Effect of multi-purpose primer on bonding of acrylic resin to cast titanium and gold alloy after airborne-particle abrasion.

PURPOSE: To clarify the effect of a multi-purpose primer combining several functional monomers on two prosthodontic materials (cast titanium and a gold alloy) after airborne-particle abrasion. METHODS: Disk-shaped adherends were prepared from cast titanium (CP Titanium JIS2) and a gold alloy (Casting Gold M.C. Type IV). A silane-containing two-liquid primer (M&C primer (MC)) and two silane-free single-liquid primers (Alloy Primer (AP) and V-Primer (VP)) were used as surface-treatment agents. The shear bond strengths were determined before and after thermocycling to evaluate the adhesive durability, and the results were compared using a non-parametric statistical analysis. The effect of airborne-particle abrasion with alumina on the titanium surface was analyzed by X-ray photoelectron spectroscopy (XPS). RESULTS: There was no significant difference in bond strength between the MC and AP before and after thermocycling, whereas VP showed significantly lower values. XPS revealed that the titanium acquired hydrophilic properties after the airborne-particle abrasion. CONCLUSIONS: The novelty of this study is that it shows that the presence/absence of the silane had no effect on the bonding of cast titanium with an acrylic resin. The study also showed that the multi-purpose primer can be used without any problems with both cast titanium and gold alloy, in combination with airborne-particle abrasion with alumina.

Iron-gold alloy nanoparticles serve as a cornerstone in hyperthermia-mediated controlled drug release for cancer therapy.

INTRODUCTION: The efficacy of a chemotherapy drug in cancer therapy is highly determined by the ability to control the rate and extent of its release in vivo. However, the lack of techniques to accurately control drug release drastically limits the potency of a chemotherapy drug. MATERIALS AND METHODS: Here, we present a novel strategy to precisely monitor drug release under magnetic stimulation. Methotrexate (MTX), an anticancer drug, was covalently functionalized onto iron-gold alloy magnetic nanoparticles (Fe-Au alloy nanoparticles or NFAs) through 2-aminoethanethiol grafting and the ability of this drug-nanoparticle conjugate (NFA-MTX) in limiting HepG2 (liver carcinoma) cell growth was studied. Well-dispersed NFAs were prepared through pyrolysis. RESULTS AND DISCUSSION: Transmission electron microscopy revealed the average nanoparticle size to be 7.22±2.6 nm, while X-ray diffraction showed distinct 2θ peaks for iron and gold, confirming the presence of iron and gold nanoparticles. Inductively coupled plasma mass spectrometry revealed that the amount of NFA-MTX conjugate ingested by HepG2 cancer cells was 1.5 times higher than that ingested by L929 fibroblasts, thereby proving a higher selective ingestion by cancer cells compared to normal cells. Fourier-transform infrared spectroscopy revealed the breakage of Au-S bonds by the heat generated under magnetic field stimulation to release MTX from the NFA-MTX conjugate, triggering a 95% decrease in cellular viability at 100 µg/mL. CONCLUSION: The ability of NFA-MTX to dissociate under the influence of an applied magnetic field provides a new strategy to induce cancer cell death via hyperthermia. Applications in drug delivery, drug development, and cancer research are expected.

Assessment of Ions released from Three Types of Orthodontic Brackets immersed in Different Mouthwashes: An in vitro Study.

AIM: Herbs are used widely in medicine. The purpose of the present study was to assess the ion release from gold-plated orthodontic bracket compared with other stainless steel brackets, and based on the findings of the study, the orthodontists can choose the most biocompatible brackets and mouthwashes useful in the clinical practice. MATERIALS AND METHODS: A total of 150 orthodontic brackets from Orthotechnology™ Company, USA (50 stainless steel one-piece brackets, 50 stainless steel two-piece brackets, and 50 gold brackets) were immersed in four mouthwashes in addition to distilled water. Ten of each type of brackets in every media were immersed under 37°C for 45 days. Ions released in these mouthwashes were measured, and comparisons among different bracket types and among various mouthwashes were done by one-way analysis of variance (ANOVA) and then with Games-Howell tests. RESULTS: Increased amounts of ions released in herbal mouth-washes were recorded in gold and two-piece brackets in comparison with one-piece stainless steel brackets. CONCLUSION: Herbal mouthwashes must be used with caution as they showed an increased amount of ions released in comparison with chlorhexidine. One-piece stainless steel bracket system is the most compatible bracket type, as they released the least amount of ions. CLINICAL SIGNIFICANCE: One-piece stainless steel brackets are better than two-piece brackets in terms of ions released.

A facile and green strategy for the synthesis of Au, Ag and Au-Ag alloy nanoparticles using aerial parts of R. hypocrateriformis extract and their biological evaluation.

A facile and green strategy is reported here to synthesize gold (Au), silver (Ag) and gold-silver (Au-Ag) alloy nanoparticles (NPs) through bio-reduction reactions of aqueous corresponding metal precursors mediated by extracts of aerial parts of R. hypocrateriformis, which act as both reducing and stabilizing agents, under microwave irradiation. UV-vis spectrophotometer, XRD, FT-IR, FESEM/TEM, TGA and EDAX analysis were used to characterize the obtained NPs. The formation of NPs is evident from their surface plasmon resonance peak observed at λmax=∼550, 450 and 500nm for Au, Ag and Au-Ag alloy NPs respectively. XRD pattern revealed that fcc structure, while FT-IR spectra signify the presence of phytochemicals adsorbed on NPs. Such a biofunctionalized NPs were characterized by their weight loss, 30% due to thermal degradation of plant phytochemicals observed in TG analysis. The spherical shape of Au, Ag and Au-Ag alloy NPs (∼10-50nm) is observed by FE-SEM/TEM images. EDAX analysis confirms the expected elemental composition. Moreover, these NPs showed enhanced antimicrobial, antioxidant, and anticancer activities, though it is more pronounced for Au-Ag alloy NPs, which is due to the combining effect of phytochemicals, Au and Ag metals. Thus, the biosynthesized NPs could be applied as effective growth inhibitors for various biomedical applications.

Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments.

Cemented crowns are increasingly being used on dental implants instead of on screw-retained prostheses because of the reliability of internal Morse taper implant-abutment connections. However, there is a lack of information on the fit of metal ceramic and premachined alumina infrastructures. Therefore, the aim of this study was to evaluate the marginal and internal fits of different metal and alumina infrastructures cemented on universal post abutments. A total of 45 abutments (6 mm in height and 3.3 mm in diameter) were divided into five groups on the basis of their infrastructure material: cobalt-chromium (CoCr), nickel-chromium (NiCr), nickel-chromium-molybdenum-titanium (NiCrMoTi), gold (Au), and premachined alumina. The alumina group showed marginal overextension, and the Au group showed the highest discrepancy in marginal fit among the metal alloys. The CoCr and alumina groups showed the lowest discrepancies in internal fit. In conclusion, the alumina cylinders exhibited the best internal fit, despite their horizontal overextension. Among the metal alloys, CoCr exhibited the best fit at critical regions, such as the cervical and occlusal areas.

Treatment planning and dental rehabilitation of periodontally compromised partially edentulous patient: a case report - part II.

When planning a prosthetic rehabilitation of a periodontally compromised case, the clinician is often confronted with difficulties and dilemmas related to selecting the appropriate treatment that would provide long-term successful outcomes in function and esthetics. In such cases, a correct diagnosis and prognosis of the intraoral situation supported by evidence-based dentistry is the basis for the establishment of a proper treatment strategy. In this second part of a two-part treatment planning series, a systematic approach of patient examination and prognosis of each tooth is presented. Furthermore, different removable and fixed treatment possibilities are described and the rationale governing the decision-making process is revealed. The execution of the final treatment plan as specified by the concept of comprehensive dental care is outlined, and the final outcome is discussed according to the literature.

A comparative study on microgap of premade abutments and abutments cast in base metal alloys.

The study compared the marginal accuracy of premade and cast abutments. Premade titanium, stainless steel, and gold abutments formed the control groups. Plastic abutments were cast in nickel-chromium, cobalt-chromium and grade IV titanium. The abutment/implant interface was analyzed. Analysis of variance and Duncan's multiple range test revealed no significant difference in mean marginal microgap between premade gold and titanium abutments and between premade stainless steel and cast titanium abutments. Statistically significant differences (P < .001) were found among all other groups.

Effects of soldering methods on tensile strength of a gold-palladium metal ceramic alloy.

STATEMENT OF PROBLEM: The tensile strength obtained by conventional postceramic application soldering and laser postceramic welding may require more energy than microwave postceramic soldering, which could provide similar tensile strength values. PURPOSE: The purpose of the study was to compare the tensile strength obtained by microwave postceramic soldering, conventional postceramic soldering, and laser postceramic welding. MATERIAL AND METHODS: A gold-palladium metal ceramic alloy and gold-based solder were used in this study. Twenty-seven wax specimens were cast in gold-palladium noble metal and divided into 4 groups: laser welding with a specific postfiller noble metal, microwave soldering with a postceramic solder, conventional soldering with the same postceramic solder used in the microwave soldering group, and a nonsectioned control group. All the specimens were heat treated to simulate a normal porcelain sintering sequence. An Instron Universal Testing Machine was used to measure the tensile strength for the 4 groups. The means were analyzed statistically with 1-way ANOVA. The surface and fracture sites of the specimens were subjectively evaluated for fracture type and porosities by using a scanning electron microscope. RESULTS: The mean (standard deviation) ultimate tensile strength values were as follows: nonsectioned control 818 ±30 MPa, microwave 516 ±34 MPa, conventional 454 ±37 MPa, and laser weld 191 ±39 MPa. A 1-way ANOVA showed a significant difference in ultimate tensile strength among the groups (F3,23=334.5; P<.001). Follow-up multiple comparisons showed a significant difference among all the groups. Microwave soldering resulted in a higher tensile strength for gold and palladium noble metals than either conventional soldering or laser welding. CONCLUSION: Conventional soldering resulted in a higher tensile strength than laser welding. Under the experimental conditions described, either microwave or conventional postceramic soldering would appear to satisfy clinical requirements related to tensile strength.

Magneto-plasmonic Au-Fe alloy nanoparticles designed for multimodal SERS-MRI-CT imaging.

Diagnostic approaches based on multimodal imaging are needed for accurate selection of the therapeutic regimens in several diseases, although the dose of administered contrast drugs must be reduced to minimize side effects. Therefore, large efforts are deployed in the development of multimodal contrast agents (MCAs) that permit the complementary visualization of the same diseased area with different sensitivity and different spatial resolution by applying multiple diagnostic techniques. Ideally, MCAs should also allow imaging of diseased tissues with high spatial resolution during surgical interventions. Here a new system based on multifunctional Au-Fe alloy nanoparticles designed to satisfy the main requirements of an ideal MCA is reported and their biocompatibility and imaging capability are described. The MCAs show easy and versatile surface conjugation with thiolated molecules, magnetic resonance imaging (MRI) and computed X-ray tomography (CT) signals for anatomical and physiological information (i.e., diagnostic and prognostic imaging), large Raman signals amplified by surface enhanced Raman scattering (SERS) for high sensitivity and high resolution intrasurgical imaging, biocompatibility, exploitability for in vivo use and capability of selective accumulation in tumors by enhanced permeability and retention effect. Taken together, these results show that Au-Fe nanoalloys are excellent candidates as multimodal MRI-CT-SERS imaging agents.

Effect of pretreatments on the metal-ceramic bonding strength of a Pd-Ag alloy.

OBJECTIVES: The purpose of this study was to evaluate the efficacy of surface treatments on the bonding properties between a metal and ceramic. METHODS: Sixty metal specimens were divided equally into four groups of 15 samples each. These groups received different treatments (Gr1: 250µm Al2O3+preoxidation; Gr2: 250µm Al2O3+degassing; Gr3: 120µm Al2O3+preoxidation; Gr4: 120µm Al2O3+degassing). Bond strengths were evaluated using a three-point bending test. The results were analyzed using 2-way ANOVA and Tukey's test. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microscopic features, elemental compositions and distributions, and diffusion in the specimens. Mechanical profiler was used to measure the roughness of metal surface. RESULTS: The bond strengths of the four groups ranged from 45.00±3.63MPa to 51.61±5.91MPa, with significant differences (P<.05). The specimen that received the pretreatment of 250µm Al2O3 air-particle abrasion+degassing had the highest bond strength. Heating under different oxygen partial pressures caused the final Pd-Ag alloys to have varying degrees of internal oxidation and different quantities of metallic nodules. None of the elements in either the ceramic or the Pd-Ag alloy layer diffused into the other layer. CONCLUSIONS: The metal-ceramic specimen subjected to air-particle abrasion with 250µm Al2O3 and degassed before porcelain firing had significantly higher bond strength than specimens treated differently.

Adhesion and biofilm formation by periodontopathogenic bacteria on different commercial brackets.

AIM: To compare early bacterial adhesion and biofilm formation of common and uncommon periodontal pathogens on a variety of commercial brackets in vitro. MATERIALS AND METHODS: In vitro adhesion and biofilm formation of 4 bacterial strains on 15 different commercial brackets, in standard culture mediums with and without addition of either serum or human saliva was evaluated by quantitative real time PCR after extraction of bacterial DNA. RESULTS: Materials significantly influenced bacterial adhesiveness in a species-specific way. Titanium and gold brackets constantly yielded the lowest values with all tested bacteria and in all tested conditions. Bracket materials and medium of growth significantly influenced biofilm formation. CONCLUSION: Materials and environmental conditions significantly influence biofilm formation by periodontal pathogens at the surface of brackets. Whenever possible brackets should be kept far from the gingival margin and if this is not possible, brackets made of gold, titanium, and ceramic should be preferentially used.

Treatment of multiple ceramic alloys before recasting.

STATEMENT OF PROBLEM: Dental laboratories often reuse dental casting alloys by recasting them, but the processing methods before recasting require further research. PURPOSE: The purpose of the study was to determine the treatment methods to remove the surface contamination of the previously melted alloys before recasting. MATERIAL AND METHODS: Cobalt-chromium (Co-Cr), commercially pure titanium (CP Ti), palladium-copper-gallium (Pd-Cu-Ga), and gold-platinum (Au-Pt) ceramic alloys were investigated in the present study. Field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy (EDAX), and x-ray photoelectron spectroscopy (XPS) were used to evaluate the changes in the surface structures and compositions of Co-Cr, CP Ti, Pd-Cu-Ga, and Au-Pt ceramic alloys after airborne-particle abrasion and immersion in various chemical solutions for different time periods. The data obtained by EDAX and XPS were statistically analyzed by Kruskal-Wallis and Nemenyi tests (α=.05). RESULTS: By using appropriate mechanical and chemical treatment procedures, the contamination content of previously cast ceramic alloys was found to be below the detection limits of EDAX and XPS. The statistical results showed that, compared to the control group (new alloys after polishing), the impurity element was not detected after being treated with these methods, which was not statistically different to control group. CONCLUSIONS: The surface contamination of ceramic alloys was effectively removed by using certain mechanical and/or chemical treatment methods. Within the limitations of the present study, the most appropriate ways to treat ceramic alloys before recasting were as follows: (1) for Co-Cr ceramic alloys: Al2O3 airborne-particle abrasion and immersion in aqua regia for 15 min; (2) for CP Ti ceramic alloys: Al2O3 airborne-particle abrasion and immersion in 65% HNO3 and 40% HF 1:7 (V/V) for 60 min; (3) for Pd-Cu-Ga ceramic alloys: glass bead airborne-particle abrasion and immersion in 40% HF solution for 30 min; and (4) for Au-Pt ceramic alloys: glass bead airborne-particle abrasion.

Adhesion and biofilm formation by oral streptococci on different commercial brackets.

AIM: To compare early bacterial adhesion and biofilm formation in vitro by different oral streptococci on a variety of commercial brackets. METHODS: Adhesion and biofilm formation in vitro of 6 Streptococcus spp. on 15 different commercial brackets, in standard culture medium and in human saliva were evaluated by the MTT reduction assay. RESULTS: Significant differences were evidenced in both early adhesion and biofilm formation among the studied brackets and between the two conditions of growth. Gold brackets resulted less prone to colonisation compared to composite brackets. The growth rates of the tested species on the different tested materials were significantly different. CONCLUSION: The adopted experimental plan, dissecting the two phases of plaque formation on different brackets in different conditions, showed that composite brackets are more susceptible to adhesion and colonisation by streptococci, while the remaining tested brackets did not show differences that could be clinically relevant. Data suggest that different personal behaviours affecting the oral environment could significantly affect colonisation of brackets by oral streptococci.

Evaluation of the amount of excess cement around the margins of cement-retained dental implant restorations: the effect of the cement application method.

STATEMENT OF PROBLEM: Complete removal of excess cement from subgingival margins after cementation of implant-supported restorations has been shown to be unpredictable. Remaining cement has been shown to be associated with periimplant inflammation and bleeding. PURPOSE: The purpose of this study was to investigate and compare the amount of excess cement after cementation with 4 different methods of cement application for cement-retained implant-supported restorations. MATERIAL AND METHODS: Ten implant replicas/abutments (3i) were embedded in acrylic resin blocks. Forty complete veneer crowns (CVCs) were fabricated by waxing onto the corresponding plastic waxing sleeves. The wax patterns were cast and the crowns were cemented to the implant replicas with either an interim (Temp Bond) or a definitive luting agent (FujiCEM). Four methods of cement application were used for cementation: Group IM-Cement applied on the internal marginal area of the crown only; Group AH-Cement applied on the apical half of the axial walls of the crown; Group AA-Cement applied to all axial walls of the interior surface of the crown, excluding the occlusal surface; and Group PI-Crown filled with cement then seated on a putty index formed to the internal configuration of the restoration (cementation device) (n=10). Cement on the external surfaces was removed before seating the restoration. Cement layers were applied on each crown, after which the crown was seated under constant load (80 N) for 10 minutes. The excess cement from each specimen was collected and measured. One operator performed all the procedures. Results for the groups were compared, with 1 and 2-way ANOVA and the Tukey multiple range test (α=.05). RESULTS: No significant difference in the amount of excess/used cement was observed between the 2 different types of cements (P=.1). Group PI showed the least amount of excess cement in comparison to other test groups (P=.031). No significant difference was found in the amount of excess cement among groups MI, AH, and AA. Group AA showed the highest amount of excess cement. The volume of cement used for group PI specimens was significantly higher than for those in the other groups (P=.001). With respect to the volume of cement loaded into the test crowns no statistically significant difference was observed among other test groups (groups IM, AH, and AA). Group MI used the least amount of cement, followed by group AH and AA. No correlation between the amount of used cement and the amount of excess cement was found in any of the tested groups. CONCLUSIONS: Within the limitations of this in vitro study, the least amount of excess cement was present when a cementation device was used to displace the excess cement before seating the crown on the abutment (Group PI). With this technique a uniform layer of the luting agent is distributed over the internal surface of the crown leaving minimal excess cement when the restoration is seated.

Bacterial adhesion affinities of various implant abutment materials.

OBJECTIVES: To investigate bacterial adhesion to various abutment materials. MATERIAL AND METHODS: Thirty volunteers participated in this study. Resin splints were fabricated, and five types of disks were fabricated from pure titanium, gold-platinum alloy, zirconia, alumina, and hydroxyapatite with uniform surface roughness and attached to the buccal surface of each splint. After 4 days of use by the subjects, the plaque accumulated on the disk surfaces was analyzed. The bacterial community structure was evaluated using 16S rRNA gene profiling with terminal restriction fragment length polymorphism analysis. The total bacterial count on each disk was estimated using quantitative polymerase chain reaction. RESULTS: Terminal restriction fragment length polymorphism profiles were more similar between tested materials than between subjects, suggesting that the bacterial community structures on the abutment material were influenced more by the individuals than by the type of material. However, the total number of bacteria attached to a disk was significantly different among five materials (P < 0.001, Brunner-Langer test for longitudinal data). Fewer bacteria were attached to the gold-platinum alloy than to the other materials. CONCLUSIONS: Gold-platinum alloy appears to be useful material for abutments when considering the accumulation of plaque. However, alternative properties of the abutment material, such as effects on soft tissue healing, should also be taken into consideration when choosing an abutment material.

Effect of alloy recasting on the color of opaque porcelain applied on different dental alloy systems.

STATEMENT OF PROBLEM: The effect of different proportions of recast dental alloys on the color of overlying opaque porcelain (OP) is unknown. PURPOSE: The purpose of this study was to compare the color of OP applied on 2 different proportions (50% and 100%) of recast alloys with the color of commercially available shade tabs of OP. MATERIAL AND METHODS: Six different metal alloy systems (2 base: Metalloy CC, Cr-Co [B-MCC]; Heraenium NA, Ni-Cr [B-HNA]; 3 noble: Cerapall 2, Pd-Au [N-CP2]; Triumph, Pd-Ag [N-T]; V-Deltaloy, Au-Pd [N-VD]; and 1 high-noble: V-Gnathos Plus, Au-Pt [HN-GP]) were selected for the fabrication of disk-shaped specimens (10 mm in diameter, 1 mm in thickness). Each alloy was divided into 2 subgroups: 50% new alloy with 50% recast alloy (n=3) and 100% recast alloy (n=3). OP (B1) was applied (0.1 mm) to all specimens. The color coordinates (L*, a*, b*) of each specimen and the corresponding commercially available OP shade tab (control) were measured with a spectroradiometer, and color differences between specimens and control group were calculated. Data were statistically analyzed (2-way ANOVA, Ryan-Einot-Gabriel-Welsch multiple range test, α=.05). RESULTS: For each alloy, ΔL*(L(control)(-)L(recastalloy)) values for the 2 subgroups were not statistically different from each other. The Δa* and Δb* of different proportions of N-CP2, B-HNA, N-VD, and HN-GP were not statistically different within the alloys. However, the a* values of 100% recast N-T and B-MCC were significantly closer to the a* values of the control group, and the b* values of 50% recast B-MCC were significantly closer to the b* values of the control group (P<.05). Delta E(control-recast) alloy values for different proportions of alloys were not statistically different. However, color differences did not meet the criterion of clinical acceptability (ΔE=3.46). CONCLUSIONS: According to the results of this study, the different proportions (50% and 100%) of recast alloys used have similar effects on the color of OP. Differences between the final color of OP on the recast alloys used and the color of OP shade guide tabs did not meet the criterion of clinical acceptability considered in this study.

Effect of sandblasting conditions on alumina retention in representative dental alloys.

This study determined the effect of grit size and application pressure on alumina fragment retention after sandblasting in representative dental alloys. Plastic rectangular patterns (25×3×0.6 mm, n=240) were divided equally into four groups and cast with Au-Pt, Ni-Cr, Co-Cr alloys and grade-II cp-Ti. The specimens from each alloy were then divided into 12 subgroups. Each subgroup was then sandblasted with one of the 12 possible combinations of grit size (50, 100 and 250 microns) and propulsion pressure (0.15, 0.30, 0.45 and 0.60 MPa), and their surfaces imaged and analyzed using SEM/EDS analysis. The Al composition was statistically analyzed by two-way ANOVA with Tukey's post-test. Materials tested showed a substantial amount of retained alumina fragments, the extent of which was dependent on the grit size and propulsion pressure applied for tested alloys except cp-Ti. Importantly, sandblasting conditions different from those proposed by the manufacturers achieved lower levels of retained alumina fragments.

Wear of ceramic and titanium ball attachments in subjects with an implant-retained overdenture: a controlled clinical trial.

STATEMENT OF PROBLEM: Loss of retention of implant-retained overdentures due to wear of the patrix or matrix of the attachment system is a common clinical problem. PURPOSE: The purpose of this controlled clinical trial was to compare the wear of ceramic and titanium ball attachments and their corresponding gold matrices after 1 year of clinical function in subjects with implant-retained mandibular overdentures. MATERIAL AND METHODS: Forty subjects who had been treated with a 2-implant-retained overdenture received either 2 ruby ball attachments (20 subjects) or 2 titanium ball attachments (20 subjects). The diameter of the ball attachments and the thickness of the matrix were measured optically before insertion and after 1 year of clinical function. Differences among groups were then compared with the Wilcoxon rank sum test (α=.05). To estimate any correlation between clinical parameters and wear, the Spearman rank test was used. RESULTS: There was no significant difference (P=.73) in the median wear of ball attachments for the titanium group (5.3 µm; median 1.3 µm) and for the ceramic group (1.3 µm; median 1.3 µm). In the ceramic group, a fracture rate of 30% was observed. The mean wear of the matrices in the titanium group was 3.1 µm (median 6.8 µm) and in the ceramic group 2.1 µm (median 3.4 µm), P=.01. No correlation was found between ball attachment wear and matrix insert wear (Spearman rank test). Wear of matrices was weakly correlated with an increase in divergence between implant axes in the sagittal plane (P=-.28 and P=.021). Ball attachment wear was associated with an increase in divergence between matrix axes in the sagittal plane (P=-.34 and P=.047). CONCLUSIONS: Matrices on ceramic ball attachments showed less wear than those placed on titanium ball attachments. However, the use of ruby ball attachments cannot be recommended because of a high fracture rate.

The influence of metal substrates and porcelains on the shade of metal-ceramic complex: a spectrophotometric study.

BACKGROUND: The final esthetic outcome of a metal-ceramic restoration is influenced by several factors including the type of the underlying metal as well as the brand of the ceramic. SETTINGS AND DESIGN: An in vitro study. AIMS: The purpose of the in vitro study was to investigate the influence of four types of metal-ceramic alloys and two porcelain systems on the color co-ordinates of the metal-ceramic complex. It also aimed at establishing a color index which correlated the color of the metal-ceramic combination to the yellow-blue axis. MATERIALS AND METHODS: Twenty-four disc-shaped metal specimens of 12 mm × 1 mm were cast from base metal alloys, nickel-chromium (Ni-Cr) (Wiron 99), cobalt-chromium (Co-Cr) (Wirobond C), a palladium (Pd)-rich noble metal alloy (Spartan Plus), and a high noble gold (Au) alloy (Pontostar). These discs were covered with two commercially available feldspathic porcelains (Vita Omega and Shofu Vintage) of A3 shade to a total thickness of 1.2 mm. Each group had six specimens, of which three were coated with Vita Omega and the remaining with Shofu Vintage. Opaque and dentin layers were applied to a standardized thickness of 0.2 mm ± 0.05 mm and 1 mm ± 0.05 mm, respectively onto the metal surface after air abrasion with 50 µm alumina particles. The reflectance spectra were measured with a spectrophotometer and data were recorded in L*, a* and b* coordinates in the CIE Lab Color Order System. STATISTICAL ANALYSIS: Analysis of variance (ANOVA) and path analysis were the statistical tools employed to analyze the data. A critical difference (CD) value was calculated for each color co-ordinate to make comparisons between each metal-ceramic combination. A color index for each metal-ceramic complex was also calculated from the color co-ordinates obtained. RESULTS: ANOVA revealed that significant differences existed between the metal-porcelain combination at 0.01 ( P < 0.01) level. The L* value was significantly higher for Au and Co-Cr alloys with Vita Omega porcelain. The a* value was highest for Ni-Cr alloy when combined with Shofu Vintage ceramic. The b* value of Au alloy with Vita Omega porcelain was significantly higher than any other metal-ceramic combination. The color co-ordinates of Pd alloy with both porcelain systems did not show any significant differences. Gold alloy with Vita Omega showed the highest color index value. CONCLUSION: The variations in metal-ceramic alloy and porcelain can influence the shade of a metal-ceramic restoration. Color index value was the highest for gold alloy.