Comparison of the passivity between cast alloy and laser-welded titanium overdenture bars.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Paiva
Jose
J
Department of Prosthodontics, University of Alabama at Birmingham, Birmingham, AL 35294-0007, USA.
Givan
Daniel A
DA
Broome
James C
JC
Lemons
Jack E
JE
McCracken
Michael S
MS
D000497:Alloys; D003300:Copper / Q000737:chemistry; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry*; D015921:Dental Implants; D018772:Dental Marginal Adaptation / Q000592:standards*; D012994:Dental Soldering / Q000379:methods*; D003781:Denture Retention / Q000295:instrumentation*; D003828:Denture, Overlay; D055119:Elastic Modulus; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D010165:Palladium / Q000737:chemistry; D012834:Silver / Q000737:chemistry; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry*; D019415:Torque
D000497:Alloys; D003722:Dental Alloys; D003734:Dental Casting Investment; D015921:Dental Implants; D006047:Gold Alloys; C031462:titanium alloy (TiAl6V4); D012834:Silver; D010165:Palladium; D003300:Copper; D014025:Titanium