Heat penetrates and kills tissue. Adeniums are mostly water. Keep a bit of rotted root and let it dry, you will be amazed at how little material is left.
Here are some answers from the yahoo adenium group---
Roger in Bankok--"Not entirely amiss but there are many ways to cauterize other than the medieval hot-poker approach. Every surgeon today does multiple cauterization every day to control bleeding with high-voltage electrical arc, or chemical cauterizers for larger areas.
For the rotted adenium, that has been thoroughly cleaned out, I believe a 3% H2O2 (Hydrogen peroxide) wash, followed by forced-air drying and a good heavy dusting with cinnamon, sulfer, Bordeaux powder, et al, would be a better approach.
Traditional styling of Bonsai often incorporates light to heavy use of blowtorch and I think that might also prove to be an interesting and artistic approach to this problem ... naysayers caveat: "blow torches" come in flame sizes down to less than 1 mm in diameter :-)"
Stick with the pharmacy 3% concentration, or else dilute the 6% hairdresser form. Avoid 35% food grade as it is simply too dangerous to work with outside a proper lab environment.
Blow dry with an ordinary fan as it breaks down to water, which of course re-encourages the rot.
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Maybe hold suggestions until you have had success. Melissa-the-grouch-today. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~