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Andrea Cavalleri

Publications and source records attributed to Andrea Cavalleri.

6 recordsLinked to original sources
PubMed2006

Retention of restorations placed in noncarious cervical lesions after centric and eccentric occlusal loading in a chewing simulator--A pilot study.

PURPOSE: To evaluate in a pilot study whether (1) loading of restored teeth in a chewing simulator is an adequate method to reproduce clinical data about the retention rate of restorations placed in noncarious cervical lesions by means of the one-step self-etching adhesive system Prompt-L-Pop, and (2) whether eccentric loading contributes to the loss of Class V fillings. MATERIALS AND METHODS: In 12 extracted mandibular premolars with noncarious buccal cervical lesions of similar dimensions, restorations were placed without preparation using Prompt-L-Pop and Tetric Ceram. The adhesive was applied in one layer and cured at 650 mW/cm2 for 10 s, while the composite was placed in two increments and cured at 1200 mW/cm2 for 10 s. After storage in water at 37 degrees C for 7 days, the teeth were mounted in a chewing simulator that uses pneumatic cylinders as force actuators and subjected to a centric load of 50 N and 1,200,000 load cycles at a frequency of 1.6 Hz and simultaneously to 3125 thermocycles (5 degrees C/55 degrees C). The antagonists were standardized and made of Empress ceramic material. Every 100,000 load cycles, the fillings were evaluated with regard to retention. In the second phase, the same teeth were loaded on the lingual cusps with new antagonists for another 1,200,000 cycles. RESULTS: Neither during centric nor eccentric loading was any restoration loss observed. CONCLUSION: The short-term loading of extracted teeth with Class V fillings in a chewing simulator was inadequate to reproduce the data of clinical studies on the retention rate of a self-etching adhesive system. Obviously, long-term degradation mechanisms (eg, hydrolysis) acting on the composite/dentin interface play a more crucial role when it comes to the loss of retention of Class V restorations. Eccentric loading alone did not contribute to the loss of fillings, so that the theory--which maintains that this type of occlusal stress is a major cause for abfractions or the retention loss of restorations placed in abfraction lesions--may be questioned.

Aluminum Silicates↗
PubMed2005

Photoinduced phase transition in VO2 nanocrystals: ultrafast control of surface-plasmon resonance.

We study the ultrafast insulator-to-metal transition in nanoparticles of VO2, obtained by ion implantation and self-assembly in silica. The nonmagnetic, strongly correlated compound VO2 undergoes a reversible phase transition, which can be photoinduced on an ultrafast time scale. In the nanoparticles, prompt formation of the metallic state results in the appearance of surface-plasmon resonance. We achieve large, ultrafast enhancement of optical absorption in the near-infrared spectral region that encompasses the wavelength range for optical-fiber communications. One can further tailor the response of the nanoparticles by controlling their shape.

Journal Article↗
PubMed2005

Fluorescence microscopy for the evaluation of the margins of Class V restorations in vitro.

PURPOSE: First, to elucidate the cause of the appearance of "white lines" in Class V restorations as seen under the light microscope and their enhancement when using a fluorescent microscope (FM); second, to compare the results of the FM quantitative marginal analysis to those of the SEM quantitative marginal analysis. MATERIALS AND METHODS: Thirty-two standardized Class V fillings, with half of the preparation in dentin and half in enamel, were placed in 16 human caries-free premolars on the buccal and lingual surface using 4 adhesive systems (Clearfil SE, Syntac, 2 experimental self-etching adhesives) and the composite Tetric Ceram. All teeth were connected to a device containing horse serum to simulate dentinal fluid and subjected to thermomechanical loading (1,200,000 cycles at 49 N, 3000 cycles at 5 degrees C/55 degrees C). The restoration margins of 24 fillings were directly evaluated with FM--after the fabrication of replicas--and with SEM. Eight fillings were used to elucidate the cause of the fluorescent signal, by examining them with FM and different filters under dry and moist conditions, and also with dark field microscopy and CLSM. Further, two Class V fillings with the same composite but without the fluorescent substances were made and evaluated. Selected specimens were cut in the bucco-oral direction to analyze the restorative interface on section replicas with SEM. To detect differences between FM and SEM, the Wilcoxon test was performed (p < 0.05). To evaluate the degree of agreement between the two evaluation methods, a linear regression analysis was performed and the Spearman correlation coeffcient was calculated. RESULTS: The evaluation of Class V restorative margins by SEM, dark field microscopy, and CLSM revealed that the phenomenon seems to be an optical effect caused by the debonding of the composite from the underlying substrate creating another refractive environment when air penetrates into the gap. The effect depends on the geometry of the cavity design, the absence of moisture, and the use of a fluorescent composite material. The light source that produced the best visible results covered both ultraviolet and the blue part of white light (350 to 460 nm), producing light green lines and green areas. Those green or white areas as seen with the light microscope were related to gaps in the interface between tooth substance and composite. With the exception of one of the experimental self-etching adhesives, the mean percentage of continuous margin of the 4 groups showed no statistically signifcant dfference for the two test methods. Linear regression analysis revealed a good correlation between the two test methods for dentin margins and a moderate correlation for enamel margins. CONCLUSION: Fluorescence microscopy seems to be a useful tool for evaluating dentinal and enamel margins of Class V restorations in vitro.

Adhesives↗
PubMed2005

The marginal quality of luted ceramic inserts in bovine teeth and ceramic inlays in extracted molars after occlusal loading.

PURPOSE: To compare the marginal adaptation of adhesively luted ceramic inserts in standardized cylindrical cavities of bovine dentin and enamel with the marginal adaptation of adhesively luted ceramic inlays in extracted molars after mechanical loading, and to calculate the minimum sample size required to differentiate between material groups based on the findings of this investigation. MATERIALS AND METHODS: Ceramic inserts of similar dimension were luted in standardized cylindrical cavities of bovine dentin and enamel (n = 6, O = 4 mm) with seven different adhesive/resin cement systems (Syntac/Variolink, Prime & Bond NT/Variolink, Excite DSC/Variolink, AdheSE/Variolink, Excite DSC/Multilink, Multilink Primer/ Multilink, RelyX Unicem). The same materials were used to lute ceramic inlays (Empress II) in three-surface cavities of extracted human molars (n = 6 per group). All specimens were submitted to 2000 cycles of thermocycling. In addition, restored teeth were submitted to cyclic loading (640,000 cycles, 50 N) in a chewing simulator. Replicas after stressing were analyzed with SEM, and the percentage of continuous margin of the inserts and the inlays was calculated, differentiating the proximal part of the inlay into cervical dentin/enamel and axio-proximal enamel. The mean percentage values per material group of the insert and inlay groups were ranked using relative ranks. Sample size estimation was done for pooled standard deviations comparing between two and seven materials and assuming 20% or 10% of the mean of continuous margin to be statistically significant. RESULTS: The Spearman correlation coefficient between the variables "insert dentin" and "inlay cervical dentin" was 0.71 (p = 0.07), between "insert enamel" and "inlay axio-proximal enamel" 0.07 (p = 0.9). The variability of the test results was large for both the insert and inlay variables, especially at the resin-dentin interface. No statistically significant difference between the materials could be found for the insert method when ANOVA and Bonferroni post-hoc tests were applied (p > 0.05), while the inlays luted with Prime & Bond NT/Variolink showed significantly less continuous margin at the cervical dentin than all other groups with the exception of RelyX Unicem. At least 16 (63) inlays and 14 (57) inserts had to be used per group for differences of 20% (10%) of the mean of continuous margin. CONCLUSION: To evaluate luting agents with regard to their ability to reduce marginal discrepancies, the inlay model is inadequate due to high sample numbers which make the test time-consuming and expensive; furthermore its clinical relevance is uncertain. Alternatively, the insert method may be a suitable screening method for dentinal margins, although its clinical relevance is also unknown.

Analysis of Variance↗
PubMed2003

Femtosecond X-ray measurement of coherent lattice vibrations near the Lindemann stability limit.

The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10(-14) to 10(-12) s. Until recently, only optical techniques were capable of providing adequate time resolution, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-ray diffraction. However, the measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase, has to date remained obscure. Here we report time-resolved X-ray diffraction measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance-near the Lindemann limit-leads to a subsequent loss of long-range order, which is most probably due to melting of the material.

Journal Article↗