Characterising Dental Implant Surfaces by Topographical, Electrochemical, and Biomechanical Methods

Abstract: Replacement of extracted teeth by dental implants was first introduced in the 1950’s. From the beginning, threaded titanium implants with smooth surfaces were used. Later on, screw shaped implants with micro-scaled roughened surfaces were introduced showing bone ingrowth and improved in vivo and in vitro results and good long term stability. The rough surface induces both a larger area for mechanical interlocking and biomechanical stimulation at the micro level. Today most dental implants present on the commercial market are made of titanium or titanium alloys and have micro-scaled roughened surfaces. The unique properties of titanium implants have been attributed to the thin natural oxide film present on the surface, which interacts with the surrounding tissue and facilitates the healing process. In this thesis three studies were performed covering the fields of surface characterisation, biomechanics and electrochemistry. The overall goal is to design an implant surface that has faster and improved anchoring properties compared with commercial implants used today. In order to reach this goal, characterisation of the surface is of vital importance. In this respect, surface roughness parameters have been critically evaluated as a measure of the geometrical influence on the anchoring and a local model was developed where the mechanical properties of the implant-tissue interface were assumed to be the determining factor for success. The development of the Local model showed that the induced interfacial shear strength is dependent on the mean slope of the surface. Thus, a correlation between surface roughness parameters and in vivo performance is established. Such a relationship is beneficial for the development of new surfaces and could also minimize the need for animal studies. Further model developments are needed in order to take into account also the quality of the bone. Besides geometrical factors, physical (blasting) and chemical treatment (HF etching) were shown to influence the electric properties of the oxide film. Blasting introduces defects in the oxide and the conductivity increases compared to a turned surface. In the chemical treatment, fluoride ions are incorporated in the surface of TiO2. This results in lower surface stoichiometry and a higher number of charge carriers compared with the same surface without HF etching. The beneficial effects of HF treated surface, such as increased pull-out forces, can possibly be explained by the combined effect of increased conductivity and lower surface charge of the oxide due to incorporation of fluoride ions.