Bone inductive proteins to enhance postorthodontic stability

To evaluate the use of bone morphogenetic proteins to enhance postorthodontic stability in sheep and to develop a biological method of postorthodontic retention.

First incisors were extracted in four mature and healthy sheep, and the second incisors were tipped reciprocally toward the midline and then retained. Dried bone matrix was injected into the distal periodontal space of the left second incisor. The right second incisor was left as a control. Both incisors were retained in the tipped position for 4 weeks. Then, the orthodontic appliance was removed and the teeth were left without retention. Six weeks later, the animals were killed and serial sections were prepared for histologic observation.

Unlike the control, the experimental second incisor maintained its tipped position with minimal relapse. On the distal periodontal space of the experimental tooth, areas of focal fusion between newly formed bone and newly formed areas of hypercementosis were observed. In the distal periodontal space of the control tooth, osteoclastic activity was observed along most of the socket wall, and the periodontal space appeared narrow and compressed. This brought the tooth close to the boundary of the alveolar bone, confirming the relapse observed on that side.

This study proposes a new method of retention in which a biologically safe osteoinductive material is used to retain the teeth via induction of points of approximation between the cementum and alveolar bone.