Doxa (Sweden)

This chapter contains sections titled: Introduction Experimentals Results and discussion Conclusion

Since the introduction of the resin composites on the market marginal leakage causing secondary caries has been one of the major clinical topics. As the composites shrink during hardening they tend to develop a gap between the filling and the tooth, where bacteria can enter. This can be overcome by using bonding techniques, but bonding does not give complete success. An alternative to use shrinking composites could be the use of fully ceramic filling material based on biominerals that harden via a acid base reaction with water. The biomineral technology based on Ca-aluminate has been proven to yield a bond to living tissue and as such the filling material would naturally avoid marginal leakage without the use of any pre-treatment or extra bonding systems. In this paper the influence of thermo cycling on the marginal leakage of a restorative material based on biominerals is evaluated and compared to that of a resin composite.

To study the basic abrasive wear mechanisms of a new bioceramic dental restorative material scratch testing has been conducted. The material is a chemically bonded bioceramic with calcium aluminate as binder. It is intended to be used in small and medium sized posterior class I, II and V fillings. A spherical diamond tip scratched the surface under increasing load from 0 to 50 N. The scratch hardness was measured and the wear mechanisms were classified according to the scale suggested by Powers. For comparison a glass-ionomer cement and a polymer composite were also tested. The scratched surfaces were studied with light optical microscopy and scanning electron microcopy. The bioceramic material had a lower scratch hardness than that of the composite but higher than that of the glass-ionomer. Regarding the wear mechanisms, the bioceramic material showed a plastic deformation up to about 15 N and above cracking and flaking began. The composite material did not enter into a more severe wear until 35 N. The glass-ionomer cement was more unreliable and some samples broke completely already at low loads or showed extensive cracking.

The surface properties of materials are believed to control most of the biological reactions toward implanted materials. To study the surface structure, elemental distribution, and morphology, using transmission electron microscopy (TEM) techniques, thin foils of the surface (in cross-section) are needed. These have been cumbersome to produce, in particular, from the normally irregular screw-shaped metal implants. Focused ion beam (FIB) microscopy has been developed partly for TEM sample preparation, mainly within the microelectronics industry. Our study describes a method based on FIB for producing electron transparent foils/sections from a metal implant for TEM analysis. Using a screw-shaped titanium dental implant, it was demonstrated that thin foils can be prepared with submicron specificity and from almost any surface geometry. A comparison of different lift-out techniques showed that the in situ lift-out preparation technique allowed plasma cleaning and produced particularly good samples with excellent yield. The titanium oxide on the implant surface was analyzed using energy-filtered TEM (EFTEM) and high-resolution TEM (HRTEM) and the TiO(2) rutile phase being determined via the lattice parameters. This study provides the first set of data for the optimization of a new route for preparation and analysis of biomaterial surfaces and interfaces.

This chapter contains sections titled: Introduction Materials and Methods Results Discussion Conclusions Acknowledgments