[Show abstract][Hide abstract] ABSTRACT: Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance.
The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method.
Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4 × 13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts.
The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material.
The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.
The Journal of prosthetic dentistry 05/2014; · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract This study evaluated the effects of axial and oblique occlusal loading on implant-supported partial dentures with different connection systems (external-hexagon, internal-hexagon, and Morse-taper). Upon axial loading, all systems presented similar stress values. Stress values increased under oblique loading. Stress distribution changed for some of the internal-connection structures. It can be concluded that oblique load increases stress on bone structures and prosthetic components. Internal-connection system implants present more favorable stress distribution patterns than do external-connection system implants.
Journal of Oral Implantology 04/2013; · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract Objective. This study aimed to evaluate the influence of the casting procedure and cyclic loading of prosthetic frameworks on detorque of prosthetic screws and marginal misfit of single unit implant-supported prostheses. Materials and methods. Twenty specimens were obtained, each one consisting of a set of an implant (external hexagon 3.75 × 13 mm - Branemark type), a prosthetic abutment (entirely calcinable or overcasted UCLA) and a prosthetic screw. After the specimens were obtained, the prosthetic screws were tightened with 30 Ncm torque and released 24 h later in order to evaluate initial detorque. The screws were retightened and marginal gaps were assessed. All specimens were submitted to 10(6) loading cycles, performed with 2 Hz frequency and 130 N load. The specimens were re-evaluated for marginal misfit and detorque after the mechanical loading (final marginal misfit/final detorque). The results were submitted to analysis of variance for repeated measurements, followed by Tukey HSD test (α = 0.05). Results. No statistically significant differences were found on detorque values of the prosthetics screws for all groups and intervals evaluated (p = 0.8922). The entirely calcinable abutments showed higher initial marginal misfit compared to the overcasted ones (p = 0.0438). There was no statistically significant difference on marginal misfit before and after mechanical loading for both groups (p > 0.05). Conclusions. It can be concluded that the overcasted abutments showed lower misfit values when compared to the entirely casted abutments. No difference was observed on detorque values of prosthetic screws. After mechanical loading there was no difference on marginal misfit and detorque between the groups.
[Show abstract][Hide abstract] ABSTRACT: Objective: The aim of this study was to assess by photoelastic analysis and through a test of flexural resistance, welding techniques, Laser and TIG (Tungsten Inert Gas) in the manufacturing of NiCrTi implant frameworks.
Method: Three groups were formed with 5 samples each: framework cast in one piece, Laser welded and TIG welded. The photoelastic model was made with flexible resin, from the transfer impression of a stainless steel matrix with 4 similar implants with regular diameter and hexagonal external connection. The tensions caused by the installation of the frameworks with 20 Ncm torque on the photoelastic model, were analyzed in a circular polariscope and recorded by camera. Later, the resistance test was performed on the mechanical universal testing machine (Model 4411, Instron corp., Canton, MA). The frameworks were positioned in the mechanical testing machine which was set to move 2mm per minute until the occurrence of fracture of the cantilever.
Result: The results were tabulated and submitted to ANOVA and Tukey's test at 5% significance. The results showed no statistical difference of maximum shear stress between any of the techniques used, however, the highest stresses were found along the implants of the right side. The one piece frameworks showed higher fracture resistance when compared to the TIG welded.
Conclusion: The stresses around the implants were similar among the diffferent framework manufacturing techniques and among all evaluated areas. And one-piece casting framework and Laser welded showed better resistance, than the TIG welding techniques.
[Show abstract][Hide abstract] ABSTRACT: Objective: Aiming to obtain frameworks with better fit, this study compared one-piece casted frameworks with frameworks obtained by two different soldering techniques: Laser-welding and TIG (Tungsten Inert Gas).
Method: Thru photoelastic analysis and flexural strength tests, the stress distribution around implants and the mechanical resistance of the frameworks were evaluated. Fifteen commercially pure titanium frameworks were obtained using a steel matrix, with four external-hexagon (3.75x13mm) implants. The frameworks were divided into three groups: GI or control - one-piece casted frameworks; GII - Laser welded frameworks; GIII - TIG welded frameworks. For stress analyses a photoelastic model, reproducing the steel matrix was manufactured with photoelastic flexible resin. Each framework was screwed with 20Ncm torque to the photoelastic models implants. Using a circular polariscope the order of the isochromatic fringes around the implants was obtained. Maximum sheer stress was determined through the “stress optical law”. A mechanical test of flexural strength was performed at the hanging arms joints of each framework, using a universal testing machine (Instron 4411 Corp.Canton, Mass.) with a speed of 2 mm/min, load cell 500Kgf and maximum length of 5.00mm. The data were submitted to ANOVA followed by Tukey test (p=0.05).
Result: No difference was observed on shear stress of the welding techniques. The casted group showed lower stress values than the TIG welded group. On the mechanical test the casted group presented higher compressive resistance (291,91N/mm2), followed by laser (224,20N/mm2) and TIG welded ones (123,65N/mm2).
Conclusion: It is concluded that the conventional casting technique provides more mechanically resistant infrastructures than the welding techniques, with similar or lower stress to the supporting implants.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to evaluate the effects of adhesive primer applications on the bond strength of resin cements to cast titanium. Four adhesive primers - Metaltite, Metal Primer II, Alloy Primer and Ceramic Primer - and their respective resin cements - Bistite II DC, Link Max, Panavia F 2.0, RelyX Unicem and RelyX ARC - were tested. Cast plates were prepared from titanium ingots (n=6 specimens/cement) and had their surfaces airborne-particle abraded with Al2O3 (50 μ m). Three resin cement cylinders were built on each bonded titanium surface, using a cylindrical translucent tubing mold and were subjected to micro-shear testing. Data were analyzed statistically by two-way ANOVA and Tukey's post-hoc test (α=0.05). The application of Metal Primer II and Ceramic Primer resulted in significant higher bond strength for Link Max and RelyX Unicem resin cements, respectively, than nonuse of adhesive primers. Panavia F 2.0 and RelyX ARC yielded high bond strength means with or without adhesive primers. The use of adhesive primers might increase the bond strength to cast titanium depending on the resin cement used.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the distribution of generated stress around implants and adjacent bone tissue using different implant-retained overdenture designs through photoelastic analysis.
Over an edentulous human mandible, achieved from a human model, 2 or 4 microunit analog abutments were embedded (Master; Conexao Systems Prosthodontics, São Paulo, Brazil), settled in the interforaminal region. Three models of photoelastic resin (Araltec Chemicals Ltda, Hunstman, Guarulhos, São Paulo, Brazil), with 2 or 4 incorporated implants and microunit abutments, were obtained from molds using silicone for duplication. Inclusion, finishing, and polishing procedures were applied on the frameworks. This study was based on 3 different mechanisms of implant-retained mandibular overdentures: O'ring (GI), bar-clip (GII) (both with 2 implants), and their association (GIII) (with 4 implants). After the adaptation of each overdenture system on the photoelastic models, 100-N alternate occlusal loads were applied on back-side and front-side regions. The photoelastic analysis was made with the aid of a plain polariscope linked to a digital camera, Sony Cybershot α100, which allowed visualization of the fringes and registration of images on digital photographs.
The results demonstrated higher tension concentrated over the GIII, with a flat distribution of stress to the posterior ridge and overload on the posterior implants. GI showed the smaller stress level, and GII, intermediate level; there was distribution of stress to the posterior ridge in these 2 groups.
The use of bar attachment proved to be a better alternative, because it showed a moderate level of tension with a more uniform stress distribution and possessed higher retention than did the ball system.
The Journal of craniofacial surgery 11/2011; 22(6):2332-6. · 0.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Titanium frameworks are frequently indicated for implant supported prostheses; however, voids are usually encountered inside cast titanium. Objective: This study aimed to confirm the efficacy of a radiographic technique for inspection of porosity in commercially pure titanium castings with different diameter.
Sixty dumbbell rods (n=20) with a central 1.5, 2.0 and 3.5mm diameter were prepared by lost-wax casting. Cast specimens were finished and polished and submitted to radiographic examination (90kV, 15mA, 0.6s and 10-13mm of distance) using periapical film. The radiographs were visually analysed for the presence of porosity in the extension of the dumbbell or in the central portion of the rods. Data were submitted to Pearson Chi-square test (5%).
The tested radiographic method proved to be suitable for the evaluation of cast frameworks. Internal porosities were observed in most of the specimens (91.7%) (p=0.0005); however, only 20% occurred on the central portion of the rods (p=0.612).
Internal porosities can be visualised through radiographs and occur mostly in small diameter structures. The radiographic evaluation of metal structures can improve the quality of frameworks and thereby potentially increase the longevity of the rehabilitation.
[Show abstract][Hide abstract] ABSTRACT: The lack of passivity of the implant supported prosthesis may lead to mechanical and biological disorders such as loosening and breakage of screws, due to the tensions generated by prosthetic frameworks. The increasing use of laser welding and TIG welding (tungsten inert gas) for construction of infrastructure on implants raises issues as to the forces applied to the prosthesis-implant system and alveolar bone. Objectives: the aim of this study was to evaluate by using photoelasticity stresses generated by welding and TIG Laser in the union of cylindrical rods of titanium cp (Ti cp) to the abutment of the same metal and casting frameworks. Methods: on a steel matrix with four implants (Signovinces) was connecting the transfers abutments with acrylic resin and obtaining working model on which the laser welding were carried out (G 1), TIG welding (G 2), and casting frameworks in one-piece(G 3). The specimens were bolted on a photoelastic model with manual torque of 20 Ncm, and put into a round polariscope and took standardized digital photographs. Measurement points for the fringe order were defined. Results: tensions was present in all groups, the highest fringe order in group 1 was N = 1 and to groups 2 and 3 the higher order fringe was N = 2, with Group 3 showing more points with N = 2. Conclusions: it was concluded that the Laser welding exhibited the best passivity, followed by TIG welding in implant supported framework on 4 implants.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the effect of different accelerated aging times on permanent deformation and tensile bond strength of two soft chairside liners, acrylic resin (T) and silicone (MS) based.
Different specimens were made for each test of each reliner. The specimens (n = 10) were submitted to accelerated aging for 2, 4, 8, 16, 32, and 64 cycles. Tensile bond strength testing was performed at a crosshead speed of 5 mm/min and permanent deformation with a compressive load of 750 gf. Data were submitted to Mann-Whitney test to compare the materials at different times, and Kruskal-Wallis and Dunn tests were used for comparing aging intervals within a given reliner.
MS presented a lower percentage of permanent deformation (p < 0.0001) and higher tensile bond strength (p < 0.0001) than T in all time intervals and was not affected by the accelerated aging process, which reduced the permanent deformation and increased tensile bond strength of T (p < 0.05).
MS presented lower permanent deformation and higher tensile bond strength than T. Although T presented changes in those properties after accelerated aging, both materials might be suited for long-term use.
Journal of Prosthodontics 02/2011; 20(3):200-4. · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Implant-retained overdentures are a treatment option for patients who are not satisfied with conventional complete dentures. Although implant-retained overdentures are widely used, little data are available or provided by implant manufacturers about retentive strength and wear of attachments.
The purpose of this study was to evaluate retentive strength and fatigue resistance of 4 overdenture bar-and-clip attachment systems.
Forty bar-and-clip attachment system specimens were tested (n=10): Conexão Bar Clip (polymer clip), Sterngold Hader Bar (polymer clip), 3i Gold Hader Type Clip (metal clip), or SIN Clipo (metal clip). Specimens immersed in artificial saliva were tested to 5500 cycles at 0.8 Hz using a servohydraulic universal testing machine. Retention strength values (N) were recorded initially and after 1100, 2200, 3300, 4400, and 5500 insertion and removal cycles during the tensile test using a speed of 1 mm/min and a load cell of 1 kN. Data were submitted to a 2-way repeated-measures ANOVA and the Tukey A post hoc test (alpha = .05).
An increase in retention strength values was observed during the fatigue test after 5500 cycles of insertion and removal. No significant difference in retentive strength was observed in the groups using polymer clips (Conexão Bar Clip and Sterngold Hader Bar) (P=.729); the same occurred with metal clip systems (SIN Clipo and 3i Gold Hader Type Clip) (P=.068). The SIN Clipo system demonstrated the smallest retention strength values, which were significantly different from the other 2 attachment systems, the Sterngold Hader Bar (P<.01) and the Conexão Bar Clip (P<.01). Although the 3i Gold Hader Type Clip did not differ significantly, in terms of retentive strength, from the Sterngold Hader Bar (P=.258), its retentive strength was significantly lower than the retentive strength of the Conexão Bar Clip system (P=.030).
The systems evaluated demonstrated satisfactory retention for all time periods tested, as retention strengths from 5 to 7 N should be sufficient to stabilize overdentures. No component fracture or compromise in retention was found for any of the systems tested.
The Journal of prosthetic dentistry 08/2009; 102(2):74-80. · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study evaluated the influence of prosthetic screw material on joint stability in implantsupported dentures at two levels of fit.
Ten mandibular implant-supported dentures were fabricated. Twenty cast models were fabricated using these dentures. Four groups (n=10) were tested, according to the vertical fit of the dentures [passive and non-passive] and prosthetic screw materials [titanium (Ti) or gold (Au) alloy]. The one-screw test was performed to quantify the vertical misfits using an optic microscope. The loosening torque for the prosthetic screws was measured 24 hours after the tightening torque (10 Ncm) using a digital torque meter. Data were analyzed by two-way ANOVA and Tukey's test (alpha=0.05).
Overall, dentures with passive fit and Ti screws resulted in significantly higher loosening torque of the prosthetic screws (p<0.05). No significant interaction was found between fit level and screw material (p=0.199). The prosthetic screw material and fit of implant-supported dentures have an influence on screw joint stability. Ti screws presented higher joint stability than Au screws and minimum of misfit should be found clinically to improve the mechanical behavior of the screw joint.
[Show abstract][Hide abstract] ABSTRACT: This study investigated the effect of in vitro accelerated aging reproduced with thermocycling on the bond strength of three commercially available permanent denture soft liners (PermaSoft, Dentuflex, Ufi-gel) with one heat-polymerized polymethyl methacrylate resin denture base (QC-20) by tensile test.
Ten specimens were prepared for control and test groups of each material for a total of 60 specimens. All controls were stored in water (37 degrees C) for 24 hours before testing. All test groups received 3000 thermal cycles consisting of 1 minute at 5 degrees C and 1 minute at 65 degrees C. All specimens were submitted to a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Results were statistically analyzed (ANOVA, p < or = 0.05, Tukey's post-hoc test).
The mean bond strength of control specimens was (MPa): 0.32 (Ufi-gel), 0.49 (PermaSoft), and 1.19 (Dentuflex). There was no statistical difference (p > 0.05) between Ufi-gel and PermaSoft, but both were statistically different (p < 0.05) when compared to Dentuflex. After thermocycling, the mean bond strength was (MPa): 0.18 (Ufi-gel), 0.81 (PermaSoft), and 3.32 (Dentuflex). All materials were statistically different (p < 0.05). Ufi-gel had the lowest value and Dentuflex the highest in both control and test groups. Dentuflex presented only adhesive failure; in the remaining groups, there was no predominant failure mode, except Ufi-gel control with no adhesive failure.
Despite presenting greater bond strength, thermocycling had a deleterious effect in Dentuflex; Ufi-gel may be adequate for short-term use.
Journal of Prosthodontics 09/2008; 17(7):550-4. · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study evaluated the abrasion resistance of acrylic resin to routine dental brushing procedures using different dentifrices after the resin surface had been chemically or mechanically polished.
Eighty specimens were prepared using heat-polymerizing (HP) and autopolymerizing (AP) acrylic resin, and immediately submitted to grinding with abrasive stones and disks. The specimens were divided into two groups: the first group was mechanically polished (MP) using pumice slurry, and the second group was chemically polished (CP) using heated monomer. After polishing, the specimens were submitted to 30,000 brushing cycles. Surface roughness was measured after polishing and brushing procedures, using a Surfcorder SE 1700 rugosimeter. Data were statistically analyzed by ANOVA (alpha= 0.05).
There were significant differences in surface roughness between polishing with MP and CP (p < 0.05). Significant differences in surface roughness were also found between brushing with MFP dentifrice and Tartar Control dentifrice (p < 0.05).
MP produced smoother surfaces than CP, and surface roughness as a result of polishing technique was not influenced by acrylic resin type. Even though MP resulted in smoother surfaces initially, subjecting the acrylic resin to dentifrice brushing negated this advantage.
Journal of Prosthodontics 06/2008; 17(4):308-11. · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study investigated the influence of laser welding and electroerosion procedure on the passive fit of interim fixed implant-supported titanium frameworks. Twenty frameworks were made from a master model, with five parallel placed implants in the inter foramen region, and cast in commercially pure titanium. The frameworks were divided into 4 groups: 10 samples were tested before (G1) and after (G2) electroerosion application; and another 10 were sectioned into five pieces and laser welded before (G3) and after (G4) electroerosion application. The passive fit between the UCLA abutment of the framework and the implant was evaluated using an optical microscope Olympus STM (Olympus Optical Co., Tokyo, Japan) with 0.0005mm of accuracy. Statistical analyses showed significant differences between G1 and G2, G1 and G3, G1 and G4, G2 and G4. However, no statistical difference was observed when comparing G2 and G3. These results indicate that frameworks may show a more precise adaptation if they are sectioned and laser welded. In the same way, electroerosion improves the precision in the framework adaptation.
Stomatologija / issued by public institution "Odontologijos studija" ... [et al.] 02/2008; 10(3):96-100.
[Show abstract][Hide abstract] ABSTRACT: Purpose: The purpose of this study was to test the effect of brushing on surface roughness of two resilient liners (Luci Sof and Sofreliner) compared with an acrylic resin (QC 20).Materials and Methods: Twenty specimens of each material were prepared (25 mm × 14 mm × 3 mm). Ten specimens served as controls and were stored in distilled water and not brushed. The remaining ten specimens were subjected to mechanical brushing, using an MSEt plus machine to simulate brushing at a rate of 5.0 strokes per second (30,000 cycles). Surface roughness measurements were recorded before and after brushing. Random samples were analyzed using scanning electron microscope. Data collected were analyzed by a two-way analysis of variance using material and treatment as variables, followed by Tukey's test (α= 0.05).Results: Initial surface roughness of materials indicated that QC 20 was the smoothest (0.13 μm), and Luci Sof the roughest (0.68 μm). Sofreliner had an intermediate value (0.31 μm). All materials were significantly different. Mechanical brushing significantly increased surface roughness in all the materials. Although there was no statistical difference between QC 20 and Luci Sof after mechanical brushing (0.88 and 1.00 μm, respectively), both differed significantly from Sofreliner (7.74 μm).Conclusion: The two resilient liners and the acrylic resin became rougher, to a greater or lesser extent, when subjected to mechanical brushing.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the tensile bond strength of dual curing luting resin cements to commercially pure titanium at 10 min and 24h after removal of the oxide layer.
One hundred and twenty titanium discs were obtained by casting and polishing with silicon carbide papers. The titanium discs were sandblasted with 50 microm aluminum oxide, ultrasonic cleaned and bonded in pairs with the resin-based cements Panavia F and Rely X ARC at 10 min and 24h after the sandblasting. The tensile test was performed with a crosshead speed of 0.5mm/min in an Instron Universal testing machine.
The Rely X ARC reached the highest tensile strength value at 24h after sandblasting (18.27 MPa), but there was no statistically significant difference between the two dual curing resin cements for both times tested. All specimens showed a mixture of cohesive fracture in the resin cement and adhesive failure. However, the predominant failure mode for Panavia F was cohesive in resin cement, and the Rely X ARC exhibited a greater proportion of specimens with adhesive failure between the alloy and resin luting cement at 10 min and 24h.
Both cements had, statistically, the same tensile bond strength. But in the fracture mode analysis, the adhesive predominant fracture mode of Rely X ARC cement indicates a premature clinical adhesive failure. On the other hand, the cohesive predominant fracture mode of Panavia F indicates a longer clinical adhesive bond with titanium.
[Show abstract][Hide abstract] ABSTRACT: Difficulty in cleaning resilient denture liners remains a material disadvantage. The purpose of the present study was to evaluate the effect of denture cleansers on hardness of resilient liner materials.
Three resilient liners, Luci Sof (Dentsply), Molloplast-B (Dentax), and Sofreliner (Tokuyama), and two denture cleansers, Efferdent (Warner-Lamber), and 0.5% alkaline hypochlorite preparation were used. Twenty specimens of each material were prepared, measuring 25X15X3mm. Two denture cleansing approaches were used: 1) alkaline hypochlorite, for 20 minutes; 2) alkaline peroxide, for 30 minutes. This procedure was repeated 8 times a day, during 90 days. The specimens were evaluated before and after 360 and 720 cycles, to simulate 1 and 2 years of clinical cleaning procedures, respectively. The Shore A hardness was evaluated in a durometer (Teclock GS-709A), with a penetrating load of 10N for 1 second. Any macroscopic changes, such as loss of color or alteration in surface texture were recorded by one observer. All numeric data were subject to ANOVA with repeated measures followed by Tukey's test (alpha= 0.05).
All materials were significantly different, independently to time and treatment. Initially, Luci Sof and Sofreliner immersed in either hypochlorite or peroxide increased the hardness mean values significantly. These hardness mean values decreased significantly after 720 cycles. Molloplast-B showed no significant difference after the treatments, in any time.
Denture cleansers had no effect on hardness of the resilient denture liners evaluated after 2 years of in vivo simulated conditions of hygiene. Sofreliner was the smoothest material before and after all treatments.
Journal of applied oral science: revista FOB 09/2006; 14(4):286-90. · 0.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soldering has been suggested to achieve acceptable fit of multi-unit fixed partial denture (FPD) frameworks of 3 or more elements. However, distortion of the entire framework may occur.
The purpose of this study was to evaluate marginal fit in 1-piece-casting FPD frameworks comparing 2 casting techniques: the conventional technique (CT) and the over-refractory technique (ORT). The techniques were evaluated on castings made from commercially pure titanium (CP Ti; Tritan), titanium-aluminum-vanadium (Ti-6Al-4V), and nickel-chromium (Ni-Cr; VeraBond II) alloys.
A metal master cast including 3 preparations was created to simulate a 5-unit FPD. The metal cast was duplicated in vinyl polysiloxane for fabrication of 60 working casts. For the CT, 0.7-mm-thick patterns were waxed on the casts using an electrical wax-dipping unit. Patterns were removed from the preparations before investing. For the ORT, the silicone impressions were poured with an investment material (Rematitan for CP Ti and Ti-6Al-4V, and Talladium for Ni-Cr). The patterns were waxed on the refractory casts, and the assembly was invested. Both CT and ORT (n = 10), CP Ti, and Ti-6Al-4V frameworks were cast using an arc-melting titanium vacuum-casting machine. The Ni-Cr frameworks were cast using an automated centrifugal-casting machine. The mean marginal discrepancies of the frameworks were measured at the mesial, distal, buccal, and lingual interfaces. Marginal gap measurements were recorded 3 times for each surface to the nearest 0.5 microm using a traveling microscope (x50). The data were analyzed with 2-way analysis of variance, followed by the Tukey HSD test (alpha=.05).
Marginal discrepancies for the ORT specimens (82.8 +/- 1.7 microm for CP Ti; 64.4 +/- 1.3 microm for Ti-6Al-4V; and 77.2 +/- 1.5 microm for Ni-Cr) were significantly lower than those obtained for the CT specimens (106.3 +/- 2.6 microm for CP Ti; 75.7 +/- 0.8 microm for Ti-6Al-4V; 101.9 +/- 1.7 microm for Ni-Cr) (P < .05). For both techniques, marginal discrepancies were significantly different among the alloys evaluated, presenting the following order from greatest to least marginal discrepancy: CP Ti, Ni-Cr alloy, and Ti-6Al-4V (P < .05).
The ORT for multi-unit FPD frameworks demonstrated significantly lower marginal discrepancies than the CT.
Journal of Prosthetic Dentistry 03/2006; 95(3):243-8. · 1.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study used infrared spectroscopy to compare the degree of conversion (DC) of Z250 resin composite at different depths, using a variety of light-curing sources. Photo-activation was performed with: plasma arc (PAC) light, a blue light emitting diode (LED) and four different exposure scenarios using quartz–tungsten–halogen (QTH) light. Cured composite cylinders were transversally cut into 300 μm-thick slices corresponding to surface, 1–5 mm depths. Each disc was finely pulverized, incorporated into KBr pellets, and analyzed by FTIR. Results demonstrated that for the surface and depths of 1 and 2 mm, conversion values did not differ significantly between lights or exposure treatments. At 3 and 4 mm depths, the LED source showed significantly higher DC than did the PAC light. All QTH methods were not significantly different to either LED or PAC. At 5 mm, there was no significant difference in DC between methods, except that PAC was not able to cure the composite.