Unum has acquired National Dental Plan (NDP) from Capita plc, for £31.7m.
The deal is still subject to regulatory approval.
Currently the group dental market is seeing growth of 14% year-on-year, according to figures from Unum.
Following the deal all staff of NDP will be retained, NDP currently provides cover for 150,000 employees in 500 schemes.
Peter O'Donnell, UK CEO of Unum, said: "NDP is a great business, providing market-leading dental insurance through the workplace, and we're proud to have it become part of Unum.
"We see NDP as complementary to our existing operations, and Unum will retain NDP's current management and employees.
"They are vital for implementing our strategic vision for NDP, as well as continuing to deliver NDP's great service to their existing 500 corporate customers and 150,000 insured employees."
"Dental insurance is a natural fit with our existing portfolio, as Unum looks to grow our employee benefits footprint, particularly in the health and wellbeing arena."
Andrew Bower MD of NDP said: "Unum's purchase of NDP creates tremendous potential to expand access to dental insurance through the worksite.
"We're excited by the opportunity to broaden the reach of our proposition, through access to Unum's strong distribution network and large customer base.
"This gives firm foundations for the continuity, growth and prosperity of this business."
"We're all adapting"
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