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The purpose of this study was to evaluate in vitro the shear bond strength to enamel, flexural strength, flexural modulus, and contraction stress of one orthodontic composite and two flowable composites. Orthodontic brackets were bonded to 45 human maxillary premolars with the composites Transbond XT, Filtek Z-350 flow and Opallis flow and tested for shear bond strength. For measurement of flexural strength and flexural modulus, specimens were fabricated and tested under flexion. For the contraction stress test, cylindrical specimens were tested and an extensometer determined the height of the specimens. The data were subjected to one-way ANOVA and Tukey's test (α=0.05). The shear bond strength values were significantly lower (p<0.05) for the flowable composites compared with the orthodontic composite. For the flexural strength, no statistically significant difference was found among the composites (p>0.05) while the flexural modulus was significantly higher (p<0.05) for Transbond XT than for Filtek Z-350 flow and Opallis flow. The orthodontic composite presented significantly lower contraction stress values than the flowable composites (p<0.05). The light-activated orthodontic composite material presented higher flexural modulus and shear bond strength and lower contraction stress than both flowable composites.

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Skeletal muscle regenerates following grafting, but little is known about protein synthesis and its regulation during regeneration. We determined the sequence of changes in protein synthesis in rat extensor digitorum longus (EDL) muscle by the measurement of phenylalanine (Phe) incorporation into muscle protein at various times after grafting. Compared with control EDL, Phe incorporation in grafts doubled in 1 day, was four- to eight-fold greater from days 2 to 10 after grafting, and then subsided. Tissue mass (wet weight) increased rapidly from days 7 to 20 in EDL grafts. The maximal increase in protein synthesis occurred 7-10 days after grafting, whether or not the nerve was left intact. Autoradiography indicated that incorporated radioactivity was associated with regenerating muscle fibers on day 10. Deficiencies of insulin, pituitary or testicular hormones, or chronic in vivo administration of insulin, growth hormone, testosterone, or tri-iodothyronine did not substantially alter the elevation in incorporation of the Phe into muscle protein 10 days after grafting. The breakdown of EDL protein, measured in vitro simultaneously with protein synthesis, was increased five-fold, and overall protein degradation was elevated six-fold 10 days after grafting. These findings indicate that Phe incorporation is rapidly elevated following grafting of the EDL, and that by days 7-10 reflects synthesis in regenerating muscle fibers. The increase in protein synthesis associated with muscle regeneration at this time appears to be independent of innervation and anabolic hormones.