Mari Koike

Elemental ion release from four different fixed prosthodontic materials

OBJECTIVE Elemental release is important because it plays a significant role in material biocompatibility. The aim of this study was to investigate the release of metal ions from four fixed prosthodontic materials. METHODS Specimens were prepared using the conventional lost wax technique for gold and nickel-chromium (Ni-Cr) alloys, and by cutting blocks and bar for CAD-CAM ceramic and stainless-steel (St-St) alloy, respectively. All specimens were polished (600grit SiC paper), and ultrasonically cleaned with ethanol for 5min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 degrees C for 7 days, the elemental release (mug/cm(2)) from each material was analyzed by using inductively coupled plasma mass spectroscopy. The rate (n=5) was statistically analyzed by ANOVA/Tukey test (p<0.05). Two immersion blank solutions were used as a negative control group. RESULTS Higher elemental release (mean+/-S.D.) of all elements from all materials was evident into the lactic acid solution except for Ag. In the gold alloy, there was significant difference (p<0.05) between Zn and other released elements in the NaCl solution, and it also revealed significant difference between Pd or Ag and Cu which detection value was more than Zn (but no statistical difference) into lactic acid solution. The Ni was significantly more released from Ni-Cr alloy than the other elements into both NaCl and lactic acid solutions. The same was observed for Fe released from St-St alloy. There was more significant release of K than Al from CAD-CAM ceramic in only NaCl solution. SIGNIFICANCE Transient exposure of tested materials to an acidic environment is likely to significantly increase the elemental release from them. The significant higher release of Ni from Ni-Cr alloy, and Zn, Cu from gold alloy was evident.

Fatigue testing of electron beam-melted Ti-6Al-4V ELI alloy for dental implants†

Customized one-component dental implants have been fabricated using Electron Beam Melting(®) (EBM(®)), which is a rapid prototyping and manufacturing technique. The goal of our study was to determine the effect of electron beam orientation on the fatigue resistance of EBM Ti-6Al-4V ELI alloy. EBM technique was used to fabricate Ti-6Al-4V ELI alloy blocks, which were cut into rectangular beam specimens with dimensions of 25 × 4 × 3 mm, such that electron beam orientation was either parallel (group A) or perpendicular (group B) to the long axis of the specimens. The specimens were subjected to cyclic fatigue (R = 0.1) in four-point flexure under ambient conditions using various stress amplitudes below the yield stress. The fatigue lifetime data were fit to an inverse power law-Weibull model to predict the peak stress corresponding to failure probabilities of 5 and 63% at 2M cycles (σ(max, 5%) and σ(max, 63%)). Groups A and B did not have significantly different Weibull modulus, m (p > 0.05). The specimens with parallel orientation showed significantly higher σ(max, 63%) (p ≤ 0.05), but there was no significant difference in the σ(max, 5%) (p > 0.05). Thus, it can be concluded that the fatigue resistance of the material was greatest when the electron beam orientation was perpendicular to the direction of crack propagation.

The effect of multiple firings on the marginal integrity of pressable ceramic single crowns

STATEMENT OF PROBLEM The marginal adaptation of metal ceramic crowns is affected by firing cycles for veneering porcelain application. The effect of multiple firings on the marginal integrity of pressable ceramic core crowns is unknown. PURPOSE The purpose of this in vitro study was to evaluate the effect of repeated firing cycles on the marginal discrepancy of veneered (layered) pressable ceramic anterior crowns with 2 different finish line configurations. MATERIAL AND METHODS Forty pressable ceramic single anterior complete crowns were fabricated from 2 systems (IPS Empress Esthetic and IPS e.max Press) with 2 finish line designs (shoulder, chamfer) on epoxy resin dies. Specimens were divided into 4 groups of 10, and measurements were made after pressing (control) and after 5 veneer firing stages: 1) wash, 2) first incisal, 3) second incisal, 4) characterization and glazing, and 5) corrective. The change in vertical marginal discrepancy was measured with a light microscope at 4 locations: facial (F), mesial (M), lingual (L), and distal (D) surfaces. One-way ANOVA (α-=.05) was used to evaluate the marginal change. A Student-Newman-Keuls test was also used for comparison among the groups. RESULTS There were no significant changes in the vertical marginal integrity related to ceramic type and marginal location and their interactions. However, there was a significant marginal integrity change during the characterization and glazing firing stage. (P<.05) CONCLUSIONS The marginal gap increased for both systems during veneer application and decreased during the characterization and glazing firing cycle. The total marginal fit change after 5 firings was 0.33 μm for IPS e.max Press, and 0.27 μm for IPS Empress Esthetic.

Fabrication of titanium removable dental prosthesis frameworks with a 2-step investment coating method

STATEMENT OF PROBLEM Although pure titanium is known to have good biocompatibility, a titanium alloy with better strength is needed for fabricating clinically acceptable, partial removable dental prosthesis (RDP) frameworks. PURPOSE The mechanical properties of an experimental Ti-5Al-5Cu alloy cast with a 2-step investment technique were examined for RDP framework applications. MATERIAL AND METHODS Patterns for tests for various properties and denture frameworks for a preliminary trial casting were invested with a 2-step coating method using 2 types of mold materials: a less reactive spinel compound (Al(2)O(3)·MgO) and a less expensive SiO(2)-based material. The yield and tensile strength (n=5), modulus of elasticity (n=5), elongation (n=5), and hardness (n=8) of the cast Ti-5Al-5Cu alloy were determined. The external appearance and internal porosities of the preliminary trial castings of denture frameworks (n=2) were examined with a conventional dental radiographic unit. Cast Ti-6Al-4V alloy and commercially pure titanium (CP Ti) were used as controls. The data for the mechanical properties were statistically analyzed with 1-way ANOVA (α=.05). RESULTS The yield strength of the cast Ti-5Al-5Cu alloy was 851 MPa and the hardness was 356 HV. These properties were comparable to those of the cast Ti-6Al-4V and were higher than those of CP Ti (P<.05). One of the acrylic resin-retention areas of the Ti-5Al-5Cu frameworks was found to have been incompletely cast. CONCLUSIONS The cast biocompatible experimental Ti-5Al-5Cu alloy exhibited high strength when cast with a 2-step coating method. With a dedicated study to determine the effect of sprue design on the quality of castings, biocompatible Ti-5Al-5Cu RDP frameworks for a clinical trial can be produced.