Meningeal dendritic cells drive neuropathic pain through elevation of the kynurenine metabolic pathway in mice

Neuropathic pain is one of the most important clinical consequences of injury to the somatosensory system. Nevertheless, the critical pathophysiological mechanisms involved in neuropathic pain development are poorly understood. In this study, we found that neuropathic pain is abrogated when the kynurenine metabolic pathway initiated by the enzyme indoleamine 2,3-dioxygenase (IDO1) is ablated pharmacologically or genetically. Mechanistically, it was found that IDO1-expressing dendritic cells (DCs) accumulated in the dorsal root leptomeninges and led to an increase in kynurenine levels in the spinal cord. In the spinal cord, kynurenine was metabolized by kynurenine-3-monooxygenase-expressing astrocytes into a pro-nociceptive metabolite 3-hydroxykynurenine. Ultimately, 3-hydroxyanthranilate 3,4-dioxygenase-derived quinolinic acid formed in the final step of the canonical KYNPATH was also involved in neuropathic pain development through the activation of the glutamatergic N-methyl-D-aspartate (NMDA) receptor. In conclusion, these data revealed a novel role for DCs driving neuropathic pain development through elevation of the kynurenine metabolic pathway. This novel paradigm offers potential new targets for drug development against this type of chronic pain.

Effect of resins sealing of dentin on the bond strength of ceramic restorations

OBJECTIVES

The purpose of this in vitro study was to evaluate shear bond strengths when ceramic cylinders were bonded to dentin following the use of different dentin adhesive systems as desensitizers.

METHODS

Freshly extracted human molars were selected. Their buccal dentin was exposed and a standardized circular area was isolated. Dentin desensitizers included an experimental self-curing 'one-bottle' adhesive system, two light-curing 'one-bottle' bonding systems and a conventional three component adhesive system, which was selected as a control system. Ten teeth were prepared for each test group (40 teeth total). A layer of an eugenol-free temporary cement was applied on the treated surface and the specimens were stored in distilled water for 1 week. After the removal of cement, the dentin surfaces were cleaned, re-etched and a layer of the experimental self-curing 'one-bottle' adhesive was applied. Standardized cylindrical ceramic samples were luted using a resin cement. One week later, shear bond strengths were determined using a universal testing machine. The bond strength values obtained were tested for a statistical significance with Kruskall-Wallis one-way analysis of variance. The type of failure occurring on each specimen was observed and recorded by means of an optical and a scanning electron microscope.

RESULTS

Mean shear bond strengths of the four groups ranged from 25.84 to 27.83 MPa and they were not significantly different. Most failures were cohesive in dentin.

SIGNIFICANCE

The use of an adhesive system as a dentin desensitizing agent before cementation does not alter the retentive strength of adhesively luted ceramic restorations.

In vivo bonding mechanism of an experimental dual-cure enamel-dentin bonding system

PURPOSE

To evaluate, in vivo, the formation of hybrid layer, resin tags and adhesive lateral branches, by an experimental dual-curing "one-bottle" enamel-dentin bonding system.

MATERIALS AND METHODS

The new dentin adhesive (Excite DSC) was tested in five Class V restorations placed in vital, periodontally compromised teeth. The experimental bonding system was used in combination with a flowable composite. After 1 wk the teeth were extracted and processed for SEM evaluation. All the samples were split-fractured along their long axis. Half of the samples were used to evaluate hybrid layer formation and the other half to examine the morphology of resin tags.

RESULTS

The experimental adhesive system showed a micromechanical bonding mechanism to conditioned dentin with formation of a hybrid layer, resin tags and adhesive lateral branches. SEM photomicrographs of the decalcified samples showed a high density of resin tags and uniform distribution along the cavity walls.