium reaction layer and crown fit

This study analyzed the reaction layer and measured the marginal crown fit of cast titanium applied to different phosphate-bonded investments, prepared under the following conditions (liquid concentration/casting temperature): Rema Exakt (RE) - 100%/237 degrees C, 75%/287 degrees C, Castorit Super C (CS)-100%/70 degrees C, 75%/141 degrees C and Rematitan Plus (RP)- 100%/430 degrees C (special to titanium cast, as the control group). The reaction layer was studied using the Vickers hardness test, and analyzed by two way ANOVA and Tukey's HSD tests (alpha = 0.05). Digital photographs were taken of the crowns seated on the die, the misfit was measured using an image analysis system and One-way ANOVA, and Tukey's test was applied (alpha = 0.05). The hardness decreased from the surface (601.17 VHN) to 150 microm (204.03 VHN). The group CS 75%/141 degrees C presented higher hardness than the other groups, revealing higher surface contamination, but there were no differences among the groups at measurements deeper than 150 mum. The castings made with CS - 100%/70 degrees C presented the lowest levels of marginal misfit, followed by RE -100%/237 degrees C. The conventional investments CS (100%) and RE (100%) showed better marginal fit than RP, but the CS (75%) had higher surface contamination.

Differing Expansion Contributions of Three Investment Materials Used for Casting Titanium

This laboratory study aimed at investigating the effect of setting expansion (SE), which could enlarge a wax pattern by concurrent exothermic reaction. Two phosphate-bonded investment materials (Rematitan Plus, T-invest C & B) and alumina-magnesia-based investment material (Titavest CB) were subjected to setting temperature and SE measurements (n = 10). Full-crown wax patterns were prepared from metal dies having the same design. Crown castings (n = 6) were made using a one-chamber high-pressure casting machine. Commercially pure titanium ingot (Japanese Industrial Standard Class II) was used for each casting. Dimensional accuracy of the cast crowns was expressed by marginal discrepancy for a pair of wax pattern and casting prepared from the same die. All results were then subjected to regression analysis. Rematitan Plus gave the highest setting temperature (about 70 degrees C) and the highest SE (1.16 +/- 0.01%) almost concurrently. The result was that Rematitan Plus produced oversized crowns from the lowest thermal expansion (TE) value (0.53 +/- 0.05%) reducing the linear correlation to 0.80 (p < 0.05). No significant linear relationship was found between SE of investment material and crown-casting accuracy. The almost concurrent occurrence of high SE and high setting temperature generation in Rematitan Plus enlarged the wax pattern and effectively supplemented its low TE to produce oversized crowns. Despite this adverse effect, the correlation between TE and crown accuracy was still high. It is generally expected that the TE values given by manufacturers predict crown accuracy, when uniform TE, small SE, and minimum heat generation during setting are assured.

Effect of commercial dental investments at low temperature on the marginal adaptation of cast cp Ti inlays

Aim: The purpose of this study was to evaluate the adaptation of inlay restorations cast in commercially pure titanium (cp Ti) after inclusion of the wax patterns in either a phosphate-bonded investment (Rematitan Plus® ) or a silicon oxide-based investment (Termocast® ). Methods: The wax patterns were prepared over an inlay-type mold. After waxing, 5 measurements of the marginal adaptation were made on the mesial and distal faces. Five wax patterns were included in each type of investment under vacuum. The cast specimens were repositioned in the mold and other 5 measurements of the adaptation were made based on the same initial testing conditions. Data were analyzed statistically by two-way ANOVA and Duncan’s post-hoc (P<0.01) using the SPSS statistical software package version 12.0 (SPSS, Chicago, IL, USA). Results: The mean marginal discrepancies of the MOD inlays were higher in the Termocast® Group. Termocast® presented significantly greater marginal discrepancy than Rematitan Plus® . Due to the great permeability of the investment refractory material, internal porosity was extremely rare in Rematitan Plus® and more common in Termocast® . Conclusion: It may be concluded that Termocast® investment should not be indicated for cp Ti casting due to poor adaptation and porosity on the casting surface.

Surface Porosity of Different Investment Materials with Different Mixing Techniques

Aims: To evaluate and compare the number and surface area of surface porosities of different dental investmentmaterials by using two mixing techniques. Materials and Methods: Two mixing techniques;manual and mechanical were used to prepare specimens for four dental investment materials: Biosint Supra,Rema Exakt, Rematitan Plus, and Deguvest soft. Computer programs are used to measure the numberand surface area of the porosities to compare among them. ANOVA, Duncan multiple range test in additionto T–test were carried out to determine the significant difference at Parea of the porosities, there are high significant differences among the investment materials tested, andhigh significant difference is presented between the two mixing techniques tested with the manual mixingtechnique and showing higher value than the mechanical vacuum mixing technique. In relation to the numberof porosities, there are no significant difference among the investment materials tested, but there arevery high significant differences between the two mixing techniques tested with the manual mixing techniqueand showing higher value than the mechanical vacuum mixing technique. Conclusions: the numberand surface area of the surface porosities differ from the different materials used, and differ in the samematerial by changing the mixing technique

Internal adaptation of cast titanium crowns.

As the adaptation of titanium crowns obtained by Rematitan Plus investment, specific for titanium, is not recognized to be suitable, this study evaluated the effect of the concentration of the specific liquid and the temperature of the mold of investments on the internal misfit of crowns cast on commercially pure titanium. Individual dies of epoxy resin were obtained, representing teeth prepared for full-crown restoration with a 6-degree axial surface convergence angle and shoulder (1.0 mm). For the waxing of each crown, a ring-shaped stainless steel matrix (8.0mm internal diameter; 7.5 mm height) was adapted above the individual dies of epoxy resin. The Rematian Plus investment was mixed according to the manufacturer's instructions using two different concentrations of the specific liquid: 100%, 75%. Casting was performed in a Discovery Plasma Ar-arc vacuum-pressure casting machine with molds at temperatures of 430°C, 515°C and 600°C. The crowns were cleaned individually in a solution (1% HF + 13% HNO3) for 10 min using a ultrasonic cleaner, with no internal adaptations, and luted with zinc phosphate cement under a 5 kg static load. The crown and die assemblies were embedded in resin and sectioned longitudinally. The area occupied by cement was observed using stereoscopic lens (10X) and measured by the Leica Qwin image analysis system (mm2). The data for each experimental condition (n=8) were analyzed by Kruskal-Wallis non-parametric test (á=0.05). The results showed that liquid dilution and the increase in mold temperature did not significantly influence the levels of internal fit of the cast titanium crowns. The lowest means (±SD) of internal misfit were obtained for the 430°C/100%: (7.25 mm2 ±1.59) and 600°C/100% (8.8 mm2 ±2.25) groups, which presented statistically similar levels of internal misfit.

Evaluation of the thermal shrinkage of titanium and the setting and thermal expansion of phosphate-bonded investments

There are few studies on titanium casting shrinkage, and phosphate-bonded investments for titanium casting have not produced appropriate marginal fit. The purpose of this study was to determine the thermal shrinkage of titanium and the setting and thermal expansion of 3 phosphate-bonded investments. The thermal shrinkage between the melting temperature and room temperature was calculated using a titanium thermal expansion coefficient. The thermal and setting expansion were measured for 3 phosphate bonded investments: Rematitan Plus (RP) specific for titanium, Rema Exakt (RE), and Castorit Super C (CA), using different special liquid concentrations (100%, 75%, and 50%). Setting expansion was measured for cylindrical specimens 50 mm long x 8 mm in diameter with a transducer. The heating and cooling curves were obtained with a dilatometer (DIL 402 PC). The total expansion curve was drawn using software, and temperatures to obtain expansion equivalent to titanium casting shrinkage were determined (n=5). In addition, the total expansion of the control group (RP at 430 degrees C) was measured, as well as the temperatures at which the other groups achieved equivalent total expansion (n=5). Data were analyzed by 1-way ANOVA and the Tukey HSD test (alpha=.05). Titanium casting shrinkage was estimated as 1.55%. RP did not achieve this expansion. RE achieved expansion of 1.55% only with a special liquid concentration of 100% at 594 degrees C. CA with all special liquid concentrations attained this expansion (351 degrees C to 572 degrees C). Total expansion of the control group was 0.86%, and the other groups reached that expansion within the range of 70 degrees C to 360 degrees C. Only RE and CA demonstrated sufficient expansion to compensate for titanium casting shrinkage. All groups reached total expansion equivalent to that of the control group at significantly lower temperatures.

Influence of the final temperature of investment healting on the tensile strength and Vickers hardness of CP Ti and Ti-6Al-4V alloy.

The aim of the work was to evaluate the influence of the temperature of investment healting on the tensile strength and Vickers hardness of CP Ti and Ti-6Al-4V alloy casting. Were obtained for the tensile strength test dumbbell rods that were invested in the Rematitan Plus investment and casting in the Discovery machine cast. Thirty specimens were obtained, fiftten to the CP Titanium and fifteen to the Ti-6Al-4V alloy, five samples to each an of the three temperatures of investment: 430°C (control group), 480°C and 530°C. The tensile test was measured by means of a universal testing machine, MTS model 810, at a strain of 1.0 mm/min. After the tensile strenght test the specimens were secctioned, embedded and polished to hardness measurements, using a Vickers tester, Micromet 2100. The means values to tensile tests to the temperatures 430°C, 480 and 530: CP Ti (486.1 – 501.16 – 498.14 –mean 495.30 MPa) and Ti-6Al-4V alloy (961.33 – 958.26 – 1005.80 – mean 975.13 MPa) while for the Vickers hardness the values were (198.06, 197.85, 202.58 – mean 199.50) and (352.95, 339.36, 344.76 – mean 345.69), respectively. The values were submitted to Analysis of Variance (ANOVA) and Tukey,s Test that indicate differences significant only between the materials, but not between the temperature, for both the materias. It was conclued that increase of the temperature of investment its not chance the tensile strength and the Vickers hardness of the CP Titanium and Ti-6Al-4V alloy.

The effect of mold temperature on castability of CP Ti and Ti–6Al–4V castings into phosphate bonded investment materials

Objective The aim of this study was to evaluate the castability of CP titanium and Ti–6Al–4V alloy castings into Rematitan Plus investment at three different mold temperatures. Methods A nylon mesh pattern (20 mm with 64 squares and wire of 0.7 mm in diameter) was used for the castability testing. Initially, an image of the wax pattern was obtained by means of a digital camera and the total extension of filaments (mm) was then measured, using the Leica Qwin image analysis system. The mesh sprued was placed in the Rematitan Plus investment material and the castings were made in a Discovery Plasma machine at three different mold temperatures: 430 °C (control group), 480 °C or 530 °C. Ten castings were made for each temperature. The images of the castings were analyzed (Leica Qwin) and the castability index determined by the number of the completely cast segments as a percentage of the wax pattern. Data were analyzed by two-way ANOVA and Tukey's multiple comparison test ( a = 0.05) using materials and temperatures as discriminating variables. Results The Ti–6Al–4V alloy (60.86%) presented a better castability index than CP Ti (48.44%) ( p < 0.000001). For CP Ti, the temperature of 530 °C (23.96%) presented better castability than at other temperatures, 480 °C (14.66%) and 430 °C (12.54%), with no difference between them ( p < 0.001). For Ti–6Al–4V alloy, there was a statistically significant difference among the three temperatures: 530 °C (28.36%) > 480 °C (19.66%) > 430 °C (15.97%) ( p < 0.002). Significance Within the limitations of this study, the increase in the mold temperature of the Rematitan Plus investment resulted in a better castability index for both materials, and Ti–6Al–4V presented a better castability index than CP Ti.

Influence of investment type and sprue number on the casting accuracy of titanium crown margins

Titanium offers biocompatibility and adequate mechanical properties for fabricating dental prostheses; however, casting difficulties can compromise the accuracy of titanium crown margins. The aim of this study was to evaluate the influence of investment type and number of sprues on accuracy of crown castings made with commercially pure titanium. The casting accuracy was evaluated indirectly by determining the deficiency of titanium crown margins cast using the lost-wax technique. Crown margins were recorded in a silicone impression material. The degree of marginal rounding was measured and margin deficiencies were calculated. Seventy-five acrylic resin crown patterns with wax margins were prepared on a stainless steel stylized crown die having a 30-degree beveled finish line. Fifteen patterns were selected for the control group, and the degree of wax margin rounding was determined (group W, control). The remaining 60 were divided into 4 groups of 15 each, and cast using 2 different titanium investments: a monoammonium dihydrogenphosphate-bonded investment (Rematitan Plus; groups PI and PII), and a magnesium oxide-bonded investment (Rematitan Ultra; groups UI and UII). Each pattern was cast with either 1 (groups PI and UI) or 2 (groups PII and UII) sprues. Margin configurations for both wax pattern and cast specimens were measured and recorded with the same method, using silicone impressions of the margins. After polymerization, the silicone material was sectioned precisely in 8 locations through the margin area so that cross-sections of the margins could be observed. Marginal deficiency was determined using microscopic measurements from the silicone patterns and calculations. Data were subjected to 2-way analysis of variance (alpha=.05). Specimens from group W presented a mean marginal deficiency of 19 +/- 6 microm. The analysis of variance indicated a significant difference for the main factors, investment (P<.01) (P=91 +/- 28 microm and U=78 +/- 17 microm) and sprue number (P<.001) (I=97 +/- 23 microm and II=72 +/- 16 microm), as well as for interaction (P<.05) (PI=109 +/- 25 microm; PII=73 +/- 17 microm; UI=85 +/- 15 microm; and UII=71 +/- 16 microm). Within the limitations of this study, investment U provided better casting accuracy than investment P. Two sprues provided more accurate results than 1 sprue; however, this effect was more notable for investment P, as it produced similar results between groups PII and UII.

Titanium Casting Using Commercial Phosphate-bonded Investments with Quick Heating Method

The purpose of this study was to investigate the possible use of quick heating method for titanium casting using two commercial investments (Rematitan Plus and Tancovest). The resulting characteristics of the investments with the quick heating method were as follows: residual thermal expansion at the casting temperature was in the range of 0.39 to 0.64%; green strength and fired strength ranged from 4.4 to 10.3 MPa and from 13.8 to 17.6 MPa, respectively. Five full crown titanium castings from each casting condition were obtained using an argon arc melting and gas pressure casting machine. The thickness of cast surface reaction layer was approximately 200 microm, regardless of heating methods or investments. Further, the heating method did not significantly influence either the accuracy or surface roughness of the titanium castings. These results therefore suggested that these commercial investments for titanium could be used for the quick heating method.

Mold filling of Ti castings using investments with different gas permeability

Objectives. The aim of this work was to study mold filling during casting of standardized five-unit Ti bridges vs. the gas permeability of the investments. Methods. An Ar arc casting machine with a separate melting and mold chamber was used. Both chambers were evacuated before Ar was introduced into the melting chamber. A rubber sealer was inserted between the top of the steel ring of the mold and the steel floor between the two chambers. The mold cavity required the same Ar pressure as the melting chamber prior to casting. Four different investments for Ti casting were investigated: 1) Bellavest T (BEGO), 2) Rematitan Plus (Dentaurum), 3) Titavest CB (Morita) and 4) Titanium Vest (Ohara Co.). Three castings were made with each investment. The molds were fired according to the manufacturers' instructions and cooled to room temperature. The Ar gas pressures in the two chambers were recorded during casting, and the mold filling was evaluated initially by visual inspection and subsequently by studying the margins of the crowns in a microscope. Results. In the melting and molding chambers, the Ar pressure was found to be: 1) Bellavest T: 400 and 1 torr; 2) Rematitan Plus: 600 and 85 torr; 3) Titavest CB: 600 and 150 torr; and 4) Titanium Vest: 600 and 85 torr, respectively. This indicates substantial differences in the gas permeability of the molds. Bellavest T produced poorly filled molds, Rematitan Plus and Titanium Vest resulted in poor margins and Titavest CB produced complete castings. Significance. Proper mold filling is promoted by investments with a high gas permeability, so the gases in the mold cavity can escape through the investment to the mold chamber.