Fatigue resistance of composite resins and glass-ceramics on dentin and enamel.

STATEMENT OF PROBLEM: Composite resins and glass-ceramics are both used to restore worn teeth. Which restoration material is more durable is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the load to failure of thin composite resins and glass-ceramic restorations on enamel and dentin under increasing repetitive loads. MATERIAL AND METHODS: Glass-ceramic blocks (IPS e.max CAD; Ivoclar AG) were shaped into cylinders (Ø4.0×1.0 mm), crystallized, and adhesively luted to bovine dentin and enamel substrates that were embedded in polymethyl methacrylate (n=20). Identical direct composite resin restorations (Clearfil AP-X; Kuraray Noritake Dental Inc) were made and directly applied on the same substrates (n=20). All specimens were tested in a pneumatic device with a stainless steel ball that provided a stepwise increase of the load (N) starting at 250 N and increasing by 50 N after every 10 000 cycles to a maximum of 1150 N. Failures were detected by a displacement sensor and defined by chipping of restorative material or catastrophic failure. RESULTS: On dentin, composite resin showed a significantly higher fatigue resistance than glass-ceramic. On enamel, no significant difference was found between the 2 materials. CONCLUSIONS: When bonded to dentin, thin direct composite resin restorations were more durable than glass-ceramics. When bonded to enamel, no difference was found.

Observation of Mode-Locked Spatial Laser Solitons.

A stable nonlinear wave packet, self-localized in all three dimensions, is an intriguing and much sought after object in nonlinear science in general and in nonlinear photonics in particular. We report on the experimental observation of mode-locked spatial laser solitons in a vertical-cavity surface-emitting laser with frequency-selective feedback from an external cavity. These spontaneously emerging and long-term stable spatiotemporal structures have a pulse length shorter than the cavity round-trip time and may pave the way to completely independent cavity light bullets.

Dissipative Phase Solitons in Semiconductor Lasers.

We experimentally demonstrate the existence of nondispersive solitary waves associated with a 2π phase rotation in a strongly multimode ring semiconductor laser with coherent forcing. Similarly to Bloch domain walls, such structures host a chiral charge. The numerical simulations based on a set of effective Maxwell-Bloch equations support the experimental evidence that only one sign of chiral charge is stable, which strongly affects the motion of the phase solitons. Furthermore, the reduction of the model to a modified Ginzburg-Landau equation with forcing demonstrates the generality of these phenomena and exposes the impact of the lack of parity symmetry in propagative optical systems.

Class A mode-locked semiconductor ring laser.

We experimentally demonstrate low-repetition-rate mode-locked operation of a macroscopic semiconductor ring laser. Since antiphase periodic pulses are observed only when the two directions of operation are constrained to spatially overlap in the semiconductor medium, we interpret this regime as a result of coupling and competition between clockwise and counterclockwise emission directions. Because of its time constants and the possibility of unidirectional operation, the device could be highly suitable for the generation of temporal cavity solitons.