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ABSTRACT: The purpose of this study was to investigate the fit of cast alloy overdenture and laser-welded titanium-alloy bars by measuring induced strain upon tightening of the bars on a master cast as well as a function of screw tightening sequence.
Four implant analogs were secured into Type IV dental stone to simulate a mandibular edentulous patient cast, and two groups of four overdenture bars were fabricated. Group I was four cast alloy bars and Group II was four laser-welded titanium bars. The cast alloy bars included Au-Ag-Pd, Pd-Ag-Au, Au-Ag-Cu-Pd, and Ag-Pd-Cu-Au, while the laser-welded bars were all Ti-Al-V alloy. Bars were made from the same master cast, were torqued into place, and the total strain in the bars was measured through five strain gauges bonded to the bar between the implants. Each bar was placed and torqued 27 times to 30 Ncm per screw using three tightening sequences. Data were processed through a strain amplifier and analyzed by computer using StrainSmart software. Data were analyzed by ANOVA and Tukey's post hoc test.
Significant differences were found between alloy types. Laser-welded titanium bars tended to have lower strains than corresponding cast bars, although the Au-Ag-Pd bar was not significantly different. The magnitudes of total strain were the least when first tightening the ends of the bar.
The passivity of implant overdenture bars was evaluated using total strain of the bar when tightening. Selecting a high modulus of elasticity cast alloy or use of laser-welded bar design resulted in the lowest average strain magnitudes. While the effect of screw tightening sequence was minimal, tightening the distal ends first demonstrated the lowest strain, and hence the best passivity.
Journal of Prosthodontics 09/2009; 18(8):656-62. · 1.01 Impact Factor
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ABSTRACT: Multiple articles in the literature have used strain gauges to estimate the precision of fit of implant bars. However, the accuracy of these measurements has not been fully documented. The purpose of this study was to evaluate the response of strain gauges to known amounts of misfit in an implant bar. This is an important step in validation of this device.
A steel block was manufactured with five 4.0-mm externally hexed implant platforms machined into the block 7-mm apart. A 1.4-cm long gold alloy bar was cast to fit 2 of the platforms. Brass shims of varying thickness (150, 300, and 500 microm) were placed under one side of the bar to create misfit. A strain gage was used to record strain readings on top of the bar, one reading at first contact of the bar and one at maximum screw torque. Microgaps between the bar and the steel platforms were measured using a high-precision optical measuring device at 4 points around the platform. The experiment was repeated 3 times. Two-way analysis of variance and linear regression were used for statistical analyses.
Shim thickness had a significant effect on strain (P < 0.0001). There was a significant positive correlation between shim thickness and strain (R(2) = 0.93) for strain at maximum torque, and for strain measurements at first contact (R(2) = 0.91). Microgap measurements showed no correlation with increasing misfit.
Strain in the bar increased significantly with increasing levels of misfit. Strain measurements induced at maximum torque are not necessarily indicative of the maximum strains experienced by the bar. The presence or absence of a microgap between the bar and the platform is not necessarily indicative of passivity. These data suggest that microgap may not be clinically reliable as a measure of precision of fit.
Implant dentistry 05/2009; 18(2):151-61. · 1.51 Impact Factor
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ABSTRACT: To determine if etching technique influences the bond strength of resin cement to root canal dentin.
Fifty-five extracted teeth were endodontically treated, dowel space prepared, and divided into five groups. Each group was treated with different etchant consistencies: acid gel, semi-gel, low-viscosity gel, liquid, and a self-etching primer. After dowel cementation, four sections were removed from each root and a push-out test was performed.
Significant effects were found for etching procedure and for location within the root canal. The apical segment produced the lowest bond strength. Self-etching primer showed the highest bond strength.
The consistency of etchant material influenced the bond strength of a prefabricated dowel in the canal.
Journal of Prosthodontics 07/2008; 17(6):445-50. · 1.01 Impact Factor
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ABSTRACT: To measure and compare three-body wear and Vickers hardness at depths of 0 mm and 2 mm in two composite resin materials cured with either a low irradiance light emitting diode (LED) or a quartz tungsten halogen (QTH) light-curing unit (LCU) in which exposure duration with the LED was increased to deliver equivalent radiant exposure in the 450-490 nm wavelength range.
The VIP QTH and Freelight LED LCU's were obtained and the emission spectrum of each was determined using a Spectra Pro 750 spectrograph. Irradiance in the 450-490 nm range for each LCU was determined by calculating the area under the spectral curve. Curing of two composite resins (Z100 and Esthet-X) with equivalent radiant exposure within this prescribed wavelength range was achieved by increasing the irradiation time of the LED 33% from 30-40 seconds to compensate for its lower irradiance (Table 1). The resulting radiant exposure of 8.40 J/cm2 was roughly equivalent to the radiant exposure produced in 30 seconds by the QTH LCU (8.67 J/cm2). The cured specimens were polished with progressively fine wet silicon carbide papers to 600 grit and stored in distilled water at 37 degrees C for 24 hours prior to evaluating hardness and wear. Indentations for Vickers hardness testing were produced by applying a 0.5 kg load with a 15-second dwell time. Equivalent degree of cure was established indirectly through Vickers hardness numbers for the top and bottom surface of 2 mm thick disks of each material cured with each light (N = 3/group). Hardness ratios were computed by dividing mean bottom hardness by mean top hardness within each group. Three-body wear testing (N = 10/group) was performed on similarly fabricated specimens with a mechanical wear device using 44 microm unpolymerized PMMA beads as a simulated food bolus. The composite resin samples opposed spherical, stainless steel styli. A 75 N contact force was applied at 1.2 Hz for 100,000 cycles. Profilometry was used to quantify localized wear of the resin. Multivariate ANOVA and the Tukey-Kramer post hoc test (alpha = 0.05) were used to assess differences in hardness and wear of the materials.
With respect to hardness, no difference was noted between top and bottom specimen sides based on material or curing method. Specimens cured using the LED exhibited hardness ratios approaching unity. No significant difference in hardness was found for the main effect of light used, but the main effect of material was highly significant. This was primarily because Z100 cured with the LED demonstrated statistically higher hardness than the other three groups, which were statistically similar. No significant difference in wear was found based on the light used, with the lowest mean wear seen in Z100 cured with the LED. Overall, Z100 exhibited significantly greater surface hardness (P < 0.001) and significantly less wear (P < 0.01) compared to Esthet-X
American journal of dentistry 02/2006; 19(1):31-6. · 0.76 Impact Factor
