Effects of Surface Roughness on Mineralization; Ultrastructural Studies of Interface

Commercially available dental implants vary widely in their surface topographies, but share the goal of improving bone formation. Although, rough surfaces have been associated with enhanced osseointegration, few studies have followed the events taking place at the implant interface at the ultrastructural level. Objectives: to observe events occurring at the interface of implants varying in surface roughness in the course of mineralization in the percutaneous tissues of rats. Methods: epoxy replicas of machined, etched, blasted, titanium plasma-sprayed(TPS), sandblasted and etched(SLA), micromachined and smooth polished surfaces were coated with titanium. Surfaces produced by the replica and coating techniques have been characterized by x-ray photoelectron spectroscopy, scanning laser profilometry, and SEM. A total of 280 surfaces were implanted percutaneously over the parietal bone of 70 rats. Implants were removed between one and ten weeks, and processed for light, electron microscopy and immunohistochemical analysis. Results: initial phase of healing appeared similar among all surfaces, which showed accumulation of fibroblasts and myofibroblasts in a fibrin rich matrix. At two weeks, the collagenous matrix dominated the interface especially in implants with smoother surfaces. The thickness of collagen matrix continued to increase on smoother surface until mineralization occurred at 5 weeks. On the rougher surfaces, selective accumulation of macrophages was noted at two weeks, that persisted until mineralization occurred as early as three weeks. Macrophages were positively identified by immunohistochemical staining for ED1. The frequency of mineralization was highest on the micromachined, and SLA surfaces (P<0.05), followed by the TPS and machined surfaces while the etched and polished surfaces produced the lowest frequency of bone formation. Conclusions: mineralization on the rough surfaces appears to be dependent on the presence of macrophages at the interface, whereas on the smooth surface mineralization occurs following extensive collagenous matrix deposition. The timing and frequency of mineralization appear to be surface-dependent.