A semi-empirical computational model for the inhibition of porcine cholesterol esterase.

Cholesterol esterase significantly contributes to cell membrane structure. It also facilitates transfer of cholesterol and phospholipids across membranes. Inhibition of this enzyme by a number of xenobiotics has been reported. This research sought to confirm if a widely used methacrylate monomer, bisphenol A dimethacrylate, inhibits porcine cholesterol esterase since this and other methacrylates are known to leach from various biomaterial preparations. A quantum mechanically developed computational chemistry model is presented. Specific chemical information linking potential mechanisms of cholesterol esterase inhibition to chemical structure is shown. Model chemical descriptors identified the importance of maximum oxygen valency and molecular shape/size to cholesterol esterase inhibition. A porcine cholesterol esterase inhibition mechanism is inherent in bisphenol A dimethacrylate which mimics chemical properties of reported cholesterol esterase inhibitors. This predictive semiempirical quantum mechanical model can be used to design new cholesterol esterase non-inhibitors for biocompatible biomaterials used in an aqueous environment.

An outbreak of acute respiratory disease caused by Mycoplasma pneumoniae and adenovirus at a federal service training academy: new implications from an old scenario.

Outbreaks of Mycoplasma pneumoniae and adenovirus have been reported in military institutions for several decades. During a recent outbreak in a federal service training academy, we performed an epidemiological and laboratory investigation to better characterize and control the outbreak. Of 586 students responding to a questionnaire, 317 (54%) reported having a respiratory illness during the outbreak period. Among 42 students who underwent complete laboratory testing, 24 (57%) had evidence of M. pneumoniae infection, 8 (19%) had evidence of adenovirus infection, and 4 (10%) had evidence of both. Polymerase chain reaction testing of oropharyngeal swabs revealed more acute M. pneumoniae infections (57% positive) than did serology or culture. Multivariate analysis revealed that visiting the campus health clinic >3 times for a nonrespiratory condition, such as injury, was a significant risk factor for illness among freshmen early in the course of the outbreak, whereas having an ill roommate was a risk factor throughout the duration of the outbreak.

Photoactivated dentin bonding with N-phenyliminodiacetic acid.

OBJECTIVES: The overall objective of this study was to correlate adhesive resin and polymerization initiator chemistry with bonding to dentin that had been treated with N-phenyliminodiacetic acid (PIDAA), a self-etching primer with initiator and co-initiator potential. The hypotheses to be tested were that: (1) the nature of the adhesive resin and (2) the type of polymerization initiator system are critical factors that can influence the bonding of composite restoratives to dentin. METHODS: Three types of bonding resins: (A) a non-carboxylic acid bonding resin (BisGMA/HEMA); (B) a carboxylic acid monomer (PMDM, the control); and (C) a combination system (BisGMA/HEMA/PMDM), along with two types of initiator systems: (1) a self-curing chemical initiator system based on PIDAA and (2) a dual-cure system involving camphorquinone, PIDAA, and visible light irradiation, were tested with a randomized 3 x 2 full factorial design. Solutions of each resin in acetone were tested with and without camphorquinone. Solution (A) was a 50% solution of 1:1 BisGMA/HEMA; Solution (B), a 10% solution of PMDM; and Solution (C), a 50% solution of 2:2:1 BisGMA/HEMA/PMDM in the ratio of 2:2:1. All percents were on a mass basis. (The photoactivated solutions of A, B, and C also contained 0.5% camphorquinone based on the mass of the resin.) Ninety composite-to-dentin specimens were prepared by a 2-step protocol: 1) 60 s application of 20 microL of 0.3 mol/L PIDAA in 1:1 v/v acetone/H2O; 2) 60 s application of 20 microL of one of the six resin solutions, followed by 60 s visible light irradiation. A visible light-activated composite (Silux, 3M) was then applied to each treated surface and irradiated for 60 s. Specimens were stored in distilled H2O (22 degrees C, 24 h) before shear bond testing. The summary statistics were calculated and a two-way ANOVA and Duncan's Multiple Range test were used to discern if the two factors significantly affected the mean shear bond strength. RESULTS: Mean shear bond strengths and standard deviations were obtained (with and without camphorquinone, respectively): (A), 11.0 MPa +/- 3.9 and 4.1 MPa +/- 4.9; (B), 27.0 MPa +/- 5.3 and 13.7 MPa +/- 5.6; (C), 18.3 MPa +/- 5.3 and 7.0 MPa +/- 5.2. The use of camphorquinone significantly enhanced the mean shear bond strengths obtained with the carboxylic, non-carboxylic and combination monomer based adhesive systems (p < 0.0001). For PIDAA-treated dentin, moderate shear bond strengths were obtained with a non-carboxylic acid resin solution containing camphorquinone. The addition of both PMDM and camphorquinone to this resin further improved the shear bond strengths. The highest mean shear bond strength was obtained with the combination of PMDM and camphorquinone (p < 0.05). SIGNIFICANCE: These results suggest that formulations based on PIDAA, PMDM and camphorquinone are more effective as bonding systems than those formulations without PMDM and camphorquinone. PIDAA, a self-etching primer with initiator and co-initiator abilities, appears to interact positively with both carboxylic acid monomers such as PMDM and the photooxidant camphorquinone.

N-phenyliminodiacetic acid as an etchant/primer for dentin bonding.

Effective composite-to-dentin bonding has been achieved by the sequential use of dilute aqueous nitric acid (HNO3) and acetone solutions of N-phenylglycine and a carboxylic acid monomer, e.g., p-PMDM. Both the HNO3 pre-treatment and the surface-initiated polymerization that results from reaction of infused N-phenylglycine and PMDM have been identified as key elements of this bonding system. In this study, N-phenyliminodiacetic acid, a unique imino acid derivative with acidic and chelating potential, was evaluated as a dual etchant/primer for dentin bonding. A randomized, 2(3) factorial design was used to study the effects of 3 factors on tensile bond strength (TBS): conditioner (HNO3 vs. no HNO3), primer (N-phenylglycine vs. N-phenyliminodiacetic acid), and primer solvent (acetone vs. acetone:H2O). The three-step protocol consisting of HNO3, N-phenylglycine in acetone, and PMDM in acetone served as the control. The hypothesis tested was that N-phenyliminodiacetic acid could act as both an effective conditioner (i.e., etchant) and as a primer. Two-step protocols that included only N-phenyliminodiacetic acid and PMDM were compared with the control. TBS (n = 10 per group) were determined after 24-hour storage in H2O and analyzed by ANOVA and Duncan's Multiple Range test. Primer solvent was critical for obtaining significant bonding to dentin when HNO3 was omitted. N-phenyliminodiacetic acid in acetone without prior HNO3 etching gave the lowest ranking mean TBS (95% CI, 3.8 +/- 1.9 MPa). In contrast, the mean TBS obtained from samples treated with N-phenyliminodiacetic acid in acetone:H2O without prior HNO3 etching was not statistically different (p > 0.05) from the mean TBS for the control (95% CI, 9.3 +/- 1.8 and 9.8 +/- 1.9 MPa, respectively). Due to its dual function as etchant and primer, N-phenyliminodiacetic acid in acetone:H2O provides for a simplified bonding technique that yields strong, PMDM-mediated adhesion to dentin.

Er:YAG laser ablation of enamel and dentin of human teeth: determination of ablation rates at various fluences and pulse repetition rates.

A pulsed Er:YAG laser (2.94 microns) was used to determine ablation depths per pulse of laser energy at 2 Hz and 5 Hz in human teeth cross sections of enamel and dentin. Ablation depths per pulse at 2 Hz in enamel of intact human teeth were measured and compared to ablation depths per pulse determined in enamel cross sections at 2 Hz. Close correlation was observed for ablation depths per pulse of laser energy between teeth cross sections and intact teeth for enamel. Photographs of lased holes at 2 Hz and 5 Hz indicated minimal thermal effects in enamel at fluences below 80 J/cm2. Minimal thermal effects in dentin were noted below 74 J/cm2. Scanning Electron Microscopy (SEM) pictures of lased dentin showed an irregular serrated surface. Results of this study suggest that the Er:YAG laser can effectively ablate enamel and dentin with minimal thermal effects at 2 Hz and 5 Hz.