Second messengers: regulators of mechanically-induced tissue remodelling.

One of the most intriguing aspects of tissue reaction to mechanical forces such as in orthodontic tooth movement is the transduction of force into a meaningful cellular response. The behaviour of all eukaryotic cells is modulated by internal signalling systems which translate a wide array of external stimuli such as hormones or mechanical forces, into a very narrow range of internal signals (second messengers). Classically, the second messenger associated with mechanical force transduction is adenosine 3'5' cyclic monophosphate (cAMP); since it was virtually the only second messenger understood in any detail from 1960 to the late 1970s this is hardly surprising. A great deal more is now known about cell signalling mechanisms and for various reasons outlined in this review, the assumption that cyclic AMP is the sole messenger system in the transduction of mechanical forces is no longer tenable.