Production of extracellular glucans, that are thought to play a key role in the development of the dental plaque because of their ability to adhere to smooth surfaces and mediate the aggregation of bacterial cells and food debris. [(1->6)-alpha-D-glucosyl](n) + sucrose = [(1->6)-alpha-D-glucosyl](n+1) + D-fructose GTF-I synthesizes water-insoluble glucans (alpha 1,3-linked glucose and some 1,6 linkages), GTF-S synthesizes water-soluble glucans (alpha 1,6-glucose). GTF-SI synthesizes both forms of glucans. Belongs to the glycosyl hydrolase 70 family.