Methods: Following local ethical committee approval 84 patients, with a total of 85 fractured post crowns, were recruited. The fractured posts were retrieved using trephans, ultrasonic vibration or a combination of these. The retrieved posts were subject to scanning electron microscopy and energy-dispersive X-ray analysis.
Results: 77% of the posts were cast and 23% wrought. Cast Posts - 64% were constructed from low-gold alloys with a varying amount of gold, silver, palladium and copper. Other alloys noted were silver-palladium (20%), high-content palladium (11%), medium gold (2%) and high-gold (3%). The modes of fracture were ductile (67%) or brittle (52%) with some posts exhibiting both within the same specimen. In addition there was evidence of porosity in 48% and fatigue in 20%.
Wrought Posts - 37% were iron-chromium-nickel (stainless steel), 26% were copper-zinc, 26% were titanium-aluminium alloy, 5% pure titanium and 5% cobalt-chromium-nickel. During removal, 11 of the 19 posts were badly damaged and the mode of failure was unable to be assessed. Of the remaining, ductile failure was noted in 5 and brittle failure in 3. All fracture surfaces of the titanium based posts were completely obliterated during removal. Brittle fracture occurred only in stainless steel posts, and in one case was found in association with fatigue.
Conclusions: A variety of cast and wrought post and core alloys were retrieved. The most commonly fractured post was constructed from low gold silver palladium alloy. Although fatigue may play a part in fracture of the posts, the most common mode of failure was noted to be ductile, with some evidence of brittle, fracture. Porosity was a relatively common finding in cast posts and may contribute to their fracture.