Merohedral twins revisited: quinary twins and beyond.

A twin is defined as being an external operation between two identical crystals that share a fraction of the atomic structure with no discontinuity from one crystal to the other. This includes merohedral twins, twins by reticular merohedry as well as coherent twins by contact where only the habit plane is shared by the two adjacent crystals (epitaxy). Interesting and original cases appear when the invariant substructure is built with positions belonging to the same {\bb Z}-module as, for example, the quinary twin structure first drawn by Albrecht Dürer [(1525).

Atomic clusters and atomic surfaces in icosahedral quasicrystals.

This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space.

Anterior fiber-reinforced composite resin bridge: a case report.

A variety of therapeutic modalities, from implants to conventional Maryland bridges, can be used for the replacement of a traumatically missing anterior tooth. The reinforcement of composite resins by fibers improves their fracture toughness and resistance. Fiber-reinforced composite (FRC) bridges can be a good alternative to conventional prosthetic techniques.