Glucanohydrolases, especially mutanase [alpha-(1-->3) glucanase; EC 184.108.40.206] and dextranase [alpha-(1-->6) glucanase; EC 220.127.116.11], which are present in the biofilm known as dental plaque, may affect the synthesis and structure of glucans formed by glucosyltransferases (GTFs) from sucrose within dental plaque. We examined the production and the structure of glucans synthesized by GTFs B (synthesis of alpha-(1-->3)-linked glucans) or C [synthesis of alpha-(1-->6)- and alpha-(1-->3)-linked glucans] in the presence of mutanase and dextranase, alone or in combination, in solution phase and on saliva-coated hydroxyapatite beads (surface phase). The ability of Streptococcus sobrinus 6715 to adhere to the glucan, which was formed in the presence of the glucanohydrolases was also explored. The presence of mutanase and/or dextranase during the synthesis of glucans by GTF B and C altered the proportions of soluble to insoluble glucan. The presence of either dextranase or mutanase alone had a modest effect on total amount of glucan formed, especially in the surface phase; the glucanohydrolases in combination reduced the total amount of glucan. The amount of (1-->6)-linked glucan was reduced in presence of dextranase. In contrast, mutanase enhanced the formation of soluble glucan, and reduced the percentage of 3-linked glucose of GTF B and C glucans whereas dextranase was mostly without effect. Glucan formed in the presence of dextranase provided fewer binding sites for S. sobrinus; mutanase was devoid of any effect. We also noted that the GTFs bind to dextranase and mutanase. Glucanohydrolases, even in the presence of GTFs, influence glucan synthesis, linkage remodeling, and branching, which may have an impact on the formation, maturation, physical properties, and bacterial binding sites of the polysaccharide matrix in dental plaque. Our data have relevance for the formation of polysaccharide matrix of other biofilms.