Allelopathic effects of exogenous phenylalanine: a comparison of four monocot species.

MAIN CONCLUSION: Exogenous phenylalanine stunted annual ryegrass but not switchgrass or winter grain rye, with deuterium incorporation up to 3% from phenyalanine-d 8 . Toxicity to duckweed varied with illumination intensity and glucose uptake. Isotopic labeling of biomolecules through biosynthesis from deuterated precursors has successfully been employed for both structural studies and metabolic analysis. Phenylalanine is the precursor of many products synthesized by plants, including the monolignols used for synthesis of lignin. Possible allelochemical effects of phenylalanine have not been reported, although its deamination product cinnamic acid is known to have deleterious effects on root elongation and growth of several plant species. The effects of phenylalanine and its deuterated analog phenylalanine-d 8 added to growth media were studied for annual ryegrass (Lolium multiflorum), winter grain rye (Secale cereale), and switchgrass (Panicum virgatum) cultivated under hydroponic conditions. Growth of annual ryegrass was inhibited by phenylalanine while switchgrass and rye were not significantly affected. Growth was less affected by deuterated phenylalanine-d 8 than by its protiated counterpart, which may be a typical deuterium kinetic isotope effect resulting in slower enzymatic reaction rates. Deuterium incorporation levels of 2-3% were achieved in biomass of switchgrass and annual ryegrass. Both protiated and deuterated phenylalanine were moderately toxic (IC25 values 0.6 and 0.8 mM, respectively) to duckweed (Lemna minor) grown using a 12 h diurnal cycle under photoautotrophic conditions. A significant increase in toxicity, greater for the deuterated form, was noted when duckweed was grown under higher intensity, full spectrum illumination with a metal halide lamp compared to fluorescent plant growth lamps emitting in the blue and red spectral regions. Supplementation with glucose increased toxicity of phenylalanine consistent with synergy between hexose and amino acid uptake that has been reported for duckweed.

A Retrospective, Radiographic Outcomes Assessment of 1960 Initial Posterior Root Canal Treatments Performed by Endodontists and Dentists.

INTRODUCTION: The Air Force Dental Service has established evidence-based treatment standards for endodontics, including 3-dimensional filling of the canal system, cuspal coverage restoration of endodontically treated posterior teeth, and use of rubber dam. The purpose of this retrospective study was to determine the effect of these standards on outcomes of initial posterior root canal treatments (RCTs) completed by Air Force (AF) and civilian dentists with and without accredited postgraduate training. METHODS: Treatment and follow-up radiographs of AF members who had an initial posterior RCT completed in 2011 were evaluated. A survey of all radiographs was performed to determine the (1) RCT obturation quality, (2) healing of periapical pathosis, and (3) presence and quality of cuspal coverage restorations. RESULTS: A total of 2262 RCTs were examined, with 1960 RCTs meeting inclusion criteria for at least 1 evaluation category. For RCT obturation quality, 1810 RCTs were evaluated, and 96.0% were considered adequate. For cuspal coverage restorations, 1856 RCTs were evaluated, and of these 2.7% were inadequately restored. Healing of periapical pathosis was 91.5% and 85.7% for AF and referred civilian providers, respectively. Survivability was 94.4% for endodontists, 95.3% for AF general dentists with additional training, 87.9% for AF general dentists without additional training, and 78.4% for civilian general dentists. Overall, survivability was 94.1% for a follow-up period ranging up to 47 months, with a mean of 27 months. CONCLUSIONS: In this retrospective, radiographic analysis, evidence-based practices as followed in the Air Force Dental Service and accredited postgraduate training resulted in improved treatment outcomes.