On Ca2+ incorporation and nanoporosity of titanium surfaces and the effect on implant performance

Sammanfattning: Introduction: Titanium implants are commonly used as replacements for missing teeth with successful long-term performance. The aim of the research performed in the field is to enable successful osseointegrated implant treatments for compromised as well as healthy bone beds, and to establish a rapid osseointegration to shorten the treatment period for the patients. In some cases bone resorption occurs around oral implants and the surrounding conditions may alter when surfaces aimed at being integrated in the bone are exposed to the extensive oral microbiota. Biofilms are most probably constantly present on exposed intraoral sur-faces but may during certain conditions be associated with pathological conditions in the surrounding tissues. Implant treatments depend on a stability through the osseointegration, as well as a sealing of oral mu-cosa for the defence against extensive biofilm accumulation. Aims: The present thesis has aimed at investigating the impact on os-seointegration of Ca2+ incorporation to anodized titanium surfaces for osseointegration, and whether Ca2+ incorporation would compensate for potential shortcomings of a minimal surface roughness. We have further aimed at investigating the adhesion of oral mucosa to nanoporous TiO2 surfaces clinically as well as histologically, and at evaluating the bacte-rial adhesion and biofilm formation on the test surfaces in vitro. Methods: The osseointegration of smooth (average height deviation <0.5 µm) and moderately rough (average height deviation 1-2 µm) Ca2+ incorporated anodically oxidized surfaces, minimally (average height deviation 0.5-1 µm) and moderately rough anodically oxidized surfaces, and minimally and moderately rough Al2O3 blasted surfaces, was inves-tigated with a rabbit model in two studies: one histological and one combined biomechanical and histological study. Oral mucosa adhesion to sol-gel derived, smooth nanoporous TiO2 coated and turned surfaces with similar microtopography was investigated in an experimental study in humans, where the samples were evaluated clinically and histologi-cally at three different levels of resolution. All histological sections were evaluated both quantitatively and qualitatively. To study bacterial adhe-sion and biofilm formation on the surfaces as well as the possibility to mechanically remove adhered bacteria with a smooth toothbrush with-out dentifrice, multi-species bacterial models (with or without the pres-ence of saliva) combining 16S rRNA fluorescence in situ hybridization and confocal laser scanning microscopy were used. Surface topography and chemistry was characterized using optical interferometry, scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Results: Smooth Ca2+ incorporated anodically oxidized implants had significantly more bone in contact compared to minimally rough anodic oxidized and blasted implants when placed in rabbit tibia. Moderately rough Ca2+ incorporated anodically oxidized implants had significantly higher removal torque compared to moderately rough anodically oxidi-zed and smooth Ca2+ incorporated anodically oxidized implants, and, at the same time, the removal torque of smooth Ca2+ incorporated anodi-cally oxidized implants did not significantly differ from that of moder-ately rough blasted or anodic oxidized surfaces when placed in rabbit tibia. Nanoporous TiO2 coated abutments had significantly more oral mucosa in contact with the surface as well as significantly less marginal bone resorption when only stable implants were evaluated compared to turned control surfaces. The clinical appearance was, furthermore, as-sumed to be advantageous for the nanoporous surfaces. Increasing the surface roughness led to larger biofilm biovolumes in vitro. At the same time, Ca2+ incorporation tended to decrease biofilm formation when compared to control surfaces. Nanoporosity or Ca2+ in-corporation did not seem to effect biofilm formation when compared to turned surfaces. Moderately rough blasted surfaces generally adhered largest biofilm biovolumes and presented the greatest amount of remain-ing bacteria after mechanical cleaning. Conclusions: Within the limits of the studies in the present thesis, Ca2+ incorporation may enhance osseointegration and compensate for mini-mal surface roughness in rabbit tibia. Nanoporosity may hold advanta-ges for oral mucosa adhesion; however, no clear conclusions can be drawn. Increased surface roughness may increase bacterial adhesion and biofilm biovolume in vitro, and moderately rough blasted surfaces were most difficult to clean from adhered bacteria.