Edge chipping of translucent zirconia.

STATEMENT OF PROBLEM: More translucent dental zirconias have been developed by incorporating the cubic phase and reducing the tetragonal phase content that undergoes transformation toughening, leading to reduced mechanical properties. Whether the clinically relevant mechanical property of the edge chipping toughness of the material is also reduced is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the edge chipping toughness and translucency of translucent zirconia, 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), and lithium disilicate. MATERIAL AND METHODS: Two translucent zirconia products, Katana and Lava Esthetic; one 3Y-TZP, Lava Plus; and one lithium disilicate, IPS e.max Press were prepared and tested for phase composition via X-ray diffraction (XRD) (n=3), translucency via a spectrophotometer (n=20), and edge chipping via a universal testing machine with a custom-machined specimen holder and diamond indenter (n=20). The 3Y-TZP and lithium disilicate served as the optimal control materials for edge chipping and translucency, respectively. Translucency was compared with 1-way ANOVA and edge toughness with ANCOVA (α=.05). RESULTS: The XRD showed the 3Y-TZP to be almost completely tetragonal phase compared with the 2 translucent zirconia products that were predominantly cubic. Katana UTML and IPS e.max Press had a statistically similar (P>.05) translucency that was significantly (P<.05) greater than that of Lava Esthetic and Lava Plus. The edge toughness of Katana UTML was 304 N/mm, IPS e.max Press was 354 N/mm, Lava Esthetic was 394 N/mm, and Lava Plus was 717 N/mm, with significance rankings of Katana UTM

Edge chipping resistance and flexural strength of polymer infiltrated ceramic network and resin nanoceramic restorative materials.

STATEMENT OF PROBLEM: Two novel restorative materials, a polymer infiltrated ceramic network (PICN) and a resin nanoceramic (RNC), for computer-assisted design and computer-assisted manufacturing (CAD-CAM) applications have recently become commercially available. Little independent evidence regarding their mechanical properties exists to facilitate material selection. PURPOSE: The purpose of this in vitro study was to measure the edge chipping resistance and flexural strength of the PICN and RNC materials and compare them with 2 commonly used feldspathic ceramic (FC) and leucite reinforced glass-ceramic (LRGC) CAD-CAM materials that share the same clinical indications. MATERIAL AND METHODS: PICN, RNC, FC, and LRGC material specimens were obtained by sectioning commercially available CAD-CAM blocks. Edge chipping test specimens (n=20/material) were adhesively attached to a resin substrate before testing. Edge chips were produced using a 120-degree, sharp, conical diamond indenter mounted on a universal testing machine and positioned 0.1 to 0.7 mm horizontally from the specimen's edge. The chipping force was plotted against distance to the edge, and the data were fitted to linear and quadratic equations. One-way ANOVA determined intergroup differences (α=.05) in edge chipping toughness. Beam specimens (n=22/material) were tested for determining flexural strength using a 3-point bend test. Weibull statistics determined intergroup differences (α=.05). Flexural modulus and work of fracture were also calculated, and 1-way ANOVA determined intergroup differences (α=.05) RESULTS: Significant (P<.05) differences were found among the 4 CAD-CAM materials for the 4 mechanical properties. Specifically, the material rankings were edge chipping toughness: RNC>LRGC=FC>PICN; flexural strength: RNC=LRGC>PICN>FC; flexural modulus: RNCLRGC=PICN>FC. CONCLUSIONS: The RNC material demonstrated superior performance for the mechanical properties tested compared with the other 3 materials.

Effect of toothbrushing on shade and surface roughness of extrinsically stained pressable ceramics.

STATEMENT OF PROBLEM: The effect of toothbrushing on extrinsically stained pressable ceramic materials is unknown. PURPOSE: The purpose of this in vitro study was to investigate the effects of toothbrushing on the shade and surface roughness of extrinsically stained, pressable ceramics. MATERIAL AND METHODS: Two materials, leucite-based (IPS Empress Esthetic [EE]; Ivoclar Vivadent AG) and lithium disilicate-based ceramic (IPS e.max Press [EP]; Ivoclar Vivadent AG), were studied. For each material, 24 disk-shaped specimens, 10 mm (diameter)×3 mm (height) were fabricated. Three different methods (n=8) of applying extrinsic stains were performed on each material: glazed only (G, control group); stained then glazed (SG); and stained and glazed together (T). The specimens were brushed with a multistation brushing machine under a load of 1.96 N at a rate of 90 strokes per minute with a soft and straight toothbrush (Oral-B #35) and a 1:1 toothpaste and distilled water slurry. Shade and roughness were measured at baseline and at 72, 144, 216, and 288 hours, which is equivalent to 3, 6, 9, and 12 years of simulated toothbrushing for 2 minutes twice a day. A repeated measures ANOVA with staining technique as a fixed factor was used to evaluate shade and roughness (α=.05). RESULTS: For EE groups, no significant change was found after 12 years of simulated toothbrushing regarding shade and surface roughness, irrespective of staining techniques (P>.05). However, EP groups demonstrated a significant shade change and an increase in surface roughness after 12 years of simulated toothbrushing. Shade change was found to depend on the method of applying stain. For the EP-SG technique, a significant shade change was observed only at the 9- to 12-year interval (P=.047). However, the EP-T technique demonstrated a significant difference in shade between baseline and 3 years (P=.005) and in the 6- to 9-year interval (P=.005). Surface roughness was only significantly affected at baseline and 3 years for the EP-T group (P=.005). CONCLUSIONS: For the shade and surface roughness of the EE groups, no statistically significant difference was found after 12 years of toothbrushing, irrespective of the staining technique. The shade and surface roughness of the EP groups were significantly statistically affected by toothbrushing time; only shade changes were found to depend on technique.

Early reaction kinetics of contemporary glass-ionomer restorative materials.

PURPOSE: To investigate polyalkenoate reaction rates in conventional glass-ionomer cement (GIC) and resin-modified glass ionomer (RMGI) restorative materials using infrared spectroscopy. MATERIALS AND METHODS: Nine conventional GIC and six RMGI restorative materials were prepared according to manufacturer's directions and placed on a FTIR (Fourier transform infrared spectroscopy) diamond ATR (attenuated total reflectance) surface. FTIR spectra (700 to 1800 cm-1) were obtained each minute for 3 h. VLC specimens were light polymerized after 1 min; at 5 min, all samples were covered with gauze saturated with deionized water. Polyalkenoate reaction was determined by measuring area growth (Å/cm-1) between 1375 and 1500 cm-1. Mean peak areas were determined at 5, 15, 30, 90, and 180 min and compared using ANOVA (p = 0.05) RESULTS: For all RMGI materials, VLC polymerization inhibited the polyalkenoate reaction rate. Compared to conventional GIC, RMGI materials demonstrated less polyalkenoate reaction. Compared to dark curing, RMGI light polymerization significantly inhibited the polyalkenoate reaction rate. CONCLUSIONS: The addition of resin components to glass-ionomer products significantly retards and impedes the polyalkenoate reaction. The polyalkenoate reaction rate of RMGI products was significantly lower than that of self-curing GIC restorative materials. Furthermore, light activation of RMGI products further retards the polyalkenoate rate. When clinicians require the therapeutic benefit of a polyalkenoate product, perhaps a conventional GIC restorative product should be the first material of choice.

Die spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study.

STATEMENT OF PROBLEM: The inability to control die spacer thickness has been reported. However, little information is available on the congruency between the computer-aided design parameters for die spacer thickness and the actual printout. PURPOSE: The purpose of this study was to evaluate the accuracy and precision of the die spacer thickness achieved by combining computer-aided design and 3-dimensional printing technology. MATERIAL AND METHODS: An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone models were produced from Type IV dental stone. The dies were randomly divided into 5 groups with assigned die spacer thicknesses of 25 µm, 45 µm, 65 µm, 85 µm, and 105 µm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D Systems), were cemented onto their respective die-stone models with self-adhesive resin cement and stored at room temperature until sectioning into halves in a buccolingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die. Images of the printed resin coping/die-stone model internal gap dimensions were obtained with an inverted bright field metallurgical microscope at ×100 magnification. The acquired digital image was calibrated, and measurements were made using image analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery rate at 5% was used to adjust for multiple testing. Coefficient of variation was used to determine the precision for each group and was evaluated statistically with the Wald test (α=.05). RESULTS: The accuracy, expressed in terms of the mean differences between the prescribed die spacer thickness and the measured internal gap (standard deviation), was 50 µm (11) for the 25 µm group simulated die spacer thickness, 30 µm (10) for the 45 µm group, 15 µm (14) for the 65 µm group, 3 µm (23) for the 85 µm group, and -10 µm (32) for the 105 µm group. The precision mean of the measurements, expressed as a coefficient of variation, ranged between 14% and 33% for the 5 groups. CONCLUSIONS: For the accuracy evaluation, statistically significant differences were found for all the groups, except the group of 85 µm. For the precision assessment, the coefficient of variation was above 10% for all groups, showing the printer's inability to reproduce the uniform internal gap within the same group.

Investigation of force decay in aesthetic, fibre-reinforced composite orthodontic archwires.

BACKGROUND/OBJECTIVES: Because polymer-based materials typically exhibit viscoelastic properties, the objective was to determine if commercially available, aesthetic, fibre-reinforced composite archwires maintain continuous forces without undergoing force decay when deflected continuously. MATERIALS/METHODS: Quasi force decay was evaluated by comparing three-point bending profiles of nickel-titanium (NiTi) and fibre-reinforced composite archwires (BioMers) prior to and after 30 days of continuous deflection of either 1 or 2mm. Paired t-tests or non-parametric signed rank tests were used to statistically compare pre- and post-deflection bending forces. A control group consisting of wires not subject to the 30-day constant deflection was tested to check whether the initial testing altered the second three-point bend test. RESULTS: Significant (P < 0.01) differences in the pre- and post-deflection deactivation force delivery were most evident in the composite 2mm deflection group and all of the NiTi groups. The composite 2mm deflection group failed to deliver consistent forces as the majority of the wires experienced crazing during the 30-day deflection period. The decrease in force delivery in the NiTi groups may be attributed to the small standard deviations. CONCLUSIONS: The composite 1mm deflection group demonstrated that fibre-reinforced composite archwires are able to deliver a consistent force after 30 days of deflection. However, the clinical applicability of these fibre-reinforced composite archwires may be limited as they are unable to sustain deflections of 2mm without experiencing crazing and loss of force delivery. LIMITATIONS: Clinical efficacy of the aesthetic, fibre-reinforced composite orthodontic archwires remains to be observed.

Effect of Different Thicknesses of Pressable Ceramic Veneers on Polymerization of Light-cured and Dual-cured Resin Cements.

AIM: This study evaluated the effects of ceramic veneer thicknesses on the polymerization of two different resin cements. MATERIALS AND METHODS: A total of 80 ceramic veneer disks were fabricated by using a pressable ceramic material (e.max Press; Ivoclar Vivadent) from a Low Translucency (LT) ingot (A1 shade). These disks were divided into light-cured (LC; NX3 Nexus LC; Kerr) and dual-cured (DC; NX3 Nexus DC; Kerr) and each group was further divided into four subgroups, based on ceramic disk thickness (0.3, 0.6, 0.9, and 1.2 mm). The values of Vickers microhardness (MH) and degree of conversion (DOC) were obtained for each specimen after a 24-hour storage period. Association between ceramic thickness, resin cement type, and light intensity readings (mW/cm(2)) with respect to microhardness and degree of conversion was statistically evaluated by using analysis of variance (ANOVA). RESULTS: For the DOC values, there was no significant difference observed among the LC resin cement subgroups, except in the 1.2 mm subgroup; only the DOC value (14.0 ± 7.4%) of 1.2 mm DC resin cement had significantly difference from that value (28.9 ± 7.5%) of 1.2 mm LC resin cement (p < 0.05). For the MH values between LC and DC resin cement groups, there was statistically significant difference (p < 0.05); overall, the MH values of LC resin cement groups demonstrated higher values than DC resin cement groups. On the other hands, among the DC resin cement subgroups, the MH values of 1.2 mm DC subgroup was significantly lower than the 0.3 mm and 0.6 mm subgroups (p < 0.05). However, among the LC subgroups, there was no statistically significant difference among them (p > 0.05). CONCLUSION: The degree of conversion and hardness of the resin cement was unaffected with veneering thicknesses between 0.3 and 0.9 mm. However, the DC resin cement group resulted in a significantly lower DOC and MH values for the 1.2 mm subgroup. CLINICAL SIGNIFICANCE: While clinically adequate polymerization of LC resin cement can be achieved with a maximum 1.2 mm of porcelain veneer restoration, the increase of curing time or light intensity is clinically needed for DC resin cements at the thickness of more than 0.9 mm.

An investigation into the mechanical and aesthetic properties of new generation coated nickel-titanium wires in the as-received state and after clinical use.

BACKGROUND/OBJECTIVES: The purpose of this study was to compare the mechanical, structural, and aesthetic properties of two types of aesthetic coated nickel-titanium (NiTi) wires compared with comparable regular NiTi wires in the as-received state and after clinical use. MATERIALS/METHODS: Sixty one subjects were randomly assigned to four groups (N = 61), two groups of coated wires and two groups of comparable, non-coated controls (n = 15/group). The period in the mouth ranged from 4 to 12 weeks after insertion. In total, 121 wires (61 retrieved and 60 as-received) were used in the study. The percentages of coating retention and loss were extrapolated from scans. A brief survey of five questions with three choices was given to all patients. Differential scanning calorimetry (DSC) and three-point bending tests were done on as-received and used wires. RESULTS: The surface characterization by the percentage of resin remaining indicated that most wires in both test groups lost a significant amount of coating. A patient survey indicated that this was a noticeable feature for patients. DSC analysis of the wires indicated that the metallurgical properties of the coated wires were not similar to the uncoated wires in the as-received condition. Three-point bending results indicate a wide variation in test results with large standard deviations among all the groups. LIMITATIONS: The extent of coating loss requires investigating, as do the biological properties of the detached coating. CONCLUSIONS: Both wires lost a significant amount of aesthetic coating after varying periods in the mouth. The metallurgical testing of these findings may indicate that these wires perform differently in the mouth.

Electrochemical Properties of Nickel-Titanium Rotary Endodontic Instruments.

INTRODUCTION: Nickel-titanium rotary endodontic files have been commercially available for decades, but more recent innovations have introduced heat-treated and surface-treated files. This study investigated the corrosion properties of various nickel-titanium files in normal saline and sodium hypochlorite (NaOCl). METHODS: Ten different file brands of size 40 with a 0.04 taper were subjected to electrochemical testing in 0.9% NaCl (saline) and 5.25% NaOCl at room temperature. The Open Circuit Potential (OCP) was observed for 1 hour followed by a cyclic polarization test from -300 to 700 mV and back to -300 mV (vs OCP). Nonparametric ANOVA and a pairwise comparison (P < .05) were used for statistical analysis of the OCP at 1 hour and the corrosion current (Icorr) obtained via the cyclic polarization test. RESULTS: Significant differences (P < .05) were found between files with respect to OCP and Icorr in both solutions. Nine files exhibited significantly greater (P < .05) Icorrs in NaOCl than in saline. Conversely, pitting corrosion was observed in the saline solution but not NaOCl. Weak and/or moderate correlations existed between OCP and Icorr measures in the 2 solutions. CONCLUSION: Significant differences in electrochemical properties were observed among the 10 brands of files. Overall, there was not a clear trend between conventional, heat-treated, or surface-treated files among OCP or Icorr in either solution.

Corrosion of orthodontic temporary anchorage devices.

Corrosion of orthodontic miniscrews or temporary anchorage devices (TADs) has been proposed as a contributor to inflammation, which in turn is a factor in the clinical success of miniscrews. The purpose of this study was to measure the electrochemical properties of orthodontic miniscrews in artificial saliva with and without fluoride. The corrosion properties of three miniscrew products (VectorTAS, Ormco Corp.; Unitek TAD, 3M Unitek; and Through-Hole Screw, American Orthodontics) were tested in an artificial saliva (Fusayama-Meyer) with (1500 ppm) or without fluoride (n = 10/product/solution). Open circuit potential (OCP), polarization resistance (R p), and corrosion current (I corr) were measured and statistically analysed with the Friedman/Tukey least significant difference tests. No significant differences (P > 0.05) between miniscrews with regard to OCP, R p, and I corr were found except that the American Orthodontics miniscrews had a significantly (P < 0.05) more noble OCP compared to the others. Incorporation of 1500 ppm fluoride in the artificial saliva significantly (P < 0.001) lowered the OCP, reduced the polarization resistance, and increased the corrosion current of each miniscrew product. Few differences existed in the electrochemical properties of miniscrews from the three different manufacturers; however, exposure to fluoride was detrimental to the corrosion properties of all miniscrews.

Bonding with self-etching primers--pumice or pre-etch? An in vitro study.

The purpose of this study was to compare the shear bond strengths (SBSs) of orthodontic brackets bonded with self-etching primer (SEP) using different enamel surface preparations. A two-by-two factorial study design was used. Sixty human premolars were harvested, cleaned, and randomly assigned to four groups (n = 15 per group). Teeth were bathed in saliva for 48 hours to form a pellicle. Treatments were assigned as follows: group 1 was pumiced for 10 seconds and pre-etched for 5 seconds with 37 per cent phosphoric acid before bonding with SEP (Transbond Plus). Group 2 was pumiced for 10 seconds before bonding. Group 3 was pre-etched for 5 seconds before bonding. Group 4 had no mechanical or chemical preparation before bonding. All teeth were stored in distilled water for 24 hours at 37°C before debonding. The SBS values and adhesive remnant index (ARI) score were recorded. The SBS values (± 1 SD) for groups 1-4 were 22.9 ± 6.6, 16.1 ± 7.3, 36.2 ± 8.2, and 13.1 ± 10.1 MPa, respectively. Two-way analysis of variance and subsequent contrasts showed statistically significant differences among treatment groups. ARI scores indicated the majority of adhesive remained on the bracket for all four groups. Pre-etching the bonding surface for 5 seconds with 37 per cent phosphoric acid, instead of pumicing, when using SEPs to bond orthodontic brackets, resulted in greater SBSs.

Elemental release from CoCr and NiCr alloys containing palladium.

PURPOSE: An entirely new subclass of casting alloy composition whereby palladium (∼approximately 25 wt%) is added to traditional base metal alloys such as CoCr and NiCr was recently introduced to the market. The purpose of this study was to evaluate the elemental release of new CoPdCr and NiPdCr alloys and compare them to traditional CoCr and NiCr alloys. MATERIALS AND METHODS: Five casting alloys were investigated: CoPdCr-A (NobleCrown NF, The Argen Corporation), CoPdCr-I (Callisto CP+, Ivoclar Vivadent), NiPdCr (NobleCrown, Argen), CoCr (Argeloy N.P. Special, Argen), and NiCr (Argeloy N.P. Star, Argen). Rectangular specimens (n = 6/alloy) were prepared and immersed in a lactic acid/NaCl solution at 37°C for 7 days according to ISO 10271. Solutions were analyzed with ICP-AES to determine elemental release. The concentrations of major ions (cobalt, nickel, palladium, chromium, and molybdenum) were compared using a generalized linear model (p < 0.05). Representative specimens were examined with optical microscopy before and after immersion. RESULTS: The CoPdCr alloys released a significantly greater amount of respective ions (Co, Cr, Mo, and total ions) compared to the traditional CoCr alloy. No significant differences in elemental release were noted between NiPdCr and NiCr. Optical microscopic examination showed abundant areas of corrosion in the palladium-containing CoCr alloys after immersion, whereas little difference was observed for the other alloys. CONCLUSIONS: Corrosion resistance measured via elemental release was compromised when CoCr was alloyed with palladium, but this effect was not observed with NiCr.

Corrosion of CoCr and NiCr dental alloys alloyed with palladium.

STATEMENT OF PROBLEM: A new subclass of casting alloy composition involving the addition of palladium (25 wt%) to traditional base metal alloys, thereby raising their classification to that of a noble alloy, has been recently introduced. Little is known about this class of casting alloy, particularly its corrosion properties, which influence its biocompatibility and esthetics. PURPOSE: The purpose of this study was to evaluate the corrosion properties of 2 new CoPdCr and one new NiPdCr alloy and compare them to traditional CoCr and NiCr alloys. MATERIAL AND METHODS: The casting alloys investigated were: CoPdCr-A (NobleCrown NF), CoPdCr-I (Callisto CP+), NiPdCr (Noble Crown), CoCr (Argeloy N.P. Special), and NiCr (Argeloy N.P. Star). Cylindrical (4.8-mm diameter) as-cast and oxidized specimens were assessed electrochemically in phosphate-buffered saline at 24°C (n=8 and n=6, respectively). The open circuit potential (OCP) was monitored for 20 hours, followed by linear polarization and cyclic polarization tests. A generalized linear mixed model was used to determine whether differences existed between alloys and to examine the effect of oxidation (α=.05). Representative alloy surfaces were scanned and examined with light microscopy. RESULTS: The palladium-containing alloys possessed a significantly greater OCP (P<.001); however, their polarization resistance was less and the corrosion current density was significantly greater (P<.05) than their traditional CoCr and NiCr alloy counterparts. Additionally, a greater incidence of pitting was observed in the palladium-containing alloys. Some differences were noted within alloys between the as-cast and oxidized conditions, but a major trend was not observed. CONCLUSIONS: Overall, the inclusion of palladium in CoCr and NiCr alloys had deleterious effects on electrochemical corrosion properties.

Galvanic corrosion between various combinations of orthodontic brackets and archwires.

INTRODUCTION: The purpose of this study was to compare galvanic currents generated by different combinations of commonly used brackets and archwires. METHODS: As-received stainless steel, nickel-titanium, and beta-titanium wires were coupled to stainless steel and titanium brackets in an artificial saliva medium. The galvanic current and amount of charge transferred for each pair were monitored with a zero resistance ammeter for 10 hours. RESULTS: Two-way analysis of variance (ANOVA) showed a significant difference in charge and galvanic currents when factored for type of bracket (P <0.001), but no significant difference between them when factored by type of wire (P >0.05). Specifically, a brazed stainless steel bracket was significantly greater in charge transferred and 10-hour galvanic current than metal injection molded stainless steel and titanium brackets (P <0.001), which were not different from each other (P >0.05). CONCLUSIONS: The method of bracket manufacturing might be of equal or more relevance to galvanic corrosion susceptibility than bracket composition.

Hardness of three resin-modified glass-ionomer restorative materials as a function of depth and time.

STATEMENT OF THE PROBLEM: The polymerization of bulk-placed resin-modified glass-ionomer (RMGI) restoratives is compromised when penetration of the curing light is limited because of the materials' thickness. It is unknown if additional post light-curing resin polymerization and/or glass-ionomer setting occurs over time to ensure adequate polymerization. PURPOSE: The primary objective was to evaluate the depth of cure of various thicknesses of RMGI restorative products over 1 year using Knoop hardness (KH) testing. MATERIALS AND METHODS: The materials were placed in Delrin molds having an internal diameter of 5.0 mm and heights of 2, 3, 4, and 5 mm and were photopolymerized with a halogen light-curing unit. Five specimens of each depth were prepared for each time period evaluated. Specimens were stored in darkness at 37 +/- 2 degrees C and 98 +/- 2% humidity until being tested at 24 hours, 1 week, and 1, 3, 6, 9, and 12 months after fabrication. Mean KH values were calculated for the bottom and top surfaces of each thickness group and used to determine bottom/top hardness ratios. Data were compared using two-way analysis of variance (factors of time, thickness) at a 0.05 significance level with Scheffé's post hoc analysis, where required. RESULTS: The materials had relatively stable top surface KH, which permitted valid assessment of changes in bottom surface KH over time. The bottom surface KH of some RMGIs changed significantly over time (p < 0.001), but degrees of change were material dependent. Certain RMGIs demonstrated a potential for statistically significant post light-activation hardening; however, that too was material dependent. As compared with top surface KH, deeper layers of the thicker RMGI specimens consistently failed to achieve an adequate degree of polymerization. CONCLUSION: Although certain RMGI materials demonstrate a potential for post light-activation chemically initiated resin polymerization and/or polyalkenoate acid/base reaction, these reactions may not be sufficient to ensure that the material is adequately polymerized for long-term success. This is particularly true when RMGI materials are placed in thicker layers where curing light penetration may be compromised. CLINICAL SIGNIFICANCE: RMGI materials should not be placed in bulk but photopolymerized in layers to ensure adequate light activation. The results of this study suggest that Photac-Fil Quick be placed in layers no thicker than 2 mm while Fuji II LC and Vitremer may be placed in layers up to 3 mm in thickness.

Influence of stress and phase on corrosion of a superelastic nickel-titanium orthodontic wire.

INTRODUCTION: The purpose of this investigation was to study the effect of stress and phase transformation on the corrosion properties of a superelastic nickel-titanium orthodontic wire. METHODS: The phase transformation profiles of superelastic nickel-titanium (Sentalloy, GAC International, Bohemia, NY) and beta-titanium (TMA, Ormco, Orange, Calif) archwires were analyzed by using differential scanning calorimetry. The force/deflection behavior of the wires at 37 degrees C was measured in a 3-point bending test per modified American Dental Association specification no. 32. Electrochemical testing consisted of monitoring the open circuit potential (OCP) for 2 hours followed by polarization resistance and cyclic polarization tests on archwire segments engaged in a 5-bracket simulation apparatus with bend deflections of 0.75, 1.5, or 3 mm in artificial saliva at 37 degrees C. Nondeflected segments were also tested. Sentalloy was additionally examined for bending and corrosion at 5 degrees C, where it exists as martensite and is devoid of stress-induced phase transformation. OCP at 2 hours and corrosion current density (i(corr)) were analyzed by using ANOVA and Tukey tests (alpha = .05) (n = 10 per deflection). RESULTS: Significant differences (P < 0.05) in OCP with deflection were found for the TMA and the Sentalloy wires at 5 degrees C, but not for Sentalloy at 37 degrees C. Significant differences (P < 0.05) in i(corr) with deflection were also observed. All 3 wire groups had their lowest mean i(corr) values when not deflected. The i(corr) for superelastic Sentalloy (37 degrees C) peaked at 0.75 mm deflection before the wire's stress-induced phase transformation point and then decreased with further deflection and transformation. The i(corr) values for TMA and Sentalloy at 5 degrees C, both of which do not undergo phase transformation with deformation, continuously increased from 0 to 1.5 mm deflection before decreasing at the 3.0-mm deflection. CONCLUSIONS: Stress increased the corrosion rate in nickel-titanium and beta-titanium orthodontic wires. Alterations in stress/strain associated with phase transformation in superelastic nickel-titanium might alter the corrosion rate in ways different from wires not undergoing phase transformation.

Structure, composition, and mechanical properties of Australian orthodontic wires.

OBJECTIVE: To investigate the surface morphology, structure, elemental composition, and key mechanical properties of various sizes and tempers of Australian wires. MATERIALS AND METHODS: Three types of Australian wire were used: 0.016'' regular, 0.018'' regular+, and 0.018'' special+ (A.J. Wilcock, Whittlesea, Victoria, Australia). Each type of wire was subjected to scanning electron microscopy (SEM) analysis, x-ray energy dispersive spectroscopy (EDS) investigation, Vickers hardness testing, and tensile testing. The modulus of elasticity and ultimate tensile strength were determined. Hardness, modulus, and strength data were analyzed with one-way analysis of variance (ANOVA) and Tukey testing at the .05 level of significance. RESULTS: All three types of Australian wire were found to possess considerably rough surfaces with striations, irregularities, and excessive porosity. All three wire types had high levels of carbon and a similar hardness, which ranged within 600 VHN (Vickers hardness number), and a similar modulus of elasticity (173 to 177 GPa). The 0.018'' special+ had a significantly lower tensile strength (1632 MPa) than the 0.016'' regular and the 0.018'' regular+ wire (2100 MPa). CONCLUSIONS: Australian wires did not show variation implied by the size or temper of the wires.

Metal-ceramic interface evaluation of a gold-infiltrated alloy.

PURPOSE: The success of metal-ceramic systems partially depends on the formation of a stable bond between metal and porcelain. The purpose of this study was to investigate the porcelain/metal interface and the mechanism of interfacial bonding in a gold-infiltrated alloy (Captek). MATERIALS AND METHODS: Captek specimens with feldspathic porcelain were evaluated by optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and the Schwickerath crack initiation test for metal-ceramic bond compatibility. Specimens were processed with or without Capbond, a bonding agent. A traditional metal-ceramic alloy was also analyzed with microscopy for comparative purposes. RESULTS: Optical and scanning electron micrographs of Captek specimens processed with Capbond revealed close adaptation of porcelain to the surface of the metal with sporadic nodules extending from the Captek surface. In contrast, the specimens of Captek without Capbond showed a much flatter porcelain/metal interface. Comparatively, the porcelain/metal interface of the traditional metal-ceramic crown showed greater surface roughness than the Captek specimens. No metal oxides were observed at the porcelain/metal interface of the Captek specimens with XRD. During the Schwickerath test, the Captek specimens permanently deformed, not allowing for crack initiation at the porcelain/metal interface. CONCLUSIONS: Microscopy and XRD analysis showed that micromechanical interlocking is the primary mechanism of porcelain adherence to Captek metal. The use of Capbond prior to porcelain application to Captek results in gold nodules on the surface to aid retention. Existing metal-ceramic bond compatibility standardized tests are not sufficient for evaluating Captek, primarily due to the flexibility of the material.

Metal-ceramic alloys in dentistry: a review.

PURPOSE: The purpose of this article is to review basic information about the alloys used for fabricating metal-ceramic restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. In addition to reviewing traditional noble-metal and base-metal metal-ceramic alloys, titanium and gold composite alloys are also discussed. MATERIALS AND METHODS: A broad search of the published literature was performed using Medline to identify pertinent current articles on metal-ceramic alloys as well as articles providing a historical background about the development of these alloys. Textbooks, the internet, and manufacturers' literature were also used to supplement this information. RESULTS: The review discusses traditional as well as more recently-developed alloys and technologies used in dentistry for fabricating metal-ceramic restorations. Clear advantages and disadvantages for these alloy types are provided and discussed as well as the role that compositional variations have on the alloys' performance. This information should enable clinicians and technicians to easily identify the important physical properties of each type and their primary clinical indications. CONCLUSIONS: A number of alloys and metals are available for metal-ceramic use in dentistry. Each has its advantages and disadvantages, primarily based on its specific composition. Continuing research and development are resulting in the production of new technologies and products, giving clinicians even more choices in designing and fabricating metal-ceramic restorations.

Corrosion behavior of shape memory, superelastic, and nonsuperelastic nickel-titanium-based orthodontic wires at various temperatures.

OBJECTIVE: Nickel-titanium orthodontic wires have various temperature-dependent phases. The purpose of this study was to investigate temperature-dependent corrosion characteristics of shape memory, superelastic, and nonsuperelastic orthodontic wires. METHODS: Four orthodontic wires were investigated: 27 and 40 degrees C copper Ni-Ti (superelastic and shape memory, respectively), superelastic Ni-Ti, and nonsuperelastic Nitinol Classic. Differential scanning calorimetry (DSC) was used to confirm phase/temperature behavior of the wires. Sectioned halves of as-received archwires were assessed electrochemically in artificial saliva at 5, 24, 37, and 45 degrees C. Open circuit potential (OCP) was monitored for 2h followed by polarization resistance and cyclic polarization tests. RESULTS: DSC results showed Nitinol was primarily martensitic-stable whereas NiTi, 27 degrees C CuNiTi, and 40 degrees C CuNiTi possessed austenite-finish temperatures of approximately 19, 21, and 38 degrees C. The OCP of the CuNiTi wires was significantly greater than NiTi and Nitinol but no apparent trend in values was apparent with regard to temperature or phases present. Corrosion current density (i(corr)) increased with temperature for all wires, but not all were equally influenced. The two lowest austenite-finish temperature wires (27 degrees C CuNiTi and NiTi) approximately tripled in i(corr) from 37 to 45 degrees C. Greater incidence of pitting was observed in the CuNiTi wires. SIGNIFICANCE: This study showed the corrosion rate of various nickel-titanium wires increase with temperature and different phases present may influence corrosion rate trends.