Clenching teeth and pressing tongue against roof of mouth This may sound similar to this question, but it's not the same.

This practice appears to be similar to the Khecari Mudra of Hindu yoga, but it's not the same, because the tongue need not be inserted into the nasal cavity. It is sufficient if it is pressed against the roof of the mouth.

This is based on the quote below from the Vitakkasanthana Sutta.

My questions are:


Since this appears in the Pali Canon, do contemporary Theravada teachers teach this?
How does it work? Does it stimulate certain nerves?
Is this considered a last resort to controlling the mind, or is it a regular part of Buddhist practice?



  "If evil, unskillful thoughts — imbued with desire, aversion or
  delusion — still arise in the monk while he is attending to the
  relaxing of thought-fabrication with regard to those thoughts, then —
  with his teeth clenched and his tongue pressed against the roof of his mouth — he should beat down, constrain, and crush his mind with
  his awareness. As — with his teeth clenched and his tongue pressed
  against the roof of his mouth — he is beating down, constraining, and
  crushing his mind with his awareness, those evil, unskillful thoughts
  are abandoned and subside. With their abandoning, he steadies his mind
  right within, settles it, unifies it, and concentrates it. Just as a
  strong man, seizing a weaker man by the head or the throat or the
  shoulders, would beat him down, constrain, and crush him; in the same
  way, if evil, unskillful thoughts — imbued with desire, aversion or
  delusion — still arise in the monk while he is attending to the
  relaxing of thought-fabrication with regard to those thoughts, then —
  with his teeth clenched and his tongue pressed against the roof of his
  mouth — he should beat down, constrain, and crush his mind with his
  awareness. As — with his teeth clenched and his tongue pressed against
  the roof of his mouth — he is beating down, constraining, and crushing
  his mind with his awareness, those evil, unskillful thoughts are
  abandoned and subside. With their abandoning, he steadies his mind
  right within, settles it, unifies it, and concentrates it.
In Mahayana, we take such things as expression devices - not literal instructions. In this case clenched teeth are a pointer to great effort, great application of willpower.

The objectives of samatha are to disidentify from the mind, to learn to control attention, to acquire concentration/willpower, to integrate the disjointed layers of psyche, and generally to attain a "tamed", "pliable" mind.

It is towards these that we apply the great effort. Especially when the inappropriate thoughts arise, and if other techniques did not work (such as switching attention to antidotes and other techniques described in that sutra), as a last resort, we apply the sheer willpower.