Importance of Ca2+ Modifications for Osseointegration of Smooth and Moderately Rough Anodized Titanium Implants - A Removal Torque and Histological Evaluation in Rabbit

Background: Incorporation of Ca2+ into the titania of anodized titanium surfaces has been found to enhance osseointegration. It provides a stable surface when the ions are incorporated into the oxide layer during the anodizing process. The Ca2+ may suggestively be prominent sites for mineral induction, attract proteins, and catalyze intracellular cascades. Purpose: The aim of the present study was to evaluate the osseointegration of smooth (Sa < 0.5 mu m) and moderately rough (Sa 1.02.0 mu m) commercially pure titanium implants, with and without Ca2+, in order to reflect on the importance of surface chemistry in relation to topography. Materials and Methods: Anodized implants with (OxCa) or without Ca2+ (Ox), blasted implants (Bl), and blasted anodized implants, with (BlOxCa) or without Ca2+ (BlOx), were inserted in rabbit femur and tibia. The implant surfaces were characterized using interferometry, scanning electron microscopy, and X-ray photoelectron spectroscopy prior to implant installation. Removal torque (RTQ) measurements were executed on all implants after a healing period of 12 weeks. The implants were, thereafter, removed en bloc with surrounding tissues and prepared for histological evaluations. Results: RTQ measurements of tibial implants revealed significantly higher values for BlOxCa implants (90.7 +/- 23.3 Ncm) compared to OxCa (64.6 +/- 18.2 Ncm) and BlOx implants (69.7 +/- 17.5 Ncm) (p = 0.029). Ca2+ modification of smooth implants placed in the femur did not reveal any differences. Conclusion: Ca2+ modification of smooth implants resulted in similar interfacial shear strength as moderately rough implants and Ca2+ modification of moderately rough implants demonstrated the significantly strongest interfacial shear strength when placed in rabbit tibia. This possibly demonstrated surface chemistry compensating for lesser roughness.