Farnaz Fattahi, Assistant professor, Department of Prosthodontics, Faculty of Dentistry, Shiraz University of Medical Sciences
Milad Motamedi, Postgraduate student, Department of Prosthodontics, Faculty of Dentistry, Shiraz University of Medical Sciences*
Introduction: 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. Specimens were tested with the gap distances of 0.1 mm, 0.25 mm, 0.5 mm and 0.75mm.
Methods and Materials: According to ADA/ ISO 9693 specifications for tensile test, specimens were fabricated and cut at the midpoint and placed at desired positions by a specific designed device.Specimens were divided into four groups according to the 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 Universal testing machine by the speed of 0.5mm/min with a preload of 10N. Specimens were investigated after the test for defects, voids and location of the failure. Cross sections were observed by a stereomicroscope with the magnification scale of 40X.
Results: The mean tensile strength for groups was 162, 307.8, 206.1 and 336.7 MPa respectively. The group with 0.75mm gap had the highest and the group with 0.1mm gap had the lowest tensile strength. Group1 and Group4 had statistically different values (p-value=0.023), which means solder joints with the gap distance of 0.75mm had more tensile strength than those with 0.1mm gap distance. But the difference between other groups was not significant.
Conclusions: There was no consistent relationship between increasing soldering gap distance and tensile strength of the solder joints. Solders with 0.1mm gap distance were the weakest joints, whereas specimens with 0.75mm gap distance were the strongest joints tested in this study, and their difference was statistically significant. No other significant relationship was found in this study. All the specimens were fractured at the solder joint space. Porosities and voids were found in specimens could be attributed to flux entrapment or solder inability to flow in gap space.Keywords: Solder, Base metal, Tensile strength*Corresponding author: Dr Milad Motamedi, Department of Prosthodontics, Faculty of Dentistry, Shiraz University of Medical Sciences, phone number:09171131793 email: email@example.com