Glass Ionomer Versus Self-adhesive Cement and the Clinical Performance of Zirconia Coping/Press-on Porcelain Crowns.

OBJECTIVE: This split-mouth clinical study investigated the effect of luting cement on the performance of veneered yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) zirconia crowns. METHODS AND MATERIALS: A total of 60 crowns prepared with Y-TZP coping and press-on porcelain were made with a split-mouth design in 30 participants. The crowns were cemented either with glass ionomer cement (GIC) (Meron, Voco) or with self-adhesive resin cement (Bifix-SE, Voco). The restorations were assessed immediately after treatment and after 6, 12, 24, 36, and 48 months using the modified United States Public Health Service criteria. The parameters analyzed were retention, color stability, marginal discoloration, marginal adaptation, surface roughness, anatomic form, and secondary caries. The differences between the groups were analyzed by the Fisher exact test in each period of evaluation. The survival rate was analyzed with the Kaplan-Meier and log-rank test (α=0.05). RESULTS: After 48 months, 20 participants attended the recall. During the period of evaluation, 1 crown cemented with glass ionomer cement and 1 crown cemented with resin cement lost retention. Color match, marginal discoloration and adaptation, surface roughness, and anatomic form did not change in any of the periods evaluated, and no secondary caries was observed. No significant differences were found between the 2 luting cements for any of the clinical parameters analyzed, nor for the survival rates during the study. CONCLUSIONS: The type of cement did not influence the performance of the crowns after 48 months of clinical use. Both cements resulted in adequate retention rates, aesthetic and functional outcomes, and biological response.

Influence of dentin thickness on intrapulpal temperature under simulated pulpal pressure during Nd:YAG laser irradiation.

The aim of this study was to evaluate the effects of dentin thickness and pulpal pressure simulation (PPS) on the variation of intrapulpal temperature (∆T) when submitted to an adhesive technique using laser irradiation. Sixty sound human molars were sectioned and randomly divided into two groups (n = 30): group 1-1 mm of dentin thickness; group 2-2 mm of dentin thickness. Each group was divided into two subgroups (n = 15): subgroup A-absence of PPS; subgroup P-presence of PPS (15 cm H2O), sequentially treated with the following: 37 % phosphoric acid, adhesive system (Adper Single Bond), irradiation with Nd:YAG laser (1064 nm, 10 Hz, 60 s) using 60, 80, and 100 mJ/pulse energy parameters and light-curing (10 s). The ∆T was evaluated during the laser irradiation with a digital thermometer. Data were analyzed by three-way ANOVA and Tukey tests (p < 0.05). Three-way ANOVA revealed no significant differences for dentin thickness (p = 0.6512) on ∆T. PPS significantly reduced ∆T (p = 0.0001). The laser energy parameters (p = 0.0027) indicated that 100 mJ presented with significantly greater ∆T when compared to the groups irradiated with 80 and 60 mJ. Dentin thickness did not affect ∆T. The presence of PPS reduced the mean temperature values. The Nd:YAG laser energy parameters had a negative influence on the variation of temperature in the absence of PPS. In the presence of PPS, there was no risk to the pulp, since this study obtained temperature increases below 5.5 °C for all energy parameters, showing the technical viability for in vivo conditions.

Influence of Nd:YAG laser on intrapulpal temperature and bond strength of human dentin under simulated pulpal pressure.

The aim of this study was to evaluate the effects of simulated pulpal pressure (SPP) on the variation of intrapulpal temperature (ΔT) and microtensile bond strength (µTBS) to dentin submitted to an adhesive technique using laser irradiation. One hundred sound human molars were randomly divided into two groups (n = 50), according to the presence or absence of SPP (15 cm H2O). Each group was divided into five subgroups (n = 10) according to Nd:YAG laser energy (60, 80, 100, 120, 140 mJ/pulse). The samples were sequentially treated with the following: 37 % phosphoric acid, adhesive (Scotchbond Universal), irradiation with Nd:YAG laser (60 s), and light curing (10 s). ΔT was evaluated during laser irradiation using a type K thermocouple. Next, a composite resin block was build up onto the irradiated area. After 48 h, samples were submitted to microtensile test (10 kgf load cell, 0.5 mm/min). Data were analyzed by two-way ANOVA and Tukey tests (p = 0.05). ANOVA revealed significant differences for ΔT and TBS in the presence of SPP. For ΔT, the highest mean (14.3 ± 3.23 °C)(A) was observed in 140 mJ and without SPP. For µTBS, the highest mean (33.4 ± 4.15 MPa)(A) was observed in 140 mJ and without SPP. SPP significantly reduced both ΔT and µTBS during adhesive procedures, lower laser energy parameters resulted in smaller ΔT, and the laser parameters did not influence the µTBS values.

Relaxation in kinetic models on alternating linear chains.

A restricted dynamics, previously introduced in a kinetic model for relaxation phenomena in linear polymer chains, is used to study the dynamic critical exponent of one-dimensional Ising models. Both an alternating isotopic chain and an alternating-bond chain are considered. In contrast with what occurs for Glauber dynamics, in these two models the dynamic critical exponent turns out to be the same. The alternating isotopic chain with the restricted dynamics is shown to lead to Nagel scaling for temperatures above some critical value. Further support is given relating the Nagel scaling to the existence of multiple (simultaneous) relaxation processes, the dynamics apparently not playing the most important role in determining such scaling.

Synthesis, characterization, and comparative 32P-postlabeling efficiencies of 2,6-dimethylaniline-DNA adducts.

2,6-Dimethylaniline (2,6-diMeA) is a ubiquitous environmental pollutant that is used in industry as a synthetic intermediate. It is also found in tobacco smoke and as a major metabolite of lidocaine. Although the potential carcinogenicity of 2,6-diMeA in humans is presently uncertain, this aromatic amine has been classified as a rodent carcinogen. In addition, it is known to form hemoglobin adducts in humans, which indicates a profile of metabolic activation similar to that of typical arylamine carcinogens. Like other aromatic amines, 2,6-diMeA has been shown to yield N-(deoxyguanosin-8-yl)-2,6-dimethylaniline (dG-C8-2,6-diMeA) as a major DNA adduct in vitro. In this study, we show that 2,6-diMeA yields an unusual pattern of DNA adducts. In addition to dG-C8-2,6-diMeA, we have isolated two new adducts, 4-(deoxyguanosin-N(2)-yl)-2,6-dimethylaniline (dG-N(2)-2,6-diMeA) and 4-(deoxyguanosin-O(6)-yl)-2,6-dimethylaniline (dG-O(6)-2,6-diMeA), from the reaction of N-acetoxy-2,6-dimethylaniline with deoxyguanosine. A similar reaction conducted with deoxyadenosine yielded 4-(deoxyadenosin-N(6)-yl)-2,6-dimethylaniline (dA-N(6)-2,6-diMeA). All four adducts were detected in DNA reacted with N-acetoxy-2,6-dimethylaniline, with the relative yields being 46% for dA-N(6)-2,6-diMeA, 22% for dG-N(2)-2,6-diMeA, 20% for dG-O(6)-2,6-diMeA, and 12% for dG-C8-2,6-diMeA. This product profile contrasts markedly with the usual pattern of adducts obtained with aromatic amines, where C8-substituted deoxyguanosine products typically predominate. We further analyzed the kinetics of the T(4) polynucleotide kinase (PNK)-catalyzed phosphorylation of the C8 and N(2) deoxyguanosine 3'-phosphate adducts from 2,6-diMeA. The kinetic parameters obtained with these two structurally different adducts are compared to those determined with the parent nucleotide (dG3'p), and with (+/-)-anti-10-(deoxyguanosin-N(2)-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene 3'-phosphate, the major adduct derived from the environmental pollutant benzo[a]pyrene. The results indicate that all the adducts were labeled with lower efficiencies than dG3'p, stressing the likely underestimation of adduct levels in typical 32P-postlabeling protocols. Nonetheless, the N(2) adducts derived from 2,6-diMeA and benzo[a]pyrene were both labeled with higher efficiencies than the C8 adduct derived from 2,6-diMeA, with the benzo[a]pyrene adduct being the best substrate for PNK. Thus, the data suggest that N(2) adducts from dG3'p are intrinsically better substrates than their C8 analogues for PNK, and that bulkier aromatic fragments may favor the enzyme-substrate interaction during the labeling step.

Magnetic polarity fractions in magnetotactic bacterial populations near the geomagnetic equator.

The relative numbers of North-seeking and South-seeking polarity types in natural populations of magnetotactic bacteria were determined at sites on the coast of Brazil. These sites were South of the geomagnetic equator and had upward geomagnetic inclinations of 1-12 degrees . For upward inclinations >6 degrees , South-seeking cells predominated over North-seeking cells by more than a factor of 10. For upward inclinations <6 degrees , the fraction of North-seeking cells in the population increased with decreasing geomagnetic inclination, approaching 0.5 at the geomagnetic equator. We present a simple statistical model of a stochastic process that qualitatively accounts for the dynamics of the two polarity types in a magnetotactic bacterial population as a function of the geomagnetic field inclination.