Phase behaviors of colloidal analogs of bent-core liquid crystals.

Bent-core liquid crystal (LC) molecules are known to form mesophases with fascinating polar order and supramolecular chirality despite the achiral nature of the mesogens. The assembly of colloidal particles with geometrical similarity to bent-core molecular mesogens not only provides new insights into the physical behaviors of atoms or molecules but also leads to new materials with broad applications. Despite tremendous progress in colloidal synthesis and assembly, there has been a lack of colloidal model systems of bent-core molecular mesogens for LC property discovery and application development.

High modulus nanopowder reinforced dimethacrylate matrix composites for dental cement applications.

Results from the study of a novel, high modulus nanopowder filled resin composite are presented. This composite is developed to serve (1) as a high stiffness support to all-ceramic crowns and (2) as a means of joining independently fabricated crown core and veneer layers. Nanosized Al(2)O(3) (average particle size 47 nm) reinforcement provides stiffness across joins.

Materials design in the performance of all-ceramic crowns.

Results from a systematic study of damage in material structures representing the basic elements of dental crowns are reported. Tests are made on model flat-layer specimens fabricated from various dental ceramic combinations bonded to dentin-like polymer substrates, in bilayer (ceramic/polymer) and trilayer (ceramic/ceramic/polymer) configurations. The specimens are loaded at their top surfaces with spherical indenters, in simulation of occlusal function.

Scratch hardness and chipping of dental ceramics under different environments.

Objective: The goal of this program was to identify promising environments that could efficiently minimize machining-induced damage of dental materials.

Methods: Single point abrasion (SPA) scratch testing was used on five materials to determine the scratch hardness and amount of edge chipping as functions of chemical environment, including air, water, saline and glycerol solutions. Limited testing was also done under additional environments expected to promote chemomachining effects via crack growth promotion or debris removal.

Characterization of damage modes in dental ceramic bilayer structures.

Results of contact tests using spherical indenters on flat ceramic coating layers bonded to compliant substrates are reported for selected dental ceramics. Critical loads to produce various damage modes, cone cracking, and quasiplasticity at the top surfaces and radial cracking at the lower (inner) surfaces are measured as a function of ceramic-layer thickness. It is proposed that these damage modes, especially radial cracking, are directly relevant to the failure of all-ceramic dental crowns.