OBJECTIVETo investigate expansion characteristics of two kinds of commercial investment (Cristo balite Micro II and Cristo Quick), and their effects on cast accuracy of a dental Ag-Pd casting alloy.

METHODSTwo kinds of investment were mixed at the ratio of 1:3. The setting and thermal expansion curves of the investment were recorded according to the requirements of ISO7490 and expansion rate calculated, respectively. Plate-like wax-patterns with pre-marked points were invested in casting rings (lined with ceramic fiber liners with thickness of 0.45 mm). Castwell M.C dental alloy were melted with gas flame and cast with a centrifugal casting machine. The differences between the castings and the wax patterns at corresponding points were calculated to represent the dimensional changes of the investment.

RESULTSThe setting, thermal and total expansion rates were 0.68, 1.18, 1.86 for Cristo balite Micro II, and 0.94, 1.03, 1.97 for Cristo Quick. The setting and thermal expansion rates were statistically significant between two kinds of investment (P < 0.05), while not for the total expansion rates (P > 0.05). Effect of different investment on the precision of castings was not statistically significant (P > 0.05).

CONCLUSIONWithin the scope of this study, gypsum-bonded investment with similar total expansion rates but different expansion characteristics has no effect on the casting precision of Ag-Pd dental alloys.

Calcium Sulfate ; Ceramics ; Dental Alloys ; Dental Casting Investment ; Dental Casting Technique ; Investments

OBJECTIVETo observe the influence of different investing methods and mold cooling methods on pure titanium castings invested in the self-made investment, and to provide theoretic base for the development for the investment.

METHODSThe influence of investing methods (one-step investing method and two-step investing method) on castability and crown fit of titanium castings were investigated, and the influence of cooling methods on reaction layers, mechanical properties and crown fit of titanium castings were investigated.

RESULTSBoth the investing methods exhibited good castability, but only the titanium full crowns by one-step investing method showed clinically acceptable fit. Although the quenching group showed thinner reaction layer(100 microm), lower strength and similar elongation rate, the titanium castings by bench cooling showed clinically acceptable full crown fit with 115 microm thick reaction layer as cast.

CONCLUSIONThe one-step investing method and the bench cooling are recommended for the self-made investment.

Crowns ; Dental Casting Investment ; Dental Casting Technique ; Dental Materials ; Fungi ; Investments ; Materials Testing ; Surface Properties ; Titanium

OBJECTIVEThe purpose of this study was to compare the compressive strength of phosphate-bonded investments.

METHODSThe three sorts of investments were mixed according to manufacturer's recommendation before poured in the molds. After heated up to 900 degrees C, every sample was mounted on a universal experimental machine to test its compressive strength in ambient.

RESULTSSignificant differences were found between the four groups(P < 0.01).

CONCLUSIONFrom the data above it is concluded that the compressive strength of X-20 Chrome Investment mixed with the special liquid was the highest.

Compressive Strength ; Dental Bonding ; Dental Casting Investment ; chemistry ; Dental Casting Technique ; instrumentation ; Materials Testing ; Phosphates ; chemistry

OBJECTIVETo investigate the surface roughness property of the titanium castings cast in a new investment for titanium casting.

METHODSSix 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.

RESULTSThe 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].

CONCLUSIONSThe 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.

Dental Casting Investment ; chemistry ; Dental Casting Technique ; Materials Testing ; Surface Properties ; Titanium ; chemistry

OBJECTIVETo investigate the effect of self-developing investment (FUS-invest) on the reactive layer of titanium castings.

METHODSThree 10 mm x 10 mm x 1 mm pure titanium castings were founded using FUS-invest. Metallographical structure of reactive layer was observed. X-ray diffraction (XRD) and scanning electron microscope with energy-dispersive spectrum (EDS) were used to analyze the status of composition of the casting surface. Micro-Vickers hardness was measured.

RESULTSThe metallograph indicated that the reactive layer was composed of coarse flake-shaped alpha phase of grains. The value of micro-Vickers hardness with the range 243 to 314 MPa had not significantly difference under the depth of 105 microm beneath the surface. The XRD pattern clearly showed the peaks of ZrO2, SiO2, Mg2TiO4 and TiO2. EDS analysis demonstrated that the main elements were Al, Si, Zr and Cl.

CONCLUSIONFUS-invest is suited for pure titanium casting because of the thin reactive layer and less change to metallographical structure.

Crowns ; Dental Casting Investment ; Dental Casting Technique ; Hardness ; Humans ; Investments ; Silicon Dioxide ; Surface Properties ; Titanium

OBJECTIVETo investigate the effects of the improved FUS-invest investment for zirconium-oxide titanium crown and bridge on the reaction layer.

METHODS10 mm x 10 mm x 1 mm titanium castings were invested. Spectrum analysis was done to its reaction layer, the metallographic examination was observed and Vickers hardness was measured.

RESULTSThe reaction layer was not obvious by the metallographic examination. The layer with plenty of Si was hardly detectable. The needle crystal layer diffused distribution on the surface of the titanium matrix. The depth was about 55 microm. Spectrum analysis showed that the contents of Si and Zr decreased as the depth increased. The microhardness, which obviously decreased from the surface to the matrix, tended to be equal with the hardness of the matrix after the depth reached 75 microm from the surface.

CONCLUSIONThe thickness of the reaction layer of the improved FUS-invest investment for zirconium-oxide titanium crown and bridge was decreased to 55 microm from 85 microm, which was the thickness before improvement.

Crowns ; Dental Casting Investment ; Dental Casting Technique ; Hardness ; Humans ; Investments ; Oxides ; Surface Properties ; Titanium ; Zirconium

OBJECTIVETo study the effects of different heating timings after mixing the materials and different heating methods on the expansion characters of a quick-heating gypsum-bonded investment.

METHODSThe setting expansion rate of GC Cristoquick II gypsum-bonded investment was measured with a setting expansion tester 30, 60, 120 min after mixing the material respectively. The thermal expansion rates of the material at different setting time (30, 60, 120 min after mixing) and under different heating treatment methods (quick and conventional heating techniques) were also determined using a thermal dilatometer for dental investments, the total linear expansion rate were calculated. The effects of heating time and heating methods on the expansion of the investments were statistically analyzed with SPSS 11.0 software, using ANOVA multiple comparison (alpha=0.05).

RESULTSStatistical differences were found among the setting and thermal expansion rates of the investment at different heating timings after mixing the material (P<0.01). Setting expansion, thermal expansion and total expansion rates increased with the setting time before heat treatment, while thermal expansion rates under different (quick and conventional) heating methods were not statistically significant (P>0.05).

CONCLUSIONThe expansion characters of the quick-heating gypsum-bonded investment are influenced by different heating timings after mixing the material. The heat treatment technique of this quick-heating investment recommended needs to be modified to ensure casting precision.

Calcium Sulfate ; Dental Casting Investment ; Dental Casting Technique ; Heating ; Hot Temperature ; Humans ; Investments

OBJECTIVETo investigate the effect of two different ring liner thickness on the deformation of resulted castings.

METHODSGC No.2 casting rings (50 mm in height and 39.5 mm in diameter) were lined with two dry ceramic fiber liners with thickness of 0.70 mm and 0.45 mm. Plate-like wax patterns with pre-marked points were invested with a gypsum-bonded investment and the rings were cast with a silver-based dental alloy. The difference between the castings and the wax patterns at corresponding points was calculated to represent the dimensional change of the investment in the rings at different directions.

RESULTSThe expansion of the investment in the ring was non-isotropic, with larger radial direction expansion than the axial direction expansion (P < 0.01). In the scope of this study, the effect of two different ring liner thickness on the casting precision was statistically non-significant (P > 0.05).

CONCLUSIONThe liners with two different thickness failed to eliminate non-isotropic deformation of the castings under the testing conditions of this study.

Calcium Sulfate ; Ceramics ; Crowns ; Dental Casting Investment ; Dental Casting Technique ; Humans ; Prostheses and Implants

OBJECTIVETo determine the optimal composition of a self-developing investment material by measuring physical and mechanical properties of mould.

METHODSL(9) (3(4)) orthogonal design was adopted. One hundred and fifty specimens with the size of 80 mm × 20 mm × 20 mm were prepared to measure the atmospheric temperature bending strength, high temperature bending strength and residual bending strength. Nine specimens with the size of 5 mm diameter 25 mm heigh were prepared to survey the thermal expansion curve from ambient temperature to 1150°C.

RESULTSStrengths were greatly affected by fine powder proportion in refractory and water/powder ratio. When the content of fine powder was 35% and water/powder ratio was 1:7.5, adequate atmospheric temperature strength and high temperature strength could be achieved. Moreover, the residual strength was moderate. The thermal extension curves of specimens in experiment group were almost similar. And the average linear expansion coefficient was (4 ∼ 5) × 10(-6)/°C.

CONCLUSIONSThe three kinds of bending strength of self-developing investment material are compared with commercialized investment material for titanium casting when water/powder ratio and the content of fine powder are carefully controlled.

Crowns ; Dental Casting Investment ; Dental Casting Technique ; Dental Stress Analysis ; Hot Temperature ; Materials Testing ; Pliability ; Powders ; Surface Properties ; Titanium ; chemistry

OBJECTIVETo compare the influence of different investment materials, methods and crown height on the cast shrinkage of full crowns made of dental base metal alloy.

METHODSAll of the 288 wax patterns were made and divided into three groups according to their crown height. In every group, wax patterns were invested in metal rings and paper rings with three types investment material and cast with base metal alloys. Then the inside diameters of castings were measured and analyzed by statistical package SPSS.

RESULTSDifferences between groups invested with the three types of material were significant(P < 0.01). There were significant difference between the groups investing with metal rings and paper rings(P < 0.01).

CONCLUSIONThe component of investment material and invested ring can affect the cast shrinkage of dental base metal alloy apparently.

Crowns ; standards ; Dental Alloys ; standards ; Dental Casting Investment ; Dental Casting Technique ; instrumentation ; Humans ; Inlay Casting Wax ; chemistry ; classification ; Materials Testing ; instrumentation ; methods ; Metal Ceramic Alloys ; standards ; Prosthesis Fitting