Abstract
Background and aims. In order to fabricate prostheses with high accuracy and durability, soldering techniques have
been introduced to clinical dentistry. However, these prostheses always fail at their solder joints. The purpose of this study
was to evaluate the effect of gap distance on the tensile strength of base metal solder joints.
Materials and methods. Based on ADA/ISO 9693 specifications for tensile test, 40 specimens were fabricated from a
Ni-Cr alloy and cut at the midpoint of 3-mm diameter bar and placed at desired positions by a specially designed device.
The specimens were divided into four groups of 10 samples according to the desired solder gap distance: Group1: 0.1mm;
Group2: 0.25mm; Group3: 0.5mm; and Group4: 0.75mm. After soldering, specimens were tested for tensile strength by a
universal testing machine at a cross-head speed of 0.5mm/min with a preload of 10N.
Results. The mean tensile strength values of the groups were 162, 307.8, 206.1 and 336.7 MPa, respectively. The group
with 0.75-mm gap had the highest and the group with 0.1-mm gap had the lowest tensile strength. Bonferroni test showed
that Group1 and Group4 had statistically different values (P=0.023), but the differences between other groups were not significant
at a significance level of 0.05.
Conclusion. There was no direct relationship between increasing soldering gap distance and tensile strength of the solder
joints.