Vertical discrepancy and microleakage of laser-sintered and vacuum-cast implant-supported structures luted with different cement types

Objectives

This study aimed to evaluate the vertical misfit and microleakage of laser-sintered and vacuum-cast cement-retained implant-supported frameworks.

Methods

Three-unit implant-fixed structures were constructed with: (1) laser-sintered Co–Cr (LS); (2) vacuum-cast Co–Cr (CC); and (3) vacuum-cast Pd–Au (CP). Every framework was luted onto 2 prefabricated abutments under constant seating pressure. Each alloy group was randomly divided into three subgroups (n = 10) according to the cement used: (1) Ketac Cem Plus (KC); (2) Panavia F 2.0 (PF); and (3) RelyX Unicem 2 Automix (RXU). After 30 days of water ageing, vertical discrepancy was measured by SEM, and marginal microleakage was scored using a digital microscope. Three-way ANOVA and Student–Newman–Keuls tests were run to investigate the effect of alloy/fabrication technique, FDP retainer, and cement type on vertical misfit. Data for marginal microleakage were analysed with Kruskal–Wallis and Dunn's tests (α = 0.05).

Results

Vertical discrepancy was affected by alloy/manufacturing technique and cement type (p < 0.001). Despite the luting agent, LS structures showed the best marginal adaptation, followed by CP, and CC. Within each alloy group, KC provided the best fit, whilst the use of PF or RXU resulted in no significant differences. Regardless of the framework alloy, KC exhibited the highest microleakage scores, whilst PF and RXU showed values that were comparable to each other.

Conclusions

Laser-sintered Co–Cr structures achieved the best fit in the study. Notwithstanding the framework alloy, resin-modified glass-ionomer demonstrated better marginal fit but greater microleakage than did MDP-based and self-adhesive dual-cure resin cements. All groups were within the clinically acceptable misfit range.

Clinical significance

Laser-sintered Co–Cr may be an alternative to cast base metal and noble alloys to obtain passive-fitting structures. Despite showing higher discrepancies, resin cements displayed lower microleakage than resin-modified glass-ionomer. Further research is necessary to determine whether low microleakage scores may guarantee a suitable seal that could compensate for misfit.     

Vertical misfit of laser-sintered and vacuum-cast implant-supported crown copings luted with definitive and temporary luting agents

Objectives. This study aimed to evaluate the vertical discrepancy of implant-supported crown structures constructed with vacuum-casting and Direct Metal Laser Sintering (DMLS) technologies, and luted with different cement types. Study Design. Crown copings were fabricated using: (1) direct metal laser sintered Co-Cr (LS); (2) vacuum-cast Co-Cr (CC); and (3) vacuum-cast Ti (CT). Frameworks were luted onto machined implant abutments under constant seating pressure. Each alloy group was randomly divided into 5 subgroups (n = 10 each) according to the cement system utilized: Subgroup 1 (KC) used resin-modified glass-ionomer Ketac Cem Plus; Subgroup 2 (PF) used Panavia F 2.0 dual-cure resin cement; Subgroup 3 (RXU) used RelyX Unicem 2 Automix self-adhesive dual-cure resin cement; Subgroup 4 (PIC) used acrylic/urethane-based temporary Premier Implant Cement; and Subgroup 5 (DT) used acrylic/urethane-based temporary DentoTemp cement. Vertical misfit was measured by scanning electron microscopy (SEM). Two-way ANOVA and Student-Newman-Keuls tests were run to investigate the effect of alloy/fabrication technique, and cement type on vertical misfit. The statistical significance was set at α = 0.05. Results. The alloy/manufacturing technique and the luting cement affected the vertical discrepancy (p < 0.001). For each cement type, LS samples exhibited the best fit (p < 0.01) whereas CC and CT frames were statistically similar. Within each alloy group, PF and RXU provided comparably greater discrepancies than KC, PIC, and DT, which showed no differences. Conclusions. Laser sintering may be an alternative to vacuum-casting of base metals to obtain passive-fitting implant-supported crown copings. The best marginal adaptation corresponded to laser sintered structures luted with glass-ionomer KC, or temporary PIC or DT cements. The highest discrepancies were recorded for Co-Cr and Ti cast frameworks bonded with PF or RXU resinous agents. All groups were within the clinically acceptable misfit range. Key words:Dental alloy, laser sintering, implant-supported prostheses, vertical discrepancy, vertical misfit.     

Marginal fit and microleakage of cast and metal laser sintered copings—An in vitro study

PurposeThis study aimed to compare the marginal fit and microleakage of metal laser sintered Co–Cr alloy copings and conventional cast Ni–Cr alloy copings using a stereomicroscope.MethodsForty extracted maxillary premolars were randomly divided into two groups. One group was subjected to coping fabrication using conventional lost wax (LW) technique while the other group was subjected to coping fabrication using metal laser sintering (MLS) technology. The marginal fit of these copings were compared before and after ceramic addition using images obtained with a steromicroscope and an ImageJ analysis software. All the specimens were cemented using Type 1 glass ionomer cement and were subjected to thermocycling. The specimens were evaluated for microleakage using stereomicroscope and 2% methylene blue die used as a tracer. The data were subjected to statistical analysis using paired t-test, Mann–Whitney test and Chi-Square test.ResultsThe mean marginal fit of copings before and after ceramic addition in Group B (MLS) was better than the copings in Group A (LW) and was statistically significant (P < 0.05). The influence of ceramic firing had a significant (P < 0.05) increase in mean marginal gap in Group A (LW) but not in Group B (MLS). And the difference in mean microleakage between the groups was not statistically significant (P ≥ 0.05).ConclusionThe copings fabricated using MLS technique had a better marginal fit and an observable decrease in microleakage when compared to the copings fabricated using the conventional lost wax (LW) technique.     

Effect of water aging on microtensile bond strength of dual-cured resin cements to pre-treated sintered zirconium-oxide ceramics

ObjectivesTo evaluate the hydrolytic stability of different dual-cure resin cements when luted to zirconia ceramic.MethodsEighteen cylinder-shaped zirconia blocks (Cercon Zirconia, Dentsply) were conditioned with: Group 1, no treatment; Group 2, sandblasting (125 μm alumina–Al₂O₃-particles); Group 3, tribochemical silica coating (50 μm silica-modified Al₂O₃ particles). Ceramic blocks were duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent). Composite disks were luted to pre-treated ceramic surfaces using: (1) Clearfil Esthetic Cement (CEC; Kuraray); (2) Rely X Unicem (RXU; 3M ESPE); (3) Calibra (CAL; Dentsply Caulk). After 24 h, bonded samples were cut into microtensile sticks (1 mm²). Half of the sticks were loaded in tension until failure (cross-head speed of 0.5 mm/min). The remaining half was tested after 6 months of water storage at 37 °C. Data was analyzed with three-way ANOVA and Tukey’s test (P <0.05). Fractographic analysis was performed by SEM.ResultsAfter 24 h, bond strength of CEC to zirconia was significantly higher than that of RXU and CAL, independently from the ceramic pre-treatment (P <0.001). Using CAL, all samples failed prematurely except when luting to sandblasted surfaces. After 6 months of water aging, bond strength of CEC significantly decreased. RXU did not significantly alter bond strengths. Adhesion of sandblasted specimens luted with CAL fell over time. Micromorphological alterations were evident after water storage.SignificanceResin–ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. CEC and RXU were both suitable for luting zirconia. Water aging played an important role in the durability of zirconia-to-composite chemical bonds.     

Laser surface treatment to improve mechanical properties of cast titanium

ObjectiveThe aim of this study was to investigate the effect of laser surface treatment on the mechanical properties of cast titanium and to compare with those of the Co–Cr alloy.MethodsDumbbell-shaped cast specimens were prepared for commercially pure titanium (grade 2) and Co–Cr alloy. The cast titanium specimens were laser-treated on the surface using a dental Nd:YAG laser machine at 240 V and 300 V. After laser treatment, tensile testing was conducted to obtain the tensile strength, percent elongation and modulus of elasticity. The hardness depth profile was made from the cast subsurface (25 μm) to 1500 μm in depth using the cross-sections of the cast rods with the same diameter as the dumbbell. The data were statistically analyzed by ANOVA/post hoc tests (p < 0.05).ResultsThe highest tensile strength was obtained for the titanium specimens laser-treated with 300 V followed by the 240 V and the control specimens. The laser-treated titanium specimens with 300 V showed a tensile strength equivalent to the Co–Cr alloy. Although the highest modulus of elasticity was found for the specimens laser-treated with 240 V, there were no significant differences in elastic modulus among 240 V, 300 V and Co–Cr. The laser-treated groups showed significantly lower hardness at the subsurface of 25 μm and maintained their hardness until the depth of 400 μm. The hardness of the control group was very high at 25 μm depth, and dramatically decreased until the 200 μm depth.ConclusionThe results of tensile testing and hardness depth-profiling indicated that the laser treatment significantly improved the mechanical properties of cast titanium by improving the surface integrity of the cast surface contamination.     

Retention and stress distribution in distal extension removable partial dentures with and without implant association

PurposeThe present study aimed to evaluate the retention and stress distribution of conventional (C) RPD and compare to RPD associated to implant for support (IS) and retention (IR).MethodsFrameworks were cast from cp Ti (n = 18) and Co–Cr alloy (n = 18) by plasma and injected by vacuum–pressure. Conventional RPDs were compared to implant associated RPDs using a distal implant to support (IS) or to support and retain (IR) RPD. The specimens were subjected to insertion/removal cycles simulating 5 years of use and the retention force (N) was measured or evaluated. A mixed linear model was used to analyze the data (α = 0.05). Photoelastic models were qualitatively examined for stress when an occlusal load of 15 kgf was applied over support teeth and RPD.ResultsRetention force of IR RPDs is greater than IS and C RPDs for both cp Ti and Co–Cr alloy specimens. Retention force of cp Ti RPDs increased initially and was maintained throughout 5 years of simulation test while Co–Cr RPDs presented a decrease at the beginning of the test and had their retention force maintained throughout the test. Implant placement at residual alveolar ridge decreased stress around teeth, mainly in the first premolar. Stress concentration in the IS RPD is slightly greater than in the IR RPD.ConclusionThe results suggest that implant placement at the distal extension improves retention and stress distribution of RPDs.     

Effect of mold temperatures on interface between primary and secondary castings of cast-on method for precision metal frameworks

PurposeThe purpose of the present study was to obtain fundamental data for application of the cast-on method by evaluating the effect of mold temperatures on the interface between primary and secondary castings in detail.MethodsSilver–palladium–gold alloy (Ag–Pd–Au), type-4 gold alloy (Type4), and chromium–cobalt alloy (Cr–Co) were used in the present study. A polished flat, square metal plate, 10.0 mm × 10.0 mm × 1.0 mm, was used as the primary casting. A wax pattern, 2.0 mm in diameter and 2.0 mm thick, was prepared for the secondary casting and invested together with the primary casting. The mold was heated at 600, 700 and 800 °C for Ag–Pd–Au and Type4, and 700, 800 and 900 °C for Cr–Co. After casting, the mold was embedded and sectioned. The cross-section was observed using a scanning electron microscope (SEM) and analyzed using energy dispersive X-ray spectroscopy (EDS). The gaps between the primary and secondary castings were analyzed for each alloy by analysis of variance and Tukey's honestly significant difference test. The significance level was set at 0.05. The heated primary casting without the secondary casting was examined using a thin film X-ray diffractometer (XRD).ResultsGaps were observed between the primary and secondary castings in all examined conditions. The primary casting surface was covered with oxide layers such as CuO and Cr₂O₃, and became rough with an increase of the mold temperature.ConclusionsThe results suggested that the cast-on method was influenced by the mold temperature.     

Influence of different flask systems on tooth displacement and framework misfit in mandibular fixed implant-supported complete dentures

PurposeTo evaluate the influence of different metallic flask systems for acrylic resin denture processing on tooth displacement and framework misfit of mandibular fixed implant-supported complete dentures.MethodsStandard mandibular implant-supported complete dentures in five implants were waxed and randomly assigned to three groups: G1 – conventional flask, G2 – double flask, and G3 – occlusion flask. Framework misfit in all the implants and the linear distances between teeth (I-I – incisor-to-incisor; P-P – premolar-to-premolar; M-M – molar-to-molar; RI-RM – right-incisor-to-right-molar; and LI-LM – left-incisor-to-left-molar) were measured before and after denture processing using an optical microscope. Dentures were processed by hot water curing cycle (9 h/74 °C). Collected data were analyzed by paired Student's t-test and one-way ANOVA (α = 0.05).ResultsAll the measured distances presented changes in tooth displacement after denture processing. However, the M-M distance for G1 (p = 0.003) and the P-P (p = 0.042) and LI-LM (p = 0.044) distances for G3 showed statistically significant differences. Differences between the flask systems were not statistically significant. Statistically significant differences in the framework misfit due to denture processing were found for all the implants and groups, with the exception of right median implant for G2 and right distal implant for G3. A comparison of the flask systems found statistically significant differences in which G1 presented an increase in the misfit values and G2 and G3 a decrease.ConclusionsDifferent flask systems did not cause significant changes in tooth displacement. Frameworks misfit values were influenced by the different flask systems. The conventional flask presented an increase in the framework misfit, while the experimental flasks showed a decrease.     

Fatigue resistance and retentive force of cast clasps treated by shot peening

PurposeThe fatigue failure of denture clasps has often been observed in removable partial denture rehabilitation. To increase their fatigue strength, shot peening was evaluated as a surface treatment. In this study, we evaluated the fatigue resistance and retention of cast clasps by using a shot peening treatment.MethodsA cobalt–chromium (Co–Cr) alloy, commercial pure titanium (CP Ti), silver–palladium–gold (Ag–Pd–Au), and a gold–platinum (Au–Pt) alloy were cast and then treated with shot peening. The retentive forces of the clasps were measured up to a repetition of 10,000 insertion/removal cycles in distilled water at 37 °C. A fatigue test was also performed using a 15-mm cantilever. Specimens were loaded with a constant deflection of 2.0 mm with 20 Hz. A shot peening treatment indicated a better stability of retentive forces than that without shot peening. The retentive force of Co–Cr clasps without shot peening was remarkably decreased at 500 cycles of insertion/removal repetition.ResultsThe clasps with a shot peening treatment provided approximately 1.4–3.6 times higher fatigue strengths than those without a shot peening treatment.ConclusionTo prevent the fatigue failure of the denture clasps and use the dentures for long term, a shot peening treatment would be recommended.     

Characterization of two Ni–Cr dental alloys and the influence of casting mode on mechanical properties

PurposeThe aim of this study was to evaluate the tensile strength, elongation, microhardness (MHV), composition and microstructure of two Ni–Cr based alloy, cast under different casting conditions.MethodsBefore casting, the alloy ingots were evaluated as regards composition (EDX) and microstructure (Optical microscopy, SEM and EDX). The casting conditions were as follows: electromagnetic induction in an environment controlled with argon (EWA), electromagnetic induction in an environment under vacuum (EWV), electromagnetic induction without atmosphere control (EWNC) and blowtorch (BT). For each condition, 16 specimens were obtained, each measuring 25 mm high and 2.5 mm in diameter. The ultimate tensile strength (UTS) and elongation (EL) tests were performed in a Kratos machine (1.0 mm/min). Fractured specimens were embedded in bakelite resin and polished for Vickers Microhardness analysis (1000 g/10 s) with 4 penetrations in each specimen. The UTS, EL and MHV results were evaluated for two-way ANOVA and Tukey's test (α = 0.05).ResultsThe cross-product interaction was statistically significant for all properties evaluated (p < 0.0001), lower UTS, VHN and higth elongation means were observed for the Ni–Cr–Mo–Be alloy tested when cast under the induction/argon (p < 0.05). Higher UTS means were found for Ni–Cr–Mo–Ti alloy tested when cast under the induction/vacuum, and induction/air and flame/air condition (p < 0.05). The two alloys show a microstructure with a dendritic formation with the presence of eutectic presence.ConclusionThe Ni–Cr–Mo–Ti alloy showed higth UTS, MHV and lowest EL comparaded with the tradicional Ni–Cr–Mo–Be, that show lowest UTS, MHV and higter EL when cast on induction/argon.     

Elemental ion release from four different fixed prosthodontic materials

ObjectiveElemental 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.MethodsSpecimens 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 (600 grit SiC paper), and ultrasonically cleaned with ethanol for 5 min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 °C for 7 days, the elemental release (μg/cm²) 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.ResultsHigher 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.SignificanceTransient 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.     

Cytotoxicity of alloying elements and experimental titanium alloys by WST-1 and agar overlay tests

ObjectiveThis study was performed to evaluate the biocompatibility of nine types of pure metals using 36 experimental prosthetic titanium-based alloys containing 5, 10, 15, and 20 wt% of each substituted metal.MethodsThe cell viabilities for pure metals on Ti alloys that contain these elements were compared with that of commercially pure (CP) Ti using the WST-1 test and agar overlay test.ResultsThe ranking of pure metal cytotoxicity from most potent to least potent was: Co > Cu > In > Ag > Cr > Sn > Au > Pd > Pt > CP Ti. The cell viability ratios for pure Co, Cu, In, and Ag were 13.9 ± 4.6%, 21.7 ± 10.4%, 24.1 ± 5.7%, and 24.8 ± 6.0%, respectively, which were significantly lower than that for the control group (p < 0.05). Pure Pd and Pt demonstrated good biocompatibility with cell viabilities of 93.8 ± 9.6% and 97.2 ± 7.1%, respectively. The Ti–5Pd alloy exhibited the highest cell viability (128.4 ± 21.4%), which was greater than that of CP Ti. By alloying pure Co or Cu with Ti, the cell viabilities for the Ti–xCo and Ti–xCu alloys increased significantly up to 10 wt% of the alloying element followed by a gradual decrease with a further increase in the concentration of the alloying element. Based on the agar overlay test, pure Ag, Co, Cr, Cu, and In were ranked as ‘moderately cytotoxic’, whereas all Ti alloys were ranked as ‘noncytotoxic’.SignificanceThe cytotoxicity of pure Ag, Co, Cr, Cu, and In suggests a need for attention in alloy design. The cytotoxicity of alloying elements became more biocompatible when they were alloyed with titanium. However, the cytotoxicity of titanium alloys was observed when the concentration of the alloying element exceeded its respective allowable limit. The results obtained in this study can serve as a guide for the development of new Ti-based alloy systems.     

Fracture loads of screw-retained implant-supported zirconia prostheses after thermal and mechanical stress

PurposeThe objective of the present study was to evaluate fracture loads of screw-retained implant-supported zirconia prostheses after artificial aging.MethodsFour types of screw-retained implant-supported prostheses were fabricated (n = 11 each); porcelain-veneered zirconia prosthesis (PVZ), indirect composite-veneered zirconia prosthesis (IVZ), porcelain-fused-to-metal prosthesis (PFM), and monolithic zirconia prosthesis (ML). The specimens were subjected to 10,000 thermocycles and cyclic loading for 1.2 million cycles. Fracture loads were measured, and the data were analyzed with the Kruskal–Wallis and Steel–Dwass tests (α = 0.05).ResultsAll specimens survived the artificial aging procedures. The fracture loads for the PVZ (1.52 kN), IVZ (1.62 kN), and PFM groups (1.53 kN) did not significantly differ; however, the fracture load for the ML group (6.61 kN) was significantly higher than those for the other groups. The fracture load for the IVZ group was comparable to those for the PVZ and PFM groups.ConclusionsThe monolithic zirconia prostheses exhibited significantly higher fracture loads than the bilayered prostheses. All the investigated types of screw-retained implant-supported zirconia prostheses appear sufficient to resist posterior masticatory forces during long-term clinical use.     

Comparison of microleakage and shear bond strength of ribbon and twisted wire retainers bonded on human mandibular incisors with two different types of adhesives with and without primer: An in-vitro study

Background and objectivesShear bond strength and microleakage are the success factors of fixed retainers. Recently, primer-free composites were introduced to reduce chair time. The main objectives of this study were to compare the shear bond strength (SBS) and microleakage of GC Ortho Connect^TM Flow (OF) and Transbond^TM XT (TXT) with two types of common retainer wires (0.0175-inch twisted wire and 0.028 × .0.008-inch ribbon dead soft wire retainers). The secondary objectives of the study were to compare enamel-adhesive interface and wire-adhesive interface microleakages.Materials and methodsThis in vitro study was conducted on 132 human mandibular incisors (96 for bond strength and 36 for microleakage). The teeth were randomly divided into four groups for use of ribbon and twisted wires with OF and TXT adhesives. The bond strength was measured by a universal testing machine. Microleakage was evaluated by the dye penetration test using 0.05% fuchsine. Data were analysed by two-way ANOVA (alpha = 0.05).ResultsNo significant difference was noted in bond strength among the four groups (P > 0.05). However, the microleakage of OF was significantly higher than that of TXT at both the enamel-adhesive and wire-adhesive interfaces (P < 0.001). The microleakage at the wire-adhesive and enamel-adhesive interface was not significantly different in groups 1 and 4 and was significant in group 2 and 3.ConclusionType of adhesive significantly affected the microleakage, and OF resulted in higher microleakage than TXT at both the enamel-adhesive and wire-adhesive interfaces. Type of wire had no significant effect on microleakage. Although OF showed comparable SBS to TXT, its higher microleakage may compromise its successful long-term clinical service.     

An evaluation of microleakage of various glass ionomer based restorative materials in deciduous and permanent teeth: An in vitro study

AimTo evaluate the microleakage of recently available glass ionomer based restorative materials (GC Fuji IX GP, GC Fuji VII, and Dyract) and compare their microleakage with the previously existing glass ionomer restorative materials (GC Fuji II LC) in primary and permanent teeth.MethodOne hundred and fifty (75 + 75) non-carious deciduous and permanent teeth were restored with glass ionomer based restorative materials after making class I cavities. Samples were subjected to thermocycling after storing in distilled water for 24 h. Two coats of nail polish were applied 1 mm short of restorative margins and samples sectioned buccolingually after storing in methylene blue dye for 24 h. Microleakage was assessed using stereomicroscope.ResultSignificant differences (P < 0.05) were found when inter group comparisons were done. Except when GC Fuji VII (Group III) was compared with GC Fuji II LC (Group II) and Dyract (Group IV), non-significant differences (P > 0.05) were observed. It was found that there was no statistically significant difference when the means of microleakage of primary teeth were compared with those of permanent teeth.ConclusionsGC Fuji IX GP showed maximum microleakage and GC Fuji VII showed least microleakage.     

Corrosion mechanism of Ti–Cr alloys in solution containing fluoride

ObjectiveThe objective of this study was to clarify the influence of chromium content on surface reaction of Ti–Cr alloys in an acidic fluoride-containing saline solution.MethodsFour Ti–Cr alloys containing 5, 10, 15 or 20 mass% chromium were characterized in terms of dissolution of metals in an acidic fluoride-containing saline solution and surface structure by X-ray photoelectron spectroscopy and Auger electron spectroscopy.ResultsTotal amount of metals dissolved from each alloy decreased with increase in chromium content. The surface oxide films of Ti–Cr alloys before and after immersion in an acidic fluoride-containing saline solution consisted of titanic and chromic species, such as oxide, hydroxide, and hydrate. The [Cr]/([Ti] + [Cr]) ratio in the surface oxide film on as-polished Ti–Cr alloys was closely correlated with chromium content. However, the ratio in any alloy approximately doubled after immersion. Although thick oxide films were observed after immersion, all alloys showed a thinner oxide film than commercially pure titanium.SignificantIn all alloys, concentration of chromic species such as oxide and hydroxide in the surface oxide film was associated with chromium content, and chromic species improved corrosion resistance to fluoride.     

Effects of a fluoride etchant and a phosphate primer on bonding of veneering composite to Ti–6Al–4V alloy for CAD/CAM restorations

PurposeTitanium abutments and superstructures are commonly veneered or covered with esthetic materials. The present investigation was carried out to evaluate the effects of an experimental surface treatment using etchant and primer on bond strength between a resin composite and Ti–6Al–4V alloy.MethodsDisk-shaped Ti–6Al–4V alloy was machine milled, the surface was air abraded with alumina, and the alloy was chemically etched with 5wt% ammonium hydrogen fluoride (F-etch) for 30 s. A phosphate primer (MDP-primer) was applied to the bonding area, and then a resin composite, with or without milled-fiber resin composite (FRC), was veneered on the specimen. Shear bond strengths were determined after thermocycling for 20,000 cycles. Bond strength data were analyzed by means of ANOVA and a multiple comparison test (α = 0.05). The surface of Ti–6Al–4V alloy was observed using a scanning electron microscope before and after the etching procedure.ResultsNo-FRC/F-etch/MDP-primer exhibited the highest bond strength (28.2 MPa), followed by No-FRC/No-etching/MDP-primer (24.2 MPa), FRC/F-etch/MDP-primer (19.9 MPa), FRC/No-etching/MDP-primer (17.8 MPa), No-FRC/No-etching/No-primer (13.6 MPa), while FRC/No-etching/No-primer (2.5 MPa) resulted in the lowest value. Microphotographs showed that numerous micro and nano pits were created on the Ti–6Al–4V alloy surface modified with F-etch.ConclusionsThe bond strength between Ti–6Al–4V alloy and the veneering resin composite was the highest when the alloy surface was modified with alumina blasting, fluoride etchant, and phosphate primer successively.     

Effect of implant support on mandibular distal extension removable partial dentures: Relationship between denture supporting area and stress distribution

PurposeThis study explored the relationship between implant support and the denture-supporting area by comparing the stability of an implant-supported distal extension removable partial denture and a conventional distal extension removable partial denture.MethodsA model simulating a mandibular bilateral distal extension missing (#34–37 and #44–47) was fabricated using silicone impression material as soft tissue (2 mm thick) on an epoxy resin bone model. The denture base was reduced by 5 mm cutting part of both the retromolar pad and the lingual border. Loads of up to 5 kg were applied, and the pressure and displacement of the RPDs were simultaneously measured and analyzed using the Wilcoxon test (α < 0.05).ResultsThe pressure on the bilateral first molar and the middle areas of the implant-supported distal extension removable partial denture (ISRPD) was significantly less than on the conventional RPD (CRPD). As the supporting area of the denture base decreased, the pressure and the denture displacement of the CRPD were greater than for the ISRPD.ConclusionThis study indicated that implant placement at the distal edentulous ridge can prevent denture displacement of the distal extension bases, regardless of the supporting area of the denture base.     

Metal-ceramic bond strength of Co-Cr alloy fabricated by selective laser melting

ObjectivesThis study was to evaluated the metal–ceramic bond strength of a Co–Cr dental alloy prepared using a selective laser melting (SLM) technique.MethodsTwo groups comprised of twenty Co–Cr metal bars each were prepared using either a SLM or traditional lost-wax casting method. Ten bars from each group were moulded into standard ISO 9693:1999 dimensions of 25 mm × 3 mm × 0.5 mm with 1.1 mm of porcelain fused onto an 8 mm × 3 mm rectangular area in the centre of each bar. Metal–ceramic bonding was assessed using a three-point bending test. Fracture mode analysis and area fraction of adherence porcelain (AFAP) were determined by measuring Si content of specimens by SEM/EDS.ResultsStudent's t-test within the groups demonstrated no significant difference for the mean bond strength between the SLM and traditional cast sample groups. While SEM/EDS analysis indicated a mixed fracture mode on the debonding interface of both the SLM and the cast groups, the SLM group showed significantly more porcelain adherence than the control group (p < 0.05).ConclusionsThe SLM metal–ceramic system exhibited a bonding strength that exceeds the requirement of ISO 9691:1999(E) and it even showed a better behaviour in porcelain adherence test comparable to traditional cast methods.     

Evaluation of interface characterization and adhesion of glass ceramics to commercially pure titanium and gold alloy after thermal- and mechanical-loading

ObjectivesThis study evaluated the effect of thermal- and mechanical-cycling on the shear bond strength of three low-fusing glassy matrix dental ceramics to commercial pure titanium (cpTi) when compared to conventional feldspathic ceramic fused to gold alloy.MethodsMetallic frameworks (diameter: 5 mm, thickness: 4 mm) (N = 96, n = 12 per group) were cast in cpTi and gold alloy, airborne particle abraded with 150 μm aluminum oxide. Low-fusing glassy matrix ceramics and a conventional feldspathic ceramic were fired onto the alloys (thickness: 4 mm). Four experimental groups were formed; Gr1 (control group): Vita Omega 900–Au–Pd alloy; Gr2: Triceram–cpTi; Gr3: Super Porcelain Ti-22–cpTi and G4: Vita Titankeramik–cpTi. While half of the specimens from each ceramic–metal combination were randomly tested without aging (water storage at 37 °C for 24 h only), the other half were first thermocycled (6000 cycles, between 5 and 55 °C, dwell time: 13 s) and then mechanically loaded (20,000 cycles under 50 N load, immersion in distilled water at 37 °C). The ceramic–alloy interfaces were loaded under shear in a universal test machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were noted and the interfaces of the representative fractured specimens from each group were examined with stereomicroscope and scanning electron microscope (SEM). In an additional study (N = 16, n = 2 per group), energy dispersive X-ray spectroscopy (EDS) analysis was performed from ceramic–alloy interfaces. Data were analyzed using ANOVA and Tukey's test.ResultsBoth ceramic–metal combinations (p < 0.001) and aging conditions (p < 0.001) significantly affected the mean bond strength values. Thermal- and mechanical-cycling decreased the bond strength (MPa) results significantly for Gr3 (33.4 ± 4.2) and Gr4 (32.1 ± 4.8) when compared to the non-aged groups (42.9 ± 8.9, 42.4 ± 5.2, respectively). Gr1 was not affected significantly from aging conditions (61.3 ± 8.4 for control, 60.7 ± 13.7 after aging) (p > 0.05). Stereomicroscope images showed exclusively adhesive failure types at the opaque ceramic–cpTi interfacial zone with no presence of ceramic on the substrate surface but with a visible dark titanium oxide layer in Groups 2–4 except Gr1 where remnants of bonder ceramic was visible. EDS analysis from the interfacial zone for cpTi–ceramic groups showed predominantly 34.5–85.1% O₂ followed by 1.1–36.7% Al and 0–36.3% Si except for Super Porcelain Ti-22 where a small quantity of Ba (1.4–8.3%), S (0.7%) and Sn (35.3%) was found. In the Au–Pd alloy–ceramic interface, 56.4–69.9% O₂ followed by 15.6–26.2% Si, 3.9–10.9% K, 2.8–6% Na, 4.4–9.6% Al and 0–0.04% Mg was observed.SignificanceAfter thermal-cycling for 6000 times and mechanical-cycling for 20,000 times, Triceram–cpTi combination presented the least decrease among other ceramic–alloy combinations when compared to the mean bond strength results with Au–Pd alloy–Vita Omega 900 combination.