bind "?" "detdispenser"

Dispensers are able to be detonated and will kill enemies close by... as for sentries and teleports, they're probably separate binds.

Opened "tfc.dll" in Notepad++ and found:

detsentry
detentryteleporter
detexitteleporter
detdispenser
detdispensor

Loosely related to this, det commands for the demoman:

detstart (Sets a detpack if you have one. Parameter is time in seconds. Default=20, min=5, max=50.)
+det5 (Sets a detpack with 5s timer. Binds starting with a "+" exchange it with a "-" upon key release. Example: bind , +det5 ; bind . +det20 ; bind / +det50 ; )
+det20
+det50
detpipe (Detonates green-yellow pipes.)
detstop / -det5 / -det20 / -det50 (Aborts setting a detpack.)

Huge thanks pizzahut, I've got everything running perfectly now. Really weird that detonation is four separate commands when building and dismantling are each a single command with four arguments.

I checked that file you mentioned and on the same line found a pair of standalone build commands for the sentry and dispenser that don't seem to work. Probably replaced by the unified build command at some point during development, likely before teleporters were added given the lack of commands for those. I also found the sentry rotation commands so now I've got everything I need to avoid that clunky-ass command menu entirely.

Originally posted by Spiteful_Guru:

I checked that file you mentioned and on the same line found a pair of standalone build commands for the sentry and dispenser that don't seem to work.

building_dispenser, building_sentrygun, building_sentrygun_base, building_teleporter
These are internal names (entity class names) for the structures. (Though "building_dispenser" also appears in console or log file if someone is killed by it.)
Plugins can use these names to deal with buildings.