Comparison of two contemporary rotary systems in a pre-clinical student course setting.

AIM: To assess two contemporary rotary instrumenting systems subjectively and objectively in a pre-clinical student course setting. METHODOLOGY: Undergraduate dental students (n = 44) prepared mesiolingual canals of 3D-printed mandibular molar replicas (RepliDens, Zurich, Switzerland). The HyFlex and BioRace rotary systems, both previously unknown to the students, were used according to the manufacturers' guidelines after a short theoretical introduction. For comparison, a first-generation rotary system (ProFile .04), which the students knew from their previous education, was then used in a third RepliDens. Questionnaires were issued to note subjective experiences immediately after instrumentation. Objectively, time to instrument to size 40, .04 taper and shaping outcomes were analysed. Categorical data were compared using chi-square and Fisher's exact tests, numerical data according to goodness of fit to the normal distribution, P < 0.05. RESULTS: Subjectively, the students liked the file size and sequence designation in the BioRace system significantly (P < 0.05) better than in the HyFlex counterpart, whilst they found better controllability with the HyFlex (P < 0.05), and reported no difference in cutting efficiency. They preferred both systems to the ProFile. Objectively, canal transportation was significantly less with the HyFlex (and the ProFile) systems compared to BioRace (P < 0.05). Both systems under investigation were statistically similar in terms of file fractures (nil), length control, and instrumentation time, which was considerably faster than with the ProFile control system. CONCLUSIONS: HyFlex and BioRace had perceived and quantifiable strengths and weaknesses. Both systems were equally liked by the students and preferred over the ProFile first-generation rotary system.

Primary assessment of a self-adhesive gutta-percha material.

AIM: To evaluate a prototype gutta-percha material (Bio-Gutta), which is claimed to work without sealer because of its incorporated ultrafine bioactive glass particles, in terms of its induction of pH and calcium phosphate (CaP) precipitates, and its self-adhesiveness in root canals. METHODOLOGY: Bio-Gutta was compared with conventional gutta-percha (GP, composition: 70 wt% ZnO, 30 wt% polyisoprene). Test and control materials (N = 3) were immersed in phosphate-buffered saline (PBS) at 37 °C for 30 days. The pH in the solution was monitored. Apparent CaP formation was assessed using scanning electron microscopy (SEM). The root canals of 33 single-rooted teeth were filled by vertical compaction of heated Bio-Gutta, 33 control canals were filled with vertically compacted GP without sealer. Push-out bond strengths associated with the filling materials in root cross-sections from middle root thirds was determined 1, 8, and 30 days after root filling (N = 11 per group). These values were compared between groups using one-way anova (α < 0.05). RESULTS: Bio-Gutta induced a high pH in the PBS solution, which plateaued at values between 11.4 and 11.8. Apparent CaP crystals covered the Bio-Gutta material after 30 days of immersion in PBS, whilst no such structures were observed on GP. Both materials under investigation had similar initial push-out bond strength values (P > 0.05). The adherence of Bio-Gutta increased from day 1 to 8 and was significantly higher than that of conventional GP at 8 and 30 days (P < 0.05). CONCLUSIONS: The experimental gutta-percha material under investigation was alkaline and caused CaP precipitates on its surface. It improved its adherence to the root canal wall within 1 week.

Initial apical fit of K-files versus LightSpeed LSX instruments assessed by micro-computed tomography.

AIM: To compare the apical fit in two dimensions of the first K-file versus the first Lightspeed LSX instrument binding at working length after an initial crown-down preparation. METHODOLOGY: Twenty maxillary molars with fully developed roots and four separate root canals were selected. Canals were pre-flared with ProFile.04 taper instruments to three quarters of estimated working length. Working length was electronically determined using a size 06 K-file. Progressively larger K-files were inserted passively to working length. The first binding K-file was termed initial apical file (IAF). Then, the first binding LSX initial apical lightspeed-instrument (IAL) was determined. Teeth were scanned with and without instruments in place using micro-computed tomography. Cross-sections of the apical part of the root canals were analysed as follows: the largest and smallest diameters of the root canal and the diameter of the instrument were calculated and related to each other. Statistics were performed using Kruskal-Wallis test and Wilcoxon test. The alpha-type error was set at 0.05. RESULTS: Initial apical file sizes ranged from 8 to 30 and were lowest in second mesiobuccal and highest in palatal canals. IAL sizes ranged from size 20 to 40. The apical large canal diameter was assessed more accurately by the LSX instruments (P < 0.0001). However, the smallest available LSX instrument (i.e. size 20) did not reach working length in 39 of 80 canals. CONCLUSIONS: Instruments with a flat widened tip were found to determine apical cross-sectional diameter better than round, tapered instruments.

Apical fit of initial K-files in maxillary molars assessed by micro-computed tomography.

AIM: To two- and three-dimensionally assess the fit of the first K-file binding at working length after a crown-down canal procedure. METHODOLOGY: Twelve maxillary molars with fully developed roots and four separate root canals were selected. Canals were pre-flared using ProFile 0.04 instruments to three quarters of estimated working length (WL). WL was electronically determined using an ISO 06 K-file. Progressively larger K-files were inserted passively to WL. The first binding file was termed initial apical file (IAF). On micro-computed tomography (microCT) scans, cross-sectional areas of IAFs and canals and the largest and smallest root canal diameters were measured 1 mm from instrument tips. Volumes of the apical 2 mm of the instruments and corresponding root canal sections were calculated, and file binding was assessed. RESULTS: IAF sizes ranged from ISO-size 0.08-0.30 and were lowest in second mesiobuccal and highest in palatal canals. Files bound in the apical 2 mm in 96% of the canals. The mean canal area filled by the instruments 1 mm from the tip was below 40% in all canal types, the filled volume below 50% (anova, P > 0.05). The mean ratio (+/-SD) between largest and smallest canal diameter was 3.0 +/- 2.6 for first mesiobuccal, 3.3 +/- 2.6 for second mesiobuccal, 4.1 +/- 3.5 for distobuccal and 1.6 +/- 0.4 for palatal canals, indicating oval to flattened cross-sections. CONCLUSIONS: Two- and three-dimensional analysis of microCT scans revealed that whilst IAFs bound in the apical area, their fit was poor, because their shape does not correspond to maxillary molar canal anatomy.

Effect of sodium hypochlorite on human root dentine--mechanical, chemical and structural evaluation.

AIM: To investigate the mechanical, chemical and structural alterations of human root dentine following exposure to ascending sodium hypochlorite concentrations. METHODOLOGY: Three-point bending tests were carried out on standardized root dentine bars (n = 8 per group, sectioned from sound extracted human third molar teeth) to evaluate their flexural strength and modulus of elasticity after immersion in 5 mL of water (control), 1% NaOCl, 5% NaOCl or 9% NaOCl at 37 degrees C for 1 h. Additional dentine specimens were studied using microelemental analysis, light microscopy following bulk staining with basic fuchsin, and scanning electron microscopy (SEM). Numerical data were compared using one-way ANOVA. Bonferroni's correction was applied for multiple testing. RESULTS: Immersion in 1% NaOCl did not cause a significant drop in elastic modulus or flexural strength values in comparison to water, whilst immersion in 5% and 9% hypochlorite reduced these values by half (P < 0.05). Both, carbon and nitrogen contents of the specimens were significantly (P < 0.05) reduced by 5% and 9% NaOCl, whilst 1% NaOCl had no such effect. Exposure to 5% NaOCl rendered the superficial 80-100 mum of the intertubular dentine permeable to basic fuchsin. Three-dimensional SEM reconstructions of partly demineralized specimens showed NaOCl concentration-dependent matrix deterioration. Backscattered electron micrographs revealed that hypochlorite at any of the tested concentrations left the inorganic dentine components intact. CONCLUSIONS: The current data link the concentration-dependent hypochlorite effect on the mechanical dentine properties with the dissolution of organic dentine components.

Scanning electron microscope appearances of Lightspeed instruments used clinically: a pilot study.

The cutting heads of the first 18 instruments in six sets of clinically used Lightspeed instruments (sizes 20-65) were examined in a scanning electron microscope (SEM). Three sets had been used by full-time faculty and discarded as follows: instrument sizes 20-32.5 after 18 treated root canals; instrument sizes 35-47.5 after 36 treated root canals; and instrument sizes 50-65 after 54 treated root canals. Three other sets had been used by a private clinician who discarded all Lightspeed instruments after preparing 20 root canals. The cutting heads of the 108 instruments were examined for the presence of surface debris, metal strips, metal flash, disrupted cutting edges, microfractures, tears, pitting and fretting and fatigue cracks. Fewer instruments ultrasonically cleaned before examination in the SEM had debris than those not cleaned before examination. The prevalence of metal strips and metal flash was similar for both groups. In contrast, microfractures and tears were more prevalent in instruments used by the full-time faculty group, who used their instruments more frequently before discarding them. Pitting and fretting occurred equally frequently in both groups whilst no fatigue cracks were noted in any of the 108 instruments. Overusage of Lightspeed instruments may predispose the flutes of the cutting heads to microfractures and clinicians should be aware of this possibility.