Optimization of Osteogenic Protein 1 for Dentinogenesis

Rutherford, R

Abstract

Insults to the dental pulp tissues, in the form of trauma, caries, tooth preparation, or bacterial leakage around restorative materials can result in several sequelae, including the formation of """"""""protective"""""""" reparative dentin, chronic inflammatory cell infiltrates within the pulp tissues with clinical symptoms, or frank pulpal necrosis. The latter two conditions may necessitate root canal therapy. Severe wear of the dentition, or loss of substantial tooth structure via repeated restorative procedures and/or caries may result in a tooth with a vital pulp that has insufficient remaining tooth structure to retain the planned restorative material. Consequently, estimates exist that between 20 and 30% of teeth requiring root canal therapy have vital pulps, the root canal therapy being required solely to provide enhanced retention of the restorative material by utilizing the anatomy of the root canal space. Genetically engineered materials may have the ability to promote dentin formation lateral to the root canal space, rather than at its expense, which could lead to a significant reduction in the numbers of teeth requiring root canal therapy nationally. OPs and bone morphogenetic proteins (BMPs) comprise a subgroup of the TGF-B superfamily; proteins from this family have demonstrated diverse biological activities, including differentiation, tissue morphogenesis, regeneration, and repair. Recombinant human OP-1, when complexed with an insoluble type I collagen matrix (CM), has been shown to be a potent stimulator of reparative dentinogenesis. Previous studies by the principal investigator in noncarious teeth of nonhuman primates has demonstrated that exposed pulp tissue responded to the use of 2.5 ug of OP-1 per mg of CM by fibroblastic and angiogenic invasion of the material, resulting in a mineralizing mass of new pulp tissue which formed in place of (and which replaced) the OP-1/CM. In addition, the reparative dentin was formed superficial to (rather than at the expense of) the existing pulp tissues, and the amount of reparative dentin formed was proportional to the total mass of the OP-1/CM placed on the exposed pulp. Finally, mineralization of the reparative dentin was 95% complete by 6 months. The OP-1/CM material apparently provides the potential to regenerate the dentin component of missing tooth structure, rather than replace it with restorative dental materials. However, all studies to date have focused on noncarious teeth with normal pulpal architecture and vitality.
The specific aims of this proposal are 1) to optimize conditions for inducing coronal pulpitis in baboon teeth; 2) to characterize the inflammatory response, and 3) to optimize the concentration of OP-1/unit mass of CM for induction of reparative dentinogenesis in radicular pulp tissue deep to inflamed coronal pulps.
Specific Aims 1 and 2: Pilot experiments will test the ability of different concentrations of LPS placed on exposed and amputated dental pulps to induce pulpitis.
Specific Aim 3 : Four animals will provide a total of 65 teeth for evaluation of the OP-1/CM response to """"""""infected"""""""" pulp tissues. Following the induction of pulpitis, the teeth will be reopened, the surgical site cleansed mechanically and rinsed with sterile saline, the access to the pulp chamber enlarged, and all coronal pulp tissue removed with dental rotary instruments. OP-1/CM concentrations of 2.5, 7.5, and 25 ug/mg will be placed over the exposed root tissues. Control groups include placement of 2.5 ug/mg OP-1/CM control in a """"""""sham infected"""""""" tooth, and placement of CM alone. All teeth will be restored with a glass ionomer base, varnish, and amalgam. Tissue samples will be collected after 4 weeks. Conventional histology (H&E, Masson's Trichrome, and von Kossa's), histomorphometry, and immunohistochemistry will be performed using prescribed techniques. All experimentation is expected to conclude within 6-7 months.