An In Vitro Study of Fluid Contaminations Influences on Reverse Torque Values of Implant-Abutment Connections.

Purpose: To examine the effects of fluid contamination on the reverse torque value (RTV) of abutment screws. 484 titanium fixtures were mounted into the stainless-steel holders. Methods: 11 groups (44 specimens in each group) of implants were mounted in acrylic resin. Ten groups of fixture screw holes were contaminated with chlorhexidine, saliva, blood, fluoride, or combination groups, and one group served as a control without contamination. To simulate the oral environment, samples were subjected to thermal cycling and cyclic loading. Results: The RTV means were less than the initial torque in both control and contamination groups. The maximum RTV mean was observed in the fluoride group (26.00 ± 1.02 Ncm). In other groups, this rate for control, blood, saliva, and chlorhexidine groups were 18.00 ± 1.78 Ncm, 22.12 ± 1.56 Ncm, 21.56 ± 1.43 Ncm, and 21.89 ± 1.02 Ncm, respectively. In combination groups, the maximum RTV mean was observed in the saliva+CHX group (23.89 ± 1.92 Ncm). In other combination groups, this rate for the blood+CHX, blood+saliva, saliva+fluoride, fluoride+CHX, and fluoride+blood groups were 22.56 ± 1.73 Ncm, 22.00 ± 1.54 Ncm, 20.11 ± 1.58 Ncm, 23.51 ± 1.19 Ncm, 21.02 ± 1.38 Ncm, and 20.11 ± 1.58 Ncm, respectively. The RTV was statistically significant (p < 0.05) for the contamination groups (except saliva) and combination groups compared to the control group. There is no statistically significant difference (p > 0.05) between the reverse torque value mean of the blood and saliva groups and between that of the fluoride and chlorhexidine groups. Conclusion: Implant-abutment specimens are suggested to be placed in a saliva environment and should be subjected to cyclic loading.

Adsorption of chromium(III) on lignin.

In order to assess the possibility of using lignin to remove Cr(III) from waters, the adsorption of Cr(III) on lignin isolated from black liquor, a waste product of the paper industry, was investigated. The influences of pH, lignin dosage, contact time, ionic strength, Cr(III) concentration and other metals were investigated. The Cr(III) adsorption was strongly dependent on pH and adsorbent dosage, but independent of ionic strength and other metal ions. The adsorption kinetic data can be described well with pseudo-second-order model and the equilibrium data can be well fitted using Langmuir two-surface model with a maximum adsorption capacity of 17.97 mg/g. Cr(III) adsorption on lignin was mainly through the ion-exchange mechanism and formed inner-sphere complexes with lignin. Successful application in removing Cr(III) was achieved by using a real wastewater sample. This study indicates that lignin has the potential to become an effective and economical adsorbent for the removal of Cr(III) from wastewaters.

Adsorption of metal ions on lignin.

This study investigated the adsorption of the heavy metal ions Pb(II), Cu(II), Cd(II), Zn(II), and Ni(II) on a lignin isolated from black liquor, a waste product of the paper industry. Lignin has affinity with metal ions in the following order: Pb(II)>Cu(II)>Cd(II)>Zn(II)>Ni(II). The adsorption kinetic data can be described well with a pseudosecond-order model and the equilibrium data can be fitted well to the Langmuir isotherm. Metal ion adsorption was strongly dependent on pH and ionic strength. Surface complexation modelling was performed to elucidate the adsorption mechanism involved. This shows that lignin surfaces contain two main types of acid sites attributed to carboxylic- and phenolic-type surface groups and the phenolic sites have a higher affinity for metal ions than the carboxylic sites.