A disposable extension member for joining a dental handtool to a disposable, hollow, dental tip. The dental handtool includes a chuck for releasably retaining the extension member. The extension member has at least one fluid-tight passageway extending through its body for fluid flow from the dental handpiece to the dental tip. The extension member includes an adaptive releasable locking member having an internally threaded, cuplike end portion dimensioned for releasable threading engagement with the dental tip. The chuck provides easy and efficient clamping means to secure the extension member within the handtool.