Bone inductive proteins to enhance postorthodontic stability

Abstract

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

Materials and methods: 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.

Results: 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.

Conclusion: 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.

Figure 1

(a) The appliance used: brackets on lower second incisors, pulled toward the midline using power chain and a closed coil spring. (b) Complete approximation of the incisors. (c) Retention using labial fixed wire, followed by DynaGraft II injection of the distal PDL of the lower left incisor. (d) Six week after removing the fixed retainer. Note the stability of the experimental tooth (left) and the complete relapse of the control tooth (right).

Figure 2

(a) and (b) The remodeling on the mesial socket wall of the experimental tooth (a) sheep 1 (b) sheep 2. (H&E, ×400).

Figure 3

(a) The widened PDS was reduced in dimension via new bone formation. Distal side of the experimental tooth (H&E, ×100). (b) New bone formation on the bony socket boundary. Distal side of the experimental tooth (H&E, ×100). (c) New bone formation within the PDS. Thin plates of newly formed bone parallel to the socket wall and surrounded by osteoblasts (arrows) (H&E, ×100).

Figure 4

(a) and (b) Formation of multiple bone spicules (arrows) throughout the periodontal space and at the apical region of the socket adjacent to the hypercementosed root apex (a: H&E, ×100, b: trichrome stain, ×100).

Figure 5

(a) A socket boundary consisting of newly formed bone protrusions at different magnifications (H&E, ×100). (b) Distal side of the experimental tooth; the arrows show the newly formed bone (H&E, ×400).

Figure 6

Fibroblast proliferation and depositional activity on the newly formed bone spicules and outlining areas of osteoid deposition. Distal side of the experimental tooth (H&E, ×400).

Figure 7

(a) A site of active remodeling in distal side of the experimental tooth showing new bone filling area of bone resorption (H&E, ×100). (b) Note the irregular and concave dark lines of previous resorption (arrows) and subsequent filling with new bone, also note the osteoblastic activity on the bone boundary (H&E, ×400). (c) Appositional activity at the alveolar crest of the interdental septum of the distal side of the experimental teeth (H&E, ×100). (d) Higher magnification of the remodeling lines and osteoblastic activity (H&E, ×400).

Figure 8

(a) The apical hypercementosis and its directivity to the distal side of the socket. Note the cellular proliferation adjacent to the apex (arrows) (trichrome stain, ×100). (b) Fusion between newly formed bone spicules (arrows) and the irregular hypercementosis on the root apex (H&E stain, ×100). (c) Actual fusion between the hypercementosed root apex and a large forming bone spicule (arrow) (trichrome, ×100).

Figure 9

(a) Resorption bays and osteoclast activity (arrows) on both of the PDL and endosteal surfaces of the socket wall. Distal side of the control tooth (H&E, ×200). (b) Distal side of control tooth revealing bone remodeling, PDL compression, and narrowing (H&E, ×100). (c) Higher magnification of inset 1, showing resorption bays and osteoclasts (arrows) on the socket wall (H&E, ×400).

Figure 10

Pattern of bone remodeling on the mesial side of control teeth. Note the organization of the PDL fibers and cells (H&E, ×100).