Biomedical subjects

K Narva

Publications and source records attributed to K Narva.

3 recordsLinked to original sources

PubMed2003

Anterior Z250 resin composite restorations: one-year evaluation of clinical performance.

The purpose of this practice-based study was to compare the clinical performance of a new universal composite resin material (Z250) used for Class III and V cavities in anterior teeth. Restorative materials (Z250 and Z100; 3 M ESPE) placed by six operators were used for a total of 150 restorations during the 6-month enrollment period. After 1 year, 141 restorations (76 Z250 and 66 Z100) were available and evaluated for overall quality, color match, marginal adaptation, surface appearance and the presence of secondary caries, using modified USPHS criteria. The overall quality was excellent for both materials and no significant changes were noted during the follow-up. None of the scores between the two materials were statistically significant. Major changes were seen in color match and surface appearance. At baseline, the color match of 71% of Z250 and 62% of Z100 was rated as Alfa, after 1 year the figures were 60 and 65%. Regarding surface appearance, 97% of the Z250 were rated Alfa at baseline, whereas at 1 year the figure was 76%. For Z100, the scores were 94 and 79%, respectively. After 1 year, the clinical performance of Z250 restorative composite resin was clinically acceptable and similar to that of Z100.

Adult↗

PubMed2001

Insecticidal proteins from Bacillus thuringiensis protect corn from corn rootworms.

Field tests of corn co-expressing two new delta-endotoxins from Bacillus thuringiensis (Bt) have demonstrated protection from root damage by western corn rootworm (Diabrotica virgifera virgifera LeConte). The level of protection exceeds that provided by chemical insecticides. In the bacterium, these proteins form crystals during the sporulation phase of the growth cycle, are encoded by a single operon, and have molecular masses of 14 kDa and 44 kDa. Corn rootworm larvae fed on corn roots expressing the proteins showed histopathological symptoms in the midgut epithelium.

Animals↗

PubMedDate not supplied

Impact strength of a modified continuous glass fiber--poly(methyl methacrylate).

The effect of fiber reinforcement of autopolymerizing poly(methyl methacrylate) was investigated. The impact strength of continuous E-glass fiber-poly(methyl methacrylate) composite was determined. Rectangular test specimens (n = 10 per group) were modified by incorporating an additional fiber reinforcement of untreated E-glass fibers, silanized E-glass fibers, or aramid fibers in the test specimens. Controls were either unreinforced or reinforced from the middle of the test specimen only. The impact strength of the specimens was measured by using a charpy-type pendulum impact tester after the specimens had been stored in water at 37 degrees C for 4 weeks. After the impact strength test, the length of the delamination of poly(methyl methacrylate) from the fibers was measured and plotted to the impact strength of the test specimens by using a linear regression model. The impact strength of unreinforced autopolymerizing poly(methyl methacrylate) was 7.8 kl/m2, while incorporation of glass fiber reinforcement with a fiber concentration of 12.4 wt% increased the impact strength to 74.7 kl/m2 (P = .000). The additional fiber reinforcement of the test specimen did not affect the impact strength (P = .363). Delamination negatively correlated with the impact strength of the test specimens (r = -.72, P = .000). The results of this study suggest that glass fiber reinforcement enhanced the impact strength of autopolymerizing poly(methyl methacrylate), while the use of additional fiber reinforcement made of aramid or glass fibers in the test specimens did not have an effect on the impact strength.

Analysis of Variance↗