Influence of different heat treatments on the corrosion behavior of a new type of high palladium dental alloy / 口腔疾病防治

Objective@#To evaluate the influence of different heat treatments on the corrosion behavior of a new Pd-Ag-In-Ga alloy. @*Methods @#The corrosion of a new Pd-Ag-In-Ga alloy was tested according to ISO 10271：2001/cor.1:2005(E). Taken as comparison, a commercial high-palladium alloy (Spartan® Plus) was also employed in the study. For electrochemical corrosion test, the open-circuit potential (Eocp) and potentiodynamic polarization curve were recorded and then the electrochemical parameters, namely corrosion potential (Ecorr) and corrosion current density (Icorr) calculated. The surfaces of the specimens that before and after corrosion test were observed by scanning electron microscopy (SEM). @* Results @#Both of the high-palladium alloys had lower corrosion tendency and higher corrosion resistance by heat treatment in the ISO 10271 electrochemical corrosion test. For both alloys, heat treatment at 500 ℃ was found to be effective in improving the corrosion resistance as the best datas of electrochemical parameters (Eocp, Ecorr, Icorr) were detected among the four temperature groups. However, no evidence showed that there was significant difference in corrosion resistance between the two alloys. Comparison of surface morphology of the specimens before and after electrochemical experiments by SEM demonstrated that all groups of the two alloys were visible of pitting corrosion and crevice corrosion phenomenon that gradually became less with increasing heat treatment temperature. Horizontal comparing among the groups of the two alloys, no apparent differences in the distribution of pitting and crevice corrosion was found. @*Conclusin @#The variation in compositions of high-palladium alloys did not cause significant difference in corrosion behavior due to the identical palladium matrix. The similarity in corrosion behavior among the two high-palladium alloys might be attributed to the predominant palladium content.

Study on electrical measurement stress analysis of root attachment overdenture of three different mechanisams / 口腔疾病防治

Objective@#To analyze the stress difference of alveolar bone around the abutment and alveolar ridge of edentulous of three different kinds of root-attachment-supported overdenture under different load conditions, in order to provide a reference for the choice of clinical root attachment. @*Methods @#The occlusal force of overdenture was simulated by electrical resistance strain measurement in vitro. The stress of the alveolar bone, the central part of the mandibular arch and the first molar correspond to the alveolar ridge were measured. The stress difference of 3 kinds of attachment overdenture under different loading conditions were compared and analyzed.@*Results@#Under the same loading condition, all three kinds of overdentures had a certain degree of slip of the denture (magnetic attachment denture) or rotation (3 kinds of attachment dentures). The abutment neck in different parts of the dental arch and alveolar bone, anterior free end edentulous alveolar ridge stress distribution was significantly different. @*Conclusion@# ERA attachment overdenture was the most preferable, followed by the magnetic attachment overdenture. Suitable attachment should be selected based on specific clinical cases.

[Metameric effect between natural teeth and resin teeth of A2 shade].

OBJECTIVE: The aim of this study was to determine the metameric color differences between natural teeth and three brands of commercially available resin teeth. METHODS: The spectral reflectance and color coordinates of natural teeth and three brands of commercially available resin teeth of A2 shade were measured with a spectrophotometer (PR-650) according to the CIE L*, a*, b* and CIE XYZ color scale relative to illuminant D65, A, cool white fluorescent (CWF) and ultraviolet (UV), and the metameric indices were calculated to determine the metameric color differences between natural teeth and resin teeth. RESULTS: CIE L*, a*, b* values were influenced by the type of illuminants in both natural teeth and resin teeth. The pattern of spectral reflectance curves for natural teeth and resin teeth of A2 shade were different, while there were more than three crossing points among each curves, which meant the color of natural teeth and resin teeth of A2 shade might be the same under certain illuminant. The metameric indices between natural teeth and resin teeth of A2 shade were 3.48, 2.52 and 3.36 under illuminant A; 1.21, 1.90, and 2.79 under illuminant CWF; 1.59, 2.07, and 4.07 under illuminant UV. The metameric indices between resin teeth of different brand were 1.08, 0.10, and 1.01 under illuminant A; 1.46, 2.23, and 0.94 under illuminant CWF; and 2.55, 2.69, and 4.64 under UV. CONCLUSION: Changes in optical properties of resin teeth of A2 shade relative to the different illuminants were different from those of natural teeth, the metameric effect between natural teeth and resin teeth of A2 shade were significant. Therefore, shade matching between natural teeth and resin teeth should be performed under more than one illuminant.

[Comparison of casting precision of two kinds of commercially available gypsum-bonded investment with different setting and thermal expansion characteristics].

OBJECTIVE: To 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. METHODS: Two 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. RESULTS: The 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). CONCLUSION: Within 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.

[The expansion characters of a quick-heating gypsum-bonded investment under different heating methods].

OBJECTIVE: To 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. METHODS: The 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). RESULTS: Statistical 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). CONCLUSION: The 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.

[Wear behavior of enamel and veneering ceramics].

OBJECTIVE: To compare the wear between the enamel and two types of dental decoration porcelains for all-ceramic restorations (Vita-alpha, Vintage AL). METHODS: Friction coefficients, wear scar width, element concentrations and wear surface evolution were considered relatively to the tribology of that in vivo situation. The wear scars of the samples were characterized by means of dynamic atomic force microscopy (DFM). The different element concentrations of the surface before/after the wear test were determined with energy dispersion spectrometry (EDS). RESULTS: The friction coefficient varied from time in each kind of material. The statistical differences between materials were observed in wear scar width and properties of materials (P<0.05). DFM results showed wear surface of natural tooth full of abrasive particles and denaturation of dental texture. Wear surface of veneering ceramics consisted mainly of abrasive particles, plough and microcracking. EDS results showed that the element concentration of Fe was obviously found on the samples after wear. CONCLUSION: The main underlying mechanisms of natural teeth wear are abrasive, and denaturation of dental texture. Abrasive wear, adhesion and fatigue of veneering ceramics characterize the wear patterns which plays different role in Vita-alpha and Vintage AL. The wear patterns of veneering ceramics can be described as mild wear.

[Compatibility between high-strength dental ceramic (type A) and vintage AL veneering porcelain].

OBJECTIVE: To investigate the interface bond strength and compatibility between High-Strength Dental Ceramic (type A) and Vintage AL veneering porcelain. METHODS: Twenty bar-shape specimens (ten Vintage AL and ten Vitadur alpha) were fabricated, and shear test was conducted to determine the bond strength. A bilayered composite (1 mm core ceramic and 0.8 mm Vintage AL) was prepared and then fractured for scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. Ten all-ceramic anterior crowns were fabricated and the temperatures of thermal shock resistance were tested. RESULTS: The mean values of the bond strength measured were (55.52 +/- 14.64) MPa and (59.37 +/- 13.93) MPa for Vintage AL and Vitadur alpha respectively (P>0.05). SEM showed tight connection between the High-Strength Dental Ceramic (type A) and the veneering porcelain. Element diffusion was also confirmed by energy dispersive spectroscopy (EDS) analysis. The temperature of thermal shock resistance of this system was (179 +/- 15) degrees C. CONCLUSION: Vintage AL veneering porcelain has good thermal and chemical compatibility with High-Strength Dental Ceramic (type A).