Ex vivo shaping ability of reciprocating instruments operated by new users: Reciproc versus WaveOne.

OBJECTIVES: To compare two reciprocating NiTi systems operated by novices for use in curved root canals. METHODS: Fifty mesial roots of extracted mandibular first molars, with 2-2 canal configuration, were scanned with micro-CT and divided into 2 groups according to canal length and curvature: Reciproc and WaveOne. Each system was used to prepare one of the two canals by fourth-year dental students, who were new to reciprocating files and were blinded to the system being used. After another scanning, the pre- and post-instrumentation images were compared 3-dimensionally in software. RESULTS: Some 43 to 46% of the canal wall area remained un-instrumented. Significantly higher proportions of canals were transported towards the isthmus or furcation aspect than the mesial or external aspect. Mean transported distance was the greatest in the coronal one-third. Remaining dentine wall was the thinnest at the furcal aspect near the middle root region. No significant difference was noted between the two brands in the parameters examined. CONCLUSIONS: Both brands of reciprocating file left similar amounts of un-instrumented canal wall, and resulted in similar extent of canal transportation. CLINICAL RELEVANCE: NiTi reciprocating files can safely be used by new users to prepare curved root canals into a predictable shape.

Three-dimensional morphologic classifications and analysis of canal isthmuses in permanent molars.

PURPOSE: To investigate the three-dimensional morphology of isthmuses in molars according to their boundary characteristics using micro-computed tomography (micro-CT). METHODS: Micro-CT reconstructed images of 248 molars were evaluated. Isthmuses were classified into four types based on the boundary characteristics: isthmus with roof, isthmus with floor, band-shaped isthmus, and isthmus without boundary. The tooth and root with isthmuses, the number and location of the isthmuses in the root, and the canal configurations were recorded. The maximum of the major diameter of all canal cross-sections in one isthmus (dmax), the minor diameter of the canal in same cross-section (dmin), the distance between the dmax cross-section and apex (Dm-a), isthmus length (Li), and distance from the isthmus ending cross-section to apex (De-a) were measured and analysed with a significance threshold set to 5%. RESULTS: Isthmuses were present in 75.4% specimens. The four types of isthmuses were found in various molars and roots. Their distribution in different root locations and canal configurations was significantly different. The dmax, dmin, Li, and De-a were analysed according to different molars and different isthmus types; their respective median values were 2.508 mm, 0.07 mm, 3.09 mm, and 3.96 mm. CONCLUSION: The three-dimensional classification of isthmuses according to the boundary characteristics provides a comprehensive picture of the isthmus in molars. Their corresponding distributions in different molars, location in roots, and canal configurations will be helpful in predicting the type of isthmus based on the tooth position and canal configurations.

Effect of root canal dimensions, injection rate, and needle design on the apical extrusion of an irrigant: an in vitro study.

AIM: The purpose of this study was to determine the effect of root canal dimensions, type of needle, and injection rate on the apical extrusion of an irrigant in a simulated root canal. METHODS: Ten students used two types of 28-gauge needles, to deliver 3 mL irrigant solution into artificial canals prepared in acrylic blocks to a standard size of ISO 25, 30, or 40 (0.06 taper; n = 10). Each block was preweighed to the nearest microgram before and after irrigation once the canal was dried with paper points. This was repeated with a syringe pump at a flow rate of 50, 100, 200 or 300 µL/s with the needle inserted to a standard depth. RESULTS: Significant differences were observed between the side-vented and notched-end needles when the rate of irrigation was higher than 100 µL/s, and when the apical size was below ISO 40 (P < 0.001). The amount of extrusion was more variable and significantly higher when irrigation was performed manually, compared with the syringe pump groups. CONCLUSIONS: Injection rates above 100 µL/s increased the risk of extrusion, whereas increasing the apical canal size to ISO 40 reduced the amount of extrusion in all groups. The use of a side-vented needle negates the injection-rate effects.

Microbial invasion of dentinal tubules: a literature review and a new perspective.

Various features of endodontic microbiology have been investigated using various methods. The aim of the present study was to review the existing literature on endodontic microbiology in dentinal tubules, and to present the features of two cases with endodontic pathology. An electronic search was performed with a search string created ad hoc. Ex vivo and in vitro studies were included, recording the method of detection and characteristics of analyzed teeth. Twenty studies fulfilled the inclusion criteria. Seven of them were in vitro laboratory studies on teeth inoculated after extraction, while 13 were ex vivo studies on extracted, infected teeth. Endodontic bacteria were detected in dentinal tubules, both as single units and as biofilm aggregates. Two similar in vitro cases presented here corroborate the latter findings. A number of techniques have been utilized to observe bacteria in the dentinal tubule ecosystem. Dentinal tubules are favorable niches for microbial survival, either in the form of monomicrobial or polymicrobial communities.

Comparison of the antibacterial effect and smear layer removal using photon-initiated photoacoustic streaming aided irrigation versus a conventional irrigation in single-rooted canals: an in vitro study.

OBJECTIVE: The Er:YAG laser with photon-induced photoacoustic streaming (PIPS) technique was reported to be effective in root canal disinfection. This study attempted to further investigate the antibacterial efficacy and smear layer removal ability of PIPS in comparison with conventional syringe irrigation in vitro. METHODS: For antibacterial analysis, 48 single-rooted human teeth were prepared and inoculated with Enterococcus faecalis, and then divided into six groups of eight roots each. The colony-forming units (CFUs) per milliliter were determined after infection as the baseline. Then, the teeth were subjected to either PIPS plus 3% sodium hypochlorite (PIPS+NaOCl) or conventional syringe irrigation with 0.9% saline, 3% NaOCl, 17% ethylenediaminetetraacetic acid (EDTA), 0.2% chlorhexidine gluconate (CHX), or 3% NaOCl alternating with 17% EDTA. The reduction of CFUs in the individual group was determined. Additionally, scanning electron microscopy (SEM) examination of the canal walls for E. faecalis colonization was performed. For comparing the smear removal efficacy, another 48 single-rooted teeth, assigned to different groups as mentioned, were irrigated after mechanical instrumentation. The presence of a smear layer at different levels of the root canal was scored by SEM examination. RESULTS: No significant differences were found in CFU reduction. No bacteria could be observed by SEM in the NaOCl, NaOCl+EDTA, and PIPS+NaOCl groups. The scores of smear layer of the NaOCl+EDTA and PIPS+NaOCl groups were significantly lower than those of the other groups in the coronal and middle third of the root canal. None of the methods can effectively remove smear layer in the apical third. CONCLUSIONS: PIPS system supplied with NaOCl and conventional syringe irrigation with NaOCl+EDTA are comparable in their ability to remove E. faecalis and smear layer in single-rooted canals.

Electropolishing enhances the resistance of nickel-titanium rotary files to corrosion-fatigue failure in hypochlorite.

INTRODUCTION: The aim of this study was to examine the fatigue behavior, especially at the low-cycle fatigue (LCF) region, of an experimentally electropolished FlexMaster and a commercial electropolished nickel-titanium (NiTi) instrument (RaCe) in a corrosive environment. METHODS: A total of 90 NiTi rotary instruments were subjected to rotational bending at various degrees of curvatures while immersed in 1.2% sodium hypochlorite solution until broken. The maximum surface strain amplitude, calculated from the curvature of the instrument and the diameter of the cross section at break, was plotted against the LCF life. The results were compared with data for a non-electropolished commercial product tested by using the same methodology. RESULTS: The fatigue life of both instruments generally declined with increasing surface strain amplitude; there was a significant difference between the 2 instruments. Comparing the surface-treated FlexMaster with its commercially available non-electropolished counterpart, an improved resistance to fatigue breakage as a result of electropolishing was noted (P < .05). CONCLUSIONS: The LCF life of a NiTi instrument rotating with a curvature in a corrosive environment is enhanced by electropolishing. The design, both cross-sectional and longitudinal, appears to have an effect on the fatigue behavior of NiTi rotary instruments.