Effect of thickness of externally characterized stains on optical properties of high-translucency zirconia.

OBJECTIVES: There is insufficient information about the effects of the thickness of externally characterized stains or glazes on CIELAB color parameters and the translucency parameter (TP) of 5 mol% yttria partially stabilized zirconia (5Y-PSZ). The present study evaluated the effect of a thickness reduction of the externally characterized or glazed layer on its CIE2000 color parameters and TP00 of 5Y-PSZ. MATERIALS AND METHODS: Twenty-eight specimens were sectioned from 5Y-PSZ blanks. Three brands of powdered stains (namely VI, SH, and IV) and a glaze (GL) were used to extrinsically stain the specimen surfaces (n = 7 per group). After measuring the final thickness and color, specimens of each group were carefully ground and finally polished. The reduced thickness was carefully controlled in decrements of 0.02 mm on the characterized stains or glazed layers at each reduction cycle until the surface of the un-stained zirconia was exposed. The CIELAB color parameters of specimens were measured using a spectrophotometer. Subsequently, differences in lightness (∆L'), chroma (∆C'), and hue (∆H'), and TP00 values and color differences (ΔE00) were calculated using the CIEDE2000 formula to determine differences between the specimen and the un-stained zirconia at each reduction cycle. A paired-samples t-test, two-way mixed-design analysis of variance, and Pearson correlation coefficient were used to analyze the data (α = 0.05). RESULTS: There were no significant differences in lightness, chroma, hue, or TP00 values before or after glazing or after each reduction cycle of the glazed layer. Mean ΔE00 values ranged between 20.94 and 33.55 after applying the externally characterized stains. With a decreased thickness of the characterized stain layer, there were observed that significant decreases in ∆L', ∆H', ∆C', and ΔE00, and significant increases in TP00. CONCLUSIONS: Increasing the thickness of externally characterized stains decreased the lightness and caused the alternation of chroma and hue, whereas these phenomena were not observed in the glazed group. There was a slight change of CIE2000 color parameters and TP00 when the thickness of the characterized layer exceeded 0.06 mm. CLINICAL RELEVANCE: The application and thickness of externally characterized stains can sensitively affect CIE2000 color parameters and translucency of 5Y-PSZ.

Effect of retention hole designs in artificial teeth on failure resistance of the connection with thermoplastic resin.

This study aimed to evaluate the effect of retention hole designs in artificial teeth on failure resistance of the connection with a thermoplastic denture base resin. Artificial teeth with the following retention hole designs were attached to polyester and polyamide resins: no hole, vertical hole, horizontal hole, and vertical and horizontal holes. An artificial tooth with no hole attached to polymethyl methacrylate was prepared as the control. The load was applied until connection failure occurred between the artificial tooth and resin, and failure resistance was detected. Although the control showed the highest resistance, the artificial tooth with vertical and horizontal holes showed higher resistance than those with other retention hole designs in both thermoplastic resins. Providing vertical and horizontal retention holes in artificial teeth may be effective in improving failure resistance of the connection with thermoplastic resins.

Fracture resistance of CAD/CAM restorative materials in mismatched removable partial denture rests: An in vitro experimental and finite element analysis.

To evaluate the fracture resistance of computer-aided design and computer-assisted manufacturing restorations as the abutment of removable partial dentures, experimental blocks, with the rest seat made of feldspar, hybrid resin composite, lithium disilicate glass ceramic, or zirconia, were subjected to loading by a metallic occlusal rest. The rest contacted the rest seat with an accurate fit and two mismatch contact conditions: bottom and sidewall contact. Zirconia exhibited the highest fracture load, and the fracture load of the accurate fit was significantly higher than that of the sidewall contact (p<0.05) and insignificantly higher than that of the bottom contact (p>0.05). A finite element analysis of the sidewall contact revealed a higher tensile stress concentration at the bottom of the rest seat than the other contact conditions. The mismatch between the rest and the restoration reduced fracture resistance, while zirconia as the abutment withstood the average occlusal force of the posterior region.

Effect of toothbrushing on the optical properties and surface roughness of extrinsically stained high-translucency zirconia.

OBJECTIVES: The effect of toothbrushing on the color, relative translucency, and surface roughness of extrinsically stained zirconia dental restorations is still unclear. The purpose of the present study was to evaluate the optical properties and surface textures of extrinsically stained or glazed partially stabilized zirconia with 5 mol% yttria (5Y-PSZ) after toothbrushing by determining changes in the color, translucency parameter (TP), and surface roughness. MATERIALS AND METHODS: Specimens (2 mm thick; n = 50) were sectioned from 5Y-PSZ blanks. Three brands of powdered stains (namely VI, SH, IV) and a glaze (GL) were used to extrinsically stain the specimen surfaces (n = 10 per group). The specimens were subjected to 10,000-50,000 simulated toothbrushing strokes using a toothpaste slurry (Ora2 PREMIUM Stain clear paste). The color parameters were measured before staining or glazing and before and after simulated brushing. The color changes and TP values can be calculated before and after simulated brushing. The surface roughness was also evaluated. RESULTS: Significant changes were found in the shade and TP values of 5Y-PSZ after extrinsic staining, but no significant changes were found after toothbrushing, irrespective of the staining brand (p > 0.05). The surface roughness of the characterized 5Y-PSZ specimens decreased after toothbrushing, whereas that of the non-characterized 5Y-PSZ group increased. CONCLUSIONS: Toothbrushing markedly affects the surface roughness of extrinsically stained or glazed 5Y-PSZ specimens, whereas no impacts on the color or translucency were observed. CLINICAL RELEVANCE: For esthetic reasons, clinicians and dental technicians prefer to apply extrinsic stains to zirconia restorations, which profoundly affects its appearance. The limited influence of toothbrushing on color and translucency of 5Y-PSZ is promising for clinical applications.

Effects of build orientation on adaptation of casting patterns for three-unit partial fixed dental prostheses fabricated by using digital light projection.

STATEMENT OF PROBLEM: The lost-wax technique is commonly used for fabricating partial fixed dental prostheses. The casting patterns can be fabricated by using vat photopolymerization (a type of additive manufacturing), but the adaptation of these casting patterns has not been elucidated. PURPOSE: The purpose of this in vitro study was to evaluate the effect of build orientation on the adaptation of casting patterns fabricated by digital light projection (DLP). MATERIAL AND METHODS: A 3-unit partial fixed dental prosthesis with mandibular left second premolar and second molar abutment teeth was scanned and virtually designed with a computer-aided design software program. The cement space was designed to be 30 µm. Specimens were fabricated with 3 build orientations: 0 degrees (with the occlusal surface parallel to the platform), 30 degrees, and 45 degrees (by rotating the file along the long axis). The casting patterns were fabricated by using DLP (Cara Print 4.0) with a photopolymerizable monomer (dima Print Cast Q). Photopolymerization, cleaning, and postpolymerization processes were performed according to the manufacturer's instructions. The adaptation of the specimens was examined by using a silicone replica method. The vertical marginal discrepancy and axial wall, occlusal, and marginal gaps were measured by using a digital measuring microscope. The effect of build orientation at each cross-sectional area was statistically analyzed by using the Kruskal-Wallis test followed by the pairwise Wilcoxon rank sum test with Bonferroni correction (α=.05). RESULTS: Excess polymerized resin was observed along the intaglio buccal wall at build orientations of 30 degrees and 45 degrees. Vertical marginal discrepancies in the buccolingual section ranged from -50 to 248 µm, while those in the mesiodistal section ranged from -25 to 182 µm. The gaps in the buccolingual section ranged from 0 to 236 µm, while those in the mesiodistal section ranged from 0 to 177 µm. According to the observation of vertical marginal discrepancies and gaps, the 30-degree specimens inclined during insertion, and the 45-degree specimens were not completely seated. However, the marginal gaps of the 0- and 30-degree specimens were within the clinically acceptable limit of 120 µm. CONCLUSIONS: The limited data indicated that the build orientation influenced the adaptation of casting patterns for 3-unit partial fixed dental prostheses fabricated by using DLP. A build orientation of 0 degrees is recommended for fabricating casting patterns for 3-unit partial fixed dental prostheses because no excess polymerization of the intaglio buccal wall was observed.

Flexural and fatigue properties of polyester disk material for milled resin clasps.

To evaluate the flexural and fatigue properties of a polyester disk material used in milled resin clasps of removable partial dentures, experimental polyester disk (mPE), injection-molded polyester (iPE), and polymethyl methacrylate disk (mPMMA) were examined by three-point bending tests and cyclic fatigue tests at 0.75 or 1.50 mm deflection. The mPE exhibited significantly higher flexural strength than the iPE (p<0.05). Meanwhile, the mPMMA displayed higher flexural modulus and strength than the polyesters. The mPE exhibited a significantly lower residual strain than the iPE at the cyclic 0.75 mm deflection (p<0.05); however, microcracks were observed in the mPE at the 1.50 mm deflection. The mPMMA showed a high residual strain at the 0.75 mm deflection and fractured within 1,000 cycles at the 1.5 mm deflection. The higher flexural strength and lower residual strain of the mPE compared with the iPE suggest the advantages of milled resin clasps within a limited deflection.

Application of Glass Fiber and Carbon Fiber-Reinforced Thermoplastics in Face Guards.

Face guards (FGs) are protectors that allow for the rapid and safe return of athletes who are to play after sustaining traumatic facial injuries and orbital fractures. Current FGs require significant thickness to achieve sufficient shock absorption abilities. However, their weight and thickness render the FGs uncomfortable and reduce the field of vision of the athlete, thus hindering their performance. Therefore, thin and lightweight FGs are required. We fabricated FGs using commercial glass fiber-reinforced thermoplastic (GFRTP) and carbon fiber-reinforced thermoplastic (CFRTP) resins to achieve these requirements and investigated their shock absorption abilities through impact testing. The results showed that an FG composed of CFRTP is thinner and lighter than a conventional FG and has sufficient shock absorption ability. The fabrication method of an FG comprising CFRTP is similar to the conventional method. FGs composed of commercial FRTPs exhibit adequate shock absorption abilities and are thinner and lower in weight as compared to conventional FGs.

Effects of build conditions and angle acuteness on edge reproducibility of casting patterns fabricated using digital light projection.

The aim of the present study was to evaluate the effects of build conditions and angle acuteness on edge reproducibility of the casting patterns fabricated using a digital light process. The prism-shaped patterns with various vertex angles were fabricated in three build orientations. The height from the base to the vertex angle point of the fabricated pattern was measured and the incomplete height was calculated as the discrepancy between the original and measured heights. Two-way ANOVA revealed that the vertex angle and build orientation and their interaction were significant (p<0.05). The incomplete height significantly decreased with an increase of the vertex angle. When the vertex angle was 20° and the build-up direction was parallel to the edge of vertex angle and perpendicular to the triangular base, the incomplete height was the smallest. Therefore, build orientation and angle acuteness influenced the edge reproducibility of the casting patterns fabricated using a digital light process.

Effect of fiberglass orientation on flexural properties of fiberglass-reinforced composite resin block for CAD/CAM.

A fiberglass-reinforced composite resin (FRP) block using a plain woven fiberglass sheet for CAD/CAM has been introduced in dental practice. The aim of the present study was to evaluate the effects of the fiberglass sheet orientation on the flexural properties of an FRP block. The flexural properties of five types of fiberglass sheet-assigned specimens were examined using a three-point bending test. A one-way analysis of variance revealed that the orientation of fiberglass sheet significantly influenced the flexural strength, 0.2% yield strength, and flexural modulus. The values of the flexural properties of the FRP were the largest when the fiberglass sheets were perpendicular to the applied force, and the smallest when the fiberglass was parallel to the same. The flexural properties of the FRP block were anisotropic and they were significantly influenced by the orientation of fiberglass sheet.

Improvement of the Shock Absorption Ability of a Face Guard by Incorporating a Glass-Fiber-Reinforced Thermoplastic and Buffering Space.

This study aimed to evaluate the shock absorption ability of trial face guards (FGs) incorporating a glass-fiber-reinforced thermoplastic (GF) and buffering space. The mechanical properties of 3.2 mm and 1.6 mm thick commercial medical splint materials (Aquaplast, AP) and experimental GF prepared from 1.6 mm thick AP and fiberglass cloth were determined by a three-point bending test. Shock absorption tests were conducted on APs with two different thicknesses and two types of experimental materials, both with a bottom material of 1.6 mm thick AP and a buffering space of 30 mm in diameter (APS) and with either (i) 1.6 mm thick AP (AP-APS) or (ii) 1.6 mm thick GF (GF-APS) covering the APS. The GF exhibited significantly higher flexural strength (64.4 MPa) and flexural modulus (7.53 GPa) than the commercial specimens. The maximum load of GF-APS was 75% that of 3.2 mm AP, which is widely used clinically. The maximum stress of the GF-APS only could not be determined as its maximum stress is below the limits of the analysis materials used (<0.5 MPa). Incorporating a GF and buffering space would enhance the shock absorption ability; thus, the shock absorption ability increased while the total thickness and weight decreased.

Effect of incorporation of surface pre-reacted glass ionomer filler in tissue conditioner on the inhibition of Candida albicans adhesion.

We investigated the effects of incorporation of surface pre-reacted glass ionomer (S-PRG) filler in tissue conditioner (TC) on Candida albicans adhesion. We prepared specimens containing 0, 5, 10, or 20 wt% of S-PRG filler, and measured the amount of C. albicans on the surface using a colony forming unit (CFU) assay and scanning electron microscopic images. In addition, we measured the consistency, penetration depth, and surface roughness (Ra). CFU values for 10 and 20 wt% were significantly lower than that for the control (p<0.05). Hyphal density on the surface was greater in the control. The 10 and 20 wt% specimens showed significantly higher consistency and Ra, lower penetration depth ratio than control (p<0.05). These results suggest that incorporation of S-PRG filler may reduce C. albicans adhesion onto TC surface; however, the optimal amount of filler is dictated by the influence of filler incorporation on mechanical and surface characters of TC.

Effect of long-time immersion of soft denture liners in water on viscoelastic properties.

Aim of this study was to investigate the effect of long-time immersion of soft denture liners in 37°C water on viscoelastic properties. Six silicone-based and two acrylic resin-based soft denture liners were selected. Cylindrical specimens were stored in distilled water at 37°C for 6 months. Viscoelastic properties, which were instantaneous and delayed elastic displacements, viscous flow, and residual displacement, were determined using a creep meter, and analyzed with 2-way analysis of variance and Tukey's comparison (α=0.05). Viscoelastic properties and their time-dependent changes were varied among materials examined. The observed viscoelastic properties of three from six silicone-based liners did not significantly change after 6-month immersion, but those of two acrylic resin-based liners significantly changed with the increase of immersion time. However, the sum of initial instantaneous elastic displacement and delayed elastic displacement of two acrylic resin-based liners during 6-month immersion changed less than 10%, which might indicate clinically sufficient elastic performance.

Discoloration of various CAD/CAM blocks after immersion in coffee.

OBJECTIVES: This study evaluated color differences (ΔEs) and translucency parameter changes (ΔTPs) of various computer-aided design/computer-aided manufacturing (CAD/CAM) blocks after immersion in coffee. MATERIALS AND METHODS: Eight CAD/CAM blocks and four restorative composite resins were evaluated. The CIE L*a*b* values of 2.0 mm thick disk-shaped specimens were measured using the spectrophotometer on white and black backgrounds (n = 6). The ΔEs and ΔTPs of one day, one week, and one month immersion in coffee or water were calculated. The values of each material were analyzed by two-way ANOVA and Tukey's multiple comparisons (α = 0.05). The ΔEs after prophylaxis paste polishing of 1 month coffee immersion specimens, water sorption and solubility were also evaluated. RESULTS: After one month in coffee, ΔEs of CAD/CAM composite resin blocks and restorative composites ranged from 1.6 to 3.7 and from 2.1 to 7.9, respectively, and ΔTPs decreased. The ANOVA of ΔEs and ΔTPs revealed significant differences in two main factors, immersion periods and media, and their interaction except for ΔEs of TEL (Telio CAD, Ivoclar Vivadent). The ΔEs significantly decreased after prophylaxis polishing except GRA (Gradia Block, GC). There was no significant correlation between ΔEs and water sorption or solubility in water. CONCLUSIONS: The ΔEs of CAD/CAM blocks after immersion in coffee varied among products and were comparable to those of restorative composite resins. The discoloration of CAD/CAM composite resin blocks could be effectively removed with prophylaxis paste polishing, while that of some restorative composites could not be removed.

Evaluation of the flexural properties of a new temporary splint material for use in dental trauma splints.

The present study evaluated the flexural properties of a new temporary splint material, G-Fix, for use in dental trauma splints in comparison with other resin materials. Four types of resin materials were considered in the present study: MI Flow II, light-cured composite resin (MI); G-Fix, light-cured resin for splinting teeth (GF); Super-Bond C&B, adhesive resin cement (SB); and Unifast III, self-cured methyl-methacrylate resin (UF). The flexural properties of these four materials were tested according to ISO 4049. The flexural strength significantly increased in the order of UF (64.9 MPa) < SB (76.5 MPa) < GF (94.3 MPa) < MI (161.2 MPa). The elastic modulus significantly increased in the order of UF (2.11 GPa) ≒ SB (2.23 GPa) < GF (2.62 GPa) < MI (7.39 GPa). A splint made of GF may be more flexible than a composite splint, which is categorized as a rigid splint.

Color stability of adhesive resin cements after immersion in coffee.

OBJECTIVES: Marginal discoloration of luting cement may affect the appearance of esthetic restorations. This study evaluated the color stability of current adhesive resin cements after immersion in coffee. MATERIALS AND METHODS: Four dual-cured resin cements (Clearfil SA cement Automix Universal, Maxcem Elite Clear, Maxcem Elite Yellow, and RelyX Unicem2 Automix A2) and two chemical-cured resin cements (Super-Bond C&B Clear and Super-Bond C&B Esthetic) were examined. The CIE L*a*b* of 2.0-mm-thick disc-shaped specimens was measured using a spectrophotometer on a white background (n = 6). The color differences (∆E) after 1-day and 1-week immersion in 37 °C water or coffee were analyzed by two-way ANOVA by selecting immersion solution and product as main factors, followed by Tukey's HSD test (α = 0.05). Water sorption and solubility were also evaluated. RESULTS: The two-way ANOVA of the ∆Es suggested that the two main factors and their interaction were significant. The ∆Es after coffee immersion were significantly greater than those after water immersion, except for Super-Bond C&B Esthetic. The ∆Es after water immersion were not significantly different among the products; those of Maxcem Elite Clear and Maxcem Elite Yellow after coffee immersion were significantly greater than the others. The water sorption and solubility significantly correlated with the ∆Es. CONCLUSIONS: The ∆Es of the adhesive resin cements examined after 1-week coffee immersion were significantly different among the products. The product showing greater water sorption and solubility displayed greater color change. CLINICAL RELEVANCE: Adhesive resin cements should be carefully selected when the marginal appearance of the ceramic restoration is important.

Mechanical properties of composite resin blocks for CAD/CAM.

This study compared commercial composite resin blocks with one ceramic block for use in computer-aided design/computer aided manufacturing (CAD/CAM). Four composite resins, one composite ceramic, and one feldspar-ceramic block were investigated. Flexural strength (FS), flexural modulus (FM), and Vickers hardness (VH) were determined under three conditions: dry storage; immersion in water at 37°C for 7 days; and immersion in water at 37°C for 7 days followed by 10,000 thermocycles. After dry storage, FS ranged from 127 to 242 MPa, FM from 9.6 to 51.5 GPa, and VH from 64 to 455. Two-way ANOVA was performed for FS, FM and VH followed by Tukey's multiple comparison (α<0.05). Results demonstrated that the materials degraded after water immersion and thermocycling, but their properties were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008).

Effect of immersion time of restorative glass ionomer cements and immersion duration in calcium chloride solution on surface hardness.

OBJECTIVES: The objective of this study was to evaluate the effect of immersion time of restorative glass ionomer cements (GICs) and immersion duration in calcium chloride (CaCl2) solution on the surface hardness. METHODS: Two high-viscosity GICs, Fuji IX GP and GlasIonomer FX-II, were selected. Forty-eight specimens were randomly divided into two groups. Sixty minutes after being mixed, half of them were immersed in a 42.7wt% CaCl2 solution for 10, 30, or 60min (Group 1); the remaining specimens were immersed after an additional 1-week of storage (Group 2). The surface hardness of the specimens was measured and analyzed with two-way ANOVA and the Tukey HSD test (α=0.05). The surface compositions were examined using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. RESULTS: The surface hardness of Group 1 significantly increased as the immersion duration in CaCl2 increased; that of Group 2 significantly increased only after 60-minute CaCl2 immersion. After CaCl2 immersion, the amounts of Ca increased as the immersion duration increased. The surface hardness after CaCl2 immersion significantly correlated with the amount of Ca in Group 1, but not in Group 2. The binding energy of the Ca2p peak was similar to that of calcium polyalkenoate. These findings indicated that the Ca ions from the CaCl2 solution created chemical bonds with the carboxylic acid groups in the cement matrix. SIGNIFICANCE: Immersion of GICs in CaCl2 solution at the early stage of setting was considered to enhance the formation of the polyacid salt matrix; as a result, the surface hardness increased.

Texture of composite resins exposed to two- and three-body wear in vitro.

PURPOSE: To analyze on scanning electron microscopy (SEM) pictures from eight composite resins, taken in the centers of the initial, the middle and the terminal thirds of in vitro produced wear tracks morphological features to explain causative mechanisms for the material wear observed under two- and three-body wear. MATERIALS AND METHODS: In vitro wear behavior of eight composite resins, three conventional and five nanofiller containing marketed products was evaluated using a custom-made Zr-ball-on-disk sliding device. The composite specimens were subjected to 50,000 one-way sliding cycles (1.2 Hz, 50 N load), either simulating two-body wear with water as the intermediate medium or three-body wear using aqueous suspensions of polymethyl methacrylate (PMMA) beads and poppy seeds, respectively. Volume loss of the materials was determined in previous study. Representative specimens were selected for inspection by scanning electron microscopy at 500-fold magnification. From each of the 24 wear tracks microphotographs were taken in the central deepest parts of the initial, middle and terminal thirds of the tracks. RESULTS: For most materials morphological differences were detected depending on the location within the wear track. As a rule, the surface deterioration found increased toward the final part of the wear scar. According to common classification in tribology abrasive wear and fatigue wear, or a combination of both mechanisms were found for all materials tested. Wear was dependent both on the testing mode and on the composition of the individual composite resin material. CONCLUSION: The morphological assessment of wear tracks refects the nature of the abrasive and reveals insight into the mechanism generating wear patterns. Morphological details confirmed abrasive and fatigue-related wear as main failure mechanisms. Selection of food-like slurries as third-body media, such as poppy seed suspension is mandatory to simulate wear of composite restorations in occlusal cavities where three-body wear is the dominating determinant of loss of substance and surface deterioration.

Effect of ultraviolet light irradiation and sandblasting treatment on bond strengths between polyamide and chemical-cured resin.

The aim of this study was to evaluate the effects of ultraviolet light (UV) irradiation and sandblasting treatment on the shear bond strength between polyamide and chemical-cured resin. Three types of commercial polyamides were treated using UV irradiation, sandblasting treatment, and a combining sandblasting and UV irradiation. The shear bond strength was measured and analyzed using the Kruskal-Wallis test (α=0.05). Comparing shear bond strengths without surface treatment, from 4.1 to 5.7 MPa, the UV irradiation significantly increased the shear bond strengths except for Valplast, whose shear bond strengths ranged from 5.2 to 9.3 MPa. The sandblasting treatment also significantly increased the shear bond strengths (8.0 to 11.4 MPa). The combining sandblasting and UV irradiation significantly increased the shear bond strengths (15.2 to 18.3 MPa) comparing without surface treatment. This combined treatment was considered the most effective at improving the shear bond strength between polyamide and chemical-cured resin.

Effect of fabrication process on the bond strength between silicone elastomer and acrylic resin for maxillofacial prosthesis.

This study evaluated the effects of the fabrication process on tensile bond strength between maxillofacial silicone elastomer and acrylic resin. A common maxillofacial silicone elastomer (VST-50), two primers (Sofreliner primer and R-SI-LINE Plasticbond), and two acrylic resins (Unifast III and Palapress Vario) were selected. Silicone elastomer between primed acrylic resin plates were polymerized using a metal flask mold or a flaskless stone mold. Bond strength of the specimens was measured by a tensile test and analyzed using two-way analysis of variance (ANOVA) with Tukey's honest significant difference test. All fracture surfaces showed interfacial fracture. Both the fabrication process and the primer-acrylic resin combination affected bond strength, and two-way ANOVA indicated a significant interaction. Bond strength was generally greater when silicone elastomer was polymerized using a flaskless stone mold.