Both players will be available for seven games that fall between England's winter tours to Sri Lanka and the West Indies.
Root went unsold in the lucrative Indian Premier League (IPL) auction in January and has played just 12 T20I matches since England's defeat by West Indies in the World T20I final in April 2016 due to a combination of his Test commitments and poor form.
Root urges beaten England to follow Buttler and Stokes's lead
By contrast, Buttler is one of most in demand players in the world in the short form of the game and is fresh from hitting his first Test century in England's third Test defeat to India.
Buttler starred for the Rajasthan Royals in the IPL this year and returns to Sydney Thunder after scoring 202 runs in six innings during last year's Big Bash.
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