Precision-milled simulated curved root canals in bovine dentine for the assessment of chemo-mechanical root canal preparation.

AIM: The aim was to develop a standardized curved root canal model in bovine dentine and to assess whether that natural substrate would behave differently from the resin in standard plastic training blocks when prepared chemo-mechanically. The impact of substrate microhardness on simulated canal transportation was considered. METHODOLOGY: High-precision computer numerical control (CNC) milling was used to recreate a simulated root canal from a resin training block (Endo Training Bloc J-Shape, size 15) in longitudinally sectioned, dis- and re-assembled bovine incisor roots. Optical overlays obtained from 10 resin blocks were used to identify an average canal and program the CNC milling apparatus accordingly. Resin and dentine microhardness were measured. Simulated root canals in resin training blocks and their bovine counterparts were then instrumented at 37°C using Reciproc R25 instruments (VDW) with water or 17% EDTA (n = 10). Open-access image processing software was used to superimpose and analyse pre- and postoperative images obtained with a digital microscope. Centering ratios were averaged to indicate canal transportation. The effects of substrate and irrigant on canal transportation were assessed by two-way anova. RESULTS: Superimposed images showed that resin blocks under investigation varied considerably in terms of simulated canal length and curvature, whilst the milled canals were highly similar. The microhardness of dentine was more than three times higher than that of the resin. Conversely, canal transportation was considerably greater in dentine compared to resin, and in dentine had a tendency to be increased by EDTA. There was a strong effect of substrate on canal transportation (p < .001), no overall effect of irrigant, and a marginally significant interaction between irrigant and substrate (p = .077). CONCLUSIONS: CNC milling allows to create standardized simulated curved root canals in bovine dentine. These models may be useful to test and compare materials and concepts of chemo-mechanical root canal instrumentation. Microhardness is a bulk feature that does not predict the response to chemo-mechanical instrumentation of a composite material such as dentine.

The Impact of Changing from First- to Fifth-Generation Nickel-Titanium Rotaries on Root-Filling Quality in a Clinical Undergraduate Course

In this retrospective study, it was investigated whether the use of a fifth-generation rotary system (ProTaper Next) resulted in improved radiological root filling quality compared to a first-generation counterpart (ProFile) in a controlled student course setting. Cases treated by fourth-year dental students in the 2020/21 academic year were collected and compared to those treated in 2019/20. Root canals in the former group were all instrumented using the ProTaper Next system, and the latter using the ProFile system. All other clinical parameters were similar between the two academic years, including the time of pre-clinical teaching, hands-on course hours, endodontic auxiliaries, and chemicals used for treatment. After excluding patients who were not available or refused to give their informed consent to this study (n = 20), and excluding teeth with missing or poor radiographs (n = 16), the fillings in 178 roots could be assessed by two calibrated observers blinded to the system that was used. The primary outcome was the radiographic quality of the root fillings according to the five-scale modified MOLANDER score. The secondary outcome was the number of separated rotary instruments by group. Both instrumenting systems resulted in a similar number of "excellent" root fillings (score I), 59 % in the ProTaper Next group and 60% in the ProFile group, with no statistically significant difference in outcome scores between groups (Probability > ChiSquare = 0.70). Furthermore, there was merely one separated instrument in the ProTaper Next group, and none in the ProFile group (Fisher's exact test, p = 1.00).

Activity of Fosfomycin- and Daptomycin-Containing Bone Cement on Selected Bacterial Species Being Associated with Orthopedic Infections.

The purpose of this study was to determine activity of fosfomycin/gentamicin and daptomycin/gentamicin-containing PMMA bone-cement against Staphylococcus aureus (MRSA, MSSA), Staphylococcus epidermidis, Enterococcus faecium (VRE), and E. coli (ESBL; only fosfomycin). Test specimens of the bone cement were formed and bacteria in two concentrations were added one time or repeatedly up to 96 h. All fosfomycin-containing cement killed ultimately all MSSA, Staphylococcus epidermidis, and E. coli within 24 h; growth of MRSA was suppressed up to 48 h. Activity of daptomycin-containing cement depended on the concentration; the highest concentrated bone cement used (1.5 g daptomycin/40 g of powder) was active against all one-time added bacteria. When bacteria were added repeatedly to fosfomycin-containing cement, growth was suppressed up to 96 h and that of MRSA and VRE only up to 24 h. The highest concentration of daptomycin suppressed the growth of repeated added bacteria up to 48 h (VRE) until 96 h (MSSA, MRSA). In conclusion, PMMA bone cement with 1.5 g of daptomycin and 0.5 g of gentamicin may be an alternative in treatment of periprosthetic infections caused by Gram-positive bacteria.