Effect of Recombinant Human Growth Hormone on Osseointegration of Titanium Implants: A Histologic and Biomechanical Study in Rabbits
To evaluate the action of recombinant human growth hormone (rhGH) on osseointegration of titanium implants in rabbits. Fourteen adult New Zealand rabbits, aged 30 weeks, were used in the study, and randomly divided into 2 groups. In each animal, 2 (2.2 mm × 6 mm) pure titanium implants were placed in the left tibia. In one group (test group), 1 IU (0.3 mg) of rhGH as a lyophilized powder was applied to each osteotomy site prior to implant placement. Only titanium implants were placed in osteotomy sites of the other group (control). Animals were humanely killed at 14 and 42 days after surgery, and samples were then prepared for histologic analysis and biomechanical test. The biomechanical test showed tensile pull-out stress values of 33.88 N/cm2 for controls and 59.26 N/cm2 for the rhGH group at 14 days and 25.99 N/cm2 and 29.69 N/cm2 for the control and the test group, respectively, at 42 days. Scanning electron microscope analysis showed more uniform and abundant bone tissue in contact with the implants for the test group at 14 days, and no differences between groups at 42 days. Furthermore, histologic analysis also showed accelerated bone repair in 14 days and a more advanced stage of bone remodeling for the rhGH-treated group when compared to controls after 42 days of repair. Such results show that the topical use of rhGH induces new bone formation in the early stages of bone repair and hence accelerates osseointegration of titanium dental implants.
Macroscopic view of 2 tibiae obtained from rabbits sacrificed at 14 days. Figure 1. Control group A. Figure 2. Recombinant human growth hormone (rhGH)-treated group B. Figures 3 and 4. Scanning electron microscopy at 14 days. Bright area corresponds to metal and the gray area to calcified tissue. Figure 3. rhGH-treated group. Figure 4. Control group.
Figures 5 and 6. Reflection light microscopy of peri-implant bone area around an rhGH-treated implant at 14 days (original magnification ×20). Figure 5. Bright field illumination. (A) Cortical reaction. (B) Newly formed lamellar bone. (C) Bone marrow and the arrow indicates Haversian canal. Figure 6. Dark field illumination. (A) Intimate bone-to-implant contact. (B) Endosteal bone formation. Figure 7. Bright field illumination of peri-implant bone area around a control implant at 14 days (original magnification ×20). Arrows indicate a boundary between immature newly formed bone in contact with the implant and lamellar bone.
Light microscopy at 42 days (bright field illumination in ×40 magnification). (A) Original bone. (B) Newly formed bone. Filled arrows indicate the boundary between original and newly formed bone, and hollow arrows indicate the Haversian system. Figure 8. rhGH-treated group. Peri-implant area showing mature newly formed bone with lamellar features. Figure 9. Control group. Peri-implant area showing maturing newly formed bone.
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