An Evaluation of the Effectiveness of Various Luting Cements on the Retention of Implant-Supported Metal Crowns.

Background and objective Cement-retained prostheses have replaced screw-retained prostheses as the preferred restoration in recent years in order to overcome the latter's limitations. In this study, four different luting cements were compared to evaluate their efficacy on the retention of cement-based metal crowns to implant abutments. Materials and methods In the right and left first molar regions, four implant analogs (Internal Hex, Adin Dental Implant Systems Ltd., Tel-Aviv, Israel) were screwed into epoxy resin casts (Araldite CY 230-1 IN, India) that were positioned perpendicular to the cast's plane. Four metal copings were created and cemented. Group A: polycarboxylate cement (DUR) (DurelonTM, 3M Espe, St. Paul, MN); Group B: PANAVIA™ F 2.0 dual-cure resin cement (Kuraray America, Inc., New York, NY); Group C: resin-modified glass ionomer (3M™ RelyX™ Luting, 3M Espe); and Group D: non-eugenol temporary resin cement (Kerr-Temp, KaVo Kerr, Brea, CA) were used to cement crowns. To check the retention capacity, samples were put through a pull-out test on an Instron universal testing machine (TSI­Tecsol, Bengaluru, India) with a crosshead speed of 0.5 mm/min. Each coping's de-cementing load was noted, and average values for every sample were computed and statistically analyzed. Results The findings demonstrated that non-eugenol temporary resin implant cement has the lowest retention value at 138.256 N, followed by resin-modified glass ionomer cement at 342.063 N, polycarboxylate luting cement at 531.362 N, and resin cement at 674.065 N. The average difference in retentive strength across all four groups was statistically very significant (p=0.001). Conclusion Based on our findings, non-eugenol temporary resin implant cement enables simple retrievability of the prosthesis in the event of a future failure and is appropriate for implant restorations with cement retention. Also, cements made of polycarboxylate and resin have the highest retention values.

Strategy for identification and characterization of small quantities of drug degradation products using LC and LC-MS: application to valsartan, a model drug.

The present study demonstrates the applicability of a strategy involving use of liquid chromatography (LC) and liquid chromatography-mass spectrometry (LC-MS) techniques for the identification and characterization of minute quantities of degradation products, without their isolation from the reaction matrix in pure form. Valsartan was used as a model drug. It was subjected to forced degradation studies under the International Conference on Harmonisation (ICH) prescribed conditions of hydrolysis (acid, base and neutral), photolysis, oxidation and thermal stress. The drug showed lability under acid/neutral hydrolytic and photolytic conditions, while it was stable to base hydrolytic, oxidative and thermal stress. Three small degradation products were formed, which were separated on a C-18 column using a gradient method. The same were characterized with the help of their fragmentation pattern and accurate masses obtained upon LC-MS/TOF analyses and online H/D exchange studies. The structures were supported by appropriate mechanistic explanation. The strategy involving use of LC and LC-MS for the identification and characterization of minute quantities of degradation products was applied on a model drug, valsartan. Three degradation products were successfully characterised without their isolation from the reaction matrix in pure form. The structures were supported by appropriate mechanistic explanation.

LC and LC-MS/TOF studies on stress degradation behaviour of candesartan cilexetil.

Stress degradation studies were conducted on candesartan cilexetil under the ICH prescribed conditions of hydrolysis (acidic, basic and neutral), photolysis, oxidation and thermal stress. Maximum degradation was observed on hydrolysis, especially in the neutral condition. The drug was also degraded significantly under photolytic conditions. However, it was stable to oxidative and thermal stress. A total of eight degradation products were formed, the separation of which was successfully achieved on a C-18 column employing a gradient method. In order to characterize each degradation product, a complete mass fragmentation pathway of the drug was initially established with the help of MS(n) and MS/TOF accurate mass studies. Subsequently, degradation products were also subjected to LC-MS/TOF investigations, which resulted in their fragmentation pattern and also accurate masses. The latter helped in the elucidation of the structure of all the degradation products, which was achieved through comparison of their fragmentation pattern with that of the drug. The major product was isolated and its structure was confirmed through NMR studies. On the whole, a more comprehensive fragmentation behaviour and degradation profile of the drug was established than reported in the literature.

The Med8 mediator subunit interacts with the Rpb4 subunit of RNA polymerase II and Ace2 transcriptional activator in Schizosaccharomyces pombe.

Several proteins are involved in separation of cells following division. However, their mutual interactions leading to cell separation is complex and not well understood. To explore the protein network that regulates this process at the transcriptional level in Schizosaccharomyces pombe, we have investigated the role of three proteins Med8, Rpb4 and Ace2. Using genetic and biochemical approaches we demonstrate that Ace2 binds Med8, which in turn interacts with Rpb4. We have delineated regions of Med8 and Rpb4 involved in their binding. We show that Med8 carboxyl-terminal region is necessary for its interaction with Rpb4 and can partially complement the sep15-598 mutant. Our results suggest that Med8 mediator subunit is involved in transmitting regulatory information from Ace2 to RNA polymerase II via Rpb4.

The fission yeast Rpb4 subunit of RNA polymerase II plays a specialized role in cell separation.

RNA polymerase II is a complex of 12 subunits, Rpb1 to Rpb12, whose specific roles are only partly understood. Rpb4 is essential in mammals and fission yeast, but not in budding yeast. To learn more about the roles of Rpb4, we expressed the rpb4 gene under the control of regulatable promoters of different strength in fission yeast. We demonstrate that below a critical level of transcription, Rpb4 affects cellular growth proportional to its expression levels: cells expressing lower levels of rpb4 grew slower compared to cells expressing higher levels. Lowered rpb4 expression did not affect cell survival under several stress conditions, but it caused specific defects in cell separation similar to sep mutants. Microarray analysis revealed that lowered rpb4 expression causes a global reduction in gene expression, but the transcript levels of a distinct subset of genes were particularly responsive to changes in rpb4 expression. These genes show some overlap with those regulated by the Sep1-Ace2 transcriptional cascade required for cell separation. Most notably, the gene expression signature of cells with lowered rpb4 expression was highly similar to those of mcs6, pmh1, sep10 and sep15 mutants. Mcs6 and Pmh1 encode orthologs of metazoan TFIIH-associated cyclin-dependent kinase (CDK)-activating kinase (Cdk7-cyclin H-Mat1), while Sep10 and Sep15 encode mediator components. Our results suggest that Rpb4, along with some other general transcription factors, plays a specialized role in a transcriptional pathway that controls the cell cycle-regulated transcription of a specific subset of genes involved in cell division.

Mapping the interaction site of Rpb4 and Rpb7 subunits of RNA polymerase II in Saccharomyces cerevisiae.

Rpb4 and Rpb7, the fourth and the seventh largest subunits of RNA polymerase II, form a heterodimer in Saccharomyces cerevisiae. To identify the site of interaction between these subunits, we constructed truncation mutants of both these proteins and carried out yeast two hybrid analysis. Deletions in the amino and carboxyl terminal domains of Rpb7 abolished its interaction with Rpb4. In comparison, deletion of up to 49 N-terminal amino acids of Rpb4 reduced its interaction with Rpb7. Complete abolishment of interaction between Rpb4 and Rpb7 occurred by truncation of 1-106, 1-142, 108-221, 172-221 or 198-221 amino acids of Rpb4. Use of the yeast two-hybrid analysis in conjunction with computational analysis of the recently reported crystal structure of Rpb4/Rpb7 sub-complex allowed us to identify regions previously not suspected to be involved in the functional interaction of these proteins. Taken together, our results have identified the regions that are involved in interaction between the Rpb4 and Rpb7 subunits of S. cerevisiae RNA polymerase II in vivo.