Fracture Load and Phase Transformation of Monolithic Zirconia Crowns Submitted to Different Aging Protocols.

Monolithic zirconia crowns have many favorable properties and may potentially be used to solve dental problems such as chipping. However, monolithic zirconia crown resistance can be affected by its phase transformation when subjected to low temperatures, humidity, and stress. This study evaluated the fracture load and phase transformation of monolithic zirconia crowns submitted to different thermal and mechanical aging tests. Seventy monolithic zirconia crowns were randomly divided into the following five groups: control, no treatment; hydrothermal aging at 122°C, two bar for one hour; thermal fatigue, 104 cycles between 5°C and 55°C, dwell time, 30 seconds; and mechanical fatigue, 106 cycles with a load of 70 N, sliding of 1.5 mm at 1.4 Hz; and combination of mechanical plus thermal fatigue. Fracture load was measured with a universal testing machine. Surface changes and fracture mode and origin were examined with a scanning electron microscope. Monoclinic phase content was evaluated by x-ray diffraction. The fracture load was analyzed using one-way analysis of variance at a level of 5%, and Weibull distribution was performed. No statistically significant differences were observed in the mean fracture load and characteristic fracture load among the groups (p>0.05). The Weibull modulus ranged from 6.2 to 16.6. The failure mode was similar for all groups with the crack origin located at the contact point of the indenter. Phase transformation was shown at different surfaces of the crown in all groups (1.9% to 8.9%). In conclusion, monolithic zirconia crowns possess high fracture load, structural reliability, and low phase transformation.

Effect of antimicrobial agents incorporated into resilient denture relines on the Candida albicans biofilm.

OBJECTIVE: The antimicrobial action of five drugs incorporated in temporary denture relines on the fungal biofilm was evaluated. MATERIALS AND METHODS: A Candida albicans biofilm (SC5314) was formed on specimens (10 × 1 mm) of materials (Trusoft and Softone) modified or not (control) by the drugs (nystatin, miconazole, ketoconazole, itraconazole, and chlorhexidine diacetate). Cell viability was determined spectrophotometrically by the tetrazolium salt reduction assay (XTT) after 24 h, 48 h, and 7 and 14 days of incubation. The minimum inhibitory concentrations (MICs) were those which inhibited 90% or more of fungal growth. Fungal susceptibility was confirmed by confocal laser scanning microscopy analysis. RESULTS: The MICs of drugs incorporated in the materials were 0.032, 0.256, 0.128, 0.256, and 0.064 g ml(-1) for nystatin, miconazole, ketoconazole, itraconazole, and chlorhexidine, respectively. Images from nystatin, chlorhexidine, and ketoconazole demonstrated no viable cells. CONCLUSIONS: The antimicrobials incorporated in the resilient materials inhibited fungal growth during 14 days, with lower MICs for nystatin and chlorhexidine.

Salivary pellicle composition and multispecies biofilm developed on titanium nitrided by cold plasma.

OBJECTIVE: The aim of this study was to evaluate the composition of the salivary pellicle (SP) and multispecies biofilm developed on titanium nitrided by cold plasma. METHODS: Titanium discs were allocated into a control group (Ti) and an experimental group (TiN - titanium-nitrided by cold plasma). The disc surface topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The chemical composition of the disc surface was determined by X-ray photoelectron spectroscopy (XPS). Stimulated, clarified, and filtered saliva was used to form pellicles on the discs. Proteome analysis of the adsorbed SP proteins was performed by liquid chromatography-mass spectrometry (LC-MS). The surface free energy (SFE) was evaluated before and after SP formation. A multispecies biofilm composed of Actinomyces naeslundii, Streptococcus oralis, Streptococcus mutans, Fusobacterium nucleatum, Veillonella dispar, and Candida albicans was developed on the SP-coated discs. Viable microorganism counts were determined. The biomass and average thickness of biofilms were analyzed by confocal laser-scanning microscopy (CLSM) with COMSTAT software. The biofilm organization was visualized by SEM. RESULTS: The surface topography was similar in both groups. The SFE of the TiN group did not differ from that of the Ti group (p>0.05), although the adsorption of pellicle proteins increased the SFE in both pellicle-coated groups (p<0.001). Different proteins were identified on the Ti and TiN surfaces. The amount of biofilm was similar for both groups (p=0.416), but the counts of F. nucleatum and S. oralis were higher in the TiN group (p<0.001). Similar biofilms were characterized by the COMSTAT data, CLSM images, and SEM images. CONCLUSION: The titanium nitrided by cold plasma exhibited differences in SP composition and multispecies microbial biofilm population compared to the control titanium surface.

Effect of acidulated phosphate fluoride gel application time on enamel demineralization of deciduous and permanent teeth.

Although the effect of acidulated phosphate fluoride gel (APF gel) on caries reduction in permanent teeth is based on evidence, the relevance of the clinical application time is still under debate. Also, the effect of 4- versus 1-min application has not been evaluated in deciduous enamel. In a blind, crossover, in situ study of 14 days, 16 adult volunteers wore palatal appliances containing slabs of human permanent and deciduous enamel. At the beginning of each phase, the slabs were submitted to one of the following treatments: no APF application (negative control); APF gel (1.23% F) application for 1 or 4 min. Biofilm accumulation on the slab surface was allowed and the slabs were subjected eight times a day to 20% sucrose, simulating a high cariogenic challenge condition. On the 15th day of each phase, fluoride retained as CaF(2) and fluorapatite (FAp) was determined on the enamel of the slabs and demineralization was assessed by cross-sectional microhardness. Fluoride as CaF(2) and FAp, formed by APF gel application on the enamel slabs not subjected to the cariogenic challenge, was also determined. APF gel reduced demineralization in both enamel types (p < 0.05), but the difference between 1 and 4 min was not statistically significant (p > 0.05). CaF(2) and FAp formed and retained on deciduous and permanent enamel was significantly higher in APF gel groups (p < 0.05), but no significant difference was found between 1 and 4 min (p > 0.05). The findings suggest that 1 min of APF gel application provides a similar effect on inhibition of demineralization as 4 min, for both permanent and deciduous enamel.

Patients' satisfaction and functional assessment of existing complete dentures: correlation with objective masticatory function.

The aim of this study was to evaluate the correlation between patients' and dentist's assessment of dentures and to correlate these variables with objective measures of masticatory function. A sample of 28 edentulous individuals was selected, all wearing both complete dentures for at least 6 months and with no signs or symptoms of temporomandibular joint disorders. They rated their level of satisfaction with their dentures from 0 to 100 by means of a visual analogue scale, and dentures were scored by a dentist from 0 to 9 considering functional aspects. Tooth wear was evaluated on the posterior teeth of dentures considering the lack of occlusal anatomy. Masticatory performance and swallowing threshold tests were performed with an artificial test food (Optocal), and the median particle size was determined by the sieving method. The results showed that the mean satisfaction value of volunteers with their dentures was 49·1 and the median score of dentist's evaluation was 6. The Spearman correlation coefficient revealed no significant correlation between patients' and dentist's assessment of dentures (P>0·05). The median particle size for masticatory performance and swallowing thresholds was 5·5 ± 1·0 and 4·9 ± 1·2 mm, respectively. Data of both masticatory tests showed no significant correlation with patients' satisfaction or with dentist's evaluation of dentures. There was no difference of food comminution between subjects with and without excessive posterior tooth wear. It can be concluded that dentist's and patients' assessment of dentures were not correlated, and no correlation was observed between these variables and masticatory function.

Role of positive end-expiratory pressure changes on functional residual capacity in surfactant treated preterm infants.

Both surfactant replacement and positive end-expiratory pressure (PEEP) increase lung volume in infants with respiratory distress syndrome (RDS). We measured pulmonary mechanics and functional residual capacity (FRC) in 21 preterm infants with RDS, > 48 hr post-surfactant therapy (BW, 1,168 +/- 441 g; GA, 28.3 +/- 2.8 weeks; postnatal age, 3-7 days). A non-linear but significant increase in mean FRC was noted as PEEP increased from 2 to 5 cmH2O: 18.4 +/- 4.7 mL/kg at 2 cmH2O; 19.7 +/- 4.3 mL at 3 cmH2O; 22.6 +/- 5.5 ml/kg at 4 cmH2O; and 26.2 +/- 6.2 mL/kg at 5 cmH2O (P < 0.01). Because of the synergistic combined effect on lung volume, surfactant treated neonates should be weaned cautiously from PEEP during ventilatory management. Our study also suggests that the occurrence of inadvertent end-distending pressure during FRC measurement in the ventilated neonate lead to erroneous results.

Lysine-ketoglutarate reductase activity in developing maize endosperm.

Lysine-ketoglutarate reductase activity was detected and characterized in the developing endosperm of maize (Zea mays L.). The enzyme showed specificity for its substrates: lysine, alpha-ketoglutarate, and NADPH. Formation of the reaction product saccharopine was demonstrated. The pH optimum of the enzyme was close to 7, and the K(m) for lysine and alpha-ketoglutarate were 5.2 and 1.8 millimolar, respectively.

Glutamate synthase: a possible role in nitrogen metabolism of the developing maize endosperm.

Glutamate synthase activity was demonstrated in the developing endosperm of maize (Zea mays L.). The enzyme shows specificity for glutamine and alpha-ketoglutarate as amino donor and acceptor, respectively. Both NADH and NADPH function as electron donors although lower activities were often, but not always, obtained with NADPH. The apparent K(m) values for glutamine, alpha-ketoglutarate, and NADH were 1.35 mm, 0.57 mm, and 7 mum, respectively.The pattern of activity during endosperm development revealed a well defined peak coinciding with the period of most active N accumulation. Activity in general was related to the rates of accumulation throughout development. Maximum glutamate synthase activity was the order of 56 nmoles of glutamate formed per minute per endosperm compared with a rate of N accumulation of 9.5 nmoles per minute.It is suggested that glutamate synthase plays a key role in the N nutrition of the maize endosperm providing a means whereby N transported in the form of glutamine is made available for the synthesis of other seed protein amino acids via transaminase reactions. Transaminase activity involving glutamate, the product of the glutamate synthase reaction, was also demonstrated.