Evaluation and comparison of the film thicknesses of six temporary cements before and after thermal cycling.

AIM: Temporary cement can be applied for both permanent and temporary cementation of implant-supported fixed restorations. These cements must have certain physical and mechanical properties. Specifically, the film thickness directly affects the cement's clinical success. The aim of this study was to evaluate and compare the film thicknesses of six temporary cements before and after thermal cycling. MATERIALS AND METHODS: Eighty-four metal copings with uniform holding loops were fabricated and divided into 12 groups of seven samples each. Six of these groups were subjected to a thermal cycling process. The copings were cemented to solid implant abutments (Implance Solid Abutment, 3.5-mm cervical diameter, 2 mm high, 6° taper, Implance Dental Implant System; AGS Medical, Trabzon, Turkey), using six different types of cement. The fitting surfaces were coated with the luting cements. After steeping in artificial saliva for 24 hours, the specimens were subjected to pull-out testing using an Instron machine. Specimens in the thermal cycling groups were subjected to 700 thermal cycles (36-55°C) prior to pull-out testing. RESULTS: The Mann-Whitney U test revealed significant differences between the retention values of the thermal cycling (+) and thermal cycling (-) groups (U = 153.0, P < 0.01). The retention values of the groups subjected to thermal cycling were significantly lower than those of the cements that were not subjected to thermal cycling. Thermal cycling also affected the film thickness significantly (Wilcoxon signed rank test, Z = -5.533, P < 0.001). CONCLUSIONS: Thermal cycling affects the film thickness and retention of temporary cements significantly. The retention value was significantly higher for glass ionomer cement than for the other cements tested, and this cement also exhibited greatest film thickness.

A new metabolic cell-wall labelling method reveals peptidoglycan in Chlamydia trachomatis.

Peptidoglycan (PG), an essential structure in the cell walls of the vast majority of bacteria, is critical for division and maintaining cell shape and hydrostatic pressure. Bacteria comprising the Chlamydiales were thought to be one of the few exceptions. Chlamydia harbour genes for PG biosynthesis and exhibit susceptibility to 'anti-PG' antibiotics, yet attempts to detect PG in any chlamydial species have proven unsuccessful (the 'chlamydial anomaly'). We used a novel approach to metabolically label chlamydial PG using d-amino acid dipeptide probes and click chemistry. Replicating Chlamydia trachomatis were labelled with these probes throughout their biphasic developmental life cycle, and the results of differential probe incorporation experiments conducted in the presence of ampicillin are consistent with the presence of chlamydial PG-modifying enzymes. These findings culminate 50 years of speculation and debate concerning the chlamydial anomaly and are the strongest evidence so far that chlamydial species possess functional PG.