Effect of burn-out temperature on magnetic keepers in cast noble metal alloy posts.
BACKGROUND
Early loss of magnetic keepers in cast gold posts is seen in clinical practice.


OBJECTIVE
The purpose of this vitro study was to investigate the effect of burn-out temperature on the retention of magnetic keepers in cast gold alloy and on the thickness of the oxide layer at the keeper-alloy interface.


METHODS
One hundred and five keepers (Magfit EX) were cast with gold alloy (Protor 3) at 3 different burn-out temperatures: 500 degrees C, 600 degrees C, or 700 degrees C (n=35). To test for retention of keepers, 60 specimens (n=20) were tested to failure in tension mode in a universal testing machine (UTM); 45 specimens (n=15) were sectioned, and the interface was evaluated under a scanning electron microscope (SEM). Tensile force data were analyzed with 1-way ANOVA, and SEM data were analyzed with 1-way repeated measures ANOVA. Bonferroni multiple comparisons were performed for post hoc analysis (alpha=.05).


RESULTS
Retention of the keepers was significantly higher at lower burn-out temperatures (P<.001). The retention of the keepers became unpredictable and immediate failures were observed at a burn-out temperature of 700 degrees C. Oxide formation at the keeper-alloy interface was significantly less at lower burn-out temperatures (P<.001).


CONCLUSIONS
A burn-out temperature of 500 degrees C for casting the Magfit EX keeper with type IV high-strength gold alloy is recommended.
Pow
Edmond H N
EH
Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China. ehnpow@hkusua.hku.hk
Chan
Kingsley H C
KH
Luk
Henry W K
HW
Dias
Andrew P L H
AP
McMillan
Anne S
AS
D002133:Calcium Sulfate; D003722:Dental Alloys; D003734:Dental Casting Investment; D003735:Dental Casting Technique; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003781:Denture Retention / Q000295:instrumentation*; D003828:Denture, Overlay; D006047:Gold Alloys / Q000737:chemistry; D006358:Hot Temperature; D008280:Magnetics / Q000295:instrumentation*; D010087:Oxides; D011176:Post and Core Technique; D013193:Stainless Steel; D013718:Tensile Strength
D003722:Dental Alloys; D003734:Dental Casting Investment; D006047:Gold Alloys; D010087:Oxides; D013193:Stainless Steel; D002133:Calcium Sulfate