Triantafillos Papadopoulos

Thermal expansion and microstructural analysis of experimental metal-ceramic titanium alloys

UNLABELLED Statement of problem Low-fusing porcelains for titanium veneering have demonstrated inferior color stability and metal-ceramic longevity compared to conventional porcelains. PURPOSE This study evaluated the microstructure and thermal expansion coefficients of some experimental titanium alloys as alternative metallic substrates for low-fusing conventional porcelain. MATERIALS AND METHODS Commercially pure titanium (CP Ti) and various metallic elements (Al, Co, Sn, Ga, In, Mn) were used to prepare 8 titanium alloys using a commercial 2-chamber electric-arc vacuum/inert gas dental casting machine (Cyclarc). The nominal compositions of these alloys were the following (wt%): I: 80Ti-18Sn-1.5In-0.5Mn; II: 76Ti-12Ga-7Sn-4Al-1Co; III: 87Ti-13Ga; IV: 79Ti-13Ga-7Al-1Co; V: 82Ti-18In; VI: 75.5Ti-18In-5Al-1Co-0.5Mn; VII: 85Ti-10Sn-5Al; VIII: 78Ti-12Co-7Ga-3Sn. Six rectangular wax patterns for each test material (l = 25 mm, w = 3 mm, h = 1 mm) were invested with magnesia-based material and cast with grade II CP Ti (control) and the 8 experimental alloys. The porosity of each casting was evaluated radiographically, and defective specimens were discarded. Two cast specimens from CP Ti and alloys I-VIII were embedded in epoxy resin and, after metallographic grinding and polishing, were studied by means of scanning electron microscopy and wavelength dispersive electron probe microanalysis. One specimen of each material was utilized for the determination of coefficient of thermal expansion (CTE) with a dilatometer operating from room temperature up to 650 degrees C at a heating rate of 5 degrees C/minute. RESULTS Secondary electron images (SEI) and compositional backscattered electron images (BEI-COMPO) revealed that all cast specimens consisted of a homogeneous matrix except Alloy VIII, which contained a second phase (possibly Ti(2)Co) along with the titanium matrix. The results showed that the coefficient of thermal expansion (CTE) varied from 10.1 to 13.1 x 10(-6)/ degrees C (25 degrees -500 degrees C), depending on the elemental composition. CONCLUSION The CTE of titanium can be considerably changed by alloying. Two-phase alloys were developed when alloying elements were added in concentrations greater than the maximum solubility limit in alpha-titanium phase.

Color stability and degree of cure of direct composite restoratives after accelerated aging.

PURPOSE This study evaluated the color changes and amount of remaining C = C bonds (%RDB) in three dental composites after hydrothermal- and photoaging. METHODS AND MATERIALS The materials tested were Estelite sigma, Filtek Supreme and Tetric Ceram. Specimens were fabricated from each material and subjected to L* a* b* colorimetry and FTIR spectroscopy before and after aging. Statistical evaluation of the deltaL,* deltaa,* deltab,* deltaE and %deltaRDB data was performed by one-way ANOVA and Tukeys test. The %RDB data before and after aging were statistically analyzed using two-way ANOVA and Student-Newman-Keuls test. In all cases an alpha = 0.05 significance level was used. RESULTS No statistically significant differences were found in deltaL*, deltaa*, deltaE and %deltaRDB among the materials tested. Tetric Ceram demonstrated a significant difference in deltab*. All the materials showed visually perceptible (deltaE >1) but clinically acceptable values (deltaE < 3.3). Within each material group, statistically significant differences in %RDB were noticed before and after aging (p < 0.05). Filtek Supreme presented the lowest %RDB before aging, with Tetric Ceram presenting the lowest %RDB after aging (p < 0.05). The %deltaRDB mean values were statistically significantly different among all the groups tested. No correlation was found between deltaE and %deltaRDB.

The effect of a ceramic coating on the cpTi-porcelain bond strength

OBJECTIVES To investigate the bond strength between cpTi and low fusing porcelains after different treatments. METHODS 72 patterns were covered with a ceramic coating and invested with phosphate-bonded material (group A), another 72 were invested with magnesia material (group B) and all cast with cpTi. 31 solid castings were selected from each group. The castings of group B were ground and sandblasted, while the castings of group A were only sandblasted. Aluminum content of the metal surface was determined by EDS and castings were submitted to a 3-point bending test to determine the modulus of elasticity (E). The porcelains Duceratin Plus, Noritake Ti22 and Triceram were applied respectively and specimens were submitted to a 3-point bending test. The fracture mode and the remaining porcelain were determined by optical microscopy and SEM/EDS. Bond strength and fracture mode were calculated by two-way ANOVA. RESULTS The E of groups A and B was 98.3 GPa and 98.6 GPa respectively. The bond strength was 26+/-3 MPa (Duceratin Plus), 28+/-3 MPa (Noritake Ti22), 27+/-2 MPa (Triceram) for group A and 24+/-1 MPa, 29+/-2 MPa, 27+/-1 MPa for group B respectively. No significant differences were found for the same porcelain between the two groups (p<0.05). A significant difference was found between Duceratin Plus and Noritake Ti22, for group B (p<0.05). The mode of failure was mainly adhesive for all specimens. A significant reduction in aluminum was recorded in all subgroups. SIGNIFICANCE The special coating of patterns makes the Ti casting procedure inexpensive, without reducing the metal-ceramic bond strength.

Effectiveness of different adhesive primers on the bond strength between an indirect composite resin and a base metal alloy.

STATEMENT OF PROBLEM There is a need for achieving reliable chemical bond strength between veneering composites resins and casting alloys through the use of simplified procedures. PURPOSE The purpose of this study was to examine the shear bond strength of an indirect composite resin to a Ni-Cr alloy, using 4 primers and 2 airborne-particle-abrasion procedures. MATERIAL AND METHODS Fifty-six Ni-Cr (Heraenium NA) discs, 10 mm in diameter and 1.5 mm in height, were fabricated. Twenty-four discs were airborne-particle abraded with 50-microm Al2O3 particles, while another 24 were airborne-particle abraded with 250-microm Al2O3 particles. The following primers were applied on 6 discs of each airborne-particle-abrasion treatment group: Solidex Metal Photo Primer (MPP50, MPP250), Metal Primer II (MPII50, MPII250), SR Link (SRL50, SRL250), and Tender Bond (TB50, TB250). The Rocatec system was used on another 6 discs, airborne-particle abraded according to the manufacturers recommendations, which served as the control group (R). Two more discs were airborne-particle abraded with 50-microm and 250-microm Al2O3 particles, respectively, to determine the Al content on their surfaces, without any bonding procedure. The indirect composite resin used was Sinfony. Specimens were thermally cycled (5 degrees C and 55 degrees C, 30-second dwell time, 5000 cycles) and tested in shear mode in a universal testing machine. The failure mode was determined with an optical microscope, and selected specimens were subjected to energy dispersive spectroscopy (EDS). Mean bond strength values were analyzed using 2-way ANOVA followed by Tukeys multiple comparison tests (alpha=.05) and compared to the control group using 1-way ANOVA followed by Tukeys multiple comparison tests (alpha=.05). RESULTS The groups abraded with 50-microm particles exhibited significantly higher bond strength compared to the groups abraded with 250-microm particles. Group MPII50 exhibited the highest mean value (17.4 +/-2 MPa). Groups MPP50, MPP250, and TB50, TB250 showed adhesive failures and significantly lower bond strength compared to group R. Groups MPII50, MPII250, and SRL50, SRL250 showed combination failures and no significant difference compared with group R. EDS revealed interfacial rather than adhesive failures. CONCLUSIONS Airborne-particle abrasion with 50-microm Al2O3 particles may result in improved bond strength, independent of the primer used. The bond strength of Metal Primer II and SR Link specimens was comparable to that of specimens treated with Rocatec.

The influence of alendronate on osseointegration of nanotreated dental implants in New Zealand rabbits

OBJECTIVES Growing clinical demands for stronger and faster bone bonding to the implant have motivated the development of methods enhancing osseointegration. Lately, the application of bisphosphonates (bis) in order to optimize bone healing has become a topic of great interest. N-containing bis, such as alendronate (ALN), are the more potent drugs of this class. It was the aim of this study to determine the effect of ALN on the osseointegration of a well-documented nanotreated implant system in a rabbit femoral condyle model. MATERIAL AND METHODS Thirty-two adult female New Zealand White rabbits received one implant (3.25 mm in diameter and 10 mm in length) in their left femoral condyle, a week after they were ovariectomized. Half of them were saline treated (control, group A) and the other half were ALN treated (group B). Rabbits from both groups were euthanized after 6 and 12 weeks, respectively. RESULTS The specimens were evaluated histologically and histomorphometrically. Upon histological evaluation, no obvious differences were found between the control and the treatment group. Implants showed good integration into the bone tissue surrounding them. There were also no statistically significant differences in bone-to-implant contact and the amount of bone tissue in the immediate neighborhood of the implant at both healing periods. CONCLUSIONS The systemic administration of ALN was not found to affect histological osseointegration of implants in animals with a hormonal status resembling that of postmenopausal healthy women. Further research will be needed to investigate this approach.

Surface characterization of three titanium dental implants.

Purpose:The aim of this study was to evaluate topographically and compositionally the rough surface of 3 different commercial titanium dental implants. Materials:Bio Com Standard, Osseotite Implant, and Fixture MT Osseospeed were analyzed using scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy. Results:The scanning electron microscopy and atomic force microscopy analyses showed that the rough surface of Bio Com Standard presents numerous impressions superimposed by sharp pits, of Osseotite Implant many discrete sharp pits, and of Fixture MT Osseospeed a mixed feature appearance. The energy dispersive spectroscopy analysis of the rough implant surfaces revealed a small trace of Si found on the surface of Osseotite Implant. Fixture MT Osseospeed showed a nonhomogeneous distribution of the detected elements. Conclusion:The examined implants had a different rough surface topography, which was directly dependent on the type of treatment used. The differences concerning the surface morphology were leading in a characteristic nanotopography, which might influence the biologic activities at the implant–tissue interface. Surface oxygen concentrations also indicated differences in the oxide layer width between the examined implants, being minimal in Osseotite Implant and maximal in Fixture MT Osseospeed.

Microstructure effect on the properties of a commercial low-fusing dental porcelain

The aim of this study was to investigate the effect of firing cycle on a dental porcelain microstructure in order to correlate microstructure changes with mechanical and thermal properties. A commercial low-fusing dental porcelain powder (Omega 900, Vita) was investigated for this purpose. The powder was treated at different temperatures in the range 750–1000 °C. The fired samples were characterized in terms of their morphology and microstructure, and their mechanical and thermal properties were evaluated. The results showed that firing temperature affects porcelain microstructure influencing significantly in this way both the mechanical properties and the thermal expansion coefficient of the fired objects. Firing at 800 °C led to a homogeneous structure. After treatment at this temperature, the leucite crystals exhibit their maximum concentration and they are well dispersed into the glassy phase. As a consequence the optimum mechanical strength and the maximum thermal expansion coefficient are observed in these samples.

Effects of cleansing methods on 3-D surface roughness, gloss and color of a polyamide denture base material

Abstract Objective. The purpose of this study was to determine the effects of two denture cleansing methods on 3-D surface roughness, gloss and color of denture base materials. Materials and methods. Thirty disks from nylon (Valplast) and 30 from heat-polymerized acrylic denture base material (Paladon 65) were made and 10 of each material were immersed in water (control), Val-Clean (peroxide cleanser) and Corega Extradent (peroxide cleanser) plus microwaving for a period simulating 30 days of daily cleansing. 3-D surface roughness, gloss and color parameters were measured before and after cleansing using an interferometric profilometer, a gloss meter and a colorimeter. The results were statistically analysed by regression, paired-t, Mann-Whitney and Kruskal-Wallis tests at α = 0.05 level of significance. Results. The results showed significant differences at baseline in L* and b* parameters between materials (p < 0.01), with a significantly lower gloss (p < 0.05) and higher roughness (p < 0.05) for Valplast. After cleansing, Δε* was significantly greater in Valplast than Paladon 65 (p < 0.05). Gloss of both materials decreased significantly within the Corega Extradent plus microwave solution (p < 0.05), while roughness increased significantly only for Paladon 65 (p < 0.05). Conclusions. Valplast was found to have a significantly lower gloss and a higher roughness than Paladon 65 before cleansing. After cleansing, ΔE* increased more in Valplast than in Paladon 65, gloss of both materials decreased and roughness only of Paladon 65 increased within the Corega extradent plus microwaving method.

Experimental and numerical determination of the mechanical response of teeth with reinforced posts

The aim of this study was to evaluate the mechanical behavior of endodontically treated teeth restored with fiber reinforced composite posts versus titanium posts, by both experimental testing and numerical simulation (finite element analysis (FEA)). Forty maxillary central incisors were endodontically treated to a size 45 file and then obturated using gutta-percha points and sealer with the lateral condensation technique. The teeth were divided into four groups of ten teeth each. All the posts were of similar dimensions. The first group was restored using carbon fiber reinforced posts (CB), the second and third groups were restored using glass fiber reinforced posts (DP and FW, respectively), and the fourth group (control group) was restored using conventional titanium posts (PP). Half of the specimens of every group were submitted to hydrothermal cycling (2000 cycles, at 5 °C and 55 °C, respectively). All specimens were loaded until failure at a 45° angle with respect to the longitudinal axis at a cross head speed of 0.5 mm min(-1). A two-dimensional finite element model was designed in order to simulate the experimentally obtained results. Mechanical testing revealed that teeth restored with titanium posts exhibited the highest fracture strength. Debonding of the core was the main failure mode observed in glass fiber posts, whereas vertical root fractures were observed in the titanium posts. FEA revealed that the maximum stresses were developed at the interface between the post, dentin and the composite core critical regions in all three cases. Hydrothermal cycling had no significant effect on the fracture behavior of fiber reinforced composite posts.

Dynamic mechanical properties of a maxillofacial silicone elastomer incorporating a ZnO additive: the effect of artificial aging.

The main objective of the current study was to investigate the dynamic mechanical properties of a room-temperature vulcanizing silicone incorporating different fractions of zinc oxide (ZnO) after indoor and outdoor photoaging. Forty-eight samples were produced by adding different amounts of ZnO into a commercial maxillofacial silicone (EPISIL-E). The samples were divided into 4 groups containing 0.0, 0.2, 0.5, and 1 wt% ZnO additive, respectively. Samples were exposed to sunlight (subgroup 2), ultraviolet (subgroup 3), and fluorescence (subgroup 4) aging, whereas nonaged samples comprised the control subgroup (subgroup 1). Dynamic mechanical analysis was used to determine the storage modulus (E&vprime;), loss modulus (E″), and damping capacity (tan&dgr;). General linear statistic model was conducted to evaluate the effects of aging, testing frequency, and composition on the dynamic mechanical properties of the silicone with the ZnO additive. Post hoc analysis was performed using Tukey test. Statistical analysis revealed a significant impact of composition on tan&dgr; (P < 0.05). Aging influenced E&vprime; and E″ (P < 0.01). The combination of aging and composition had a significant effect on all dynamic properties (P < 0.01).