Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice.

We study an array of coupled optical cavities in the presence of two-photon driving and dissipation. The system displays a critical behavior similar to that of a quantum Ising model at finite temperature. Using the corner-space renormalization method, we compute the steady-state properties of finite lattices of varying size, both in one and two dimensions. From a finite-size scaling of the average of the photon number parity, we highlight the emergence of a critical point in regimes of small dissipations, belonging to the quantum Ising universality class. For increasing photon loss rates, a departure from this universal behavior signals the onset of a quantum critical regime, where classical fluctuations induced by losses compete with long-range quantum correlations.

Influence of adhesive techniques on fracture resistance of endodontically treated premolars with various residual wall thicknesses.

STATEMENT OF PROBLEM: The choice of restorative method is commonly based on the cavity configuration and the residual number of cavity walls. However, the residual wall thickness could be a valuable clinical parameter in the choice of restoration for endodontically treated teeth. PURPOSE: The fracture resistance of endodontically treated premolars was compared with different wall thicknesses restored with direct composite resin with and without cuspal coverage and with and without fiber post insertion. MATERIAL AND METHODS: This study included 104 intact human maxillary premolars extracted for periodontal or orthodontic reasons. Standardized mesio-occluso-distal cavities were prepared with different palatal wall thicknesses (1.5, 2, and 2.5 mm) and a buccal wall thickness of 2 mm. Teeth were restored with or without a fiber post and with or without cuspal coverage. Specimens were subjected to thermocycling (3000 cycles, 5 to 55°C) and embedded in polymerized acrylic resin. Teeth were submitted to cyclic fatigue followed by a static fatigue test with a universal testing machine; a compressive force was applied 30 degrees to the long axis of the teeth until fracture. The results were statistically analyzed by 3-way ANOVA (α=.05). RESULTS: Residual wall thickness (P=.004), the type of adhesive restoration (P<.001), and fiber post insertion (P<.001) significantly influenced the fracture resistance of endodontically treated premolars. CONCLUSIONS: In specimens with a cavity wall thickness >2 mm, direct intracuspal composite resin restorations supported by a fiber post achieved comparable fracture resistance. With a residual wall thickness <2 mm, only cuspal coverage with or without a fiber post provided satisfactory fracture resistance.

Is fracture resistance of endodontically treated mandibular molars restored with indirect onlay composite restorations influenced by fibre post insertion?

OBJECTIVES: The aim of this study was to investigate the influence of post placement on fracture resistance of endodontically treated mandibular molars restored with adhesive overlay restorations. METHODS: Endodontically treated human molars with two- and one-wall cavities either underwent or did not undergo fibre post insertion within composite build-up before cementation of indirect composite onlay restorations. The specimens were thermocycled, exposed to cyclic loading, and submitted to the static fracture resistance test. Fracture loads and mode of failure were evaluated. RESULTS: Statistical analysis revealed that specimens with fibre posts demonstrated similar failure loads (p=0.065) but more favourable fracture patterns compared with specimens without fibre posts. No difference was found between two- and one-wall cavities. CONCLUSIONS: Within the limitations of this study, the insertion of fibre posts did not improve support under indirect composite overlays. CLINICAL SIGNIFICANCE: When restoring heavily broken down endodontically treated mandibular molars with an indirect overlay composite restoration, the fibre post inserted within the composite build-up do not provide any increase in fracture resistance.

Fiber post adhesion to radicular dentin: The use of acid etching prior to a one-step self-etching adhesive.

The aim of this study was to evaluate the bond strength of fiber posts luted with a one-step self-etching adhesive with the push-out test after phosphoric acid conditioning of the root dentin. Thirty-six single-rooted teeth were endodontically treated. Teeth were sectioned perpendicularly to the cementoenamel junction, and a 10-mm post space was prepared with a calibrated bur. Specimens were then divided into three groups according to the adhesive protocol: A, total-etch three steps; B, self-etch one step; and C, 32% phosphoric acid conditioning and self-etch one step. Fiber posts were luted with self-curing resin-based cement. Teeth were cut in 1-mm slices and pushed until failure with an Instron machine. Results were statistically analyzed with the ANOVA and Bonferroni tests (P < .05). Two additional specimens from each group were examined under the scanning electron microscope (SEM). The 32% phosphoric acid significantly influenced the push-out bond strength of fiber posts luted with self-etch adhesives (P < .05). SEM analysis showed a continuous hybrid layer with resin tags and lateral branches in groups A and C, while group B showed smear layer dissolution with poor infiltration of the tubules.

The effect of the post length and cusp coverage on the cycling and static load of endodontically treated maxillary premolars.

In endodontically treated teeth, cuspal coverage plays a fundamental role in reducing the risk of fracture. However, the adhesive techniques with or without fiber post increased the possibilities in restoring root-filled teeth. The aim of this study was to determine the effect of the fiber post and/or post length and/or cuspal coverage on the fracture resistance of endodontically treated maxillary premolars. Seventy intact single-rooted maxillary premolars were selected and divided in seven groups of ten each: "intact teeth" (control), "inlay without fiber post" (G1), "inlay with long fiber post" (G2), "inlay with short fiber post" (G3), "onlay without fiber post" (G4), "onlay with long fiber post" (G5), and "onlay with short fiber post" (G6). Except for intact teeth, all specimens were prepared with a mesio-occluso-distal (MOD) cavity, endodontically treated and restored with or without long or short post, with or without cusp coverage. All specimens were thermal-cycled, exposed to a cyclic loading, and then submitted to the static fracture resistance test. Fracture loads and mode of failure were evaluated. A statistically significant difference in fracture resistance was found between group 1 and the other groups (p < 0.001). χ2 test showed statistically significant differences in the patterns of fractures between the groups (p < 0.001). The highest number of favorable fractures was observed in groups 3 and 4. Similar fracture resistance was detected in maxillary premolars endodontically treated with MOD cavity preparations, restored with either direct resin composite with fiber post or cusp capping. The "short post" direct restoration may be a valid alternative in the restoration of root-filled premolars.